Temperate Nut Crops

Cultivation, Science, and Innovation

Temperate Nut Crops

Cultivation, Science, and Innovation

Ab Waheed Wani, PhD

Rajni Rajan, PhD

Faheem Ahmad, PhD

Editors

First edition published 2026

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Title: Temperate nut crops : cultivation, science, and innovation / Ab Waheed Wani, PhDRajni Rajan, PhDFaheem Ahmad, PhD, editors.

Names: Wani, Ab Waheed, editor.

Description: First edition. | Includes bibliographical references and index.

Identifiers: Canadiana (print) 20250183684 | Canadiana (ebook) 20250183706 | ISBN 9781779643506 (hardcover) | ISBN 9781779643513 (ebook)

Subjects: LCSH: Nut trees. | LCSH: Nuts.

Classification: LCC SB401.A4 T46 2025 | DDC 634/.5—dc23

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CIP data on file with US Library of C ongress

ISBN: 978-1-77964-350-6 (hbk)

ISBN: 978-1-77964-351-3 (ebk)

About the Editors

Ab Waheed Wani, PhD Assistant Professor, Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Ab Waheed Wani, PhD, is currently an Assistant Professor in the Department of Horticulture at Lovely Professional University, Phagwara, Punjab. He completed his Bachelor’s degree in Horticulture in 2014, graduating with a gold medal, and earned his Master’s in Fruit Science, also with a gold medal. He completed his doctoral degree with a score of 86.54%. Dr. Wani was an INSPIRE fellow during his PhD program and a Junior Research Fellowship (JRF) awardee. He is an expert in population genetics, genomics, and metabolomics, particularly in walnuts, almonds, apples, and saffron for distinctness, uniformity, and stability (DUS) guidelines. Dr. Wani has published research articles and review papers in national and international journals and conferences, along with several book chapters. He has received multiple awards, including Young Scientist and Best Thesis awards, and has attended advanced conferences and training programs in fruit science, molecular biology, and artificial intelligence. He is currently working on various projects related to production technology and breeding of fruit crops.

Rajni Rajan, PhD Assistant Professor (Fruit Science), Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India Rajni Rajan, PhD, is currently an Assistant Professor of Fruit Science in the Department of Horticulture at Lovely Professional University, Phagwara, Punjab. Her research focuses on fruit breeding, biotechnology, tissue culture, abiotic stress management, and mutation breeding in fruit crops. She is particularly interested in genomics, metabolomics, genome editing, and the application About the Editors of artificial intelligence in fruit crop research. Dr. Rajan has qualified in Junior Research Fellowship–National Testing Service (JRF-NTS), Senior Research Fellowship–National Testing Service (SRF-NTS), and Agricultural Scientists Recruitment Board (ASRB) NET in Fruit Science. She received the Outstanding MSc Thesis Award at the International Conference on Food Security through Agriculture and Allied Sciences in Kathmandu, Nepal, and has won several best oral and poster presentation awards at international and national conferences. Dr. Rajan has published 21 research papers, eight book chapters, and numerous popular articles in reputed journals and magazines. She has also published two patents, and one design patent has been granted by the Ministry of Commerce and Industry, Government of India.

Faheem Ahmad, PhD Senior Assistant Professor, Department of Botany at Aligarh Muslim University, Aligarh, India

Faheem Ahmad, PhD, is a Senior Assistant Professor in the Department of Botany at Aligarh Muslim University, Aligarh, India. His research focuses on plant-pathogen interactions, biotic and abiotic stress management, and agricultural biotechnology. Dr. Ahmad is the author of over 57 research papers, an associate editor of the Journal of Plant Diseases and Protection (Springer), and an academic editor of PeerJ – Life and Environment. He has supervised one PhD student and several M.Sc. students to date. Dr. Ahmad has received numerous fellowships and awards, including the NRF, TSRO Young Scientist, SERB-DST Young Scientist, and TUBITAK Foreign Researcher Award. He is a fellow of both the International Society for Development and Sustainability (Japan) and the Bose Science Society (India). Dr. Ahmad has gained postdoctoral experience at Ehime University (Japan), North-West University (South Africa), Ege University (Turkey), and National Sun Yat-Sen University (Taiwan).

Contents

Contributors

Foreword

Preface

Introduction, Importance, History, and Scope of Temperate Nut Crops

Kondle Ravi and Kushagra Sharma

Floral Biology, Pollination, and Genetic Resources in Nut Crops

Tulsi D. Gurjar, Avnish K. Pandey, and Rahul R. Rodge

Role of Plant Growth Regulators on Growth and Development of Temperate Nuts

A. B. Khalangre, Jadhav Akash, Anis Mirza, and T. P. Ahamed Shabeer

Phytochemical Properties and Their Utilization in Temperate Nut Crops

Gholamreza Abdi and Sahar Zamani

Scope of AI- and ML-Mediated Advancement in Temperate Nut Crops

Pooja Purushotham, Namburi Karunakar Reddy, Gaurav Y. Rakhonde, and J. Madhu

Microbial Diversity in Nut Crops: Understanding Plant-Microbiome Association

Ab Waheed Wani, Lakhwinder Singh, Harjinder Kaur, Shaifali, G. I. Hassan, and Rajni Rajan

Advancement of Propagation in Temperate Nut Crops

Grandhi N. V. G. K. S. Nimita, Vikanksha, Jagruti Singh, Arun Kumar, and Jatinder Singh

Production Constraints and Improvement Strategies of Temperate Nut Crops

A. Laxman Kumar, S. Venugopal, H. Vittal, B. Maruthi, D. Ashok Kumar, and B. Priyanka

Disease and Pest Management in Temperate Nut Crops

Bekri Xhemali and Hysen Kokiçi

Pest Status and Its Management in Temperate Nut Crops: Opportunities and Challenges

V. Gopinath, D. Gouthami Bai, Nisha Thakur, Jasti Sri Vishnu Murthy, Sanjay Kumar Sahoo, Sanhita Chowdhury, and Vinod Kumar Dubey

Pre-Harvest Factors Influencing the Production and Quality Attributes in Fruit Crops

Lakhwinder Singh, Harjinder Kaur, and Ab Waheed Wani

Preharvest, Postharvest, and Processing Factors Influencing the Phytochemicals and Fatty Acids of Temperate Nuts

Tafadzwa Kaseke, Priscilla Livhuwane Mukwevho, Kwanele Andy Nxumalo, Tobi Fadiji, Umezuruike Linus Opara, and Olaniyi Amos Fawole

Genetic Diversity, Breeding Challenges, and Achievements of Temperate Nut Crops

Rahul R. Rodge and Rajni Rajan

Advancement in the Micropropagation of Temperate Nut Crops

Jagveer Singh, Kuldeep Pandey, Pramod Verma, Vishal Sharma, Popat Gaikwad, Ankush Sharma, and Prabhat Kumar

Omics Technology for Elite Temperate Nut Crop Development

Gaurav Y. Rakhonde, Namburi Karunakar Reddy, Pooja Purushotham, Shivani Jha, M. L. Supriya, Farooqkhan, Shalaka Ahale, and Ananya Deshkar

Genetic Manipulation and Genome Editing in Temperate Nut Crops

Kuldeep Pandey, Jagveer Singh, Reena Prusty, Rajni Rajan, Manish Srivastav, and Avdhesh Kumar

Index

Contributors

Gholamreza Abdi Department of Biotechnology, Persian Gulf Research Institute, Persian Gulf University, Bushehr, Iran

Shalaka Ahale Department of Plant Pathology, Punjab Agricultural University, Ludhiana, Punjab, India

Jadhav Akash ICAR–National Research Center for Grapes, Pune, Maharashtra, India

D. Gouthami Bai Department of Agricultural Entomology, College of Agriculture, Kerala Agricultural University, Thrissur, Kerala, India

Sanhita Chowdhury Department of Entomology, Post-Graduate College of Agriculture, Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar, India

Ananya Deshkar Department of Horticulture, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

Vinod Kumar Dubey Department of Genetics & Plant Breeding, College of Agriculture, Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

Tobi Fadiji Postharvest and Agroprocessing Research Center, Department of Botany and Plant Biotechnology, University of Johannesburg, South Africa; Plant Science Laboratory, Cranfield University, United Kingdom

Farooqkhan Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

Olaniyi Amos Fawole Postharvest and Agroprocessing Research Centre, Department of Botany and Plant Biotechnology, University of Johannesburg, South Africa

South African Research Chairs Initiative in Sustainable Preservation and Agroprocessing Research, Faculty of Science, University of Johannesburg, Johannesburg, South Africa

Popat Gaikwad School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, Punjab, India

V. Gopinath Department of Plant Pathology, Post-Graduate College of Agriculture, Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar, India

Tulsi D. Gurjar ASPEE College of Horticulture, Navsari Agricultural University, Navsari, Gujarat, India

G. I. Hassan Sher-e-Kashmir University of Agricultural Science and Technology, Kashmir, Jammu and Kashmir, India

Shivani Jha Division of Plant Pathology, Indian Agriculture Research Institute, New Delhi, India

Tafadzwa Kaseke Postharvest and Agroprocessing Research Center, Department of Botany and Plant Biotechnology, University of Johannesburg, South Africa; Center of Excellence for Molecular Food Sciences, Department of Biochemistry, University of Belgrade – Faculty of Chemistry, Belgrade, Serbia

Harjinder Kaur Department of Horticulture, School of Agriculture, Lovely Professional University, Phagwara, Punjab, India

A. B. Khalangre Deparment of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Interdepartmental Centre for Agri-Food Industrial Research, Alma Mater Studiorum, University of Bologna, Cesena (FC), Italy

Hysen Kokiçi Institute for Sustainable Plant Protection, National Research Council (CNR), Via Amendola, Bari, Italy; Institute of Plant Genetic Resources, Agricultural University of Tirana, Rruga Paisi Vodica, Tirana, Albania

A. Laxman Kumar Sri Konda Laxman Telangana Horticultural University, Telangana, India

Arun Kumar Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Avdhesh Kumar Department of Fruit Science, CHF, Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

D. Ashok Kumar Department of Fruit Science, CHF, CAU (Imphal), Pasighat, Arunachal Pradesh, India

Prabhat Kumar Department of Fruit Science, College of Horticulture and Forestry, Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

J. Madhu Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

B. Maruthi Department of Vegetable Science, BCKV, Mohanpur, Nadia, West Bengal, India

Anis Mirza Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Priscilla Livhuwane Mukwevho Postharvest and Agroprocessing Research Center, Department of Botany and Plant Biotechnology, University of Johannesburg, South Africa

Jasti Sri Vishnu Murthy Department of Agricultural Entomology, College of Agriculture, Kerala Agricultural University, Thrissur, Kerala, India

Grandhi N. V. G. K. S. Nimita Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Kwanele Andy Nxumalo Postharvest and Agroprocessing Research Center, Department of Botany and Plant Biotechnology, University of Johannesburg, South Africa; Department of Horticulture, Faculty of Agriculture, University of Eswatini, Luyengo, Kingdom of Eswatini

Umezuruike Linus Opara South African Research Chair in Postharvest Technology, Africa Institute for Postharvest Technology, Faculty of AgriSciences, Stellenbosch University, Stellenbosch, South Africa; UNESCO International Center for Biotechnology, Nsukka, Enugu, Nigeria

Avnish K. Pandey ASPEE College of Horticulture, Navsari Agricultural University, Navsari, Gujarat, India

Kuldeep Pandey Department of Fruit Science, College of Horticulture and Forestry (CHF), Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

B. Priyanka Dr. Y. S. Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh, India

Reena Prusty ICAR-Central Institute of Temperate Horticulture, Srinagar, J&K

Pooja Purushotham Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

Rajni Rajan Department of Horticulture, School of Agriculture, Lovely Professional University, Phagwara, Punjab, India

Gaurav Y. Rakhonde Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

Kondle Ravi Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Namburi Karunakar Reddy Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

Rahul R. Rodge Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Sanjay Kumar Sahoo Department of Entomology, Post-Graduate College of Agriculture, Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar, India

T. P. Ahamed Shabeer ICAR–National Research Center for Grapes, Pune, Maharashtra, India

Shaifali Department of Horticulture, School of Agriculture, Lovely Professional University, Punjab, India

Ankush Sharma Plant Genome Mapping Laboratory, University of Georgia, Athens, Georgia, USA

Kushagra Sharma Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Vishal Sharma School of Biotechnology, Faculty of Applied Sciences and Biotechnology, Shoolini University of Biotechnology and Management Sciences, Solan, Himachal Pradesh, India

Jagruti Singh Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Jagveer Singh Department of Fruit Science, College of Horticulture and Forestry (CHF), Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

Jatinder Singh Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

Lakhwinder Singh Faculty of Agriculture, Guru Kashi University, Talwandi Sabo, Bathinda, Punjab, India

Manish Srivastav ICAR–Indian Agricultural Research Institute, New Delhi, India

M. L. Supriya Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

Nisha Thakur Department of Plant Pathology, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh, India

S. Venugopal CSIR–Central Institute of Medicinal and Aromatic Plants, Research Center, Boduppal, Hyderabad, Telangana, India

Pramod Verma Department of Fruit Science, College of Horticulture, Dr. Yashwant Singh Parmar University of Horticulture and Forestry, Nauni, Himachal Pradesh, India

Vikanksha Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

H. Vittal Division of Fruits and Horticultural Technology, ICAR–Indian Agricultural Research University, New Delhi, India

Ab Waheed Wani Department of Horticulture, School of Agriculture, Lovely Professional University, Phagwara, Punjab, India

Bekri Xhemali Kosovo Institute of Agriculture, Pejë, Kosovo

Sahar Zamani Department of Horticultural Sciences, Faculty of Agricultural Sciences, Guilan University, Rasht, Iran

Foreword

In the world of agriculture, there exists a unique realm where science and nature intertwine to produce some of the most cherished and economically significant resources. The focus of our exploration lies within this realm: temperate nut crops. With great pleasure, I introduce the enlightening and comprehensive volume Temperate Nut Crops: Cultivation, Science, and Innovation. This book is a testament to the dedication and expertise of a community of scholars, researchers, and enthusiasts who have devoted their careers to cultivating, studying, and celebrating temperate nut crops.

This volume offers a wealth of knowledge covering the entire life cycle of these remarkable plants. The journey through this book provides an opportunity to explore the diverse regions where temperate nut crops flourish. It offers a glimpse into the laboratories and orchards where dedicated individuals push the boundaries of what is known and possible.

As we embark on this intellectual journey, it is important to recognize that the study and cultivation of temperate nut crops have never been more relevant. These crops offer valuable solutions in a world facing challenges of climate change, food security, and sustainable agriculture. Their ability to thrive in diverse climates, combined with their nutritional value and potential for agroforestry, makes them a crucial component of a resilient and sustainable food system.

This book is not merely a source of information but an invitation to join a community of individuals passionate about temperate nut crops. I hope that Temperate Nut Crops will inspire readers to explore, appreciate, and contribute to the world of these remarkable plants.

The commitment and efforts of the editors, who have poured their wisdom and passion into crafting this volume, are both appreciated and commendable. Their collective work has produced a valuable resource that will undoubtedly influence the future of temperate nut crops. I extend my compliments to the editors and contributing authors for compiling this insightful book on temperate nut crops.

—Dr. Vishwa Bandhu Patel, PhD, FIAHS, FISNS

Assistant Director General (Fruits and Plantation Crops),

Indian Council of Agricultural Research, New Delhi 110012

Preface

Welcome to Temperate Nut Crops: Cultivation, Science, and Innovation—a comprehensive journey into the captivating world of temperate nut-bearing trees. This book delves into the intricate aspects of these remarkable plants, offering a thorough exploration of their cultivation, utilization, and the cutting-edge research shaping their future. The chapters provide a structured and insightful tour of the world of temperate nut crops.

Chapter 1: Introduction, Importance, History, and Scope of Temperate Nut Crops: Our journey begins with an introduction to the fascinating world of temperate nut crops, setting the stage to explore their historical significance, modern importance, and the vast scope they offer for research, agriculture, and industry.

Chapter 2: Floral Biology, Pollination, and Genetic Resources in Nut Crops: This chapter delves into the intricate processes of nut tree reproduction, covering floral biology, pollination mechanisms, and the invaluable genetic resources that support breeding programs for these temperate crops.

Chapter 3: Role of Plant Growth Regulators on Growth and Development of Temperate Nuts: This chapter demonstrates how plant growth regulators play a pivotal role in the growth and development of nutbearing trees, enhancing fruit quality and yield. It reveals the optimal applications of PGRs for nut crops.

Chapter 4: Phytochemical Properties and Their Utilization in Temperate Nut Crops: This chapter explores the fascinating world of phytochemicals in nut crops and their impact on human health. It details the diverse culinary and medicinal applications of these nutrient-rich nuts.

Chapter 5: Scope of AI- and ML-Mediated Advancements in Temperate Nut Crops: This chapter examines the transformative potential of artificial intelligence and machine learning in research, cultivation, and management of temperate nut crops.

Chapter 6: Microbial Diversity in Nut Crops: Understanding PlantMicrobiome Association: This chapter explores plant-microbiome associations in nut crops, examining the role of microbes in tree health, soil ecology, and nut quality.

Chapter 7: Advancement of Propagation in Temperate Nut Crops: This chapter details the latest innovations in propagating nut-bearing trees, from traditional methods to advanced micropropagation techniques.

Chapter 8: Production Constraints and Improvement Strategies of Temperate Nut Crops: This chapter examines production challenges in nut crops and explores strategies and technologies to overcome these constraints for sustainable and efficient cultivation.

Chapter 9: Disease and Pest Management in Temperate Nut Crops: This chapter presents methods for safeguarding nut orchards from pests and diseases, with a focus on environmentally friendly integrated pest and disease management practices.

Chapter 10: Pest Status and Management Strategies in Temperate Nut Crops: Opportunities and Challenges: This chapter details strategies to protect nut orchards from pests and diseases while adopting environmentally friendly, integrated pest management practices.

Chapter 11: Pre-Harvest Factors Influencing the Production and Quality Attributes in Fruit Crops: This chapter examines the pre-harvest factors that impact nut crop production and the attributes that determine the quality of these nutritious treats.

Chapter 12: Pre-Harvest, Post-Harvest, and Processing Factors Influencing the Phytochemicals and Fatty Acids of Temperate Nuts: This chapter provides insights into essential practices for preserving nut quality and extending shelf life through effective post-harvest management.

Chapter 13: Genetic Diversity, Breeding Challenges, and Achievements in Temperate Nut Crops: This chapter explores the complexities of breeding nut trees, including challenges, achievements, and the rich genetic diversity these crops offer.

Chapter 14: xviiAdvancement in the Micropropagation of Temperate Nut Crops: This chapter demonstrates how micropropagation techniques are transforming the production of elite nut crop varieties.

Chapter 15: Omics Technology for Elite Temperate Nut Crop Development: This chapter shows how omics technologies are reshaping our understanding and enhancement of temperate nut crop varieties.

Chapter 16: Genetic Manipulation and Genome Editing in Temperate Nut Crops: This chapter uncovers the potential of genetic manipulation and genome editing in developing resilient and high-quality nut-bearing tree varieties.

This book brings together a wealth of knowledge, research, and innovation in the field of temperate nut crops, offering valuable insights for horticulturists, scientists, growers, and nut enthusiasts alike. We hope this journey proves both enlightening and inspiring as you explore these remarkable trees and the many opportunities they offer for advancing science, agriculture, and sustainable nutrition.

We hope you enjoy this voyage through the world of temperate nut crops as much as we have enjoyed creating it. Let the journey begin, dear reader, and may it deepen your understanding and appreciation of the remarkable world of nut crops.

—Ab Waheed Wani, PhD

Department of Horticulture, Lovely Professional University, Punjab, India

Rajni Rajan, PhD

Department of Horticulture, Lovely Professional University, Punjab, India

Faheem Ahmad, PhD

Department of Botany, Aligarh Muslim University, Uttar Pradesh, India

Chapter 1 Introduction, Importance, History, and Scope of Temperate Nut Crops

KONDLE RAVI* and KUSHAGRA SHARMA

Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

* Corresponding author

ABSTRACT

Temperate nut crops, such as almonds, walnuts, chestnuts, and hazelnuts, hold immense importance in the global food and agriculture industry. Thriving in regions with moderate climates, these crops offer nutritional benefits, culinary versatility, and economic opportunities. Understanding the characteristics, cultivation practices, market dynamics, and historical significance of temperate nut crops is crucial for stakeholders involved in their production and trade. These crops have a rich history, providing sustenance and economic prosperity to communities worldwide. Today, they continue to be cultivated in suitable regions, contributing significantly to local and global markets. With their high nutritional value and culinary applications, temperate nut crops play a vital role in a balanced diet and offer diverse options for consumers. They also provide economic benefits, generating income, employment, and rural development opportunities. As the demand for healthy, plant-based foods grows, temperate nut crops have a promising scope for market expansion and innovation. Additionally, their cultivation aligns with sustainable agriculture practices, promoting biodiversity and ecosystem services. Temperate nut crops play a vital role in the global food system, and understanding their characteristics, cultivation practices, and market dynamics is essential for harnessing their full potential in the agricultural industry.

____________________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

1.1 Introduction

1.1.1 Understanding Temperate Nut Crops: A Comprehensive Overview

Temperate nut crops, including almonds, walnuts, chestnuts, and hazelnuts, have gained significant attention in the global food and agriculture industry. These crops are cultivated in regions with moderate climates and offer valuable nutritional benefits, culinary versatility, and economic opportunities. A comprehensive understanding of temperate nut crops is crucial for farmers, researchers, and stakeholders involved in their production and trade. This chapter aims to explore the characteristics, cultivation practices, and market dynamics of temperate nut crops, highlighting the importance of research and knowledge dissemination in this field. Temperate nut crops have specific growth requirements and climatic preferences that contribute to their successful cultivation. These crops thrive in regions characterized by moderate temperatures, distinct seasons, and suitable rainfall patterns. While there are variations among different nut species, most require a chilling period during winter to break dormancy and ensure proper flowering and fruit set in the following growing season. Understanding the specific chilling requirements for different nut crops is essential for selecting appropriate cultivars and managing orchards effectively (FAO, 2019; Du, 2021). For example, almonds (Prunus dulcis) are well-suited to Mediterranean climates, where they benefit from mild winters and long, warm summers. They require a minimum number of chilling hours, typically between 300–600 hours, to break dormancy and initiate optimal bud development (FAO, 2019; Du, 2021). Similarly, walnuts (Juglans regia) thrive in temperate regions with cool winters and warm summers. They have higher chilling requirements, often ranging from 400–1500 hours, depending on the variety (FAO, 2019). Understanding these specific climate preferences is crucial for selecting appropriate growing regions and cultivars, ensuring successful nut production. Successful cultivation of temperate nut crops also relies on specific cultural practices tailored to the unique characteristics of each crop. These practices encompass planting techniques, orchard management, irrigation strategies, and pest and disease control measures. Adhering to best practices ensures optimal crop health, productivity, and quality. Proper planting techniques are essential for establishing healthy orchards. Nut crops are typically propagated through grafting or budding onto rootstocks to ensure desired traits, such as disease resistance or growth vigor. Adequate spacing between trees is also crucial to provide sufficient light, air circulation, and room for root expansion (FAO, 2019). In walnut orchards, for instance, wider spacing between trees is recommended due to their large size and extensive root systems (Ayars et al., 2015). Orchard management practices, including pruning, training, and fertilization, are crucial for maintaining tree health and productivity. Pruning is particularly important to control tree shape, optimize sunlight exposure, and promote adequate air circulation, reducing the risk of diseases (Nath et al., 2019). Nut crops like almonds benefit from regular pruning to remove dead wood, maintain an open canopy structure, and rejuvenate older trees (Khalil et al., 2023). Irrigation strategies play a vital role in ensuring optimal water management, as nut crops have different water requirements at various growth stages. Proper irrigation scheduling, considering factors such as soil moisture levels, climatic conditions, and tree growth stages, helps prevent water stress and enhances crop productivity (Fernández García et al., 2020). Efficient irrigation systems, such as drip irrigation, can also minimize water loss and nutrient leaching, improving water use efficiency in nut crop production (Yang et al., 2023).

Pest and disease control is a significant aspect of temperate nut crop management. These crops face various pest and disease pressures that can significantly impact yields and overall orchard health. Integrated pest management (IPM) practices that combine cultural, biological, and chemical control methods are crucial for effective pest management while minimizing environmental impacts (FAO, 2019). Regular monitoring, early detection, and targeted interventions are key components of IPM programs (Bennett et al., 2016). For instance, codling moth (Cydia pomonella) is a common pest in walnut and apple orchards, and its control often involves the use of mating disruption techniques, insecticides, and cultural practices such as orchard sanitation (Lukehart, 2018). Research and development efforts play a pivotal role in advancing our understanding of temperate nut crops and addressing the challenges faced by growers. Researchers continuously work to develop improved cultivars with enhanced disease resistance, improved yields, and desirable nut quality traits. For instance, the development of disease-resistant almond varieties, such as those resistant to the devastating pathogen Xylella fastidiosa, has been a significant focus of research (Walker et al., 2023). Research also plays a crucial role in identifying sustainable production practices, including nutrient management, soil health improvement, and water use efficiency. Nut crops are often grown on a large scale, making sustainable production practices essential for minimizing environmental impacts. Studies exploring the use of cover crops, organic fertilization methods, and precision irrigation techniques have shown promise in improving sustainability and resource efficiency in nut crop production (FAO, 2019). Understanding market dynamics is crucial for nut crop growers to make informed decisions and capitalize on opportunities. Market trends, consumer preferences, and trade policies significantly influence the demand, pricing, and profitability of temperate nut crops. Monitoring market volatility and price fluctuations is essential for growers to manage risks and ensure profitability. One significant opportunity lies in the growing demand for healthy, plant-based foods and snacks. Nut crops are recognized for their nutritional benefits, including being rich in healthy fats, protein, fiber, and antioxidants. Consumer awareness of the health benefits of nut consumption, such as improving heart health and reducing the risk of chronic diseases, continues to grow (Lockyer et al., 2016).

Nut growers can capitalize on this trend by promoting the nutritional value of their products and highlighting the sustainability of nut crop production. Product diversification and value-added offerings provide another avenue for nut growers to enhance profitability and meet consumer preferences. By exploring opportunities to produce value-added products such as nut oils, nut flours, nut-based spreads, and nut milk alternatives, growers can cater to consumers seeking specialty and gourmet ingredients, gluten-free options, and plant-based alternatives (Xypolitaki, 2023). Value-added products can help farmers capture higher profit margins and differentiate themselves in the market. Direct-to-consumer sales and farm tourism offer unique opportunities for nut growers to establish a direct connection with consumers. Selling directly through farmers’ markets, on-farm stands, or online platforms allows farmers to share their story, educate consumers about their products, and receive immediate feedback. Additionally, incorporating farm tourism activities, such as u-pick experiences, farm tours, or agritourism events, can create additional revenue streams and enhance the overall farm experience for visitors (Budiasa, 2014). The growing demand for organic and sustainably produced food presents opportunities for nut growers who adopt environmentally friendly and socially responsible practices. Organic certification provides access to niche markets and allows farmers to command premium prices for their products. Embracing sustainable practices, such as organic fertilization, water conservation, and habitat preservation, can enhance the sustainability profile of nut crops and appeal to conscious consumers seeking eco-friendly options (Williamson et al., 2018).

1.2 Importance

1.2.1 Nutritional And Economic Significance Of Temperate Nut Crops

Temperate nut crops, such as almonds, walnuts, and hazelnuts, are not only delicious and versatile ingredients but also provide valuable nutritional and economic benefits. These crops are packed with essential nutrients, healthy fats, protein, vitamins, and minerals, making them an important component of a balanced diet. Furthermore, they contribute significantly to the global economy through agricultural production, trade, and value-added products. This chapter will delve into the nutritional and economic significance of temperate nut crops, highlighting their impact on human health and their role in global markets.

1.2.1.1 Nutritional Benefits

Temperate nut crops offer an array of essential nutrients that contribute to overall health and well-being. Almonds, for instance, are a rich source of monounsaturated fats, which can help reduce bad cholesterol levels and lower the risk of cardiovascular diseases (Berryman et al., 2011). They are also packed with vitamin E, an antioxidant that protects cells from oxidative damage (Ryan et al., 2010). Walnuts are known for their high content of omega-3 fatty acids, which have been linked to improved cognitive function and reduced inflammation (Fatima et al., 2018). These fatty acids also play a crucial role in heart health by lowering blood pressure and reducing the risk of heart disease (Calder, 2004). Hazelnuts, on the other hand, are rich in vitamins, minerals, and dietary fiber. They provide a good source of vitamin E, folate, and magnesium, all of which play important roles in maintaining overall health and well-being (Dobhal et al., 2018). In addition to their nutrient content, temperate nut crops offer other health benefits. Regular consumption of these nuts has been associated with reduced risks of chronic diseases such as diabetes, certain types of cancer, and neurodegenerative disorders (Bilikis and Olanrewaju, 2015). They are also a valuable source of dietary fiber, which promotes healthy digestion and helps control blood sugar levels (De, 2020). The combination of essential nutrients, healthy fats, and antioxidants in temperate nut crops makes them an important dietary component for maintaining optimal health. In addition to their macro and micronutrient content, temperate nut crops offer several other health benefits. They are a rich source of phytochemicals, including flavonoids, phenolic compounds, and phytosterols, which possess antioxidant and anti-inflammatory properties (Martínez-García et al., 2019). These bioactive compounds have been associated with various health benefits, such as reduced oxidative stress, improved cardiovascular health, and enhanced immune function. Furthermore, the healthy fats present in temperate nut crops, such as monounsaturated and polyunsaturated fats, are known for their positive impact on cardiovascular health. Consuming these fats in moderation can help lower LDL (bad) cholesterol levels, reduce the risk of heart disease, and improve lipid profiles (Lovell et al., 2023). The fiber content in nut crops also contributes to heart health by promoting healthy cholesterol levels and aiding in weight management (Amao, 2018).

1.2.1.2 Economic Benefits

The economic significance of temperate nut crops cannot be overlooked. These crops are grown and traded on a global scale, contributing to agricultural production and generating substantial economic value. Almonds, for example, have witnessed a significant increase in global production and consumption in recent years. According to FAOSTAT (2021), the global production of almonds reached over 3.2 million metric tons in 2019, with the United States being the largest producer. Almonds are highly sought after in international markets, with major export destinations including countries in Europe, Asia, and the Middle East (FAOSTAT, 2021). The economic impact of the almond industry extends beyond primary production, as almonds are also processed into various value-added products such as almond milk, almond flour, and almond oil, contributing to a diverse market (Volpe et al., 2015). Similarly, walnuts and hazelnuts also hold significant economic value. The global production of walnuts has seen consistent growth, driven by increased demand for their health benefits and culinary applications. According to FAOSTAT (2021), the global production of walnuts surpassed 4 million metric tons in 2019, with China, the United States, and Iran being the largest producers.

Walnuts are exported worldwide and are used in various industries, including the food, pharmaceutical, and cosmetic sectors (FAOSTAT, 2021). Hazelnuts, too, have a substantial economic impact. Turkey is the largest producer of hazelnuts, with significant global export markets, including the European Union and the United States (FAOSTAT, 2021). Hazelnuts are widely used in confectionery and baking industries and have a high market demand for products such as chocolate spreads and pralines (FAOSTAT, 2021). Furthermore, the economic significance of temperate nut crops extends beyond primary production and trade. These crops provide employment opportunities in rural areas, supporting local economies and livelihoods. They also contribute to rural development by promoting sustainable agriculture practices and diversifying farming systems (Bosco and Thomas, 2023). The value-added processing and manufacturing of nutbased products further enhance the economic benefits by creating additional jobs and fostering entrepreneurship. The economic impact of temperate nut crops extends beyond direct production and trade. These crops also play a crucial role in supporting rural economies and livelihoods. The cultivation, harvesting, and processing of nut crops create employment opportunities, particularly in rural areas where these crops are predominantly grown. This not only helps to alleviate poverty and reduce unemployment but also promotes rural development and contributes to the overall economic stability of farming communities (Nagubadi et al., 2020). Moreover, the growth of the nut industry has stimulated innovation and diversification in the food and agricultural sectors. The increasing demand for nut-based products has led to the development of value-added products such as nut butters, nut milk, nut flours, and nut-based snacks. These products cater to the evolving dietary preferences and lifestyles of consumers, creating new market opportunities and enhancing the economic value of temperate nut crops (Hoang et al., 2017). Additionally, the export of temperate nut crops contributes to global trade and foreign exchange earnings for producing countries. Many nutproducing countries heavily rely on export revenues, which play a significant role in their overall economic growth. For example, the export of almonds is a major source of income for countries like the United States, Spain, and Australia (FAOSTAT, 2021). The global demand for nuts continues to rise, driven by increased awareness of their nutritional benefits and changing dietary patterns, providing further economic opportunities for nut-producing regions.

1.2.1.3 Sustainable Agriculture

The cultivation of temperate nut crops aligns with the principles of sustainable agriculture. These crops have several characteristics that contribute to sustainable farming practices. Firstly, they are often drought-tolerant and well-adapted to specific climatic conditions, allowing for efficient water management in regions prone to water scarcity (Aradhya et al., 2014). Additionally, nut trees have extensive root systems that enhance soil structure, increase organic matter, and improve water infiltration, thereby reducing soil erosion and promoting soil health (Kremer and Kussman, 2011). Furthermore, nut crops can be integrated into agroforestry systems, where they provide multiple benefits such as shade, windbreaks, and habitat for beneficial organisms. This approach enhances biodiversity and ecosystem services, contributing to the overall sustainability and resilience of farming systems (Wolz et al., 2018).

1.2.1.4 Research And Innovation

Ongoing research and innovation play a vital role in advancing the cultivation, processing, and utilization of temperate nut crops. Scientific studies focus on improving crop productivity, disease resistance, and nut quality through breeding programs and the development of new cultivars. Research also explores post-harvest handling techniques to optimize the storage, processing, and preservation of nut crops, ensuring their quality and extending shelf life (Lovell et al., 2023). Innovation in processing technology has led to the development of value-added nut products, expanding market opportunities and diversifying the ways in which nut crops are consumed. For example, the extraction of nut oils and the production of nut-based spreads, confectionery items, and bakery products have gained popularity, appealing to a wider consumer base (Rebezov et al., 2021)

1.2.2 Health Benefits Of Incorporating Temperate Nut Crops Into The Diet

Temperate nut crops, including almonds, walnuts, and hazelnuts, have long been recognized for their nutritional value and potential health benefits. Incorporating these nutrient-dense foods into a balanced diet can provide a wide range of positive effects on human health. This chapter explores the extensive research conducted on the health benefits of temperate nut crops and their impact on various aspects of well-being, including cardiovascular health, weight management, diabetes control, and overall disease prevention.

1.2.2.1 Cardiovascular Health

One of the most well-established health benefits of temperate nut crops is their positive impact on cardiovascular health. Numerous studies have demonstrated that regular nut consumption is associated with a reduced risk of cardiovascular diseases, including heart disease and stroke. Almonds, in particular, have been extensively studied for their cardioprotective effects. A systematic review and meta-analysis of randomized controlled trials (RCTs) found that almond consumption significantly reduces total cholesterol, LDL cholesterol, and triglyceride levels, all of which are risk factors for cardiovascular diseases (Phung et al., 2009). The study also noted that almonds have no significant impact on HDL cholesterol levels, indicating that they have a favorable effect on lipid profiles. Another meta-analysis of 25 RCTs showed that almond consumption significantly reduces systolic blood pressure, a key risk factor for heart disease (Kalita et al., 2018). Walnuts, rich in alpha-linolenic acid (ALA), an essential omega-3 fatty acid, have also been extensively studied for their cardiovascular benefits. A systematic review and meta-analysis of 13 RCTs demonstrated that walnut consumption significantly reduces total cholesterol, LDL cholesterol, and triglyceride levels (Marangoni et al., 2007). The study further revealed that walnuts have a modest but significant effect in improving endothelial function, which plays a vital role in maintaining healthy blood vessels. Hazelnuts have also shown promising effects on cardiovascular health. A review of observational studies and clinical trials indicated that hazelnut consumption may lead to a reduction in total cholesterol and LDL cholesterol levels, contributing to improved cardiovascular health (Gorji et al., 2018).

1.2.2.2 Weight Management

Incorporating temperate nut crops into the diet can also support weight management efforts. Despite being energy-dense, nuts have been associated with weight maintenance and even weight loss when consumed as part of a calorie-controlled diet. A systematic review and meta-analysis of 33 RCTs found that nut consumption does not lead to weight gain, contrary to the concerns associated with their high energy content (Xiao et al., 2018). Moreover, the analysis revealed that participants who consumed nuts had a significantly lower body mass index (BMI) and a reduced risk of obesity. The high fiber and protein content of nuts contribute to their satiety effects, helping individuals feel full and satisfied after consumption. Additionally, the presence of healthy fats in nuts, such as monounsaturated and polyunsaturated fats, can promote increased energy expenditure and fat oxidation, potentially aiding in weight management (Ros and Mataix, 2006).

1.2.2.3 Diabetes Control

Temperate nut crops have demonstrated potential benefits for individuals with diabetes or at risk of developing the condition. Research suggests that incorporating these nuts into the diet can help improve glycemic control and reduce the risk of complications associated with diabetes. A systematic review and meta-analysis of 12 RCTs indicated that almond consumption significantly reduces hemoglobin A1c levels, a marker of long-term blood sugar control, in individuals with type 2 diabetes (Asbaghi et al., 2021). The study also highlighted that almond consumption improves fasting insulin levels and insulin resistance, contributing to better glycemic control. Walnuts have also shown promising effects on glycemic control. A meta-analysis of 11 RCTs demonstrated that walnut consumption significantly reduces fasting insulin levels and improves insulin sensitivity in individuals with or at risk of developing type 2 diabetes (Mates et al., 2022). Furthermore, walnuts have been associated with a lower risk of developing type 2 diabetes in prospective cohort studies (Li et al., 2009).

1.2.2.4 Overall Disease Prevention

In addition to their specific effects on cardiovascular health, weight management, and diabetes control, temperate nut crops have been associated with a reduced risk of overall disease development. Their nutrient composition, including antioxidants, fiber, and various bioactive compounds, contributes to their protective effects against chronic diseases. Epidemiological studies have consistently shown an inverse association between nut consumption and the risk of developing various types of cancer. A meta-analysis of 36 studies indicated that higher nut consumption is associated with a reduced risk of colorectal, pancreatic, and endometrial cancers (Witlox et al., 2020). The presence of bioactive compounds in nuts, such as polyphenols and phytosterols, has been suggested to have anti-carcinogenic effects, protecting against cancer development (Rusu et al., 2018). Furthermore, the consumption of temperate nut crops has been associated with a lower risk of all-cause mortality and mortality from specific causes, such as cardiovascular disease and cancer (Lovell et al., 2023). A systematic review and meta-analysis of prospective studies demonstrated that nut consumption is associated with a significantly reduced risk of all-cause mortality (Mayhew et al., 2016). These findings highlight the potential of temperate nut crops in promoting overall health and longevity.

1.2.2.5 Brain Health

In recent years, there has been growing interest in the potential effects of temperate nut crops on brain health and cognitive function. Several studies have suggested that regular consumption of nuts may have positive impacts on brain health and reduce the risk of cognitive decline. Walnuts, in particular, have received attention for their potential cognitive benefits. A randomized controlled trial conducted on older adults found that walnut consumption was associated with improved cognitive function, including memory and information processing speed (Sala-Vila et al., 2020). Another study involving over 2,500 adults demonstrated that higher walnut intake was associated with better cognitive scores and a lower risk of cognitive impairment (Gervasi et al., 2021). These findings are attributed to the high content of omega-3 fatty acids, antioxidants, and other bioactive compounds found in walnuts, which may have neuroprotective effects and support brain health. Similarly, almonds have been associated with cognitive benefits. A study involving older adults showed that regular almond consumption was associated with improved cognitive function, including memory and attention (Coates et al., 2020). Almonds are rich in nutrients such as vitamin E, which has been linked to cognitive health and reduced risk of cognitive decline (Mustra Rakic, et al., 2022).

1.2.2.6 Gut Health

The gut microbiota, the collection of microorganisms residing in the digestive tract, plays a crucial role in human health. Emerging research suggests that temperate nut crops may have a positive impact on gut health by promoting a diverse and beneficial gut microbiota. Nuts, particularly almonds and walnuts, contain prebiotic fibers that serve as nourishment for beneficial gut bacteria. These fibers can stimulate the growth and activity of beneficial bacteria in the gut, such as Bifidobacteria and Lactobacilli, which are associated with improved gut health and enhanced immune function (Sugizaki and Naves, 2018). A study investigating the effects of almond consumption on the gut microbiota found that regular almond intake increased the levels of beneficial gut bacteria and improved the microbial composition (Ukhanova et al., 2014). Another study demonstrated that a walnut-rich diet resulted in favorable changes in the gut microbiota, including increased populations of beneficial bacteria and reduced markers of inflammation (Ni et al., 2022). These findings suggest that incorporating temperate nut crops into the diet may have a prebiotic-like effect, positively influencing the gut microbiota and contributing to gut health.

1.2.2.7 Inflammation And Oxidative Stress

Chronic inflammation and oxidative stress are underlying factors in the development of various chronic diseases, including cardiovascular diseases, diabetes, and certain cancers. The anti-inflammatory and antioxidant properties of temperate nut crops have been studied extensively. Walnuts, for example, are rich in polyphenols and antioxidants, which can help reduce inflammation and oxidative stress. A review of human studies found that walnut consumption was associated with lower levels of inflammatory markers, such as C-reactive protein (CRP) and interleukin-6 (IL-6) (Bhardwaj et al., 2016). Similarly, almonds have been shown to have anti-inflammatory effects. A study involving overweight and obese individuals found that almond consumption led to a significant reduction in CRP levels, indicating reduced inflammation (Hong et al., 2018). Hazelnuts, known for their high antioxidant content, have also demonstrated anti-inflammatory effects. A study investigating the effects of hazelnut consumption in individuals with metabolic syndrome found a decrease in markers of inflammation, including CRP and tumor necrosis factor-alpha (TNF-α) (Açik and Çakiroğlu, 2020). These findings highlight the potential of temperate nut crops in reducing inflammation and oxidative stress, thus contributing to the prevention and management of chronic diseases.

1.2.2.8 Bone Health

Temperate nut crops may also play a role in supporting bone health. They contain several nutrients that are essential for maintaining bone strength and density, including calcium, magnesium, phosphorus, and vitamin E. Almonds, for instance, are a good source of calcium, a mineral vital for bone health. A study involving postmenopausal women found that regular almond consumption improved bone mineral density and reduced the risk of osteoporosis (Thorning et al., 2016). Additionally, the high content of vitamin E in almonds may have a protective effect against bone loss (Peh et al., 2016). Walnuts, with their omega-3 fatty acids and antioxidants, may also support bone health. A study conducted on mice demonstrated that walnut consumption improved bone microstructure and strength (Gammone et al., 2019). The researchers attributed these effects to the anti-inflammatory and antioxidant properties of walnuts. While more research is needed to fully understand the relationship between nut consumption and bone health, the available evidence suggests that incorporating temperate nut crops into the diet may contribute to the maintenance of strong and healthy bones.

1.3 Contribution Of Temperate Nut Crops To Sustainable Agriculture

Temperate nut crops, such as almonds, walnuts, and hazelnuts, play a crucial role in sustainable agriculture practices. These crops are not only valuable sources of nutrition and economic benefits but also contribute to environmental sustainability and biodiversity conservation. This chapter explores the various ways in which temperate nut crops contribute to sustainable agriculture, including their resilience to environmental challenges, promotion of biodiversity, soil health improvement, water conservation, and climate change mitigation.

1.3.1 Resilience To Environmental Challenges

Temperate nut crops have proven to be resilient in the face of various environmental challenges, making them well-suited for sustainable agricultural practices. They can adapt to a wide range of climates and soil conditions, allowing for cultivation in diverse regions. For example, almonds are grown in Mediterranean climates with hot, dry summers and mild winters, while hazelnuts thrive in temperate regions with moderate temperatures (An et al., 2020). This adaptability enables farmers to diversify their agricultural practices, reducing reliance on a single crop and enhancing the resilience of agroecosystems (Altieri et al., 2015). Furthermore, temperate nut crops have demonstrated the ability to withstand extreme weather events, such as droughts and heatwaves. Almond trees, for instance, have deep root systems that enable them to access water from lower soil layers, making them more drought-tolerant compared to other crops (Romero et al., 2022).

1.3.2 Promotion of Biodiversity

Temperate nut crops provide habitats and food sources for a wide range of plant and animal species, contributing to biodiversity conservation in agricultural landscapes. The flowering and fruiting stages of nut trees attract pollinators, such as bees and butterflies, enhancing pollination services and promoting the diversity of insect species (Smith et al., 2013). This, in turn, benefits other plant species in the vicinity and supports ecosystem stability. Additionally, nut orchards can serve as habitat corridors and refuges for wildlife. The presence of nut trees in agricultural landscapes offers shelter, nesting sites, and food resources for various bird species, mammals, and insects (Pekarsky et al., 2021). The conservation of these habitats supports biodiversity conservation and contributes to the overall ecological balance.

1.3.3 Soil Health Improvement

Temperate nut crops play a vital role in improving soil health and fertility. Their deep root systems penetrate the soil profile, promoting soil aeration and nutrient cycling (Alkharabsheh et al., 2021). The roots of nut trees can reach several meters into the soil, accessing nutrients and moisture that may not be available to other shallow-rooted crops (Liste et al., 2008). This deep rooting helps prevent soil erosion and enhances water infiltration, reducing the risk of water runoff and improving overall soil structure (Lal, 2015). The accumulation of organic matter from fallen leaves, husks, and pruned branches in nut orchards also contributes to soil fertility and carbon sequestration (Sullivan et al., 2012).

1.3.4 Water Conservation

Water scarcity is a significant concern in many regions, making efficient water management a crucial aspect of sustainable agriculture. Temperate nut crops are generally more water-efficient compared to other tree crops, making them suitable for cultivation in water-limited areas (Wezel et al., 2014). The deep root systems of nut trees enable them to access water from lower soil layers, reducing the need for excessive irrigation. Furthermore, precision irrigation techniques, such as regulated deficit irrigation and microirrigation systems, have been developed and implemented in nut orchards to optimize water use efficiency. These techniques ensure that water is applied only when and where it is needed, minimizing water wastage and reducing the ecological footprint of nut crop production (Shah and Wu, 2019).

1.3.5 Climate Change Mitigation

Temperate nut crops contribute to climate change mitigation through carbon sequestration and the reduction of greenhouse gas emissions. Nut orchards, with their long lifespan and perennial nature, can sequester significant amounts of carbon dioxide from the atmosphere, thereby mitigating climate change (Granata et al., 2020). Additionally, the accumulation of organic matter in nut orchards enhances soil carbon storage, further contributing to carbon sequestration (Dhyani et al., 2020).

1.3.6 Community And Socioeconomic Benefits

The cultivation of temperate nut crops has significant community and socioeconomic benefits. Nut orchards provide employment opportunities, particularly in rural areas where these crops are often grown. This supports local economies, reduces unemployment, and enhances rural development (Shigaeva and Darr, 2020). The nut industry also contributes to local value addition and processing activities, creating additional employment opportunities and stimulating economic growth in rural communities.

1.4 History

1.4.1 Tracing The Historical Roots Of Temperate Nut Crops

Temperate nut crops, such as almonds, walnuts, and hazelnuts, have a long and rich history dating back thousands of years. These crops have played significant roles in various civilizations, cultures, and culinary traditions. Understanding the historical roots of temperate nut crops provides insights into their domestication, cultivation, and utilization over time. This chapter explores the historical origins and development of almonds, walnuts, and hazelnuts, shedding light on their cultural, economic, and culinary importance throughout history.

1.4.2 Almonds

Almonds (Prunus dulcis) have a fascinating history that can be traced back several millennia. Originating from the eastern Mediterranean and Western Asia, almonds were among the earliest domesticated nut crops. Archaeological evidence suggests that almonds were cultivated in ancient civilizations, including Mesopotamia, Egypt, and Persia. In ancient Egypt, almonds were highly regarded and considered a symbol of fertility and abundance. They were included in burial rituals and tombs, indicating their cultural and religious significance (Fărcaş et al., 2015). Almonds were also used in culinary preparations, including desserts, baked goods, and beverages. The abundance of almond trees in the Nile Delta region allowed for widespread cultivation and utilization of almonds in various forms. The cultivation of almonds spread throughout the Mediterranean region, particularly in Greece and Rome. Greek literature mentions almonds, and Greek physicians, such as Hippocrates, recognized their medicinal properties. Almonds were highly valued for their nutritional benefits and were commonly consumed by athletes and soldiers for energy and strength (Albala, 2009). During the Middle Ages, almonds were introduced to Northern Europe through trade routes and agricultural expansion. The Romans brought almond trees to Britain, and almonds became popular among European aristocracy. Almonds were widely used in medieval cooking, as documented in various recipe books of the time. They were often incorporated into both sweet and savory dishes, showcasing their versatility (Figure 1.1) (Woolgar, 2018).

Figure 1.1 Different growth stages of almond. ⏎

1.4.3 Walnuts

Walnuts (Juglans regia) have a rich history dating back thousands of years. Originating from the regions of Central Asia, particularly modern-day Iran and Afghanistan, walnuts were among the earliest cultivated nut crops. Walnuts were highly esteemed in ancient Persia (present-day Iran), where they were considered the “royal nut” and associated with fertility, abundance, and wisdom. Persian literature and artwork depict the cultural and symbolic importance of walnuts (Samanian et al., 2022). Persian traders and explorers introduced walnuts to various regions, including Greece, Rome, and China. In ancient Greece, walnuts were associated with the gods and were a symbol of divine intelligence. Greek philosopher Hippocrates regarded walnuts as a brain tonic and believed they enhanced mental acuity (Nebelkopf, 1981). The Greeks also recognized the nutritional value of walnuts and incorporated them into their cuisine. In fact, the ancient Olympic athletes consumed walnuts for their energy-boosting properties. The cultivation of walnuts spread throughout the Roman Empire, and they became popular across Europe during the Middle Ages. The Romans introduced walnuts to Britain, where they were grown in monastic gardens and used in culinary preparations (Salas-Salvadó et al., 2011). The popularity of walnuts continued to rise, and they became associated with wealth and social status (Figure 1.2).

Figure 1.2 Different growth stages of walnut. ⏎

1.4.4 Hazelnuts

Hazelnuts (Corylus avellana) have a long history that can be traced back to ancient times. They are native to Europe and western Asia and were widely utilized by various civilizations. In ancient Greece, hazelnuts were associated with divine protection and were considered symbols of fertility and rebirth. They were often used in religious ceremonies and offerings (Håland, 2005). The Greek physician Dioscorides documented the medicinal properties of hazelnuts in his herbal writings. During the Roman era, hazelnuts were widely cultivated and consumed. They were appreciated for their flavor and versatility in cooking. Roman culinary texts mention the use of hazelnuts in sweet and savory dishes, as well as in the production of oils (Chabrán, 2002). In medieval Europe, hazelnuts played a significant role in the culinary traditions of various regions. They were used in confectionery, baked goods, and traditional dishes. Hazelnuts were also associated with folklore and superstitions, believed to bring good luck and protection (Figure 1.3)

FIGURE 1.3 Different growth stages of hazelnut.

1.4.5 Trade and Cultural Exchange

The historical cultivation and trade of temperate nut crops have played a significant role in cultural exchange and the spread of culinary traditions. As civilizations developed trade networks and explored new territories, the exchange of goods, including nuts, facilitated cultural connections and influenced local cuisines. The Silk Road, an ancient network of trade routes connecting Asia, Europe, and Africa, played a crucial role in the spread of almonds, walnuts, and hazelnuts. These nuts were among the valuable commodities traded along the Silk Road, allowing for cultural exchange and the introduction of new flavors and culinary techniques (Zhang, 2019). The popularity of temperate nut crops grew during the medieval period, as trade routes expanded and explorers discovered new lands. The Crusades, in particular, played a significant role in introducing almonds, walnuts, and hazelnuts to Europe. Crusaders returning from the Middle East brought back various crops, including nuts, which were then cultivated in European gardens and incorporated into local cuisines (Adamson, 2004). Furthermore, temperate nut crops have made their way into global culinary traditions through exploration, colonization, and trade. Almonds, for example, were introduced to the Americas by Spanish explorers and have become key ingredients in Latin American cuisines. Walnuts have been incorporated into dishes in North America, particularly in traditional Native American cuisine and European-inspired recipes. Hazelnuts are prominent in European desserts, including the famous Italian gianduja and the French praline.

1.5 Evolution of Cultivation Techniques For Temperate Nut Crops

The cultivation of temperate nut crops, such as almonds, walnuts, and hazelnuts, has evolved over centuries through advancements in agricultural practices and the development of specialized cultivation techniques. These crops have been cultivated for their nutritional value, economic benefits, and cultural significance. This chapter explores the evolution of cultivation techniques for temperate nut crops, highlighting the innovations and practices that have contributed to their successful cultivation, improved productivity, and enhanced sustainability.

1.5.1 Early Cultivation

The cultivation of temperate nut crops dates back thousands of years. Early farmers relied on traditional farming practices and local knowledge to cultivate these crops. Ancient civilizations, such as those in Mesopotamia, Egypt, Persia, and Greece, recognized the value of nut crops and developed techniques to cultivate and harvest them. In the early stages, cultivation was often limited to regions with suitable climatic conditions. Farmers selected suitable planting sites with adequate sunlight and well-drained soil to ensure optimal growth and development of the nut trees. They relied on natural rainfall and local water sources for irrigation, ensuring adequate water supply for the trees during dry periods.

1.5.2 Propagation

The propagation of temperate nut crops has evolved from simple seed sowing to more sophisticated methods, including grafting and budding. Early cultivation relied on seed propagation, where nuts were collected and planted directly in the field. However, this method resulted in variability in tree quality and nut characteristics. Grafting and budding techniques were later developed to ensure the propagation of desirable traits and to improve tree uniformity. Grafting involves joining a scion (a selected portion of a desirable tree) with a rootstock, allowing for the transfer of desired characteristics to the new tree. Budding is a similar technique where a bud from a selected variety is inserted into a cut made in the rootstock. These techniques have played a significant role in the cultivation of improved cultivars and the maintenance of genetic diversity in nut crops (Khan et al., 2021).

1.5.3 Orchard Management

Over time, cultivation techniques for temperate nut crops have expanded to include various orchard management practices that optimize tree growth, health, and productivity. Pruning is an essential practice that helps maintain tree structure, improve light penetration, and enhance air circulation within the canopy. Pruning also aids in disease and pest management, facilitates harvest, and promotes overall tree health (Aristizábal et al., 2016). Nutrient management is crucial for the healthy growth and productivity of nut crops. Early cultivation relied on natural nutrient cycling and the addition of organic matter, such as animal manure or plant residues, to maintain soil fertility. In modern cultivation, nutrient requirements are assessed through soil and leaf analysis, and fertilizers are used to address specific nutrient deficiencies. Nutrient management practices aim to provide the necessary nutrients for tree growth while minimizing nutrient runoff and environmental impacts (Zhang et al., 2012).

1.5.4 Irrigation

Irrigation techniques have evolved to ensure optimal water management and improve water use efficiency in nut crop cultivation. Early cultivation relied on natural rainfall and traditional irrigation methods, such as flooding or furrow irrigation, where water is applied to the soil surface. These methods were often inefficient and resulted in water loss through evaporation and runoff. Modern cultivation has seen the adoption of more efficient irrigation systems, such as drip irrigation and micro-sprinklers. Drip irrigation delivers water directly to the root zone of the trees, minimizing water loss and improving water use efficiency (Ma et al., 2020). Micro-sprinklers provide uniform water distribution over the orchard, reducing water wastage and ensuring even moisture distribution. These irrigation systems allow for precise control of water application, tailored to the specific needs of the nut crops, resulting in improved water conservation and enhanced crop productivity.

1.5.5 Pest and Disease Management

The evolution of cultivation techniques for temperate nut crops includes advancements in pest and disease management. Early farmers relied on natural methods, such as manual removal of pests and disease-affected plant parts, to control infestations. However, as agriculture intensified and production systems expanded, the need for more effective pest and disease management practices arose. IPM approaches have gained prominence in modern cultivation. IPM combines various strategies, including cultural, biological, and chemical control methods, to manage pests and diseases while minimizing environmental impacts (Barzman et al., 2015). These strategies may include the use of pheromone traps, biological control agents, and targeted pesticide applications when necessary. The adoption of IPM practices helps reduce pesticide use, preserve beneficial insects, and promote long-term sustainability in nut crop cultivation.

1.5.6 Mechanization

Mechanization has played a significant role in improving efficiency and productivity in nut crop cultivation. The introduction of machinery and equipment has reduced labor requirements, increased production capacity, and improved overall efficiency in various cultivation tasks. Mechanical harvesters have been developed to streamline the harvesting process, especially for almonds and walnuts. These machines shake the trees, causing the nuts to fall onto catch frames or collection systems. Mechanical harvesters have significantly reduced labor costs and increased harvesting speed, making nut crop production more efficient and cost-effective (Brondino et al., 2021).

1.5.7 Genetic Improvement

Advancements in genetic improvement techniques have also contributed to the evolution of temperate nut crop cultivation. Traditional breeding methods, such as controlled pollination and selection of desirable traits, have been used to develop improved cultivars with enhanced characteristics, such as higher yield, disease resistance, and better nut quality. In recent years, molecular breeding techniques, including marker-assisted selection and genetic engineering, have accelerated the genetic improvement of nut crops. These techniques allow for more precise selection and manipulation of specific traits, such as drought tolerance, pest resistance, and enhanced nutritional profiles (Munaweera et al., 2022). Genetic improvement efforts aim to develop nut cultivars that are well-adapted to specific growing conditions, have improved yield potential, and exhibit resilience to environmental stresses.

1.5.8 Water Management

Efficient water management has been a crucial area of focus in the evolution of nut crop cultivation techniques. As water scarcity becomes a global concern, optimizing water use efficiency and implementing sustainable irrigation practices are essential. Precision irrigation techniques, such as deficit irrigation and regulated deficit irrigation, have been developed and adopted in nut crop cultivation. These techniques involve providing water to nut trees based on their specific water requirements at different growth stages. By carefully managing irrigation, farmers can reduce water use, minimize runoff, and maintain optimal tree health and productivity (Ayars et al., 2015). In addition to precision irrigation, water recycling and reuse systems have been implemented in nut crop cultivation. Wastewater from processing facilities or other agricultural activities is treated and reused for irrigation purposes. This reduces reliance on freshwater resources and contributes to sustainable water management (Hekmatnia et al., 2023).

1.5.9 Climate Change Adaptation

The evolution of cultivation techniques for temperate nut crops also includes adaptation strategies to cope with the challenges posed by climate change. Changing climatic conditions, such as increasing temperatures, altered precipitation patterns, and more frequent extreme weather events, require proactive measures to ensure the resilience and productivity of nut crop cultivation. Farmers are implementing strategies such as selecting cultivars that are more tolerant to heat and drought, adjusting planting dates, and modifying orchard management practices to mitigate the impact of climate change. The use of shade structures, windbreaks, and mulching materials can help regulate temperature and moisture levels within the orchard, providing a more favorable environment for nut tree growth (Mechergui et al., 2021). Research efforts are focused on developing climate-resilient nut cultivars through breeding and genetic engineering approaches. These cultivars are being bred to exhibit improved tolerance to heat, drought, pests, and diseases, enabling them to thrive in changing climatic conditions (Meyer et al., 2017). The use of molecular markers and genomic selection techniques accelerates the breeding process, allowing for the development of new cultivars with desired traits more efficiently (He et al., 2020).

1.6 Cultural and Culinary Traditions Associated With Temperate Nut Crops

Temperate nut crops, such as almonds, walnuts, and hazelnuts, have been an integral part of cultural and culinary traditions around the world for centuries. These nuts have played significant roles in various cuisines, religious practices, and festive celebrations. This chapter explores the cultural and culinary traditions associated with temperate nut crops, highlighting their historical significance, symbolic meanings, and diverse culinary uses across different cultures.

1.6.1 Historical Significance And Symbolism

Temperate nut crops have held historical significance and symbolic meanings in many cultures throughout history. They have been associated with fertility, abundance, prosperity, wisdom, and religious rituals. In ancient civilizations, such as Mesopotamia, Egypt, and Persia, almonds, walnuts, and hazelnuts were revered for their nutritional value and were considered symbols of fertility and abundance (Hageneder, 2020). Almonds, in particular, held symbolic importance in ancient Egyptian culture and were often included in burial rituals and tombs, signifying rebirth and immortality (Mustafa, 2019). The association of nuts with wisdom and intelligence is also evident in various cultures. Walnuts, with their distinctive brain-like appearance, have been linked to knowledge and wisdom. In ancient Persia, walnuts were known as the “royal nut” and were associated with divine intelligence (Wilke, 2017). In Greek mythology, walnuts were considered a symbol of divine intelligence and were associated with gods such as Zeus and Athena (Bernal, 2020).

1.6.2 Culinary Uses in Traditional Cuisine

Temperate nut crops have been utilized in traditional cuisine across different cultures, adding flavor, texture, and nutritional value to a wide range of dishes. The culinary uses of almonds, walnuts, and hazelnuts vary across regions, reflecting local food traditions and preferences. In Mediterranean cuisine, almonds have been widely used in both savory and sweet dishes. Almond-based desserts, such as almond pastries, marzipan, nougat, and almond milk, are popular in countries like Spain, Italy, and Greece (Mason, 2018). Almonds are also used in savory dishes, such as almond-crusted fish or chicken, rice pilaf with almonds, and almond-based sauces. Walnuts are prominent in European and Middle Eastern cuisines. In Eastern Europe, walnuts are used in a variety of dishes, including walnut-filled pastries, cakes, and traditional nut rolls (Shafia, 2013). In Mediterranean cuisine, walnuts are commonly used in savory salads, grain dishes, and sauces, as well as in sweet preparations, such as baklava, walnut cakes, and confections (Davidson, 2014). Hazelnuts are widely used in European culinary traditions. In Italy, hazelnuts are a key ingredient in the famous chocolate-hazelnut spread, Nutella, and are used in various desserts, such as cakes, cookies, and gelato (Sullivan et al., 2012). In Turkish cuisine, hazelnuts are incorporated into desserts like baklava and are also used in savory dishes, including meat and vegetable preparations (Samancı et al., 2020).

1.6.3 Religious and Festive Celebrations

Temperate nut crops play a significant role in religious and festive celebrations in many cultures. They are often featured in religious ceremonies, offerings, and festive meals. In Judaism, almonds hold symbolic importance during the celebration of Tu B’Shevat, the New Year for Trees. Almond trees are associated with the awakening of nature and the arrival of spring, and almonds are included in the traditional meal as a reminder of the importance of trees and nature (Marks et al., 2010). During Christmas in many Western countries, nuts, including walnuts and hazelnuts, are commonly featured in traditional holiday desserts, such as Christmas cakes, cookies, and confections (Mason, 2018). Nuts are also used in festive dishes, such as stuffing for roast meats or as an ingredient in savory side dishes (Uğurlu, 2016). The rich and indulgent nature of nut-based desserts is associated with celebrations and joyful gatherings.

1.6.4 Symbolic Meanings In Folklore And Superstitions

Temperate nut crops have been associated with various folklore, superstitions, and beliefs in different cultures. In many regions, nuts are believed to bring good luck, wealth, and protection. In European folklore, hazelnuts are associated with wisdom and protection against evil spirits. Hazelnuts were often used as charms or amulets and were believed to possess magical properties. In some cultures, the act of cracking or breaking nuts during festive gatherings is believed to bring good luck and fortune to the individuals involved. It is a common practice during celebrations, such as New Year’s Eve or weddings, where family members and friends gather to crack nuts together and share the kernels (Oxfeld, 2017).

1.6.5 Medicinal And Health Traditions

In addition to their culinary uses, temperate nut crops have been valued for their medicinal properties in traditional medicine systems. Ancient cultures recognized the health benefits and healing properties of almonds, walnuts, and hazelnuts. In traditional Chinese medicine, almonds have been used for their medicinal properties, particularly in promoting respiratory health and relieving coughs (Cao et al., 2020). Almonds are believed to have a soothing effect on the lungs and are often used in remedies for respiratory conditions, such as asthma and bronchitis. Walnuts have been used in traditional medicine to support brain health and improve cognitive function. In Ayurvedic medicine, walnuts are considered a “brain food” and are recommended for enhancing memory and promoting mental clarity (Tabish and Jawaid, 2012). The high content of omega-3 fatty acids and antioxidants in walnuts is believed to contribute to their neuroprotective effects (Blondeau et al., 2015). Hazelnuts have been associated with various health benefits in traditional medicine. In ancient Greece, hazelnuts were believed to have aphrodisiac properties and were used to enhance fertility. Hazelnuts have also been used in traditional remedies for digestive disorders, as they are believed to aid digestion and relieve stomach discomfort (Table 1.1) (Asadi et al., 2021).

Table 1.1 Nutritional and Medicinal Properties of Temperate Nut Crops ⏎

Nut Crop | Nutritional Properties | Medicinal Properties | References
Almonds | Rich in monounsaturated fats, fiber, vitamin E, antioxidants, magnesium | Anti-inflammatory properties, potential anti-cancer effects | De and De, 2021
Walnuts | High in omega-3 fatty acids, protein, fiber, antioxidants, vitamin E | Cardiovascular health benefits, anti-inflammatory properties, potential anti-cancer effects | Camara and Schlegel, 2016
Hazelnuts | Good source of monounsaturated fats, fiber, vitamin E, minerals (magnesium, phosphorus) | Cardiovascular health benefits, antioxidant properties | De, 2020
Pistachios | Rich in healthy fats, fiber, protein, antioxidants, vitamin E, carotenoids (lutein, zeaxanthin) | Cardiovascular health benefits, antioxidant properties | Yuan et al., 2022
Chestnuts | Low in fat, high in carbohydrates, fiber, vitamins B and C, minerals (potassium, magnesium) | Anti-inflammatory properties, antioxidant effects, potential vascular health benefits | Goncalves et al., 2023
Pecans | Rich in healthy fats, fiber, antioxidants, minerals (manganese, copper) | Cardiovascular health benefits, antioxidant properties, potential anti-cancer effects | Gupta and Mishra, 2021
Cashews | Good source of healthy fats, protein, dietary fiber, vitamins B and E, minerals (magnesium, zinc) | Cardiovascular health benefits, anti-inflammatory properties | De, 2020
Macadamia Nuts | Rich in monounsaturated fats, dietary fiber, antioxidants, vitamins B and E | Cardiovascular health benefits, potential antiinflammatory effects | Hong et al., 2018
Brazil Nuts | High in healthy fats, protein, dietary fiber, antioxidants, selenium | Antioxidant properties, potential anti-inflammatory effects | Medina-Vera et al., 2021
Pine Nuts | Good source of healthy fats, protein, dietary fiber, antioxidants, vitamins E and K | Appetite suppression, potential anti-inflammatory effects | Mohammed and Qoronfleh, 2020
Beech Nuts | Rich in healthy fats, protein, dietary fiber, antioxidants, vitamins B and E | Antioxidant properties, potential anti-inflammatory effects | Oracz et al., 2023

1.6.6 Nuts in Cultural Celebrations and Symbolism

Temperate nut crops hold symbolic meanings and are featured in cultural celebrations and rituals in different parts of the world. These nuts are often associated with fertility, abundance, prosperity, and well-being. In Hindu culture, almonds, walnuts, and hazelnuts are included in traditional wedding ceremonies and rituals. The nuts are considered symbols of fertility and are offered to the bride and groom as a blessing for a prosperous married life (Burch, 2019). In the Middle East, nuts play a significant role in celebrations such as Eid al-Fitr, which marks the end of Ramadan. Nuts, including almonds and pistachios, are often served as part of festive sweets and desserts during this joyous occasion (Roufs, 2014). The inclusion of nuts in these celebrations symbolizes abundance and good fortune. During the Jewish holiday of Passover, almonds hold symbolic importance and are featured in traditional dishes. Almonds are used in charoset, a sweet paste made from fruits and nuts, which represents the mortar used by the Israelites during their slavery in ancient Egypt (Marks, 2010). The presence of almonds in this symbolic dish serves as a reminder of hope and liberation.

1.6.7 Nuts As Culinary Staples And Traditional Ingredients

Temperate nut crops have been culinary staples in various cuisines, and their unique flavors and textures have inspired a multitude of traditional recipes. In Moroccan cuisine, almonds are a key ingredient in savory dishes such as tagines and couscous, adding richness and depth of flavor (Norman, 2021). Almonds are also used in traditional sweets like pastries and cookies, such as the famous almond-filled Moroccan pastry known as gazelle horns. Walnuts are commonly used in traditional dishes across Europe, particularly in Eastern European cuisines. In countries like Romania and Bulgaria, walnuts are used in savory dishes like stuffed peppers and cabbage rolls, as well as in desserts like walnut-filled pastries and cakes (Pérez- Shafia, 2013). In English cuisine, walnuts are a key ingredient in classic desserts such as the walnut tart or the traditional Christmas cake.

1.6.8 Nuts In Culinary Innovation

The cultural and culinary traditions associated with temperate nut crops continue to evolve, adapting to modern tastes and culinary trends. Chefs and food enthusiasts are exploring innovative ways to incorporate nuts into contemporary dishes, showcasing their versatility and unique flavors. Almond milk, a popular plant-based alternative to dairy milk, has gained popularity in recent years. It is used in a variety of recipes, including smoothies, baked goods, and savory dishes, providing a creamy texture and a subtle nutty flavor (Howard, 2021). Nuts are also being used as ingredients in innovative culinary creations such as nut-based cheeses, nut flours for gluten-free baking, and nut butter variations beyond the classic peanut butter. These creative uses of nuts add depth, richness, and nutritional value to a wide range of dishes, catering to diverse dietary preferences and culinary experiences.

1.7 Scope Of Temperate Nut Crops

1.7.1 Current State And Future Potential Of Temperate Nut Crop Production

Temperate nut crops, including almonds, walnuts, and hazelnuts, have gained significant attention in recent years due to their nutritional value, economic importance, and environmental benefits. The global demand for these nuts has been steadily increasing, leading to expanded cultivation and improved production practices. This chapter provides an overview of the current state of temperate nut crop production, highlighting key production regions, market trends, and challenges. Additionally, it explores the future potential of nut crop production, considering emerging markets, technological advancements, and sustainability initiatives.

1.7.2 Current State Of Temperate Nut Crop Production

1.7.2.1 Almonds

Almonds are the most widely cultivated nut crop among the temperate nut varieties. The United States, particularly California, is the largest producer of almonds, accounting for over 80% of global production (USDA, 2020). Other significant almond-producing countries include Spain, Australia, Iran, and Italy. California’s Central Valley, with its Mediterranean climate and ideal growing conditions, is the primary almond production region. The expansion of almond cultivation in California has been driven by increased global demand, particularly from emerging markets such as China and India. Almond production in California has also benefitted from advancements in irrigation technology, improved orchard management practices, and ongoing research and development efforts (Jha et al., 2022).

1.7.2.2 Walnuts

Walnuts are another important temperate nut crop, cultivated worldwide for their nutritional value and versatile culinary uses. The major walnut-producing countries include China, the United States, Iran, Ukraine, and Turkey. China is the largest producer of walnuts, followed by the United States, primarily in California. California’s Central Valley is the primary walnut production region in the United States, accounting for the majority of the country’s production. The favorable climate, extensive orchard infrastructure, and efficient post-harvest processing facilities contribute to California’s success in walnut production (USDA, 2020). In recent years, China has significantly expanded its walnut production, driven by increasing domestic demand and growing exports to international markets (Pigato and Tang, 2015).

1.7.2.3 Hazelnuts

Hazelnuts, also known as filberts, are predominantly grown in regions with a temperate climate. The major hazelnut-producing countries include Turkey, Italy, the United States, Azerbaijan, and Georgia. Turkey is the largest producer and exporter of hazelnuts globally, accounting for approximately 70% of the total global production (FAO, 2020). In recent years, there has been an increased interest in hazelnut production in countries like Italy and the United States. In the United States, Oregon is the primary hazelnut-producing state, with a climate and soil conditions suitable for hazelnut cultivation (USDA, 2020). Italy, particularly the region of Piedmont, is known for high-quality hazelnuts used in confectionery and the production of hazelnut-based spreads.

1.7.3 Market Trends And Consumer Demand

The demand for temperate nut crops has been driven by their nutritional value, health benefits, and versatile culinary uses. Consumer awareness of the health benefits associated with nut consumption, such as heart health, weight management, and nutrient density, has contributed to increased demand worldwide (Vadivel et al., 2012). In addition to the traditional consumer markets in North America and Europe, emerging markets in Asia, particularly China and India, have witnessed significant growth in nut consumption. Rising incomes, changing dietary preferences, and increased awareness of the nutritional value of nuts have fueled demand in these markets (Baker et al., 2020). There has also been a growing interest in plant-based diets and the demand for plant-based protein sources. Nuts, including almonds and walnuts, are recognized for their protein content and are considered valuable alternatives to animal-based proteins (Qamar, 2020). The increased adoption of vegetarian and vegan diets has further fueled the demand for nut-based products and ingredients (Table 1.2).

Table 1.2 Major Cultivation Regions and Notable Facts of Temperate Nut Crops ⏎

Nut Crop | Major Cultivation Regions | Additional Cultivation Regions | Notable Facts | References
Almonds | United States (California), Spain | Australia, Iran, Italy, Morocco, Portugal, Greece, South Africa | Almonds are California’s top agricultural export and account for over 80% of the world’s almond production. | Gradziel et al., 2017
Walnuts | United States (California), China, Iran | Turkey, France, Romania, Ukraine, Chile, New Zealand, Australia | Walnuts are the oldest known tree food, dating back to 7000 BCE. | Vahdati et al., 2019
Hazelnuts | Turkey, Italy, United States (Oregon) | Georgia, Azerbaijan, Spain, France, United Kingdom, Poland, Hungary | Turkey is the largest producer of hazelnuts, accounting for approximately 70% of the global production. | Jeanmart, 2021
Pistachios | United States (California), Iran | Turkey, Syria, China, Greece, Italy, Australia, Uzbekistan | Iran is the largest producer and exporter of pistachios, followed by the United States. | Nezami and Gallego, 2023
Chestnuts | China, South Korea, Italy, Portugal | United States (Michigan, Wisconsin), Japan, France, Turkey, Greece | China is the largest producer of chestnuts, accounting for more than half of the global production. | Beccaro et al., 2023
Pecans | United States (Georgia, Texas) | Mexico, South Africa, Australia, China, Brazil | The United States is the largest producer of pecans, with Georgia being the top pecan-producing state. | Prabhakar et al., 2022
Cashews | India, Vietnam, Nigeria, Ivory Coast | Brazil, Tanzania, Mozambique, Indonesia, Benin, Ghana, Philippines | India is the largest producer and exporter of cashews, accounting for about 50% of the global production. | Tola and Mazengia, 2019
Macadamia Nuts | Australia, South Africa, Kenya | United States (Hawaii, California), Malawi, New Zealand | Australia is the largest producer of macadamia nuts, followed by South Africa. | Zuza et al., 2021
Brazil Nuts | Brazil, Bolivia, Peru, Colombia | Venezuela, Ecuador, Guyana, Suriname | Brazil is the largest producer and exporter of Brazil nuts, accounting for the majority of the global production. | Tenorio, 2018
Pine Nuts | China, Russia, South Korea, Italy | Afghanistan, Mongolia, Pakistan, Turkey, Iran, United States | The Korean pine (Pinus koraiensis) is the primary species cultivated for pine nut production in South Korea. | Awan and Pettenella, 2017
Beech Nuts | United States (Maine), Europe, Asia | Asia, Europe | Beech nuts are small triangular nuts that are often foraged rather than cultivated due to the trees’ wild growth habit. | Duke, 2019

1.7.4 Challenges and Opportunities

Despite the growth and opportunities in temperate nut crop production, several challenges need to be addressed for sustainable and resilient production systems. Water availability is a critical factor in nut crop production, as these crops require adequate water throughout the growing season. In regions where water resources are limited or subject to competing demands, efficient irrigation practices and water management strategies are crucial. The ongoing water challenges faced by almond production in California have prompted significant efforts to improve water use efficiency. Technologies such as precision irrigation systems, soil moisture sensors, and deficit irrigation techniques are being employed to optimize water use and minimize environmental impacts (Abioye et al., 2020). Furthermore, research is focused on developing drought-tolerant rootstocks and cultivars to enhance the resilience of nut crops to water stress (Palanivel and Shah, 2021).

1.7.5 Future Potential

The future potential of temperate nut crop production lies in several areas, including technological advancements, emerging markets, and sustainability initiatives. Technological advancements, such as remote sensing, precision agriculture, and robotics, offer opportunities to enhance productivity, reduce labor requirements, and optimize resource use in nut crop cultivation. Drones equipped with multispectral sensors can provide real-time data on crop health, nutrient status, and water stress, enabling targeted interventions and improved management practices (Nhamo et al., 2020). Robotic technologies for tasks such as harvesting and pruning can increase efficiency and reduce production costs (Vasconez et al., 2019). Emerging markets, particularly in Asia, present significant growth opportunities for nut crop producers. The rising middle class, increasing disposable incomes, and changing dietary preferences in these markets contribute to the growing demand for nuts. Developing strategic partnerships and establishing market access in these regions can help nut producers expand their customer base and diversify their export markets. Sustainability initiatives, such as organic production, agroforestry systems, and regenerative agriculture practices, offer potential avenues for enhancing the sustainability and resilience of nut crop production. Organic production methods can meet the increasing demand for organic nuts and cater to consumers seeking environmentally friendly and socially responsible products. Agroforestry systems that integrate nut crops with other crops or livestock can enhance biodiversity, soil health, and ecosystem services (Jose, 2019).

1.7.6 Research And Development

Ongoing research and development efforts play a crucial role in the advancement of temperate nut crop production. Researchers are actively exploring various areas to enhance yield potential, improve quality, and address production challenges. Breeding programs aim to develop improved nut cultivars with desirable traits, such as disease resistance, higher yield, and improved nut quality. Traditional breeding methods, as well as modern molecular breeding techniques, are employed to accelerate the development of new cultivars. Genetic resources and germplasm repositories are vital for preserving genetic diversity and facilitating breeding programs (Grumet et al., 2021).

1.7.7 Nutritional Enhancement

Nutritional enhancement of temperate nut crops is an area of growing interest. Researchers are focusing on enhancing the nutritional profiles of nuts by increasing the levels of beneficial compounds, such as antioxidants, vitamins, and minerals. For example, efforts are underway to increase the levels of beneficial polyphenols, particularly in almonds and walnuts, as these compounds have been associated with various health benefits (BarralMartinez et al., 2021).

1.7.8 Processing And Value-Added Products

The processing and development of value-added products offer opportunities to expand the market potential of temperate nut crops. Innovations in processing technologies and techniques can improve product quality, extend shelf life, and create new product forms. Nut milk, nut butter, and nut-based spreads have gained popularity as plant-based alternatives to dairy and other spreads. These products cater to consumers with dietary restrictions, allergies, or ethical considerations (Xypolitaki, 2023). Additionally, the utilization of nut by-products, such as shells and husks, for energy generation or the production of bioactive compounds contributes to waste reduction and sustainability in the nut processing industry.

1.7.9 Expanding Market Opportunities For Temperate Nut Crops

Temperate nut crops, such as almonds, walnuts, and hazelnuts, have gained significant popularity and recognition due to their nutritional value, versatility, and health benefits. As consumer demand for plant-based protein sources, healthy snacks, and natural ingredients continues to rise, the market for temperate nut crops has expanded beyond traditional boundaries. This chapter explores the expanding market opportunities for temperate nut crops, including emerging consumer trends, new product developments, and global market dynamics.

1.7.10 Consumer Trends And Market Drivers

Several consumer trends and market drivers have contributed to the increasing market opportunities for temperate nut crops:

Healthy Snacking and Plant‑Based Diets: The growing awareness of health and wellness has led to a shift in consumer preferences towards healthier snack options. Nuts are considered nutritious, convenient, and satisfying snacks, making them a popular choice among health-conscious consumers. The rise of plant-based diets, driven by concerns for sustainability, animal welfare, and personal health, has further fueled the demand for plant-based protein sources like nuts (Hemler and Hu, 2019).

Nutritional Benefits: Temperate nut crops are rich in nutrients, including healthy fats, protein, fiber, vitamins, and minerals. These nutritional profiles have been linked to various health benefits, such as heart health, weight management, and improved cognitive function (Mandalari et al., 2021). Consumers seeking natural and nutrient-dense foods are increasingly incorporating nuts into their diets.

Snacking On‑the‑Go: The busy lifestyles of modern consumers have led to an increased demand for convenient, portable, and healthy snack options. Nuts are naturally well-suited for on-the-go snacking, as they require minimal processing and packaging. This convenience factor has contributed to the growth of the nut snack market, with products like nut mixes, single-serve packs, and nut bars gaining popularity.

Culinary Applications: The culinary versatility of temperate nut crops has opened up new market opportunities. Nuts are used in a wide range of culinary applications, including baking, confectionery, savory dishes, and plant-based alternatives. The use of nut flours, nut butters, and nut-based spreads has expanded beyond traditional applications, catering to the demand for gluten-free, vegan, and allergy-friendly products.

1.7.11 Market Developments And Innovations

The expanding market for temperate nut crops has spurred several developments and innovations, creating new product categories and value-added offerings:

Nut‑Based Milks and Dairy Alternatives: The demand for plantbased milks and dairy alternatives has increased significantly in recent years. Almond milk, walnut milk, and hazelnut milk have become popular choices among consumers seeking dairy-free alternatives. These nut-based milks are used in various applications, including cereal, coffee, smoothies, and as a replacement for cow’s milk in recipes (Cardello et al., 2022). The market for dairy alternatives continues to expand, with new formulations and flavors entering the market.

Nut Snacks and Trail Mixes: The demand for convenient and healthy snacks has led to the development of a wide variety of nut-based snacks. Nut mixes, trail mixes, and flavored nuts offer consumers a convenient and nutritious snacking option. Manufacturers are incorporating different flavor profiles, such as spicy, sweet, and savory, to cater to diverse consumer preferences. Additionally, the inclusion of other ingredients like dried fruits, seeds, and chocolate adds variety and enhances the taste experience.

Nut‑Based Spreads and Butters: Nut-based spreads and butters, such as almond butter, walnut butter, and hazelnut spread, have gained popularity as alternatives to traditional spreads like peanut butter. These spreads are used as toppings for toast, as ingredients in baked goods, and as a versatile component in various recipes. The demand for natural, preservative-free, and premium-quality nut spreads has created opportunities for small-scale producers and artisanal brands.

Nut‑Based Protein Products: The increasing interest in plant-based protein sources has driven the development of nut-based protein products. Nut protein powders, protein bars, and protein-enhanced nut butters cater to consumers seeking protein-rich options for fitness, sports, and general wellness. These products offer a convenient and sustainable alternative to animal-based proteins, particularly for vegetarian, vegan, and flexitarian diets.

1.7.12 Global Market Dynamics

The global market for temperate nut crops is influenced by several factors, including production trends, trade dynamics, and consumer preferences:

Production and Supply: The production of temperate nut crops is geographically concentrated, with specific regions dominating global production. For example, California is a major producer of almonds and walnuts, while Turkey leads in hazelnut production (USDA, 2020; FAO, 2020). Weather conditions, crop yields, and farming practices in these key production regions can affect global supply and prices.

International Trade: The international trade of temperate nut crops plays a vital role in meeting global demand and balancing supply and demand dynamics. Trade agreements, tariffs, and market access regulations influence the flow of nuts between countries. Importing countries, such as China and India, play a significant role in driving global trade and consumption patterns. Understanding trade dynamics and establishing market access are essential for nut producers and exporters.

Sustainability and Traceability: Consumer demand for sustainably produced and ethically sourced products is growing. Certifications such as organic, fair-trade, and sustainability labels provide assurances to consumers regarding production practices and social and environmental responsibility. Traceability systems and supply chain transparency are becoming increasingly important as consumers seek to make informed choices and support ethical and sustainable nut production.

Emerging Markets: The global market for temperate nut crops is witnessing significant growth in emerging markets, presenting new opportunities for nut producers. The rising middle class, increasing disposable incomes, and changing dietary preferences in countries such as China, India, Brazil, and Southeast Asian nations have fueled the demand for temperate nut crops. China, in particular, has emerged as a major consumer and importer of almonds, walnuts, and hazelnuts. The country’s growing middle class, coupled with increasing awareness of the health benefits of nuts, has driven the demand for these products (Tripathi et al., 2019). Nut producers are actively targeting the Chinese market by establishing trade partnerships, participating in international trade shows, and adapting their marketing strategies to cater to Chinese consumers’ preferences.

1.8 Research And Innovation In Temperate Nut Crop Development

Research and innovation play a crucial role in the development and improvement of temperate nut crops, such as almonds, walnuts, and hazelnuts. Through scientific studies, breeding programs, and technological advancements, researchers and industry professionals have made significant contributions to enhancing the productivity, quality, and sustainability of nut crop cultivation. This chapter explores the research and innovation in temperate nut crop development, highlighting key areas of focus, breeding strategies, and technological advancements that drive progress in the field.

1.8.1 Breeding And Genetic Improvement

Breeding programs have been instrumental in developing improved cultivars of temperate nut crops. Through traditional breeding methods and modern molecular techniques, researchers aim to develop cultivars with enhanced traits, such as disease resistance, yield potential, nut quality, and adaptability to changing environmental conditions. One key area of focus in breeding programs is disease resistance. Diseases such as fungal pathogens and insect pests can significantly impact nut crop yields and quality. Researchers are identifying genetic markers associated with resistance to diseases such as navel orange worm in almonds, walnut blight in walnuts, and Eastern filbert blight in hazelnuts (Sheikhi et al., 2019). This knowledge allows breeders to incorporate disease resistance traits into new cultivars, reducing the reliance on chemical pesticides and enhancing the sustainability of nut crop production. Additionally, researchers are using molecular techniques, such as marker-assisted selection and genomic selection, to expedite the breeding process. These techniques allow for the identification of specific genes or genetic markers associated with desirable traits, enabling breeders to select individuals with those traits more efficiently (Fiedler et al., 2017). The integration of molecular breeding approaches with traditional breeding methods accelerates the development of new cultivars with improved traits.

1.8.2 Technological Advancements

Technological advancements have revolutionized the nut crop industry, enabling growers to improve productivity, optimize resource use, and enhance overall efficiency. Several key areas of technological innovation have had a significant impact on temperate nut crop development.

1.8.3 Precision Agriculture

Precision agriculture involves the use of technologies, such as remote sensing, geographic information systems (GIS), and global positioning systems (GPS), to gather data and make informed decisions regarding crop management. In nut crop production, precision agriculture techniques help optimize irrigation, fertilizer application, and pest management, leading to improved resource use efficiency and enhanced crop health (Shah and Wu, 2019). For example, remote sensing technologies can detect water stress in nut orchards, allowing growers to apply water precisely where and when it is needed, minimizing water waste.

1.8.4 Sensor Technologies

Sensor technologies, including soil moisture sensors, weather stations, and plant sap flow sensors, provide real-time data on environmental conditions and plant health. These sensors help growers monitor water status, nutrient availability, and pest pressure, enabling timely interventions and precise management decisions (Sinha and Dhanalakshmi, 2022). By monitoring critical parameters, growers can optimize inputs and adjust cultivation practices, resulting in improved crop performance and resource efficiency.

1.8.5 Mechanization And Robotics

Mechanization and robotics have significantly improved efficiency and labor productivity in nut crop production. Technologies such as mechanical harvesters, automated pruning systems, and robotic pollinators reduce the need for manual labor and lower production costs (Karkee et al., 2021). Mechanical harvesting, in particular, has become increasingly prevalent in the almond industry, allowing for faster and more efficient nut collection.

1.8.6 Post-Harvest Technology

Post-harvest technology advancements have focused on nut processing, storage, and value-added product development. Innovations in sorting, grading, and processing equipment have improved nut quality, reducing the incidence of damaged or defective nuts (Miltner et al., 2018). Additionally, advancements in storage technologies, such as controlled atmosphere storage and modified atmosphere packaging, help extend the shelf life of nuts and maintain their freshness. These advancements not only benefit nut producers but also contribute to the overall quality and consumer satisfaction of nut products.

1.8.7 Sustainability And Environmental Considerations

Research and innovation in temperate nut crop development also address sustainability and environmental concerns. Nut crops require efficient resource management to minimize environmental impacts and ensure longterm sustainability.

1.8.8 Water Use Efficiency

Water scarcity is a significant challenge in nut crop production, particularly in regions with limited water resources. Researchers are developing irrigation strategies, such as deficit irrigation and regulated deficit irrigation, to optimize water use while maintaining crop productivity (Galindo et al., 2018). Furthermore, the use of precision irrigation technologies and soil moisture monitoring helps growers apply water precisely, reducing water waste and improving water use efficiency.

1.8.9 Climate Change Resilience

Climate change poses challenges to nut crop production, including increased temperatures, altered precipitation patterns, and extreme weather events. Researchers are exploring climate-resilient cultivars and management practices to mitigate the impact of climate change on nut crops (Acevedo et al., 2020).

1.8.10 Emerging Technologies

Emerging technologies, such as gene editing and genome sequencing, hold promise for advancing temperate nut crop development. Gene editing techniques, such as CRISPR-Cas9, enable precise modifications in the plant genome, accelerating the development of desired traits (Msanne et al., 2020). Genome sequencing projects provide valuable insights into the genetic makeup of nut crops, facilitating the identification of key genes and the understanding of complex traits (Pazhamala et al., 2021). These technologies have the potential to revolutionize nut crop breeding and contribute to the development of improved cultivars.

1.9 Conclusion

Temperate nut crops including hazelnuts, chestnuts, walnuts, and almonds are crucial to the world food and agriculture industries. These crops, which thrive in areas with mild weather, provide economic opportunity, dietary advantages, and culinary variety. For those interested in their production and trading, it is critical to comprehend the traits, cultivation methods, market dynamics, and historical relevance of temperate nut crops. These plants have a long history of sustaining life and bringing wealth to communities all across the planet. They are still grown today in favourable areas, making a considerable contribution to both domestic and international markets. Temperate nut crops, which have a high nutritional value and many culinary uses, are essential to a balanced diet and provide customers with a variety of alternatives. They also support the economy by creating jobs, revenue, and chances for rural development. Temperate nut crops have a promising future for market development and innovation as the demand for healthy, plantbased diets rises. Their production also supports biodiversity and ecosystem services by adhering to sustainable agricultural practices. Understanding the traits, cultivation methods, and market dynamics of temperate nut crops is crucial for maximizing their contribution to the global food chain and to the agricultural sector as a whole.

KEYWORDS

almond milk

breeding

global market

mechanization

nut crops

robotics

sustainability

temperate

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Chapter 2 Floral Biology, Pollination, and Genetic Resources in Nut Crops

TULSI D. GURJAR,1* AVNISH K. PANDEY,¹ and RAHUL R. RODGE²

¹ ASPEE College of Horticulture, Navsari Agricultural University, Navsari, Gujarat, India

² Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

*Corresponding author

Abstract

Nut fruits are among the most important horticultural crops, with production and consumption dramatically increasing due to their high nutritional and economic value. Floral biology of nut crop has prime practical implications, in addition to its scientific relevance, given that flower characteristics and bloom affect fruit characteristics and yield. Yield obtains from fruit quality and quantity, which, in turns, rely on flower quantity and quality. Flowers must be suitable to become fruits, and then must be pollinated and fertilized, and must set fruits, which must then grow. Pollination is an important link of successful plant reproduction, and is often dependent on mutualistic interactions with pollinators. Yields of most nut crops benefit to a great extent from biotic pollination, often by increasing the total number of nuts produced. Inadequate pollination and sexual incompatibility are significant factors contributing to poor bearing and low yield. so it is important to know the pollination and compatibility requirements of the nut crops. Besides this, understanding the floral and reproductive biology of nut crop is crucial for the development of strategies in plant breeding systems also. The genetic venerability of nut crops becomes increasingly important among plant breeders for finding particular characters, such as resistance genes for diseases, pests and nematodes or for adaptation to wider ecological amplitudes and stress conditions.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

2.1 Introduction

Floral biology, pollination, and the preservation of genetic resources play crucial roles in the cultivation and conservation of nut crops. Understanding these fundamental aspects is essential for optimizing yields, ensuring genetic diversity, and maintaining sustainable production practices. Floral biology forms the cornerstone of nut crop cultivation, encompassing the intricate processes involved in flower development, structure, and reproductive mechanisms. The study of floral biology elucidates the intricate relationships between floral morphology, phenology, and the reproductive strategies employed by nut-bearing plants. By comprehending the complex interplay between the floral anatomy and the reproductive cycle, researchers and growers can strategically manipulate environmental factors and cultural practices to enhance pollination success and fruit set. Pollination, a pivotal process in nut crop production, influences fruit quality and yield. The diverse mechanisms of pollination, including selfpollination, cross-pollination, and the role of pollinators, directly impact nut crop reproduction. Understanding the specific pollination requirements of different nut species is crucial for implementing effective management strategies. Encouraging pollinator diversity and promoting habitat conservation are essential for ensuring successful pollination and maximizing crop productivity.

Preserving the genetic resources of nut crops is integral to safeguarding the diversity and resilience of these valuable plant species. The conservation of genetic resources involves the collection, preservation, and utilization of genetic material to maintain genetic variability and adaptability within nut crop populations. By preserving diverse genetic resources, researchers can identify and harness desirable traits, such as disease resistance, improved yield, and enhanced nutritional content, to develop superior cultivars and sustain the long-term viability of nut crop production.

2.2 Almond

2.2.1 Floral Biology

2.1.1.1 Floral Bud Development

The almond is the earliest deciduous fruit and nut tree to bloom in spring, ascribable to its relatively low chilling requirements and rapid response to warm growing temperatures in the spring. Its plants are dormant during the winter season when the buds are subjected to chilling. The blooming and vegetative growth initiation takes place in late winter or early spring when temperatures become mild. The Blossom opening pattern of almonds is a typical sigmoid response curve in which blossoms start to open relatively slowly, the rate increases to a maximum and then slows down during the last part of the season. Growth refrains in late spring as the moisture in the ground is drained and a dormant condition develops during the dry, hot, rainless summers.

2.2.1.2 Flower

Flowering occurs laterally on the last season’s growth and on the long shoots and spurs, before the leaves open. Almond flower buds develop laterally on short spurs which may be 12.5–25 cm long and have 1–5 flower buds, although sometimes there are even more. Both self-incompatible and compatible germplasm are available in almonds. Flower color is white or pink. Flower buds encase in a single terminal flower and no leaves. Almond produces a typical perigynous hermaphrodite flowers and have five fused sepals, pubescent, purple-red in colour, five petals, variable in colour white, pink or rose colored, round at tip, a varying number of stamens (20–40), only one ovary enclosed in the floral cup with two ovules. In some cultivars, ovary abortion occurs in flowers on the long shoots and rarely in spurs. Ovule abortion was studied by Pimienta and Polito (1982) in Nonpareil almond, the earliest indication is the deposit of callose, 2 days after pollination, starting from chalazal region occupying progressively the nucellus, blocking translocation of metabolite supply, but whether this was the cause or consequence of ovule abortion was uncertain.

Flower induction occurs in the year preceding blooming, usually from May to June. The time of flowering also varies, from 10–30 days, based on the cultivars and climate; in continental areas blossom is almost simultaneous for all the cultivars, on the contrary in Mediterranean-like climate it is quite long. Flowering precedes leaf emergence and takes place in a very early season, occurring between January and April depending on the cultivar. Agabbio and Ortu (1974) demonstrated by removing the leaves that the period of induction depends on the cultivar; the more floriferous cultivars tending to differentiate earlier, around the middle of May. Heavy crop may reduce flower bud differentiation, although biennial bearing depends on the cultivar, even in good growing conditions. Nitrogen fertilization increases the number of flowers/trees rather than by increasing flower receptivity and percentage of fruit set (Weinbaum et al., 1980b). According to Grasselly and Crossa-Raynaund (1980a) Ferragnes, Nonpareil and Peerless have a slight tendency to biennial bearing, while cultivars Marcona and Tuono have more a tendency and Rachele has a strong tendency.

Morphological differentiation takes place in August, and at the beginning of autumn flower primordia emerge in the buds. Depending on the cultivar, pollen grain formation (microsporogenesis) occurs between December and January, while the ovary maturation (macrosporogenesis) occurs just before flowering, in contrast to other Prunus species (Pimienta and Polito, 1983). The flower buds develop on three types of shoot: (i) around the tip of short spurs, 3–10 cm long with less than 8 nodes, which have 1–5 or more flower buds; while the terminal bud is always vegetative, which maintains the elongation of the spur for subsequent years; (ii) on longer spurs or short shoots with 8–25 nodes; (iii) on long shoots, with more than 25 nodes, mainly at the distal end, where each pointed vegetative bud is subtended by swollen, rounded flower buds which normally contain only one flower, exceptionally two.

2.2.1.3 Stigma Receptivity

The percentage of stigma receptivity was maximum on the day of anthesis. Stigma receptivity declines rapidly within 3–5 days of anthesis. Stigma receptivity is reduced during unfavorable weather conditions. It is observed that the stigma is more receptive 2–3 days prior to anthesis and remained receptive till 2–3 days later anthesis.

2.2.2 Pollination

Almost all the cultivars of almond are self-unfruitful but there are others which are capable of setting fruits with their own pollen, such as, Tuono, Filippo Ceo, Genco (Grasselly and Olivier, 1976); Falsobarese, Ferrante, Palatina, Sannicandro, Scorsa Verde (Godini et. al., 1977) and Mollisona (Crescimanno, 1960) and also local strain Sloh (Peach x Almond) are selffertile; almost all others are self-incompatible. To overcome this problem, self-fruitful varieties have been developed and which claimed to have achieved a success in this direction. However, these selections have not yet attained commercial significance on account of poor nut quality and inherently being poor yielders. Only under very favorable environmental conditions the pollen tube can occasionally overcome this incompatibility (Ducom, 1968). So, almond should be cross-pollinated (Milella, 1959). The pollination is a must for a cultivar to be fruitful. Usually, two pollenizers are possibly used for commercial importance; one flowering a bit before and the other just after the main cultivar (Micke and Kester, 1981). Effective pollination can be obtained by single row of the main cultivar and the pollinator. The percentage of pollenizers (15%–20%), normally used for many other crops, is not enough for almond. Pollination is mainly by honey-bees; usually one or two colonies per hectare, but four or five colonies will ensure good pollination even during less favorable seasons with lower temperatures, more competition from herbaceous plants or wind (Thorp, 1981).

In the self-incompatible variety, the male gametophyte is rejected on the stigma and the style. It is characterized by reduced pollen grains on the stigma, reduced and delayed pollen germination and less development of pollen tubes from the style from when pollens are able to germinate. Depending on the cultivar, 15°C–23°C temperature (lower than other deciduous fruits) is necessary for germination of pollen and the growth of pollen tubes that reach the embryo sac in 3 days. Loreti and Viti (1984) observed that the pollen tubes of the early flowering Kapareil germinated at lower temperature (2°C–6°C) compared with others. Garcia et al. (1980) studied the influence of temperature on pollen germination of several almond varieties. According to Garcia (1977), pollen tubes grown in vitro, elongated about 3 times more at 15°C than at 10°C, although there was a marked difference between cultivars. For self-compatible cultivars, where pollen tube grows slowly and the best temperature is around 25°C instead of 15°C for frozen pollen. Stigma receptivity declines rapidly within 3–5 days. At petal fall stage a temperature lower than 1°C kill the styles and ovules. Usually one egg is fertilized, depending upon the cultivars and climatic conditions (Brewer, 1981).

Pimienta and Polito (1983) studied the development of the sac in the Nonpareil cultivar. They found that it occurs before anthesis, and is stimulated by the presence of compatible pollen tubes in the style; cross-pollination promotes its final elongation growth. They also found that abnormalities in megagametophyte development, including delayed megaspore mother cell differentiation, abortion of embryo sac and lack of polar nuclei fusion, and embryo sac elongation were frequently observed in the ovules of self- pollinated and non-pollinated flowers. Although there are two ovules, usually only one seed is produced. When one ovule developed after anthesis, the development of the other one is inhibited and remain much smaller than the other and both are not mature 1–2 days after pollination. Sometimes two kernels are also seemed to occur and this is the drawback of breeding. This is controlled by genotype and environment; earlier blooming flower produces the higher number of double kernels that receive the low temperature at blooming is considered as the major reason and justifying phenomena.

2.2.3 Genetic Resources

Some of the more than 30 species of almond identified by botanists may represent subspecies or ecotypes in a large collection of genotypes adapted to various ecological niches in the deserts, steppes, and Central Asian mountains. In the genus Prunus, the almond is closely related to the peach but separated from it by evolution in the xerophytic environment of Central and Southwest Asia (Watkins, 1979). Scientists have found that cultivated almond originated by spontaneous crosses among wild species, such as Prunus fenzliana, Prunus bucharica, and Prunus kumarica, among others, occurring in their local habitats where they coexisted, as suggested by several Russian botanists (Grasselly and Crossa-Raynaud, 1980b). However, another possible origin could be the domestication of Prunus communis L. population, which shares many morphological features with P. dulcis (Kester et al., 1990). In some regions, another possible ancestor, Prunus webbii, found in various regions in the Balkans, Sicilian, and other Mediterranean regions (Socias I Company, 1998), including Spain, may also have contributed (Felipe, 2000).

Currently grown almonds are generally divided into distinct groups, one grown for its nut or kernel and the other one as the ornamentals or the flowering type. The former belongs to P. dulcis and the later to P. trilobite, P. glandulosa, and P. japonica and are valued for their white, pink or rose, single or double flowers. Almond fruit is a dry drupe with two distinct properties; the bitter and sweet almonds (Table 2.1).

Table 2.1 Botanical Relationship of Almond Species of Subgenus Amygdalus with their Ranges⏎

Almond Group | Range
Section Euamygdalus Spach | Central Asia to Southern Europe
P. dulcis (Miller) D.A.Webb |
P. communis Fritsch | South eastern Russia and Afghanistan
P. bucharica Korshinsky | Steppes of south-eastern USSR, the lower north slopes of the Hindu Kush and Pamir Mountains and in Afghanistan
P. fenzliania Fritsch | Caucasus Mountains of North-easter Turkey, and Soviet Armenia in the USSR
P. orientalis (Mill.) |
P. kuramica Korchinsky | Slopes of the Hindu Kush Mountains and the sides of valley in Afghanistan extending into Western Pakistan
P. argentea, (Lam). | Syria and North West Iran
P. kotschyi (Boissier and Hohenm.(Nab,) and Rehd.) | Mountains of Iraq, Syria and Western Iran to the Turkey
P. webbii (Spach) Vieh. | Western Turkey into the Balkan Peninsula including Greece, Bulgaria and Yugoslavia
P. zabulica Serifimov. |
P. korschinskii Hand-Mazz. | Mountains of Iraq, Syria and Western Iran to the Turkey
Section Spartioides Spach | Southern Asia
P. prunusscoparia Spach |
P. spartioides Spach | Indigenous to arid mountains of central Iran and Southern Soviet Armenia
P. glauca Browicz | Deserts of Arabia, Iraq, Syria and Turkey
P. arabica Olivier | Deserts of Arabia, Iraq, Syria and Turkey
Section Chameamygdalus Spach | Balkan Peninsula to the Altai Mountains.
P. nana (Stock) | Russia and West Asia
P. petunnikowi Lits. | Tian-Shan and steppes of Turkistan
P. ledebouriana Schle. |
P. tangutica Batal. (P. dehiscens) Koehne Section Lycioides Spach | North-eastern Iraq, through Iran, Afghanistan, southern Soviet Armenia and into southern Tajikistan
P. spinosissima Franchet | Iran, Turkestan, Tajikistan and Northern Afghanistan
P. turcomanica Lincz. |
Section Leptopus Spach. | Western China and Mongolia
P. pedunculata Pall. |
P. mongolica Maxim ex. | Mongolia and adjoining area of USSR and Kansu Province, China

2.2.3.1 Section Euamygdalus (Syn.: Amygdalus) Spach

This section includes the ancestral species of the modern cultivated almond. Trees are medium sized 3–4 m with spines. It is similar to the cultivated almonds and evolved from Central Asia to Southern Europe. These species are very diverse and can be very easy to hybridize.

P. fenzliania Fritsch: Tree small very hardy, nuts are flat, hard shelled. Early flowering and very showy type. Compared to cultivated almond this species is low growing thornier and bushier.

Prunus argentea (Lam.) Rehd.: It is shrub and leaves are silvery white, shell netted, not pitted.

P. bucharica Korschinsky: Trees are medium sized with distinctive somewhat rounded leaves with long petioles. It is late leafing, relatively hardy and requiring moderate to high chilling requirement.

Prunus ulmifolia Franchet.: Small bushy trees, shoots and young leaves are pubescent.

Prunus communis Fritsch.: Tree and nut size is larger than any other species, includes bitter and sweet, soft and hard shelled types. It is the natural hybrid of P. fenzliana, P. bucharia and P ulmifolia.

P. kuramica Korchinsky: Growing in the rocky screed on slopes with very low moisture. Trees are moderate to large in size and resembles to cultivated almond and have sweet and bitter kernel.

P. orientalis Koehne(Mill), P. kotschyi (Boissier and Hohen), P. korschinskii Hand Mazz: Small shrubs up to 10 feet tall. Flower single per bud, and open before the leaves, pink or rose colored.

P. tangutica Batal (P. dehiscens Koehne): The plant is small bushy, thorny and small leaves. Bloom is late. Few nuts are produced but pollen has produced hybrids with other almond species.

P. webbii (Spach): The plant is a small, very thorny, very hardy bush with small leaves. Flowering is dense on many small spurs. The kernels are bitter. Some of trees in this species are self-fertile.

P. zabulica Serafimov: The tree is very upright, about 2.3m tall with rounded pear like leaves. Fruits round fleshy. The nuts are smooth and kernels slightly bitter.

2.2.3.2 Section Spartioides Spach

This section represents a complex number of species with similar morphology adapted to the extreme xerophytic conditions that found on the steppe and low desert areas. They were evolved from southern Asia and include a mixture of morphologically similar species making them difficult to identify.

P. spartiodes (Spach) Schneid.: Small shrub, 1.5 meter tall, branches pliant/ flexible long and green, leaves small.

P. scoparia (Spach) Schneid: Similar to P. spartiodes, plants grow 3–4 m tall, with slender. Kernels are small, dark brown, smooth and bitter.

P. arabica (Olivier).: Indigenous to the deserts of Arabia, Iraq, Syria and Turkey.

P. glauca Browicz: Similar to P. arabica in range and morphology but has glaucous green leaves.

P. agretis (Boissier): Similar to P. spartiodes, leaves are narrower.

2.2.3.3 Section Lycioides Spach

It is another large group of variable plants. These species may represent either a widely extended variable species or a complex of many species adapted to extremely xerophytic conditions.

P. spinosissima Franchet: Tree small, 2–2.5m xerophytic and very spiny, kernels with 60% oil.

P. tureomanica Lincz.: Essentially same species as P. spinosissima but grows at a lower elevation.

P. brachuica (Boissier): 1–2 m tall, shrub or small tree, xerophytic very shiny small leaves.

P. nairica (Feetchenko).: Small bush 1 m, very spiny, leaves very small, fruits very large.

P. webbi (Spach).: Small shrub, leaves pubescent, nut smooth.

2.2.3.4 Section Chameamygdalus Spach

In this section, species are genetically very diverse. Intercrossing of the species with cultivated almond is reported to be difficult. The plants have non-spiny, elongated leaves with flat asymmetrical fruits. The trees may be most winter hardy of the almonds.

P. nana Stokes.: Very hardy species. It is a distinctly a low bush, 3–5 feet tall. Flower single per bud, white or pink about 1 inch across, open before leaves. Fruit hairy, hard and small and bitter in taste.

P. ledebouriana (Schlechtendal): Though close to P. nana, but tree leaves and nuts are larger.

P. georgia (Desfontaine): Small shrub one m. tall, leaves lens like, large flowers, nuts large and flat.

P. petunnikowkii (Litwin) Rehd.: Small shrub, one meter tall, nuts symmetrical.

2.2.3.5 Section Leptopus Spach

This section species is very different from other sections and have evolved from western China and Mongolia. The important species includes: P. pedunculata Pall. and P. mongolica Maxim.

P. mongolica Maxim: Extremely winter hardy and being tested as rootstock in Northwest China

Pedunculata Pall: It has a long peduncle and is known as the long handled almond.

2.2.3.6 Amygdalus

The subgenus Amygdalus is distributed widely and due to self-incompatibility, it has a tendency of cross-pollination. This has potential to hybridize between P. communis and more distinctive species that belong to other sections or subgenera, including Euamygdalus and Spartioides, but hybridization is difficult with Lycioides and more difficult with the Chameamygdalus and Leptopus sections. It has number of botanical forms for example:

P. amygdalus var. alba Plena: Flowers may be in double whorls and white in colour.

P. amygdalus var. rosa Plena: Flowers are red in colour

P. amygdalus var pendula: Branches are drooping type.

P. amygdalus var. compacta: The tree is markedly dwarfed.

P. amygdalus var. variegate: The leaves are distinctly with white and yellow

2.3 Chestnut

2.3.1 Floral Biology

Chestnut is monoecious with flowers borne on long spikes (catkins) emerging from the leaf axils of current season’s growth. Male flowers appear in cylindrical catkins with 10–20 stamens and 6-parted calyx. Each flowering shoot usually bears several (up to 10 or more) catkins, which occur in a contiguous region more or less in the middle of the current season’s shoot. The catkins are initiated during the summer before the season in which they bloom. Catkin primordia can be found inside dormant winter buds with the aid of a dissecting microscope. As shoot growth begins in the spring, the small, developing catkins can be seen long before they reach anthesis, which occurs about 10 weeks after bud break. Two types of catkins are commonly found on trees: male or unisexual catkins and bisexual catkins with both male and female flowers (Abbe, 1974). Staminate catkins appear toward the base of the shoot. The staminate flowers are born in long (15–30 cm), slender, unisexual catkins located on the lower portion of the shoot or on the distal part of the bisexual catkin near the terminal portion of the shoot. The bisexual catkins, of which there are usually one to three, occur toward the tip of the shoot (Westwood, 1978). These catkins bear one or two (sometimes more) pistillate inflorescences at their basal end, which develop into burs. The pistillate inflorescences usually consist of three flowers clustered in prickly involucres at the base of bisexual catkins. The female flowers are inconspicuous, odorless, and elongated style (Botta et al., 1995). The first to flower are the long finger like male catkins near the terminal portion of the shoot.

2.3.1.1 Anthesis, Receptivity of Stigma And Pollen Viability

Vilkomerson (1960) found that the sequence of bloom of the male and female flowers is not always the same in all the trees. Male catkins on the lower portion of the shoot are the first to shed pollen. Several days later the staminate catkins near the tip of the shoot on the base of which pistil-late flowers are located shed pollen. Flowering begins when most of the basal catkins begin shedding pollen. Generally, few days later the pistillate flowers become receptive and remain receptive for 1–2 weeks. Pollen shedding is completed within 2–3 weeks. Chestnuts produce very less pollen than one would think. The pollen is more difficult to preserve and its viability is only for few hours. Pollen can be stored for 2 years if desiccated and frozen without losing viability. Each flower normally has six to nine styles and contains 16 eggs (two at the base of each style) within each ovary. For several weeks after pollination, all of these presumed embryos slowly enlarge at more or less the same rate. In mid-season one or two (sometimes more) of the embryos begin rapid enlargement to become the nut kernel(s). The remainder of the embryo’s cases development and degenerate, but their remnants can easily by identified as a cluster of small, tear drop-shaped pellicles in the stylar end of the chestnut fruit at maturity. This phenomenon explains the occurrence of double seeded nuts and offers a possible mechanism for post zygotic selection, which may distort expected segregation ratios, thereby offering an explanation for the sometimes-confusing results of inheritance studies.

Each species has a unique floral pattern that remains constant from season to season (Zimmerman, 1972). The Chinese chestnut is one of the latest to bloom in the season, the flowers appearing early in the month of June. Unusual flower arrangements in the inflorescence and vivipary, have also been reported (Bencat, 1964).

There are normally three fruits per bur, but up to seven may be found, and there is normally one seed per fruit, but double-and multiple-seeded fruits are common. The French term, “marron,” is often used to refer to single-seeded fruits, i.e., single-kernel nuts.

As the shoot continues to grow beyond the catkin-bearing area, the leaf axils bear vegetative buds, in which develop the following season’s flower buds. The buds most likely to contain flower primordia are those at or near the tips of vigorous branches in well-lighted parts of the tree canopy. There are a few buds below the catkin region of the shoot, but these buds seldom contain flower primordia. Dormant buds containing flower primordia are noticeably larger than purely vegetative buds. All chestnut species and clones have similar enough flowering times that most tree-pairs will have overlapping periods of pollen shed and pistillate receptivity on a given site. Chestnuts are considered to be mostly wind pollinated, but insects are attracted to the male flowers and can assist in pollination.

After pollination, the burs steadily enlarge until ripening time, which generally occurs sometime between early September and late October (somewhat later for long-season cultivars in warm climates). Ripening date is not precisely determined by flowering date, as evidenced by the fact that a given clone may flower 2 months earlier in the South than in the North, but ripen only a week earlier. The time period from flowering to ripening is generally 10 weeks or longer. However, during the last 2 weeks before nut drop, about half of the kernel dry weight accumulation occurs (Miller, 1987). Therefore, it is important not to remove the nuts from the tree before they are mature, or the kernels will be soft and shriveled.

Flower bud differentiation in all types of chestnut cultivars, early, medium and late. It takes place in July, the most active stage of flower bud development is August (Rhee, 1978). Thereafter, floral bud remains inactive up to the month of February. Phenological observations recorded by Bencat and Tokar (1978) revealed that the buds grew actively from mid-March to mid-April, leafing out started in mid-April and anthesis took place in early June. Sex expression of Chinese chestnut has been noted to be influenced by ethephon, GA and urea treatments (Young et al., 1985). Ethephon (100–500 mg/l) inhibit the development of pistillate flowers and promoted that of staminate flowers. Young leaves and buds sprayed with GA3 (50–500 mg/l) decreases the number of male flowers but increased the number of female flowers. The soil application of urea decreases the number of male flowers and increases the number of female flowers. Spraying the trees with GA, or urea or a mixture of both at the onset of floral primordia differentiation increased the female to male flower ratio.

2.3.2 Pollination

Since all cultivars and species of chestnuts are self-sterile, more than one cultivar or seedlings are planted together to ensure cross pollination. Fruit setting is low on young plants because of lack of pollens for cross-pollinated fruit crop (Clapper, 1954). Clapper (1954) reported that chestnuts are polli-nated by wind, while others believe that they are pollinated by insects like small thrips and bees (Gallastegui, 1926). But McKay and Jaynes (1969) reported that it is both wind as well as insect pollinated. Some cultivars are considered to be good pollen producers, viz., Catagnodella Costa, Morethina and Morte Grossa (Bergamini, 1975). Whether the agency of pollination is wind or insects, two trees should not be more than a city block apart in order to ensure nut production. Chestnuts are obligate self-sterile and generally protandrous (Stout, 1926).

2.3.2.1 Controlled Pollination Techniques

Hand pollination of chestnuts is a labor intensive process, considering the difficulty in collecting pollen, the in access ability of the flowers, the low seed yield per pollinated flower, and the precise timing required for both pollination and seed harvest. These reasons provide incentive to consider natural wind pollination as an alternative to hand pollination for breeding and genetic work. Open pollination can be exploited if the desired parents are reproductively isolated from undesired parents. This may be accomplished by grafting a pollen source into an isolated mother tree, enclosing parents in a greenhouse (flowering may be forced out of season), or placing parents in isolated blocks. Pollen dilutes quickly with distance; a gap of 100 m or more between isolated blocks would result in minimal cross contamination, especially if the trees are small and closely spaced within blocks. In some cases, individuals in open pollinated seedling populations may be selected or rogued out if seedling characteristics indicate the desired or undesired pollen parent.

Despite the copious display of staminate flowers, chestnut pollen is difficult to collect. The pollen grains are very tiny, about 12 µm long, and the pollen shed from a given catkin is spread over several days. Catkins shedding pollen can be identified by their “fuzzy” appearance as many hundreds of cream-colored anthers emerge. When anthers begin to turn brown, it is too late to collect pollen.

Branches from which pollen is to be collected should be bagged with paper bags containing insecticide dust several days prior to collection. The bags exclude foreign pollen and insects, and keep the pollen from blowing away. When the anthers are shedding pollen, the bag is carefully removed and pollen is collected by shaking the branch over a sheet of clean, dry glass (Rutter, 1989). The haze of pollen on the glass plate is scraped together with a single-edged razor blade and, after removing trash and insects, is finally scraped into a vial. The freshly collected pollen should be placed in a desiccator for 4–24 hours, then refrigerated for short-term storage and frozen for long-term storage. Pollen can be stored frozen for a year or more (Jaynes, 1964). Pollen viability can, and should, be checked by floating a sample on 1% sucrose solution held at 30°C for 1 h. Good pollen should germinate at a rate of 15%–60%.

Pistillate flowers to be pollinated should be bagged prior to receptivity, but not any earlier than necessary, since long-term bagging is detrimental. Bagging should be done when the first unisexual catkins begin shedding pollen. The whole shoot should be bagged after pinching off all unisexual catkins and staminate portions of bisexual catkins. The bags should be secured with wire around 1-year-old wood wrapped with a cotton ball. Since chestnuts are essentially not self-pollinating, it would seem unnecessary to bag isolated mother trees. However, such isolated trees seem to benefit from bagging, perhaps by preventing an overload of self-pollen.

There is some difficulty in determining when pistillate flowers are receptive. As a general guide, optimum receptivity occurs when the unisexual catkins are all shedding pollen, but the staminate portions of the bisexual catkins have not yet begun shedding. The star-shaped pistils should be cream-colored. Contrary to what might be expected, the whole star is not the stigma. The stigmas are just the pointy ends of the star. So, pollen needs to be applied to the points. This can be done with a freshly picked catkin from the bagged male parent. Stored pollen can be spread using a camel hair brush or from a glass microscope slide, which is more conservative of pollen. The glass slide is placed over the pollen vial, which is inverted and then righted. The film of pollen adhering to the slide is gently wiped over the pistil tips (stigmas). After pollination, the shoot should be bagged again until pollen shed ceases (2–3 weeks), then the bag should promptly be removed. After the pollination bags are removed, they may be replaced with coarse mesh bags to mark and contain the results of the pollination.

2.3.3 Genetic Resources

Chestnuts belongs to genus Castanea, which has 13 species which also has important forest plants like oak (Quercus), and beech (Fagus). Two lesser-known genera Castanopsis and Chrysolepis, are closely related to the genus Castanea and share the common name “chinquapin.” Castanopsis and Chrysolepis are evergreen shrubs or trees, which is the most obvious distinction from the deciduous genus Castanea.

The different species of chestnuts are native to western Asia, Europe and northern America (Anon., 1959; Vavilov, 1951). Chinese chestnut (Castanea mollissima) is native to China, Japanese chestnut (C. crenata) to Japan and South Korea, and European chestnut (C. sativa) is native to Mediterranean countries of South Europe and Asia Minor (McKay and Jaynes, 1969). Western America is the native place for American chestnut (C. dentata). Beside chestnuts, chinkapins also belong to this genus and C. pumila, C. ozarkensis and C. alnifolia (trailing chestnut) are native to southeastern USA. Henry chestnut (C. henry) and Seguin chestnut, (C. seguinii) are shrubs, native to China. In China, they were cultivated 6000 years ago. In Europe, ancient Greeks were the first to cultivate the nut, at least 3000 years ago, and introduced the European chestnut from Asia Minor to South Europe and North Africa.

2.3.3.1 Description Of Some Important Species

C. mollissima (Chinese Chestnut): The name mollissima means soft hair and it is recognized by dense hair on young leaves. During dormancy, it can withstand cold temperature up to −28.8°C. It is resistant to chestnut blight fungus (Endothia parasitica) and most of the cultivars belong to this species.

C. crenata (Japanese Chestnut): The kernel is less sweet as compared with Chinese chestnut and the pellicle is fibrous and adheres with the kernel. The tree is more susceptible to chestnut blight and are less winter-hardy.

C. sativa (European Chestnut): Also known as Italian or Spanish chestnut. Pellicle is more fibrous and frequently folded into the folds of kernel and thus is removed with difficulty. It is very susceptible to the chestnut blight.

C. dentata (American Chestnut): The trees are tall and straight. The trees are highly susceptible to blight and this caused a complete annihilation of entire plantations in the United States during the starting of this century (McKay and Jaynes, 1969).

2.3.3.2 Chinkapin

Chinkapins unlike chestnuts have only one nut in each bur and this is the characteristic difference between chestnuts and chinkapins (Jaynes, 1969).

C. pumila (Allegany Chinkapin): Grown for ornamental purpose and for plantation in wild-life sanctuaries for food and also be used as dwarf rootstock, but abundant suckering is a drawback.

C. ozarkensis (Ozark Chinkapin): The species can be grown into small trees and often produces grows wild in Arkansas and Missouri states of USA and serves as wild-life food.

C. alnifolia (Trailing Chinkapin): This species produces small shrubs, one meter in height and is naturally propagated by stolon’s in sandy barrens.

C. henryi (Henry Chinkapin): It is a forest tree growing in wild forms in southwestern China. The leaves are toothed and narrow. The species is susceptible to blight.

C. seguinii (Seguin Chestnut): The small trees or shrubs are native to China. Plants are dwarf in nature and bears heavily at young age and these attributes are important for breeding programme. The burs have three nuts unlike American chinkapins.

2.4 Hazelnut

2.4.1 Floral Biology

All Corylus species are monoecious, bear unisexual anemophilous flowers and wind-pollinated shrub that blooms in midwinter (December to March, depending on the ambient temperature and the cultivar). In the moderate climates of commercial growing regions, the flowering period is earlier and more extended than in regions having more severe winters followed by abrupt change to warmer weather in spring.

Differentiation started with the catkins in mid-April and with female flowers in mid-May in filberts (Kavardzhikov, 1984). The flowering period may be as high as three months from pollen shedding to full bloom of female flowers. Staminate flowers which produce pollen are borne in catkins at nodes on 1-year wood. The staminate catkins emerge in late winter and fully open by spring when new leaves and the pistillate flowers appear. The male catkins elongate to nearly double of their dormant length during pollen shedding in spring. Pistillate clusters which develop into the nuts are borne in three locations, the ratio at each site is differ with the cultivar. They occurred singly at nodes on 1-year wood, in groups of 1–6 on catkin peduncles and on very short spurs in old trees. The female inflorescence has a compact cluster of 4–14 very small flowers, borne within the overlapping bud scales at the apex of a compound bud. In the hazelnut, male and female flowers appear in winter after the dormancy of inflorescence breaked. The ovary is not formed at the time of flowering. The female flower bearing bud cannot be distinguished from vegetative buds till anthesis.

Figure 2.1 Almond flower bud (a), Almond flowering (b) and Almond fruiting (c).

Figure 2.2 Chestnut flower bud (a) Chestnut flowering (b) and Chestnut fruiting (c).

Compatible pollination is necessary for the development of ovary, or nut shell; without it the flowers will not produce an ovary and will wither and fall off. Blank nuts (those that develop to full size but lack a kernel) result from compatible pollination with subsequent failure of normal embryo development.

Although most cultivars are dichogamous, being either protogyous or protandrous, there is usually some overlapping of male and female anthesis. However, because of self-incompatibility, no or few nuts set with self-pollination either in dichogamous types with slight overlap or in homogamous forms. The need for cross-pollination in hazelnuts was first demonstrated by Schuster (1924). Later, Thompson (1979 b) reported that Corylus avellana has a sporophytic self-incompatibility system controlled by a single gene with multiple alleles (S alleles).

Partial self-compatibility has been observed in “Tombul” and “Monte-bello.” Although the level is insufficient to allow development of completely self-compatible cultivars (Mehlenbacher and Smith, 1991). Self-compatibility may be present in other Corylus species. The heavy production in one year is usually followed by a light crop in the following year. Frost, rain and other factors may cause low yield or crop failure. It is thought that heavy renewal pruning may correct or modify the natural alternate bearing tendency (Painter, 1962).

2.4.2 Pollination

All the species in genus Corylus are monoecious and pollinated by wind. In hazelnuts, the peak periods of male and female flowering do not coincide for a single variety. Self-incompatibility in filbert cultivars is common which also makes interplanting a necessity in order to provide cross pollination. The blooming season under normal condition extends over a period of three months, beginning from pollen shedding by early cultivars to full bloom of late cultivars. The pollination generally occurs between December and March depending upon the cultivar. Generally about 12% trees of pollinizer cultivar are sufficient to carry out pollination of main cultivar under favourable conditions. The use of about 20% pollenizer trees is also not uncommon in areas having unfavorable conditions during flowering.

If the styles are impaired by harsh winter the basal parts of the style emerge out form the bud scales for pollination. After a compatible pollination the stigmatic surface turn black and the pollen tubes grows till the base of the styles. The sperm and vegetative nuclei form an irregular shaped structure rest there for around 5 months. The stimulation of the pollination leads to the development of the ovary and the embryo sac. Ovary growth and the female flower development begin in April when the nut is half of its actual size. The embryo sac develops fully around end of May to mid of June. After this the pollen tubes resumes growth and fertilize the egg. A compatible pollination reaction is very important for the embryo sac development (Thompson et al., 1996). In periods following April, the ovary development of some female flowers ceases. Some of the pistillate flowers do not develop ovary. Beyhan and Marangoz (2007) reported that the average percentage of functional ovaries in single cluster was 40%–60% in May for the cultivar “Tombul” and for 40%–55% for the “Palaz” cultivar. Blank nuts may appear, if fertilization does not occur or the kernel does not grow enough after fertilization,. A compatible pollination followed by failure to develop embryo sac and subsequent pollination leads to the development of empty or blank nuts decrease the yield and kernel percentage and cause financial losses also (Silva et al., 1996).

The blooming in filbert is dichogamous and, therefore, appearance of staminate and pistillate flowers may not be synchronized. Protandry, protogyny and homogamy occur depending on cultivar, growing conditions and season. Bodecs (1987) reported that almost all filberts are partially self-sterile and crop successfully in mixed plantings. In open-pollinated orchards of Barcelona filberts supplied with several different pollenizers, the percent-ages of fruit set was 55%–65 % although over 90 % individual flowers were pollinated. A large proportion of the ovaries failed to mature up to the time of fertilization and only 15 % developed into mature nuts. These studies indicate that poor pollination is not a casual factor to have such a low fruit set but it is a varietal weakness (Thompson, 1968).

Figure 2.3 Hazel Nut catkins (a) Hazel nut female flower (b) and Hazel nut fruiting (c).

Figure 2.4 Macadamia nut flowering (a) and macadamia nut fruiting (b).

It is recommended that a range of varieties (3–4) be planted to ensure the dissemination of cross-compatible pollen. The pollinizer placement ratio should be 8:1 (every 3rd tree in every 3rd row will be a pollinizer), but in unfavorable conditions it can be increased to 5:1. At favourable hazelnut sites, pollinizer ratios as low as 17:1 (every 6th tree in every 3rd row ) is kept as pollen can travel up to 18 meters with wind. Tree is planted in triangular or square system with 3–4.5 m tree spacing which accommodates 15–250 trees per acre. Hazelnut fruit is a nut, borne in clusters of 1–12.

Normal flowering in filbert was found at the temperature between 0.4°C and 14.6°C. Fruit set was highest under artificial pollination than self-pollination. Nemasa was best pollenizer for cvs. Cherkessi-2, Zorinkii, Khachapura; Futkurami and Dedoplis-Titi (Makhno, 1981). Daviana, Lansing and Butler are most effective pollenizer for Barcelona. Pollens of Woodford and Montabello reduced a high percentage of blank nuts. Barcelona was almost self-incompatible. The combination of Corylus colurna x C. avellana cv. Barcelona was completely incompatible (Zielincki and Thompson, 1967). Wide variations were observed in the time of receptivity of the pistillate flowers of different cultivars, whereas the male flowers shed their pollen over a short period. In general, American cultivars had receptive pistils before the pollens were shed but in European cultivars except Barcelona and Du Chilly, the reverse was true (Talbott, 1959).

Temperature is an important factor for pollination. When temperature in late winter were relatively high, protandry occurred but in cooler atmosphere protogyny was common. In controlled conditions the critical temperature for the development of protandry was found to be 9°C (Stritzke, 1962).

2.4.2.1 Controlled Pollination

In hazel, it is relatively easy to produce large numbers of seeds from controlled pollinations. Because an average of 50% of the flower clusters pollinated develops into nut clusters that average 2–4 nuts per cluster, one can expect to obtain 1–3 hybrid seeds per pollination.

The first step in planning the crosses is to identify the S alleles of the potential parents so that compatibility between the desired combinations can be insured. This is easily done by dipping detached pistillate clusters of each parent in vials containing a series of previously collected tester pollens with known 5 alleles, placing them in a petri dish lined with damp filter paper, and leaving them overnight in the laboratory for pollen tubes to grow. The following day styles are separated, squashed on a slide in a drop of aniline blue, and observed with a fluorescence microscope (Thompson 1979 b). If one cannot prepare the flowers for immediate observation, the petri dish with pollinated flower clusters can be placed in a freezer and styles squashed whenever time permits. In compatible pollinations, masses of long tubes penetrate the styles, whereas in incompatible pollinations, very short tubes form, often with a pronounced bulb at the end, which cannot penetrate the stigmatic surface.

In autumn, before any pollen is flying and pistillate flowers are barely visible, clones selected as female parents must be isolated to exclude unwanted, wind-bore pollen. When large numbers of hybrid seeds are desired, the entire tree is caged (Fig. 8). A wooden frame is erected around the tree and covered with opaque, white polyethylene. In one corner, the lath to which the polyethylene is attached is initially not nailed tightly, so at pollination time it can be removed for access and then, when pollinations are completed, secured tightly. If more than one pollen is to be used on one caged tree, and it is critical to keep the progeny separate for precise genetic studies, individual limbs can be bagged within the cage. Also, if pruned appropriately, the tree branches can be separated by hanging a polyethylene curtain from ground to ceiling.

If the tree is small, or only a few crosses are to be made on a larger tree, bags are placed over limbs. Polyethylene is not suitable for bags because, in this small enclosure, the heat buildup damages the flowers and the high humidity fosters much mold growth. Therefore, double bagging with other materials has proven successful in Oregon. First, a bag consisting of Tyvek house wrap (Dupont) is used to exclude the very small-sized pollen and to provide rigidity to protect pistillate flowers from being damaged by bags whipping around in the wind (Fig. 9). Next, a light-weight polyester bag is placed over the inner bag to protect it from tearing in the wind, rain, hail, or snow. Due to the long time span of pollen shedding in the Oregon breeding plots, cages and bags are kept on the trees from November through March. Although most clones will set few or no nuts with their own pollen, it is necessary to clip off the catkins on the caged trees or bagged limbs in order to eliminate the inconvenience of the mass of pollen that will be everywhere within the enclosure and on the technician who enters it.

Pollen is collected from selected male parents by picking catkins from the tree just after they have elongated. Detached catkins are placed on sheets of paper in the laboratory overnight where the dry, relatively warm (15°C–20°C) conditions indoors cause anthers to dehisce and shed pollen onto the paper. The next morning. Catkins are discarded and pollen is poured into a vial, which is then stoppered with a cotton plug. Because hazelnut pollen is very sensitive to warm temperatures and low relative humidity, after catkins have shed out in the laboratory the pollen must be put promptly into the freezer until needed. Stored in the freezer at −18°C with no humidity control, pollen remains sufficiently viable to be used the following year for laboratory compatibility tests or for breeding (Zielinski, 1968). Even though viability decreases in storage, the pollen is effective because of the huge amount applied in hand pollinations.

Figure 2.5 Pecan nut catkins (a), pecan nut female flower (b) and pecan nut fruiting (c).

Figure 2.6 Pistachio nut flowering (a) and pistachio nut fruiting (b).

Entering cages or removal of bags to apply pollen should be done on a calm, windless day, preferably when the humidity is very high, in order to prevent unwanted, wind-blown pollen from landing on the pistillate flowers. Pollen can be applied with a brush or, more efficiently, with the end of one’s finger. The latter method consists of first coating the end of the finger with pollen by turning the vial upside down on it and then gently touching the tuft of stigmatic styles.

2.4.3 Genetic Resources

Corylus avellana L. is the major recognized species in this genus. All the species in the genus produce edible nuts. The term hazelnut is generally used for all the nuts in the Corylus species. The term “filbert” may be derived from “full beard” to differentiate the long-husked type from the short-husked type. Hazelnut plantations were done by Romans and domestication was probably initiated in Italy (Spiegel-Roy, 1986). Ozkurt (1950) hypothesized that hazel-nuts were first cultivated in Turkey in Giresun province, and from there its cultivation spread to adjacent Ordu province. Hazelnuts are now grown along the Black Sea coast having favourable ecological conditions (Kafkas et al., 2009). Though it is known to have been cultivated by the Romans, but the history of the domestication of C. avellana is still under debate (Tallantire, 2002). Now-a-days, C. maxima cultivars and their hybrids with C. avellana dominate the hazelnut trade in the world (Zohary et al., 2012).

2.4.3.1 Description of Some Important Species

Corylus americana Marsh. American Hazel: Used in breeding programs because of its cold hardiness, productivity, good quality nuts, and resistance or tolerance to eastern filbert blight.

C. avellana, L.: It is known as European filbert and is the most commercially grown specie.

C. colurna L.Turkish Hazel: Young bark is light grey and deeply furrowed, still very soft, later turn rough and fall off in vertical plates.

Corylus commuta Marsh.(= C. rostrata Ait.), Beaked Hazel: Very wide distribution. It has bristly hairs that are irritating to human skin. However, this northern variety may have breeding value for its extreme cold hardiness (-50°C), resistance to eastern filbert blight, and very early nut maturity.

Corylus cornuta var, Californica (A. DC.): More desirable for breeding, especially in mild climates, because of its more desir-able growth habit and the shorter, less constricting husks of some selections.

Corylus heterophylla Fisch., Siberian Hazelnut: Many similarities to the North American species, C. americana, including good quality nuts with relatively open husks.

Corylus sieboldiana: Plants are medium-large shrubs to 5 m and extreme cold hardy. The long husks are tubular, 1.5–4 cm long, tightly constricted above the nut, and densely covered with bristles.

Corylus fargesii Schneid: The plant as a small tree, the tubular husk that is constricted above the nut and the synonyms of this taxon, C. rostrata var. fargesii Franch. and C. mandshurica var. fargesii Burkill, suggest its close affinity to the shrubby species, C. sieboldiana var. mandshurica.

Corylus columna I., Turkish Tree Hazel: Widely used as an ornamental tree because of the nonsuckering growth habit and graft compatibility with C. avellana, there has been some interest in this species for rootstock development.

Corylus jacquemontii Decne., Himalayan or Indian Tree Hazel: Due to very limited availability of germplasm of this species in the western world, it has not been used in breeding. The nonsuckering tree growth habit may be useful for rootstock development.

Corylus chinensis Franch, Chinese Tree Hazel: The potential of this species for nonsuckering rootstocks for Cavellana cultivars has not been adequately investigated as yet.

C. maxima Mill: Native to southern Europe and Asia Minor, grows up to an elevation of 1300 meters.

Corylus ferox Wall, Himalayan Hazel: Readily distinguished from all others by its spiny husks, which resemble a chestnut bur because of the abundant branched spines on the upper margins.

Corylus wangii Hu, Weixi Hazel: Trees are planted as ornamentals because of the peculiar shape of the husks. There are commonly 4–5 nuts per cluster.

C. tabetica Batal. Tibetan Filbert: Edible oil is obtained from the seed.

2.5 Macadamia Nut

2.5.1 Floral Biology

2.5.1.1 Flowering

The flowers are about half inch long, are perfect but incomplete in that they are petal less. But four petaloid sepals. M. integrifolia has creamy white flowers emerge in clusters that is 6–12 inches long, while the flowers of M. tetraphylla are creamishor pinkish colored and emerge in clusters up to 15 inches long. Flowers are borne on long, pendulous racemes that emerge from the leaf axils or from the scars of fallen leaves. Each flower contains four perianth lobes to which are attached four stamens. The pistil has an ovary with two ovules and a long (10 mm) style with a small stigmatic area at the tip (Sedgley, 1981). They are bisexual and self-fertile. Nonetheless, the plants are often self-sterile, so almost every plantation grows different varieties to encourage cross pollination (Sharma et al., 2015).

Figure 2.7 Walnut catkins (a) Walnut female flower (b) and Walnut fruiting (c).

Flowers may be borne on the new growth if it is mature, but more commonly on the growth of two or three seasons preceding the latest matured flushes. Flower initiation occurs when temperatures drop and trees go in to dormancy in autumn, the optimum temperature being 18 C. Initially it remains quiescent for 50–96 days; racemes elongate after increased temperature and some rain.

In Australia, high yields are associated with heavy and early spring flush before anthesis which is followed by minimal shoot growth during the 6-month nut development period. A late summer flush occurs at the end of nut development; meanwhile, the nuts may remain on the tree for another 3 months, but gradually fall off. The bunch-like flower clusters appear to 30 cm long with 100–300 flower blossoms (Sharma et al., 2015).

In Australia, initiation and differentiation of macadamia inflorescence buds emerge during the shortening days of early May. At that period of year night temperatures are 11–15°C, about 4°C–5°C cooler than the better macadamia cultivating areas of Hawaii (Shigeura, 1981). Floral development of macadamias is greatest at night temperature of 18°C (Nakata, 1976) and is further enhanced by a 5°C reduction during the period old floral bud dormancy (Stephenson and Gallagher, 1987).

Whereas night temperature falls to as low as 7°C during this dormant stage in Australia, it remains relatively constant in Hawaii. Low night temperature may be a factor causing excessive flower production in Australia which is thought to deplete carbohydrate resources and compete with nut development and yield.

In an investigation on growth manipulation and carbohydrate reserves, Stephenson and Gallagher (1987) observed that the reduced carbohydrate reserves were due to demand from the developing crop rather than a small spring vegetative flush. In the following year, flowering was more advanced and intense on trees that were prevented from cropping, but this did not result in an increased yield.

Nagao et al. (1994) studied the flowering patterns of the macadamia cultivars Kau (Haes 344), Keaau (Haes 660), and Kakea (Haes 508) over three consecutive seasons in an orchard near Hilo (elevation 27.4 m a.m.s.l.). These studies showed that all cultivars exhibited broad flowering peaks, with maximum anthesis occurring between January and April. Vegetative flushing emerged throughout the year in all cultivars but was more pronounced in autumn, coinciding with the nut maturation period.

2.5.1.2 Anthesis And Dehiscience Of Anthers

Macadamia flowers open for 6–12 days on an individual raceme. The peak of flower opening is variable from as early as two days from the start of flowering up to six days, so that flowers on some racemes open synchronously, while on other racemes they open gradually (Sharma et al., 2015). Anthesis leads to offering pollens to flower visitors. It is a major factor influencing the flower visitor’s behaviour (Heard, 1993). In Australia, macadamias start flowering in August-September (Quinlan and Wilk, 2005). The flowers are protandrous, the anthers dehiscing 1–2 days prior to anthesis, while the stigma will not support growth of pollen tube until 1–2 days after anthesis.

2.5.1.3 Receptivity of Stigma

The stigma receptivity of the two Protea cultivars was studied by observing seed set, development of pollen tube and the opening and closing of the stigma groove. Both of these cultivars have been observed to be protandrous. Peak stigma receptivity, measured by setting of seeds, was found to appear during the period of two to six days after anthesis in Flrepens (L.) cv. Sneyd and at three days in P. eximia (Salis. Ex Knight) Fourcade cv. Fiery Duchess. Peak stigma receptivity in P. repens Sneyd (measured by growth of pollen tube) was found to occur during the period of two to six days after anthesis when the maximum mean number of pollen tubes per ovary was 2.5. Peak stigma receptivity, based on the width of the stigmatic groove, was found to be at three to six days after anthesis. After anthesis, pollen tubes reach the ovary after four days, and most of the pollen tube number in the ovary appeared at seven days (Sharma et al., 2015). It is proposed that Protea spp. hand-pollinated two to six days after anthesis for maximum seed set. For pollen tubes studies in the ovary, inflorescences should be harvested seven days after pollination (Vanderwalte and Littleejohn, 1996).

2.5.2 Pollination

Macadamias can be self-pollinated, but varieties range from being completely self-compatible to almost self-sterile. Wind pollination may play a role, but bees are important agent in pollination. Artificial cross pollination by hand has been shown to improve nut set and quality. There are more chances for cross-pollination when racemes opening over a long period. The duration of attractiveness, from anthesis to withering of the perianth, is the period corresponding to insect visits. This is the period when cross-pollen arrives so its duration will partly determine the possibilities of cross-pollination. Polli- nation is by insects; most cultivars are at least partially self-incompatible. It is very important to plant to plant pollinator trees and introducing bees for good fruit set. After bloom, fruitlets continue to shed up to two months (Sharma et al., 2015).

The anthers dehisce takes place 1–2 days before anthesis (Protandry) but the stigma does not support growth of pollen tube until 1–2 days after anthesis (Ito and Hamilton, 1980; Sedgley, 1981). Furthermore, macadamia is often at least partly self-incompatible (Sedgley, 1981; Sedgley et al., 1990), confirming earlier observations that nut set was enhanced where cross pollination was promoted by introducing honeybees into the orchards (Urata, 1954; Ito and Hamilton, 1969; Ito et al., 1970, Shigeura et al., 1970, Vithanage and Ironside, 1986). In fact, Ito and Hamilton (1980) reported that yields were increased in blocks of mixed cultivars. It is common to plant every third row with a second, pollinizer cultivar, yields of macadamia in South Africa were closely related to the amount of hives of honey bees. Both initial and final fruit were increased with increasing hours of insect viz., Apis mellifera and Trigona spp. Visitation days, although there was not significant variation in final nut set (Heard, 1994).

2.5.3 Genetic Resources

It belongs to the family Proteaceae of which has about 1000 species, including the Banksias, Grevilleas, Stenocarpus, Dryandra, Hakea and Telope (Mc Conachie, 1980; Ben-Jaacov and Silber, 2006). The family is popularly known for other genera such as Banksia, Grevillea, and Hakea.

Macadamia has nine species; Macadamia integrifolia, M. tetraphylla, M. ternifolia, M. jansenii, M. whelani, M. claudiensis, and M. grandis which are originated to Australia, M. hildebrandii which is native to Sulawesi in Indo-nesia and M. neurophylla is originated to New Caledonia (IBPGR, 1986; O'Neil, 1996; Costello et al., 2008). However, edible nuts obtained from only two species of genus Macadamia: M. integrifolia Maiden and Betche, which is known as the smooth-shell type; and M. tetraphylla L.A.S. Johnson is often referred to as the rough-shell type, and their hybrids.

Macadamia is a new crop first cultivated in 1858 in Australia. It is the only originated Australian plant ever developed as a commercial food crop. The first commercial macadamia orchard was established around 1888 in Australia. European settlers in Australia like macadamia and started to collect more nuts from wild trees during 1860’s and 1870’s. By this time, the macadamia nut had acquired several common names in English and was known as the “Queensland nut,” the “Australian nut,” the “Bush nut,” the “Bauple nut” and the “Australian hazelnut.”

M. ternifolia is the species upon which Mueller established the genus in 1858. The species of Macadamia occurred naturally into four distinct intra- generic groups (Sharma et al., 2015).

Group 1: The three extra-tropical Australian species, M. ternifolia, M. integrifolia, and M. tetraphylla.

Group 2: The two extra tropical Australian species, M. prealta and M. heyana. These species were belonged to the allied genus Helicia considered by early botanists.

Group 3: The two tropical species of northeastern Queensland and Celebes, M. whelani and M. hildebrandii, respectively.

Group 4: The three tropical New Caledonian species, M. rousselii, M. vieillardii, and M. francii.

2.5.3.1 Description of Some Important Species

Macadamia integrifolia (Vernacular Names: Macadamia Nut; Queensland Nut; Smooth-Shell Macadamia Nut; Australian Nut; Bush Nut; Bauple Nut; Nut Oak): Perennial, long-lived, evergreen, mid-storey, subtropical rainforest tree up to 20 m tall, with raised lenticels with dotted greyish branchlets (Hauser and Blok, 1992). Flowering time is from August to October and kernel maturation from December to March, after that mature nuts fall to the ground (Sharma et al., 2015). Inflorescence pendulous occur axillary on mature wood of current season growth, long (30cm) with 100–500 flowers which are creamy white, occurs in groups of 2–4, measuring 1–1.2 cm long, short pedicelled (3–4mm); perianth tubular with is petaloid sepals, stamen in 4 in number inserted above the base of the tube, long pistil, ovary carpellate, 2 ovuled, ovary superior1.

Macadamia jansenii (Vernacular Names: Bulburin Nut Tree): Creamish brown flowers have tepals, blooms in July and September. Kernel is slightly cyanogenetic and inedible (Sharma et al., 2015)2.

Macadamia ternifolia (Vernacular Names: Gympie Nut, Marcoochy Nut, Small-Fruited Queensland Nut): Axillary pinkish flowers are placed in brush-like hanging racemes of 4–20 cm long. Compressed rounded fruits are grey in colour, The seed kernels are cyanogenetic and inedible. Flowering is from August to September and fruiting occurs in March to April (Hauser and Blok, 1992)3.

Macadamia tetraphylla (Vernacular Names: Macadamia Nut; Rough Shell Macadamia; Spiny Leaf Macadamia; Rough Shell Queensland Nut; Australian Nut; Bush Nut): Axillary pinkish purple flowers are placed in brush-like hanging 15–45cm long racemes. Compressed rounded fruits are greyish-green in colour, and has a hard inner shell to protect the nut. The seed kernel is edible and do not produce cyanogenetic. Flowering is from August to September and fruit maturing and falling starts from March (Hauser and Blok, 1992)4.

2.6 Pecans

2.6.1 Floral Biology

Flowering of Carya species (hickory) is complicated. Pecan has compound buds enclosing floral and mixed buds in separate bud scales but within a common outer scale covering (Sparks. 1986 b). During development, floral buds give rise to catkins but mixed buds grow into vegetative shoot or in a single pistillate inflorescence. The catkins emerged on current season’s shoot and not on 1-year-old wood (Wetzstein and Sparks, 1984). Mature pecan trees is monoecious in nature and dichogamy is also observed. Dichogamy in pecan is under single gene control, with protogyny being dominant (Thompson and Romberg, 1985). The phenomenon of occurring both protandrous and protogynous individual in pecan is known as heteo dichogamy. Smith and Romberg (1940) have confirmed only two groups protandrous and protogynous, which remain stable in their behaviour every year though the time of shedding of the pollens or receptivity of stigma may vary from season to season.

2.6.1.1 Staminate Inflorescence

In the spring, the staminate inflorescence (catkin group) begin to form. The two catkin groups are differentiated at the same time, on opposite sides of the shoot bud. Sometimes another pair of catkin groups is formed, positioned opposite to each other and at right angles to the first two groups. Each catkin group is enclosed by bud scales, and the outer bud scale completely encloses the bud, including all catkin groups and the shoot bud. The inflorescence differentiates in early mid-May and flower primordia by early June. There- after, bracted and imbricated floral primordia development is different in protandrous and protogynous cultivars (Wetzstein and Sparks, 1984). The floral apex, bracteoles and anther primordia in the former differentiate in June and July. While in the latter, this organogenesis takes place late in March and April just before anthesis.

Processes of catkin formation at various stages in protandrous and protogynous cultivars: Protandrous cultivars begin to produce anthers on catkins in the summer, before pollen is shed, while protogynous cultivars begin to produce anthers on catkins in the spring, after pollen has been shed (Wetzstein and Sparks, 1984; Haulik and Holtzhausen, 1988). Three aments or catkins are connected to a single stalk, or peduncle, to form the staminate inflorescence, or catkin groups. Protandrous cultivars often have shorter, larger-diameter catkins than protogynous often have long, thin catkins. The central catkin of a catkin group is typically the longest, regardless of dichogamy class.

According to statistics from Wood-roof (1924), protandrous cultivars have 72 staminate flowers per catkin, while protogynous cultivars have 122.8 staminate flowers per catkin. Three to seven stamens are present in each staminate flower, which is made up of a central bract and two lateral bracteoles (Rathore, 1991).

During development, each anther has four pollen sacs, or thecae. The filament is barely noticeable because it is so short. According to Woodroof’s (1930) estimation, each pollen sac held on average 365 pollen grains. Pecan pollen is produced in large quantities, as is typical of anemophilous species. 15–20 days before pollen sheds, microspores are free inside the pollen sac (Woodroof, 1930) after the tapetum disintegrates. About the time anthers are externally visible, the four pollen sacs fuse together to form two chambers. by the dissolution of the separating wall (Yates and Sparks, 1992). This coincides with the development of binucleate pollen grains. Lipids and polyphenols are first recovered from binucleate pollen grains at that period (Yates and Sparks, 1992). Yates and Sparks suggested that for the greatest chance of success in haploid anther culture, catkins should be collected when bracts and bracteoles are visible, but prior to spreading of the bracts. This coincides with the earliest period of free microspores and precedes starch accumulation and nuclear enlargement.

Carya pollen is triporate paraisopolar (the position of the pores is never completely equatorial, although they are drawn to the distal pole) and suboblate with a textate surface (Whitehead, 1965; Wetzstein and Sparks, 1985). The average pollen diameter is 46 µm and ranges from 38–55 µm (Whitehead, 1963). Although pollen from the diploid species of Carya is generally smaller than that of the tetraploid species (Stone, 1963), the taxo- nomic value of pollen at the subgeneric level is questionable (Whitehead 1963, 1965).

Catkins must be collected at the proper time for maximum pollen recovery and viability: Catkins collected too early will wilt without dehiscing pollen; those collected too late will have already shed pollen, reducing the amount recovered. Catkins at the ideal stage of development for collection will be 7.6–15.2 cm long, with plump, yellow-green anthers, some of which are splitting.

The best way to monitor catkin development is to visit trees several days prior to collection and observe catkin length and anther color. Since pollen shed is cultivar dependent, the optimum date for collection will vary among cultivars. On an individual tree, catkins on low limbs near the interior of the tree usually shed first. Catkins at the top of the tree are the last to shed. Since seasonal growth of catkins begins with bud growth, a tree that has uniform bud break throughout its canopy will have relatively uniform pollen shed also. Alternatively, trees that are uneven in bud break will also have uneven pollen shed. As discussed above, rates of development are increased by warm temperatures. Once catkins are mature, pollen dehiscence may occur within a short period, especially if conditions are dry and windy. Pollen shed is delayed by rainy conditions or high relative humidity (>85%). Pollen shed often begins in midmorning after relative humidity decreases.

As catkins approach the proper stage for collection, anthers become plump, yellow-green, and begin to dehisce pollen. Anthers at the base of the catkin (closest to the limb) will often dehisce first. When lightly tapped, ripe catkins will release a cloud of yellow pollen. At this stage (or slightly before), catkins should be carefully pulled from the tree and placed in a large paper bag.

The viability of pollen is influenced by the temperature, humidity, and duration of storage. Pollen maintained viability when stored for almost two years at −80 and −196°C but pollen stored at −10°C did not maintain viability (Yates and Sparks, 1989). Pollen that had been stored for 10 months at −196°C could be rehydrated and germinated when held at room tempera- ture for 59 days.

Pollen dried in a mechanical convection oven at 35°C, placed in air-tight containers, and stored in a freezer at −12°C for 2 years was comparable to fresh pollen in germination efficiency (Yates et al., 1991). Undried pollen stored under the same condition’s lost viability.

Stored pollen benefits by rehydration prior to incubation in germination media for in vitro determinations of pollen viability (Yates and Sparks, 1989). Pollen can be rehydrated at 97.2% relative humidity and 25°C for 4 h. Constant 97.2% relative humidity is maintained with CuSO₄, in desiccation vessels, as reported by Yates et al. (1991).

If placed under appropriate conditions, pecan pollen hydrates rapidly, changing from a concave to a spherical shape and germinating in as little as 1 h (Wetzstein and Sparks, 1985). Fresh pollen had a range of percent germination, with “Mohawk,” “Wichita,” and “Curtis” germination rates of 72, 64, and 51%, respectively. Tube lengths were about equal to pollen grain diameter after 4 h. Marquard (1992) estimated in vivo pollen tube growth to be-150 µm/h from 3–8 h after pollination and was not significantly influ- enced by self-versus cross-pollination.

Most germination tests are conducted at 20°C (Wetzstein and Sparks, 1985) or at 25°C (Yates and Sparks, 1990; Yates et al., 1991). Marquard (1992) reported that tube growth was strongly influenced by temperature, with 27°C being optimal for “Cape Fear pollen. Thompson and Yates (1991) reported a reduction in polles germination at temperatures of 30°C, consis- tent with the report of Marquard (1992).

Wetzstein (1990) reported that thphenyltin hydroxide, benomyl with triphenyltin hydroxide, and phosalone, three commercial pesticide formu- lations, totally prevented pecan pollen germination when added to in vitro germination media at one-fourth the recommended rates. Although in vivo tests also showed inhibited pollen germination, results were not as severe.

2.6.1.2 Pistillate Inflorescence

Pistillate flowers are emerged at the end of the current season’s shoot in a spike (cluster). The number of flowers per cluster varies from 1–10 or more and is cultivar dependent. Pistillate flowers are differentiated in the early spring, when outer bud scales are shed and buds swell, but prior to inner scale split (Wetzstein and Sparks 1983b).

Amling and Amling (1983) reported that pistillate flower initiation, which occurs in late July or early August, requires exposure to cold temperatures. When current season’s growth in spring resumes, the pistillate flower devel- opment takes place a few weeks before anthesis. The sequence of development has been categorized into 9 stages (Wetzetein and Sparks, 1983). The number of female flowers on a spike varies from 2–10 determined by the cultivar and vigor of the shoot.

Cultivars have not been distinguished in terms of the amount of chilling required for flower development, but cultivars are known to differ in chilling required for initiation of bud growth (McEachern, 1973). The influence of chilling on flower formation and bud growth should be evaluated in northern and southern pecan cultivars. Protandrous and protogynous cultivars differ- entiate pistillate flowers at nearly the same period. In walnut, protogynous and protandrous individuals’ pistillate flowers are differentiated in the season before blooming (Polito and Li, 1985).

Pistillate flowers in pecan are first visible as a flattened area at the shoot terminal. As growth continues, individual flowers become visible. Flower development proceeds from the base of the peduncle toward the apex (acropetally). Each flower consists of a 4–5 segmented floral envelope (the involucre, formed by an abaxial bract and bracteoles) surrounding the ovary and surmounted by a stigma. Flowers from different cultivars are extremely variable in size, stigma colour, and stigma shape at receptivity. Stigma colour ranges from green (e.g., “Desirable”) to deep red (e.g., “Pawnee”) and is often somewhat variable between flowers of a single tree. Stigma colour is not a reliable index of receptivity. Stigmas are typically bilobed, but lobes may be inconspicuous or pronounced and either upright or reflexed. Given the variability between cultivars, the extent of stigma lobe exertion is not a reliable index of receptivity across cultivars.

Receptivity has been determined by the presence of a “viscous fluid” on the surface of stigma (Mullenax, 1970) and by adherence of applied pollen to the stigmatic surface. Adherence of applied pollen is the method recom- mended for evaluating receptivity in breeding orchards.

2.6.2 Pollination

Because of hetero dichogamy, most pecans are cross-pollinated, and self-pollination is quite uncommon. The pollen is light, dry and pale yellow in colour. Pollen can be transported by wind over a distance of around 900 meters. It has been suggested to plant 5% pollenizers to ensure adequate pollination (Romberg, 1931; Woodroof, 1930). Currently, every 10th row in the orchard is planted with a pollenizer, increasing percentage up to 10. Protogynous and protandrous cultivars are grown together which, besides the pollination, is desirable in view of other horticultural benefits.

The duration of both pollen dehiscence and stigma receptivity ranges from about 8–16 days depending on the seasons and cultivars (Sparks, 1986 b). Pollen dehiscence is hampered by high relative humidity (above 85%) and very low temperature. The pecan stigma is of dry type. Pollination is not a problem in pecan under normal conditions.

The techniques of making controlled crosses in pecan were reported by Smith and Romberg (1940) and have changed little. Pistillate flower clusters are encased prior to receptivity in 3 cm diameter viscose casings cut into 15 cm lengths and tied closed on one end. The casing is placed over the cluster and tied to the shoot below the inflorescence, with a band of cotton placed under the casing and around the shoot. When stigmas are receptive, pollen is blown into the casing using an aspirator. Critical aspects of the controlled pollination process are the proper timing of pollen application in relation to stigma receptivity and application of an adequate, but not overabundant, quantity of pollen. Application of excessive amounts of pollen may make nutlets dehisce (Romberg and Smith, 1950).

The flattened pecan pollen grains become rounded and hydrated 1 h after pollination, with pollen tube emergence being visible within 3 h (Wetzstein and Sparks, 1989). After pollen hydration and germination, stigmatic cells collapse and degenerate, resulting in a darkening of the stigmatic surface (Wetz stein and Sparks, 1989).

About 4 days after pollination, the polar-fusion nucleus joins one of the gametes from the pollen tube (McKay, 1947). This results in the forma-tion of the large primary endosperm nucleus, which is the most prominent aspect of the embryo sac for about 2 weeks after pollination. The second male gamete from the pollen tube unites with the egg 4–7 days after polli-nation. The interval between union of the polar-fusion nucleus with one male gamete and the union of the egg with the other male gamete may be only a matter of hours, since both fusions were seen in ovules fixed 4 days after pollination. This is consistent with observations made on C. glabra by Langdon (1934).

2.6.3 Genetic Resources

Pecan is a native of North America but the opinions differ whether it origi- nated further north and was water borne to the south or appeared simultane- ously over a wide region. The natural habitat of pecan ranges from Texas in the southwest to Alabama in the southeast extending up to southern Illinois (Hanna, 1987).

Pecans and hickories constitute the genus Carya, which is the only genus in the tribe Hicoreae (Manning, 1978). Recognition of species follows Manning (1978) with the exception that Carya carolinae-septentrionalis is considered a species rather than variety australis of C. ovata.

The potential breeding value of the Asian Carya species cannot be accu- rately evaluated due to the paucity of information and lack of germplasm for study. Two of the Asian species of hickory (C. cathayensis Sargent and C. hunanensis Cheng & R. H. Chang) are cultivated to a moderate extent, while two others (C. sinensis Dode and C. tonkinensis Lecomte) are cultivated only to a very small extent.

C. sinensis Dode: Nuts with an acuminate apex, weakly developed secondary septa, and lacking lacunae in the walls of the shell. The Chinese name for the tree refers to the “beak-like” or acuminate apex of the nut.

Carya cathayensis Sargent, The Chinese Hickory: Kuang and Li (1979) report that nuts have good flavor and produce a fragrant oil used in foods and in making paint.

Carya hunanensis Cheng & R.H. Chang, The Hunan Hickory: Nuts can be eaten fresh or fried or are pressed for comestible oil. Additionally, they are a component of a traditional medicine used to treat cough, heart as well as lung problems (Grauke et al., 1991).

Of the North American species of hickory, those with the greatest potential for use in breeding are C. aquatica and C. cordiformis of Section Apocarya, and C. ovata and C. laciniosa of Section Carya.

C. poilanei (Chev.), The Poilane’s Hickory: First described as Juglans poilanei and later transferred to the Carya genus. It was described as having “persistant” or “evergreen” leaves. C. poilanei has lacunae and lacks hairy anthers and this associates it with C. kweichowensis, as does its rounded.

C. tonkinensis Lecomte., The Vietnam Hickory: It is known as the “May-chau” by the Thais who extract from the nuts an oil used cooking.

C. aquatica, The Water Hickory: Water hickory is later to flush growth in the spring and to blossom. The most distinguishing feature of C. aquatica is its extremely flattened, sharply four-angled, and gritty nuts. Compared to other hickory species, water hickory wood is thought to be inferior.

C. myristiciformis., The Nutmeg Hickory: It is often found as a minor companion in the Swamp Chestnut Oak-Cherry Bark Oak Forest Type on moist rich soil. The wood of C. myristiciformis is inferior to other hickories and comparable to that of C. aquatica.

C. palmeri Manning, The Mexican Hickory: The tree frequently grows alongside C. myristiciformis on steep slopes. Nuts with bitter, convoluted kernels, which superficially resemble C. cordiformis.

C. cordiformis (Wangenh.) K. Koch, The Bitternut Hickory: Because of its characteristic buds, leaves, nuts, and bark, bitternut can be easily identified. “Cordiformis” is Latin meaning “heart-shaped.” Kernels are bitter and crinkled.

Within section Carya the two diploid species C. ovata and C. laciniosa have potential breeding value. Each has been the source of numerous named hickory cultivars and each hybridizes with pecan.

C. ovata, The Shagbark Hickory: C. ovata has more named, over 130 cultivars than any other hickory, with the exception of pecan (Grauke, 1988). One of the best woods in the genus belongs to the shagbark hickory.

C. ovata var. pubescens: The tree resembles C. tomentosa because of the extremely dense pubescence on the lower leaf surface and twigs. This variety has only had one named cultivar, called “Kentucky.” “Barnes” might also be a member of this group.

Carya carolinae-septentrionalis (Ashe) Engl. & Graebn, The Southern Shagbark Hickory: It is a minor species which has little commercial importance there have been cultivars named from the species: “Guilford,” and “Nugget.” “Nugget,” from Alabama, suffers frost damage in North Carolina.

C. laciniosa (F. Michx.) Loudon, The Shellbark Hickory: Shellbark normally found on deep terrain. The flavor of the kernels is considered by many to be inferior to that of the shag- bark hickory.

All other members of Section Carya are tetraploid (which increases the difficulty of genetic hybridization) and less palatable than shagbark and shellbark (which reduces the incentive to use them in breeding) (Table 2.2).

Table 2.2 Carya Species and Their Distribution⏎

Species | Distribution
Sect. Rhamphocarya |
C. sinensis Dode. | Taiwan and to some extent in Vietnam
Sect. Apocarya |
C. aquatica (F. Michx.) Nutt. | Texas east to Florida and north to Illinois and Virginia
C. cordiformis (Wangenh.) K. Koch. | Gulf Coast of Louisiana and southern Quebec, New Hampshire south to Florida, and west to Minnesota and eastern Texas
C. cathayensis Sarg.* | Zhejiang and Anhui, China
C. illinoinensis (Wangenh.) K. Koch. |
C. hunanensis Cheng & R. H. Chang* | Chinese provinces of Hunan, Guizhou, and Guangxi
C. myristiciformis (F. Michx.) Nutt. | Selma, Alabama
C. kweichowensis Kuang & Lu* |
C. palmeri Manning | Mexico, mountains of Nuevo Leon, Tamaulipas, and Veracruz
C. tonkinensis Lecomte* | Vietnam, southern Yunnan province in China, northwestern Yunnan province bordering upper Burma, and the Imphal area of India
C. poilanei (A. Chev.) J. Leroy* | Vietnam and Laos
Sect. Carya |
C. carolinae-septentrionalis (Ashe) Engl. & Graebn. |
C. glabra (Mill.) Sweet | Southwestern New Hampshire west to eastern Illinois, south to eastern Texas, and from there east to central Florida
C. ovalis (Wangenh.) Sarg. | Southern Missouri into northeastern Oklahoma and across northern Arkansas
C. floridana Sarg. | U.S.A., confined to about 20 counties in central Florida centered around Osceola County
C. laciniosa (F. Michx.) Loudon | Western New York to southeast Iowa
C. ovata (Mill.) K. Koch | West Maine to Minnesota’s southeast, with Quebec, Canada, along the St. Lawrence River
C. pallida (Ashe) Engl. & Graebn. | Virginia west to Tennessee, south into Louisiana, and east into northwestern Florida
C. tomentosa (Poir.) Nutt. | Eastern Massachusetts to Florida west across eastern and central New York and northern Ohio to southeastern Iowa, Missouri, southeastern Kansas, eastern Oklahoma, and eastern Texas
C. texana Buckley. | West of the Mississippi River from Missouri south to central Texas
C. × brownii (C. cordiformis × C. illinoinensis) Sarg. |
C. × demareei (C. cordiformis × C. ovalis) Palmer |
C. × collina (C. texana × C. tomentosa) Laughlin |
C. × laneyi (C. cordiformis × C. ovata) Sarg. |
C. × dunbarii (C. laciniosa × C. ovata) Sarg. |
C. × lecontei (C. aquatica × C. illinoinensis) Little |
C. × ludoviciana (C. aquatica × C. texana) (Ashe) Little** |
C. × nussbaumeri (C. illinoinensis × C. laciniosa) Sarg. |
C. × schneckii (C. illinoinensis × C. tomentosa) Sarg.** |
C. cordiformis × C. tomentosa (see Reed [1944])** |
C. illinoinensis × C. ovata (see Manning [1962]) |
C. illinoinensis × C. cathayensis (see Yeh and Wu [1965]) |
C. illinoinensis × C. myristiciformis (see Windham et al. [1981]) |

* Notes:Asian species

** Disputed parentage.

Carya tomentosa (Poir.), The Mockernut Hickory. The tomentose rachises, lower leaf surfaces, and twigs that give the tree its scientific name make mockernut easy to identify. Nuts often have thick shells that are light brown in color and have sweet kernels.

Carya texana Buckley, The Black Hickory. The black hickory has thick, furrowed bark of black hickory, which is often dark grey to black, gives the tree its common name. According to reports, the tetraploid black hickory can hybridize with the tetraploid mockernut to create the C. x collina Laughlin and with the diploid water hickory to create the C. x ludoviciana (Ashe).

Carya glabra (Mill.) Sweet, The Pignut Hickory. The sole cultivar of C. glabra is evidently wrongly attributed to that species, “Brackett,” was given that name in 1896 from a specimen that received from the G. B. Brackett from Denmark, Lowa.

Carya ovalis (Wangenh.) Sarg., The Red Hickory. It has two cultivars with the names “Green” and “Huff,” both named in 1929 and both from southern Michigan. The only putative hybrid involving C. ovalis is C. x demareei Palmer (C. ovalis x C. cordiformis).

Carya pallida (Ashe) Engl. and Graebn., The Sand Hickory. The species grows on sandy, dry upland sites that often with pine.

Carya floridana Sarg., The Scrub Hickory. It may be distin-guished by the rust-colored scales on the buds and lower leaf surface that separate the species from all others except C. texana. Its habit ranges from a multi-trunked shrub with fruit-bearing stems 3–4 feet in height to a single-trunked tree 50–70 feet tall (Rathore, 1991).

2.7 Pistachio Nut

2.7.1 Flowering

Since pistachio is small to medium sized, dioecious plant. The buds in the axil of leaves are initially vegetative for four to five years before developing into floral buds as the plant enters its productive phase. The brownish-green flowers do not have petals and have five sepals; the male flowers have five stamens and; female flowers do not have stamens but, have single tricarpe- lary superior ovary. Axillary staminate and pistillate floral bud primordia develop rapidly along with the elongation of terminal buds in the month of March, and with subsequent development of axillary meristem, the first sepals may appear in May (Crane, 1986). Thereafter, further development of pistallate primordia occurs in October and that of staminate primordia the following March. Inflorescences of both pistillate and staminate types commonly bloom in the first fortnight of April on one year old wood.

2.7.2 Pollination

Staminate and pistillate inflorescence may consist of several hundred indi-vidual flowers which are apetalous. Cross-pollinating agent is wind which necessitates the proper placement of pollenizers in relation to pistillate trees. Bees exclusively visit male flowers because of pollen; they do not visit female flowers since they do not contain pollen and nectar. Typically, one pollinizing tree is planted for every eight pistillate plants; however, this ratio can increase to 1:10 or even 1:12. A solid row of pollenizer trees along the wind direction of the orchard is also planted in addition to those located throughout the orchard. Fruit set varies between 8% and 12% on average.

When pistillate trees are sprayed with the mineral oil dinitro-o-cresol (DNOC) during their rest phase, the blooming dates of the pistillate trees are advanced by about three weeks, coincident with the staminate plants’ flow- ering date (Procopious, 1973). Inadequate numbers of staminate trees with various flowering dates, especially late flowering cultivars, and varied flow- ering periods in female trees have been attributed for insufficient pollination of pistachio plants (Pontikis, 1975). Procopious (1973) recommended the use of DNOC (5%–20%) sprays to overcome such problems. Aqueous paclobutrazol at 100–4000 mg/L when sprayed at the end of June (when shoot extension ceases) delays flowering of the staminate cultivars the following season and coincides with the flowering period of the pistillate cultivars (Porlingis and Voviatzis, 1986). Pontikis (1989) successfully advanced the flowering of female cultivars by about 19 days with the application of hydrogen cyanamide during their rest period which ensured pollination and a good crop.

2.7.3 Genetic Resources

Six species of Pistacia were identified by Linnaeus in his Species Plantarum in 1753: P. lentiscus, P. narbonensis, P. simaruba, P. terebinthus, P. vera and P. trifolia. Pistacia narbonensis and P. trifolia are synonyms of P. vera. All the species in Pistacia exude turpentine or mastic but, Pistacia vera is the only edible species in the genus.

The common Pistachio is native to Western Asia and Asia Minor from Mediterranean region to India. There have been two centers of diversity identi-fied. One includes the Southern Europe’s Mediterranean region, Middle East and Northern Africa. The second includes West and Central Asia (Thakur et al., 2015). In the middle of Central Asia (Uzbekistan, Tadzhikistan, Kirgizia and southern Turkmenia and Kazakhstan) the P. vera forests are spread over an area of 3,00,000 ha. (Parfitt, 2012). The wild forms have smaller edible fruits. P. atlantica and P. khinjukare the other two species which grows wild in Central Asia. The domesticated varieties of P. vera are grown in Central and South-West Asia, Iran, and South-Eastern Turkey. During the regime of Emperor Tiberius it was introduced in Mediterranean region (Zohary et al., 2012). Romans were responsible for its spread in the Mediterranean basin.

Zohary (1952) has earlier classified Pistacia integerrima as a subspecies of P. chinensis. In the taxonomic revision of the genus Pistacia L., Al-Saghir and Porter (2012) stated that Pistacia khinjuk Stocks. Is a separate species from Pistacia integerrima Stewart. Further, they also stated that Pistacia integerrima is a basionym for Pistacia chinensis Bunge subsp. integerrima (Stew. Ex Brand.) Rech.

2.8 Walnut

2.8.1 Floral Biology

Walnut is a monoecious plant. The walnut’s staminate (male) flowers are small, densely grouped, emerge laterally on the growth from the previous season, and hang in catkins. The catkins are green yellow in colour borne in spring usually solitary or in pairs, 5–8 cm long. Pistillate flowers emerge in pairs in the form of nutlets at the tip of current season’s growth, 1–4 per terminal. Single pistillate flower has 4 perianth segment that surround 2 lobed style, stigma fan shaped, ovary inferior, unilocular formed from 2 fused carpels.

Persian walnut commonly has one or two buds in the axil of each leaf; some of the other species commonly have three or more. Catkin buds differ- entiate early in the growing season as the first flush of growth occurs. If the new growth is examined about when the first flush stops, two kinds of buds are apparent: the leaf buds with scales and the naked catkin buds. The catkin bud is commonly the lower bud in leaf axils with two buds. Indi- vidual staminate flowers lack petals and comprise of a whorl of green sepals (comprises of irregular perianth segments), which encloses variable number of stamens. The following spring each of these catkins produces a great deal of pollen. Impiumi and Romina (1967) reported that each flower on the catkin had 13–18 anthers and each anther with about 900 pollen grains, about 1.8 million pollen grains per catkin. Pollens are very sensitive to weather, frost causes partial to complete abortion of normal meiosis, produces sterile pollen. Maturation of grain occurs before or after female flower bloom.

The petals of the pistillate flower are pubescent, small, and green and lack visible sepals. The female flower consists of a hairy involucre fused to four sepals that enclose the pistil, that has a swollen base, the ovary, and a short style with a forked stigma with two feathery stigmatic lobes. The ovary wall encloses the ovary, and inside the single locule is divided into four parts by the major and minor septa. A single ovule enclosed by a single integument is attached to the ovary. Tissues of involucre and sepals makes hull of walnut. Ovary includes enlarged basal portion of the pistil, short style and feathery bilobular stigma. This feathery structure facilitates the interception of wind- borne pollen. Recognition of walnut pollen and exclusion of pollen from unrelated species. The shell develops from the ovary wall. The kernel is the embryo. Fruit variable, large oval egg shaped, globe or pear shaped, covered with glabrous dark green dotted husk (epicarp and mesocarp fused) that splits at maturity.

During late winter, some of the leaf buds develop pistillate flowers, thereby becoming mixed buds. Though the fruit bud formation of a pistillate flower is initiated during summer, yet evidence of flower part differentiation can be detected three to five weeks before they open in spring. Mid-April marks the peak flowering period for walnut under Shimla conditions, which is extended until the first week of May in late flowering cultivars. The pistil- late flowers are borne on shoots up to 60 cm length. Walnut shoots do not start new growth flushes at the same time. In moderately cool summers or in poor soils, the last flush is short and in the following spring its buds are appropriate to produce shoots that are terminated by flower clusters. While trees growing in good soil with late summer temperature favorable for strong growth, the shoots in the last growth flush of the season tend to be long and rather succulent and have buds that open into shoots in next spring.

In less fruitful cultivars, terminal buds become mixed while in most fruitful cultivars nearly all leaf buds including lateral ones, become mixed and bear pistillate flowers. Before winter dormancy, all the floral organ differentiates; male flower buds differentiated between 35 and 45 days after bud burst and the pollen grains and embryo sacs developed in the following spring. It was also reported that the differentiation of buds remained revers- ible for 25–35 days for male and 115–125 days for female.

Lin et al. (1977) studied the initiation of pistillate flowers of 7 walnut cultivars in USA. For the cvs. Chico, Vina, Serr, Tehama, and Pedro, flower formation was discovered in the first two weeks of June, and for Hartley and Franquette it occurs in the middle of July. Depending on the cultivar, floral parts initiated at various times. Chico’s pistil development started in February, while Franquette’s started in April. The majority of the cultivars were fertil-ized throughout April, although Franquette fertilized in the middle of May. In Bulgaria, the female and male flowers were found to appear at a mean daily temperature of 14.5°C in cvs. Proslavski, Lyubimets and Sheinovo and at 10°C in Dryanovski, Plovdiski and Perushtenski. Mass flowering in all these cultivars was found at a mean daily temperature range of 9°C–20°C. The phase which lasted for the formation of floral organs until the end of flowering occurred at mean daily temperatures in the range 15.5°C–19°C (Draganov and Nedev, 1973). Draganov and Nedev (1977) further reported that both male and female flowers appeared at a minimum of 50% RH and 4–5 mbar vapor pressure deficit (VPD). Flowering was optimal at 60%–70% RH and 6–8 mbar, whereas 75% RH and 10 mbar were detrimental for flowering.

2.8.2 Pollination

Walnuts are self-fertile or self-fruitful and cross-compatible or cross fruitful and in majority of the cultivars, pollen dehiscence and stigma maturity synchronize, hence pollination is not a problem. But the phenomenon of dichogamy occurs in walnut. Furthermore, the situation is aggravated by the short durations of both stigma receptivity and pollen viability (Polito, 1985). Walnut flowers are anemophilous, exhibiting all the features of wind pollination, including non-stickiness, abundant production of light pollen, protruded and feathery stigma, and remains receptive for few days. Theoreti- cally. A single pollen grain is sufficient to fertilize the single ovule and set fruit, however, required pollen loads is ranging from 30–50 times the number of ovules for set. It often require cross pollination.

Crop set requires effective pollination, although only approximately 10% of pollinizers are needed, and the main cultivar’s staminate and pistillate flowers overlap well (Forde and Griggs, 1975). Usually, the pollinators are planted in complete rows alongside the main cultivar. During walnut bloom, there may be a lot of pollen in the air in areas where walnut plantings are common. To ensure appropriate pollination, this may be sufficient or may require the addition of a small number of additional pollinizers.

Walnut pollen had highest germination capacity when it was first shed, under simulated natural conditions lost its viability 2–3 days after collection and on exposure to light at 25°C–30°C, its viability was lost in 1–3 hours. However, its pollen germinated on the stigma within 1–3 days after pollina- tion. The viability of walnut pollen lasted for 100 hours at 14°C–15°C and 55 hours at 22°C–25°C and 0°C while temperatures above 25°C and humidity below 33 % during pollen maturation resulted in pollen sterility.

Walnut crops fail as a result of unfavorable weather conditions including snowfall, hail, frost, or rain during the spring blossoming period. Pollen of late varieties is less susceptible to spring frost damage than those of early varieties. If the fruit set is inadequate even when the plant health is normal, inadequate pollination may be the cause and artificial pollination can be the answer for this problem. With this, the inadequate pollination due to dichogamy can also be rectified. The walnut catkins can be collected and stored for 2–3 weeks in a desicator at 0°C or in a refrigerator maintained at low humidity. Pollen could be stored even for 3–8 months at −20°C. While comparing early, mid and late season cultivars it was observed and found that the optimum temperature for pollen germination was positively related to mean staminate bloom date. However, other found that in vitro pollen germinability was completely lost after 1 month of storage at 4°C or −20°C but it remains viable in vivo germination test on stigmas. But few reported that storage at −1°C to −2°C reduced viability and impaired fruit set.

The pollen can be used for pollinating the same cultivar or other cultivars at the same location or different locations. However, cross pollination results in higher fruit set. Even mixture of pollen from 2–3 cultivars or different species – Juglans mandshurica and Juglans cinerea increased fruit set. When stigmas begin to be receptive, about ten catkins, placing each in a small cloth open-mesh bag, are thrown on the top of the trees and stirred two or three times in a day with a pole. A few branches can also be top-worked in the orchard with the pollinating cultivar to improve pollination.

Walnut pollen showed the highest germination capacity when it was first shed. Pollen stored under simulated natural conditions lost its viability 2–3 days after collection. In some cases freshly collected pollen lost its viability 1–3 hours after exposure to sunlight at 25°C–30°C. The pollens usually germi- nate on the stigma within 1–3 days after pollination (Rud and Zhadan, 1972).

The stigmas start to separate as the pistillate flower develops. Sticky exudates are secreted by cells on the stigma’s surface, which catches pollen grains and serves as a substrate for germination. The stigma lobes stop secreting exudates and cease to be receptive once they have opened to about a 45° angle. Pollen grains are carried by the wind, deposit on the stigma, and begin to germinate after 7–8 hours in a warm, sunny conditions. After germi- nation on stigma, multiple pollen tubes grow through the style; few able to penetrate in the ovary but only one reach the ovary sac and fertilize the egg cell. The zygote divides 7–10 days after fertilization to start the period of development that ultimately leads to the development of the embryo (the kernel). Pollination takes about 1 week. Before falling from the tree, unpol- linated flowers will continue to grow for a few weeks. The elongation of catkins begins in the spring (Verma et al., 2015).

After bloom, the nut can be harvested 19–22 weeks later. When choosing walnut cultivars, timing of leaf emergence and harvest has always been a crucial factor. Early-leafing varieties are more vulnerable to frost, walnut blight, and insects issues in California. However, early-leafing and flowering cultivars typically harvest early (in September) and have the benefit of being able to enter the holiday nut trade earlier. Late-harvesting (mid-October) cultivars can be subject to challenges like rain, which can interfere with harvesting operations. Vigorous late-harvesting cultivars that continue growing late into the autumn may also be more susceptible to injury by early frosts and winter injury (Verma et al., 2015).

2.8.2.1 Factors Affecting Flower Types

Types of flower and their proportion in the walnut inflorescence are influenced by several factors. Several types of flowers namely staminate, pistillate and hermaphrodite flowers appear in walnut inflorescence and are influenced by the time of inflorescence emergence with transition from female to hermaphrodite and then to female flower. Exposure of spurs to light and vegetative condition of spurs in the previous season resulted in more number of pistillate flowers. Besides these factors, gibberellins like substances control sex differentiation in pistillate flowers and stimulate their production, whereas differentiation in pistil- late flowers in the terminal buds, during the end of growth period is associated with the presence of auxins. This together with an increased level of inhibitors regulates the number of pistillate flowers. IBA use can alter twig bud ratios and control the number of flowers in staminate and pistillate inflorescences.

2.8.3 Genetic Resources

Juglans regia L., the from the Carpathian Mountains in eastern Europe, to Turkey, Iraq, Iran, the southern USSR and Afghanistan to the northern Himalayas, Persian walnut has been found to grow in a wide variety of habitats (Woodroof, 1979; Forde, 1975; Serr, 1969). The genus Juglans contains roughly 18 other species that are native to North and South America, central China, Manchuria, and Japan. Romans liked it so much that they named it in honor of the king of all their Gods, Jupiter’s Acorn, or in Latin. Jovis-glans which later on became Juglans. According to Forde (1975), the walnut trees were introduced in England by 1562, where it was not successful because of very cold summer. In India, walnut remained confined to Kashmir and it appears that it has spread to Himachal Pradesh and Uttar Pradesh hills during the past century only because there has been lack of direct contact among these states. The walnuts grown in the North America and France were extremely susceptible to severe winters restricting the extension of their cultivation further into the north but the introduction of cold-hardy race of walnut from the Carpathian mountains of Poland greatly solved this problem and the term “Carpathian walnut,” thus, came into existence which can survive winter temperature falls to –35°C (Table 2.3).

Table 2.3 Species of Juglans⏎

Species |  | Range
Section a. | Juglans | Southeastern Europe, Iran to the
| J. regia | Himalayas, and China
| Subs p. turcomanica |
| Subsp. fallax |
Section b. | Rhysocaryon | Argentina
| J. australis |
| J. boliviana | Western South America
| J. californica | California
| J. hindsi | California
| J. hirsuta | Northeastern Mexico
| J. jamaicensis | West Indies
| J. major | Southwestern United States,
| var. major | Northwestern Mexico
| var. glabrata | South-central Mexico
| J. microcarpa var. microcarpa (J. rupestris) var. stewartii | Southwestern United States, Northwestern Mexico
|  | Northern Mexico
| J. mollis | Central Mexico
| J. neotropica | Northwestern South America
| J. nigra | Eastern United States
| J. olanchana |
| var. olanchana | Guatemala
| var. standleyi | Southeastern Mexico
| J. pyriformis | Southeastern Mexico
| J. soratensis | Bolivia
| J. steyermarkii | Guatemala
| J. venezuelensis | Venezuela
Section c. | Cardiocaryon |
| J. ailantifolia |
| (J. sieboldiana) |
| var. allanifolia | Japan
| var. cordiformis | Japan
| J. cathayensis | Eastern China, Taiwan
| J. mandshurica | Manchuria, Northeastern China, Korea
Section d. | Trachycaryon |
| J. cinerea | Eastern United States

a Arranged according to the classification in Manning (1978).

2.8.3.1 Brief Description Of Important Species

J. ailantifolia Carr. (J. sieboldiana Maxim.), Japanese Walnut: Nuts are usually smooth to rugose and elongated to nearly round, with a hard shell. The heartnut, J. ailantifolia var. cordiformis, (Maxim) Rehd., is a botanical variety of J. ailantifolia.

J. nigra L., Eastern American Black Walnut: Nuts have a thick, hard, rough shell with a thick, adhering hull.

J. cinerea L., Butternut: This is the most cold-resistant species of American Juglans.

J. macrocarpa Berlander, Texas Black Walnut: This small tree is rarely over 10 m and the nuts are small and round with a very hard, smooth shell and an adhering hull.

J. major Heller, Arizona Black Walnut: Usually under 15 m tall, with ideal conditions the trees can attain 25 m or more. Nuts are nearly round, almost smooth, and hard-shelled with an adhering hull.

J. californica S. Wats, Southern California Black Walnut: Usually grow near small streams, most of which have water only when it rains. The tree is shrubby, usually branching at or near the ground.

J. hindsii Jeps., Northern California Black Walnut: It is use as a street tree and rootstock. The nuts are round, smooth, and hard-shelled with an adhering hull.

J. sieboldiana Maxim. Japanese Butternut: One botanical variety J. sieboldiana var. cordifornis.

J. cathayensis Dode. Chinese Walnut or Chinese Butternut: Trees are tall growing 75 feet or more. Both leaves and branches are pubescent and glandular.

J. mandschurica Maxim. Manchurian Walnut: Tree tall growing, 60 feet, round topped head, leaves, petioles heavily pubescent and glandular beneath and shiny above.

J. sigillata Dode: This species, sometimes referred to as the “iron walnut” locally, has been grown for its oil in Yunnan Province for a very long time, and various cultivars have been developed.

J. hopeiensis Hu: It exhibits leaves and fruiting structures similar to those of J. regia but nut characteristics similar to J. mandshurica.

Juglans Hybrids (Verma et al., 2015).

J. × bi× byi Rehd. (J. ailantifolia × J. cinerea);

J. × intermedia Carr. (J. nigra × J. regia);

J. × notha Rehd. (J. ailantifolia × J. regia);

J. × quadrangulata (Carr.) Rehd. (J. cinerea × J. regia);

J. × sinensis (D. C.) Rehd. (J. mandschurica × J. regia);

J. × parado× Burbank (J. hindsii × J. regia);

J. × royal Burbank (J. hindsii × J. nigra).

2.9 Conclusion

In conclusion, the flowering of temperate nut crops is a critical stage in their growth cycle, with significant implications for yield and quality. Proper management practices, including pollination, environmental considerations, and disease control, are essential for successful nut production. Ongoing research and adaptation to changing environmental conditions will be crucial for the future of this agricultural sector.

Keywords

anthesis

dichogamy

floral biology

Juglans

pollen viability

pollination

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Chapter 3 Role of Plant Growth Regulators on Growth and Development of Temperate Nuts

A. B. KHALANGRE,1,2* JADHAV AKASH,³ ANIS MIRZA,¹ and T. P. AHAMED SHABEER³

¹Deparment of Horticulture, Lovely Professional University, Phagwara, Punjab, India

²Interdepartmental Centre for Agri-Food Industrial Research, Alma Mater Studiorum, University of Bologna, Cesena (FC), Italy-47521.

³ICAR–National Research Center for Grapes, Pune, Maharashtra, India

*Corresponding author

Abstract

Growth-regulating chemicals, often called as phytohormones where, Phyto means plant, these are substances that plants naturally create to govern their own growth. Phytohormones are very effective chemicals for plants. The synthesized plant hormones or phytohormones are called as the plant growth regulators (PGRs). These have major role in controlling growth and development of plants. Similarly, in temperate nut crops such as walnut, pecan, pistachio, and so forth these PGRs regulates the growth and development also, these are useful in manipulating production of temperate nut crops by utilizing them during tissue culture practices which help to reduce long juvenility in temperate nut crops. So, in this chapter we will discuss about different plant growth regulators and their general roles in growth and development of temperate nut crops.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

3.1 Introduction

For millennia, beginning with the collecting of wild nuts, humans have ingested the high-calorie, nutrient-dense seeds of nut crops. Some ancient peoples used these nuts in place of meat, especially in isolated areas like islands, as they are a great source of protein. There are many more products developed and utilized from temperate nut crops such as their oils, flours and other food products. The wood of the temperate nut crops is having very strong among which chestnut, have good rot resistance which is most used for fence posts. The tannin present in the bark of temperate nuts is used for tanning and coloring purpose, addition to culinary purposes. These temperate nut crops are widely grown because they are delicious and an essential component of a balanced diet, and they provide a significant economic contribution to local and national economies. Given their significance, temperate nut crops require regulation of their growth and a rise in their output, which is where plant growth regulators come into play.

Growth-regulating chemicals, known as phytohormones (with “phyto” meaning plant), are substances that plants naturally produce to regulate their growth. Growth regulators are very effective chemicals for plants. Artifi- cially synthesized phytohormones are called as the plant growth regulators (Davies, 2010; Rademacher, 2015; Santner et al., 2009). A range of external and endogenous signals must be integrated throughout plant growth and development in order, for the intrinsic genetic programme and other factors to influence plant morphology. Regulators of plant development are neces- sary for this process. The primary phytohormones (PGRs) contain conven- tional groups or other compounds. They include indol-3-butyric acid (IBA), indol-3-acetic acid (IAA), gibberellic acid (GA3), 2,4-dichlorophenoxy acetic acid (2,4-D), 1-naphthyl acetic acid (NAA), benzyladenine (BA), 6-benzylaminopurine (BAP), ethylene or ethephon (CEPA), abscisic acid (ABA). According to its features, each PGR has a different nature, transport, incidence, and effects. In many agricultural domains, plant growth regula- tors can be incredibly helpful allies in the effort to increase yields with higher Phyto-technical, phytosanitary, and commercial quality. In light of this, attempts to reveal, consider, and discuss the usage of phytohormones in temperate nut crops and its potential role. This chapter starts out by outlining the technical aspects of plant growth regulators. Then, it discusses the functions and application of them particularly in temperate nut crops.

3.2 Plant Growth Regulators

Plant growth regulators are regularly used in agricultural activities having various roles. A few examples include regulating growth, developing abiotic and biotic stress, fruit set management, fruit quality, bud dormancy breaking, fruit ripening, fruit storage, morphological structure, to increase yield (Alcázar et al., 2010; Tripathi et al., 2022; Bergstrand, 2017; EL Sabagh et al., 2022; Fahad et al., 2016; Rademacher, 2015; Choudhury et al., 2013 Hossain et al., 2022). “Plant growth regulator” describes synthetic chemicals that work in very small doses typically at sites other than their initial production site and regulate all plant processes of plants. It is a cluster of small molecules, don’t have similarities in structure and are produced from several key metabolic activities (Davies, 2010; Gill et al., 2023; Santner et al., 2009). These have very crucial role in regulating growth and modulating responses to abiotic and biotic stresses. Plants Adaptability to environment fluctuations also, depends on the phytohor- mones, according to Peleg and Blumwald (2011), by regulating nutrient allocation, growth, development, and source/sink transitions. Despite the fact that ABA has gotten the greatest attention, the role of auxins, cytoki- nins, and brassinosteroids during the period of environmental stress is less as we understood. Plant hormones are engaged in a variety of functions, according to a recent study. Plant hormones interact with one another, these interactions develops synergistic or antagonistic effects which decides the response of plant to various abiotic stresses (Tripathi et al., 2022; Zahid et al., 2023; Alcázar et al., 2010; Kumar et al., 2023; Peleg and Blumwald, 2011; Verma et al., 2016).

Table 3.1 Role of Plant Growth Regulators

Plant Growth Regulators
Role
References

Auxin

Cell elongation, Cell division and differentiation, apical dominance, parthenocarpy, fruit development, flowering.

Zang et al., (2022); Song et al., (2023).

Gibberellins

Cell division and elongation, seed germination, dormancy, flowering, fruit size, induction of maleness in flower.

Métraux (1987); Castro-Camba et al., (2022).

Cytokinins

Cell division, cell enlargement and differ- entiation, bud initiation, root growth.

Liu et al., (2020); Prasad (2022).

Abscisic Acid

Regulate abiotic stress, dormancy induction, senescence.

Brookbank et al., (2020); Kumar et al., (2022).

Ethylene

Ripening of fruits and vegetables, senescence of leaf.

Cocetta and Natalini (2022).

3.3 Plant Growth Regulators on Growth and Development of Temperate Nuts

PGRs have been employed effectively in numerous plant development stages, which includes flowering, fruit development, ripening of fruits, harvesting of fruits, and post-harvesting of fruits.

Gibberellic acid is having great importance as it have influence on normal growth on many plant species. Flowers’ sense of their sexual identity is affected (Khryanin, 2002). GA is required for the development of the male and female flowers in a plant that is it influences the initiation and develop-ment of the male and female flowers in plant. Griffiths et al. (2006) assert that GA is not in charge of floral organ differentiation. Since the discovery and evaluation of GA responses, our understanding of GA metabolism and signaling pathways has substantially increased. For instance, in cucumbers development of male flowers enhance or promoted by the GA (Ueguchi- Tanaka and Matsuoka, 2010; Galoch, 1978; Iwahori et al., 1970; Galun et al., 1965). According to Takahashi and Jaffe (1984) auxin can hasten femaleness in a plant by enhancing the synthesis of ethylene. But in maize, GA and cytokinin result in a higher proportion of female flowers (Young et al., 2004). Maleic hydrazide (MH) and IAA have been found to promote the growth of branch buds, according to Sladk (1972). Growth hormones frequently affect sex expression differently depending on the type of plant. Malus domestica B., a temperate deciduous tree, blooms on its own. The vegetative growth during the period of growth to anthesis influences the floral initiation. Envi-ronmental influences, vegetative growth, the functions of carbohydrates and plant growth regulators, as well as advances in molecular biology, all have an impact on a tree’s ability to bloom (Wilkie et al., 2008; Trebitsh et al., 1987).

phytohormones are utilized and employed in agriculture in numerous real-world situations. A plant cannot generate blooms without auxins (Okada et al., 1991). The growth of flower primordia requires auxins. Cytokinins also regulate growth and differentiation in addition to cell division, apical bud dominance, food metabolism, senescence, flowering, nodulation, circa-dian rhythms and production of chloroplast (Gangwar et al., 2014; Roitsch and Ehneb, 2000). Cytokinin have the ability to skip senescence during the flowering. Gibberellic acid has a role in number of pathways that affect floral induction, photoperiodism, stress responses and autonomous pathways, according to Chen et al. (2018). Gibberellic acid is primarily responsible for signaling “to induce fertility” in the flowering pathway. Gibberellins also influence how quickly seeds and buds come out of dormancy and promote growth in colder climates (Gangwar et al., 2014; Shah et al., 2023). Ethylene suppresses blooming in Arabidopsis, which is a key factor in control of floral initiation (Achard et al., 2007). Due to its part in the mechanisms of drought stress and its capacity to postpone flowering, abscisic acid is known as a “floral repressor” and is used to treat many plant ailments. The hormone salicylic acid stimulates proteins to create floral buds during abiotic stress. The hormone Jasmonic acid influences the development of flowers (Campos- Rivero et al., 2017).

3.3.1 Bud Break And Flowering

Flowering is a three-step process that involves induction, initiation, and differentiation. High levels of GA₄ , ABA, and certain cytokinins may have a favourable impact on olive flower formation, as compare to the inhibitory effects of high GA₃ levels during the induction and initiation stages. (Ulger et al., 2004). By limiting the number of female flowers and flowering stalks per cluster, GA prevented pecans from blossoming. (Wood, 2011). Cytokinin and GA both exhibit simulative effects on the induction of floral develop-ment in perennial trees (Bangerth, 2006). P P-Ca, an ethylene generator, and ethephon, an inhibitor of GA synthesis, performed better when used separately as compared to when used in combination to raise the proportion in pecan flowering shoots at terminal portion and the average number of female flowers per cluster. (Wood, 2011). Treatment with GA₃ induced peak flowering to happen 4 weeks earlier with cool temperatures, according to Aliyu et al. (2011), indicating that it may be useful in increasing flowering since it caused flower initiation and development in cashew nut. Exogenous hormone therapies may encourage flowering in tree crops, according to some study. Apple spurs treated with exogenous cytokinin therapy during flower initiation produced more flowers and a return to bloom (Davenport et al., 2000). The bioregulators TIBA and BA, showed positive effect on flowering of pecan nut; but, separately, they had no effect (Wood, 2011). A more dependable bud break is achieved with Dormex®, a dormancy breaking agent based on hydrogen cyanamide (HC). The application of hydrogen cyanamide to pecans before to vegetative bud break increased male and female floral growth, bud break, and nut maturity without affecting nut production or phytotoxicity (Wood, 1993). Four weeks before to bud break, a spray of Dormex® + potassium nitrate was applied to pecan trees to encourage faster, and more synchronized flowering of the female and male cultivars (Fayek et al., 2008). “Curtis” pecan tree hydrogen cyanamide treat- ments in December resulted in significantly larger and earlier spring bud openings than controls in 2014 and 2015 (Bakry, 2007). Recently, “Wichita” and “Navaho” pecan trees responded to Dormex® in terms of bud break time in a comparable manner. They discovered that plants treated with Dormex® had considerably higher rates of bud break (Dekekind, 2020).

3.3.2 Delaying Bloom

The most vulnerable times to external conditions, particularly spring frosts, are bud break and bloom. The production of ethylene in plant tissues is accelerated by application of ethylene, which reduces crop height and cell elongation (Khalil et al., 2016). Rates that are greater than recommended could harm the tree by causing excessive defoliation, a reduction in the number of catkins produced, and twig dieback. For a reaction to occur, any plant growth regulator must be applied and administered at the proper time (Beede, 2011).

3.3.3 Lateral/Axillary Buds

One of the mechanisms that regulates bud growth and may be influenced by auxin-cytokinin interactions is apical dominance (Tworkoski and Miller, 2007). Abscisic acid, gibberellic acid, and ethylene can either stimulate or inhibit the formation of axillary buds (Wood, 1995). If given enough time to fully mature, the majority of pecan axillary buds have the potential to produce blooms. (Wood, 1995). Only the benzyl adenine and Promalin treat- ments significantly accelerated the growth of the axillary bud (Wood, 1988).

3.3.4 Alternate Bearing (Ab) And Return Bloom

According to Baktir et al. (2004), higher GA₃ concentrations encouraged the growth of vegetative buds whereas a lower GA₃ level encouraged the development of floral buds. GA₃ :ABA ratio greatly influences blooming and fruit set. The interaction between flowering and inhibitor hormone content is nuanced. The subsequent year’s heavy crop load prevented the return bloom and raised the concentrations of phytohormone inhibitors. When used at a higher concentration (500 mg/L) during the filling stage of pre-kernel nut development in a “off” year, GA synthesis inhibitor P-Ca proved particu- larly efficient in producing pecan pistillate blooms. Even at larger doses, when used post-kernel filling, have no effect on return bloom (Wood, 2011). Samuolien et al. (2016) also found that non-fruiting trees with substantial positive relationships between inhibitor hormones and sugars for IAA, GA1, GA3, and GA7 had the highest rates of return bloom the following year. In pecan flowering in upcoming season depends upon growth regulators which is complex. In terms of their return bloom, “Western” pecan fruiting and non- fruiting stems reacted differently to treatments with plant growth regulators. The responses of young “Pawnee” shoots to the same plant growth regulator treatments did not differ statistically significantly. Young “Western” trees were sprayed with GA3, which reduced the quantity of flowers per new shoot by 88.2% the following season (Thompson et al., 2019). Same results were observed in “Pawnee” when GA3 and GA4+7 was used (Wood, 2011). AVG (Aminoethoxyvinylglycine- block ethylene production), increased fruit retention in “off” years had a spillover effect that decreased the crop load the next season in “on” years (Wood, 2011; Thompson et al., 2019; Wood et al., 2009). However, young pecan trees treated with ethephon developed more new branches with blooms and more nuts per cluster the following season when compared to control plants (Wood, 2011). Ethephon treatment enhanced the “Wichita” pecan crop’s quality; on the other hand, it reduced the amount of nuts produced in years with an excessive nut crop load (Beede, 2011). Water samples containing GA3, ethephon, and AVG b increased and decreased pecan yield through making impacts on return bloom. A two- year experiment was conducted on 12-year-old “Western Schley” pecans to investigate the effects of GA3, P-Ca, and TDZ (thidiazuron) application (Orozco-Melendez et al., 2021). These PGRs, including GA3, ethephon, and AVG, can be used as an alternative to mechanical methods for reducing excessive nut output because mechanical methods run the risk of harming trees and making them more susceptible to pests and insects, in addition to harming the nuts (Khalil et al., 2016).

3.3.5 Shoot Growth

In the late 1970s, the first important discoveries of commercially viable tree growth retardants (TGRs) that could be used on a broad scale were cell elongation inhibitors such uniconazole (UCZ), paclobutrazol (PBZ), and flurprimidol. PBZ is more efficient than the other PGRs and only has to be present in very tiny quantities to inhibit shoot growth. PBZ limits internode elongation, which significantly reduces tree height and encour- ages leaves greening, more compact development. The compact growth of PBZ causes an increase in chlorophyll concentration per unit leaf area, which causes the leaves to become greener (Mog et al., 2018). The higher photosynthetic activity could possibly due to the increased chlorophyll per unit area of leaf. According to Allan et al. (1993) and Arzani and Robusta (2004), the use of PBZ greatly slowed the growth of fruit trees like apricot, peach, and pecan trees. The main goal of high-density plants is to maintain productivity by restricting vegetative development. PGRs have the ability to control pecan nut size, yield, and vegetative shoot growth. Following PGR spraying, several trials revealed decreased growth of terminal shoot, increase in area of leaf, poorer yields and larger nuts (Wood, 1998). Gaash and David (1998) did succeed in managing the growth of pecan tree shoots using PBZ or “Cultar®.” “Stuart” pecan trees treated with paclobutrazol at 75 years of age experienced a four-year reduction in growth of terminal shoot and leaf area. However, larger doses might result in damage to produce fewer nuts (Wood, 1998). When applied to “Wichita” pecans (ten-year-old trees), UCZ enhanced trunk diameter but decreased shoot growth, the number of lateral shoots per terminal, internode length, and the number of leaflets per compound leaf. UCZ application on the walnut (cultivar “wichita”) increased the diameter of tree trunk but, this resulted in decrease in growth of shoot, internodal length, lateral shoots per terminal and leaflets per compound leaf (Graham and Storey, 2000). Therefore, it is conceivable to interpret the tree’s restricted shoot growth as a strategy to better stimulate the production of flower and fruit. Short branches may more swiftly deliver nutrients to terminally growing blooms and nuts (Gaash and David, 1989).

3.3.6 Perfect Flowers And Improved Sex Ratio

Trees of fruit can produce blooms with male or female reproductive organs, with perfect blossoms having both. Apple, peach, cherry, and cashew trees have flawless blossoms, whereas pecan, walnut, and pistachio trees have flawed ones. Exogenous hormones have been topically injected into cashew plants to increase productivity and the amount of lovely blossoms. Ethrel, 1-NAA, Kinetin, and GA3 were used as foliar treatments, and this resulted in a rise in the number of flawless blooms (Aliyu et al., 2011; Ghadge et al., 2016; Gawankar et al., 2010; Jena et al., 2018; Baguma et al., 2023).

All of this suggests that hormone therapy could be useful for causing male or female blooms to emerge on nut trees. Pecan blossoms, for example, are often more male than female one. The production of more female blooms might hypothetically boost the output.

3.4 Tissue Culture

3.4.1 Almond

According to Gürel and Gülen (1998), the mixture of 0.1 mg/L IBA and BA produced the greatest results for development of shoot of almond and growth. Findings reported by Channuntapipat et al. (2003), they asserted that Nonpareil15-1 shoot tips needed to be propagated in AP media with 0.049 mM and 3 mM, IBA and BA, respectively. However, findings of Almehdi and Parfitt (1986), indicated that for shoot growth, using BA alone on medium was preferable to using auxin and cytokinin together. According to Yapar et al. (2006), mature shoots and shoot tips from the Yaltsinki almond cultivar were nodally explanted and grown on MS media supplemented with different concentrations and mixtures of cytokinins (2.0 and 4.0 mgL–1 BA) and auxins (IAA). In vitro micropropagation was aided by this action. Only the generation of roots and stems from embryos as well as the development of non-embryogenic calluses from shoot tips, according to their findings, were successful. However, they made no mention of the expansion or matu- ration of new shoots.

Hisajima (1982) noted that MS media added with 0.005 mg/L IBA+ 0.2 mg/L BA produced the best results for almond proliferation. According to Isikalan et al. (2008), MS medium mixed with 2 mg/L BA provided the best multiple shoot initiation for almond, with 1.04 mg/L of shoots per explant. Use of MS medium with half strength along with 2.4 mg/L IBA showed greater rooting in shoots of almond (Channuntapipat et al., 2003). To achieve best percentage of in vitro rooting in almond varieties “Nec plus ultra” and “Nonpariel” seedlings, auxins such as IBA and NAA are best suited (Ainsley et al., 2001).

3.4.2 Walnut

As the main explant source, debarked shoots of Juglans nigra were used by Cumnins and Ashby in 1969 to report callus growth on a modified White’s medium supplement with NAA (5.0 mg/L) and kinetin (0.2 mg/L). Callus cultures stayed alive for 4 weeks after being withdrawn from explants that had been cultured for 15 weeks. There was no evidence of organogenesis in this callus. A few years later, Lenartowicz and Millikan (1977) started a meristem tip project to create black walnut clones devoid of pathogens. Eight times the size of meristems (0.8–1.0 nm) was added prior to “lethal browning.” Rodriquez and Sanchez-Ternes (1981) started cultures from stem segments, discs of leaf, cotyledons and segments of root of seedlings of Juglans regia and exposing them to different levels of Cheng’s basal medium with auxins (IBA, NAA, and 2,4-D) and cytokinins (kinetin, BAP), with or without a 12% coconut milk supplement. The growth of the cotyledons in kinetin (0.5 mg/L) and NAA (5 mg/L) produced greatest results.

In 1982, a more thorough examination of Rodriquez’s using cotyledons grown on Cheng’s basal media at half-strength with various cytokinin and auxin concentrations was published. Although the cytokinins were not necessary for callusing or rooting, they did increase the proportion of rooted plants when paired with IBA or NAA at low doses (2 M). There is a lot of evidence connecting anthocyanin and globular foundation development to root differentiation.

The first investigation into the in vitro clonal propagation of Juglans was also published in 1981. Chalupa accomplished shoot multiplication in a modified Murashige Skoog (MS) medium using nodal explants from Juglans regia seedlings. Additionally, roots formed, and explants with roots were placed in a peat and perlite combination.

3.4.3 Pistachio Nut

Ramon Dolcet-Sanjuan and Elisabet Claveria (1995) reported that one week after culture on auxin-containing MSPV medium, a white callus was observed at the shoot base. To promote root elongation, a second transit on auxin-free MSPV for two weeks was sufficient. For the percentage of shoots that formed roots during incubation at 25°C, interaction type of auxin and conc. of auxin have significant effect. Ramon Dolcet-Sanjuan and Elisabet Claveria (1995) also claimed that NAA produced roots more successfully than IBA or IAA. No discernible differences were discovered between IBA or IAA, regardless of their concentration. With 31.6 M NAA, a substantial percentage of shoots (62%) developed roots, but only 15% of shoots cultured in MSPV with 31.6 M IBA or IAA did.

According to research by Tilka et al. (2008), the newest micro shoots per explant (5.64 ± 0.07) were discovered 4 weeks after growing on MS media supplemented with 1.0 mgl–1 BA. Once more, the shoot length rose to 1.0 mgl–1 BA and subsequently fell as the BA concentration rose. They found that IBA effective at encouraging root growth. Explants with a length of 4.0 cm showed the highest frequency of micro shoot roots (73%) four weeks after culture.

3.4.4 Chestnut

Mato and Vieitez (1986) examined the top and bottom portions of chestnut (Castanea sativa Mill.) shoots for auxin protectors and IAA oxidase activity that had undergone IBA pretreatment during in vitro cultivation. Auxin protectors are seen to be increased in the bottom sections of shoots and decreased in upper parts during rhizogenesis. Throughout the rooting stage, IAA oxidase activity likewise fluctuates, increasing in upper sections while decreasing in basal ones. The concentration of IAA would rise in the rooting zone of the shoots as a result of these metabolic processes. The basal portions of the shoots continue to have strong IAA oxidase activity while the higher areas continue to have low activity in untreated, non-rooted cuttings.

3.5 Conclusion

Temperate nuts are rich sources of nutrient’s particularly proteins, which makes them food of great importance. These crops significantly contribute local and national economies. Considering this of importance there is greater development of growth and development of temperate nuts using phytoharmones. The primary phytohormones contain conventional groups or other compounds. They include IBA, IAA, GA3, 2,4-D, NAA, BA, BAP, CEPA, and ABA. Each PGR has unique characteristics, transport methods, impacts, and effects. In many agricultural areas, PGRs can be valuable allies in the quest to boost yields while enhancing phyto-technical, phytosanitary, and commercial quality. These have been utilized in temperate nut crops to regulate bud break, flowering, latera bud development, delay blooming, reduce alternate bearing, shoot growth, tissue culture practices, and so forth. These showed positive effects on improving these phenomena in temperate nuts, which ultimately increasing production.

KEYWORDS

abscisic acid

cytokinins

gibberellic acid

phytohormones

plant growth regulators

tannin

temperate nut crops

tissue culture

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Chapter 4 Phytochemical Properties and Their Utilization in Temperate Nut Crops

GHOLAMREZA ABDI¹ and SAHAR ZAMANI²

¹Department of Biotechnology, Persian Gulf Research Institute, Persian Gulf University,Bushehr, Iran

²Department of Horticultural Sciences, Faculty of Agricultural Sciences, Guilan University,Rasht, Iran

*Corresponding author

ABSTRACT

Temperate nut crop contains a wide variety of phytochemicals, some of which are listed in nutrient databases, such as phytosterols, phenolic acids, carotenoids, and polyphenols (proanthocyanidins, flavonoids, and stilbenes), while many others such as alkylphenols, phytates, sphingolipids, and lignans are not. By nut type, genotype, pre-and post-harvest settings, as well as storage conditions, the phytochemical content of temperate nuts can vary greatly. Flavonoids, phenolic acids, stilbenes, and different phytosterols are influenced by genotype, but data on many additional phytochemical groups are missing. Phytochemicals such as flavanols, isoflavones, and flavanols were shown to be more heat-resistant than other chemicals like anthocyanins and trans-resveratrol after roasting. Methods and types of solvents have significantly affected their quantification. Temperate nuts contain phytochemicals that have been linked to antiviral, antiproliferative, antioxidant, anti-inflammatory, chemopreventive, and hypocholesterolemic effects. These actions are all known to have an impact on the beginning and development of a number of pathogenic processes. Nut phytochemicals are both bio-accessible and bioavailable for human use, however, there have only been a few intervention experiments done thus far. The goals of this chapter are to provide an overview of temperate nut phytochemicals and its utilization.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

4.1 Introduction

Nuts are considered to be highly nutritious foods and are commonly included in human diets (Alasalvar and Shahidi, 2008). Temperate nuts, hazelnut (Corylus avellana L.), pistachio (Pistacia vera L.), including almond (Prunus amygdalus Batsch, syn. Prunus dulcis), pecan (Carya illinoinensis), walnut (Juglans regia L.), and chestnut (Castanea sativa Mill), are commercially important. Temperate nuts are consumed for their delicious taste as well as their benefits (Taş and Gokmen, 2017). Nuts can be eaten as a snack or any meal as raw, roasted, or salted. Nuts and their oils, flours, and other edible products can also be found in many commercial products including chocolates, cookies, cakes, and ice creams (Preece and Aradhya, 2019). Temperate nuts are an excellent source of nutrition; unsaturated fatty acids, vitamins, protein, and minerals. They also contain various phytochemical compounds with numerous health benefits (Bodoira and Maestri, 2020). Phenolic acids, stilbenes, flavonoids, lignans, condensed tannins (proanthocyanidins), hydrolysable tannins, phytosterols, squalene, carotenoids, alkyl phenols, chlorophylls, phytates, and others are some of the most prominent phytochemicals found in temperate nuts (Alasalvar and Bolling, 2015; Bolling et al., 2011). Phytochemical compounds have been shown to possess significant biological activities such as antioxidant, anti-inflammatory, anti-carcinogenic, and antimutagenic effects, as well as cholesterol-lowering effects. Numerous studies have indicated that incorporating a daily serving of nuts (about 30- 40 g of mixed nuts) can potentially lower the risk of cardiovascular disease (CVD), high blood pressure, inflammation, type II diabetes, cancer, and neurodegenerative diseases (Grosso et al., 2015; Afshin et al., 2014). The beneficial effects of nuts on human physiology may be attributed to the synergistic interaction of their phytochemical compounds (Figure 4.1) (Chang et al., 2016; Oliver Chen and Blumberg, 2008).

Figure 4.1 Different phytochemicals in nuts. ⏎

4.2 Phytochemical Compounds of Temperate Nuts

4.2.1 Phenolic Compounds

Plant phenolic compounds, found in plants across various species, are a diverse group of secondary metabolites. They are characterized by hydroxyl groups attached to an aromatic hydrocarbon group. This group encompasses a wide range of compounds, including phenolic acids, flavonoids, tannins (both hydrolysable and condensed), stilbenes, lignans, and more. These phenolics play multiple ecological and physiological functions within plants, such as providing pigmentation, safeguarding against UV radiation, and acting as a defense mechanism against pests and pathogens (Rathod et al., 2023). Studies demonstrated that the consumption of phenolic compounds can offer health benefits by lowering the risk of chronic diseases such as cancer, diabetes, cardiovascular and neurodegenerative diseases. This is due to anti-oxidation, anti-inflammation, and detoxification properties (Rahman et al., 2022). Temperate nuts contain high levels of phenolic compounds; however, each nut has specific phenolic profile and content. For instance, chestnuts had a high concentration of phenolics including vanillic acid, catechin, naringin, quercetin, and ellagic acid (Liu et al., 2016), while almonds have high levels of quercetin, kaempferol, and isorhamnetin (Smeriglio et al., 2015). Based on reports, gallic acid, ellagic acid, resveratrol, and catechin are the most commonly discovered phenols in nuts (Alasalvar and Shahidi, 2008). Flavonoids such as epicatechin, quercetin, kaempferol, isorhamnetin, apigenin, naringenin and galangin were reported in nuts. Additionally, they contain aromatic acids for example syringic, caffeic, ferulic, coumaric and vanillic acids. Various experiments have documented the content of total phenolic compounds (TPCs) in different nuts. Walnuts have been identified as having the highest concentration of hydrolysable tannins, followed by hazelnuts and almonds. Furthermore, almonds, chestnuts, hazelnuts, and pistachios have been found to contain stilbenes, specifically resveratrol. Isoflavones, on the other hand, have only been reported in pistachios. Moreover, hazelnuts have been found to possess the highest overall quantity of proanthocyanidins (Alasalvar et al., 2020). Wojdyło et al. (2022) stated that the total phenolic content in nuts recorded about 5.9 mg/100 g (pistachios) to 432.9 mg/100 g (walnuts), with polymeric procyanidins were the dominant polyphenols. According to Kalogeropoulos et al. (2013), the TPC of nuts was recorded between 43–1513 mg GAE/100 g, and the highest and lowest TPC was observed in walnut and chestnut, respectively. Additionally, almonds, pistachio, and hazelnut had high TPS amounts. Kornsteiner et al. (2006) reported that the temperate nuts contained different amount of TPCs (32- 1650 mg GAE/100 g), and walnut, pecan, and pistachio have been found to have the highest values. Similarly, in another report, the total phenolic content of nuts varied significantly, ranging from 50–2499 mg/100 g FW, and walnuts> pecans, pistachios having the highest values followed by almonds, hazelnuts, and chestnuts (Abe et al., 2010). Similar to other crops, the quantity and quality of phenolic compounds in nuts are highly related to cultivar, environmental conditions, harvest time, fruit ripeness stage, extraction methods, processing (pasteurization, bleaching, and roasting), and post-harvest conditions (Chang et al., 2016; Taş and Gokmen, 2017; Wojdyło et al., 2022).

4.2.2 Phenolic ACIDS

Phenolic acids can be categorized into two structural types: hydroxybenzoic acid derivatives (C6–C1 structure) and hydroxycinnamic acid derivatives (C6–C3 structure). They are composed of an aromatic ring, at least one carboxylic group, and one or more hydroxyl or methoxyl groups (Rathod et al., 2023; Rahman et al., 2022). Examples of hydroxybenzoic acid derivatives include gallic acid, p-hydroxybenzoic acid, protocatechuic acid, vanillic acid, syringic acid, and salicylic acid. On the other hand, common hydroxycinnamic acid derivatives found in plants encompass p-coumaric acid, caffeic acid, ferulic acid, and sinapic acid. These natural compounds are renowned for their potent antioxidant and anti-inflammatory properties, contributing to a wide range of health benefits (Rathod et al., 2023; Rahman et al., 2022). Many phenolic acids are commonly found in temperate nuts; however, the phenolic profile of each nut varies depending on several factors including location, variety, and processing conditions (Bodoira and Maestri, 2020). Walnuts and pecans are particularly rich in gallic acid and its derivatives (Jan et al., 2022; Slatnar et al., 2015).

Walnuts were found to contain not only gallic and ellagic acids but also other phenolic acids like ferulic, caffeic, and cinnamic acids (Wozniak et al., 2022). Additionally, the skin of walnuts was found to have protocatechuic, chlorogenic, trans-p-coumaric, vanillic, and 5-hydroxybenzoic acids (Monagas et al., 2007). Pecans were identified to predominantly contain gallic, ellagic, protocatechuic, chlorogenic, p-hydroxybenzoic, and caffeic acids (Flores-Córdova et al., 2017; Taş and Gokmen, 2017). Pistachios were found to have phenolic acids like syringic acid, ferulic acid, and coumaric acid (Gültekin-Ozgüven et al., 2015; Gonçalves et al., 2023). Almonds showed high levels of protocatechuic acid, vanillic acid, and p-hydroxybenzoic acid as hydroxybenzoic acid derivatives, and chlorogenic acid as the primary hydroxycinnamic acid derivative (Bolling, 2017). Furthermore, almond kernels were reported to contain mainly ferulic and protocatechuic acids among the phenolic acids, along with caffeic acid, p-coumaric acid, and gallic acid (Gültekin-Özgüven et al., 2015; Smeriglio et al., 2015). Chestnuts exhibited gallic acid, vanillic acid, syringic acid, and ellagic acid as the most predominant phenolic acids (Gonçalves et al., 2023; Chang et al., 2020; Mustafa et al., 2021; Otles and Seleck, 2012). Gallic, ellagic, vanillic, ferulic, protocatechuic, and p-hydroxybenzoic acids were detected in raw chestnuts (Mustafa et al., 2021). Chestnuts in various regions of Turkey were found to contain gallic, ellagic, vanillic, p-coumaric, chlorogenic, syringic, caffeic, and ferulic acid (Otles and Seleck, 2012). Gallic and ellagic acids are considered the primary phenolic compounds in chestnuts. Hazelnuts are plentiful source of phenolic acids, including hydroxybenzoic acid derivatives such as gallic, protocatechuic, p-hydroxybenzoic, vanillic, and syringic acids, as well as cinnamic acid derivatives like caffeic acid, p-coumaric acid, ferulic acid, and sinapic acid. These compounds can exist in both free and esterified forms (Gonçalves et al., 2023; Wozniak et al., 2022; Aktaş et al., 2016; Shahidi et al., 2007). Among the detected phenolic acids, protocatechuic and gallic acids were found to be the most abundant, followed by p-coumaric and ferulic acids (Gültekin-Ozgüven et al., 2015). Additionally, according to Contini et al. (2008), hazelnut kernels had high amounts of p-coumaric acid, with an average content of 2.5 μg/g, while gallic acid is the most dominant in the skin and hard shell, with 39.1 and 81.0 μg/g, respectively.

Gallic acids have several positive health effects, including antioxidant and anti-inflammatory properties. It can also exhibit other beneficial activities like antimicrobial, gastro-protective, neuro-protective, cardioprotective, anticancer, antidiabetic, and anti-inflammatory effects. (Ruwizhi and Aderibigbe, 2020). Gallic aciD's antioxidant properties have been shown to have a hepatoprotective effect. According to research conducted by Vu et al. (2020), gallic acid has been found to possess hepatoprotective properties and can help mitigate liver damage caused by fluoxetine. This effect is attributed to its ability to scavenge free radicals and its anti-inflammatory effect related to TNF-α. Furthermore, various phenolic acids present in nuts exhibit biological activities such as neuroprotective effects, including caffeic, ferulic, sinapic, coumaric, and syringic acids. These phenolic acids also display antioxidant properties, such as caffeic, cinnamic, sinapic, ferulic, and vanillic acids. Additionally, cinnamic acid demonstrates antitumor activity, syringic acid exhibits hepatoprotective effects, and caffeic and coumaric acids demonstrate antiviral activity (Wozniak et al., 2022).

4.2.3 Flavonoids

Flavonoids are a diverse group of polyphenolic compounds and phenylpropanoid derivatives that are widely distributed in the plant kingdom (Revutska et al., 2021). They possess a characteristic C6–C3–C6 structure consisting of two aromatic rings (A and B rings) linked together by a heterocyclic ring (C). Flavonoids encompass various classes, including flavones, flavanols, flavanones, anthocyanidins, and isoflavones (Dias et al., 2021). Scientific studies have indicated that a diet rich in flavonoids is associated with a reduced risk of several chronic diseases. Flavonoids exert their health benefits through multiple mechanisms, including antioxidation, anti-inflammation, anti-proliferation, and modulation of signal transduction pathways (Oliver Chen and Blumberg, 2008). Furthermore, flavonoids have been reported to potentially provide therapeutic benefits for conditions such as chronic venous insufficiency, dermatopathy, diabetes, gastrointestinal diseases, rhinitis, lymphocytic leukemia, menopausal symptoms, traumatic cerebral infarction, and others (Kumar et al., 2023).

Bolling et al. (2011) observed that the temperate nuts had total flavonoid nuts about 0.5 mg/100 g in walnuts to 2700 mg/100 g in pecans. Alasavar and Bolling (2015) reported that pecan, walnut, hazelnut, and pistachio contained high flavonoid content. Nuts contain flavanols (flavan-3-ols), flavanols, and anthocyanins as their main flavonoids, while smaller amounts of flavanones and isoflavones can also be reported. Pecans have the highest flavonoid content (34 mg/100 g) among temperate nuts, mainly comprising flavanols and anthocyanins. Catechin and epicatechin and their gallic acid esters are abundant in some temperate nuts such as pistachio, hazelnut, and walnut (Bodoira and Maestri, 2020). Epicatechin is a prominent plant phenol with notable biological activities such as antioxidant, antitumor, anti-inflammatory and anti-diabetic effects. Additionally, beneficial effects of epicatechin have been reported to include enhancing muscle performance and improving cardiac function, as well as protecting the cardiovascular system and supporting the nervous system. (Qu et al., 2020). Catechin is present at high levels in nuts that provide pharmacological properties such as anti-inflammatory, antioxidant, hepatoprotective, antihypertensive, anti-coagulant, anti-arthritis, neuroprotective, antidiabetic, and memoryenhancing properties (Baranwal et al., 2021). Catechin has been studied for its potential in combating certain cancers. Findings suggest that catechin and its derivatives may work together with anti-cancer agents to significantly improve the suppression of cancer cell growth and apoptosis in breast, lung, colorectal, and prostate cancers (Vu et al., 2020). The skins of almonds, hazelnuts, and pistachios are rich in flavanols such as catechin and epicatechin. According to Ozdemir et al. (2014), natural hazelnuts contain flavanols catechin, epicatechin gallate, and epicatechin.

Various flavanols, such as hyperoside, quercetin, kaempferol-3-glucoside, quercitrin, isoquercitrin, isorhamnetin, rutin, myricetin, and kaempferol have been detected in seeds and shells of chestnut (Beccaro et al., 2020; Mustafa et al., 2021; Alasavar and Bolling, 2015). Hyperoside was found to be the major flavanol at a concentration of 2.91 mg/kg, while isorhamnetin was the minor one with a concentration of 0.07 mg/kg in raw seed samples. Additionally, phloridzin, a dihydrochalcone, was found to be more abundant in chestnut shells compared to the seeds (Mustafa et al., 2021). Among temperate nuts, pecans had the highest concentration of flavonoids at 1.169 μg/g fresh weight, while pistachios had the lowest amount (0.007 μg/g fresh weight) (Wozniak et al., 2022). Flavanols are the major flavonoids are present in almond, hazelnut, and pistachio skins. The skins of these nuts commonly contain Quercetin-3-O-rutinoside, which is a type of flavanol (Taş and Gokmen, 2017). Almonds are particularly rich in flavanols, including quercetin, kaempferol, isorhamnetin, their glycosylated derivatives (galactoside, rutinoside, and glucoside), and the flavanone naringenin (as aglycone and glucoside derivative) (Karimi et al., 2020; Bolling et al., 2010). Kaempferol-3-O-rutinoside, kaempferol, and kaempferol-3-O-glucoside are the most abundant flavanols found in almond skins. Kaempferol-3-O-glucoside has only been reported in almonds, whereas quercetin-3-O-rutinoside, quercetin-3-O-galactoside, and quercetin-3-O-glucoside have been reported in both almonds and pistachios (Smeriglio et al., 2015; Grace et al., 2016). Myricetin-3-O-glucoside was only detected in pistachio skins (Grace et al., 2016). Hazelnut skins also contain monomeric and oligomeric flavanols, and dihydrochalcones (Del Rio et al., 2011). Quercetin glycosides such as quercetin-3-O-galactoside, quercetin-3-O-arabinoside, quercetin-3-pentoside, and quercetin-3-O-rhamnoside have been detected in black walnut extracts which shown anti-inflammatory and wound-healing properties (Vu et al., 2020). According to Wozniak et al. (2022), insignificant amount of apigenin and pinostrobin (flavanones) were present in most of the nut samples studied, and pecan nuts had a higher concentration of these compounds compared to other nuts. Flavanones including eriodictyol, eriodictyol-7-O-glucoside, naringenin, and naringenin-7-O-glucoside, have been identified in almonds and pistachios, with eriodictyol-7-O-glucoside being the common flavanone found in their skin. Naringenin-7-O-neohesperidoside has only been detected in pistachios (Chang et al., 2016). The main flavanones present in whole almonds are naringenin and naringenin-7-O-glucoside. On the other hand, eridicytol-7-O-glucoside is predominantly found in almond skin and blanched water (Karimi et al., 2020). Naringenin can protect vulnerable neurons and improve the function of neuronal structures. It is believed that naringenin’s interactions with cellular signaling pathways are responsible for these benefits in the brain which led to enhanced antioxidant defense, prevention of neurotoxin-induced apoptosis, and stimulation of neuronal survival (Vu et al., 2020). Nuts contain relatively low levels of isoflavones, but pistachios contain genistein and daidzein as both aglycone and glycosylated derivative forms (Ballistreri et al., 2009). According to Bolling et al. (2010), the isoflavone content in pistachios is 3.63 mg/100 g, which is significantly higher compared to other nuts. Additionally, genistein, daidzein, glycitein, and formononetin are the isoflavones found in almond (Karimi et al., 2020). Anthocyanins with various concentrations were identified in different types of nuts. Anthocyanins such as procyanidin B2, and procyanidin A2 were detected in chestnuts (Mustafa et al., 2021). According to reports, pecans contain the highest levels of cyanidin and delphinidin. Glycosylated anthocyanidins such as cyanidin-3-O-galactoside and cyanidin-3-O-glucoside are mostly present in pistachios (Ballistreri et al., 2009). Interestingly, the skin of pistachios contains luteolin as a flavone along with anthocyanins such as cyanidin-3-O-glucoside, and eriodictyol-7-O-glucoside (Grace et al., 2016).

4.2.4 Tannins

Tannins are polyphenolic compounds that contain enough hydroxyl and other functional groups, like carboxyls, to create strong complexes with different macromolecules (Das et al., 2020). These compounds have high molecular weights and can be found widely distributed in many plant species. Tannin’s main function in plants is to act as a defensive agent, protecting them from fungi, insects, pathogens, and herbivorous (Smeriglio et al., 2017). Tannins can be classified into two main groups: hydrolysable tannins and condensed tannins, also known as proanthocyanidins. Hydrolysable tannins are composed of glucose or other polyhydric alcohols esterified with gallic acid (gallotannins) or hexahydroxydiphenic acid (ellagitannins) (Kemppainen et al., 2014). Based on the type of esterification, hydrolysable tannins are further categorized as gallotannins or ellagitannins. Gallotannins consist of a central molecule, such as glucose, surrounded by multiple gallic acid units. In contrast, ellagitannins contain hexahydroxydiphenic acid or its dilactone form, known as ellagic acid (Das et al., 2020; Kemppainen et al., 2014). Numerous studies have indicated that ellagic acid is one of the most abundant compounds found in temperate nuts (Gonçalves et al., 2023; Wozniak et al., 2022; Taş and Gokmen, 2017).

Ellagic acid is considered for its various advantageous characteristics. It exhibits strong antioxidant activity and has been shown to have antiinflammatory and antidiabetic effects. Furthermore, it may provide hepatoprotection, neuroprotection, and protection against cancer and cardiovascular disease (Vu et al., 2020). Condensed tannins, also known as proanthocyanidins, are oligomers of flavan-3-ols that are linked together through carboncarbon bonds. Proanthocyanidins can be classified into two types including Type-A and B. Type-A proanthocyanidins are characterized by both a C4 to C6 or C8 interflavan bond and a C2-ether bond to the flavanol extension, while Type-B proanthocyanidins have a single C4 to C6 or C8 interflavan bond. Temperate nuts contain mostly (+)-catechin and (-)-epicatechin as their proanthocyanidins, although they also contain afzelechin (almonds) and epigallocatechin (hazelnuts, pecans, and pistachios). Most proanthocyanidins in nuts are highly polymerized, typically consisting of more than 10 monomeric units (Bolling et al., 2011; Oliver Chen and Blumberg, 2008). Proanthocyanidins can be categorized into different subgroups based on their hydroxylation pattern, such as procyanidins and prodelphinidins (Kemppainen et al., 2014). Both hydrolysable and condensed tannins were found in some temperate nuts (Bodoira and Maestri, 2020; Alasalvar and Bolling, 2015). Hydrolysable tannins are found in most nuts, but almonds, pecans, and walnuts have been found to contain the highest amounts(Shahidi et al., 2007). According to Pelvan et al. (2018), Turkish hazelnut samples were found to contain five hydrolysable tannins and related compounds, including flavogallonic acid dilactone, mevalonic acid dilactone, sanguisorbic acid dilactone, bis (hexahydroxydiphenoyl)-glucose (HHDP-glucose), ellagic acid, and derivatives. Bolling (2017) reported that hydrolysable tannins, including gallotannins, ellagitannins, and phlorotannins, ranged from 0.73–0.91 mg/g in almond kernels. Walnuts are known for their high concentration of hydrolysable tannins and related compounds, such as ellagic acid and its derivatives, as well as galloyl and digalloyl hexosides. Moreover, walnuts contain esters of ellagic acid with polyols like pentoside, hexoside, and rhamnoside (Labuckas et al., 2016). Hydrolysable tannins, including glansreginins A and B, as well as glansrins A-D, have been identified in walnuts (Regueiro et al., 2014). Slatnar et al. (2015) discovered several new hydrolysable tannins in walnuts, such as B-type dimer gallate, vescalagin isomers, di-hexahydroxydiphenoyl glucose isomers, galloyl bis HHDP glucose, HHDP digalloyl glucose isomers, and digalloylglucose. Pecans also contain ellagic acid and its derivatives, including methyl, galloyl, pentosyl, hexosyl, glucosyl, and bis-hexahydroxydiphenoyl groups (Jia et al., 2018).

Proanthocyanidins are the predominant polyphenols in many types of nuts for example almonds, hazelnuts, pecans, and pistachios (Alasalvar and Bolling, 2015). According to Gu et al. (2004), temperate nuts including hazelnuts, pecans, pistachios, almonds, and walnuts had proanthocyanidins at 501, 494, 237, 184, and 67mg/100 g, respectively. It has been found that hazelnuts and pecans have the maximum concentrations of proanthocyanidins with 501 and 494mg/100 g, respectively (Monagas et al., 2007). These compounds are also present in other nuts such as almonds, pistachios, and walnuts, with varying content ranging from 9–494 mg/100 (Oliver Chen and Blumberg, 2008). Hazelnuts contain high levels of procyanidin dimers, trimmers, and tetramers (Slatnar et al., 2014). Although B-type proanthocyanidins are most common in nuts, A-type proanthocyanidins have been identified in almond and hazelnut (Monagas et al., 2009). According to reports, proanthocyanidins in pecans are mainly composed of A- and B-type dimers, but monomers, trimers, tetramers, pentamers, and hexamers also had identified (Robbins et al., 2015Proanthocyanidins, which are a type of polyphenol, are found in abundance in almond. The most prevalent types of proanthocyanidins in almonds are (−)-epicatechin and (+)-catechin, with lower amounts of (−)-epiafzelechin. The interflavan bonding in almond proanthocyanidins is mainly B-type, although A-type bonding is also observed. In addition to proanthocyanidin polymers, researchers have identified B-type dimers (such as procyanidin B1, B2, B3, B5, and B7), A-type dimers, B-type oligomers, and mixed B-/A-type oligomers in almonds (Pérez-Jiménez and Torres, 2012).

Tannins are known to possess various pharmacological properties, such as acting as antioxidants and free radical scavengers, exhibiting antimicrobial, anti-cancer, anti-inflammatory, cardiovascular, and neurological protective activities (Rauf et al., 2019). Additionally, tannins have been found to have positive impacts on metabolic disorders and can inhibit the development of various diseases related to oxidative stress (Das et al., 2020; Smeriglio et al., 2017). Elagitannins and their metabolites such as ellagic acid and urolithins have been widely researched for their potential anti-cancer properties. Based on in vitro and in vivo studies, these compounds are capable of inducing a dose-dependent inhibition of colon, breast, and prostate cancer cell growth (Bodoira and Maestri, 2020). Research indicates that increased consumption of proanthocyanidins is related to a decreased risk of various metabolic disorders, such as metabolic syndrome, non-alcoholic fatty liver disease (NAFLD), type 2 diabetes mellitus, and non-alcoholic steatohepatitis (NASH), as well as complications associated with diabetes such as nephropathy and neuropathy (Márquez Campos et al., 2020). Furthermore, research has shown that proanthocyanidins can modulate glucose and lipid-lowering effects in the body by affecting digestive processes through their ability to bind digestive enzymes and dietary proteins (Mannino et al., 2021).

4.2.5 Stilbenes

Stilbenes are a class of polyphenolic compounds that are synthesized by plants via the shikimate and phenylalanine/poly malonate pathways (Xie and Bolling, 2014). These compounds are identified by C6–C2–C6 structure, which consists of an ethylene moiety situated between two benzene rings (Nagumo et al., 2019). Stilbenes act as phytoalexins and help to protect plants from pathogens, bacterial and fungal growth, and the damaging effects of UV light. Additionally, stilbenes have many benefits such as anti-inflammatory, antioxidant, and anticancer properties (Al-Khayri et al., 2023). Stilbenes compound such as resveratrol can be detected in several plant-based foods, including almonds, chestnuts, hazelnuts, and pistachios (Chang et al., 2016). Trans-resveratrol-3-O-glucoside as a derivative of resveratrol and has been identified in almonds (Rimando et al., 2005). Grippi et al. (2008) found that pistachios contain two stilbenes including trans-resveratrol (0.07–0.18 mg/ kg) and trans-resveratrol-3-O-β-glucoside (trans-piceid) (6.20–8.15 mg/kg). The total concentration of resveratrol found in the pistachios ranged from 6.38–8.27 mg/kg. Additionally, trans-resveratrol has been recorded ranging from 1.7mg/100 g DM in unripe kernels to 1.2mg/100 g DM in ripe kernels (Ballistreri et al., 2009). Resveratrol (3, 4′, 5-trans-trihydroxy-stilbene) and piceatannol (3,3′, 4′, 5-trans-tetrahydroxy-stilbene) are the most wellknown stilbenes that are known for its antioxidant, anti-inflammatory, and anti-cancer properties. These stilbenes compounds have beneficial effects on various disease types, such as neurological disorders, cardiovascular disease, and cancer (Park et al., 2021; Bolling et al., 2010; Rimando et al., 2005). Research suggests that resveratrol may protect against atherosclerosis, have antiproliferative and proapoptotic effects on breast, colon, prostate, and leukemia cells, and inhibit LDL oxidative susceptibility and platelet aggregation (Azadmard-Damirchi et al., 2011). According to a report, piceatannol is a superior anti-adipogenic compound compared to resveratrol in the VASCs model of visceral obesity. The additional hydroxyl group in piceatannol’s structure gives it a higher radical scavenging capacity than resveratrol, which allows it to effectively scavenge reactive oxygen species (ROS) (Park et al., 2021). According to Xie and Bolling (2014), almond stilbenes were identified in almond meat, skin, and water. Piceatannol+ oxyresveratrol were detected in almond water while polydatin (resveratrol-3-O-glucoside) was identified in almond skin (7.19–8.52 μg/100 g of almond). Stilbenes exhibit synergistic bioactivities when combined with other polyphenols. For instance, resveratrol acted synergistically with ellagic acid and quercetin in eliciting caspase-3 activity in cultured human leukemia cells (MertensTalcott and Percival, 2005). Similarly, it was also observed that resveratrol acted synergistically with epigallocatechin gallate and c-tocotrienol in induction quinone reductase activity in cultured MCF-7 breast cancer cells (Table 4.1) (Hsieh and Wu, 2008).

Table 4.1 Main Phytochemicals Present in the Temperate Nuts⏎

Nuts
Main Phytochemical Compounds
References

Almond
Gallic acid, cis-p-coumaric acid, hydroxybenzoic acid, protocatechuic acid, trans-p-coumaric acid, chlorogenic acid,(+)-catechin, naringenin, kaempferol-3-O-glucoside, isorhamnetin-3-O-rutinoside, isorhamnetin-3-O-glucoside, ß carotene
Oliveira et al., 2019

Proanthocyanidins (dimers or larger), gallotannins, ellagitannins, phlorotannins, flavonoids (non-isoflavone), protocatechuic acid, vanillic acid, p-hydroxybenzoic acid, chlorogenic acid, isoflavones, stilbenes, Lariciresinol)
Bolling, 2017

protocatechuic acid, ferulic acid, kaempferol-3-O-rutinoside, kaempferol, naringenin, kaempferol-3-O-glucoside, eriodictyol-7-O-glucoside
Smeriglio et al., 2015

Protocatechuic acid, o-coumaric acid, ferulic acid, gallic acid, caffeic acid, p-coumaric acid, catechin, epicatechin, kaempferol
Gültekin-Ozgüven et al., 2015

Stilbenes such as polydatin (resveratrol-3-β-glucoside), piceatannol, oxyresveratrol, pterostilbene
Xie and Bolling, 2014

Proanthocyanidin polymers, B-type (procyanidin B1, B2, B3, B5, B7) and A-type dimers, B-type oligomers, and mixed B/A-type oligomers
Pérez-Jiménez and Torres, 2012

Chestnut
Gallic acid, p-hydroxybenzoic acid, protocatechuic acid, syringic acid, caffeic acid, p-coumaric acid, ferulic acid, cinnamic acid, chlorogenic acid, catechins ((+)-catechin, (−)-epicatechin, naringin, rutin, myricetin, quercetin, isorhamnetin, apigenin, pinocembrin, t-resveratrol
Ciucure et al., 2022

Gallic acid, ellagic acid, vanillic acid, ferulic acid, protocatechuic acid, p-hydroxybenzoic acids, p-coumaric acid, (+)-catechin, (−)-epicatechin, hyperoside, quercetin, kaempferol-3-glucoside, isorhamnetin, kaempferol phloridzin, phloretin, procyanidin A2, procyanidin B2
Mustafa et al., 2021

Chlorogenic acid, gallic acid, 7-hydroxycoumarin, quercetin, and quercetin-3-rhamnoside
Chang et al., 2020

Ellagic acid, caffeic acid derivative, catechin, epicatechin, apigenin-7-O- rutinoside, epigallocatechin, procyanidin polymers, trimeric proanthocyanidins, luteolin-7-O- rutinoside, tetrameric proanthocyanidins
Lameirao et al., 2020

Lignans (secoisolariciresinol, lariciresinol, isolariciresinol, pinoresinol, matairesinol
Durazzo et al., 2018

Hazelnut
ß-sitosterol, catechin, stigmasterol, gallic acid, protocatechuic acid, quercitrin, hyperoside, vanillic acid, campesterol, Isoquercitrin, syringic acid, p-coumaric acid, ferulic acid, epicatechin
Rusu et al., 2019

Catechin, epicatechin gallate, and gallic acid, protocatechuic acid, quercetin, quercitin
Yuan et al., 2018

Gallic acid, proto-catechuic acid, catechin, rutin, o-coumaric acid, p-coumaric acid, epicatechin, ferulic acid, caffeic acid
Gültekin-Ozgüven et al., 2015

Flavanols, quercetin-3-O-rhamnoside, myricetin-3-O-rhamnoside, hydroxybenzoic acids,epicatechin-3-gallate, procyanidin (dimer, trimer, tetramer), (+)-catechin, (−)-epicatechin, phloretin-2-O-glucoside, p-coumaric acid hexoside, quinic acid, dihydrochalcones, hexose ester of syringic acid, glansreginin A, glansreginin B
Slatnar et al., 2014

Pecan
Epicatechin, cinnamic acid, sinapic acid, syringic acid, pinostrobin, galangin, caffeic acid, myricetin, vanillic acid
Wozniak et al., 2022

Ellagic acid, gallic acid derivatives including methyl, galloyl, pentosyl, Hexosyl, glucosyl, and bis-hexahydroxydiphenoyl groups, ellagitannins, (+)-catechin, (−)-epicatechin, procyanidin dimer B-type
Jia et al., 2018

Ellagic acid, ellagic acids derivatives, gallic acid derivative, protocatechuic acid, (+)-catechin, proanthocyanidins A- and B-type dimers, monomers, trimers, tetramers, pentamers, hexamers
Robbins et al., 2015

Ellagic acid, catechin, gallic acid, hydroxybenzoic acid, trans-cinnamic acid, syringic acid, caffeic acid, p-coumaric acid, ferulic acid, naringenin, apigenin, quercetin, rutin, kaempferol, isorhamnetin, resveratrol
Abe et al., 2010

Pistachio
Gallic acid, monogalloyl glucoside, monogalloyl quinic acid, penta-O-galloyl-β-d-glucose, hexagalloyl hexose, quercetin 3-O-galactoside, quercetin 3-O-glucoside, quercetin 3-O-glucuronide, anacardic acid
Ersa̧n et al., 2016

Gallic acid, protocatechuic acid, catechin, epicatechin gallate, (epi)catechin hexoside, luteolin, quercetin, quercetin-O-hexoside, quercetin-3-O-galactoside, quercetin-3-O-glucoside, quercetin-3-O-rutinoside, procyanidin B1, procyandin trimer and tetramer, procyanidin B gallate, cyanidin 3-O-galactoside, cyanidin 3-O-glucooside, eriodictyol-7-O-glucoside
Grace et al., 2016

Syringic acid, gallic acid, protocatechuic acid, catechin, epicatechin, rutin, o-coumaric acid, p-coumaric acid, ferulic acid, caffeic acid
Gültekin-Ozgüven et al., 2015

Daidzein, genistein, daidzin, quercetin, eriodictyol, luteolin, genistin and naringenin, cyanidin 3-O-galactoside, cyanidin 3-O-glucooside, trans-resveratrol
Ballistreri et al., 2009

β-sitosterol, stigmasterol, campesterol,clerosterol, sitostanol, Δ5, 24-stigmastadienol, Δ7-stigmastenol, Δ7-avenasterol, poriferasta-7, 25-dienol
Miraliakbari and Shahidi, 2007

Walnut
Chlorogenic acid, caffeoylquinic acid, ferulic acid, p-coumaric acid, p-hydroxybenzoic, syringic acid, vanillic acid, catechin, epicatechin gallate, naringin, quercetin-3-b-D-glucoside, quercetin-3-O-rutinoside, quercetin-3-O-arabinoside, quercetin-3-O-galactoside, quercetin-3-pentoside, quercetin-3-O- rhamnoside, 1,3,6-trigalloylglucose penta-O-galloyl-b-D-glucose, ellagic acid, Glansreginin A b-Sitosterol
Vu et al., 2020

Ellagic acid, galloyl-hexoside, digalloyl-hexoside, gallic acid, glansreginin A, glansreginin B, catechin, ellagic acid pentoside, procyanidin dimer
Labuckas et al., 2016

Ellagic acid, ellagic acid pentoside, hydroxybenzoic acids, procyanidin (dimer, trimer and tetramer), glansreginin A, glansreginin B, catechin hydroxycinnamic acids, 3-O-caffeoylquinic acid, B-type dimer gallate, vescalagin isomers, di-hexahydroxydiphenoyl (Di-HHDP) glucose isomers, galloyl bis HHDP glucose, HHDP digalloyl glucose isomers, and digalloylglucose
Slatnar et al., 2015

4.3 Other Phytochemical Compounds

4.3.1 Lignans

Lignans are a class of diphenolic compounds that result from the combination of two phenylpropanoid C6–C3 units at the β and β’ carbon positions, and they can form additional bonds such as ether, lactone, or carbon linkages (Rodríguez-García et al., 2019). Lignans display a diverse array of structures and possess a wide range of biological activities, with commonly occurring compounds including secoisolariciresinol, lariciresinol, matairesinol, pinoresinol, medioresinol, and syringaresinol (Durazzo et al., 2018). Lignans offer various beneficial properties, such as anti-estrogenic, anti-inflammatory, antioxidant, antitumor, and anticarcinogenic activities. Current evidence suggests that lignans have the potential to promote health in humans, and the consumption of lignan-rich foods may prove advantageous in preventing chronic diseases, including certain types of cancer and cardiovascular conditions (Rodríguez-García et al., 2019).

Lignans are present as negligible constituents in various temperate nuts. Matairesinol, lariciresinol, pinoresinol, and secoisolariciresinol are frequently found in nuts. Bolling (2017) reported that almonds contain a higher amount of lariciresinol, with reaching up to 2.4 μg/g. According to studies, walnuts, hazelnuts, and pecans, all contain varying amounts of lignans. For example, a study by Kuhnle et al. (2008) found that walnuts had one of the highest lignan contents among nuts, with levels ranging from 0.18–1.08 mg/100 g. Hazelnuts and pecans were also found to contain lignans, although at lower levels than walnuts. Also, lignans are a small class of polyphenols in almonds. The amount of lignans in nuts can vary based on several factors such as the variety, growing conditions, and processing methods. For example, roasting nuts led to a decrease in their lignan content (Adlercreutz, 2007). Pecans have been found to contain secoisolariciresinol and matairesinol, with levels ranging from 0.1–3.4 mg/100 g and from 0.1–1.2 mg/100 g, respectively (Kornsteiner et al., 2006). Chestnuts have also been found to contain various lignan compounds, including isolariciresinol, lariciresinol, secoisolariciresinol, and pinoresinol, with total lignan content recorded at 980.03 μg/100g DW (Durazzo et al., 2013).

4.3.2 Alkylphenols

Alkylphenols are a group of organic compounds formed through the alkylation of phenols. These phenolic compounds have been detected in certain plants belonging to the Anacardiaceae family, including cashew nuts (Anacardium occidentale L.). Cardanols as alkylphenols compounds, demonstrate antioxidant activity by preventing xanthine oxidase activity and superoxide anion formation (Trevisan et al., 2006). According to Saitta et al. (2009), 16 different 3-alkylphenols (cardanols = 44 mg/100 g) were detected in pistachio kernels. Among them, monounsaturated pentadecenyl cardanols were found to be the most abundant.

4.3.3 Naphthoquinones

Naphthoquinones are phenolic compounds belonging to the quinones group. Naphthoquinones are significant interest due to their remarkable chemical reactivity and allelopathic effects. Juglone (5-hydroxy-1,4-naphthoquinone) is a naphthoquinone compound that uses in the field of medicine because of its antibacterial, antiviral, antifungal, and anticancer potential (Medic et al., 2022). Okatan et al. (2022) stated that 18 different walnut cultivars had trace amounts of juglone detected in the range of 6.2–11.1 mg/kg. Variations in juglone contents of walnut across different tissues during different seasons were recorded at 1–16 and 0.5–9.5 mg/g dry weight for Rubina and Franquette cultivars, respectively (Medic et al., 2022). According to Colaric et al. (2005), in 10 cultivars of walnut, significant amounts of juglone were found in 10 cultivars of walnut, with levels ranging from 6.93–19.16 mg/100 g of kernel and 190.47 − 279.04 mg/100 g of pellicle).

4.3.4 Phytates

Plant-derived foods such as legumes, cereals, and nuts are abundant sources of phytate/phytic acid, which act as a storage form of phosphorus (Kumar et al., 2010). In almonds and hazelnut, phytates consist of different inositol phosphates including inositol phosphate-1 to inositol phosphate-6 (Liu et al., 2009). The phytate contents of nuts are ranging from 150–290 mg/100 g. Among temperate nuts, almond had the highest phytate content, followed by pistachio, hazelnut, walnut, and pecan (Venkatachalam and Sathe, 2006). The phytic acid amount in nuts reported about 0.1–9% (dw), with almonds, walnuts, and pecans having the highest phytate content (Schlemmer et al., 2009). According to Harland et al. (2004), the oil of roasted blanched almonds (2.111%), pistachio nuts (2.835%), shelled dried hazelnuts (2.340%), pecans (1.907%), shelled dried black walnuts (4.029%), and shelled dried English walnuts (1.385%) exhibited significantly higher phytate contents. Recent scientific studies indicate that phytates offer several beneficial effects, including the prevention of kidney stone formation, reduced incidence of diabetes, lowered risk of coronary heart disease (CHD) by decreasing serum cholesterol and triglyceride levels, as well as protection against certain types of cancers (Nissar et al., 2017).

4.3.5 Squalene

Squalene (C30H50) is a polyunsaturated hydrocarbon that serves as a precursor to all steroids in both plants and animals. It has several beneficial properties, including reducing the risk of different cancers and lowering total cholesterol, LDL, and triglyceride levels. These protective effects can be due to its antioxidant activities. Additionally, squalene is used as a component of skin-care products. Based on studies, squalene is effective in inhibiting chemically induced tumorigenesis in rodents, particularly in the skin, colon, and lungs (Huang et al., 2009). Squalene has been identified in six nut samples and among three temperate nuts; hazelnut had the highest squalene content (257.6 μg/g of oil). Pecans and pistachios also contain squalene at 208.2 and 82.1 µg/g of oil, respectively (Derewiaka et al., 2014). Maguire et al. (2004) reported that the oil of hazelnuts, almonds, and walnuts had 186.4, 95, and 9.4 μg/g squalene content. Furthermore, Ryan et al. (2006) reported the squalene contents of pecan and pistachio were 151.7 and 91.4 mg/g, respectively.

4.3.6 Carotenoids

Carotenoids are important pigments belonging terpenoid class (tetraterpene) that have antioxidant properties and have been correlated with a reduced risk of CVD and various types of cancer (Terzo et al., 2017). The pistachio had significant xanthophyll carotenoid content (lutein and zeaxanthin) among nuts and the predominant carotenoid in pistachios is lutein, which provides yellow color (Pumilia et al., 2014). An analysis of the pigments in pistachio nut samples detected lutein, β-carotene, chlorophyll a, and chlorophyll b. In addition, neoxanthin and its ester, luteoxanthin, violaxanthin, and some chlorophylls such as pheophytins a and b, as well as the chlorophylls a’ and b’ were identified in pistachio nuts (Giuffrida et al., 2006). Based on Kornsteiner et al. (2006), only traces of β-carotene and lutein (<5 mg/100 g oil) were recorded in pistachios compared to almond, hazelnut, and walnut oils which did not contain any lutein. However, it has been reported lutein was the main carotenoid detected in pecan kernel and pistachio (Bouali et al., 2022; Bellomo and Fallico, 2007). Furthermore, Bouali et al. reported that the total xanthophyll content in two pecan cultivars was significantly higher (0.22–0.23 mg/kg of oil) than that of the Burkett cultivar previously studied (0.14 mg/kg of oil) (Bouali et al., 2013). They also found that the concentration of lutein was higher in pecan kernels than in pistachio kernels. The levels of pigments such as chlorophyll a, b, lutein, and β-carotene in raw pistachio nuts were found to be 25.2, 14.1, 28.8, and 4.6 mg/kg, respectively (Dini et al., 2019). It is worth noting that the concentrations of these pigments can vary based on several factors such as geographic origin, degree of ripeness, storage conditions, and processing methods.

4.3.7 Phytosterols

Phytosterols are a group of fat-soluble compounds that belong to the triterpene family and are exclusively found in plants. They have a similar structure to cholesterol, but their side chain differs from that of cholesterol. Phytosterols are characterized by a steroid skeleton with a hydroxyl group attached to the C3 atom of the A-ring and an aliphatic side chain attached to the C17 atom of the D-ring (Poli et al., 2021; Moreau et al., 2018). There are over 200 different types of phytosterols identified in various plant species, with β-sitosterol, campesterol, stigmasterol, brassicasterol, and avenasterol being the main ones. Phytosterols can exist in their free form or as esters bound to fatty acids, steryl glycosides, or acylated glycosides (Poli et al., 2021; Vecka et al., 2019). Due to their structural similarity to cholesterol, phytosterols effectively inhibit the absorption of cholesterol in the intestines, leading to lower total plasma cholesterol and LDL levels. This property may potentially reduce the risk of heart disease since high cholesterol levels are a significant risk factor for cardiovascular disease (Moreau et al., 2018). Moreover, phytosterols have demonstrated other health-promoting effects such as anti-inflammatory, immunomodulatory, antioxidant, and anticancer activities. Studies have indicated that dietary phytosterols can provide protection against various types of cancers, including colon, breast, and prostate cancers (Witkowska et al., 2022; Azadmard-Damirchi et al., 2011).

Plant-based foods are the primary source of dietary intake of phytosterols, including β-sitosterol, campesterol, and stigmasterol. It has been reported a diet provides 150–400 mg/day of these plant sterols (Witkowska et al., 2022). Phytosterols are mainly found in oils and nuts, with β-sitosterol being the main phytosterol present in tree nuts (Witkowska et al., 2022). The study by Vecka et al. (2019) suggests that temperate nuts have a total sterol content of 4.5–5.9 mg/g oil, with β-sitosterol being the predominant sterol in nuts. Pistachios, in particular, were found to have a high total phytosterol content, with 86wt% being comprised of β-sitosterol. Among the almonds, pecans, pistachios, and walnuts studied, stigmasterol was found to have a higher average content than campesterol and sitostanol. Kornsteiner-Krenn et al. (2013) reported that the total phytosterol content in the temperate nuts varied between 112.9 mg (pecan) and 271.9 mg/ 100 g oil (pistachios). β-sitosterol was found to be the most abundant phytosterol across all types, ranging from 86.2 mg (hazelnuts) to 254.8 mg/100 g oil (pistachios). Campesterol was found in higher content in walnuts and pistachios, whereas almonds and hazelnuts contained only traces of campesterol (less than 6 mg per 100 g of oil). Additionally, minor content of stigmasterol (less than 11 mg per 100 g of oil) was found in almonds, hazelnuts, and pistachios. β-sitosterol, campesterol, and stigmasterol have been identified as the most abundant phytosterols in various nuts, as shown by AzadmardDamirchi et al. (2011). Pistachios, in particular, have the highest total phytosterol content among temperate nuts, with a concentration of 279/100 g. Other phytosterols such as clerosterol, sitostanol, Δ5, 24-stigmastadienol, Δ7-stigmastenol, Δ7-avenasterol, poriferasta-7, 25-dienol, and β-sitostanol have also been found in nuts (Phillips et al., 2005; Miraliakbari and Shahidi, 2007). The phytosterol content of various nuts ranges from 113 mg/100 g in hazelnuts to 280 mg/100 g in pistachios, according to Oliver Chen and Blumberg (2008). Walnut, almond, and hazelnut oils have been found to contain significant amounts of β-sitosterol, campesterol, and stigmasterol, with walnut oil having the highest total sterol content ranging from 150–290 mg/100 g of oil (Miraliakbari and Shahidi, 2007). Almond oil typically contains approximately 2.2–2.8 g/kg of phytosterols, mainly in the form of β-sitosterol, along with trace amounts of stigmasterol, Δ5-avenasterol, and campesterol (Maguire et al., 2004; Miraliakbari and Shahidi, 2007). Vu et al. (2019) identified 13 phytosterols in black walnut kernels, with β-sitosterol being the most predominant among them, and the samples tested showed a total sterol concentration ranging from 1236.0 mg/kg to 1542.3 mg/kg (Figures 4.2 and 4.3).

Figure 4.2 Phytochemicals of nuts. ⏎

Figure 4.3 Some of main phytochemicals in temperate nuts. ⏎

4.4 Benefits of Temperate Nut on Human Health

Numerous studies have demonstrated the beneficial effects of temperate nuts in reducing the risk of CVD, atherosclerosis, hypertension, type 2 diabetes mellitus (T2DM), inflammation, certain types of cancer, and several other chronic diseases (Gonçalves et al., 2023; Pinto et al., 2021; Terzo et al., 2017). In addition to these benefits, temperate nuts also have positive effects on human health, such as cardioprotective, neuroprotective, hypolipidemic, weight management, modulation of glucose levels, and more (Figure 4.4) (Sultana et al., 2022).

Figure 4.4 Temperate nuts health benefits. ⏎

Cardiovascular Disease (CVD) Protection: Epidemiological studies have indicated that nut consumption can be reducing CVD, CHD, hypertension, and associated mortality (Alasalvar et al., 2020). Nuts phytochemicals, For example polyphenols have been shown to decrease the risk of cardiovascular disease through multiple mechanisms. These include improving lipid and glucose homeostasis, reducing hypercholesterolemia, oxidative and inflammatory biomarkers, and enhancing antioxidant defenses (Sultana et al., 2022; Hong et al., 2018; Alasalvar and Bolling, 2015). Studies have also shown that consuming nuts can have positive effects on various CVD risk factors, such as improving lipoprotein cholesterol, total cholesterol levels, and triglycerides (Berryman et al., 2017). For instance, incorporating hazelnuts into one’s diet has been associated with a decreased risk of CHD and atherosclerosis. Moreover, hazelnut consumption has been found to effectively lower blood cholesterol levels, particularly in individuals with mild hypercholesterolemia, leading to a significant reduction in low-density lipoprotein (LDL) cholesterol (Zhao et al., 2023; Alalwan et al., 2022).

Antioxidant Activity: Excessive production of free radicals, such as ROS and reactive nitrogen species (RNS), can lead to oxidative stress, causing damage to biomolecules and contributing to various chronic conditions including coronary heart disease, neurodegenerative diseases, cancers, type 2 diabetes, hypertension, inflammation, and more (Mates et al., 2023; Bolling et al., 2010). However, regular consumption of nuts has been associated with a decreased risk of these conditions. Temperate nuts contain natural antioxidants in the form of nutrients (such as vitamins A, C, and E and the mineral Se) and non-nutrient phytochemicals (including phenolic compounds like catechin, quercetin, tannins, ellagic acid, chlorogenic acid, and cyanidin, as well as carotenoids like β-carotene and lycopene) (Alasalvar and Bolling, 2015). Research indicates that the consumption of almonds, rich in polyphenolic compounds, can protect against oxidative stress and DNA damage in smokers (Karimi et al., 2020). Pistachios, on the other hand, are abundant in polyphenols, phytosterols, and other dietary antioxidants that act as scavengers, neutralizing ROS and enhancing endogenous antioxidant defenses. A study conducted on rats demonstrated significant hepatoprotective effects of pistachio oil, which reduced oxidative damage by chelating redox metals and decreasing lipid peroxidation (Klibet et al., 2016). Phenolic compounds found in nuts play a crucial role in preventing lipid oxidation by acting as free radical scavengers. Antioxidants can exert their effects through direct mechanisms, such as scavenging ROS and chelating metal ions, as well as indirect mechanisms, including the induction of antioxidant enzymes, prevention of pro-oxidant enzymes, and reduction of inflammatory mediator molecules to mitigate inflammation (Bodoira and Maestri, 2020).

Anti-inflammatory Activity: Inflammation is a characteristic feature of different diseases, such as diabetes, arthritis, cancer, and respiratory pathologies, and plants’ phytochemicals are considered potential anti-inflammatory agents (Karbab et al. 2020). Numerous reports suggest that regular consumption of nuts can play a beneficial role in protecting against inflammatory processes and oxidative stress which is due to the abundance of bioactive phytochemicals present in the kernel and skin of nuts, such as carotenoids, flavonoids, and phenolic compounds (Sultana et al., 2022). According to findings in several animal models, the anti-inflammatory activities of nuts polyphenols confirmed and are attributed to the reduction of inflammatory mediator molecules synthesis (Bodoira and Maestri, 2020). Pecans and walnuts are rich sources of epigallocatechin3-gallate (EGCG), a compound that has been shown to alleviate kidney dysfunction caused by oxidative stress and inflammation in models of kidney disease. The restorative effect of EGCG on renal function is attributed to its ability to restore Nrf2 signaling (Wang et al., 2015). According to Vu et al. (2020), black walnut exhibits inhibitory effects and anti-inflammatory activity, which can be attributed to various phenolic compounds such as gallic acid, quercetin glycosides, 3-methyl quercetin, and ellagitannins. Squillaci et al. (2018) reported that phytochemicals present in chestnut shells possess protective properties against inflammation, as evidenced by their ability to reduce the production of inflammatory markers nitric oxide (NO) and inducible nitric oxide synthase (iNOS). Furthermore, certain extracts containing proanthocyanidins have demonstrated strong anti-inflammatory effects, particularly in conditions such as gastric inflammation (Pinto et al., 2021).

Anti-Cancer Properties: Several studies have revealed the beneficial effects of consuming nuts in decreasing the incidence of cancer and its-cause mortality rates. In walnut septum, certain phytochemicals such as p-coumaric acid hexoside, quercetin 3-O-glucoside, and quercetin 3-O-rhamnoside (quercitrin) have been identified as potential contributors to its antitumor properties. These compounds can act as pro-apoptotic agents by stimulating caspase-3 expression, along with epigallocatechin and epigallocatechin gallate, which are also expected to promote apoptosis (Genovese et al., 2020). Hilbig et al. (2018) stated that the aqueous extracts of pecan nuts had abundant amounts of EGCG, gallic acid, 4-hydroxybenzoic, vanillic, chlorogenic, caffeic, and ellagic acids, were effective in inducing apoptosis and cell cycle arrest in breast cancer cells. Chen and Blumberg (2008) also reported significant effects of almond skin polyphenols, which are mainly composed of flavonoids and phenolic acids. These compounds can scavenge free radicals and induce the production of quinone reductase, which is an enzyme commonly utilized as a biomarker for phase II metabolic activity and elimination of carcinogens.

Antidiabetic Activities: Type 2 diabetes mellitus (T2DM) is a chronic metabolic disease that is prevalent among overweight and obese adults, can increase the risk of developing CVD, diabetic retinopathy, renal failure, and mental health disorders (Davies et al., 2022). Inhibiting the activity of α-amylase and α-glucosidase, two digestive enzymes commonly present after a meal, is one way to prevent an increase in blood glucose levels following a meal (Mates et al., 2023). Evidence indicated the role of nuts in reducing the risk of insulin resistance and type 2 diabetes. Flavonoids such as catechin, quercetin-3-O-rhamnoside, quercetin 3-β-D-glucoside, and quercetin 3-D-galactoside, which were isolated from the walnut septum, could impede the activity of α-glucosidase (Rusu et al., 2020). Additionally, polyphenols in temperate nuts can limit blood sugar levels by inhibiting the digestion of carbohydrates. Studies have identified almond and chestnut tannins to be potent α-amylase inhibitors and blood glucose reduction was confirmed in mice that were fed corn starch (Alasalvar and Bolling, 2015). The beneficial role of temperate nuts in glucose and insulin metabolism is related to the secondary active metabolite, minerals, lipids, and fiber content. In this case, Parham et al. (2014) stated that polyunsaturated fatty acids (PUFA), carotenoids such as β-carotene and lutein, γ-tocopherols and procyanidins found in pistachios are effective on glucose metabolism.

Neuroprotective Activity: Acetylcholinesterase (AChE) is an enzyme responsible for the breakdown of the neurotransmitter acetylcholine (ACh), which plays a crucial role in synaptic transmission. Inhibiting AChE activity leads to increased levels of ACh, resulting in improved synaptic function. AChE inhibitors like galantamine have shown efficacy in treating conditions such as dementia, Parkinson’s disease, and Alzheimer’s disease by enhancing the cholinergic system and improving cognitive functions such as learning and memory (Giacobini, 2004; Vu et al., 2020). Almonds, hazelnuts, and walnuts have been found to possess neuroprotective effects against Alzheimer’s disease due to their high content of tocopherols and phenolic compounds (Gonçalves et al., 2023). Chestnut-derived polyphenols have also demonstrated a neuroprotective effect on human neuroblastoma cells, suggesting their potential in mitigating neurodegenerative issues (Brizi et al., 2016). Additionally, pistachios’ phenolic compounds have been associated with neuroprotective effects by reducing oxidative stress and inflammation in the mouse brain. These phytochemicals can attenuate ROS generated in mitochondria and induced by redox, leading to decreased brain apoptosis, reduced brain lipid damage, and improved mitochondrial function (Nuzzo et al., 2020).

Antimicrobial Activity: Temperate nuts exhibited antimicrobial properties against numerous microbial agents. According to reports, phenolic compounds and flavonoids possess antimicrobial properties due to their ability to strongly bind with microbial proteins and glycoproteins. Pyrogallol, ethyl gallate, and p-hydroxybenzoic acid, which are isolated from almond seeds, demonstrate powerful antibacterial effects against bacteria of both the Gram-positive and Gram-negative types (Bolling, 2017). Epicatechin and catechin of almond skin were able to stop the growth of Staphylococcus aureus (Gonçalves et al., 2023). Blanched almond extract has been demonstrated to hinder the growth of Escherichia coli, Serratia marcescens, and Streptococcus mutans colonies (Smeriglio et al., 2016). Phenolic acids present in chestnut shells exhibit antibacterial properties against Gram-negative bacteria (Silva et al., 2020). The inhibitory effects of phenolic compounds on bacterial growth involve various mechanisms, including the disruption of membrane structure and inhibition of DNA synthesis. Black walnut has been found to contain glansreginin A, catechin derivatives, quercetin glycosides, and eriodictyol-7-O-glucoside, which contribute to its antibacterial activity (Vu et al., 2020). Barekat et al. (2022) have reported that walnut extract displays antimicrobial properties attributed to both polar compounds such as phenolic acids, as well as non-polar compounds like tocopherols, sterols, monoterpenes, and juglone. Walnut pellicle extract (WPE) has demonstrated notable antimicrobial activity against viruses (including Herpes simplex virus type 1 and 2), bacteria, and fungi. Phytochemicals such as protocatechuic acid, myricetin, gallic acid, ellagic acid, kaempferol, and β-sitosterol in WPE contribute to its antiviral properties, while flavonoids like quercetin, myricetin, and rutin are responsible for its antifungal activity against various Candida species (D'Angeli et al., 2021).

4.5 Conclusions

Temperate nuts are not only a great source of valuable nutritional compounds but also contain a wealth of phytochemicals, particularly phenolic compounds, and phytosterols. These bioactive compounds have a significant impact on human health and have demonstrated the ability to decrease the risk of several chronic diseases, including CVD, hypertension, type 2 diabetes mellitus (T2DM), atherosclerosis, inflammation, cancer, and neurodegenerative diseases. Moreover, the consumption of these nuts has been associated with improved brain function. Including temperate nuts in one’s diet can contribute to overall health and longevity.

KEYWORDS

alkyl phenols

carotenoids

chemopreventive

chlorophylls

flavonoids

lignans

phenolic acids

phytates

phytosterols

proanthocyanidins

squalene

stilbenes

tannins temperate nut crops

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Chapter 5 Scope of AI- and ML-Mediated Advancement in Temperate Nut Crops

POOJA PURUSHOTHAM,* NAMBURI KARUNAKAR REDDY, GAURAV Y. RAKHONDE, and J. MADHU

Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

*Corresponding author

Abstract

The domain of artificial intelligence (AI) called machine learning (ML) originated from its inherent learning capability. With the goal of building models that categorize data first and then make predictions, machine learning algorithms have been developed. Diverse amalgamations of artificial neural networks (ANNs), fuzzy logic, and genetic algorithms have been employed to simulate intricate in vitro procedures, such as shoot multiplication, rhizogenesis, and acclimatization, seed germination, formulation of plant culture media, and stimulation of the accumulation of bioactive compounds. Using machine learning and statistical modeling techniques, the impact of change in climate on the financial well-being of fruit growers has been investigated. In recent times, micropropagation research has incorporated computer-based techniques like Design of Experiment (DoE) and machine learning algorithms to address the intricacies of complex systems. Creating new domestication processes, manipulating genomes, and expediting growth through breeding techniques and other modern fast breeding techniques used in crop wild relatives, as well as the use of computational techniques that could hasten the realm of crop wild relatives in breeding programs for enhancing crop adaptability and yield. This chapter highlights the ongoing revolution in temperate nut crops and the potential impact of neural networks on productivity. Automated farming, drones monitoring production lines, and intelligent quality control through visual devices are all possibilities for future advancements in nut crop production.

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Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

5.1 Introduction

Indian agriculture continues to operate at the level of subsistence as a result of persistent traditional farming systems. Recently, food (Soffar, 2019) and nutritional security have come under new threat from climate change (Joshiba and Kumar, 2019). Automation in horticulture appears to be urgently needed given the rising population and forthcoming obstacles. Numerous issues that orchard growers are having on the ground can be solved by automation in the horticulture industry. Artificial intelligence aids farmers in selecting the best crop for the soil and climate, potentially increasing productivity. The various ripening stages of agricultural produce can be determined by sensors (Soffar, 2019). Diverse cutting-edge technologies, such as artificial intelligence (AI), machine learning (ML), blockchains and big data analytics, will assist producers in improving output which will contribute to sustainable agriculture.

AI, one of the earliest branches of computer science, reached the zenith of its popularity during the 1950s. However, the demands promptly exceeded the capabilities of digital computer systems available at that point in terms of computing power. Because of this, AI was only theoretically fascinating but was unsustainable practically particularly economically, which undoubtedly caused fascination with AI to decline in the 1980s. Merely 10 years in the past did AI experience a significant resurgence as a consequence of the enormous achievements in data-centric statistical machine learning. The artificial neurons created by McCulloch and Pitts in 1943 are during which artificial neural networks gained their beginnings. Today’s neural networks use a unique type of compositionality where characteristics from one stratum are amalgamated in diverse manners to generate more conceptual attributes in the subsequent stratum (Bengio et al., 2021). These neural networks have an extensive quantity of connections and a substantial number of layers. The computational capacity accessible in the present day has allowed for the performance of this sort of AI known as “deep learning.” Naturally, the growing intricacy of these deep learning models has introduced limitations and novel challenges regarding the interpretability of their outcomes. This deficiency in understanding can be particularly significant, especially when employing such AI systems to real-world challenges (Holzinger et al., 2021). Numerous pivotal concepts in AI have existed since the mid-20th century. Their present achievements stem from a confluence of three interconnected factors:

Robust, affordable, and accessible technology cantered around digital computation;

Expandable statistical machine learning techniques;

The phenomenal expansion of datasets that are currently available.

Because of its indisputable capacity to enhance society and the environment, AI has achieved degrees of recognition and advancement that enable it to penetrate virtually every sector and domain of application. Consequently, it stands as the primary driving force behind the ongoing digital transformation. Governments, policymakers, businesses, and academia collectively bear the responsibility of guaranteeing that AI development takes place with an awareness of and regard for these potential risks. AI applications must consistently ensure aspects related to security, traceability, transparency, explainability, validity, and verifiability (Holzinger et al., 2021). To ensure safety, and security, and establish reliable AI, the approach of Human-Centered AI (HCAI) becomes an inclusive strategy that harmonizes AI solutions with human values, ethical tenets, and legal mandates. Now, numerous prestigious organizations and top researchers around the globe are supporting this HCAI concept (Shneiderman, 2022). Upcoming intelligent agriculture and forestry will require an approach centered around humans and AI, one that encompasses sociological, ethical, and legal factors. Artificial intelligence should be used as “power steering for the brain,” enhancing natural intelligence rather than swapping it. The human-in-the-loop strategy addresses this void by leveraging the wisdom, and proficiency grasp of mankind experts to reinforce, and supplement mankind capacities with AI, rather than substituting them entirely.

To surmount the challenge of high dimensionality and ultimately attain a state of “practical intelligence” we need to:

Acquire knowledge from data;

Uncover fresh insights and understanding;

Attain broad applicability from a limited set of instances;

Decipher the information (Holzinger, 2019).

5.2 Classification of AI

AI systems operating autonomously that carry out complex, tasks demanding significant labor within a specific domain and finish them automatically. These have tasks with defined objectives. Automated forest management and industrial robotic process automation are two examples (Van der Aalst et al., 2018; Liu et al., 2021). autonomous AI systems, such as fully autonomous self-driving cars (Levinson et al., 2011) and autonomous drones (Floreano and Wood, 2015), that make decisions without human intervention.

Assisted AI systems, such as those used in weather forecasting and ambient assisted smart living (Singh et al., 2015), that aid humans in accomplishing monotonous and routine tasks with enhanced speed and precision.

Augmenting AI systems that involve humans or at least allow humans to maintain control for the purpose of integrating human intelligence with machine intelligence, as well as vice versa. Examples include basic, inexpensive augmented reality applications (Nischelwitzer et al., 2007), enhanced AI in agriculture (Silva et al., 2021), and interactive machine learning ideas (Ramos et al., 2020).

5.3 Machine Learning: A Work Horse of AI

The objective of the worldwide machine-learning community was to devise algorithms that could autonomously learn from datasets and enhance their performance over time, without requiring human intervention (Shahriari et al., 2016). The term “big data” has no negative connotations; rather, it is essential to these automatic learning techniques (Sonnenburg et al., 2006). However, in some circumstances, we lack given the imperative reliance on substantial volumes of data, we encounter intricate challenges. In certain scenarios, achieving the application of entirely automated methods becomes highly challenging. For instance, this difficulty might arise due to ethical or legal concerns (Muller et al., 2021; Stöger et al., 2021). This human-in-the-loop dynamic can occasionally—though not universally—introduce human expertise, experience, and conceptual comprehension to address challenges that cannot be autonomously resolved or to refine algorithms that are struggling with suboptimal solutions and uncertain paths for progress (Holzinger et al., 2016).

5.4 Advancement in Temperate Nut Crops Through AI and ML

5.4.1 Effective Micropropagation and Conservation of Germplasm of Temperate Nut Crops Employing New Computer-Based Tools

In the past, germplasms were generally saved using conventional micropropagation methods employing in-situ habitats or even ancient orchards, as well as ex-situ (off-site) methods through their relocation from their native habitats to germplasm banks and botanical gardens. These methods include cryopreservation for extended-term storage, controlled slow-growth conditions, development of synthetic seeds for intermediate preservation, and micropropagation for short-term conservation. These innovative approaches offer valuable perspectives on the preservation of Pistachio species. (Ozden-Tokali et al., 2010; Akdemir et al., 2013; Pathak et al., 2014; Benmahioul et al., 2016).

Compared to traditional propagation methods, micropropagation has many benefits, including the ability to rapidly and massively multiply elite genotypes and to save other genotypes from extinction. All these benefits are easily applicable to temperate nut crops that are difficult to propagate by conventional methods. Regardless of whether micropropagation methods are started from adventitious shoots, somatic embryos, or apical or axillary meristems, their success or failure depends heavily on a variety of variables, that involve not only the genotype and cultivation environment but also, of paramount importance, the composition of the growth medium (mineral nutrients, PGRs, and vitamins) (Figure 5.1). However, when these three basic culture media have been used, The progress of micropropagation for Pistacia species has been impeded by a limited rate of multiplication, compounded by certain physiological abnormalities such as basal callus (BC), shoot tip necrosis (STN), excessive moisture-induced hyperhydricity (H), leaf yellowing (LY), and vascular necrosis (VN) (Marin et al., 2016; Onay, 1996; Abousalim and Mantell, 1994; Barghchi and Alderson, 1996).

Figure 5.1 Diagram representing factors affecting the plant quality in in vitro culture conditions. Source: Adapted from Nezami and Gallego (2023).⏎

Micropropagation faces issues like contamination and culture browning due to phenolic compound secretion. Plant biotechnology researchers face challenges in creating effective culture media for various plant species. Protocols for micropropagating Pistacia spp. vary greatly, with methods like mineral nutrient composition, plant growth regulators, and culture systems varying significantly from species to species (Benmahioul, 2018). The Ishikawa diagram displays the most common in vitro multiplication components. In the realm of micropropagation research, computer-driven tools such as Design of Experiments (DoE) and machine learning algorithms are employed to comprehend the intricate interplay of diverse elements and their effects on complex systems (Hameg et al., 2020; Nezami-Alanagh et al., 2018).

5.4.1.1 Tools for Design of Experiments (Doe)

Niedz and Evens (2016) characterized the DoE as a knowledge-driven method that integrates precise assessments of productivity and quality into the experimental procedure. In contrast to traditional design methods, DoE holds a notable edge by reducing data volume while enhancing data integrity. Rooted in hierarchical arrangement and the concept of sparse effects, DoE facilitates enhanced comprehension of intricate multifactorial processes. Its benefits surpass those of established tactics like trial and error, single-factor exploration (one factor at a time or OFAT), and triangulation methods (Hameg et al., 2020). In a recent instance, DoE was harnessed to condense an extensive experimental design spectrum, shrinking it from 3125 to just 29 distinct treatments. This strategic approach aimed to gain a deeper grasp of how macro- and micronutrients influence the ideal growth conditions for two pistachio rootstock varieties: P. vera cultivars “Ghazvini” and “UCB1” (Nezami-Alanagh et al., 2018). Combining neural network techniques and fuzzy logic principles was applied to establish causal links between physiological disorders and the factors investigated (Chitzanidis, 2008; Nezami-Alanagh et al., 2019).

5.4.1.2 Tools for Artificial Neural Networks

The main objective of artificial intelligence was to create machines capable of learning from data through symbolic techniques, primarily focused on neural networks. The foundational element of every artificial neural network is a perceptron, which is an individual processing unit that mimics a biological neuron (Gallego et al., 2011). These machine-learning algorithms made use of techniques from probability, fuzzy logic, and statistics (Langley, 2011). The primary distinction between AI and ML is that while ML has the capacity to learn and predict from passive observations, artificial intelligence necessitates an engaged external agent to learn and execute specific actions aimed at enhancing the likelihood of accomplishing the defined objective (Joshi, 2020). Artificial Neural Networks (ANNs), ML, and Fuzzy Logic (FL) algorithms are among the various AI tools, and they are regarded as the most significant scientific advancements in recent years. These algorithms have a variety of significant applications in comprehending intricate biological processes within plants (Gallego et al., 2011; Hesami and Jones, 2020), and they have many advantages over conventional statistics (Landin et al., 2009; Gago et al., 2010). Modelling complex in vitro processes like acclimatization (Gago et al., 2010), seed germination (Ayuso et al., 2018), designing plant culture media (Arteta et al., 2022; Maleki et al., 2021), and elicitation of bioactive compound accumulation (Garcia-Perez et al., 2020) has been done using various combinations of ANNs, FL, and genetic algorithms.

The successful utilization of both ANN and DoE has also been applied to unravel the essential significance of certain ion relationships in relation to shoot quality, proliferation rate, and shoot development. length (NezamiAlanagh et al., 2018). Furthermore, these methodologies have been employed to uncover the physiological shifts in Pistacia in response to the constituents of in vitro culture media. To sum up, the integration of contemporary computational approaches, such as DoE and ANNs, proves exceptionally advantageous in devising precise culture media for the effective micropropagation and safeguarding of pistachio, along with other susceptible temperate nut crop germplasms that could serve as valuable cultivars and rootstocks. These technologies aid in streamlining treatment combinations by minimizing their count, while concurrently enhancing data quality through DoE. In parallel, ANNs facilitate a deeper grasp of the pivotal factors influencing each parameter, contributing to the development of optimized culture media (Nezami-Alanagh et al., 2019).

5.4.2 Employment of Crop Wild Relatives (CWR) in Presentday Breeding Through Computational Techniques

The discovery and deployment of novel genes would be a more effective strategy for combating the effects of climate change, and present crop genetic variety may not be sufficient (Reddy et al., 2023; Ahale et al., 2023). The accessibility of reference genomes for various plant species, combined with advancements in genome sequencing technology, has brought to light previously undiscovered genetic variation present in CWRs. Unfortunately, throughout the history of crop domestication and intensive breeding, CWRs have not been fully utilized. By tapping into the genetic reservoir of CWRs, breeders can access a wider range of selection sources beyond the existing crop varieties, which will be crucial in meeting future demands for food quality and quantity. To fully leverage the potential of CWRs, a multiresource integrative strategy should be employed. This approach allows for the effective utilization of essential genetic variations found in CWRs. With adequate support and investment in research and breeding programs, we can harness the diversity represented in CWRs and ultimately enhance crop growth and productivity (Hajjar and Hodgkin, 2007).

Various tools and databases are accessible to both researchers and breeders to aid in the study and utilization of CWRs. However, it is crucial to continuously update and maintain these resources, which necessitates close collaboration between ecological and biological conservation sectors responsible for managing CWR ex-situ and in-situ conservation to prevent extinction. Additionally, involving computer scientists and plant biologists in these efforts is essential to ensure the availability of food for future generations (Tirnaz et al., 2022).

5.4.2.1 Tools for Accessing, Managing CWR Data, and Metadata

User-friendly systems play a crucial role in assisting breeders and scientists in accessing and utilizing CWR resources, including germplasm and genomic data. They address various challenges related to data formatting, sharing, versioning, and historical data management in phenotyping and genotyping. One such open-source software used for data creation and management by gene bank workers is GRIN-global. Genesys and CGIAR are other platforms that facilitate plant species conservation and access (Raubach et al., 2021). For data visualization, structure, and understanding of genebank accessions, software and tools are essential. Crop wild photoreactive platforms, introduced one can predict phylogenetic distance and compatibility for breeding programs (Viruel et al., 2021). PlaBiPD is a tool used to visualize phylogenetic relationships in flowering plant genomes, while Mercator provides functional annotations (Bolger et al., 2021). Germinate v3, for example, is a genotyping platform that allows for the import and export of plant genetic data, making it effective in CWR breeding and CWR studies (Raubach et al., 2021). By utilizing these tools and databases, researchers can efficiently analyze substantial breeding, pedigree, QTL, and molecular data, particularly for temperate nut crops.

5.4.2.2 Genomic Databases

PLAZA platform compares monocot and dicot genetic data to centralized databases, using interactive phylogenetic tree-style images and a bioinformatic workbench (Van Bel et al., 2022). It generates gene family charts, calculates collinearity statistics, determines localization, and performs direct BLAST against PLAZA protein sequences (Dash et al., 2016). These nut crop databases will be crucial in developing the initiatives for improving the crop.

5.4.2.3 Machine Learning Employment in CWRS

ML techniques have gained popularity in various plant science fields, including gene identification, classification, and biodiversity analysis (Bayer et al., 2021). ML is also being utilized in the early stages of plant development to estimate yield by leveraging image and genotype data (Danilevicz et al., 2022). Understanding environmental factors, including the distribution of CWR populations, is essential for selecting specific populations for introgression purposes (Cortes and Lopez Hernandez, 2021). ML algorithms can effectively integrate information from germplasm resources and environmental variables to identify candidate germplasms with desirable traits. One such method, called FIGS (Focused Identification of Germplasm Strategy), assists in the identification of adaptive features based on environmental data (Bailey-Serres et al., 2019).

ML models have proven effective in identifying germplasm with desirable traits and predicting traits like stripe rust resistance in wheat. ML techniques have also played a crucial role in research, facilitating the identification of genetic resources in crops that possess valuable agronomic features. To support research on CWRs, a global database has been established to document their distribution. This database enables researchers to access geographical information and prospective environmental parameters associated with CWRs (Bari et al., 2014).

5.4.2.4 Constraint in Uses of CWRS in Crop Breeding

Several obstacles hinder the widespread utilization of CWRs as a source of superior alleles to be included in mainstream cultivated germplasm.

Relatedness, compatibility with cross ability of CWRs with cultivated crops pose challenges for directly incorporating CWR traits through traditional breeding methods.

CWRs have been exposed to different selection pressures and environments in the wild compared to their domesticated counterparts, making them potentially valuable resources for crop improvement.

Assessing the yield of CWRs accurately can be particularly challenging due to their sometimes-unpredictable growth patterns and characteristics.

Even when beneficial traits from wild relatives are successfully introgressed into cultivated crops, an undesirable linkage drag effect often occurs, negatively impacting yield and other yield-related traits.

While the insertion of biotic stress tolerance genes, like disease resistance genes, can enhance resistance and tolerance to certain stresses, it may have negative repercussions on other agronomic properties of the crop (Summers and Brown, 2013).

Furthermore, sterility concerns may arise when CWR genetic material is introduced into an elite background, most typically during the F1 or BC1 generation (Bohra et al., 2022).

Through ongoing research and technological advancements, these barriers are gradually being overcome, unlocking the potential of CWRs as valuable resources for crop improvement and increasing agricultural resilience in the face of changing environmental conditions (Dempewolf et al., 2017).

5.4.2.5 Modern Breeding and CWRS

CWRs can be used to introduce wild-derived genes with desirable alleles into elite backgrounds using precise genome editing, bypassing linkage drag and fertility issues. Genomics allows for the investigation of genetic diversity and the uncovering of agronomically useful genes or QTLs (Saintenac et al., 2013). Recent methodologies, like resistance gene enrichment sequencing (RenSeq), aided the discovery of numerous key genes and QTLs in CWRs. CRISPR technology can maintain valuable wild-derived features like stress tolerance or increased nutritional quality, potentially leading to the development of innovative crops through de novo domestication. This would improve the ability to harness wild genetic diversity, resulting in more nutritious and climate-resilient de novo domesticated crops (Arora et al., 2019; Gasparini et al., 2021).

The delivery mechanism of genome editing reagents presents a significant obstacle in utilizing CWRs for crop improvement. However, germplasm conversion, which serves as an alternative to genome editing, offers a potential solution to incorporate beneficial traits from CWRs into cultivated crops through hybridization and MAS. Unlike genome editing, germplasm conversion does not require precise knowledge of target sequences, but it can be more challenging and time-consuming. Despite its complexity, germplasm conversion has the potential to introduce important features from CWRs into cultivated crops. By integrating CWRs into rapid breeding programs, it may be possible to reduce the time needed to incorporate multiple generations of CWR germplasm into economically viable crops, making them more adaptable and resilient to changing environmental conditions (Bhatta et al., 2021).

5.4.3 Implementation of Machine Learning Algorithms to Select Genotypes with Superior Traits in Temperate Nut Crops

Tolerance to biotic and abiotic environmental challenges in temperate nut crops is influenced by a complex interplay of genetic and environmental factors (Panahi et al., 2013). Developing new cultivars with spring frost tolerance traits through traditional breeding methods can take time. To expedite the process, leveraging the existing diversity found in the center of origin of the nut crops can be advantageous in identifying superior and promising genotypes (Godeanu et al., 2002; van Nocker and Gardiner, 2014). To predict which genotypes will display tolerance and sensitivity to environmental challenges, supervised ML models will be employed. Pomological characteristics specific to temperate nut crops will be measured and analyzed, along with physiochemical properties, to identify the most suitable genotypes for further breeding efforts. These ML models will aid in streamlining the selection process and accelerating the development of new nut crop cultivars with desirable traits.

Pattern identification techniques including ML algorithms, have emerged as a promising approach for identifying important traits and their combinations, contributing to environmental tolerance (Farhadian et al., 2021). To enhance ML-enabled high-throughput stress phenotyping (HTSP) and expedite the screening process for complex quantitative features like biotic and abiotic stress, innovative selection techniques are being developed (Singh et al., 2016). Supervised ML models, including classification models, predict a response using labeled features in a subset of data with a set of rules. The accuracy of the predictions is then assessed by means of the cross-validation method on test data (Nami et al., 2021). In the context of walnut trees, economic indicators for performance include kernel percentage, nut and kernel weight, shell seal, shell thickness, closed aperture nuts, and ease of kernel removal (EKRN) from the shell. These traits are crucial for assessing the overall quality and productivity of walnut trees. Such features may be selected using ML and other accessible data, which improves the selection efficiency of temperate nut crops.

5.4.4 Machine Vision and Deep Learning to Measure Nut Growth to Better Understand the Fruit Growth Curve

Understanding temperate nut crop development dynamics and thermal needs is crucial for predicting nut size and harvest timing. Monitoring growth stages, including shuck, shell, and embryo, is laborious and requires multiple measurements. A computer vision system can play a crucial role in the process of assessing nut development by employing pixel-by-pixel semantic segmentation. Mask-RCNN technique was utilized for object identification and semantic segmentation, allowing for the estimation of the areas of shuck, shell, and embryo in the pecan. The dataset was categorized as little (young) nuts and large (older) nuts. The selected network demonstrated high performance, with F1 scores ranging from 95.3%–100%, resulting in a mean absolute percentage inaccuracy of 10.14%–28.06%. This computerized measurement provides a comprehensive understanding of nut development components, beneficial for creating better models of nut growth phenology and predicting nut production accurately (Costa et al., 2021).

The picture gathering and analysis technique is reliable for nut defect classification using low-resolution X-ray pictures (Mathanker et al., 2011). This non-destructive method evaluates nut growth without enhancing accuracy due to lower resolution. The accuracy and MAPE of the model indicate that the proposed technique is acceptable for automating the tedious task of calculating nut areas across growth phases, but measuring embryo area remains problematic. The Mask R-CNN model detects tissue areas and predicts sigmoid growth trends in shuck, shell, and embryo regions. Other fruits have sigmoid fruit development patterns, while peaches and blueberries have double sigmoid growth curves (Pavel and DeJong, 1993; Godoy et al., 2008). Logistic and Gompertz models are commonly used sigmoid models for explaining plant growth. Plant tissue phenological development over time is often described using non-linear models (Tudela and Santib’a Nez, 2016; Paine et al., 2012). A system for detecting and estimating temperate nut crop development has been developed, achieving high object detection precision. The MAPE for area estimate models ranges from 10.14%–28.06%. Further training with more pictures will improve precision. The system can be linked to an embedded computer for AI models, potentially automating the entire measuring process for pecans and other tree nuts (Costa et al., 2021).

The Convolutional Neural Network (CNN) method is employed for deep learning-based fruit categorization, classifying fruits as raw, ripe, and overripe. This technology has the potential to replace manual hand picking and categorization of fruits by using computer vision, resulting in significant time savings. Deep learning is a subset of machine learning, and both are components of AI. Deep learning is specifically focused on learning hierarchical representations from data through multiple layers of neural networks, while machine learning encompasses a broader range of techniques and algorithms used to enable computers to learn and improve from experience without being explicitly programmed (Dandavate and Patodkar, 2020). CNN can learn from picture input, eliminating the need for human feature extraction. Convolutional neural networks assign the given input pictures to objects and are capable of distinguishing one from another (Al-Shawwa, 2020). The supervised learning approach may be used to label the classified data in CNN and then group it with existing data (Azizah et al., 2018).

5.4.5 AI to Predict Outbreak of Diseases and Pests in Temperate Nut Crops with Eco-Climatic Drivers

Unmanned aerial vehicles (UAVs) have become more accessible and offer a cost-efficient solution for conducting field surveys and monitoring tasks due to their ability to efficiently cover expansive areas. In the realm of agriculture, UAVs have found diverse applications, such as identifying plant diseases, predicting crop yields, creating inventories of trees, and evaluating different plant varieties. Scientists have effectively employed multispectral sensing with UAVs to distinguish between two similar-looking vineyard diseases that commonly manifest comparable symptoms across most red grape varieties (Albetis et al., 2018). Hyperspectral imaging and machine learning have been combined in a UAV-based approach for detecting citrus canker in the field, enabling the detection of the disease even in its early stages (Abdulridha et al., 2020). Additionally, a deep convolutional neural network (DCNN) was employed in conjunction with UAV-based hyperspectral imaging to develop an automated approach for identifying yellow rust in winter wheat to help in the categorization of healthy and diseased plants (Zhang et al., 2019). By employing UAVs and advanced imaging technologies with ML algorithms, agricultural practices can be significantly improved, leading to more efficient and targeted disease management strategies.

5.4.6 Site Specific Management of Temperate Nut Crops

Site-specific crop management (SSCM) plays a pivotal role within the realm of precision agriculture, encompassing a range of methodologies including spatial referencing, monitoring of crops and weather conditions, mapping of specific attributes, utilization of decision support systems, and implementing differential actions. While SSCM has proven beneficial for enhancing costbenefit analysis in row crop farming, it has shown relatively less effectiveness when applied to cash crops such as fruit and nuts (Panda et al., 2010).

In the context of fruit and nut crops, SSCM involves the integration of aerial or satellite imagery, GPS, and GIS (Sevier and Lee, 2005). This technological combination enables farmers to optimize resource utilization and maximize net returns in horticultural crops (Panda et al., 2009). Geospatial technology, with its orchard delineation and spatial analysis capabilities, provides valuable data for management decision-making processes, such as estimating fruit yield, scheduling fertilizer, irrigation, and pesticide application, ultimately leading to increased producer income. The integration of remote sensing for orchard growth and health detection, alongside digital imaging technology for site-specific management (e.g., leaf area index and crown cover), further enhances the precision of SSCM. Geospatial technologies, including global positioning systems (GPS), geographic information systems (GIS), remote sensing, and information technology or data management, play a vital role in this context (Panda, 2003).

5.4.6.1 Fruit and Nut Crop SSCM by Employing Remote Sensing

Remote sensing plays a crucial role in assessing spatial variations in crops, including horticultural ones. Numerous studies have been conducted to classify various vegetation types, including horticultural plants, using both satellite and aerial photographs (Holmgren and Thuresson, 1998). Fruit and nut orchards are often found near forested land, making it challenging to distinguish between plants and forest trees. However, remote sensing and image processing can help identify orchards (Franco-Lopez et al., 2001).

5.4.6.2 Fruit and Nut Crops SSCM by Image Processing Approach

Remote-sensing photos can be processed using various image-processing techniques and models to extract digital information related to fruit and nut crops (Panda, 2003). These methods often involve categorization and algebraic manipulation to assess spatial variability (Senay et al., 1998). Utilizing multi-spectral photography with the three visible bands (red, green, and blue) allows researchers to gather valuable data on land use and land cover (Jain et al., 1999). When it comes to identifying horticulture plants in satellite images, advanced image classification methods are used. However, it is worth noting that processing high-quality photographs can be computationally expensive. Nonetheless, leveraging the information from all three bands in multi-spectral photography proves to be beneficial in capturing the diverse land uses (Panda et al., 2010).

5.4.6.3 Fruit and Nut Crop SSCM By Implementing Gis

GIS are of utmost importance in the implementation of SSCM strategies for fruit and nut crops. By delineating study areas, digitizing orchard boundaries, and preparing spatial data, GIS aids in developing models for yield prediction, water-demand forecasting, and soil nutrient availability assessment. The advanced utilization of GIS can assist in developing geospatial models for conducting suitability analyses tailored to specific crops (Reed et al., 2021).

5.4.6.4 Fruit and Nut Crop SSCM by Implementing GPS

GPS are extensively employed in precision farming and SSCM, providing valuable functionalities such as recording ground truth points, utilizing GPS for differential correction, and exporting GIS shapefiles for image categorization. For improved accuracy in image categorization of fruit and nut crops, it is possible to construct a polygon layer outlining the orchard border using GPS data.

5.4.7 Robotic Crop Harvesting of Temperate Nut Crop With Help of AI and Deep Learning

The impending transition from a labor-intensive industry to a technologydriven one is on the horizon, facilitated by the incorporation of high-speed computing devices and their integration with agricultural machinery. This shift will require the adoption of systems that emulate human intelligence in one or more aspects, such as function, structure, behavior, capability, or principle (Wang et al., 2008) given this transition, the focus will lean towards data-driven processes, aiming to automate various agricultural tasks. Within the realm of agriculture, AI has the potential to transform data collected from agricultural fields into actionable commands through the process of comparing this data against necessary datasets. Robotic components or sensors can then carry out the orders to produce the desired outcome. Fulfilling the requirements of precision agriculture while also making an effort to balance the labor requirements of the sector, the steps of crop selection, fertilization, seeding, irrigation, pest control, and harvesting make up a standard agricultural cycle (McClellan et al., 2018; Sane et al., 2021; Wang et al., 2008; Kour et al., 2020; Jha et al., 2019). Since harvesting is the last step before the produce is processed or delivered, it has required difficult human labor since the beginning of farming. An AI-driven agricultural harvester may use a different mechanism at different layers or systems and help in the harvesting of fruits without human labor. There is scope for utilization of these artificial intelligence-mediated technologies and harvesting robots in crop harvesting practices of temperate nut crops which makes harvesting easy and more reliable compared to conventional manual harvesting methods.

Different layers or systems involved in the mechanism of an AI-driven harvester are the data sensing layer, decision-making layer, and robotic actuating layer (Figure 5.2).

Figure 5.2 Different systems involved in the mechanism of AI-driven harvester. Source: Adapted from Sane and Sane (2021).⏎

5.4.7.1 Data Sensing System

Data is collected by a sensor or a vision system in this layer/system and used by the decision-making layer. In order to avoid impediments, the actuation system can also be controlled using the data. The data such as fruit data can be used for fruit detection and positioning data may be used for location or arm manipulation for fruit harvesting. Robots and machines can now see thanks to computer vision, which makes use of a camera system and a computer with image-processing capabilities (Tian et al., 2020). The choice of vision system to be used depends upon the type of pictures and features required.

5.4.7.2 Decision-Making AI System

The processed data is used to make decisions at this layer. A mapping of the plant area is frequently done prior to the data processing in order to identify crop regions or specific crops as data points or action points that would be taken. It can be employed for identifying crop plants and ripened fruits in a tree. Once such data is available then it can be used to command fruitharvesting robots. Various processes take in decision-making AI systems and it is depicted in Figure 5.3.

Figure 5.3 Different processes incorporate AI decision-making systems. Source: Adapted from Sane and Sane (2021).⏎

5.4.7.3 Actuating Navigation/Harvesting Systems

In this layer, the robotic competence carries out the instructions provided by the decision-making layer. The robot would need to address localization issues, efficiently go to the action location, and finish the action in order to perform the instructed action. These can be drilling, sowing, weeding, irrigation, and fruit picking and harvesting (Sane et al., 2021). Robotic motion is mostly utilized for navigation and crop/fruit picking in fields or greenhouses. It appears that navigation in a farm environment, canopy, or tunnel is more of a navigation in organized area difficulty than it is in an unstructured one.

5.4.8 A Machine Learning Approach for Predicting Yield of Temperate Nut Crops at the Orchard Level

Crop production forecasting has seen widespread use of both process-based “crop models” and statistical “machine learning models” are utilized. The “crop model” methodology encompasses the modelling of crop growth, nutrient cycling, water dynamics, and energy balance at consistent time intervals to forecast crop yield. These estimates are based on the physiological traits of plants. On the other hand, machine learning techniques have been applied to predict temperate nut crop production at the orchard level. Deep learning techniques, particularly object recognition and growth monitoring, can be employed by automating the identification and computation of each nut component independently to estimate size. In this context, the utilization of vision-based techniques involving object detection and segmentation holds significance. Within agriculture, machine learning and deep learning algorithms rooted in vision-based methodologies have been investigated to monitor the condition of fruits and crops, pests (Partel et al., 2019) and diseases (Abdulridha et al., 2020).

For instance, Zeng et al. (2008) used machine vision to track grape growth, while Gongal et al. (2018) utilized 3D machine vision for apple growth tracking. The Mask R-CNN (Region Convolutional Neural Networks) has emerged as a cutting-edge convolutional neural network for object recognition and categorization (He et al., 2018). It has been successfully applied to identify trees and fruits (Ampatzidis et al., 2020; Yu et al., 2019).

Process-based “crop models” necessitate a substantial amount of input data, encompassing factors like cultivar, management practices, and soil conditions. These models simulate crop yield by adhering to established principles and processes that influence crop growth (Cai et al., 2018). Nonetheless, their calibration can prove intricate due to the complexities inherent in the processes, scarcity of field data across diverse environmental conditions, and the multitude of unidentified input parameters. Conversely, machine learning-based models draw upon historical data from various sources to formulate empirical prediction algorithms. An advantage they offer is the capability to estimate yield without heavy dependence on specific factors unique to various crops, as their predictions are not directly tied to recognized physiological mechanisms governing plant development (Medar and Rajpurohit, 2014).

A comprehensive approach for creating a machine learning model for this task is summarized as below that involves series of steps from data collection to building up of model and optimization.

5.4.8.1 Data Collection

Gather a comprehensive dataset that includes historical information on nut crop yields at the orchard level. This dataset should contain features that can influence the yield, such as weather conditions, soil characteristics, orchard management practices, and any other relevant factors.

5.4.8.2 Data Preprocessing

Enhance the dataset’s quality by addressing missing values and eliminating outliers, and normalizing or standardizing the features as necessary. This step is crucial for ensuring the quality and consistency of the data.

5.4.8.3 Feature Selection

Conduct a dataset analysis to pinpoint the pivotal features that exert a substantial influence on nut crop yield. Explore methodologies like correlation analysis, deriving feature importance from tree-based models, or leveraging domain knowledge to accomplish this task to select the optimal set of features for the model.

5.4.8.4 Model Selection

Select a suitable machine learning algorithm for the prediction objective. Regression algorithms like linear regression, decision trees, random forests, support vector regression (SVR), or gradient boosting models such as XGBoost or LightGBM are commonly applied for yield prediction. Opt for a model that aligns with the dataset’s characteristics and the sought-after prediction accuracy level.

5.4.8.5 Model Training

Partition the dataset into separate training and testing sets. Employ the training set to educate the chosen model by aligning the data with the algorithm. Through this process, the model will acquire an understanding of the underlying patterns and associations between the features and the target variable (nut crop yield)

5.4.8.6 Model Evaluation

Evaluate the trained model’s performance using the designated testing set. Standard evaluation metrics for regression tasks encompass mean squared error (MSE), root mean squared error (RMSE), mean absolute error (MAE), and coefficient of determination (R-squared). Gauge the model’s effectiveness and iterate if adjustments are warranted.

5.4.8.7 Model Optimization

Refine the model’s hyperparameters to enhance its performance. This endeavor entails modifying algorithm-specific parameters like learning rate, regularization strength, or tree depth. Contemplate the utilization of methods such as grid search or Bayesian optimization to pinpoint the optimal hyperparameter configuration.

5.4.8.8 Prediction

Upon completing the model’s training and optimization, apply it to generate predictions on novel, unseen data. Furnish the model with pertinent input features specific to a particular orchard, such as weather conditions and management practices, and obtain the projected yield as the resulting output.

5.4.8.9 Monitoring and Updating

Regularly monitor the model’s performance and retrain/update it with new data as it becomes available. Nut crop yield can be influenced by various factors that may change over time, so it’s important to keep the model up to date. The success of the machine learning model depends heavily on the quality and representativeness of the dataset, as well as the choice of appropriate features and algorithms. Domain knowledge and expert input can be valuable throughout the entire process to ensure accurate predictions and practical insights.

5.4.9 Enhanced Agricultural Production of Temperate Nut Crops Via Machine Learning Analytics

ML analytics can indeed contribute to enhanced agricultural production of temperate nut crops. It’s worth noting that the success of ML analytics in agriculture relies on the availability of high-quality and representative data. Therefore, it is essential to ensure proper data collection, preprocessing, and ongoing monitoring to maintain the accuracy and effectiveness of the ML models. Additionally, collaboration between domain experts and data scientists is crucial to develop ML solutions that align with the specific needs and challenges of temperate nut crop production. Here are some examples of specialized applications for ML analytics for enhanced agricultural production of temperate nut crops.

5.4.9.1 Disease and Pest Detection

ML algorithms can analyze data from various sources such as images captured by drones or sensors in the orchard to identify signs of diseases or pests (Liu and Wang, 2021). By detecting early symptoms, farmers can take timely actions to prevent or mitigate the spread of these issues, leading to improved crop health and higher yields.

5.4.9.2 Optimal Irrigation and Nutrient Management

ML models can leverage historical data on soil moisture, weather patterns, and nutrient levels to determine the optimal irrigation and nutrient management strategies for nut crops (Abioye et al., 2022). By considering factors such as plant water requirements, soil moisture retention, and nutrient uptake, ML algorithms can provide insights and recommendations to optimize resource allocation and enhance crop productivity.

5.4.9.3 Yield Prediction

As mentioned earlier, ML models can be trained to predict nut crop yields based on various factors such as weather conditions, soil characteristics, and orchard management practices (Van Klompenburg et al., 2020). By accurately forecasting yields, farmers can make informed decisions regarding harvest planning, resource allocation, and marketing strategies.

5.4.9.4 Crop Monitoring and Growth Stage Prediction

ML algorithms can analyze real-time data collected from sensors, satellite imagery, or drones to monitor the growth and development of nut crops. By tracking factors like leaf area, canopy coverage, and phenological stages, ML models can provide insights into the health and growth progress of the crops (Goel et al., 2022). This information can guide farmers in making informed decisions related to pruning, harvesting, and pest management.

5.4.9.5 Harvesting Optimization

ML analytics can help optimize the timing and efficiency of nut crop harvesting. By analyzing factors such as crop maturity indicators, weather forecasts, and labor availability, ML models can provide recommendations on the optimal time to initiate harvesting operations (Atitallah et al., 2020). This can minimize yield loss due to over-ripening or unfavorable weather conditions while maximizing the utilization of labor and machinery resources.

5.4.9.6 Decision Support Systems

ML analytics can be integrated into decision support systems that provide personalized recommendations to farmers. By considering a combination of historical and real-time data, these systems can offer customized guidance on crop management practices, disease control strategies, pest management, and resource allocation, ultimately leading to enhanced productivity and profitability (Rudnichenko et al., 2020).

5.5 Future Prospects

Cutting-edge technologies, spanning from sensors to highly efficient augmented reality visualization techniques, have now reached a level of affordability that has led to their widespread adoption. Consequently, these technologies are increasingly serving as indispensable decision-support tools across a broad spectrum of applications. The infrastructure for technological progress is already in place; the current focus needs to shift towards imbuing hardware with intelligence. This is precisely where human-centered AI assumes its role—beyond merely furnishing domain experts with pertinent contextual knowledge, it actively engages them in the decision-making process. Often, a human expert possesses a wealth of experiential wisdom, making it advantageous to synergize this innate intelligence with artificial intelligence. The temperate nut crops depend heavily on the weather for many different processes; hence weather forecasting is an essential part of the sector. Utilizing algorithms in conjunction with satellites, machine learning technology can be useful for daily weather forecasting. The health of crops can also be predicted using these algorithms without having to interact with vast areas. Additionally, machine learning broadens the range of pest and pathogen prediction and detection in the farmer’s orchard.

Nut crops need healthy soil that is rich in nutrients and moisture. Rich soils in nutrients and moisture not only boost (Sennaar, 2019) yield but also improve fruit quality. For the identification and measurement of moisture and nutrients in the soil, artificial intelligence and machine learning may create algorithms and sensors. Robots can be used to measure soil nutrients, which can then be utilized to perform predictive (Baruha, 2019) analysis to determine the appropriate amount of irrigation and fertilizer. Cashew nut is labor-intensive and demands high nutritional doses. Robots and machine learning (Kamilaris and Prenafeta, 2018) may be able to solve these issues in certain crops. As sensor technologies and data analysis tools like AI gain broader adoption, further prospects will emerge to regulate the timing, pace, and volume of irrigation water administered to temperate nut crops. These advancements will enable the optimization of water efficiency and nutritional content.

When it comes to producing nuts, tree crops have quite intricate processes that take into account factors like bee activity, flowering phenology, tree development physiology, and more (Connell, 2000; Tombesi et al., 2016; Chen et al., 2019a; Chen et al., 2019b). Gaining insights into the limitations affecting yield gaps at both plot and field levels necessitates a substantial dataset spanning diverse environmental conditions. Alongside this, more advanced data analysis techniques, such as AI-encompassing ML algorithms, are crucial components (National Academies of Sciences Engineering Medicine, 2019).

Compared to other cereal crops, horticultural crops are more susceptible to pests and diseases. In addition to lowering output and quality, these pests and diseases also result in lower market prices. Algorithms can identify the type of disease and further forecast how it will be treated when combined with (Singh et al., 2016) images that have been recorded. This technology can be used in orchards to identify diseased leaves. Due to poor information, farmers frequently spray insecticides and fungicides evenly on all plants, increasing input costs and chemical waste. As a result, machine learning can create algorithms that tell farmers exactly where to apply these pesticides, lowering input costs and waste (Sennar, 2019).

For high output and quality, temperate nut crops need a variety of synthetic compounds, including weedicides, insecticides, and plant growth regulators. These substances have a propensity to stay in the soil and plants, increasing toxicity. Additionally, these compounds enter the food chain, causing a number of metabolic disruptions. By taking pictures of pathogens, weeds, and pests, machine learning and big data analytics can be utilized to create models that could aid in the manufacturing of suitable agrochemicals (Baruha, 2019). AI can be used to complete post-harvest tasks like cleaning, sorting, and grading. To find pests and pathogens that have been stored in storage and warehouses, sensors can also be utilized (Kamilaris, 2018).

The prevalent sensors utilized in AI applications are RGB and CCD cameras, yet these cameras are restricted to capturing superficial attributes like shape, color, and size. To enhance the identification of internal diseases and defects, more sophisticated sensors and techniques can be adapted. Elevating the performance of on-farm sorting requires research in the realm of ripeness and quality detection. Optimization of AI models and systems for on-farm sorting should draw from established factory sorting lines, ensuring reliability and functionality under field conditions. However, the dataset used to construct AI models for on-farm sorting is constrained, featuring limited varieties and cultivars. This can lead to issues like model overfitting and bias, owing to data collection taking place either indoors or outdoors. To enhance generalization, it is recommended to amass supplementary data samples from diverse sources, incorporate open-source image datasets, and establish a comprehensive dataset encompassing various fruit types and varieties in varying environmental scenarios. This augmentation will fortify the dataset’s breadth, aiding the advancement and general application of AI algorithms (Xu et al., 2020; Sahu et al., 2023).

The quality and productivity of such crops may be harmed at any time by biotic and abiotic stresses. For instance, digital image processing might aid in spotting such strains, and machine learning, as a result of using an algorithm, might aid in reducing such stresses (Singh et al., 2016). IoT, AI, and cloud technologies, among others, can be used to control stress.

5.6 Conclusion

A constantly evolving technology, machine learning and artificial neural networks are unquestionably the waves of the future. AI is being used more and more frequently across a variety of economic sectors. The creation of artificial intelligence, among other things, resulted from the accessibility of computers. They were able to set new benchmarks in various decisionmaking processes thanks to their abundant computational power and limitless disc capacity resources. Various studies are being done to ensure that artificial intelligence will increasingly replace processes at various levels in modern horticulture. Numerous issues are currently plaguing the horticulture sector, reducing crop productivity and yield. Farmers cannot earn from this sector, despite it being profitable, due to these factors. AI, BDA, digital image processing, and blockchain technology are examples of automation technologies that can address actual problems that will either directly or indirectly increase the output and quality of agricultural products. Additionally, these technologies can be applied to lessen environmental harm caused by improper usage of synthetic chemicals utilized in the production of fruits and nut crops.

One issue is the dearth of supercomputers in many academic institutions and research centers. Supercomputers must be programmed and supervised properly to assure the effectiveness, validity, and verification of artificial intelligence. The proper choice of input and output parameters while constructing AI algorithms is another problem. It is possible to anticipate an ongoing revolution in temperate nut crops as well as an increase in creative uses. It is very likely that neural networks will soon have a significant impact on nut crop productivity. In the future, it will be feasible to envision automated farming and drones that monitor the health of production lines that process raw materials, or even intelligent quality control of temperate nut crops through the swift movement of visual devices.

Keywords

artificial intelligence

deep learning

ex-situ fuzzy logic

genomes

horticulture

in-situ

machine learning

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Chapter 6 Microbial Diversity in Nut Crops: Understanding Plant-Microbiome Association

AB WAHEED WANI,¹ LAKHWINDER SINGH,² HARJINDER KAUR,¹ SHAIFALI,¹ G. I. HASSAN,³ and RAJNI RAJAN¹

¹Department of Horticulture, School of Agriculture, Lovely Professional University, Punjab, India

²Faculty of Agriculture, Guru Kashi University, Talwandi Sabo, Bathinda, Punjab, India

³Sher-e-Kashmir University of Agricultural Science and Technology, Kashmir, Jammu and Kashmir, India

* Corresponding author

Abstract

Microbial diversity plays a crucial role in shaping the health and productivity of nut crops, as well as their overall ecological sustainability. The intricate interactions between plants and their associated microbiomes are fundamental to establishing a balanced and functional ecosystem. This chapter synthesizes the current state of knowledge regarding microbial diversity in nut crops and aims to deepen our understanding of the plantmicrobiome association. In this comprehensive review, we explore recent research focusing on the diversity, composition, and function of microbial communities inhabiting various nut crop species. Emphasizing the significance of the plant-microbiome interaction, we investigate the mechanisms that underpin this association and the potential factors influencing microbial colonization in nut tree rhizospheres and phyllospheres. Furthermore, this chapter highlights the importance of beneficial microorganisms in promoting plant growth, enhancing nutrient acquisition, and protecting nut crops against pathogens and environmental stressors. Finally, we identify current gaps in knowledge and propose future research directions to advance our understanding of microbial diversity in nut crops. We underscore the importance of employing cutting-edge techniques, such as metagenomics and functional genomics, to unravel the complex interactions between nut crops and their microbial inhabitants. By illuminating the intricacies of the plant-microbiome association, we aim to foster innovative approaches that optimize nut crop productivity while maintaining environmental integrity.

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Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

6.1 Introduction

Extreme settings offer a specialized habitat that supports different microbial life. The world’s 25 richest and most threatened eco-regions are found in India, one of the 12 mega-biodiversity countries, making it the perfect place to study these extremophiles. Thermophiles, such as those found in hot springs, create enzymes that are active at higher temperatures and facilitate the breakdown process. On the other hand, cold-climate desert psychrophiles can be an important source of anti-freezing chemicals. Osmolyte-encoding genes are discovered in halophiles and osmophiles, which are salt- and drought-tolerant transgenic plant candidates. These organisms are found in hypersaline soils and saltwater bodies. In-depth surveys were carried out in a number of Indian regions, including the cold deserts of Leh and Rohtang, the mangroves of Sundarbans and Bhitarkanika, the thermal springs of Rajgir, Manikaran, Bakreshwar, Balrampur, and Vashisht, the hypersaline soils of the Rann of Kutch, Pullicat Lake, Sambhar Salt Lake, and Chilka Lake, and the acidic soils. Each isolated specimen was subjected to biochemical examination to determine features that promote plant growth before being further characterized using 16s rRNA gene sequence analysis. Numerous additional genera and species that had not before been documented in the nation were identified as a result of the intensive research. A thorough database was also developed, offering essential background data on microbial life in India’s harsh settings.

A sizable number of microorganisms, particularly 1,540 bacteria, 157 archaea, 260 fungus, and 200 actinomycetes, were isolated during the surveys that were done. Arya et al. (2010) evaluated the predominance of Bacillus, its derivative genera, and other prominent genera. To better understand the molecular and functional diversity of the archaeal and bacterial isolates, more research was done on them. As a result, a sizable database of microbes resistant to a variety of environmental conditions, including high salinity, extremely high or low temperatures, drought, and low pH, was developed. These microbes from harsh habitats have the potential to be used as inoculants for plants grown under stress. The growth and productivity of nut crops were improved by using inoculants made of eubacteria and archaea that were isolated from saline habitats to reduce salt stress. Plants that were vaccinated with these microbes accumulated more proline and total soluble sugar while having a lower Na:K ratio (Bücking et al., 2015). Additionally, a preliminary investigation on archaea from the hypersaline Rann of Kutch region of Gujarat, India, revealed their function in promoting growth of plants in saline soils.

20 of the 157 archaeal isolates showed phosphate solubilization in broth and on plates. The potential to disintegrate tricalcium phosphate ranged from 51.92 0.8–1986.86 1.8 g mg-1 protein, with the Halococcus hamelinensis strain IARI-SNS2 producing the highest amount (1986.9 mg l–1) and the Natrinema sp. strain IARI-WRAB2 producing the second-highest amount (1341.5 mg l–1). The Chapter also revealed for the first time the ability of some archaeal isolates to solubilize potassium and produce IAA, Zeatin, gibberellic acid, and siderophore at high salt concentrations. Additionally, bacteria that can withstand acid were identified from Keralan soils and used as inoculants to promote the growth of nut crops like walnut. Following inoculation, psychophilic bacteria found in Leh and Rohtang Pass dramatically affected walnut development (Bailey et al., 1976). In order to find the strains that can produce lignocellulolytic enzymes active in such settings, a collection of microbial strains that are resilient to low temperatures was screened. To prepare compost at temperatures between 4 and 10°C, a consortium made up of two bacteria (Bacillus atropheus and Bacillus spp.) and two fungus (Eupenicillium crustaceum and Penicillium citrinum) was creat ed (Baylis et al., 1967).

A variety of regions in the Indian Himalayas, involving high mountain passes (Khardungla and Rohtang), rivers (Indus, Zanskar, I-Z confluence, and Beas), and sub-glacial lakes (Pangong, Dashair, and Chandratal), have yielded psychrophilic bacteria, which are known for their capacity to produce cold-active enzymes. For instance, plants can be protected from frost damage by psychrophilic bacteria that can create antifreeze proteins to counteract ice nucleation proteins made by other bacteria like Pseudomonas syringae and Erwinia herbicola. Antifreeze proteins have been discovered in a variety of bacteria from cold settings over the past 20 years (Barto et al., 2012). The best source of enzymes for use in industry and agriculture is microbes isolated from harsh environments. Cellulases, amylases, and proteases were discovered to be produced by a large number of the isolated microorganisms (Brundett et al., 1991). Additionally, some extremophiles have their candidate genes for abiotic stress tolerance amplified, which might be used to create transgenic plants that can withstand salt, drought, or temperature stress (Carding et al., 2015). Several genes from several extremophiles, including Oceanobacillus iheyensis, Bacillus licheniformis, Halobacillus sp., cyanobacteria Lyngbya sp., and Bacillus pumilus, were amplified, cloned, sequenced, and produced in heterologous strains.

In addition, Nut crops and the microbial communities they are connected with engage in critical interactions that are essential to the host’s survival and functionality. Although a variety of plant-associated microbial communities have been highlighted in nut crops by recent research, their relevance has largely gone unnoticed, especially in relation to the human diet and gut microbiota. According to the hypothesis, the variety of the consumable plant microbiome in the nuts and how it affects the human immune system might have a big impact on how well people feel. In order to test these predictions, the study investigates the culinary plant microbiomes of nut crops and contrasts them with other pertinent studies. The edible plant microbiome’s biotechnology potential is also evaluated.

6.2 Plant-Associated Microbial Diversity

According to Chen et al. (2009), the variety of microorganisms related to all types of food plants is still being completely characterized and is partly peculiar to the specific host species or even several food plant cultivars. Although the rhizosphere has been the focus of the majority of research on particular microbiomes, other compartments, including the carposphere, have also demonstrated species-specific diversity (Azcon et al., 1992). Given that there are approximately 370,000 species of higher plants, a lot more effort is still required to properly understand the specifics of the variety of the global plant microbiome. Our everyday food is largely composed of plants, including nuts, fresh vegetables, fruits, herbs, and medicinal plants. Therefore, every component of plants, including their microhabitats and microbial habitats, is present in our meals. These environments can support anywhere between 104 and 1010 bacteria per gramme of plant material. The health of people may be impacted by this exposure to microbes associated with plants in a number of different ways. Organisms that improve the nutritional content of plants, particularly their concentration of active bioactive chemicals, are linked to indirect benefits. Only a few examples of such effects are known, and most of them are associated with medicinal plants and their bioactive constituents (Borkowska et al., 2002). For instance, certain microbes produce antimicrobial compounds such maytansine in Putterlickia verrucosa, apigenin in Chamomille matricaria, and taxol in endophytic fungus of Taxus baccata. Additionally, it has been demonstrated that nutassociated bacteria affect crop’s scent expression, where Methylobacterium treatment increases the formation of aromatic furaneol compounds (Beutal et al., 1976).

On the other hand, the detrimental indirect impacts of microbes linked with plants have been extensively researched. Changes in the plant microbiome that result in the presence of small pathogens are frequently linked to the emergence of plant diseases. In addition to producing mycotoxins in the nuts, which are highly poisonous and carcinogenic substances, these microbes also contribute to unpleasant taste and odor (Wu et al., 2014). Fusarium mycotoxins continue to have a significant impact on human health, even though food hygiene can help with some of these issues (Wu et al., 2014). The long-term consequences of bioactive substances at low concentrations are also still poorly understood, and recent data suggests that endophytes may be able to create novel and insufficiently understood chemicals. More accurate detection of certain beneficial interactions between plants and microorganisms that are important for human health will be made possible by advanced technology.

Most of the information that is currently available on the direct impacts of plant microbiomes on people when we eat them comes from fermented foods like yoghurt, which are known to include probiotic strains. However, a large percentage of our diet is made up of nuts, which may introduce millions of germs into our bodies with each meal. Many germs are anticipated to enter our bodies through the food we eat, even after cleaning or rinsing food surfaces. The main theory is that the microbiome of edible nut food and the diversity of its microbes play significant roles in human health, contributing to the diversity of our gut microbiome and enhancing our immune response. A wide variety of bacteria can be found in walnut as a home (Brundett et al., 2009). However, the majority of the attention paid to microbes associated with walnut has been in relation to isolated disease outbreaks. The variety and specificity of relationships within walnut’s microbial communities are two important characteristics that may make it susceptible to infections.

Overall, 12.5% of the bacteria in the root zone of eight various nut crops were found to be cultivar-specific. Additionally, they discovered a sizable core microbiome made up of 68 operational taxonomic units from nine major phyla, with Proteobacteria accounting for 48.8% of the microbiome and being the most prevalent. According to a correlation analysis, co-occurrence in the nutplant-microbiome outweighed co-exclusion. It is unclear how biotic factors affect the microbiota. Every disruption of the native microbiomes, according to the researchers’ theories, might lead to significant changes in the community, and each disease outbreak might be accompanied by “minor,” less dangerous pathogens.

The researchers found significant effects on the microbiome caused by a plant pathogenic fungus, herbivorous gastropoda, or visiting pets in mesocosm and outdoor experiments utilizing a combination approach, combining network analysis of 16S rRNA gene amplicon libraries and FISH microscopy. Although a core microbiome composed of the genera Enterobacter, Stenotrophomonas, Pseudomonas, and Acinetobacter, all three unsettling factors led to major changes in the community and enhanced species richness with regarding to nut crops.

6.3 Walnut Microbiome Association

Walnut consumption is associated with better health. In a prior investigation, we found that an eight-week walnut-enriched diet (43 g/day) significantly improved lipid profiles in healthy subjects. In a randomized, controlled, prospective cross-over design, 194 healthy adults (134 women; age 63 ± 7 years; BMI 25.1 ± 4.0 kg/m²) participated in the study. After a run-in period during which nuts were not allowed, participants were randomized into two diet phases, each lasting eight weeks. Some participants transitioned to a nut-free diet after consuming a walnut-enriched diet, while others did the reverse. During the walnut-enriched diet phase, participants were instructed to adjust their fat or carbohydrate intake—or both—to account for the additional calories from walnuts.

At the conclusion of each diet phase, fecal samples from 135 participants were collected for microbiome analysis using 16S rRNA gene sequencing. Sequencing data were grouped into Operational Taxonomic Units (OTUs) with 97% similarity. The Kruskal-Wallis rank sum test was used to determine differential abundance, and UniFrac distances were employed to evaluate group diversity. The findings revealed that walnut consumption significantly influenced the diversity and composition of the gut microbiome. Multi-dimensional scaling showed that the walnut and control diets differed by approximately 5% (p = 0.02).

Notably, with walnut consumption, the abundance of Ruminococcaceae and Bifidobacterium significantly increased (p = 0.02), while the abundance of Clostridium sp. cluster XIVa species (Blautia and Anaerostipes) significantly decreased (p = 0.05). Whether respondents supplemented fat, carbohydrates, or both while following the walnut diet appears to have had minimal impact on the microbiota. After eight weeks of daily consumption of 43 g of walnuts, significant changes were observed in the gut microbiota of healthy individuals, favoring the expansion of probiotic and butyric acidproducing species. Further research is necessary to ascertain whether these modifications persist over longer periods of walnut consumption and how they relate to changes in lipid metabolism.

Diet significantly influences the composition of gut microbiota. In healthy adults, the gut microbiota is typically dominated by bacterial clusters from the phyla Bacteroidetes and Firmicutes, with lower amounts of Actinobacteria, Proteobacteria, and Verrucomicrobia. Animal studies have shown that dietary modifications can alter the proportion of Bacteroidetes to Firmicutes, but these changes are often reversible. The precise mechanisms through which walnuts, as part of a Western-style diet, modify the gut microbiota remain unclear due to limited human data on walnut consumption’s effects on key bacterial phyla ratios and microbial dispersion. However, our study demonstrated a distinct grouping within the walnut and control groups, indicating that the walnut diet affected beta diversity. Five operational taxonomic units (OTUs) were strongly associated with walnut consumption.

Specifically, an increase in the abundance of Bifidobacteriaceae species and members of the Ruminococcaceae group was observed. Probiotic Bifidobacterium species, commonly present in a healthy human gut, are well known for their beneficial properties. Changes in their relative abundance and composition are often linked to gastrointestinal conditions such as colorectal cancer and inflammatory bowel disease. Ruminococcaceae species, key members of the Clostridiales order (Clostridium sp. cluster IV), play critical roles in metabolic processes due to their production of butyric acid and constitute a significant portion of the human gut microbiota. Our findings align with prior research in which participants consumed 42 g/day of walnuts over three weeks. That study also reported a significant increase in the relative abundance of the Clostridiales group. Similar results were observed in studies on rats, where feeding walnuts for 10 weeks increased species diversity and the abundance of probiotic-like bacteria, including Lactobacillus spp., Ruminococcus spp., and Roseburia spp. Our findings further revealed a notable decrease in two members of the Lachnospiraceae family, in addition to the significant increase in Ruminococcaceae and Bifidobacteriaceae. These microorganisms, commonly found in the human microbiome, are known for producing butyric acid. Additional investigation is required to understand this discrepancy, as the intervention duration and walnut serving size were greater in the rat studies.

Participants were instructed to alter their diets during the walnut intake phase by reducing fat, carbohydrates, or both. To assess whether these dietary changes influenced the gut microbiota, we conducted a subgroup analysis. Substantial differences in the relative abundance of three microbial species (Ruminococcaceae, Lachnospiraceae, and Bacteroidaceae) were observed across different food types. However, pairwise comparisons revealed no consistent patterns or trends, making it difficult to draw definitive conclusions about the effects of macronutrient restriction. Notably, the substitution of fat or carbohydrates (or both) with walnuts suggests that participants’ overall diets remained relatively unchanged despite varying dietary advice. Moreover, because this study was conducted as a “free-living study,” consumption of phytonutrients such as flavonoids, carotenoids, and polyphenols, as well as dietary fiber, may have varied among participants.

The prebiotic effects of nuts, particularly walnuts, have only been briefly explored in feeding experiments. Therefore, the specific mechanisms by which walnuts alter the composition of the microflora to favor butyrate-producing microorganisms and shift the relative abundance of microbial communities remain unclear and require further investigation.

Additionally, the indigestible components of nuts, particularly their polyphenols and polysaccharides, which are similar to dietary fiber, appear to have a prebiotic impact. This effect is achieved by encouraging the development of beneficial bacteria, including Lactobacillus and Bifidobacterium species, which convert these indigestible components into butyrate and other short-chain fatty acids (SCFAs) (Amarlal et al., 2004). Butyrate has been shown to potentially exert positive effects on metabolic and inflammatory processes associated with disorders such as obesity, diabetes, and inflammatory bowel diseases (Dolcet et al., 1996).

Our findings indicate a link between walnut consumption and changes in the gut microbiome, suggesting potential prebiotic and probiotic advantages that could enhance the diversity and composition of the microbiome. Human clinical feeding studies further support the prebiotic characteristics of various tree nuts. For instance, a study comparing the effects of consuming almonds and pistachios found that pistachios had a stronger effect than almonds on the growth of beneficial butyrate-producing bacteria in the Firmicutes phylum. Research on raw, roasted, and almond seed and skin, conducted both in vitro and in vivo, indicates that consumption may stimulate the growth of beneficial Lactobacillus spp. and Bifidobacterium spp. in the digestive tract (Barbas et al., 1993).

Although our results are observational, they suggest that nuts, particularly walnuts, could serve as an important dietary supplement for improving gut microbiome health and blood lipids. However, the precise relationship between the observed microbiome changes and fasting lipid metabolism remains unclear, and the substantial heterogeneity in microbiome changes detected in our study precludes definitive conclusions. Future research should investigate the relationship between specific metabolites and microbial community structures to better understand the interactions between the microbiome and the host, particularly in the context of specific diseases and therapeutic interventions (Brookshire et al., 2003). Analyzing metabolic signatures could provide insights into how regular walnut consumption affects microbial architecture.

Further interventional nutritional studies are necessary to elucidate the mechanisms by which walnut components influence microbiome composition and enhance the abundance of butyrate-producing bacteria. Additional investigation is also needed to determine whether the gut microbiota changes associated with walnut consumption persist over extended periods.

6.4 Variation in Microbiome (Mycobiome) in Peanuts

The oral microbiomes of peanut-allergic participants showed fewer species of Lactobacillales, Bacteroidales (Prevotella), and Bacillales, along with more Neisseriales spp. Peanut consumption was associated with notable decreases in short-chain fatty acids (SCFAs) such as acetate, butyrate, and propionate, as well as a significant increase in interleukin-4 (IL-4) production, correlating with a unique oral microbiome profile. In peanuts from LN, SD, HB, and GD, there were 88, 98, 85, and 56 operational taxonomic units (OTUs) on average, respectively, and 33, 43, 35, and 22 fungal genera were detected. These findings suggest that peanuts stored in SD had the highest fungal diversity, indicating that SD’s moderate climate supports fungal variety. Conversely, peanuts stored in GD exhibited the lowest fungal diversity, despite higher temperatures and relative humidity (RH) than in other locations.

Among the 22 fungal genera identified, Eurotium, Aspergillus, Emericella, and Penicillium were the most prevalent, collectively accounting for over 85% of the total relative abundance. Emericella and Rhizopus predominated in peanuts stored across all four locations, possibly due to superior substrate adaptation, particularly during storage (Ding et al., 2015). The presence of Aspergillus, Penicillium, and Rhizopus aligns with prior studies on peanuts from Brazil, which utilized conventional isolation, enumeration, and identification methods on DRBC and AFPA media. However, fungi such as Eurotium, Clonostachys, and Emericella were undetected in those studies, likely because they do not thrive on DRBC or AFPA media.

The relative abundance of Aspergillus increased significantly between the seventh and 12th months of storage. Peaks were observed during the 11th month in LN, the 7th month in SD, and the 12th month in both HB and GD, with a marked increase in HB peanuts reaching 40.40% from months 9–12. These results align with earlier findings from Brazil and India, where Aspergillus sp. frequencies were higher in peanut kernels stored for 7–12 months compared to the first six months.

The increase in Aspergillus and Penicillium species, often classified as storage fungi, can explain the rise in Aspergillus sp. abundance (Xing et al., 2016). This phenomenon supports the idea that aflatoxin-related risks for peanuts increase with prolonged storage, especially beyond six months. During the seventh to 10th months of storage—summer months characterized by high temperature and RH—the concentration of aflatoxin B1 (AFB1) was elevated but remained below 5 µg/kg. Similar contamination levels have been frequently reported in Chinese studies examining aflatoxins in peanuts and derived products (Ding et al., 2012).

Interestingly, the relative abundance of Aspergillus flavus was low (0.06–6.04%). This outcome can be attributed to the low water activity (aᵥ) of 0.40–0.70, which falls below the minimal range of 0.70–0.80 for A. flavus growth (Hocking, 1997) and 0.80–0.90 for aflatoxin formation (Passone et al., 2010, 2012). Additionally, RH ranged from 48% to 83%, and the mean temperature varied from 1°C to 30°C. These conditions were below the optimal range of 32–33°C for A. flavus growth and 83–85% RH for aflatoxin production, as reported by Hocking (1997).

Despite the rising relative abundance of Aspergillus spp. from months 9–12, particularly in peanuts from HB and GD, the AFB1 content of peanuts declined over the same period. It was hypothesized that this decrease was due to binding with peanut-derived compounds or degradation by other fungi. For instance, molds such as Alternaria sp., Cladosporium sp., Mucor sp., and A. niger were found to restrict A. flavus mycelial growth and diminish AFB1 production in co-culture experiments using yeast extract sucrose (YES) broth. Notably, A. niger has been shown to inhibit AFB1 synthesis, potentially through mechanisms such as substrate acidification. Oxalic acid and gluconic acid released by A. niger may block AFB1 formation (Brundett et al., 2009), while antifungal peptides (AFPs) derived from A. niger have also been suggested to inhibit A. flavus development and AFB1 synthesis (Lee et al., 2018; Xu et al., 2016). Furthermore, Xu et al. (2016) demonstrated that strain FS10 culture filtrates could effectively degrade AFB1.

In this study, 20 A. niger strains isolated from stored peanuts were observed to degrade AFB1. Specifically, strains A. niger N-01, N-02, and N-03 exhibited notable AFB1 degradation capabilities.

This research is the first to employ ITS2 sequencing technology to provide a comprehensive view of the mycobiome and its variation in stored peanuts. Peanuts stored in SD exhibited the highest fungal diversity, with 98 OTUs and 43 genera, followed by LN, HB, and GD. The predominant fungi were Aspergillus, Rhizopus, Emericella, Penicillium, Eurotium, and Clonostachys. Notably, Aspergillus prevalence increased with latitude (from LN to GD), indicating a greater risk of aflatoxins in peanuts due to higher temperatures and RH. The storage period also influenced aflatoxin risk, with higher Aspergillus levels during months 7–12 compared to the first six months. AFB1 levels rose during months 7–10 but declined thereafter, potentially due to A. niger-mediated degradation or interactions with peanut compounds.

6.5 Diversity and Spatial Distribution of Microbiome in Hazelnut

The current study found that various endophytic fungal species inhabit hazelnut (Corylus avellana) trees. Based on morphological and molecular traits, a total of 791 isolates were identified and classified into 24 species, most of which belonged to the phylum Ascomycota. Ascomycota are often the most frequently reported endophytic fungi in various woody plants (Comas et al., 2014), whereas Basidiomycota endophytes have received comparatively little attention. The frequency and diversity of fungi in hazelnut tissues revealed that leaves had a higher fungal frequency than other tissues. Additionally, leaves showed greater colonization by endophytic fungi than stems, while stems exhibited higher fungal diversity despite lower abundance. This may be attributed to the longer lifespan of woody plant stems, which makes them more susceptible to endophytic colonization and results in greater fungal richness throughout the plant’s life cycle (Comas et al., 2014).

Woody plant stems and bark, due to their extended lifespan and continuous exposure to air, rain, and dust, may promote fungal colonization, leading to increased frequency and species richness. In contrast, the shorter lifespan of leaves, even in evergreen trees, may explain their lower species richness. The chemical composition of plant tissues—such as terpenoids, phenols, and tannins—may also influence the distribution and frequency of endophytic fungi in hazelnuts (Mehlenbacher et al., 2014). Certain fungi, however, demonstrate tissue specificity, thriving in particular organs. For instance, in this study, Paraphaeosphaeria sporulosa was isolated exclusively from roots, while Pyrenochaetopsis sp. and Bjerkandera adusta were found only in stems and roots. Similarly, Angustimassarina sp. was detected only in leaves and stems. Tissue-specific endophytes have also been documented in earlier studies of other plant species (Amini et al., 2014).

Despite tissue-specific tendencies, some hazelnut endophytes were present in multiple tissue types. The study identified dominant species such as Alternaria alternata, Epicoccum nigrum, Fusarium equiseti, and Fusarium fujikuroi at varying frequencies across different tissues and sampling sites. For instance, A. alternata predominated in roots and stems at the Golestan site but was most abundant in leaves and roots in Mazandaran. In Zanjan, F. equiseti was the dominant endophyte in leaves and roots, while in Qazvin, Golestan, and Mazandaran, it was found exclusively in roots. Similarly, E. nigrum was prevalent in leaves, stems, and roots in Mazandaran and foliage in Golestan. This distribution suggests that specific endophytes may favor particular tissues (Fajardo et al., 2014) or migrate between host tissues during symbiosis establishment.

Geographic and climatic factors also play a significant role in shaping the colonization patterns of endophytic fungi in hazelnut tissues. Variations in fungal communities can be attributed to environmental selection, host domain range, and regional adaptations. For example, the northern regions of Iran (Golestan, Mazandaran, and Guilan) showed greater richness and diversity of C. avellana endophytes, likely due to favorable geographic positions and climatic conditions. Seasonal factors, such as cold and frosty temperatures, may influence the colonization rates and fungal diversity in hazelnut tissues. Studies have shown that endophyte diversity is highest in tropical and temperate climates, with microbial abundance decreasing at higher altitudes. These findings are consistent with reports on psychrophilic endophytes and Mediterranean plants (Mehlenbacher et al., 2014).

Geographical differences also affect endophyte composition in plant tissues, particularly when sampling locations have distinct topographies or climates. Using the Jaccard similarity index (Jc) to compare total isolates from six sites, Golestan, Mazandaran, and Guilan showed the highest overlap in C. avellana endophyte populations. This highlights the impact of regional variables on fungal community structure in hazelnuts.

The results of this study confirm a high density and diversity of fungal endophytes in hazelnut tissues, influenced by geographic and environmental factors. Common fungi found in hazelnut ecosystems include Aspergillus, Rhizopus, Emericella, Penicillium, Eurotium, and Clonostachys. Notably, fungal diversity was highest in peanuts stored in SD, followed by LN, HB, and GD. Variations in endophyte richness and distribution may provide insights into the ecological and functional roles of these fungi.

This study, the first to examine fungal endophytes in hazelnuts across diverse environmental and geographic conditions, underscores the need for further investigation. Understanding how endophytic fungi contribute to host ecosystems by producing secondary metabolites, regulating biochemistry, and responding to environmental changes is crucial for exploring their ecological significance.

6.6 Functional Modulation of Microbiome Association in Pistachionut

Restoring a normal microbial population has emerged as a new goal for both the prevention and treatment of disease. The gut microbiota has been recognized as a critical environmental factor contributing to the development of type 1 diabetes (T1D). The cytotoxic actions of T1D specifically target the β-cells of the islets of Langerhans, causing rapid and irreversible necrosis, which is the primary mechanism of its diabetogenic effect. The short-term toxicity of streptozotocin (STZ) to β-cells is attributed to its excretion, while the subsequent impairment of remaining β-cell function is linked to hyperglycemic toxicity. However, uncertainty remains regarding the direct impact of STZ-induced T1D on the host’s intestinal microbiota composition. Although the mechanisms underlying the onset of T1D in pistachio nut studies may differ, the microbial alterations following β-cell death are comparable. Consequently, the observed microbial shifts are noted to result from factors other than STZ treatment.

Notably, individuals at risk for metabolic syndrome have demonstrated higher faecal bifidobacteria levels when consuming a diet rich in monoun-saturated fatty acids. While not all gut microorganisms are evenly distributed in the faeces, the faecal microbiota generally reflects the microbial composi-tion of the colon, particularly the descending colon and rectum. Its broad use as a study tool is favored due to the simplicity and non-intrusiveness of stool sampling, which is widely adopted to investigate potential microbial associations with faecal microbiota.

Hyperglycemia induced by STZ significantly increased coliform and Enterobacteriaceae levels in pistachio nut studies. Compared to other nuts in the control diet, the diabetes group exhibited significantly lower populations of colonic enterococci. Interestingly, discrepancies were noted between findings from the faecal microbiota and the small intestine. For example, cecal and colonic coliforms, as well as E. coli counts, were lower in STZ-induced diabetes. Khorramirad et al. (2021) reported that although the luminal and mucosal microbial communities overlap significantly, they exhibit notable radial segregation in pistachio nut studies. Pistachio supplementation normalized Enterobacteriaceae and coliform populations in the ileum and jejunum while increasing bifidobacteria and lactobacilli levels. Similarly, pistachio consumption reduced enterococci, coliforms, and E. coli counts in the caecum while simultaneously increasing bifidobacteria and lactobacilli populations.

Faecal samples are commonly used to study gut microbiota due to ease of collection. However, questions remain about the extent to which faecal composition and functionality differ from those of mucosal microbiota. In this investigation, microbial communities in faeces were found to be distinct from colon-associated microbiota but shared similarities with microbial associations in pistachio nut studies. The term “intestinal microbiota” encompasses the diverse microbial communities within the gut, including luminal and mucosa-associated microbiota. The colon is divided into three main sections—proximal, mid, and distal—and its mucus layers generate varying microenvironments, supporting distinct microbial species. Consequently, discrepancies between faecal microbiota and colon-associated microbial communities adhering to or colonizing pistachio are both expected and justifiable.

Understanding the relationships between pistachio dietary elements, gut microbiota, and the etiology of T1D remains a compelling research focus. The connection between dietary pistachios, microbial shifts, and disease pathways offers valuable insights for future studies.

6.7 Microbiome (Metagenomic) Analysis in Chestnut

Potential biocontrol agents for soil-borne diseases in chestnut (Castanea spp.) include the widespread Pseudomonas spp. and the genus Bacillus, both recognized for their antagonistic properties against various plant pathogenic bacteria. The identified bacterial strains DAC17225011 and DAC17225014 exhibited a high degree of similarity (99%) to Bacillus sp. and Pseudomonas sp., respectively, and demonstrated strong antagonistic activity against Ink and root rot diseases of chestnut. Greenhouse studies using vaccinated chestnut seedlings showed no overt symptoms. However, hyphal patches observed in stained roots suggested potential Phytophthora cambivora and Armillaria mellea infection. Compared to roots inoculated solely with these pathogens, the number of infection spots was reduced in roots co-inoculated with antagonistic bacteria and/or arbuscular mycorrhizal fungi.

This finding indicates that antagonistic bacteria may exhibit similar effects under in vivo conditions, although symptoms in shoots may take time to appear, or the plants may develop resistance (Lee et al., 2018), even while carrying the pathogen. Another possible explanation for the absence of above-ground symptoms is that abiotic and biotic environmental factors influence the efficacy of these isolates. Infections may persist until the plant is completely decomposed, meaning that the in vivo performance of antagonistic bacteria may not always correspond to their in vitro effects. This highlights the necessity of direct in vivo screening for some biocontrol agents, as the opposite scenario—no inhibitory impact in vitro but positive effects in vivo—can occasionally occur.

Metagenome analysis revealed fungal community profiles in soils from four locations with conventional, organic, and wild chestnut cultivation systems. Soil management practices strongly influenced microbial profiles, with organic systems significantly altering fungal populations compared to conventional systems. In conventionally managed areas, the family Cerato-basidiaceae, which includes many pathogenic species, was more prevalent. In contrast, organic plots were dominated by the families Russulaceae and Boletaceae, which suggests that management strategies may foster certain fungal populations while suppressing others. Organic systems, in particular, appear to promote symbiotic fungi and reduce pathogen activity, although this does not confer complete immunity to root infections.

Some fungal species may serve as indicators for both natural areas and specific soil management practices in chestnut cultivation. While long-term organic management might increase fungal richness, other factors, such as sampling time and season, may have a more substantial impact on fungal communities than crop type or farming system. These variations are likely influenced by climatic changes and the legacy effects of previous crops. Additionally, the organic farming system exhibited higher soil pH levels compared to conventional and wild systems. Previous studies have shown that soil pH significantly contributes to variations in microbial populations associated with chestnut (Table 6.1).

Table 6.1 Examples of Significant P (< 0.05) of Arbuscular Mycorrhizal (Am) Fungal Inoculation in Nut Crops ⏎

Inoculum
Nut Crop
Parameter
AM
MR (%)
MPI
Substrate
References

G. fasciculatum

Walnut

Survival (%)

65

53.8

5

Fumigated soil

Kormanik et al. (1982)

G. mosseae (BEG12)

Walnut

60

66.6

9

Natural nursery field

Dolcet-Sanjuan et al. (1996)

G. intraradices (BEG72)

Walnut

80

75.0

9

Fumigated soil

G. mosseae and G. etunicatum

Walnut

Root collar diameter (mm)

6.7

11.9

5

Fumigated soil

Schultz et al. (1981)

G fasciculatum

Walnut

7.9

27.8

5

Fumigated soil

Kormanik et al. (1982)

G microcarpus and G. fasciculatum

Walnut

6.5

12.3

6

Steam sterilized soil

Melichar et al. (1986)

G. deserticola

Walnut

8.7

19.1

4.5

Fumigated soil

Dixon (1988)

G. mosseae and G. etunicatum

Walnut

Root mass (g)

48.3

69.2

5

Fumigated soil

Schultz et al. (1981)

G fasciculatum

Walnut

75.4

80.2

5

Fumigated soil

Kormanik et al. (1982)

G.microcarpus and G. fasciculatum

Walnut

102.0

52.9

6

Steam sterilized soil

Melichar et al. (1986)

G. microcarpus and G. fasciculatum

Walnut

Total root length (cm)

4897

20.8

6

Steam sterilized soil

Melichar et al. (1986)

G. etunicatum

Walnut

4500

33.3

4.5

Fumigated soil

Dixon (1988)

G intraradices

Walnut

Root volume (ml)

55.6

14.4

8

Fumigated soil

Brookshire et al. (2003)

G microcarpus and G. fasciculatum

Walnut

Total number of lateral roots

132

22.7

6

Steam sterilized soil

Melichar et al. (1986)

Gigaspora. margarita

Walnut

Number of lateral roots < 2 mm

15.5

13.5

4.5

Fumigated soil

Dixon (1988)

G. deserticola

Hazelnut

17.2

22.1

Steam sterilized soil

G. deserticola

Hazelnut

Stem height (cm)

32.1

12.1

4.5

Fumigated soil

Dixon (1988)

G. etunicatum

Hazelnut

49.6

10.1

8

Fumigated soil

Brookshire et al. (2003)

Dentiscutata heterogama

Hazelnut

60.0

33.3

3

Gamma irradiated soil

Fajardo et al. (2014)

G. mosseae and G. etunicatum

Cashewnut

Stem mass (g)

3.3

21.2

5

Fumigated soil

Schultz et al. (1981)

G.microcarpus and G. fasciculatum

Cashewnut

5.5

34.5

6

Steam sterilized soil

Melichar et al. (1986)

G deserticola

Cashewnut

5.6

30.3

4.5

Fumigated soil

Dixon (1988)

G intraradices

Cashewnut

6.5

13.8

8

Fumigated soil

Brookshire et al. (2003)

G microcarpus and G. fasciculatum

Pistachionut

Leaf area (cm)

1950

32.8

6

Steam sterilized soil

Melichar et al. (1986)

G deserticola

Chestnut

726

20.9

4.5

Fumigated soil

Dixon (1988)

Dentiscutata heterogama

Peanuts

7098

45.3

3

Gamma irradiated soil

Fajardo et al. (2014)

G mosseae and G. etunicatum

Peanuts

Leaf count

ND

Positive

5

Fumigated soil

Schultz et al. (1981)

Dentiscutata. heterogama

Macadamianut

17

29.4

3

Gamma irradiated soil

Fajardo et al. (2014)

The mycorrhizal response (MR) was calculated according to Plenchette et al. (1983) as follows: MR = 100* (mean value of AM plants-mean value of non-inoculated plants)/mean value of AM plants. Glomus is abbreviated GAM mean values measured in inoculation.

6.8 Mycological Quality of Pecan Nuts

The third most frequent genus identified was Fusarium, well known for producing mycotoxins, and it was present in a substantial number of samples from all geographical areas. Approximately 30% of the samples contained Cladosporium, a fungus associated with “scab” disease in pecan nuts. Alternaria sp., which was linked to pecan kernels with dark discoloration, was only detected in samples from the southwestern region. These findings are consistent with a prior study conducted in Paraná (Egamberdieva et al., 2017), which also identified significant mycotoxin-producing micro-organisms in pecan nuts, including Alternaria sp., Aspergillus ochraceus, A. and Penicillium sp. However, the current study did not include aflatoxin testing, making it the first analysis of aflatoxins in Brazilian pecan nuts.

Three pecan cultivars (Frotcher, Burkett, and Moneymaker) were examined, showing variability in contamination by toxigenic Aspergillus species (A. flavus, A. niger, and A. ochraceus) during storage, with the Frotcher cultivar being the most susceptible. This variability suggests the potential for selecting pecan cultivars with higher resistance to aflatoxigenic microbiome species to control mycotoxins. A. flavus infection susceptibility appears to differ significantly among pecan genotypes.

Analytical methods for aflatoxin quantification included a limit of quantification (LOQ) of 1 µg/kg and a limit of detection (LOD) of 0.1 µg/kg for aflatoxins B1 and B2, and 0.3 µg/kg for aflatoxins G1 and G2, based on signal-to-noise ratios of LOQ = 10:1 and LOD = 3:1, respectively. Matrix effects were assessed by comparing analytical curves with and without matrix addition to ensure accuracy. The absence of aflatoxins in Brazilian pecans aligns with findings from the United Kingdom and Portugal (n=2 each) (CAC, 2004; Gatheru et al., 2017).

In contrast, aflatoxin contamination has been reported in pecans from Mexico and the United States. Sixteen pecan samples from Mexico contained total aflatoxin levels ranging from 0.23–1.30 ng/g, while walnuts and cashew nuts showed values between 0.05–12.10 ng/g. Additionally, aflatoxin contamination of various nuts and nut products was documented by the European Commission’s Rapid Alert System for Food and Feed (RASFF) in 2016, with pistachios, groundnuts, and hazelnuts being the most frequently contaminated. However, pecan nuts were not mentioned in that report.

As a result, pecans may present a safer option compared to other nuts in terms of aflatoxin exposure. In early storage of pecan nuts harvested in Southern Brazil, our study identified ten fungal species. Although there were commonalities in the isolated fungi, contamination levels varied by region. The most frequently observed species included xerophilic Aspergillus spp. (A. wentii, A. ruber, and A. chevalieri), known as potential spoilers of low-water-activity foods. These species typically cause off-flavors rather than producing significant toxins. Fortunately, no aflatoxigenic species were isolated, and no aflatoxins were detected in the examined pecan nuts.

From a public health perspective, the absence or rare occurrence of highly carcinogenic mycotoxins in pecans grown in Brazil is a positive outcome with implications for the nut industry. Compared to other nuts, pecan nuts appear to offer a safer option for consumers in terms of microbiological safety and toxin exposure.

6.9 Plant-Microbiome Association in Cashew Nut

Cashew nut trees (Anacardium occidentale) are a type of plant whose health and productivity are significantly influenced by their interactions with microbiomes. These trees form intricate relationships with various microbial communities in the soil and on their root surfaces, which play a crucial role in overall plant health and development. A diverse range of microorganisms, including bacteria, fungi, archaea, and others, engage in dynamic interactions with the root system of the cashew nut plant (Kuipur et al., 2004). These microorganisms are essential for resilience and productivity, contributing to nutrient cycling, disease prevention, and stress tolerance.

Mycorrhizal fungi are a key group of microorganisms in the cashew nut microbiome. They form mutualistic associations with cashew nut roots, enhancing the plant’s ability to absorb water and essential nutrients like phosphorus and nitrogen from nutrient-poor soils. Additionally, the cashew nut microbiome is abundant in nitrogen-fixing bacteria, which convert atmospheric nitrogen into a plant-usable form. This reduces the dependence on synthetic fertilizers and promotes sustainable farming practices.

Beyond supporting growth, the diverse microbial communities in the cashew nut microbiome also play a role in disease prevention. Some microbes act as natural antagonists against plant pathogens, protecting cashew nut plants from harmful diseases and ensuring healthy harvests. Factors such as soil type, climate, and agricultural practices significantly influence the microbial diversity within the cashew nut microbiome. Sustainable farming practices, including reduced pesticide use and organic soil management, can enhance the richness and variety of beneficial microorganisms in the plant’s environment.

Understanding the complex interactions between cashew nut trees and their microbiomes is of great interest to researchers and agricultural specialists. Insights into these relationships may lead to innovative agricultural practices aimed at improving cashew nut productivity, quality, and resilience to environmental stressors. However, due to the complexity and contextdependence of plant-microbiome interactions, further research is required to elucidate the specific roles and functions of different microbial species within the cashew nut microbiome and their potential applications in sustainable agriculture (Fukami et al., 2018).

In conclusion, the microbial diversity of the cashew nut microbiome is essential for maintaining the health and productivity of cashew nut trees. This symbiotic interaction facilitates nutrient uptake, disease prevention, and stress tolerance, ultimately determining the viability and performance of cashew nut farming. As we continue to explore and understand the intricacies of plant-microbiome relationships, we can leverage this knowledge to develop advanced agricultural practices that benefit both the cashew nut industry and the environment.

6.10 The Edible Plant Microbiome: Diversity and Human Health

There is an intriguing overlap in terms of species diversity and function with regard to our first hypothesis on the relationship between the plant and human gut microbiome (Ling et al., 2022). The idea that low pH values act as severe barriers for microbial passage has been called into question by recent research that shows the stomach is colonized by a wider variety of microbial species than previously thought (Pausch et al., 2013). Notably, strains, including probiotics, have been demonstrated to successfully develop in the gut after surviving the stomach passage (Arya et al., 2010). This shows that our immune system may be significantly stimulated by bacteria found in our diet, such as Enterobacteriaceae. The second theory holds that microorganisms found in the diet, such as Enterobacteriaceae, stimulate the immune system. Atopy and bacterial diversity are correlated. They also discovered a favorable correlation between interleukin-10 expression in healthy people and the prevalence of Acinetobacter. To maintain immunologic tolerance to benign substances, interleukin-10, an anti-inflammatory cytokine, is essential. Endotoxin from Gram-negative bacteria, such as Enterobacteriaceae, has been shown to have immunomodulatory and allergy-protective effects.

Plant microhabitats operate as a reservoir for Enterobacteriaceae, which may include harmful bacteria like enteric pathogens. These human intestinal infections are more prevalent after intermediate disruptions. While outbreaks of enteric pathogens linked to fresh food, such as uncooked or lightly processed nuts, have grown recently (Bakker et al., 2013), Gatharu et al. (2017) note that the ecology of enteric diseases outside human and animal hosts is still poorly known. If Enterobacteriaceae are naturally found in some nut plants, this suggests that they have long been a part of the human diet. These outbreaks seem more like accidents than the usual given the broad consumption of nuts and fruits around the world and the custom of eating food without considerable preparation or sterilization. The likelihood of the plant-associated microbiota playing a pathogenic rather than immunostimulant or “natural vaccination” role is higher (Figure 6.1).

Figure 6.1 Plant-microbiome association in nut crops.⏎

6.11 Conclusion

In conclusion, this chapter has delved into the intricate relationship between nut crops and their associated microbial communities, shedding light on the pivotal role of microbial diversity in shaping the health, productivity, and ecological sustainability of nut crop systems. Through an exploration of the current state of research, we have gained valuable insights into the mechanisms underlying the plant-microbiome association, as well as the potential benefits and challenges it presents for nut crop cultivation. The diversity, composition, and function of microbial communities in nut crops have been shown to have significant implications for plant health and growth. Beneficial microorganisms, acting as biofertilizers, biocontrol agents, and growth promoters, have emerged as promising tools for enhancing nut crop productivity while reducing reliance on chemical inputs. Concurrently, we have also recognized the importance of understanding the pathogenic microbial agents that can lead to devastating diseases, threatening both the quality and yield of nut crops. By advancing our understanding of the plant-microbiome association, we can unlock the full potential of microbial diversity in nut crop systems, ushering in a new era of sustainable and resilient agriculture.

Keywords

extremophiles

halophiles

microbial diversity

microbiomes

nutrient acquisition

osmophiles

temperate nuts

thermophiles

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Chapter 7 Advancement of Propagation in Temperate Nut Crops

GRANDHI N. V. G. K. S. NIMITA, VIKANKSHA, JAGRUTI SINGH, ARUN KUMAR, and JATINDER SINGH*

Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

*Corresponding author

Abstract

Plants won’t be true to type, when grown from seeds, so the best alternative and most used method of propagation is either by roots or cuttings or layering or through budding, grafting using rootstocks of other plant roots. Sexual propagation can be explained as multiplication of plants through seeds developed by the union of female and male gametes. Whereas asexual propagation, also called clonal propagation, is a technique independent of female and male gametes. Nut crops like hazelnut, pecan nut, cashew nut, almond, and chestnut, have high nutritional importance and are consumed daily all over the world. With the increase in market and consumer demand, and increased consciousness of health production needs to be exponential, which is only possible by clonal propagation techniques because fruits crops consume a longer growth and vegetative phases when grown sexually. In this chapter, we discuss the advancements in propagation techniques over the decades in temperate nut crops.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

7.1 Introduction

Consuming fruit nuts enhances health by promoting anti-cancer, and antidiabetic activities and meets the requirement of essential nutrients to humans. Nuts show high lipid content. In almonds, lipids comprise 40–67% dry weight, with similar values for pistachio, around 50–62% (Rabadán et al., 2018). In walnuts, this concentration is even higher, reaching 60–72% of walnut dry weight (Grilo and Wang, 2021). Nuts are a significant source of vitamin E as they have a good content of tocopherols (Lu et al., 2019). Total tocopherol concentration ranges from 194–297 mg/kg in walnut and 350–550 mg/kg in almonds with average values around 350 mg/kg in pistachios (Puri et al., 2021). The nutritional composition varies significantly based on the area, climate and rootstocks used during early growth stages (Gautier et al., 2020). Using resistant planting material along with favorable climatic factors influences the quality and vigorous nature of trees (Freitas et al., 2021).

Production of nuts starts with the production of seedlings. True seedlings can be produced by different propagation techniques i.e., asexual, and sexual (Chauhan et al., 2021). Propagation of nut trees can generally be multiplied through seeds, cuttings, layering, budding, grafting, and micropropagation (Figure 7.1). In Iran, nut tree crops are typically propagated by sowing seeds and grafting them onto seedling rootstocks (Rovira, 2021). Although hardwood and semi-hardwood cuttings can also be used to propagate nut trees, they are not frequently employed due to their poor success rate. Layering is a low-efficiency strategy for nut tree propagation, much to chopping (Mir et al., 2019).

Figure 7.1 Different propagation methods in apple, pear, plum and cherry. ⏎

7.2 Different Propagation Techniques for Nut Crops

7.2.1 Propagation by Seeds

Over time, there have been significant developments in propagation techniques that have revolutionized the propagation of fruit and nut crops. These advancements have resulted in improved yields, disease resistance, and adaptability to changing environmental conditions (Dwivedi et al., 2023). The field of fruit and nut crop propagation has seen remarkable progress, ranging from traditional methods like seed propagation to cutting-edge techniques such as tissue culture and genetic engineering (Gantait et al., 2021).

Preserving desirable traits from parent plants is crucial in horticulture for plant reproduction (Ak et al., 2021). Various techniques can be employed to optimize nursery production systems and address different challenges, depending on the species (An et al., 2021). Propagation methods play a vital role in enhancing temperate nut crops as they allow for the multiplication of plants with desired characteristics, including disease resistance, improved nut quality, and higher yield potential (Savadi et al., 2020). For example, NBF, which leads to the failure of new vegetative buds to grow in almonds (Prunus dulcis Mill.), is a significant problem in fruit cultivation (D'Amico-Willman et al., 2022). To tackle such issues, it is essential to adopt appropriate nursery practices, utilize suitable plant materials, and employ accurate methods.

Vegetative propagation is an economically important technique used in seedling production for a wide range of fruit species and rootstocks (Awotedu et al., 2021). This method involves using plant organs such as roots, branches, and leaves to produce clones of plants (Eliyahu et al., 2020). The strength, longevity, and durability of the trunk, especially in woody plants, depend on various factors, including air and humidity conditions, the position of organs (proximal and distal), aboveground and underground parts, as well as the sequential development of adventitious roots (Freschet et al., 2021). Vegetatively propagated rootstocks have specific and consistent effects on the variety (Jananai et al., 2020). Consequently, it is possible to achieve complete standardization of fruit and nut production and streamline marketing using representative samples and standardized rootstocks.

Various propagation techniques and advancements have emerged for commercial purposes (Ali et al., 2020). This book chapter aims to provide a comprehensive overview of the latest advancements in propagation techniques for temperate nut crops. In recent years, significant progress has been made in the field of propagation of temperate nut crops, including the development of new techniques and applications of existing methods.

7.2.2 Micropropagation

Clonal propagation refers to the process of producing genetically identical copies of a cultivar through asexual reproduction (Devi and M., 2021). In nature, clonal propagation occurs through apomixis, which involves the development of seeds without meiosis and fertilization, as well as vegetative propagation, where new plants are regenerated from vegetative parts (Ibañez and Quadrana, 2023). Tissue culture has become a popular method for vegetative propagation of plants (Tripathi et al., 2021). The aseptic technique used for clonal propagation is known as micropropagation, which offers the advantage of producing many true-to-type plantlets from a single individual within a relatively short time and space (Sivagamasundari, 2020). It is important to note that micropropagation is currently the most commercially viable method for clonal propagation of most horticultural crops.

7.3 Some Salient Advances in Propagation Techniques in Individual Crops

7.3.1 Hazelnut

Hazelnut (Corylus avellana L.) is a multi-stemmed big shrub that has an elevated level of antioxidant and plant-based nutrients, that help to avoid the development of heart and cancer disorders by neutralizing free radicals (Mars, 2016). The training strategy for hazelnut production entails the elimination of suckers which arise throughout the year. In big fruit trees, maintaining suckers constitutes a substantial agricultural effort, including several herbicide applications across the year and sometimes human eradication over winter. Cristofori et al. (2015) have lately advised the introduction of non-suckering rootstocks, together with alternative orchard administration techniques including sub-irrigation networks and automated pruning, as novel innovations for hazelnut growers. Silvestri et al. (2021) conducted a study on the impact of nut and kernel quality based on variety selection (Figure 7.2). Their findings indicated that pruning on mature trees significantly increased intensity and yield, leading to improved kernel quality. In heavily trimmed plants, there was a 1% increase in the kernel/nut proportion. Machine pruning has also emerged as a new trend and has been implemented in many orchards (Karkee et al., 2021).

Figure 7.2 Growth cycle of the hazelnut tree. ⏎

7.3.1.1 Hazelnut Rootstock Materials

Corylus colurna L. have been extensively studied to determine their suit-ability as rootstocks (Rovira, 2021). These seedlings offer several benefits, including an extensive network of roots and a lack of suckering tendency. They form strong calluses and heal quickly at graft connections. C. colurna seedlings have been found to be compatible with all genotypes and species of Corylus tested (Vahdati et al., 2021). The association between C. colurna rootstock and C. avellana scion is easily distinguishable due to variations in bark texture and color. However, C. colurna has some drawbacks as a nursery tree (Karp and Gasic, 2022). Almost four years may pass between sowing and germination, and the young trees sometimes need a further two years to mature before they are ready for grafting. Digging, interacting with, shipping, and transplantation are difficult due to the existence of hard lateral roots and a strong tap root. Weak root systems in hazelnut trees can lead to difficulties in survival and slow establishment in the orchard. Additionally, asexual reproduction of Turkish tree hazel is challenging, with cutting-based propagation and layering methods being ineffective. These characteristics make it less likely for corporate breeders to regularly employ C. colurna as a clonal or seedling rootstock (Lelu-Walter et al., 2013). However, through careful selection and multiplication, C. colurna seedlings with transitional features between C. colurna and C. avellana have been identified (Rovira et al., 2022). “Dundee” has lighter and silvery bark, while “Newberg” has lighter and coarser bark, falling between “Dundee” and C. colurna. These rootstocks provide energy to the scion cultivar and do not produce suckers. However, their properties differ from those of the female parent, indicating their status as interspecific hybrids (Mehlenbacher, 1991). Despite their great potential, these clonal rootstocks have not been extensively utilized in major exporting nations. One reason is the susceptibility of “Dundee” and “Newberg” to eastern filbert blight, by the major fungal pathogen Anisogramma anomala (Peck) E. Müll (UK, 2014). Because the two rootstocks seldom generate suckers, propagating any scion on a rootstock is not recommended since the suckers may act as an indicator of fungal disease. A rootstock study at Tarragona, Spain, revealed the advantages of utilizing the rootstocks “Dundee” and “Newberg” alongside the primary hazelnut cultivars “Negret” (Botta et al., 2019). Such rootstocks decreased sucker development, enhanced efficiency, and vigor, and resulted in better nut harvests at lower prices. The grafted trees were also tolerant to iron chlorosis and kept their leaves for a greater amount of time, providing for higher nutrient absorption through the soil. Several research centers and institutions throughout the globe are now studying hazelnut rootstock (Mir et al., 2023). In Italy, the University of Torino and the University of Tuscia have begun studies focusing on grafting Italian hazelnut cultivars onto “Dundee” and “Newberg” rootstocks (Valentini, personal communication; Silvestri, 2015). The purpose of the tests is to contrast the results of grafted trees to that of self-rooted solitary and multi-stem shrubs. In a comparable manner, investigators at the University of Craiova in Valcea, Romania, grafted numerous hazelnut cultivars onto “Dundee” and “Newberg” rootstocks to assess their growth rates (trial year: 2016–2017).

In hazelnut investigations, strong cultivars that generate fewer suckers, such as “Daviana” in the United States and “Merveille de Bolwiler” in Europe, have been used (Beltramo et al., 2016; Silvestri, 2015). Trials comparing self-rooted plants to grafted plants produced variable accomplishments, with self-rooted trees displaying superior growth and production in certain circumstances. However, when grafted with the “Negret” scion cultivar, the choice of appropriate rootstocks, particularly “Tonda Bianca” and the clonal rootstock “TB-69” developed to it, has demonstrated excellent results (Rovira et al., 2022). Because of their drought and low humidity resistance, and indigenous hazelnut varieties in Karaj, Iran, were additionally chosen as appropriate rootstocks.

7.3.1.2 Types of Grafting in Hazelnut

Improved grafting techniques have revolutionized hazelnut propagation, generating renewed interest in the use of rootstocks. One such advancement is the introduction of the “hot-callusing pipe” method, which involves the targeted application of heat to the graft union while maintaining cooler temperatures for the rootstock and scion buds (Carey et al., 2013). This technique ensures optimal callusing conditions, typically at 27°C for a duration of 21–28 days, resulting in graft success rates exceeding 90%. The hot-callusing pipe has proven to be a cost-effective and efficient approach for large-scale grafting in hazelnut nurseries, thus gaining significant importance (Rovira, 2021). Several crucial factors contribute to the success of grafting, including the use of well-rooted rootstocks, appropriate moisture maintenance in the surrounding sawdust, thorough sealing of the graft union using different methods like overlapping wraps (Bradley and Garner, 2017).

7.3.2 Chestnut

Castanea is a genus containing seven species of deciduous trees and shrubs in the Fagaceae family (Alves et al., 2022). These shrubs, also known as Castanea spp., are extremely valuable owing to the widespread territorial across the globe, environmental significance, and varied uses for humans (Freitas et al., 2021). These are used for lumber manufacturing, nut gathering, and a variety of applications, demonstrating versatility (Cialdella et al., 2023). Micropropagation, especially using base branches and stub buds with immature traits, is a particularly successful strategy for clones’ multiplication of chosen peak genotypes, which are normally recognized throughout the developmental stage (Martnez Santiago, 2021). Castanea has an elevated suffix of heterozygosity and large localized genetic heterogeneity (Cavallini et al., 2022). Furthermore, the rooting responses of these kinds of plants are impacted by various genotypes, posing difficulties in developing uniform procedures that apply to the whole genus (Pavese et al., 2022). As a result, investigations should be customized to specific species and genotypes. Notwithstanding the latest developments, industrial vegetative multiplication of chestnut species continues to be a serious challenge for forestry.

7.3.2.1 Propagation by Grafting

Grafting plays a vital role in horticulture, serving various purposes such as propagating specific cultivars and supporting breeding programs (Habibi et al., 2022) (Figure 7.3). It is used to create germplasm banks and core collections, grow mature plants such trees, and rejuvenate plants for subsequent propagation through methods like cuttings, layering, and micropropagation (Gladfelter, 2019). In the case of chestnut cultivars, traditional grafting techniques like bark grafting in spring or flute grafting are commonly employed, even in newly established orchards (Nazir et al., 2023). Nurseries utilize different budding and grafting methods, with summer budding techniques such as patch budding, and T-budding being preferred due to their ease and effectiveness in rapid healing under higher temperatures (Singh, 2020). Moreover, to note that trees budded during the summer season require more time to reach market readiness, typically until the following winter. On the other hand, spring grafting techniques like chip grafting, cleft grafting (Kulaç and Nayır, 2021), and whip grafting (Uyanık et al., 2022).

Figure 7.3 Propagation in chestnut. ⏎

7.3.2.2 Propagation by Cuttings

Chestnuts may only be propagated vegetatively if the parent plant material, which is where the cuttings are taken, is under a certain age (Vielba et al., 2020). Cuttings taken using matured plant material might be difficult, even impractical, to root. The more efficient technique, nevertheless, is green-wood or softwood cuttings taken from 3–4-year-old mother plants, that may be cultivated either outdoors or in a greenhouse as potted plants. It is advised to gather cuttings with 3–4 buds and a length of 10–15 cm while propagating chestnuts using cuttings (Voigt et al., 2020). It’s crucial to preserve the highest leaf’s whole top half. Normally, this gathering procedure happens during May and July. IBA or NAA is applied to the bottom of the cuttings in quantities that vary from 1,000–4,000 ppm to improve rooting (Basuchaudhuri, 2021). The cuttings are treated, then put in pots containing the proper materials and inserted into rooting chambers with a fog system. It ought to have mentioned that the genotype of the chestnut affects the effectiveness of this multiplication technique (Rodriguez et al., 2005).

7.3.2.3 Propagation by Layering

When growing primary production vegetation, resilient Eurasian hybrids, or rootstocks by clonal propagation, chestnut stacking is a popular vegetative propagation technique in European nations (Beccaro et al., 2019). This method entails the yearly growth of sprouts from stumps that, independent of the maturity of the mother plant, exhibit an immature state of being that allows shoots to root following suitable auxin treatments (Vielba et al., 2020). Normally in May, once the sprouts measure 30–35 cm in length, the lowest 8–10 cm are meticulously defoliated. The removed portion of the sprout is covered with a paste comprising IBA, NAA, or a mixture of the two at a rate of 2 g/kg Vaseline® (Mandal et al., 2021). After that, earth is used for covering the region that has been treated. The rooted shoots are taken from the mother tree and placed in a nursery during the shoots’ resting phase, which is typically around November, in order to enhance its root structure (Clark et al., 2023). It is crucial to remember since the particular genotypes of the chestnut has a considerable impact in terms of the quantity of shoots and rooting levels.

7.3.3 Walnut

The development of several propagation techniques for walnut, including epicotyl grafting, omega grafting, side stub grafting, tongue and whip grafting, V or saddle grafting, chip budding, patch budding, shield budding, and topworking, as well as recent tissue culture systems, as well as propagation by micro shoots including somatic embryogenesis, has been the subject of extensive research over the past 25 years. In these studies, callus quality, graft combination, survival, and scion development, etc. were examined in greenhouse, shade house, and open field conditions in relation to type of grafting and time. Many walnut grafting nurseries and tissue culture labs that commercially propagate walnut cultivars and rootstocks for domestic and international markets have been established because of these projects and successful approaches.

One of the popular conventional methods for walnut propagation and topworking that was mentioned by Vahdati et al. (2002) is grafting. Above all, Vahdati and Aalifar (2016) recently reviewed each of these techniques in depth. The multiplication of nut trees, like that of other woody plants, is still frequently exceedingly challenging. Currently, the two most common methods employed in the development of grafted walnut trees are budding and grafting. It is challenging to propagate walnuts due to poor callus formation. Cutting-based walnut propagation is a challenging technique to implement. The most popular method is patch budding. Bench grafting and heated callus are further techniques. Hot callus has been effectively employed in recent years to propagate walnut cultivars, however, by the conclusion of the growing season, the height of the trees is insufficient. Epicotyl grafting is also a novel method of walnut propagation.

7.3.3.1 Propagation by Budding and Scion Grafting

Currently, the most common grafting techniques used to produce walnut trees are scion grafting and budding. In walnut, patch budding is mostly used to carry out the budding process. This is one of the most time-tested and widely used methods for growing walnuts in an outdoor nursery. The effectiveness of the grafting technique varies among the various nations (Ozkan et al., 2001). Solar et al. (2001) revealed that only 16% of walnut propagation attempts using the patch budding method were successful in Slovenia while Ozkan et al. (2001) explained that the percentage in Turkey is 88.3% in the autumn, 72.5% in the spring, and 41.25% before the trees were removed from the nursery. Success in such a scenario is probably influenced by the regional environment in the countries where the application was submitted. Although they are not the sole limiting factors, winter frosts and spring late frosts reduce the percentage of tree survival. Air temperature is crucial after grafting. As mentioned previously, post-grafting low temperatures that impede or prevent callus development might cause grafting outside to fail, according to Lagerstedt and Roberts (1972). When growing walnuts outdoors in South Bulgaria, the percentage of survival rate is decreased by the variation in temperature between day and night. Because of this, grafted trees struggle to survive in the open in West European countries where day and night temperatures differ significantly, according to research by Gandev and Dzhuvinov (2006). The primary walnut grafting method used in Bulgaria is patch budding. Unstratified seeds are spread at a depth of 8–12 cm between the middle of November and the first 10 days of December. The plants are also tilled and earthed up to form a thin and delicate soil crust where the grafting would take place. Herbicides are employed to maintain the soil free of weeds during the growing process. The formation of calluses on fruit trees is known to be influenced by temperature, with different temperature values depending on the species (Hartmann et al., 2002). According to Sitton (1931), the optimum temperature for the formation of calluses in walnuts is 27°C. According to further studies by Reil et al. (1998), callus production in walnuts is inadequate at temperatures below 20°C (Hartmann et al., 2002). Between 26°C and 27°C is the optimal range. However, Rongting and Pinghai (1993) also state that 22°C is good. Many scientists agree that a temperature of 27°C (2°C) should serve as the standard for doing successful walnut grafting under regulated temperature (Vahdati and Zareie, 2006). Regarding the selection of a particular grafting technique, there is no universally accepted viewpoint. Various improved techniques have been employed (Muzaffar and Kumar, 2011); cleft grafting; grafting of the omega type; and side grafting has also been used. Hypocotyl grafting is another technique for propagating walnuts (Avanzato, 2001). The approach has become more significant in recent years (Gandev, 2008). In that procedure, potted seedling rootstocks are employed. During the vegetation phase, grafting is done. Gandev and Dzhuvinov (2006) documented that the grafting approach has an 83% survival rate. The heated callus technique was explained by Lagerstedt in submissions from 1983 and 1984.

A heating cable maintains a temperature of 26°C (2°C) at the grafting site. After being grafted onto the one-year-old rootstocks, they are dug up from the ground and positioned horizontally over the heat source with sawdust covering the roots. Erdogan (2006) used electric heating cables to create successful results to assess the method’s efficacy. In addition to employing an electric wire, Avanzato (1999) produced a different method for heating the grafting location without removing the rootstocks from the soil. By leaving the rootstocks in the ground, the stress on them is lowered, and following the grafting technique, the growth of the graftage is promoted. Gandev (2009) evaluated and modified the electric heating system in Bulgaria. The electric cable is then laid in a groove and coated with peat in a steel-and-glass greenhouse using a simple device. The required temperature is maintained constant by the thermal regulator. The roots of the cleft grafted plants, which are spaced 10–15 cm apart parallel and perpendicular to the trench, have been covered with sand. Directly above the heating cable is where the grafting should be performed.

Wet foam is adhered firmly above the groove and the grafted plant to maintain high air humidity in the grafting area. The scions are 12–15 cm long and have 1–2 buds. The temperature should be maintained at approximately 27°C ± 1°C, with high air humidity for four weeks at the grafting site. Plants that have developed calluses are adapted and, in the spring, are planted in the fields. Nacheva and Gandev (2009) utilized radioisotopes to track the movement and concentration of ***14C-photoassimilates in hot callus-propagated walnut seedlings. Their findings showed that the transfer of photoassimilates in grafted plants was unaffected by the propagation method used.

The modified hot callus method described above has several disadvantages when using an electric line to propagate walnuts, including high energy consumption and the risks associated with electricity in a moist environment. Suk-In et al. (2006) revealed that epicotyl grafting, in addition to hypocotyl grafting, can be used for walnut propagation. Gandev and Arnaudov (2011) initiated the first epicotyl grafting research at the Fruit-Growing Institute in Plovdiv, considering the advantages of this method. Similar to previous winter scion grafting techniques, these procedures require maintaining a temperature of approximately 27°C ± 1°C and high air humidity at the grafting location for three to four weeks.

Research is being done on some aspects of the technological process, including how to bring the rootstocks to the necessary thickness before grafting and what sorts of scions are best for grafting. Walnuts are among the species that are difficult to grow in a lab environment (Preece et al., 1989). According to Rongting and Pinghai (1993), the high concentration of phenolic chemicals in plant tissue, which oxidize as a result of the injury, is what initiates this. The main challenges in walnut include setting and sustaining mature plant tips in vitro, limited multiplication competence, challenging root development, and significant losses during plant adjustment. The first era of the previous century, the 1990s, is when the early tales of cultural setup and stability triumphs began appearing. Several experiments were later carried out, the majority of which were based on the findings of Driver and Kuniyuki (1984). Every step of vegetative growth is impacted by genetic type, but the root stage is when this influence is most noticeable. In recent years, several different walnut cultivars have been successfully planted and acclimated (Nacheva, 2012).

7.3.3.2 Micropropagation of Walnut

The best technique for large-scale plant multiplication/propagation is micro-propagation. Micropropagation can be used to produce robust, disease-free plants as well as various cultivars with appropriate characteristics. Nodal segments, immature cotyledons, cotyledons, mature embryos, ovules, and meristems can all be used to micro proliferate Juglans regia (Avles et al., 2009). In the past 10 years, substantial progress has been made in the development of methods for Juglans regia micro-propagation. In Iran, one technique being investigated for the replication/propagation of walnut genotypes with favorable traits is walnut micropropagation traits.

Vahdati et al. (2004) revealed that cultivar vigor and rooting competence are certainly correlated. Rezaee et al. (2009) investigated the micropropagation of a few genotypes of dwarf walnut and showed that, compared to high vigorous genotypes, dwarf and semi-dwarf genotypes had the greatest number of axillary shoots emerging from the microshoots. Conventional tissue culture techniques typically result in anatomical and physiological problems in the plantlets. Artificial ventilation can stretch plant life and persuade the synthesis of leaf wax during in vitro plant growth (Zobayed et al., 2001). Hassankhah et al. (2014) described that natural ventilation substantially affects Persian walnut growth parameters. At concentrations of 2–5%, sucrose is often utilized as a carbon source in plant development media. Sucrose’s significance as a carbon source in micropropagation has been adequately explained (Hazarika et al., 2004) and Hassankhah et al. (2014) using 15 g L–1 of sugar resulted in healthy and improved plantlets. Further-more, Vahdati et al. (2004) shown that advancing the sucrose content of the root induction medium can lead to increased rooting. Certain justifications suggest that morphogenic developments can be prompted by minor mineral content. Based on the mineral composition of walnut explants (plant portion taken for micropropagation), a different study reviewed and described the growth rates of explants grown on DKW medium and two modified media (mDKW). Explants cultivated on mDKW media did not display any deficit. Explants grown on mDKW also grew many axillary buds and stem lengths (Najafian Ashrafi et al., 2010). The same researchers also investigated how Cu and myo-inositol affected how quickly and for how long explant shoots rooted. The growth rate and rooting percentage of walnut explants would be impacted by higher concentrations of copper and myo-inositol (Najafian Ashrafi et al., 2010). In a study, the effects of two chelates (FeEDDHA and FeNa2EDTA) on growth and roots were examined at four different iron concentrations (45, 91, 182, and 360 mg L–1). The optimal therapy was determined by the results to be 182 mg L–1 iron with EDDA chelate. Raising Fe concentration to 182 mg L–1 enhanced development and roots as opposed to raising it to 360 mg L–1, which had the reverse effect. FeNa2EDTA chelate was allegedly less beneficial for growth and roots than EDDHA chelate at the same concentration. (Vahdati et al., 2008) revealed how ABA influenced the development and germination of somatic embryos of Persian walnut. The results explained that a 41% conversion of embryos into plantlets needed a germination-optimal concentration of 2 mg L–1 ABA. However, they have shown how significant sucrose is for the development of resultant embryos.

7.3.4 Pecan-Nut

Orchards of the pecan-nut tree Carya illinoensis have existed for a very long time, extending to the 19th century. These pecan plantations were initially started by sowing seeds from pecan trees that had desirable characteristics like great nut size, resistance to scab disease, early maturity, and high yields. The early orchards primarily consisted of open-pollinated half-sib populations, where natural pollination resulted in a mix of genetic characteristics (Nunn et al., 2023). However, the advancement of clonal propagation techniques played a substantial part in the development of true cultivars (Subrahmanyeswari and Gantait, 2022). Clonal propagation involves the propagation of superior genotypes by grafting or budding a chosen cultivar onto rootstock made from seeds. Budding techniques, such as ring budding or patch budding, are typically performed during the vegetative growth phase in summer. On the other hand, grafting techniques like 3-flap grafting are typically carried out during the dormant winter season. These improved propagation methods have contributed to the widespread cultivation of Pecan trees with specific desirable traits, ensuring more consistent and reliable yields in commercial Pecan orchards (Mir et al., 2023).

7.3.4.1 Rootstock Propagation

The selection of seeds for producing rootstocks of a particular Pecan cultivar requires careful consideration and adherence to four essential conditions, as highlighted by Conner from the University of Georgia (Lötze et al., 2022). These conditions are as follows:

Uniformity: The chosen seeds should display uniformity, characterized by well-developed kernels.

Availability: To enable successful grafting of a chosen clone (cultivar) onto seed-made rootstocks, it is crucial that the seeds be available.

Vigorous Seedlings: The selected seeds should give rise to seedlings that exhibit vigorous growth.

Resistance against seedling diseases: The seeds should possess resistance against common seedling diseases. Due to the limited availability of Pecan trees, many growers opt to grow their own rootstocks by using seeds. Once the seedlings reach an appropriate diameter of around 1.5–2 cm, they can be grafted or budded with a superior Pecan nut cultivar. This process allows growers to establish orchards using their preferred choice of rootstock and cultivar (Popa et al., 2023). It is important for Pecan growers to carefully select both the rootstock and the cultivar to ensure successful establishment and optimal production in their orchards (Table 7.1).

Table 7.1 Use of Rootstock in Some Temperate Nut Crops and Their Main Features⏎

Nut Crop Name
Rootstocks
Main Characteristics
References

Almond

“Hansen 536” (P. persica x P. dulcis)

Vigorous, drought and salinity tolerant

Ozdemir et al., 2019

“GF-677”

High yielding and high vigor, chlorosis resistant

Walnut

Paradox

Vigor

Vahdati et al., 2021

Ng209 x Ra seedlings

Hybrid progeny of Julgans nigra 209 x J. regia, high vigor

Pistachio

Badami-Riez Zarand seedling

Tolerant to salinity and Phytophthora sp., Vigorous

Sheikhi et al., 2019

Pecan nut

Atlantica Elliott

High cold tolerance and less vigor. Improves nut quality, highly resistant to scab

Xiao et al., 2021

Moore

Productive, vigorous, moderately resistance to scab

Hazelnut

MB-69

Emit few suckers and high vegetative growth

Rovira et al., 2022

Chestnut

PO-11

Resistant to Phytophthora spp.

Revord et al., 2021

Marsol (C. crenata x C. sativa)

Vigorous, better compatibility with most cultivars.

7.3.4.2 Cuttings

Due to the lack of genetic heterogeneity, rootstocks can be propagated through cuttings with greater uniformity. This process doesn’t need special-ized methods and is quick, inexpensive, and reasonably easy. Indole-3-acetic acid (IAA) and other synthetic auxins have been used to improve rooting in cuttings over time (Uma et al., 2023). However, it should be noted that the response to auxin treatment can vary across plant species. Furthermore, It has been found that softwood cuttings respond to auxins more favorably than hardwood cuttings. Alternatives to auxins that can either encourage or hinder rooting may be responsible for this difference. The production of these substances fluctuates with the seasons, and their presence seems to be associated with internal factors within the plants, such as rooting cofactors (Chang et al., 2022). In the case of Pecan stem cuttings, rooting experiments have yielded highly variable results. Even the use of auxins like indole-3-butyric acid (IBA) to induce rooting has shown inconsistent outcomes, as reported in the literature. Several factors influence the success of rooting cuttings, including the time of harvest, the thickness and origin of the cuttings, as well as genetic factors (Sandhya et al., 2023).

7.3.4.3 Layering

The Layering Technique is utilized to stimulate root formation from a stem of the mother plant. Once the newly rooted plant becomes self-sustaining, it is separated or cut off from the mother. Successful root development in Pecan trees was achieved through trench-layering of budded or grafted trees and air-layering of mature trees, along with the application of an IBA treatment (Newman et al., 2022). Given the limited availability of clonal Pecan rootstocks, studies to evaluate the effectiveness of air-layering, stooling, and trench layering techniques for propagating and ensuring field survival of clonal Pecan rootstocks. These studies also aimed to assess the relative responsiveness of different genotypes (Nazir et al., 2023).

7.3.4.4 Budding and Grafting

Through methods like tissue culture and cuttings, there have been substantial advancements made in the field of pecan propagation. However, grafting and budding techniques remain the mainstays of the commercial pecan sector. These methods have shown a success rate of more than 75% (Ahmad et al., 2023).

However, there are certain drawbacks to grafting and budding. One such drawback is that it takes the seedlings two to three seasons to mature to the proper stem diameter for grafting (Pacchiarelli et al., 2022). In an experiment grafting was performed using 1-month-old “Shaoxing” Pecan seedlings obtained through open pollination. The selected germinated seeds had a hypocotyl length of less than 0.5 cm. The epicotyl diameter measured 2–3 mm, and the stems were 15 cm long. Scions from “Caddo” and “Desirable” Pecans, which were 1 year old with a diameter of 2–3 mm and at least 4 healthy buds, were used. The scions were divided into “base scions” and “terminal scions,” respectively, and sealed in polyethylene bags. Before being used for grafting, they were kept at 5°C. To compare the success rates of the grafts, buddy tape and medical tape were used.

The rootstock was carefully cut above the epicotyl during the grafting procedure, and then it was divided 2 cm deep with a grafting knife. The scion was carefully placed onto the rootstock after being cut obliquely on both sides, 2 cm from the lower end (Bhumarkar et al., 2021). The chosen grafting tape was wrapped around the cut area and the scion. The finished grafts were placed in 15–20 centimeter containers with one or two buds showing. These containers were positioned inside a greenhouse in direct sunlight on a concrete floor. After 40–45 days, successfully grafted plants started to sprout. According to the findings, “Desirable” scions had better success rates than “Caddo” scions. Furthermore, plants that were grafted early (by 20 days) had better results. Late spring saw the grafting process, with success rates for “Desirable” scions at 87.13% and “Caddo” scions at 70.51%. (Casales et al., 2018).

7.3.5 Pistachio

Pistachio (Pistacia vera L.) is a nut originating from the Middle East and Central Asia. Iran is the leading producer in the world, followed by the United States, Turkey, and Syria contributing almost 90 % of global pistachio production according to Saglam et al., 2022. A good source of oil is found in the pistachio kernel itself, providing unsaturated fatty acids that are crucial to human nutrition. Unsaturated fatty acids are required for human nutrition in 50%–60% of the food supply. It is frequently employed in the production of candy and snack foods. The pistachio is particularly favored in the ice cream and bakery companies because of the dark green color of its kernel. (Bonifazi et al., 2021). The issue of the quality of shelled pistachios thus plays a significant role in terms of economic, export and marketing (Mahdavi et al., 2008; Mahmoudi et al., 2006). Recent research has shown that pistachios have numerous health benefits, including lowering cholesterol levels, preventing cardiovascular illnesses, and having high anti-oxidant concentrations, especially Tocopherols and Polyphenols. The main components of pistachio nuts are lipids (46 g), predominantly unsaturated fatty acids (29 g), carbohydrates (28 g), proteins (21 g), and dietary fiber (10 g), however, they also contain a significant amount of phosphorus (0.5 g), potassium (almost 1 g), phytosterols, total phenolics and carotenoids (lutein and zeaxanthin), as well as 4% water when dry (Tsantili et al., 2011; Mandalari et al., 2021). To learn more about the historical gene pool, ensure its relevant protection, and ensure its application in future breeding, the research community should take into account a complete genetic characterization of the whole almond germplasm (Fernández et al., 2009, Martínez et al., 2003; Xie et al., 2006). Large-scale collections can now be examined more precisely because of developments in DNA sequencing technology. To answer all of these issues historically, markers like Simple Sequence Repeats (SSRs) have been employed. Numerous accessions of several species have been genotyped recently using a variety of markers, including Sequence-Specific Amplification Polymorphism (S-SAP), Inter-Retrotransposon Amplified Polymorphism (IRAP), Inter Simple Sequence Repeats (ISSR) and Retrotransposon-Microsatellite Amplified Polymorphism (REMAP) (Sorkheh et al., 2017).

7.3.5.1 Rootstock Propagation

The nut-bearing pistachio trees and the Pistacia spp utilized as rootstocks are both dioecious. Because they have a male and a female parent, the subsequent rootstock seeds are sexually produced. Asexual (clonal) micropropagation of pistachio rootstocks was first presented in the early 2000s (Janick et al., 2008). Better root systems are produced by seedling rootstocks, but like other sexually reproduced organisms, they are also diverse because they contain DNA from both their male and female parents. Clonally propagated root-stocks are uniform because they are genetically like the plant from whence they were derived: However, the population derived from that plant lacks diversity (Smith and Drew, 1990). Depending on how the plant population responds to pathogens and environmental factors, genetic diversity, or a lack of it can have both benefits and drawbacks. A current event in the California pistachio business serves as an example of this. A population of chosen hybrid seedling rootstocks was used to clone individual rootstocks in the early 2000s. On the effectiveness of these rootstock populations, no experimental trial data have been gathered. The many orchards grown on these clonal rootstocks, however, were strikingly homogenous and financially successful for the first 10 years. On these clonally propagated rootstocks, new orchards started exhibiting severe morphological traits more frequently in 2010. The rootstocks were found to have the bacterium Rhodococcus sp., according to further tests. The method by which Rhodoccus sp. Initially infected, these clonal rootstocks are currently being investigated, as well as the bacterium’s capacity to infect more rootstocks, both seedling and clonal, in the nursery and in the field. Years of study will be needed to develop the knowledge and techniques needed to combat or resist this bacterium. This series of events has proven that, even though clonal rootstocks might generate greater yields, they can also have vulnerability that limits their potential (Stamler et al., 2015). The susceptibilities to pests and pathogens have received little attention to date, and much less is known about the genetic diversity or cos. position of the single species or interspecific hybrids of the existing commercial pistachio rootstocks. IN the nursery, rootstock quality control involves visually assessing each seedling for type-truth (rouging) and eliminating rootstocks with various morphologies from germination until sale at 6–187 months. However, as the business grows, it is inevitable that rootstocks and cultivars will become more vulnerable to infections and pests. Due to this, the California pistachio business ought to think about creating a programme for rootstock and cultivar clonal preservation, like the one the California citrus sector has already established (Table 7.2) (Nezami and Gallego, 2023).

Table 7.2 Combined Effects of Artificial Treatment on Different Temperate Nut Crop Rootstocks Worldwide⏎

Nut Crop
Rootstocks Used
Treatments
Effects
References

Almond

GF677

Methyl Jasmonate (MeJa)

Enhanced salt tolerance by alleviating NaCl stress.

Tavallali and Karimi, (2019).

Pistachio

Badami and UCB-1

Salinity and drought stress were applied manually at 70% RH, 8/16h light-dark conditions.

Tolerant under salinity and drought stress.

Goharrizi et al. (2020).

Chestnut

SM904

Subculture in WPM media for 6 weeks.

Long shoots with small leaves, high moisture content and less dry mass.

Fernandes et al. (2020).

Hazelnut

Dundee (grafting)

-

Promoted leaf stomatal activity.

Rovira et al. (2022).

Peanuts

Peruque

Manually warm weather stress was applied.

High tolerance

Ajam Gard (2022).

Walnut

Chandler and Franquette

V method of grafting

Improved callus quality, graft survival.

Sadeghi Majd et al. (2019).

7.3.5.2 Propagation by Cutting

To any woody species where rooting is not too difficult, cuttings are used. In this instance, it has been noticed that a number of factors, including genotype, the placement of the shoot, and environmental conditions, have an impact on the proportion of cuttings from species of woody plants that establish root in nurseries. Auxin type, their concentration, day of shoot harvest, and other variables have all been thoroughly covered in other places (Ali, 2017). Pistacia spp. cuttings have traditionally been used for the clonal propagation of selected rootstocks to create similar offspring (Dunn et al., 1996). Meanwhile, attempts to commercially grow pistachio rootstocks utilizing softwood and hardwood cuttings, particularly when employing mature materials, have resulted in inconsistent outcomes. Adult pistachio tree hardwood cuttings have shown to have an extremely low rooting rate (approximately 5%), which has been associated with the aging process of mature trees that causes them to lose their rooting capacity. The initial studies using P. vera and the two clonally propagated rootstocks P. atlantica and P. palestina, which were planted with IBA at the concentration of 10 mg L–1, were utter failures (Assaf, 1977). In the 1980s, cuttings of immature (one-year-old) P. chinensis trees rooted with 92% success when softwood rather than hardwood sources of the rooting plant hormones IBA at 5 mg/l were applied (Pair and Khatamian, 1982). Moreover, after immersing softwood cuttings from seedlings in concentrated 500 and 1000 mg/l IBA, P. vera successfully rooted at significant rates (78–100%), respectively. A promisingly high rooting percentage (88%) of softwood cuttings was also achieved using a mist system in combination with IBA treatments at 35 mg/l (Barazi and Schwabe, 1982). However, using older plant material (four-year-old) resulted in just 50% rooted (Abousalim, 1990). The significant effects of genotype, the portion of the shoot from which the cutting was taken and shoot collection data on successful rooting percentage (40%) of the rootstock “UCB1” cuttings were documented by (Almehdi et al., 2002), but no effect of IBA concentration and shoot lengths was discovered.

7.3.5.3 Propagation by Grafting

Grafting was the key horticultural method that allowed pistachio production to spread from Central Asia to the nations of the Mediterranean basin (Mandalari et al., 2021; Mudge et al., 2009). From a biological perspective, grafting is the natural or artificial joining of a portion of tissue from one plant with a portion of tissue from another plant to form a single creature (Pina and Errea, 2005). From a horticulture perspective, it is a method of cloning plants through vegetative (asexual) artificial propagation in which a section of tissue (referred to as a “scion”) from a chosen cultivar (a “donor”) is joined to another (referred to as a “stock” or “rootstock”). The root system of the grafted plant is taken from a plant that was chosen for its ability to withstand biotic and abiotic challenges. This allows both plants to develop as a single, new creature. Last but not least, grafting involves the creation of a new organism by the fusing of at least two genotypes, with each genotype retaining its own genetic identity in the new grafted plant (Mudge et al., 2009). Over the past 3500 years, grafting has been utilized for a variety of biological and horticultural goals, including vegetative micropropagation, juvenility avoidance, cultivar modification, to repair mature trees, sizecontrolling grafted plants, physiological investigations, and more. Resistance to biotic and abiotic stress or detection of asymptomatic viruses.

7.3.5.4 Propagation by Budding

A short piece of shoot with a single vegetative bud is cut from the wood of the scion and grafted to the rootstock in a process known as budding. Several considerations must be made in order to increase the pistachio species’ ability to successfully budding taking into consideration the following factors: the quality of the scion wood, the use of the most practical budding technique (such as T-budding in the case of pistachio), compatibility between the scion and rootstock, the budding season, and appropriate aftercare (Mohammed, 2022; Arpaci, 1998; Onay, 2003; Sakar, 2011). Although there have been documented advances to the classic methods of conventional asexual propagation, in general, low rooting effectiveness and a lack of homogenous, high-quality plants at suitably large scales were the most significant. Pistachio nurseries have significant difficulties, and fresh unconventional propagation techniques based on plant tissue culture have been developed for this crop.

7.3.5.5 Propagation by Air Layering

One of the propagations layering techniques utilized in deciduous fruits is air layering. Peaches, plums, cherries, pomegranates, figs, and other fruit trees were planted. This technique has been used to successfully spread viruses (Reddy et al., 2014). The fundamentals of plant propagation by layering are the interruption of phloem and the accumulation of carbohydrates, proteins, root-promoting factors, auxins, and ethylene at the girdling area, as well as an increase in cellular activities like a higher respiratory rate and callus formation, which ultimately led to root formation (Hartmann et al., 2011). dropping and doing damage. Conversely, Davies and Hartmann (1988) discovered that spraying plant growth regulators (PGRs) on the stock plant enhanced physiological conditions in which propagules can establish accidental roots. Additionally, Read and Paul (1989) concluded that PGRs given to stock plants improved macro- and micro propagule rooting. Pacholczak et al., (2005) revealed that spraying stock plants with IBA or NAA at concentrations between 50 and 500 mg dm-3 was successful in promoting the growth of ornamental shrubs from stem cuttings. Additionally, pretreatment of Prunus avium cuttings with gibberellin (GA₃) for stock plants increased rooting and shoot growth rates (Ford et al., 2002). Consequently, the purpose of this study is to assess air layering of Pistacia vera under the impacts of girdling wound treatments with and without IBA and GA ₃ and IBA and spray of layered shoots.

7.3.5.6 Micro Propagation

Micropropagation is an in vitro plant tissue culture technology used to generate many identically selected plants (clones) quickly and cost-effectively from a plant stock. Other names for micropropagation include in vitro propagation that is faithful to type. It has served a variety of functions, including as bulk multiplication of high-quality plants to suit horticultural, silvicultural, genetic conservation, and industrial (food, pharmaceutical, nutraceutical, and cosmeceutical) needs (García-Pérez et al., 2020). Compared to traditional propagation methods, micropropagation offers many benefits, including the ability to rapidly and massively multiply elite genotypes and to save other genotypes from extinction. All these benefits are easily relevant to the Pistacia genus, as discussed below; but they are difficult to reproduce by normal methods (George et al., 2007). The effectiveness of micropropagation techniques, whether they are started from apical or axillary meristems, adventitious shoots, or somatic embryos, critically depends on the impact of several variables, including genotype, culture conditions, and, most importantly, the makeup of the donor material culture medium (culture media’s minerals, PGRs, and vitamins) (Lozano-Milo et al., 2022).

Mounting the production of nut crops has been a spotlight among orchardists and researchers due to the ever-increasing demand for consumption. As the population and consciousness for one’s health are rising, production needs to be increased simultaneously to meet the needs and demands (Fanzo, 2021).

7.4 Conclusion

Nut crops are often challenging to propagate in many ways like other woody trees (Awotedu et al., 2021). In the past, mostly fruit crops were propagated thru seeds and grafting on rootstocks (Sharma et al., 2020). Due to the low success rate, hardwood and semi-hardwood cuttings were not followed commercially (Gadapa and Singh, 2022). Winch (2021) reported that semi and high-vigor seedlings performed poorly than low-vigor seedlings in stool layering. However, over the past four to five decades, a significant number of clonal rootstocks with very short juvenile periods (2–3 years) and resistance to biotic and abiotic stresses in a variety of crops have been discovered and developed in advanced countries. These rootstocks have been recommended for grafting and budding elite varieties in place of conventional seedling rootstocks. The fruit sector has undergone a revolution thanks to such clonal rootstocks. Their spread and multiplication must be prioritized to commercialize their use, notably for high density orcharding and for overcoming biotic and abiotic stressors. In this chapter, recent advancements in propagation in temperate nut crops have been discussed. In general, fruit nut crops are propagated by cuttings, layering, seeds, grafting, budding and micropropagation (Polat and Aytekin, 2022).

KEYWORDS

anti-cancer

anti-diabetic

grafting

micropropagation

nut crops

rootstocks

temperate nut

vegetative propagation

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Chapter 8 Production Constraints and Improvement Strategies of Temperate Nut Crops

A. LAXMAN KUMAR,¹,* S. VENUGOPAL,² H. VITTAL,³ B. MARUTHI,⁴ D. ASHOK KUMAR,⁵ and B. PRIYANKA⁶

¹Sri Konda Laxman Telangana Horticultural University, Telangana, India

²CSIR–Central Institute of Medicinal and Aromatic Plants, Research Center, Boduppal, Hyderabad, Telangana, India

³Division of Fruits and Horticultural Technology, ICAR–Indian Agricultural Research University, New Delhi, India

⁴Department of Vegetable Science, BCKV, Mohanpur, Nadia, West Bengal, India

⁵Department of Fruit Science, CHF, CAU (Imphal), Pasighat, Arunachal Pradesh, India

⁶Dr. Y. S. Parmar University of Horticulture and Forestry, Solan, Himachal Pradesh, India

* Corresponding author

Abstract

Temperate nut crops are backbone of temperate region of India and the majority of the temperate nuts are mostly cultivated in the north-western Himalayan and north eastern parts of India. Nut crops have been playing a key role in the local economy as a means of livelihoods, employment generation and earning foreign exchange. However, the production and productivity of the nuts is low, further it is being decreasing continuously and affecting national economy. The decreasing production and productivity is mainly due to limited land, water resources, monoculture, old and traditional cultivars, limited varietal spectrum, non-adoption of high density plantation, lack of certified quality planting material and rootstocks, less use of clonal rootstocks, lack of systematic plantation of nut crops, inadequate proportion of pollinizers, lack of pollinators population, senile orchards and lack of adoption of Good Horticultural Practices (GHP), in addition to that a varied environmental, economic, and social problems. Breeding new, climate-smart, biotic, abiotic resilient cultivars through biotechnological interventions, adoption of Good Horticultural Practices, adoption of certified quality planting material and rootstocks. This chapter attempts to outline some of the important findings over a few decades that aids in overcoming the cultivation problems in nut crops.

___________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

8.1 Introduction

Nut crops hold paramount importance and their production and consumption have increased over the past decade all over the world (Nazir et al., 2023). In general, nuts are categorized as dry fruits with an edible seed and a hard outer shell (Goncalves et al., 2023). The regions that include the United States of America, China, Turkey, Iran, and India have suitable geographic characteristics and agro-climatic conditions for the growth and development of temperate nut crops (Kumar et al., 2023). The major temperate nut crops include Almond (Prunus amygdalus), walnut (Juglans regia), pecan nut (Carya illinoensis), chestnut (Castanea sativa), hazelnut (Corylus avellana), macadamia nut (Macadamia integrifolia, tetraphylla) and pistachio nuts (Pistacia vera) are the predominant temperate nut crops cultivated around the globe.

China is the globe’s leading supplier of walnuts and chestnuts, while the majority of the world’s almond and pistachio nuts is produced by United States of America, the top two dominating countries for producing hazelnuts and pecans were Turkey and Mexico during the year 2020 (FAOSTAT, 2021). The world’s leading producers of macadamia nuts were Australia (25% of the world’s production) followed by South Africa share 23%, Kenya accounts for 15%, and the finally produces 9% Hawaii of nuts (Carvalho et al., 2018). In recent years, nut crops have become more popular due to their nutritional importance, and potential health benefits. Food and Drug Administration has approved nuts as a “healthy food” that is beneficial to human health and increased intake of these nuts may improve the human body’s health-promoting chemical compounds, which may help prevent diabetes and heart diseases (Meena et al., 2023). Though there are various demands but still there are numerous production challenges in temperate nut crops. Therefore, this chapter deals with the major challenges and different approaches to the improvement of temperate nut crops.

8.2 Major Production Constraints Of Temperate Nut Crops

The production and cultivation of temperate nut crops is affected many factors that influence their yield and nut quality. The general challenges in nut crop cultivation are lack of availability of suitable rootstocks for specific problem, long breeding cycles and vegetative phase, low yielding varieties, lack of adaptability of advanced propagation techniques, poor nut yield, undesirable kernel characters, inability to develop resistant cultivars to biotic and abiotic stress, old and senile orchards (Table 8.1), improper cultivation practices, high labor cost in harvesting of nuts, lack of adopting micropropagation techniques, unavailability of climate resilient varieties, inefficient utilization of available genetic resources, irregular bearing nature of trees, lack of development of high quality nuts, dearth of novel dormancy breaking compounds, restricted cultivation to hilly areas, diversified floral patterns, inefficient pollination problems, cultivation of nut crops depends on climatic conditions of the location, cultivar specific incompatibility, improper canopy management practices, paucity of post-harvest infrastructure, low productivity, the shelf life of nuts is majorly affected by numerous factor including the amount of moisture, packaging, and conditions of storage, physiological disorders, lack of government support, policy interventions and inability to adopt molecular techniques and gene sequencing.

Table 8.1 The Production Challenges of Temperate Nut Crops ⏎

Sl. No.
Temperate Crops
Constraints

1

Walnut

The evolutionary background and genetic impacts on its development and agronomic traits are still unknown (Ji et al., 2021).

Propagation problem such as poor success rate of grafts, low numbers of high-quality saplings are the result of faulty grafting techniques (Regmi et al., 2023)

Long vegetative phase and slow bearing nature (Popa et al., 2023)

Germination percentage of pollen collected from young trees was minimum (Polito and Weinbaum, 1988)

Post-harvest deterioration is caused by damage to the seed coat pellicle during by shelling procedures (Ortiz et al., 2019).

Aflatoxin contamination during storage (Krishna et al., 2023)

2

Pecan nut

Lack of precious cultivars with the ability to bear more regularly across years (Thompson and Conner, 2012)

Post-harvest fungal deterioration has considerable effects on pecan nut quality (Ribeiro et al., 2021)

Heterodichogamous flowering nature of pecan nut and duration of pollen storage under different conditions was minimum (Wang et al., 2021)

Allergy due to consumption of pecan nuts (Clermont et al., 2023)

Poor propagation techniques lead to less survival rate of plants (Fabrizio et al., 2018)

Fungal diseases like black spot and seedling wilt in pecan causes yield reduction (Achilonu et al., 2023)

3

Hazelnut

Bacterial diseases caused by xanthomonas and pseudomonas affect nut production (Nicoletti et al., 2022)

Husk brown rot, botrytis fungal disease major threat to hazelnut cultiva¬tion (Sun et al., 2023)

Lack of availability of good rootstocks (Vahdati et al., 2021)

Suckering nature of root stocks increased the cost of cultivation (Rovira, 2021)

4

Pistachio nut

Fresh in-hull pistachio fruits have a poor storage life due to their high perishability (Rezaiyan et al., 2023)

Low pollen germination percentage affects nut yield (Polito and Weinbaum, 1988)

Diseases like crown root and root rot causes death of trees (Ozan et al., 2023)

Organic waste generated from cultivation and dehulling process (Toghiani et al., 2023)

5

Chestnut

Chestnut blight, phytophthora root rot and Chestnut rot causes yield loss (Clark et al., 2023)

Lack of disease resistant varieties to chestnut blight and Phytophthora root rot (Clark et al., 2023)

High slope areas are not suitable chestnut cultivation (Rossi et al., 2023)

Poor response of large chestnut trees to fertilizer application (Arrobas et al., 2023)

Production of poor-quality nuts, low productivity due to poor pollination and improper pollen dispersal mechanism (Nishio et al., 2019)

New invasive pest and pathogen species, climate change, inadequate scientific knowledge on cultivation and technological advancements impacts chestnut (Clark et al., 2023)

6

Macadamia nut

Low nut production is due to inadequate information on management practices in central Kenya (Maina et al., 2021)

Quality loss is due to mold and poor germination percentage (Buthelezi et al., 2019)

Stress reduces yield and quality at the stages of early nut drop and oil accumulation (Shabalala et al., 2022)

Browning of kernels in macadamia varieties affect nut quality (Srichamnong and Srzednicki, 2015)

7

Chilgoza nut

Lack of suitable packaging material for storage and packaging (Thakur et al., 2014)

Shell-less nuts are prone to rancidity (Haq et al., 2013)

Many species bearing seed rarely, dormancy-related issues, and delayed seedling growth (Kumar et al., 2016)

Lack of adaptability suitable clonal propagation like grafting (Hamadeh et al., 2018)

Expensive raw materials; labour-intensive operations, pre-and post-treatments reduced value addition products (Faraloni et al., 2023)

8.3 Improvement Strategies

To overcome the constraints in the production of these temperate crops, various approaches were made (Figure 8.1). The major traditional breeding techniques for the improvement of temperate nut trees include the use of available germplasm and selective hybridization in combination with molecular breeding helps to speed up present and future breeding procedures (Vahdati et al., 2023). High-density planting, proper pollination management, timely training and pruning operations, and good horticulture practices help in premium quality kernels, suitable packaging, and storage conditions enhance the shelf life of nuts, and proper post-harvest management practices will improve the production and post-harvest quality of nuts. Gene silencing, trans-grafting, and rootstock breeding will aid in creating novel rootstocks that are resilient to climate change as well as a wide range of diseases and pests (Vahdati et al., 2021). Advanced techniques like Genomics, genomewide association mapping, marker-assisted selection, QTLs mapping, and gene editing like CRISPAR/CAS aid in addressing long-standing issues and also helps in the improvement of perennial nut crops.

Figure 8.1 Approaches to overcome the challenges in temperate nut crops production. ⏎

8.4 Description Of Production Challenges And Improvement Approaches For Temperate Nut Crops

8.4.1 Hazelnut (Corylus Avellana L.)

It is commonly called filbert, one of the leading economically important temperate nut crops in the world, and belongs to the genus Corylus, family Betulaceae with excellent nutritional and medicinal features (Yazlik, 2023). The kernels of hazelnut are a good source of proteins, B vitamins, tocopherol, phylloquinone, monounsaturated fat, several minerals, and dietary fiber (Kavas et al., 2020) and are extensively used in the chocolates and confectionery industry (Silvestri et al., 2021). Turkey is the leading producer of hazelnut and Turkey and Italy are also the main exporters of hazelnut to various places of the world (Kumar et al., 2023). They are numerous challenges associated with the successful cultivation of hazelnut in various regions of the world.

8.4.1.1 Production Constraints

The production of hazelnut is impacted by long-standing issues like old and aged plants, senile orchards, small sized farms, poor cultural practices, higher labor cost in harvesting of nuts (Erdogan, 2018), yield loss due to weeds in orchards (Yazlik, 2023), hazel nut production is also limited by the lack of suitable propagation techniques and maximum cost of propagation (Ercisli and Read, 2001), callus browning is a major barrier in in vitro multiplication (Shirazi et al., 2020), producing explants free from contamination, disease free explants and protocol for initiation of roots, both with in vitro micropropagation and vegetative cuttings and are the key obstacles for propagation, One of the major challenge in expanding hazelnut production regions is absence of uniformity and limited availability of good quality germplasm (Pincelli-Souza et al., 2022), suckering nature of hazelnut rootstocks is also a challenge in cultivation and increased the cost of cultivation in Mediterranean countries (Rovira, 2021), pollen and nuts of filbert are a significant factor in allergic reactions in sensitive individuals and mycotoxins in hazel nut formed during fruit development creates a major problem to public health (Salvatore et al., 2023), hazelnut kernel characteristics and nutritional composition may be influenced by Xenia (Fattahi et al., 2014).

Hazelnuts are self-incompatible, the blank nut is a major bottleneck in might reduce the yield of most the varieties (Olsen, 2013), and the feasibility of production is hampered by the lack of availability of suitable cultivars that are suitable for the local climatic conditions (Dubosky, 2016), in addition, climate change also impacts hazel nut yield (An et al., 2020). Emerging serious pests big as bud mite and diseases like bacterial blight and eastern filbert blight causes yield loss (Lamichhane and Varvaro, 2014; Mehlenbacher and Molnar, 2021), and yield and quality of nuts affected by bacterial diseases caused by the Xanthomonas arboricola pv. corylina and Pseudomonas avellanae (Nicoletti et al., 2022), damage caused by hazelnut Weevil, Curculio nucum resulted in empty and blank nuts (Hamidi et al., 2022). New hazelnut orchards experience difficulties in production due to unfavorable climatic conditions that impair pollination and lower nut production (Ascari et al., 2017). As a consequence of the conversion of grasslands to agricultural lands, the soil organic carbon pool in hazelnut orchards decreases (Pacchiarelli et al., 2022).

8.4.1.2 Improvement Strategies

Successful cultivation and subsequent harvesting of filbert nuts depend on location. Novel mechanization and geospatial technology can be used to reduce the physical barriers by finding suitable locations for hazelnut production (Zambon et al., 2017). There is a huge diversity of Corylus species of about 500 cultivars such as C. heterophylla, C. americana, and C. colurna are valuable genetic resources for breeding in the creation of novel improved varieties and have regional commercial and industrial applications (Cristofori et al., 2022). Developing suitable cultivars for specific local climatic conditions, good management practices, machinery, accommodating a higher number of plants and interspecific hybridization helps in the improvement of yield and broadening the production to new locations (Mehlenbacher and Molnar, 2021). Identification of genetic resistance and transferring the desirable traits to varieties helps in the creation of new varieties to biotic and abiotic stress (Mehlenbacher and Molnar, 2021).

An effective method for enhancing yield is artificial pollination (Ascari et al., 2017). The Hazelnut confectionery sector is increasing tremendously and has recently attracted a lot of interest and impacted due to shifts in climatic zones, the supplied cultivars do not perform well, going into bare survival mode (Ayyanath et al., 2023). To overcome this issue, indoleamines are used to improve hazelnuts reproductive traits and to endure abiotic stress. Grafting is a technique used in Horticulture crops to control scion phenotype and improve yield and combat both abiotic and biotic stresses (Vahdati et al., 2021). The largescale multiplication of hybrid hazelnut (Corylus americana x Corylus avellana) under controlled environment conditions has only found limited use due to the lack of adaptability of effective methods of micropropagation like tissue culture and root organogenesis. An approach consists of indole-3-butyric acid (IBA) pretreatment and a one-week culture period in complete darkness can be used to successfully root cuttings grown in invitro conditions in hazelnut (Pincelli-Souza et al., 2022). Apex encapsulation technology helps in producing invitro virus-free apple mosaic virus, true-to-type hazelnut plantlets (Yahyaoui et al., 2021). Non-suckering rootstocks could help to improve the suckering problem and the Corylus colurna species produces no suckers, and better compatibility of graft with all Corylus avellana cultivars (Vahdati et al., 2021).

The different storage conditions of hazelnuts to lose weight and the relative humidity of the storage should be around 80% to achieve the best longevity of the hazelnut weight all through time. So, moisture analyzer-infrared radiation can be used in developing hazelnut supply chains and storage systems (Kowalska et al., 2022). In the context of soil carbon sequestration, the conversion of grassland to hazelnut orchards has a short-term detrimental effect on soil, and the tremendous potential for carbon sequestration in hazelnut is highlighted by the recovery and exponential growth of sCS30 in hazelnut orchards with proper fertilization and management (Pacchiarelli et al., 2022). Emerging techniques like Genome sequencing helps in the development of specific markers of hazel nut and develop varieties of resistance to pest and diseases (Mehlenbacher and Molnar, 2021). The various species of filbert that are the most intriguing from the perspective of genetic improvement are Corylus maxima, due to its resistance to bud mites; Corylus avellana, owing to fruit attributes, C. colurna, due to their ability to withstand low temperatures and diseases (Vahdati et al., 2021; Romisondo et al., 1976).

8.4.2 Macadamia Nut (Macadamia Species)

It is also known as Queensland nut, one of the high-value temperate nut crops belongs to the Proteaceae family, originated in southern Queensland and northern New South Wales, the two major species of Macadamia are Macadamia integrifolia and Macadamia tetraphylla, are grown for their edible quality nuts (Monselise, 1986). Australia is the second-largest producer of macadamia nuts after Hawaii followed by Brazil, South Africa, and Guatemala. Other producers of macadamia nut include New Zealand, Costa Rica, Malawi, Mexico and China (Penoni et al., 2011). There are tremendous uses for this wonder nut crop among them cold-pressed macadamia nut oil (CPMO) is used extensively nowadays because of its superior quality characteristics like bioactive phytochemicals and wider applications in various industries like nutraceutical, and pharmaceutical (Kaseke et al., 2021).

8.4.2.1 Production Constraints

One of the major diseases limiting macadamia nut cultivation in Queensland is the husk spot (Nunn et al., 2023). Climate change affects the macadamia nut quality and affects crop loss and also alleviates pests and diseases (Bouarakia et al., 2023). Lack of suitable cultivars adaptable to local climatic zones, lack of good quality planting materials, a premium cost of the good planting materials that are available, and biotic and abiotic stresses, low post-harvest quality are some of the difficulties faced by the macadamia industry in Kenya and also lack of scientific information related to the genetic diversity of macadamia germplasm hampers breeding attempts (Gitonga et al., 2017). Macadamia nut shell waste is produced during the production process, which is about greater than 70% (Samaksaman et al., 2021).

The other challenge in macadamia nut cultivation is retaining sensory and nutritional quality parameters, and a significant amount of oils, especially in the postharvest phase; macadamia cultivation is also impacted by climate change issues, particularly for nations with high relative humidity and temperatures (Mereles et al., 2022). The lack of accurate yield and production forecasting models for macadamia nuts creates a challenge to farmers and industries in taking timely decisions in the planning and harvesting of nuts (Brinkhoff and Robson, 2021). Inadequate allogamy and poor pollination are major causes of low nut yield in macadamia (Howlett et al., 2015). Genes involved with fatty acid production, seed coat formation, and heat stress response are selectively lost in macadamia cultivars and are revealed by gene sequencing in macadamia nuts (Lin et al., 2022).

In terms of duration, labor, and money, breeding to develop novel macadamia cultivars with maximum nut production is quite expensive (O’Connor et al., 2020). Lack of availability of technical experts, extension services, inadequate processing infrastructure, improper value chains in macadamia cultivation and government intervention are the major drawbacks in cultivation in most of the macadamia nut production countries (Zuza et al., 2021). There are numerous problems in exporting nuts to other countries (Sithole Pisa and Viviers, 2010).

8.4.2.2 Improvement Strategies

The ineffective pollination in macadamia orchards causes low nut yield in commercial macadamia orchards and this can be addressed by effective pollination by pollinators like honey bees, flies, stingless bees, beetles, and birds (Howlett et al., 2015). Applications of biotechnological tools like DNA markers, and marker-assisted selection in addition to conventional breeding would significantly enhance the sustainable use and conservation of macadamia germplasm (Gitonga et al., 2017). Genome analysis of macadamia nut aids in the improvement and domestication of novel crops, varieties are possible from wild crop relatives through artificial selection (Lin et al., 2022). Genetic markers and genome-wide association studies (GWAS) have the potential to facilitate early selection through marker-assisted selection (MAS) hence shortening evaluation, selection cycles, a better understanding of characters that genetically control yield and reduce the duration, money in the development of novel varieties with improved characters (O’Connor et al., 2020). Up to 70% of macadamia nuts contain nut shells, these nut shells can be converted into solid fuel by a hydrothermal carbonization process (Samaksaman et al., 2021). Providing market information is critical for maximizing exports (Sithole Pisa and Viviers, 2010).

The various model input factors along with meteorological data, and spatial temporal datasets techniques can be used for predicting macadamia nut yield at the block level before harvesting season which may help farmers in taking time based decisions (Brinkhoff and Robson, 2021). The selection of suitable cultivars for specific locations helps in the production of premium-quality nuts through macadamia nut breeding programs (Carvalho et al., 2018). Cultivars resilient to climate change, production of good quality planting material, suitable cultivars for the specific agro-climatic conditions, best processing infrastructure facilities, integrated management of pests, diseases, government subsidies, and policy support helps in macadamia farming profitable venture (Zuza et al., 2021).

8.4.3 Pecan Nut (Carya Illinoinensis (Wangenh.) K. Koch)

The Pecan Nut tree (Carya illinoinensis (Wangenh.) K. Koch) is native to North America, and is a member of the juglandaceae family (Siebeneichler et al., 2023). They are commercially grown and harvested for their nuts, which are sold both domestically and internationally. Pecans hold several important roles and benefits, contributing to their overall significance. Pecans are a nutrient-dense food, providing a range of essential vitamins, minerals, and beneficial compounds. Pecans also contain fiber, protein, antioxidants (such as vitamin E), and minerals like magnesium and zinc, all of which are important for maintaining a healthy diet (Tanwar et al., 2021). Pecan farming and industry are crucial in the southern United States, supporting farmers, processors, distributors, and retailers. Pecans are perennial trees with extensive root systems, preventing soil erosion, traded internationally, and contributing to global trade and agricultural exports (Prabhakar et al., 2022).

8.4.3.1 Production Challenges

These trees are susceptible to various diseases and pests, including pecan scabs, fungal infections, pecan weevils, aphids, and mites (Ramakuwela et al., 2020; Chesti et al., 2023). It is sensitive to weather conditions, particularly during critical stages of growth and development. Factors such as late spring frosts, excessive rain, drought, and extreme temperatures can adversely affect pecan tree health, nut production, and overall yield (Bock and Hotchkiss, 2020). Alternate Bearing is also one of the major problems, which means they may produce a maximum crop in one year (on-year) and a minimum crop the following year (off-year) (Noperi-Mosqueda et al., 2020). This natural cycle can make production planning and crop forecasting challenging for pecan growers, impacting their income and profitability. It can be prone to certain quality issues such as uneven kernel development, smallsized nuts, or shell imperfections. In addition, the process of shelling pecans can be labor-intensive and expensive, as the hard shell can be difficult to crack. Advances in mechanized shelling technology have helped alleviate this problem to some extent, but it remains a consideration for growers and processors.

The pecan market prices are subject to fluctuations in supply and demand, which can result in price volatility. Factors such as crop size, competition from other nut varieties, import/export dynamics, and consumer preferences can impact pecan prices and market conditions. The growers may need to navigate these fluctuations and adapt their strategies accordingly. They have specific requirements for optimal growth, including a long growing season, well-drained soil, and adequate water availability. As a result, pecan production is limited to certain regions with suitable climatic and soil conditions (Terrell, 2022). This can restrict the geographic distribution of pecan orchards and limit the availability of locally grown pecans in some areas.

8.4.3.2 Improvement Strategies

Controlling pecan nut pests and diseases can be challenging and often requires careful monitoring, timely treatments, and integrated pest management strategies to minimize damage to the trees and the crop (Ramakuwela et al., 2020; Chesti et al., 2023). Proteomic analysis of peanuts helps in the identification of varieties having proteins critical for desirable properties such as reduced allergen concentration, improved tolerance to salinity, biotic stress, enhanced polyphenol or lipid content, and the viability of seeds (Clermont et al., 2023). Efforts are being made by researchers, farmers, and industry stakeholders to address these challenges through improved disease-resistant cultivars, pest management techniques, irrigation practices, and market diversification. Overcoming these problems can help ensure the sustainability and profitability of pecan production in the face of various obstacles. Pecan nut varieties with proper shapes and large sizes have more value and consumer preference in the market. Pecan breeding programs focusing on nut shape characters was revealed with image-based morphometric analysis helps in the selection of varieties with desirable nut shape (Bhattarai et al., 2022). The significant diversity observed in commercial crop species is desirable, offers a valuable source of genetic variety, and can be used to improve the breeding selection of pecan crops (Ferrari et al., 2022).

8.4.4 Walnut (Juglans Regia)

8.4.4.1 Production Constraints

These are not similar all over the world; they will be specific to each growing region. Climate change, late spring frost, early fall frost, high temperature, low fertile soils, reduced use of inputs (insufficient irrigation and fertilizer management), lack of high-yielding cultivars, lack of standard propagation techniques, following traditional planting systems, the large size of the tree, long juvenile period, lack of proper canopy management techniques, presence of dichogamy, pollination difficulties, inadequate knowledge of orchard management practices among growers, increasing pest and disease activity, increased total cost of production, difficulties in harvesting, spraying, pruning of large size trees are creating problems in achieving higher yields in walnut.

Climate change limits walnut production by aggravating conditions like late-spring frost, early-fall frost, and extremities in temperature. Spring frost is associated with uneven bearing and sometimes total crop losses, high temperature (48 ̊C) during the nut development period leads to sun burning (Fallah et al., 2022). Seed-propagated walnut trees have a long juvenile period, and vegetative propagation reduces the juvenility and comes to bearing early, but propagation of walnuts through vegetative means is a big challenge compared to fruit species and traditional grafting methods are long and time-consuming tasks (Devin and Bujdoso, 2022). Walnut trees suffer from poor pollination due to decline in pollinators, weather uncertainty (frost, winds) and maturity of sex at different times impacts yield and production (Mazinani et al., 2021).

Most of the walnut varieties are terminal bearers and their yield is less. It was found that lateral-bearing cultivars yield more but they are easily affected by walnut blight and cold (Bernard et al., 2018). Trees with big stature makes all the orchard operations such pruning, spraying, and harvesting difficult. Manual harvesting leads to high costs and may pose the threat of harvest injuries and worker deaths make harvesting a difficult process (Devin and Bujdoso, 2022). The large dense canopy of the walnut tree causes shading and devours a large amount of assimilates and affect reproductive growth and increase pest and disease activity within tree canopy. Quality and yield of walnut is affected by biotic and abiotic problems. Lack of proper water and fertilizer management schedules affects fruit setting and yield (Chen and Qi, 2022).

8.4.4.2 Improvement Strategies

The problems faced by spring frost can be alleviated by breeding late-leafing cultivars with desirable nut characteristics. Lateral-bearing cultivars are associated with a higher yield. Late leafing character in lateral bearers helps avoid walnut blight spread by spring rains and to get higher yield (Fallah et al., 2020). The improvement in walnut is focused on enhancing yields, reduce the tree size, limiting juvenile period, and minimizing cost of production. Searching for genetic resources having low vigor helps to breed dwarf cultivars. Walnut breeding programs in different countries like China, Iran, French led to the release of dwarf rootstocks such as Daixiang and Daihui, Alvand, Fernette respectively, which can be used in high-density planting systems for efficient use of water and nutrients and lessen the difficulties in spraying, pruning, harvesting, enhance yield and productivity (Devin and Bujdoso, 2022). The technique, Micro grafting, can be used to produce virus-free plants (Ribeiro et al., 2021).

Pruning at regular intervals control tree vitality and pest and disease activity, promote flower bud formation and encourage early harvest and yield improvement. Measurements such as canopy management by proper training and pruning, adopting chemical control, evaluation and breeding walnut cultivars or rootstocks with biotic and abiotic resistance aid in the overcoming the challenges (Chen and Qi, 2022). Production of quality and certified plant material, and their easy availability to growers is important. The technological advances (Genetic/physical mapping and QTL detection, Next-generation mapping, Genomics and transcriptomics studies, Chloroplast and nuclear genome sequencing, Metabolomics and proteomics studies, and genetic engineering can be used to overcome the challenges like taxonomic classification, genetic diversity of Juglans species germplasm, and also can be used for walnut improvement. Solving the processing constraints by helping in post-harvest handling, grading, and marketing walnut production at the grower’s level prevents loss of yield. Creating awareness among growers through extension activities, extending walnut cultivation to new areas to boost productivity (Bernard et al., 2018). The problem of dichogamy and inadequate pollen in the initial years of walnut trees can be solved by including pollinizer genotype in orchards and or using airborne artificial pollination. Artificial pollination through drones saves time, and enhances accessibility to impossible areas by humans (Mazinani et al., 2021). The use of bio-economic models (Yield-SAFE, Farm-SAFE model) to compare the yields and profitability of walnut orchard systems by assessing various parameters critical to walnut production (Bernard et al., 2018) helps in discovering the production constraints specific to a region.

8.4.5 Chilgoza Nut (Pinus Gerardiana)

8.4.5.1 Production Constraints

Chilgoza is at risk of extinction, it is rated as Near Threatened by Red Data Book. Deforestation adversely affects the chilgoza nut industry since its restriction to mountain forest areas. Lack of information on Chilgoza ecological requirements, standard propagation techniques, genetics, cultivation practices, and manual harvesting, large tree size is the major production constraint in cultivation. Local unskilled laborers involved in nut extraction damage the nuts because of a lack of sufficient scientific expertise, decreasing their quality. Unscientific storage of nuts increases production losses (Masood et al., 2016). Heavy cone collection and over-grazing are the factors affecting the natural regeneration of Chilgoza, reducing the number of new plant regeneration in forests (Atif, 2021).

8.4.5.2 Improvement Strategies

Creating research programs to study the ecology, biology, and genetics of chilgoza, standardizing propagation techniques, and increasing awareness among those working in the chilgoza nut sector about scientific storage and nut extraction in order to boost net returns and so improve farmers’ socioeconomic condition (Masood et al., 2016).

8.4.6 Almond (Prunus Dulcis (Mill.) D. A. Webb)

8.4.6.1 Production Challenges

Almond is a temperate nut crop that requires low chilling temperature for its dormancy breaking and subsequent flowering, but due to climate change, rise in temperature during winter as well as spring have a major effect on flowering time and thus production (El Yaacoubi et al., 2019). Frost injury to flowering, high cost of fertilizer/pesticide, lack of certified and quality planting material, senile and less productive trees in the orchard, frequent fluctuation in market prices, shifting of almond orchards into apple orchards, lack of technical guidance on cultivation aspects, old traditional methods of planting, manual harvesting associated with lower almond yields (Hamid Shah et al., 2022). Fluctuations in crop water demand, pollination constraints due to frost and rains, extreme light and heat stress, disease susceptibility, and insect pest damage are all important challenges in almond production (Di Lena et al., 2018).

8.4.6.2 Improvement Strategies

Low-cost, high-quality inputs, and planting material, easy availability of improved varieties, breeding climate resilient crops for tolerating biotic and abiotic constraints, rootstocks with wider adaptability, mechanized harvesting, creating awareness regarding cultivation aspects by conducting training programs, using advanced crop yield modeling techniques to predict the yields and identifying major constraints helps in improving almond production (Hamid Shah et al., 2022).

8.4.7 Pistachio Nut (Pistacia Vera L)

8.4.7.1 Production Challenges

Pistachio nut generally known as green gold (Nezami-Alanagh et al., 2019), belongs to the Anacardiaceae family (Mandalari et al., 2021). Production and consumption of pistachio nuts is increasing worldwide due to immense nutritional and health benefits. Compared to other nuts, the pistachio nut is rich in potassium, phytosterols, phytochemicals, phylloquinone, and lutein (Toghiani et al., 2023). The top three producing countries in the production and cultivation of pistachio nuts are the United States of America (47%), Turkey (30%), and Iran (19%) in 2020 (Statista. Pistachios: Leading Global Producers 2020/2021). Indiscriminate use of pesticides and pesticide residues in the minute concentration of pistachio nuts adversely affects the health of consumers (Arabameri et al., 2022). Alternate bearing nature and abscission of inflorescence buds of pistachio nut affect nut production and cause economic loss to farmers (Khezri et al., 2020).

The genetic diversity of pistachio nut is rapidly declining due to climate change, monoculture of some cultivars, and population pressure, and the most significant obstacles for pistachio nurseries were low rooting effectiveness, a lack of uniform plants of high quality at sufficiently large proportions and commercial propagation of pistachio nut is seed is not practically feasible due to low germination rate of wild pistachio species (Nezami-Alanagh et al., 2019). The major pests that cause yield loss and economic damage in pistachio nuts around the world are stink bugs, mealy bugs, psyllids, plant bugs and leafhoppers (Mehrnejad, 2014). One of the major challenges in the post-harvest management of pistachio nuts is short storage life because it will spoil in less time (Rezaiyan Attar et al., 2023). Pecan nut growers are concerned about reduced nut output due to a decrease in vigor and stunting of some trees (Jacygrad et al., 2020). Pistachio orchards face severe salinity problems due to water shortages in saline and alkaline soils (Raoufi et al., 2020). The productivity of pistachio trees was affected by a deficiency of potassium (Roosta and Mohammadi, 2013). The correct stage of Harvesting is so crucial for pistachio quality (Mandalari et al., 2021).

8.4.7.2 Improvement Strategies

Boron toxicity can occur naturally in arid and semiarid soils. So, foliar sprays of calcium effectively reduce boron toxicity in saline-grown pistachio rootstocks (Mohit Rabari et al., 2023). The nut quality of pistachio orchards was improved with the application of manure, ammonium, and iron in alkaline soils (Roosta and Mohammadi, 2013). Genome sequencing aids in future research into the genetic basis of agronomically, and environmentally related characters and enable future evolutionary research in pistachio nut (Zeng et al., 2019). The productivity and yield of pistachio nut trees can be improved by using vigorous rootstocks like UCB1 seedling rootstock produced more clusters per tree (Vahdati et al., 2021). The loss of germinability in dried pistachio pollen may be due to a lack of other protective mechanisms (Zamani et al., 2018). Grafted cultivars and rootstocks have also a major effect on nutrient uptake, yield, and productivity in pistachio nuts. Therefore, both rootstock and cultivars can be a prime consideration for effective resource utilization and improved economic returns (Surucu et al., 2020). The management of pistachio nut orchards can be improved by employing advanced technologies such as remote sensing (Martínez-Peña et al., 2023).

8.4.8 Chestnut (Castanea Sativa)

It belongs to family Fagaceae, the same family as the oaks (Quercus) and the beeches (Fagus) (Ciucure et al., 2022). The important species in chestnut family are American chestnut (Castanea dentata), Chinese chestnut (Castanea mollissima BA), the Japanese chestnut (Castanea crenata Sieb and Zuce) and sweet or European or Spanish chestnut (Castanea sativa Mill) (Lang et al., 2007). China is leading in production of chestnuts followed by Bolivia, Turkey, Korea, and Italy as per the report of UN-FAO (Zhou et al., 2021). Chestnuts have ability to retain maximum amount of antioxidant even after roasting (Poljak et al., 2021). In order to retain higher ascorbic acid in chestnuts roast them at moderate temperatures or dry them in a food dehydrator. (Ramadan, 2021). Chestnut is rich in higher antioxidants like gallic acid and ellagic acid (Anna, 2021).

8.4.8.1 Constraints In Chestnut Production

The production of hazelnut is impacted by many factors long-standing issues like old and aged plants, senile orchards, small-sized farms, poor cultural practices, and higher labor costs in the harvesting of nuts (McKay and Crane, 1953). One of the major limiting factors is the high-slope area in hilly regions are not suitable for effective chestnut cultivation (Rossi et al., 2023). In chestnut propagation, the major challenges are to get success from micropropagation and nurse grafting (Yadav et al., 2022). Leaving organic wastes in orchards may decrease soil fertility and provide favourable conditions for fungus to multiply (Shuttleworth and Guest, 2017). The large trees of chestnut used to respond very poorly to fertilizer application (Arrobas et al., 2023). Despite a certain level of self-compatibility appears to exist in chestnut, it is fully self-sterile (Manino et al., 1991). Poor pollination and improper pollen dispersal mechanism are the other challenges in the cultivation as it leads to the production of poor-quality nuts, and low productivity (Nishio et al., 2019). Pollinators like bees and insects are attracted to pollen, but the female flowers does not contain high nectar, that may reduce the insect pollination and promote wind-pollination in chestnuts (Vossen, 2000). Chestnut cotyledons are protected by a pellicle, a membrane covering that originated as an ovule integument. (Yadav et al., 2022). The second phase of bur abscission is affected by failure of fertilization (Nakamura, 1991). The lack of disease-resistant varieties to chestnut blight and phytophthora root rot is another limitation in the cultivation (Clark et al., 2023). New invasive pest and pathogen species, climate change, inadequate scientific knowledge on cultivation and technological advancements impacts chestnut cultivation (Clark et al., 2023).

The major diseases causing the loss of productivity are chestnut blight caused by Endothia parasitica, Ink disease or root rot caused by Phytophthora cinnamomi and P. cambivora, and Blossom end rot caused by Glomerella cingulata (Jaynes et al., 1974). Chestnut blight, phytophthora root rot, and Chestnut rot cause yield loss (Silva-Campos et al., 2022). The most devastating pests that cause a huge amount of crop loss in Chestnut weevils, Gall wasp, Asiatic Oak weevil and Mites (Yadav et al., 2022).

8.4.8.2 Improvement Strategies

In hilly terrain, a sod mulch system may be applied to reduce soil erosion and retain moisture (Yadav et al., 2022). Growth of sprout was best in grafting compared to budding (McKay and Crane, 1953). In chestnut, nurse grafting is reported highly successful with cultivar Dore de Lyon (Yadav et al., 2022). During the fertilizer application of chestnut, addition of urea to soil reduced the number of male inflorescences while increasing the number of female flowers (Pan et al., 2016). Grafting, pruning, and wounding management may be beneficial against chestnut blight, but it may reduce the effect of hypo-viruses using biocontrol agents (Diamandis, 2018). Tree decline is a major disease affecting chestnut production and it can be managed by silvicultural operations and also combined with drainage interventions to prevent phytophthora from spreading to new areas (Benavent-Celma et al., 2022). Chestnut diseases can be managed by pruning in combination with biological control but these operations are time-consuming and costly for big commercial growers (Avtzis et al., 2019).

The presence of non-host trees in mixed chestnut orchard and chestnut– pine mixture reduces infestation to invasive pests (Fernandez et al., 2018). The environmentally friendly approach against the Asian gall wasp is use of entomopathogens (Sahin et al., 2020). The chestnut cultivar Shihou was reported resistant to gall wasps in chestnut (Saito et al., 2009). The value addition products of chestnut has immense importance such as chestnut flour production is widely used in preparation of fortified products and chestnut drying is critical for the safety and quality of chestnut flour. (Cappelli et al., 2021; Paciulli et al., 2019).

8.5 Conclusion

Temperate nut adds a significant contribution to the world economy, and the challenges can be overcome through traditional, contemporary, modern, biotechnological, and genomic technologies. Understanding the climate, pests, diseases, soil fertility, and crop management practices is critical for nut crop production success. Sustainable and integrated approaches like Precision farming, crop rotation, and integrated pest, disease and nutrient management can enhance yields while minimizing environmental effects. Application of advanced technologies in temperate nut crops like remote sensing, genetic engineering, and improved irrigation systems, provide prospects for increased output, disease resistance, and resource optimization. Nut producers may optimize yields, enhance profitability, and contribute to the industry’s long-term sustainability by overcoming difficulties, adopting sustainable practices, embracing technology improvements, and promoting teamwork

8.6 Future Prospects

There is tremendous scope for improvement of temperate nut crops provided with a wide variability of genetic resources, which can be explored for the development of cultivars with resistance to biotic and abiotic problems. Climate-smart cultivars suitable for changing climatic conditions and specific locations have to be bred by following advanced breeding techniques. The major bottleneck in perennial nut crops is a long breeding cycle and takes a lot of time to develop new varieties this can be improved rapidly by advanced genomics techniques. A lot of improvement work from morphological markers to recent advanced genomics and construction of genetic maps was studied in temperate nut crops but still, there is a chance of improvement using recent techniques such as the sequencing of chloroplast and nuclear genomes, gene mapping, gene editing tools CRISPR/Cas9 and multi-omics approach can be applied in near future (Pan et al., 2016).

Keywords

floral patterns

genomics

good horticultural practices

hybridization

long breeding cycles

pollination management

temperate nuts

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Chapter 9 Disease and Pest Management in Temperate Nut Crops

BEKRI XHEMALI¹ and HYSEN KOKIÇI2,3

¹ Kosovo Institute of Agriculture, Pejë, Kosovo

² Institute for Sustainable Plant Protection, National Research Council (CNR), Via Amendola, Bari, Italy

³ Institute of Plant Genetic Resources, Agricultural University of Tirana, Rruga Paisi Vodica, Tirana, Albania

*Corresponding author

Abstract

Disease and pest management in temperate nut crops is a major challenge worldwide. Depending on cultural practices, treatment efficacy, and environmental conditions, the estimated damage caused by diseases and pests in nut crops ranges from 20% to 50%. Among nut crops, walnuts and hazelnuts are widely cultivated globally, and their most serious diseases and insect pests include bacterial blight, powdery mildew, Armillaria root rot, apple mosaic virus, moths, beetles, flies, bugs, aphids, and mites. Accurate identification of plant pests and diseases is a critical first step in effective pest and disease control and management. Farmers often rely solely on chemical spraying to control these pests, which can lead to pest resistance. This chapter outlines different Integrated Pest Management (IPM) practices that successfully maintain pest and disease levels below economic thresholds. The IPM approach offers several advantages over conventional management methods, as it is more economical and environmentally friendly, contributing to a sustainable agroecosystem. This book chapter provides a brief introduction to the most common diseases and pests affecting major nut crops and serves as a valuable resource for students and agricultural specialists, aiding in the identification and management of pests and diseases while evaluating their economic impact.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

9.1 Introduction

Among all temperate nut crops, the walnut and hazelnut take center stage as two major crops. Walnut has a very substantial economic and social importance, due to its high food values and the quality of the wood used as raw material in industry. The most commercially grown nut tree worldwide is Juglans regia L. originated from Persia (Ginzel, 2010). Moreover, hazelnut has another significant importance with global commercial production in many countries, such as: Turkey, Italy, Spain, France, and the United States of America (Ali Niazee, 1996). Worldwide, orchards of temperate nut crops are usually affected by several diseases and pests that cause significant challenges in their cultivation. Among the major biotic factors, various plant pathogens can affect nut crops, but some of them are specific and need particular attention, such as Bacterial blight, Powdery Mildew and Armillaria root rot (Hassan and Ahmad, 2017). Certainly, pest management can be a significant challenge in walnut and hazelnut cultivation, particularly due to the difficulty of spraying large trees. While traditional control strategies are generally effective against many pests, walnuts and hazelnuts remain susceptible to several diseases and pests (Sharma et al., 2012).

Likewise, pests are highly important and cause serious damage to walnuts and hazelnuts. Among them, beetles, moths, bugs, flies, aphids and mites are of main importance. Typical damages of pests in nut crops cause the branch to dry and develop grey nipple specks and then the fruit appears shriveled and wrinkled. (UCIPM, 2011). Such pests mainly oviposit on the leaves, twigs and branches, where larva develops and feed insatiably, indeed these cause nut drop and damage to various parts of the tree (Khan et al., 2011; Gull et al., 2019). Filbert insect pests are important pests of hazelnuts in North America (AliNiazee, 1992). Likewise in Europe including Turkey, weevils, beetles and bugs cause serious damage in hazelnut crops (Ioachim et al., 1996; Tuncer et al., 1997; Milenkovic and Mitrovic, 2000; Ganter, 2000). In order to properly manage these pests, it is crucial to understand the biology and life cycle of insect pests. Moreover, it is also very important to understand the vulnerable stages and peak emergence times of adults for a proactive approach to control easily. Appropriate identification of these pests is a fundamental step in effective pest management. Therefore, adopting general management practices and utilizing monitoring tools are essential components of an integrated approach to pest management that emphasizes long-term prevention. An effective IPM program combines various strategies, including cultural practices, to manage pests in a sustainable manner. This approach aims to achieve balanced pest control while minimizing the negative environmental and economic impacts. Therefore, this book chapter is a brief introduction to the most common diseases and pests of the main nut crops and their management. It can serve as a valuable resource to support students and other agricultural specialists in the identification and management of pests and diseases as well as evaluating their economic impact.

9.2 Major Disease Of Temperate Nut Crops

9.2.1 Bacterial Blight (Xanthomonas Arboricola Pv. Juglandis) Bacterial Blight (Xanthomonas Arboricola Pv. Juglandis)

Bacterial blight is indeed a significant disease that can have a detrimental impact on crop production. This bacterium is considered a quarantine organism in the EU phytosanitary legislation and it is listed in the A2 list of the European and Mediterranean Plant Protection Organization (Lamichhane, 2014). The bacterial light of walnuts affects different parts of the tree. It causes typical symptoms on leaves and twigs as well as affects immature fruits and stems of walnut trees (Kałużna et al., 2014). Typical characteristic symptoms of walnut blight on leaves appear as small brown spots in an irregular form surrounded by yellow chlorotic haloes. On fruits, the symptoms appear as sunken and water-soaked lesions. Additional symptoms are the presence of cankers on the stem and damage to the kernel of immature fruit (Kim et al., 2021). The management of bacterial blight should typically involve a combination of several control measures. This integrated approach helps maximize effectiveness and minimize the development of bacterial resistance. Using healthy planting material is an important preventive measure to exclude the entrance of this pathogen into new areas and minimize the risk of bacterial blight (Lamichhane, 2014). When the pathogen enters and is established in new areas, particular control measures should focus on reducing the pathogen inoculum to minimize the spread and severity of bacterial blight. As an integrated approach, cultural practices starting with the elimination of infected plant parts and treatment with copper-based compounds are recommended in order to reduce the inoculum of bacterial blight.

9.2.2 Powdery Mildew (Phyllactinia Guttata and Erysiphe Corylacearum)

Powdery mildew is a fungal infection caused by obligate biotrophic fungal plant pathogens distributed worldwide and can infect a wide range of plants including nuts. Powdery mildew comes from the characteristic white powdery appearance of the fungal growth on infected plant surfaces and it can be observed by the naked eye (Bilge, 2020). Powdery mildew in hazelnut crops is known to be caused by two different fungal pathogens Phyllactinia guttata and Erysiphe corylacearum. The first pathogen Erysiphe corylacearum is identified as a destructive powdery mildew agent causing significant damage to hazelnut cultivation orchards (Braun and Cook, 2012). Moreover, another fungal pathogen Phyllactinia guttata causes powdery mildew in hazelnut crops (Sezer et al., 2017). Typical symptoms of these fungal pathogens can be identified by their morphological characteristics as forming white powdery patches or spots that appear white to greyish in color.

It is strongly recommended to reduce the number of mother plants in order to control successfully powdery mildew. Additionally, integrating good agricultural practices could properly help the disease control. Recent studies revealed that the effectiveness of the spraying program of tebuconazole and azoxystrobin is successfully used to control powdery mildew (Yildirim, 2022). Fungicides can be an important tool in managing powdery mildew disease. Although, relying solely on fungicides without implementing adequate cultural practices is generally insufficient for effective control.

9.2.3 Armillaria Root Rot (Armillaria Mellea)

Armillaria causes root rot disease in nut crops. This is considered an economically important pathogen that can infect a wide range of tree plants, including some herbaceous plants. This fungus lives in the soil and produces white rot roots. Additionally, this pathogen can cause various secondary symptoms, such as yellowing, reduced growth, defoliation and death (Guerrero, 2014). Armillaria mellea has a complex life cycle. It spreads through vegetative mycelium which persists in the soil for a long period. This mycelium infects and colonizes the roots of host plants, often causing root rot. During favorable conditions, such as cool and moist weather, the fungus produces mushrooms that release spores for sexual reproduction.

Armillaria root rot disease control has several changes due to its saprophytic unique ability of mycelia growth below ground. In order to develop an effective disease management strategy for Armillaria root disease requires careful consideration of the specific ecosystem and the economic value of the host plants (Bogdanski et al., 2018). An effective control strategy for Armillaria root disease has primarily focused on reducing the inoculum in the soil and preventing its spread (Heinzelmann et al., 2019). Additional control measures include improving plant vigor through proper cultural practices and providing adequate water and nutrition. Fungicide treatments are generally not effective against the pathogen due to the location of the infection within the roots of the tree. Improving microbiological soil communities is a new development method for biological control of Armillaria root rot disease (Vayssier-Taussat et al., 2014).

9.3 Major Pests Of Temperate Nut Crops

9.3.1 Codling Moth (Cydia Pomonella) Linnaeus (Lepidoptera, Tortricidae)

The codling moth (Cydia pomonella) is one of the most economically important pests of walnut trees worldwide (Ginzel, 2010; Chen and Dorn 2010). The codling moth is widely distributed and found in various regions around the world (Barnes, 1991). Females lay white-colored eggs individually on developing fruits, leaves, and twigs of their host plants. The period of egg development can range from 4–12 days, while the development of larvae varies from 21–30 days and the pupa phase goes from 8–14 days. The mature larvae behave is to go out of the fruit and fall on the ground to reach the bark of the tree. Adults are characterized by their small size and have a typical gray color. Codling moths overwinter in the larval stage in the bark or on the ground near the trunk of the tree. Although, the codling moth has multiple generations each year, only three generations are recorded to damage the crops. This insect survives in the winter in a diapause behavior as part of its life cycle which allows it to survive through the winter season (Barnes, 1991). The larva attacks the fruits in many crops (Teodorescu et al., 2003; Pejru et al., 2018). In order to detect codling moth infestations, a common and effective method is observing frass produced by the larvae at the point of entry into the husk. Moreover, larvae of the second generation enter through the side of the husk where two nuts touch. After the shell of the nut has hardened, larvae can enter the nuts through the soft tissue at the stem end. In the first generation, the larvae can cause damage that leads to the drop of nutlets. Second and third generation of larvae cause damage and feed to the kernel. The second and third generations of codling moths cause significant damage to nut crops, it affects the quality of fruits and many times leads to the presence of larvae inside the nuts. Mating disruption is suggested as a proper management strategy in nut crops which is a valuable and environmentally friendly method and significantly reduces the density of the moth (Angeli et al., 1999). Additionally, this method gave the same results on apple trees as well (Waldner, 1997). Furthermore, a recent study under the lab conditions showed that the use of microbiological control such as entomopathogenic fungi have given significant pathogenicity levels against the larvae of the moth. Such fungi are naturally available in the field and showed beneficial effects in controlling C. pomonella (Gürlek et al., 2018). Preferential heating of insects in dry nut fruits is another strategy developed as thermal treatment for controlling larvae (Wang et al., 2006). The time of the treatment is relevant to the effectiveness of chemical control. Depending on the mode of action, the application of many insecticides is recommended as a preventive method or once the eggs are hatched (UC PMG, 2020). Furthermore, once the codling moth populations increased, the application of tebufenozide and diflubenzuron can be effectively used.

9.3.2 Walnut Twig Beetle (Pityophthorus Juglandis) Blackman (Coleoptera, Curculionidae)

The walnut twig beetle is a species that originated from Mexico and the southwestern USA. In Europe, the twig beetle was first recorded in the northern part of Italy (Montecchio and Faccoli, 2014). This species is associated with the fungus Geosmithia morbida (Ascomycota: Hypocreales: Bionectriaceae), which is a destructive fungus causing a thousand cankers in walnut trees (Tisserat et al., 2011; Seybold et al., 2013). The individuals of the walnut twig beetle identified in Italy showed the ability to be vectors of G. morbida (Montecchio et al., 2014). Walnut twig beetles are reddish to brown and they are very small, which then are reproduced under the bark of nut trees (Faccoli, 2015). The beetle is very active and flies nearly whole the year. Depending in environmental conditions, this insect has two to three life generations per year. The twig beetle usually flies when temperatures are moderated in light intensity and a relatively humid environment. The beetle has been observed to fly from the middle of April until October. Furthermore, in November adults decline their flight drastically. Walnut twig beetles overwinter as larvae under the bark of host trees (Newton and Fowler, 2009; UC PMG, 2020). Early in spring, adults colonize areas of bark at the base of twigs, but they can usually infest the underside of large branches or the trunk (Figure 9.1).

Figure 9.1 Life cycle of Geosmithia morbida and its vector Pityophthorus juglandis Source: Adapted adopted from Steven Valley, Piero Amorati, Whitney Cranshaw, Lucio Montecchio and EPPO global database.⏎

Typical symptoms of yellowing and thinning of leaves may be observed usually followed by twig damage or dieback. Progressively, affected large branches could be killed and these trees eventually die (Tisserat et al., 2009). In order to have an early detection of the diseases, capturing and identifying the tiny beetle is an essential key factor. Proper managing always starts with the application of agronomic measures in the field, orchard sanitation, removal of infested woody parts, pruning during the winter and burning infested material. However, pheromone traps are useful to detect the presence of the species. Parasitic wasps such us Neocalosoter and Plastonoxus species and predaceous beetles: Narthecius simulator, Parandrita cephalotes, and Temnochila chlorodia can usually help and contribute to biological control of this pest (UC PMG, 2020; Audley et al., 2020). Insecticidal treatments and heat treatments have proven to be more than 80% effective to control P. juglandis. In laboratory conditions, suitable fungicides have the potential to inhibit or even kill Geosmithia (Sitz, 2013).

9.3.3 Walnut Weevil (Alcidodes Porrectirostris) Marshall (Coleoptera, Curculinoidae)

The walnut weevil illustrated in Figure 9.6 is highly distributed and has been recorded in many growing regions worldwide (Sharma et al., 2012). The main damage to the fruit is the primary damage caused by the cryptic stage, which refers to the hidden or concealed larval stage of the pest (Guroo et al., 2021). Weevil adults live during the whole year. They lay eggs in green fruits during the second week of May. Larvae of the first and second instar feed on the green skin and its third affects the kernel of the fruits. Therefore, infested fruits usually fall down to the ground. In early July, larvae start pupation inside the dropped fruits. Then, during the last week of July, adults start emerging inside the fruits (Shah et al., 2012). In addition, for a proper management strategy to prevent the destruction of fallen nuts, a sanitation protocol should be developed (Sharma et al., 2012). An efficient method would be spraying with carbaryl two times a week from the first attack. Another alternative strategy with promising potential is the use of Beauveria bassiana and Metarhizium anisopliaeoffer as a biological control method against several weevils (Batta et al., 2004). The growth production of these fungi may be used for managing A. porrectirostris under field conditions (Guro et al., 2021).

9.3.4 Walnut Aphids (Chromaphis Juglandicola) Kaltenbach And Callaphis Juglandis Goeze (Hemiptera, Aphididae)

One of the most economically important pest causing major damage to nut crops is the walnut aphid (Chromaphis juglandicola) and the veined dusky aphid (Callaphis juglandis) (Khan et al., 2016; UC PMG, 2020). Their colonies of nymphs as well as adults usually suck the sap to the ventral surface of the leaves. Typical symptoms are dried leaves, leaf curling and pallor darkens or shrivels kernels. High colony density may cause plant stunning. Typically, the secretion of honeydew where sooty mold develops may lead in hindrance to photosynthetic activity of the plant and further retarding its growth (Sharma et al., 2012). Its infestation may reduce nut yield and quality. Additionally, aphids in nut crops usually overwinter in the egg stage on twigs. Eggs hatch once leaf buds in early spring begin to open (UC PMG, 2020). C. juglandicola has a monoecism lifecycle and all of viviparous females are apterae. While during the overwintering season, nymphs have dark spots on the abdomen. Likewise, P. juglandis also has a monoecism holocyclic lifecycle and all of the viviparous females are alatae, meanwhile, oviparous females are apterae (Figure 9.2).

Figure 9.2 Main nut crop aphids: (A) C. juglandicola, and (B) P. juglandis Source: Adapted from Lee et al., 2018⏎

Recent studies have revealed that aphid nymphs feed on the upper part of leaves (Lee et al., 2018). Monitoring is a crucial step in the proper management of aphids and should be carried out throughout the shoot and nut growth period (Khan et al., 2016). In cases of high aphid density, the application of insecticides is recommended. The use of aphicides has shown outstanding results; however, identifying alternative eco-friendly methods is a more sustainable approach. One such method involves using parasitic wasps in combination with other biological control agents (UC PMG, 2020). The application of the parasitoid Trioxys pallidus has also been shown to reduce the population density of Chromaphis juglandicola (Frazer et al., 1973; Van den Bosch et al., 1979). Agronomic measures such as proper sanitation, collection, and destruction of fallen nuts should also be implemented. Additionally, the use of resistant cultivars has proven effective. Studies have shown that the Fernor cultivar creates a less favorable environment for aphid development and reproduction.

9.3.5 Walnut Husk Fly (Rhagoletis Complete) Cresson (Diptera, Tephritidae)

Rhagoletis completa has the origin from the North America and it has invaded in many European countries in the late 1980s (EPPO, 2013). This is a species of high economic interest (Poggetti et al., 2019). This pest has only one generation yearly (Bush, 1966). Its eggs usually laid below the skin of the nut fruits and then they will hatch after 3–7 days. Then the larvae feed for a period of 2 up to 5 weeks. It overwinters in the soil as a pupa under the trees. Adults usually begin to emerge in the middle of July (Christenson and Foote, 1960). Larvae affects husk tissues and causes shell staining to darkened kernels. Through high infestations of this pest, premature fruits may fall down and additional harvesting costs is caused (Duso et al., 2006). Monitoring usually carried out by using yellow sticky traps containing ammonium carbonate and settled inside the canopy. In addition, upon identification of this pest, agronomic measures should be carried out by removing fallen and infested fruits shall be removed. Additional measures shall be taken to destroy wild and abandoned trees. Chemical treatment using systemic organophosphates showed high effects against most species in order to kill its eggs, larvae and adults (Boller and Prokopy, 1976). Recent studies revealed that using natural enemies as well as semi-chemicals have great potential options against this pest (Figure 9.8) (Verheggen et al., 2017).

9.3.6 European Red Mite (Panonychus Ulmi) And Walnut Blister Mite (Eriophyes Erinea)

European red mite (Panonychus ulmi), and blister mite (Eriophyes erinea) are considered very important pests affecting nut crops. However, they have reached the status of disturbing the complex of their natural enemies including Chromaphis juglandicola (Kalt.), Eulecanium pruinosum (Coq.) (Sharma et al., 2012). It is well described that the European red mite feeds on the contents of the cell, meanwhile, the while blister mite feeds usually on the lower parts of leaflets. Therefore, the damages caused from the European red mite are more common in cooler areas causing light stippling and bronzed mode of the leaves. Several bronzing may reduce nut yield significantly (Khan et al., 2016). Additionally, the blister mite affects the upper surface of leaflets and causes characteristic blister-like swellings. Typically, looking at the underside of blistered leaves may see yellow to orange felt masses in depressions. At the end of the season, these masses become brown. Therefore, the damages caused by the walnut blister mite are considered aesthetic (UC PMG, 2020). For the management of mites, it is very important to take into consideration scouting and additionally treating with summer oil during the growing season. It is recommended to establish a monitoring program for the European red mites and other priority pests affecting nut crops. For the biological control management, it is recommended the predator Amblyseius finlandicus which shall be used to attack P. ulmi. Chemical treatments are used by spraying dicofol, chlorpyriphos or dimethoate for high efficiency for this mite (Figure 9.3).

Figure 9.3 Galls formed in walnut leaf caused by blister.⏎

9.3.7 Brown Marmorated Stink Bug (Halyomorpha Halys) Stål (Hemiptera, Pentatomidae)

Halyomorpha halys is originally from Asia and is present in China, Japan, Korea, and Taiwan. It is a polyphagous stinky bug (Hoebeke and Carter 2003, Lee et al., 2013 a). However, it is present also in Europe and it was first captured in Switzerland (Wermelinger et al., 2008; Malek et al., 2018). Dual white bands that appear on its antennae can easily distinguish this bug from other stink bugs. Brown marmorated stink bugs have five instars (Figure 9.4).

Figure 9.4 Life stages of BMSB. Source: Adapted from Leskey et al., (2013).⏎

Due to the climatic conditions, this bug may spawn one or even more generations. This bug usually overwinters as adults, it is easily found in large quantities, artificial and natural shelters. H. halys (Figure 9.4) causes significant damages in the reduction of quantity and quality of the product in hazelnut plantations. In the field, typical symptoms as brown tissue and shriveled hazelnuts are identified (Bosco et al., 2018). H. halys might cause even moldy or rotten hazelnuts which can indirectly damage fruits due to the secondary infections from diseases that enter through the punctures on kernels. Monitoring is carried out by lying a white sheet on the ground of the tree and shaking the branches. Another way is using aggregative pheromone to bait traps which capture all bugs affecting nut crops (Gasparri et al., 2018, 2021). Using predators as biological agent can kill all stages of this bug, however, adults and eggs may be attacked by the parasitoids. Meanwhile, pyrethroids can be applied in late spring (Rice et al., 2014)

9.3.8 Ambrosia Beetles (Coleoptera, Curculionidae)

Several species of ambrosia beetle can attack hazelnut trees. However, Tuncer et al., (2017) defined the classification of the most important species of ambrosia beetle found in hazelnut orchards that are Anisandrus dispar Fabricius, Xylosandrus germanus Blandford, and Xyleborinus saxesenii Ratzeburg. These beetles are present in the orchards along the Black Sea, and in the orchards that are located near woodlands. Enormous economic losses are cause by these species (Tuncer and Ecevit, 1997; Kushiyev et al., 2022). Ambrosia beetles have one generation per year. Females fly in spring, when temperatures start increasing. They lay eggs in the tree. Beetles overwinter as adults into trees. When the trees are under conditions of stress become more attractive by the beetles. Channels drilled prevent sap flow, which can lead to the death of young trees. For the management of these beetles agronomic measures should be taken into consideration. Infested trees and branches should be removed and burned before adult emergence starts (Tuncer and Ecevit, 1996; Bucini et al., 2005). Hazelnut trees should be supported by good fertilization, pruning and watering, in order to keep the trees vigorous against these pests. Biotechnological control such as trap baited with ethanol and denaturized with 1% toluol are found to be effective in mass trapping of these pests (Figure 9.5). (Tuncer, 2008).

Figure 9.5 An adult of ambrosia beetle. Source: Reprinted from Tuncer et al., 2017. https://creativecommons.org/licenses/by/4.0/⏎

9.3.9 Filbert Worm (Melissopus Latiferreanus) Walsingham (Lepidoptera, Tortricidae)

Filbert worm feeds into young nut fruits and destroys the kernel. Fruits then are not marketable, resulting in a reduction of the total yield production. Filbert worm has only one generation per year (Olsen, 2002). This pest overwinters in the larvae form within hibernacula, covered with plant debris of the orchard floor. Pupa begins in May from the overwintering larvae. Adults emerge from June to October when the growing season is being developed. Monitoring with pheromone traps, by placing them in the top third of the tree canopy and replacing pheromone dispensers every 4–6 weeks. Furthermore, it is relevant to change the trap bottoms when soil and insects have accumulated enough to prevent catches or easy counting. Spot spraying is successful in specific situations. When traps in the orchard’s border show a strong flight of moths, spraying with at least four to six outside rows that are nearest to the abandoned or heavily infested areas will have efficient results (Olsen et al., 2013). Microbiological control such as the application of entomopathogenic nematodes has shown that filbert worm larvae, as well as pupae, are susceptible to S. carpocapsae. In addition, S. carpocapsae field applications reduce the number of overwintering filbert worm larvae, but have a high cost. However, the costs could be reduced by confining the treated area to major infestation sources, or by decreasing the number of nematodes applied, for example, by using a more suitable entomopathogenic nematode (Figure 9.12) (Bruck and Walton, 2007; Chambers et al., 2010).

Keywords

bacterial blight

entomopathogenic nematodes

pest management

juglandis

shriveled hazelnuts

temperate nut

walnut weevil

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Chapter 10 Pest Status and Its Management in Temperate Nut Crops: Opportunities and Challenges

V. GOPINATH,¹ D. GOUTHAMI BAI,² NISHA THAKUR,³ JASTI SRI VISHNU MURTHY,² SANJAY KUMAR SAHOO,⁴ SANHITA CHOWDHURY,⁴ and VINOD KUMAR DUBEY4,*

¹Department of Plant Pathology, Post-Graduate College of Agriculture, Dr. Rajendra Prasad Central Agricultural University, Pusa, Samastipur, Bihar, India

²Department of Agricultural Entomology, College of Agriculture, Kerala Agricultural University, Thrissur, Kerala, India

³Department of Plant Pathology, Indira Gandhi Krishi Vishwavidyalaya, Raipur, Chhattisgarh, India

⁴Department of Genetics and Plant Breeding, College of Agriculture, Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

*Corresponding author

ABSTRACT

The proneness of nut crops to attack by a variety of pests is one of the primary challenges that must be overcome in order to successfully cultivate it in temperate climates. The most economically significant temperature nut crops are walnut, chilgoza, chestnut, hazelnut, pecan nut, pistachios, and almond. A broad range of pests affecting on foliage, wood, flowers, roots, and developing nuts. The pests infestation includes scab, mildew, rust, canker, bacterial blight, aphids, beetles, weevils, caterpillars, stink bugs and nematodes. Similar to agricultural crops, temperate nut crops are cultivated in monoculture, and as a result, the insect issues are entirely different and complex in nature. It is impossible for farmers to implement appropriate measures for effective control of economically significant pests until they have a basic understanding of pests identification, time of appearance, peak period, nature and extent, and recommended practices. In this chapter we examines and discusses the appropriate information is available for the management of pests of temperate nut crops, the scope and problems in the adoption of suitable management strategies that may be used in the future by pest control advisers and farmers of temperate nut crops.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

10.1 Introduction

India accounts for nearly 10% of global production of fruit and nut crops. Hazelnuts, pecans, chestnuts, chilgoza, pistachio nuts, almonds, and walnuts, among many others, are popularly grown in the temperate regions of Himachal Pradesh, Jammu and Kashmir, Uttarakhand, and other eastern hill states of India (Atteri, 2004). Infestations of disease, nematodes, and insect pests are more likely to occur in a nut orchard because of the ecosystem’s stability and permanence. High yielding cultivars, monoculture, high density planting, intensive cropping systems, high doses of fertilizers, frequent irrigation, and the use of broad spectrum pesticides have all contributed to an increase in the biotic potential of pest and pathogen species, which has had a devastating effect on the ecosystem of fruit trees. Temperate nuts crops have a high export orientation and have the potential to generate significant foreign exchange. It has been discovered that a variety of pests and illnesses infest temperate nut crops (Akbar et al., 20110). In addition to a number of other issues, the prevalence of pests and diseases is a significant concern. In addition, improper pesticide application in the agricultural system and pesticide resistance in potential pests and pathogens have resulted in enormous crop losses (Nainwal et al., 2004). In this chapter, we have discussed about the major insect pests, nematodes and diseases that cause significance damage to different temperate nut crops thereby inflicting heavy economic losses to the farmers.

10.2 Major Pests Of Walnut Crops

10.2.1 Economic Importance

Produced by trees in the genus Juglans, walnuts are most commonly associated with the English walnut (Juglans regia). According to the Food and Agriculture Organization, China produced nearly two million metric tonnes of walnuts in 2016. The most common kinds of nematodes, diseases, and insects that attack on walnut crops are listed in Table 10.1 and depicted in Figure 10.1.

Table 10.1 Major Pests of Walnut Crops⏎

Sl. No. | Common Name | Scientific Name | Order/Kingdom/Domain | Family/Phylum/Division
 1. | Walnut weevil | Conotrachelus juglandis (Leconte) | Coleoptera | Curculinoidae
 2. | Gypsy moth | Lymantria obfuscata (Walker) | Lepidoptera | Lymentriidae
 3. | Walnut aphid Dusky-veined aphid | Chromaphis juglandicola (Kaltenbach) Panaphis juglandis (Goetze) | Hemiptera | Aphididae
 4. | Walnut tree trunk borer | Aeolesthes sarta (Solsky) | Coleoptera | Cerambycidae
 5. | Walnut huskfly | Rhagoletis completa (Cresson) | Diptera | Tephritidae
 6. | Anthracnose | Gnomonia leptostyla | Fungi | Ascomycota
 7. | Armillaria root rot | Armillaria mellea | Fungi | Basidiomycota
 8. | Powdery mildew | Phyllactinia guttata | Fungi | Ascomycota
 10. | Phytophthora root and crown rot | Phytophthora spp. | Chromista | Oomycota
 11. | Crown gall | Agrobacterium tumefaciens | Bacteria | Gracilicutes
 12. | Walnut blight | Xanthomonas campestris | Bacteria | Gracilicutes
 13. | Root lesion nematodes | Pratylenchus vulnus | Animalia | Nematoda
 14. | Ring nematode | Criconemella xenoplax | Animalia | Nematoda

Figure 10.1 Major diseases and insect pests of walnut. ⏎

10.2.2 Insect Pests

10.2.2.1 Walnut Weevil

The eggs are ovoid, smooth, and grub has a head that is beige-white and reddish brown. The pupa has free body parts and is of the exarate type (IPPC, 2018).

10.2.2.1.1 Life Cycle

The female weevil will chew holes in the niches and lay her eggs there. When they hatch, grubs eat the kernels, pith, stem, and petiole. The larvae bore deeper and longer into the pith, turning the kernels into a blackened mush as they develop.

10.2.2.1.2 Damage Symptoms

Adult weevils cause damage to leaf petioles, female flower buds, young shoots, and nuts. The grubs’ burrowing larvae not only damage the shoots, leaves, and stems but also cause wide spread premature nut dropping. Weevils cause 50–60% damage to leaves and nuts during June and July (Pandey and Mall, 2016).

10.2.2.1.3 Management

Spraying on young plants with chlorpyriphos 20 EC at a concentration of 0.02% or dichlorvos at a concentration of 0.05% is recommended throughout the months of April and May. Carbaryl sprayed at a dosage of 0.2% twice within seven days after the first outbreak can also be used to stop the spread of the disease.

10.2.2.2 Gypsy Moth

The pattern of dots on the moths’ wings is shaped like an upside-down V (Khan and Kundoo, 2018).

10.2.2.2.1 Life Cycle

Adult moth lays its eggs on stones, tree bark. Each egg mass is tan and fuzzy in appearance, and it contains 500–1000 eggs. Pupation takes place in the last instar caterpillar’s molted skin (Pandey and Mall, 2016).

10.2.2.2.2 Damage Symptoms

The tree’s foliage has been heavily defoliated, with up to 51% or more of it being lost (Pandey and Mall, 2016).

10.2.2.2.3 Management

Under certain environmental conditions, nuclear polyhedrosis virus (NPV) and the fungus, Entomophaga maimaiga can cause widespread mortality. At the appropriate time and concentration, infested trees can be sprayed with chlorpyriphos 20 EC or dimethoate 30 EC (Khan and Kundoo, 2018).

10.2.2.3 Walnut Aphid

Dusky veined aphids differ from walnut aphids by the dark line that runs along the veins of their bodies, while walnut aphids are smaller and yellower (Pandey and Mall, 2016).

10.2.2.3.1 Life Cycle

Females without wings travel to walnut tree trunks in the autumn to lay their eggs in crevices. The aphids develop and reproduce on the leaflets without mating and producing new adults (Khan et al., 2015). According to (Pandey and Mall, 2016) fertilized females will lay black eggs over leaf.

10.2.2.3.2 Damage Symptoms

Adults and nymphs of the aphid family feed on plant tissues, including leaves, petioles, flowers, and fruits, causing these to shrivel, twist, and fall off. High populations of aphids can cause 25% yield reduction.

10.2.2.3.3 Management

Late in the month of May or early in the month of June is the optimal time to spray a solution that contains either dimethoate 30 EC (100 ml), methyl-o-demeton 25 EC (80 ml), phosolone 35 EC (140 ml), or chlorpyriphos 20 EC at a rate of 100 ml/100 liter of water in order to achieve effective control of both species of aphid (Pandey and Mall, 2016).

10.2.2.4 Walnut Trunk Borer

The beetle’s body is long and dark gray-brown when it’s an adult.

10.2.2.4.1 Life Cycle

Each female has potential to produce between 240 and 270 eggs over her lifetime. They begin to construct the pupation cells in the middle of July by the end of the month (Khan and Kundoo, 2018). Pupation takes place inside of these cells, and the adult beetle emerges from them around two weeks later.

10.2.2.4.2 Damage Symptoms

Grub makes small circular holes with a lot of waste. Trees that have been infested or damaged can be seen to have wilting and drying.

10.2.2.4.3 Management

The larvae of the trunk borer can be controlled by the parasitoid, Sclerodermus turkmenicus, and the adults can be controlled by the white muscardine fungus, Beauveria bassiana. The trunk borer can be effectively controlled with aluminum phosphide (Bhat et al., 2010) found a 78.78% reduction and dichlorvos for more than 45 days after treatment. Dimethoate 0.03%, chlorpyrifos 20 EC, or quinalphos 25 EC sprayed onto infested trees (1 ml/liter of water).

10.2.2.5 Walnut Husk Fly

It can reduce crop yields by as much as 80% The walnut husk fly has a yellow dot at the back of its thorax and a yellow head (Medic et al., 2022).

10.2.2.5.1 Life Cycle

Females lay 300–400 eggs. Walnut leaf flies mate and lay eggs after 1–2 weeks. Maggots expand the black area of the husk while leaving the skin intact. The development of a larva takes 30–40 days.

10.2.2.5.2 Damage Symptoms

Up to 50% loss in some commercial varieties can be attributed to the maggots of the walnut husk fly. The maggot’s feeding also destroys the husk’s outer skin, which rots and stains the nut shell.

10.2.2.5.3 Management

To make traps more appealing, 3 g of ammonium carbonate is used as bait. Spray dimethoate 30 EC/fenitrothion 50 EC, or methyl-o-demeton 25 EC as rise in the number of flies caught in the traps over a 3 day period (Medic et al., 2022).

10.2.3 Diseases

10.2.3.1 Anthracnose

10.2.3.1.1 Damage Symptoms

Leaves, petioles, shoots, and/or husks may develop brown to black spots that fade inward and sometimes have a green halo around them.

10.2.3.1.2 Favorable Condition

During the rainy season, the water that runs through diseased leaves contains pathogen spores that can cause additional infections.

10.2.3.1.3 Mode of Spread and Survival

As soon as it starts to rain in the spring, ascospores are forced out of the infected plant’s perithecia (Loreti, 2005). Wind currents carry these ascospores to the plant’s new shoots, where they cause the first infection.

10.2.3.1.4 Management

Spray zineb or captan at a concentration of 0.25% or Bordeaux mixture at a concentration of 0.8%. This should be done at each of the following stages: (i) the leafing stage; (ii) the full leaf stage; and (iii) the full leaf stage.

10.2.3.2 Armillaria Root Rot

10.2.3.2.1 Damage Symptoms

This plant’s fruiting bodies resemble mushrooms with caps ranging from yellow to orange and 5–12 centimeters in diameter. At the bottom of the plant, you might find honey-colored mushroom clusters growing.

10.2.3.2.2 Favorable Condition

Conditions that are humid and have moist soil favors disease development.

10.2.3.2.3 Mode of Spread and Survival

Rotting root pieces can sustain the fungus for years. Rhizomorphs spread the disease. The fungus can survive on dead roots for a long time.

10.2.3.2.4 Management

Root stocks that are resistant to the disease should be planted for the disease prevention.

10.2.3.3 Powdery Mildew

10.2.3.3.1 Damage Symptoms

The leaves and fruit have tiny white spots that look like powder. In the white growth, you might be able to see small black fungal fruiting bodies.

10.2.3.3.2 Mode of Spread and Survival

The fungus lives on as resting spores on the mycelium or in encased haustoria in the buds. The secondary spread happens when the conidia get into the air.

10.2.3.3.3 Management

Remove diseased leaves from the plant that are harboring the pathogen in order to lower the primary inoculum load. A fungicide that contains sulfur ought to be applied.

10.2.3.4 Phytophthora Root and Crown Rot

10.2.3.4.1 Damage Symptoms

When the bark is peeled back, cankers appear as discolored zones. Black fluid frequently seeps through holes in the cambial region and reaches the surface.

10.2.3.4.2 Favorable Condition

These fungi grow best in soils with a lot of water and at temperatures between 13°C and 21°C and poorly drained soils where water stays for a long time.

10.2.3.4.3 Mode of Spread and Survival

Sporangia can only release zoospores if they are in close proximity to a water source. Free water facilitates the transport of zoospores, enabling their movement and infection.

10.2.3.4.4 Management

Infective hyphae invade the root or collar region after zoospores have been carried to the soil’s surface by running water and have shed their flagella.

10.2.3.5 Crown Gall

10.2.3.5.1 Damage Symptoms

As the abnormalities grow larger and more advanced cell death and decay cause the surfaces to turn a dark brown or black and become rough and convoluted. Affected plants may experience stunting, chlorotic leaf development, and increased vulnerability to environmental stresses like winter injury.

10.2.3.5.2 Favorable Condition

Wet soil is a breeding ground for the pathogen.

10.2.3.5.3 Mode of Spread and Survival

When sensitive hosts are produced in such soils, the bacterium penetrates through fresh wounds in the roots or stems near the ground created by cultural practices, grafting, or insects (Yousefikopaei, 2007).

10.2.3.5.4 Management

Preventing this disease on nut fruits by dipping nursery stock roots in a suspension of Agrobacterium radiobacter containing strain K-1026 has been very effective.

10.2.3.6 Walnut Blight

10.2.3.6.1 Damage Symptoms

Black, slightly depressed spots appeared on the stem and young shoots, girdling them and causing them to die. Infected nuts that are picked too early will fall off the tree, while those that are picked too late will shrink and turn brown (Burokiene, 2010).

10.2.3.6.2 Favorable Condition

When it rains and is cool outside, that’s time walnut blight does the most damage.

10.2.3.6.3 Mode of Spread and Survival

The bacterium invades the host plant through wounds and stomata. Rain, fog, dew, and sprinkler irrigation all contribute to the blight problem by providing the pathogen with the moisture it needs to multiply and spread (Bogatzevska, 2007).

10.2.3.6.4 Management

As soon as symptoms are noticed, a solution of 1 gram of streptocycline and 20 grammes of copper oxychloride per 10 liters of water should be applied.

10.2.4 Nematodes

10.2.4.1 Root Lesion Nematodes

This species poses a risk to the walnut industry due to its high pathogenicity and global distribution. Root damage that exceeds the plant’s ability to regenerate roots can kill young trees.

10.2.4.2 Other Nematodes

The significance of the pests viz., Criconemella xenoplax and Cacopaurus pestis to walnut trees has not been documented in recent years. Thorne found that when C. pestis was allowed to parasitize the roots of Juglans regia (Persian walnut), large lesions formed on the roots (2.4 cm in diameter) and smaller roots died.

10.3 Major Pests Of Almond Crops

10.3.1 Economic Importance

One of the most widely grown nut crops, almond (Prunus dulcis (Miller) D.A. Webb) yields over 1.3 million metric tonnes annually. The US accounted for 75% of global production. Major insect pests, disease, and nematodes of almond crops are given in Table 10.2 and showed in Figure 10.2.

Table 10.2 Major Pests of Almond Crops⏎

Sl. No | Common Name | Scientific Name | Order/Kingdom/Domain | Family/Phylum/Division
 1. | Navel orangeworm | Amyelois transitella (Walker) | Lepidoptera | Pyralidae
 2. | San Jose scale | Encarsia (Quadraspidiotus) perniciosus (Comstock) | Hemiptera | Diaspididae
 3. | Poplar lace bug | Monosteira unicostata (Mulsant & Rey) | Hemiptera | Tingididae
 4. | Almond borer | Capnodis carbonaria (Klug) | Coleoptera | Buprestidae
 5. | Longhorn beetle | Cerambyx dux (Faldermann) | Coleoptera | Cerambycidae
 6. | Almond fruit wasp | Eurytoma amygdali (Enderlein) | Hymenoptera | Eurotomidae
 7. | Leaf footed stink bug | Leptoglossus zonatus (Dallas) | Hemiptera | Coreidae
 8. | Alternaria leaf spot | Alternaria alternate | Fungi | Ascomycota
 10. | Anthracnose | Colletotrichum acutatum | Fungi | Ascomycota
 11. | Brown rot blossom blight | Monilinia laxa | Fungi | Ascomycota
 12. | Hull rot | Rhizopus stolonifera, Monolinia spp. | Fungi | Zygomycota
 13. | Green fruit rot | Botrytis cinerea, Sclerotinia sclerotiorum | Fungi | Ascomycota
 14. | Shot hole | Wilsonomyces carpophilus | Fungi | Ascomycota
 15. | Verticillium wilt (Blackheart) | Verticillium dahlia | Fungi | Ascomycota
 16. | Scab | Cladosporium carpophilum | Fungi | Ascomycota
 17. | Phytophthora Crown, Collar and Root Rot | Phytophthora spp. | Fungi | Chromista
 18. | Leaf rust | Tranzschelia discolor | Fungi | Basidiomycota
 19. | Almond leaf scorch; golden death | Xylella fastidiosa | Bacteria | Gracilicutes
 20. | Crown gall | Agrobacterium tumefaciens | Bacteria | Gracilicutes
 21. | Almond decline | Peach yellow leafroll mycoplasma | Bacteria | Firmicutes
 22. | Almond kernel shrivel | Peach yellow leafroll phytoplasma | Bacteria | Firmicutes
 23. | Lesion nematode | Pratylenchus spp. | Animalia | Nematodea
 24. | Root- knot nematode | Meloidogyne spp. | Animalia | Nematodea
 25. | Pin nematodes | Paratylenchus prunii | Animalia | Nematodea

Figure 10.2 Major diseases and insect pests of almond. ⏎

10.3.2 Insect Pests

10.3.2.1 Navel Orangeworm

Silvery grey and black patterns can be seen on the forewings and legs of adult moths (Grant et al., 2020).

10.3.2.1.1 Life Cycle

On average, a female lays 84 eggs. Larave and pupae of Amyelois transitella over winter in dried, shriveled, mummified fruit left on the tree after harvest the previous year (Pathak et al., 2021).

10.3.2.1.2 Damage Symptoms

Furthermore, saprophytic fungi, Aspergillus spp., capable of producing carcinogenic toxins called “aflatoxin,” prefer to grow in the damaged kernels. Aflatoxins can cause cancer and birth defects in humans and livestock alike.

10.3.2.1.3 Management

These lepidopteran pests can be killed with bacterial pathogens, Bacillus thuringiensis, which works in conjunction with natural enemies.

10.3.2.2 San Jose Scale

The adult male is yellow-brown colored two winged insect (Baspinar et al., 2018).

10.3.2.2.1 Life Cycle

The first thing that crawlers do when they come out of their shells is start sucking tree sap. It goes through a “white cap” stage while feeding, where its waxy covering is white, and a “black cap” stage, where its waxy covering is black (Baspinar et al., 2018).

10.3.2.2.2 Damage Symptoms

Damage is caused by sucking juice from plants and injecting a toxin, which kills twigs, limbs, and decreases productivity. Scale-infested bark often exhibits red halos around the feeding area and necrotic spots visible on scraped bark.

10.3.2.2.3 Management

Several species of wasps and the predaceous beetles, Chilocoru sorbus (Casey) and Cybocephalus californicus (Horn) have been identified as bioagents.

10.3.2.3 Poplar Lacewing

The adult has a black stripe running down its belly and is a whitish brown overall.

10.3.2.3.1 Life Cycle

On the underside of the leaf, the female lays her eggs in the plant tissue (Baspinar et al., 2018). After hatching from an egg, the nymph goes through five molts while feeding on the undersides of leaves (Sanchez-Ramos et al., 2014).

10.3.2.3.2 Damage Symptoms

Almond yield is reduced due to feeding and frass deposition, which has a negative effect on photosynthesis and transpiration (Sanchez-Ramos et al., 2017b). Adult and nymphal pest infestations are characterized by browning, brittleness, and premature leaf drop.

10.3.2.3.3 Management

Together, thyme essential oil, kaolin, azadirachtin, and potassium salts of fatty acids were effective in reducing both adult and fourth-instar nymph populations (Sanches-Ramos et al., 2014). Predators of M. unicostata in almond orchards include coccinellids and hemipterans (Bolu, 2007; Tolga and Yoldas, 20110).

10.3.2.4 Almond Borer

The adult moth is a glossy black or bronze with black and white decorations on the pronotum. The eggs are an oval shape and measure 1 mm in length.

10.3.2.4.1 Life Cycle

When the larvae hatch, they move quickly to the plant’s roots, where they start to tunnel and leave behind saw dust. From egg to pupa, the whole process can take anywhere from one to two years. A pupa changes into an adult after four weeks (Talhouk, 2010).

10.3.2.4.2 Damage Symptoms

Root feeding can cause older trees to die over time. Falling leaves are a telltale sign that a tree has been damaged.

10.3.2.4.3 Management

Entomopathogenic nematode (EPN), Steinernema carpocapsae (Weiser) is highly effective (106–100% efficacy) against the neonate larvae. To protect trees from infestation, irrigate the ground near the stem with a pesticide solution such as imidacloprid or chloropyrifos insecticides (Marannino and Lillo, 2007).

10.3.2.5 Longhorn Beetle

A dark brown adult measures approximately 50–52 mm in length and has longer antennae than the body.

10.3.2.5.1 Life Cycle

A female can lay 30–40 eggs over the course of her life. Grubs that are newly hatched have a cylindrical body shape and soft, creamy white color. Pupae are initially dirty white, but turn dark as they mature.

10.3.2.5.2 Damage Symptoms

The larva damages the wood by boring a tunnel through it. During the larvae’s feeding process, the holes on the trunk make a tapping sound and a lot of sawdust or frass comes out.

10.3.2.5.3 Management

Weak woody plants are prone to attack of pest and egg laying. Therefore, it is essential to maintain the crop hygiene by irrigating, pruning, and fertilizing them regularly.

10.3.2.6 Almond Fruit Wasp

Wasps have black bodies and transparent, metallic, triangular-shaped forewings when they reach adulthood.

10.3.2.6.1 Life Cycle

Milky white in color, eggs have two appendages, one longer than the other, that stick out of the top. Larvae appear white and have scattered hairs covering their bodies. In the early stages of pupal development, the pupa is white in color, but later turns dark.

10.3.2.6.2 Damage Symptoms

There is an emergence hole of about 2 mm diameter visible after the adults emerge from the fruit.

10.3.2.6.3 Management

The gregarious ectoparasite, Adontomerus amygdali (Hymenoptera: Chalcidoidea: Torymidae) and Aprostocetus bucculentus (Hymenoptera: Chalcidoidea: Eulophidae) attacked on larvae of E. amygdale (Bolu and zgen, 2007). Pyemotes amygdali (Acarina: Pyemotidae) is an ecto-parasitoid that feeds on hymenopteran larvae, pupae, and adult insects.

10.3.2.7 Leaf Footed Bug

Two species of LFB have been identified in almonds in the central valley of California: Leptoglossus zonatus (Dallas) and Leptoglossus clypealis (Heidemann) (Zalom et al., 2012).

10.3.2.7.1 Life Cycle

It lays its eggs in a row, each of which may contain 20–50 eggs. The time it takes for an insect to mature from an egg to an adult varies from 54 days–83 days, depending on the host crops (Daane et al., 20110). In 31–34 days, a nymph matures into an adult.

10.3.2.7.2 Damage Symptoms

Almonds would fall off trees if they were feed too early in the season, while feeding them too late would cause kernel necrosis and shriveled kernels (Joyce et al., 20110; Xiao et al., 2010; Pires et al., 2011; Joyce et al., 20110; Zalom, 2017).

10.3.2.7.3 Management

The most effective egg parasitoid, Gyron pennsylvanicaus, is found in pistachios as well. The biological control of L. zonatus has been investigated more thoroughly in crops other than almonds; hymenopterans, such as Trissolcus spp., Anastus spp., and Gryon spp., and tachinids, such as Trichopoda pennipes Fab. and Trichopoda spp. (Duarte-Sanchez et al., 2008; Ingels and Haviland, 2014)), are known to be parasites (Zalom et al., 2012; Zalom, 2017).

10.3.3 Diseases

10.3.3.1 Alternaria Leaf Spot

10.3.3.1.1 Damage Symptoms

On leaves, infections look like brown, round spots that join together to form large, irregular dead zones. Most lesions get black in the middle, where a lot of spores are made.

10.3.3.1.2 Favorable Condition

In the late spring and summer, dew can linger on the ground for long periods of time, making conditions ideal for the spread of disease.

10.3.3.1.3 Mode of Spread and Survival

However, epidemics can emerge at an earlier stage and reach catastrophic levels, leading to debilitating defoliation.

10.3.3.1.4 Management

Monitoring shows that wherever the Alternaria is present, apply difenoconazole/cyprodinil @100g/100 ml (middle of April to beginning of May).

10.3.3.2 Anthracnose

10.3.3.2.1 Damage Symptoms

When anthracnose affects almonds, it can cause blossom blight, fruit infections, limbs to die back, and foliage to die but keep its leaves (Bhat, 2013). On the hull of infected nuts, there are round, orange, sunken spots.

10.3.3.2.2 Favorable Condition

It is possible to reduce the number of infected woods and slow down the spread of disease by removing diseased branches from the tree (Gramaje, 2012).

10.3.3.2.3 Mode of Spread and Survival

Orange spots can show up on infected nuts as soon as three weeks after the petals fall, or they can show up later in the season if the weather is good.

10.3.3.2.4 Management

Use 500 ml of azoxystrobin per hectare.

10.3.3.3 Brown Rot Blossom Blight

10.3.3.3.1 Damage Symptoms

Blossoms with blight, which causes the stigma and anther to turn brown and die, the flower to collapse and turn brown, and light brown, powdery fungus masses to appear on infected flowers. Spore masses that range in color from gray to tan form on sick parts of a flower.

10.3.3.3.2 Favorable Condition

The favorable conditions such as fog or rain at 75 ⁰F is ideal for development, but infection can occur at temperatures as low as 50–60 ⁰F. Heavy down pours during flowering are conducive to the emergence of diseases.

10.3.3.3.3 Mode of Spread and Survival

These structures produce spore pads in the late winter, which are used as primary inoculum the following spring. It only takes wind or rain to spread the spores (Lampinen, 2011).

10.3.3.3.4 Management

Use 500 ml of azoxystrobin per hectare.

10.3.3.4 Hull Rot

10.3.3.4.1 Damage Symptoms

The space between the hull and the shell is filled with dark grey spore masses. The leaves on the side of the shoot that is closest to the infected fruit may wither and curl, and eventually die. Black spots and numerous Rhizopus spores characterize infected fruit.

10.3.3.4.2 Favorable Condition

Rhizopus hull rot is a danger to almonds from the time the hulls start to split until they dry out (Olmo, 2016).

10.3.3.4.3 Mode of Spread and Survival

Almond pests like the carob moth (Ectomyelois ceratoniae) spend the winter in the mummified fruit that stays on the trees. The mummies carry spores of Rhizopus, which infect the fruit of the new season.

10.3.3.4.4 Management

At hull split, watering should be cut back; a demethylation inhibitor and a quinone outside inhibitor fungicide could be used. A second application of azoxystrobin may be made prior to 40% hull split, but not earlier than the 28-day pre-harvest interval.

10.3.3.5 Green Fruit Rot

10.3.3.5.1 Damage Symptoms

At the end of the flowering period, the fungus invades the dying petals and anthers, initiating the process of green fruit rot.

10.3.3.5.2 Favorable Condition

When it’s bloom time and the weather is cool and wet, it can cause a lot of damage. There could be one or more of a number of pathogens.

10.3.3.5.3 Mode of Spread and Survival and Management Difenoconazole/cyprodinil 100 mg/ml should be applied.

10.3.3.6 Shot Hole

10.3.3.6.1 Damage Symptoms

Small brown or reddish spots on the leaves grow into larger spots with tan centers and purple edges. Lesions on fruits are small, raised bumps with purple edges.

10.3.3.6.2 Favorable Condition

For spores to form, grow, and infect plant tissue, they need mild temperatures and free moisture. Rain or sprinklers that keep the ground wet for a long time can help the disease spread and get worse, especially in the lower branches.

10.3.3.6.3 Mode of Spread and Survival and Management

Spores spread when rain and irrigation water splashed on them. Apply azoxystrobin 500ml/ha.

10.3.3.7 Verticillium Wilt (Black Heart)

10.3.3.7.1 Damage Symptoms

Certain branches’ limp, green leaves dry out and turn brown. Infected branches have black streaks in their vascular tissues and a ring of discolored tissue at their cut ends.

10.3.3.7.2 Mode of Spread and Survival

Fungus stays in the soil over the winter and comes back every year. If the orchard is planted with other plants that are easily affected, like cotton, tomatoes, and melons.

10.3.3.7.3 Management

Orchards shouldn’t be planted with plants that are easy to get sick, like cotton, tomatoes, or melons. Fungi in the soil can be killed by putting it in the sun or fumigating it before planting.

10.3.3.8 Scab

10.3.3.8.1 Damage Symptoms

Symptoms of infected fruit include small, dark, circular spots that don’t penetrate deeply into the fruit’s tissues and look like soot.

10.3.3.8.2 Favorable Condition

The persistent, wet spring weather is ideal for the growth of scab.

10.3.3.8.3 Mode of Spread and Survival and Management

March winds, rain, and sprinklers spread spores. Start treatments (difenoconazole/cyprodinil @100 g/100 ml) before illness start in disease-prone environments.

10.3.3.9 Phytophthora Crown, Collar, And Root Rot

10.3.3.9.1 Damage Symptoms

Stunted development, premature senescence, and leaf drop are the results of a chronic infection, most often in the roots (Kumar, 2010).

10.3.3.9.2 Favorable Condition

Root and crown rot are less likely to occur when soil drains well and plants are irrigated more frequently but for shorter periods of time.

10.3.3.9.3 Mode of Spread and Survival

Water is used to disperse it. Managing water availability is crucial for preventing root and crown rot. Avoid having water pool or stand around the bases of trees.

10.3.3.9.4 Management

Apply 2.5 kg/ha metalaxyl + mancozeb under the tree canopy to cover the root zone with a soil spray (broadcast or band).

10.3.3.10 Leaf Rusts

10.3.3.10.1 Damage Symptoms

As the disease progresses, the yellow spots become angular, and multiple lesions combine to form irregular yellow patches of infected tissue. These patches of infected tissue are yellow and irregular in shape.

10.3.3.10.2 Favorable Condition, Mode of Spread, Survival, and Management

Diseases can more easily spread in wet environments. The fungus survives in the winter on lesions in the twigs or leaves of its host. Start with 500 ml/ ha of azoxystrobin.

10.3.3.11 Almond Leaf Scorch

10.3.3.11.1 Damage Symptoms

A chlorotic leaf edge, necrosis of leaf edges that starts at the leaf tip and spreads to the leaf base, and patches of dead tissue with chlorotic edges.

10.3.3.11.2 Mode of Spread and Survival

This bacterium is transmitted by leaf hoppers and spittle bugs, and it can infect rye, blackberry, and nettle.

10.3.3.11.3 Management

If the disease is found early, when it only affects one branch, it can be removed by pruning the primary scaffold 5–10 feet below the symptoms. If the disease is found later, the tree may need to be cut down and replaced.

10.3.3.12 Crown Gall

10.3.3.12.1 Damage Symptoms

Galls begin as light-colored bulges that eventually become larger and darker as they mature; the consistency of galls can range from soft and spongy to hard. Galling that is so severe, it girdles the trunk weakens young trees by squeezing their vascular tissues (Khan, 2010).

10.3.3.12.2 Mode of Spread and Survival

The bacterium enters host plants through wounds, proliferating and undifferentiating plant cells to form a gall.

10.3.3.12.3 Management

If a biocontrol agent (Agrobacterium tumefaciens K 84) is available, treating fresh wounds may help stop the bacterium from colonizing.

10.3.3.13 Almond Decline

10.3.3.13.1 Damage Symptoms, Mode of Spread, Survival, and Management

Trees are stunted and leaf wilting occurs. Stunted trees should be removed and replaced. Plant only certified pathogen free trees.

10.3.3.14 Almond Kernel Shrivel

10.3.3.14.1 Damage Symptoms, Mode of Spread, Survival, and Management

A late-bloomer, reduced growth, thinner, paler leaves, swelling occurred in the harvested nuts. Typically found in grafted peach trees; lop off infected branches. Cut down infected trees and replace them with healthy and certified ones.

10.3.4 Nematodes

10.3.4.1 Lesion Nematode

These are endoparasitic nematode forms that migrate. The epidermis must be broken in order for the young and the adult stages to enter the root, where they will migrate through the cortical layer while feeding on cortical cells. In many instances, the associated nematode species with these diseases belong to the genus Pratylenchus. The significance of P. penetrans and P. vulnus has been confirmed. In the absence of bacteria and fungi, Mountain and Patrick (110510) demonstrated the pathogenicity of P. penetrans. Under aseptic conditions, it invaded and killed peach roots by hydrolyzing the cyanophoric beta glucoside and amygdalin, which release the phytotoxic compounds hydrogen cyanide and benzaldehyde. Peach seedlings were more severely damaged in non-sterile growth room tests than in sterile conditions. So, it was thought that the main thing of P. penetrans did to cause peach replant failure was to cause root degeneration by giving soil microorganisms a lot of places to infect. 30% of peach trees in Himachal Pradesh were infested with this species.

The trees in the southeastern United States that was infected by C. xenoplax were vulnerable to cold injury and bacterial canker (Pseudomonas syringae pv. syringae) which is part of a group of diseases called “peach tree short life” and can infect during replanting.

10.3.4.2 Root Knot Nematode

Almond is known to be parasitized by four Meloidogyne spp. which includes M. incognita, M. javanica, M. arenaria, and M. hapla. Root galls are the typical symptom of an attack by a root-knot nematode. These trees may also exhibit symptoms of defoliation, which become more pronounced under drought condition. After six months of inoculation with 20 juveniles per gram of soil decreased 66% in shoot weight and a 44% decrease in shoot length.

10.3.4.3 Pin Nematodes

When there are more than 20 of them per gram of soil, it slows plant growth. It is more common in the peach rhizosphere in early spring than in the summer, which shows that it attacks new root growth that starts in spring

10.3.4.4 Other Nematodes

Paratrichodorus lobatus, Xiphinema americanum, and X. vuittenezi have been found to reduce peach root and top growth. Virus vectors, Xiphinema species are more valuable. The damage threshold for nepo-virus is one nematode per 100 cc soils when compared to 100 for other species. In recent years, some economically important nematodes, such as Meloidogyne incognita, Paratylenchusma crodorus, and others, have been found in almonds. In Himachal Pradesh, crown gall (Agrobacterium tumefaciens) was found to be very bad on almond trees where there were lots of nematodes.

10.4 Major Pests Of Chestnut Crops

10.4.1 Economic Importance

Chinese exports and yields of chestnuts made up 83.3% and 26.4%, respectively, of the global totals in 2017 (He et al., 2021). Major insect pests, and disease of chestnut crops are given in Table 10.3 and showed in Figure 10.3.

Table 10.3 Major Pests of Chestnut Crops⏎

Sl. No. | Common Name | Scientific Name | Order/Kingdom/Domain | Family/Phylum/Division
 1 | Lesser chestnut weevil | Curcilio sayi (Gyllenhal) | Coleoptera | Curculionidae
 2 | Gall wasp | Dryocosmus kuriphilus (Yasumatsu) | Hymenoptera | Cynipidae
 3 | Japanese beetle | Popillia japonica (Newman) | Coleoptera | Scarabaeidae
 4 | Chestnut bight | Cryphonectria parasitica | Fungi | Ascomycota
 5 | Anthracnose | Apiognomonia quercina | Fungi | Ascomycota
 6 | Phytophthora root rot | Phytophthora cambivora | Chromista | Oomycota
 7 | Nut rot | Sclerotinia pseudotuberosa | Fungi | Ascomycota

Figure 10.3 Major diseases and insect pests of chestnut. ⏎

10.4.2 Insect Pests

10.4.2.1 Lesser Chestnut Weevil

Grub is ‘C’-shaped, creamy colored with a brown head.

10.4.2.1.1 Life Cycle

Adult female weevils lay their eggs in mature chestnut burr shells. The eggs hatch within 8–10 days. Larval development takes place within 2–3 weeks but most larvae pupate after a year. During their last larva instar, chew a hole inside nuts to enter the soil for pupation (Filgueiras and Willett, 2022).

10.4.2.1.2 Damage Symptoms

As the grub emerges from the egg, it bores into the nut and consumes the internal contents. This causes premature fruit drop. At the end of the larval stage, larvae pierce the pericarp and drop to the ground through this hole.

10.4.2.1.3 Management

Filgueiras and Willett (2002) found that pyramid and trunk traps were better for keeping an eye on adults. A clear plastic jar is put on top of the pyramid trap to catch adults as they come out of the ground. Adults quickly move from the ground to traps that look like pyramids. During the post-harvest heat treatment, the product is put in 140 °F water for 30 minutes and then cooled. “Curatura” is a cold-water method that kills chestnut weevil eggs and pre-imaginal stages on fruit that looks like it doesn’t have any infestation. Entomopathogenic nematodes like Steinernema feltiae, Heterorhabditis bacteriophora, and entomopathogenic fungi, Beauveria bassiana and Metarhizium anisopliae were used to reduce the number of adult weevils.

10.4.2.2 Gall Wasp

The eggs are long, milky white, and oval. Pupae typically appear black or very dark brown (Aebi et al., 2006).

10.4.2.2.1 Life Cycle

Eggs hatch in 30–40 days in leaf and flower buds. First instars stay here till spring in winter (Borowiec et al., 2014). Galls have over 16 larval chambers (Panzavolta et al., 2013). After activity restarts, the larva stays in the gall for 30–50 days. Adult females emerge from the gall after 10–15 days (Gibbs et al., 2011; Bernardo et al., 2013).

10.4.2.2.2 Damage Symptoms

Wasps can cause galls on the petioles, stipules, midrib, and buds of a chestnut tree. These galls not only stop the development of the shoot’s apical buds but also cause the flowers to abort. Trees are more likely to be damaged by Cryphonectria parasitica (Diaporthales: Valsaceae) the causal agent of chestnut blight, when the wasp is present (Turchetti et al., 2010).

10.4.2.2.3 Management

The genus Chinquapins pumila, C. ozarkensis, and C. henryi of the Americas and China show some resistance in field observations, suggesting that they could be used to breed for insect resistance. Studies conducted in Europe have confirmed that Torymus sinensis is an efficient parasitoid (Bernardo et al., 2013).

10.4.2.3 Japanese Beetle

Adults can be identified by the prominent spines on their legs and the six white tufts of hair that run along each side of their bodies. A full-grown grub is creamy white and C-shaped body.

10.4.2.3.1 Life Cycle

It’s more likely that a female will lay eggs in a tree with strong, healthy root. As the temperature drops in late September, grubs emerge from their eggs and begin their lives as root feeders. The adult grub will dig a hole 4–8 inches deep, where it will spend the winter dormant. The adult emerges from the pupae in the soil in the spring (Krischik and Maser, 2005).

10.4.2.3.2 Damage Symptoms

In July and August, beetle damage looks like skeletonized leaves with veins. Also, they make holes in flower buds, petals, and soft fruits when they eat them.

A grub eats the roots of plants, which makes the leaves turn yellow or brown.

10.4.2.3.3 Management

Organophosphates and pyrethroids group of insecticides can have effects that last up to three days, but the effects that stick around last for 10–14 days.

10.4.3 Diseases

10.4.3.1 Chestnut Blight

10.4.3.1.1 Damage Symptoms

A fungus that grows under the bark causes cankers to grow around the trunk, stem, or branch. When chestnut blight hits a tree, it will eventually die. Branches and twigs die when patches of reddish-brown bark turn into cankers that are sunken, swollen, and cracked. Most of the time, the leaves stay on the dead branch, making a “flag” of yellow-brown leaves that stand out against the healthy green leaves.

10.4.3.1.2 Favorable Condition

Disease development favors precipitation and humid conditions.

10.4.3.1.3 Mode of Spread AND Survival

The fungus can overwinter in the bark and spread either through human contact (when pruning an infected plant). The fungus and its spores can be dispersed by a variety of vectors, including wind, water, rain splash, human, animal, and insect transport, farming practices, budding material, and cuttings taken from infected trees.

10.4.3.1.4 Management

Start a new survey to find out the exact number of sick trees that need to be cut down. If infected trees are burned to ash, they will be destroyed.

10.4.3.2 Anthracnose

10.4.3.2.1 Damage Symptoms

Infected plants will exhibit symptoms such as dry, brown, irregular spots on the leaves, as well as defoliation and foliage curling. There is also a possibility of twig dieback, and buds may perish early in the season, displaying symptoms that are similar to those of frost damage. On the undersides of affected foliage, you might also notice fungal structures that look like small bumps or pimples.

10.4.3.2.2 Favorable Condition

Temperatures in the range of 50–55°F are typically optimal for the development of anthracnose, whereas temperatures of 60°F and higher typically result in a milder form of the disease.

10.4.3.2.3 Mode of Spread and Survival

In the spring, fungus can overwinter in cankers that have formed on the branches, as well as in fallen leaves and spores that have been dispersed by the wind and water splashes, and then infect new growth.

10.4.3.2.4 Management

Fungicides, when used correctly and consistently, have the ability to prevent and treat disease.

10.4.3.3 Phytophthora Root Rot

10.4.3.3.1 Damage Symptoms

Phytophthora root rot is a disease that primarily affects the root and lower trunk of plants. Infected chestnut trees will show signs of wilting, and the branches will die back and die off. The infection is centered at the roots and the base of the trees. If the bark of an infected tree were peeled back, necrotic tissue in a dark brown or black color would be exposed.

10.4.3.3.2 Favorable Condition

When there is a lot of water in the soil, these fungi are more likely to grow.

10.4.3.3.3 Mode of Spread and Survival

The fungus can live for a long time in the soil. For zoospores to be expelled from sporangia, the availability of free water is an absolute requirement.

10.4.3.3.4 Management

Leveling the soil or installing drainage systems are both viable options for enhancing drainage. When watering trees, you should avoid getting the trunks wet.

10.4.3.4 Nut Rot

10.4.3.4.1 Damage Symptoms

On the pellicle, which is the papery layer beneath the shell, there may be a few reddish-brown spots that extend onto the kernel. The severely decayed nut shells to be covered with small, white, raised structures.

10.4.3.4.2 Favorable Condition

During the growing season, hot and dry conditions help to prevent the spread of diseases that thrive in the mild and wet conditions of summer and autumn.

10.4.3.4.3 Mode of Spread and Survival

The fungal spores can be spread through water splashes and possible for the disease to spread within the tree’s canopy during wet periods when rotten nuts are still present on the tree.

10.4.3.4.4 Management

Majority of diseases that can affect stored produce, chestnut rot can be avoided by storing the nuts at low temperatures (0°C) and preserving the cold chain throughout distribution and marketing.

10.5 Major Pests Of Hazelnut Crops

10.5.1 Economic Importance

About 70% of the world’s hazelnut supply comes from Turkey, the top producer in the globe. The most significant economic activity (monoculture) and source of income for rural households in the Black Sea Region is the production of hazelnuts. Major insect pests, and disease of hazelnut crops are given in Table 10.4 and depicted in Figure 10.4.

Table 10.4 Major Pests of Hazelnut Crops⏎

Sl. No. | Common Name | Scientific Name | Order/Kingdom/Domain | Family/Phylum/Division
 1 | Nut weevil | Curculio nucum (Linnaeus) | Coleoptera | Curculionidae
 2 | Big bud mite | Phytoptys avellanae (Nalepa), Cedidophyopsis vermiformis (Nalepa) | Acarina | Eriophyidae
 3 | Filbert worm | Cydia latiferreana (Walsingham) | Lepidoptera | Torticidae
 4 | Filbert aphid | Myzocallis coryli (Goeze) Corylobium avellanae (Schrank) | Homoptera | Aphididae
 5 | Brown marmorated stink bug | Palomena prasina (Linnaeus) Gonocerus acuteangulatus (Goeze) | Heteroptera | Pentatomidae
|  |  |  | Coreidae
 6 | Ambrosia beetle | Xyleborus dispar (Fabricius) Lymantor coryli (Perris) | Coleoptera | Scolytidae
 7 | Eastern filbert light | Anisogramma anomala | Fungi | Ascomycota
 8 | Armillaria root rot | Armillaria mellea | Fungi | Basidiomycota
 10 | Powdery mildew | Phyllactinia guttata | Fungi | Ascomycota
 11 | Bacterial blight | Xanthomonas arboricolapv. Corylina | Bacteria | Gracilicutes
 12 | Bacterial canker | Pseudomonas syringae | Bacteria | Gracilicutes
 13 | Hazelnut mosaic | Apple mosaic virus | Virus | Orthornavirae

Figure 10.4 Major diseases and insect pests of hazelnut. ⏎

10.5.2 Insect Pests

10.5.2.1 Nut Weevil

In an experiment conducted in cages, it was observed that a pair of nut weevils caused the loss of approximately 1100 nuts (Gultekin, 2020). The scutellum, a small triangular plate on the insect’s thorax, typically appears yellowish or whitish. The C-shaped larvae are cream to white in color and lack appendages (Shanovich and Aukema, 2022).).

10.5.2.1.1 Life Cycle

Female weevils lay one egg in each hole, which they create by using their snout to make a small opening just inside the inner nut shell. During the months of May to July, a single female is capable of laying approximately 45 mature eggs (Akca and Tuncer, 2004). The pupa enters a diapause state and remains in an earthen cell throughout the winter for a period of about 6–7 months.

10.5.2.1.2 Damage Symptoms

Adult weevils feed on hazel flowers, vegetative buds, and young foliage. They consume small nuts, including both the husks and developing kernels, typically from May to June. Their feeding activity leads to the creation of holes in the nutshells, the formation of “brown blank” nuts (where aborted kernels result in empty nuts), and premature nut drop.

10.5.2.1.3 Management

Varieties like Hall’s Giant, Wonder from Bollwiller, and Lenka II, which have low sugar levels and high phenol content, show resistance to weevil infestation (Wojciechowicz-Zytko, 2005). Studies have shown that Hall’s Giant, a weevil-resistant variety, displays accelerated shell hardening in the late season, which contributes to its defense against weevils (Moraglio et al., 2014; Tuncer, 20010). Biological control methods using the Vuillemin strain of the entomopathogenic fungus like Beauveria bassiana have achieved 1010.5% weevil mortality (Paparatti and Speranza, 2005). In the lab, another strain called Metarhizium anisopliae killed all of the larvae 13 days after it was introduced (Cheng et al., 2016). Steinernema feltiae, Steinernema spp. Travassos strain D122, and Heterorhabditis bacteriophora, which are called EPNs, have been found to reduce the population of C. nucum by 32%–88% in the spring (Batalla-Carrera et al., 2013; Tuncer, 2010).

10.5.2.2 Filbert Big Bud Mite

Pest can lead to yield loss about 70%. Mites are tiny, white, and cigar-shaped. They have two sets of legs near their heads.

10.5.2.2.1 Life Cycle

In the spring, between the middle and end of May, young mites called nymphs come out of winter buds and move to new axillary buds, where they eat, grow up, and mate. This migration period lasts about 30–50 days and always happens in the spring, giving a window for spraying chemicals.

10.5.2.2.2 Damage Symptoms

Damage caused by mites includes the feeding of nymphs and adult mites on plant cell fluid, resulting in the swelling and damage of vegetative and floral buds. Infested buds lead to the development of weak and unhealthy shoots, resulting in the characteristic big bud symptoms.

10.5.2.2.3 Management

The threshold for intervention is typically set at 10% for young plantations and 15–20% for productive plantations, based on the presence of galls. Give two sulfur treatments, with 8–10 days between each one.

10.5.2.3 Filbert Worm

The Filbert worm is a significant pest in hazelnut production, capable of causing 20–40% damage if left untreated. The wings of adult Filbert worms come in many different colors, from light tan to orange-red to coppery dark brown. The pupae are brown in color. The larvae of filbert worms are pale whitish in color, with visible legs and a worm-like shape.

10.5.2.3.1 Life Cycle

Females lay single eggs on or near clusters of nuts. After hatching, the young larvae find a soft spot on the nut and enter it to eat the kernel. It takes about 4–6 weeks for a larva to grow up. They spend the winter in the ground in a hard cocoon made of silk. After three weeks, they come out as adults (Olsen et al., 2013).

10.5.2.3.2 Damage Symptoms

Pests forms tunnels within the nuts, ultimately destroys them. Infested hazelnuts exhibit exit holes and larval frass.

10.5.2.3.3 Management

Effective management of filbert worms includes selecting cultivars with thicker shells, such as “Siciliana,” which are less susceptible than thinshelled cultivars like “Daviana.” Collecting and destroying premature nut drops is a highly effective control measure. The use of egg parasitoids from the genus Trichogramma spp. can be effective in parasitizing filbert worm eggs. Using spinosad as another treatment option Olsen and Pscheidt (2008).

10.5.2.4 Filbert Aphid

In recent years, it has become less of a problem because the hymenopteran parasitoid, Trioxys pallidus has been used to control it successfully on a biological level.

10.5.2.4.1 Life Cycle

The filbert aphid’s life cycle starts when the females lay eggs in cracks and around the buds. When nymphs hatch in early spring, they move towards the buds that are about to open. As soon as the new leaves grow, aphids start eating the undersides of them. Nymphs grow up between the middle of May and the beginning of June and reproduce on their own.

10.5.2.4.2 Damage Symptoms

Filbert aphids cause damage because both the nymphs and the adults feed a lot on the opened buds and the undersides of the leaves. High aphid populations can lead to excessive honeydew, which can then result in the growth of sooty mold on the leaves, potentially leading to crop losses due to reduced photosynthetic ability.

10.5.2.4.3 Management

Filbert aphids have been kept under control by introducing Trioxys pallidus. Neem-based products (like Margosan-O) and Bacillus thuringiensis based products like Dipel are safe for T. pallidus.

10.5.2.5 Brown Marmorated Stink Bug

Stink bugs primarily cause premature nut drop and kernel necrosis in hazelnut orchards. The most common stink bugs found in hazelnut orchards are the Palomena prasina and Gonocerus acuteangulatus.

10.5.2.5.1 Life Cycle

Stink bugs mate and egg deposit eggs on the undersides of various plant species. The stink bug life cycle consists of five immature stages, and the four nymphal stages, along with adults, cause damage to foliage, husks, and nuts.

10.5.2.5.2 Damage Symptoms

Once the nymphs have reached maturity, they become mobile and consume foliage, nut clusters, and plant reproductive parts such as seeds, fruits, husks, and nuts alongside the adults. Mid-season feeding can result in shriveling of kernels, while late-season feeding can cause the nut shells to turn black or discolored, hard kernel “corking,” and the appearance of distorted, necrotic spots on the kernel.

10.5.2.5.3 Management

Several beneficial insects have been identified as natural enemies of this pest, including Apanteles spp., Macrosentrus spp., Meteorus spp., Itoplectis didyma, and Pristomerus vulnerator. In some years, 100% parasitization has been observed in the prepupal stage. Additionally, as stink bugs are lepidopteran insects, Bacillus thuringiensis may be effective in their control.

10.5.2.6 Ambrosia Beetle

Four species of ambrosia beetles have been identified in hazelnuts, with

L. coryli and X. dispar being the most abundant and X. xylographus and Hypothenemus eruditus being minor (Ak et al., 2005). In Italy, Ambrosia beetles have been linked to the spread of a bacterial disease known as “Moria” (Bucini et al., 2005).

10.5.2.6.1 Life Cycle

The emergent larvae feed on the fungi their parents have introduced into the galleries, complete their development within the host tree, and then pupate. Larvae mature within the host tree over the course of four to six weeks, remaining there until the following spring.

10.5.2.6.2 Damage Symptoms

The channels that the beetles make block the flow of sap, which can kill young trees and cause older crops to suddenly die and dry up after flowering. The beetles can also transmit pathogens between plants.

10.5.2.6.3 Management

The use of red cross traps, such as the “Rebell Rosso” trap baited with ethanol and denatured with 1% toluene, has been found to be highly effective in mass trapping ambrosia beetles. For low and high infection levels, it is recommended to use 3–4 traps per day and 6–8 traps per day, especially in July and August (Ak et al., 2005c).

10.5.3 Diseases

10.5.3.1 Eastern Filbert Blight

10.5.3.1.1 Damage Symptoms

Subsequently, cankers may appear on any part of the plant, causing wilt and die back in leaves and branches, respectively. Cankers that are expanding and girdling branches and limbs can cause infected branches to suddenly die.

10.5.3.1.2 Favorable Condition

When the weather is cool and wet in the spring, disease is more likely to occur.

10.5.3.1.3 Mode of Spread and Survival

Raindrops that splash and blown by the wind carry the spores to the new growth. Most infections happen when it’s wet between the buds open and when the shoots get longer.

10.5.3.1.4 Management

It’s important to cut off any branches or twigs from the tree they have cankers. Cuts should be made 0.6–0.10 meters below the canker, and the pruning waste should be thrown away.

10.5.3.2 Armillaria Root Rot

10.5.3.2.1 Damage Symptoms

When hazelnut roots come into contact with partially decayed tree roots, the hazelnut roots become colonized by mycelium and become diseased. Also, tree roots can become infected when they come into contact with fungiproduced rhizomorphs, which resemble black shoelaces.

10.5.3.2.2 Favorable Condition

The development of disease is encouraged by conditions consisting of moist soil and high humidity.

10.5.3.2.3 Mode of Spread and Survival

The fungus can keep growing on the woody roots of its host long after the host has died. As it grows, its mycelium takes nutrients from the root wood and breaks them down.

10.5.3.2.4 Management

Deep rips should be taken in more than one direction through the soil in order to bring large roots closer to the surface. Remove Burn up all of the debris made of wood.

10.5.3.3 Powdery Mildew

10.5.3.3.1 Damage Symptoms

There are tiny, powdery white spots all over the leaves and fruit, and they spread until the entire leaf is covered. Small fungal bodies are visible in later stages of the infection and are responsible for the wilting and rolling up of the leaves prior to their death and fall to the ground.

10.5.3.3.2 Favorable Condition

Disease development is encouraged by conditions of moderate temperature, inadequate air circulation around the plant, and shaded surroundings.

10.5.3.3.3 Mode of Spread and Survival

The fungus is able to continue its existence in the buds of the plant in the form of resting spores, mycelium, or encapsulated haustoria. Conidia that are carried through the air are responsible for the secondary spread of the fungus.

10.5.3.3.4 Management

Powdery mildew on hazelnuts can be stopped by using sodium bicarbonate at a concentration of 1.5%.

10.5.3.4 Bacterial Blight

10.5.3.4.1 Damage Symptoms

On the leaves, water-soaked spots begin to appear, and the buds may subsequently turn brown and fail to open. Lesions have the potential to girdle stems, causing them to die, and have the additional potential to extend into the main scaffold or trunk (Ali, 2008).

10.5.3.4.2 Favorable Condition

It can spread quickly in late spring and early summer, especially after a long period of wet and humid weather.

10.5.3.4.3 Mode of Spread and Survival

Cankers on the branches and buds are where the bacteria spend the winter, and during wet weather, the bacteria will spread to other parts of the tree.

10.5.3.4.4 Management

The diseased portions of the tree should be removed by making cuts between 0.6 and 0.10 meters beneath the diseased area.

10.5.3.5 Bacterial Canker

10.5.3.5.1 Symptoms

The spring buds do not open, and the new growth is wilting and dying; the leaves eventually turn chlorotic and fall off.

10.5.3.5.2 Favorable Condition

The wet, humid, and acidity of the soil favors the development of disease.

10.5.3.5.3 Mode of Spread and Survival

Cankers on the branches and buds are where the bacteria spend the winter, and during the wet condition bacteria will spread to other parts of the tree. The splashing of water from tree to tree only causes a limited spread of the disease.

10.5.3.5.4 Management

Using copper-based chemicals like the Bordeaux mixture when the leaves are falling off can help keep the disease under control.

10.5.3.6 Hazelnut Mosaic

10.5.3.6.1 Damage Symptoms

Yellowing of the leaves, which look like rings, lines, flecks, or bands along the veins.

10.5.3.6.2 Mode of Spread and Survival

It spread in the hazelnut orchard through grafting, pruning (with infected tools on healthy trees), transplanting infected rooted suckers to make new trees, and wild grasses.

10.5.3.6.3 Management

Only trees that were grown from virus-free stock should be planted.

10.6 Major Pests Of Pistachio Nut Crops

10.6.1 Economic Importance

The pistachio, Pistacia vera Lin., is native of north Afghanistan (Asia) and currently commercially cultivating throughout the Mediterranean region (Tunisia, Turkey, Italy, Greece and Spain), Middle East (Syria and Iran), America (Arizona and California) and Australia (Mehrnejad, 2020; Pourmohammadali et al., 20110). The major insect pests and disease of pistachio nut crops are given inTable 10.5.

Table 10.5 Major Pests of Pistachio Nut Crops⏎

Sl. No. | Common Name | Scientific Name | Order/Kingdom/Domain | Family/Phylum/Division
 1 | Pistachio psyllids | Agonoscena pistaciae Burckhardt & Lauterer | Hemiptera | Aphalaridae
|  | Megagonoscena viridis (Baeva) |  |
|  | Agonoscena bimaculate Mathur |  |
 2 | Pistachio twig borer | Kermania pistaciella Amsel | Lepidoptera | Oinophilidae
 3 | Pistachio fruit-hull borer moth | Arimania komaroffi Ragonot | Lepidoptera | Pyralidae
 4 | Yellow pistachio hard scale | Lepidosaphes pistaciae (Archangelskaya) | Hemiptera | Diaspididae
 5 | Pistachio trunk and branch scale | Melanaspis inopinata Leonardi | Hemiptera | Diaspididae
 6 | Pistachio bark (twig borer) beetle | Chaetoptelius (= Hylesinus) vestitus Mulsant & Rey | Coleoptera | Scolytidae
 7 | Pistachio weevil | Polydrusus davatchii Hoffmann | Coleoptera | Curculionidae
 8 | Stink bugs | Acrosternum arabicum Wagner | Hemiptera | Pentatomidae
|  | Acrosternum breviceps (Jakovlev) |  |
|  | Brachynema germarii Kolenati |  |
|  | Chroantha ornatula (Linnaeus) |  |
|  | Dolycoris baccarum (Herrich-Schäffer), Carpocoris coreanus Distant |  |
|  | Campylomma diversicorne Reuter |  |
 10 | Plant bugs | Campylomma verbasci (Meyer-Dür) | Hemiptera | Miridae
|  | Campylomma unicolor Poppius |  |
 11 | Alternaria late blight | Alternaria alternate | Fungi | Ascomycota
 12 | Botryosphaeria Panicle and Shoot Blight | Botryosphaeria dothidea | Fungi | Ascomycota
 13 | Botrytis blossom and shoot blight | Botrytis cinerea | Fungi | Ascomycota
 14 | Stigmatomycosis | Nematosporacoryli, Aureobasidium pullulans | Fungi | Ascomycota
 15 | Powdery mildew | Phyllactinia guttata | Fungi | Ascomycota

10.6.2 Insect Pests

10.6.2.1 Pistachio Psyllids

Globally the Pistachio vera trees are associated with three psyllid species viz., Agonoscena pistaciae Burckhardt & Lauterer, Agonoscena bimaculate and Megagonoscena viridis (Hemiptera: Aphalaridae) (Mehrnejad, 2020). It caused severe economic damage to pistachio trees of Syria, Greece and Turkey.

10.6.2.1.1 Life Cycle

The summer-form is present and needs moderately warm temperatures with long days and rapidly mates to lay eggs immediately after emergence. The nymphal diapause is initiated when subjected to a short photoperiod (<12 hours per day) and low temperatures (<20°C). Usually, winter forms are darker and summer forms are lighter in color (Mehrnejad, 2020).

10.6.2.1.2 Damage Symptoms

Nymphal instars suck the phloem sap from the underside buds causes premature defoliation and bud drop, which then causes severe problems in kernel filling (Hassani et al., 20010).

10.6.2.1.3 Management

The specific parasitoid of pistachio psyllid, Psyllaephagus pistaciae Ferrière (Hymenoptera: Encyrtidae). These parasitoid attacks all the nymphal stages of A. pistaciae nymphs across the pistachio plantations. The Adalia bipunctata and O. conglobata are the promising predatory biocontrol agents for pistachio psyllids. High sulphur dosages (3–5 kg/100 L of water) prevent psyllids from infesting trees for 50 days (Mehrnejad, 2020).

10.6.2.2 Pistachio Twig Borer

It was first identified in 11060s considered as minor pests (Khoja et al., 20010).

10.6.2.2.1 Life Cycle

Late March or early April, female moth place eggs in clusters of flowers and fruit or sometimes it places on petioles and young shoots. The mature larvae spun into a cocoon is spun by the fully as it emerges from twigs. For around 40 days, the larvae emerge from the twigs, but the adult population often peaks when flowers are fully developed (Mehrnejad, 2020).

10.6.2.2.2 Damage Symptoms

Early signs of damage include the entire cluster turning black and falling off the branches in very young succulent clusters. The 4–7 larvae bore unripe nuts at the apex cluster and dig a tunnel through the cluster in the direction of the twigs and turn white.

10.6.2.2.3 Management

Some pistachio plants have spontaneous parasitization rates as high as 72%. Three species are primary parasitoids, two are obligatory hyperparasitoids, and the rest are facultative (Manickavasagam et al., 2008; Mehrnejad and Basirat 20010). The main pistachio plantations in Iran have an average parasitism rate of 45.5%.

10.6.2.3 Fruit-Hull Borer Moth

Brandt discovered Arimania komaroffi Ragonot (Lepidoptera: Pyralidae) in south Iran in 110310. Iran has documented insect damage, along with Iraq, Armenia, and Turkey. Kerman pistachio farmers in southern Iran call it “Krash.” It may also be a leaf borer, especially on wild pistachio trees like P. khinjuk (Mehrnejad and Speidel, 2011).

10.6.2.3.1 Life Cycle

Larvae feed inside fruits on white silk. Living in fruit clusters or bore into leaves to form silken webs is preferred. They spin delicate, grayish-silky cocoons for their young to emerge from under trees or other cover. This insect enters its pupal stage of hibernation in early October. In late April, once the fruits have finished developing, the adults emerge and lay an egg on each one (Mehrnejad and Speidel, 2011).

10.6.2.3.2 Damage Symptoms

From late April until roughly mid-May, the first-generation bores into the immature pistachio fruits to attack them. The larvae reside within the fruit nut clusters by feeding on the hull (the soft skin of the fruit) (Mehrnejad and Speidel 2011; Basirat et al., 2015).

10.6.2.3.3 Management

Spraying teflubenzeuron with chemicals is only necessary in few circumstances. In most cases, a single application of pesticide in the spring or early summer is sufficient to eliminate the insect problem (Mehrnejad, 2020).

10.6.2.4 Bud And Twig Borer Beetle

Pistachio trees in Turkey, Greece, Tunisia, Algeria, Iran, and Syria are plagued by the bud and twig borer beetle, Chaetoptelius (= Hylesinus) vestitus Mulsant & Rey (Braham, 2010; Chebouti-Meziou et al., 2010; Khoja et al., 2010).

10.6.2.4.1 Life Cycle

It can lay its eggs in pruned, injured, weakened, or diseased stems, branches, or trunks. The female lay eggs on both sides of the tunnel, and the larvae will bore galleries beneath the bark to eat and shelter themselves until they will emerge as pupae (Ziaaddini et al., 2002).

10.6.2.4.2 Damage Symptoms

The adults are primarily attack on healthy buds of pistachio trees and then burrow just beneath the buds about half an inch to make tunnel. However, about 10% of adults may dig a tunnel and eat more than one bud (FarivarMehin, 2002).

10.6.2.4.3 Management

The parasitiod, Cheiropachus colon Linnaeus (Hymenoptera: Pteromalidae) was noted attacking C. vestitus larva.

10.6.2.5 Pistachio Hard Scale

Lepidosaphes pistaciae (Archangelskaya) (Hemiptera: Diaspididae), the yellow pistachio hard scale, feeds on the leaves, berries, twigs, and branches of the Pistacia vera tree in Iran (Hosseininaveh et al., 2016).

10.6.2.5.1 Life Cycle

Around the middle of April, the first generation of nymphs emerges and begins feeding on twigs, the bases of fruit clusters, and leaf petioles (Masjedian and Seyedoleslami, 2003).

10.6.2.5.2 Damage Symptoms

These tiny insects feed on the plant’s sap, causing damage to the stems, young leaves, and ripened fruit. They can hinder the development of the stems and even crack the rinds of the fruits. When infected, nuts and plants around the scales’ feeding sites turn yellow and purple.

10.6.2.5.3 Management

A thorough field survey of pistachio plantations in the Kerman province of southern Iran turned up three parasitoid species as parasitoids of L. pistaciae, including Coccobius annulicornis Ratzeburg (Hymenoptera: Aphelinidae), Aphytis spp. near aonidiae (Mercet) (Hymenoptera: Aphelinidae) and Zaomma lambinus (Walker) (Hymenoptera: Encytridae). In addition, three species of parasitoid wasps, C. annulicornis, Z. lambinus, and Ablerus sp., were described by (Jalaeian et al., 2013) as parasitizing this scale in the middle of the country. The predatory mite, Cheletogenes spp. (Canestrini & Fanzago); Neophyllobius pistaciae Bolland & Mehrnejad (Acara: Camerobiidae) and the ladybird beetle Exochomus nigripennis (Erichson); Chilocorus bipustulatus (Linnaeus) (Coleoptera: Coccinellidae).

10.6.2.6 Trunk And Branch Scale

Melanaspis inopinata Leonardi (Hemiptera: Diaspididae), commonly found on pistachio branches and trunks, is a grey, robust, sub-circular, convex scale with a black center.

10.6.2.6.1 Life Cycle

M. inopinata is an ovoviviparous species with dark brown to red-colored crawlers that emerge in late April and early May and disperse close to where they first emerged.

10.6.2.6.2 Damage Symptoms

In case of severe infestation, the scale insect weakens the pistachio trees generally and significantly delays the bud break and early spring regeneration that reduces pistachio nut production and poses a risk of death (Mehrnejad, 2016).

10.6.2.6.3 Management

The management of M. inopinata is almost identical to that of L. pistaciae, the yellow pistachio hard scale. Nearly identical natural enemies exist for L. pistaciae, the hard scale of the yellow pistachio.

10.6.2.7 Pistachio Weevil

Almost all pistachio plantations in Iran and Syria are infested with the adult pistachio weevil, Polydrusus davatchii Hoffmann (Coleoptera: Curculionidae) (Farivar Mehin, 2002; Khoja et al., 20010).

10.6.2.7.1 Damage Symptoms

Adult weevil P. davatchii is considered a potential pest for developing flower lusters and pistachio buds in the early spring.

10.6.2.7.2 Management

Standard methods of control typically involve the use of pesticides such as Phosalone (Mehrnejad and Mirzaei, 2017).

10.6.2.8 Stink Bugs And Plant Bugs

When hollow spots on the nut’s bottom or sides regularly leak sticky fluid, this is called “epicarp lesion” (Bentley et al., 2016). Damaged pistachio nuts fall from trees due to desiccation brought on by peroxidase activity in the injured fruit (Mehrnejad, 2020).

10.6.3 Diseases

10.6.3.1 Alternaria Late Blight

10.6.3.1.1 Damage Symptoms

Chlorotic edges form around the edges of small leaf lesions. The lesions, which are black and about 1 mm in diameter, appear on green, immature nuts. Black necrotic lesions, either angular or circular in shape, can be found on the leaves, with black sporulation and sometimes forming in the center of circular lesions. Alternaria in pistachios is called “late blight” because it gets worse late in the season, when the nuts are getting ready to be picked.

10.6.3.1.2 Favorable Conditions

In low-lying areas with high humidity and abundant dew, this can be a serious issue for orchards that rely on micro-sprinklers as their primary method of watering. Diseases are more likely to spread in warmer temperatures.

10.6.3.1.3 Mode of Spread and Survival

In the wild, you can find Alternaria, which can be fed crop waste or the wilting leaves of weeds. Spores can be dispersed by wind or by being splashed by rain drop.

10.6.3.1.4 Management

Start the applications before the disease starts if the conditions are right for it. Apply difenoconazole 8.4% + cyprodinil 24.1% @12.5g/100 liter every 14–21 days.

10.6.3.2 Botryosphaeria Panicle And Shoot Blight

10.6.3.2.1 Damage Symptoms

Panicle blight, caused by secondary infection of clusters, typically begins at the blackened nodes of branching rachises. Fruit blight is caused by a secondary infection, which initially appears as tiny black lesions on the fruit and then coalesces.

10.6.3.2.2 Favorable Condition

Midway through summer and again in the fall, this fungus, which thrives in warm temperatures (27–32°C), releases a fresh crop of spores from its pycnidia.

10.6.3.2.3 Mode of Spread and Survival

Spores are the infectious agents that cause primary infections in vegetative and floral buds. Secondary infections of shoots, rachises, nuts, and leaves can be caused by the spread of spores, which can occur in water from spring and summer rains by other means (birds, insects, etc.).

10.6.3.2.4 Management

To prevent sprinkle irrigation water from reaching the tree canopy and facilitating spore dispersal, irrigation duration should be reduced and sprinklers should be lowered.

10.6.3.3 Botrytis Blossom And Shoot Blight

10.6.3.3.1 Damage Symptoms

In the spring, the first sign is that the tips of young shoots curl up like a “shepherd’s hook” as they dry. If the inflorescence is infected, there will be big holes above and below the inflorescence. These cankers can also be taken over by Botryosphaeria.

10.6.3.3.2 Favorable Condition

Disease is common in springs that are cool and wet, and it can cause losses by killing shoots from the current season. This cuts down on the amount of fruiting wood for the next season.

10.6.3.3.3 Mode of Spread and Survival

The male inflorescences on the tree or those that have fallen to the ground can support the growth of the fungus and produce spores in the damp spring time. The fungus can also spread through the wind or by producing spores on weeds that land on nearby orchards.

10.6.3.3.4 Management

By cutting off diseased shoots and taking them out of the orchard.

10.7 Major Pests Of Pecan Nut

10.7.1 Economic Importance

The pecan nut, Carya illinoinensis (Wangenh.) K. Koch, is indigenous to North America and economically important to genus Carya. The major insect pests, nematodes and disease of pecan nut crops are given inTable 10.6.

Table 10.6 Major Pests of Pecan Nut Crops⏎

SL. No. | Common Name | Scientific Name | Order/Kingdom/Domain | Family/ Phylum/Division
 1 | Pecan aphid | Melanocallis caryaefoliae (Davis)Monelliopsis pecanisMonellia caryella | Hemiptera | Aphididae
 2 | Pecan weevil | Curculio caryae (Horn) | Coleoptera | Curculionidae
 3 | Pecan nut casebearer | Acrobasis nuxvorella | Lepidoptera | Pyralidae
 4 | Hickory shuckworm | Cydia caryana | Lepidoptera | Torticidae
 5 | Nut curculio | Conotrachelus hicoriae | Coleoptera | Curculionidae
 6. | Pecan phylloxera | Phylloxera devastratrix Phylloxera notabilis | Hemiptera | Phylloxeridae
 7 | Scab | Cladosporium caryigenum | Fungi | Ascomycota
 8 | Downy spot | Mycosphaerella caryigena | Fungi | Ascomycota
 10 | Powdery mildew | Microsphaeria alni | Fungi | Ascomycota
 11 | Zonate leaf spot | Cristulariella moricola | Fungi | Ascomycota
 12 | Brown spot | Cercospora fusca | Fungi | Ascomycota
 13 | Liver spot | Gnomonia caryae | Fungi | Ascomycota
 14 | Vein spot | Gnomonia nerviseda | Fungi | Ascomycota
 15 | Anthracnose | Colletotrichum gloeosporoides | Fungi | Ascomycota
 16 | Bacterial leaf scorch | Xylella fastidiosa | Bacteria | Gracilicutes
 17 | Crown gall | Agrobacterium tumefaciens | Bacteria | Gracilicutes

10.7.2 Insect Pests

10.7.2.1 Black Pecan Aphid

Nymphs have large, light-to-olive-green bodies, and like adults, nymphs contain many knobs on the abdomen and cornicles that are not developed.

10.7.2.1.1 Life Cycle

With little perceptible damage, the young nymphs start feasting on the fresh leaves. These nymphs grow into female adults within only females grow over a period of 20–30 generations. After that, females deposit overwintering eggs.

10.7.2.1.2 Damage Symptoms

Black pecan aphid feeding is evident by yellow rectangular or multi-angular patches between the veins of the leaflets. The leaflet may fall off before these spots ultimately turn brown and result in significant defoliation.

10.7.2.1.3 Management

In order to increase populations of beneficial predatory insects like lady beetles and lacewings during the spring, one additional management approach is to establish winter legume cover crops.

10.7.2.2 Pecan Nut Case Bearer

In three-year research in central Texas, early larval instars themselves caused 8–40% of the nut damage, which resulted in 105% crop losses (Hudson, 2011).

10.7.2.2.1 Life Cycle

Over the course of 5–8 days of life, each female will lay between 50 and 150 eggs. Eggs are either white or a greenish-white color when they are first laid by their mother. The egg will appear pink because of the tiny red spots that will appear on it before the chick will hatch from it (Knutson and Ree, 2011).

10.7.2.2.2 Damage Symptoms

At this stage, a single larvae is capable of boring into two or three nutlets, resulting in a decreased yield. The larvae can only tunnel in the husk of the nut once the nutshell has hardened Knutson and Ree (2011).

10.7.2.2.3 Management

Between 8% and 18% of the eggs were parasitized by the egg parasitoid Trichogramma spp. The percentage of first-generation larvae parasitized ranged from 34% to 47%. In Florida, parasitic flies such as Exorista pyste (Walk.) (Tachinidae) and parasitic wasps like Habrobracon variabilis (Braconidae) frequently emerged from their respective larval hosts. Additionally, in New Mexico, 33% of pecan nut casebearer larvae were infected with the parasitoid Bassus acrobasidis Cushman (Hymenoptera: Braconidae). The diacyl hydrazine insecticides like tebufenozide and methoxyfenozide are toxic to Lepidoptera larvae (Amor et al., 2012; Muegge and Knutson, 2012).

10.7.2.3 Pecan Weevil

From 30.5%–80% of yield is lost due to pecan weevil infestations. The bodies of grubs are a creamy white color, and their heads are a rusty brown (Mulder, 2012).

10.7.2.3.1 Life Cycle

Eggs are laid inside the pecan shell after mating. From late summer to early autumn, larvae eat inside the nuts as they grow and develop through many stages. Adults leave their cells and emerge from the ground after a year. Two or three years are required to complete the one cycle (Mulder, 2012).

10.7.2.3.2 Damage Symptoms

In August and September, adult weevils consume pecans, which results in nut dropping. Pecan weevil grubs feed on growing kernels in September, October, and November, causing a significantly larger loss (Mulder, 2012).

10.7.2.3.3 Management

Applying insecticide (bifenthrin) or a sticky ring of Tree Tanglefoot Insect Barrier can prevent weevils from entering the canopy. When trying to cultivate larvae were the first to describe the fungus they were working with as Metarrhizium anisopliae (Metschnikoff) (Shapiro-Ilan et al., 20010a, b).

10.7.2.4 Hickory Shuckworm

10.7.2.4.1 Life Cycle

Female moths use a creamy white material that is visible on the shuck surface to attach solitary eggs to the shuck. In a few days, the tiny larva hatches, and for the next 15–20 days, it feeds by tunnelling into the husk. The moth immediately emerges after they pupate in the shuck. Over wintering adult shuck worms can be found in empty pecan shells on the ground beneath a tree or orchard.

10.7.2.4.2 Damage Symptoms

Shuckworm larvae tunnel through the husk and obstruct the flow of water and nutrients necessary for the kernels to develop normally. Nuts that have been infected typically lack quality, have scars, and mature more slowly.

10.7.2.4.3 Management

During the water and gel stages of development, pecans are at their most vulnerable stage to damage from hickory shuckworms. In the event that, shuckworms have already caused damage to pecan trees, need to apply an insecticide such as spinosad.

10.7.2.5 Nut Curculio

The nut curculio, Conotrachelus hicoriae adults are 3–16 of an inch long, dark gray to reddish brown, with a beak that is around one-third the length of the body.

10.7.2.5.1 Life Cycle

To hatch their eggs, females make shallow, crescent-shaped punctures in the shucks of developing nuts with their beaks.

10.7.2.5.2 Damage Symptoms

In July or early August, the damaged nuts fall from the tree, and for another two weeks or more, the larvae eat inside the fallen nuts.

10.7.2.5.3 Management

Because nut curculio adults are active during the same time as third-generation hickory shuckworm, insecticides used to suppress these pests can also reduce the number of nut curculio adults.

10.7.2.6 Pecan Phylloxera

The nymphs and adults measure just one-eighth of an inch in length, have a delicate body, and are cream in color.

10.7.2.6.1 Life Cycle

Offspring develop from overwintering eggs are known as “stem mothers.” After being fed by the stem mother for a few days, galls will form around them. The stem mother grows, reproduces, and dies within the gall.

10.7.2.6.2 Damage Symptoms

While the pecan leaf Phylloxera and the southern pecan leaf Phylloxera primarily feed on the foliage, the Phylloxera affects the foliage, stems, and fruit and is therefore the most destructive. Although Phylloxera, an insect similar to an aphid, is rarely seen, its galls are obvious and noticeable.

10.7.2.6.3 Management

Infestations that affect the economy can be stopped from spreading over the entire orchard by spraying of insecticides or even by eliminating these trees.

10.7.3 Diseases

10.7.3.1 Scab

10.7.3.1.1 Damage Symptoms

The scab fungus causes small, circular, olive green to black blotches or spots on leaves, nut shucks (husks), leaf blades, and leaf petioles. Early-season infections can have a devastating effect on both crop yield and quality. On nut shucks, other fungi such as Cephalo theciumroseum pink mold invade old scab lesions. It can cause off-flavors and pink rot if it invades the nut kernel.

10.7.3.1.2 Favorable Condition

Frequent precipitation and an increase in heat and humidity, as well as prolonged periods of wetness and dew on leaves and nuts, are crucial for the development of infections and diseases.

10.7.3.1.3 Mode of Survival and Spread

The scab fungus can overwinter on infected plant tissue. Dew and raindrops spread spores locally, while the wind carries them farther. Over wintering stromata on wood and nuts produce primary spores in the spring.

10.7.3.1.4 Management

Pecan trees should be planted by using Elliott, Excel, or Kanza varieties because they are resistant to scab. Improve air flow by removing lowhanging branches and overgrown trees. During “dry” seasons, two or three well-timed applications of an appropriate fungicide may be sufficient. Before pollination, one application of Bordeaux mixture 4:1:100 followed by one or two applications of Bordeaux mixture 6:2:100.

10.7.3.2 Downy Spot

10.7.3.2.1 Damage Symptoms

Late in the spring, young leaves may develop a smattering of tiny, yellow spots due to a fungal disease known as downy spot. On the upper surface of the leaf, the lesions have a coloration that can be described as yellow-brown.

10.7.3.2.2 Favorable Condition

Infection is more likely to occur on days that are cloudy, cool, and wet.

10.7.3.2.3 Mode of Spread and Survival

These leaves and nuts that have fallen to the ground are potential primary sources of new infection in the spring. Before the buds begin to form, spores are released.

10.7.3.2.4 Management

The downy spot disease can be avoided by first applying a mixture of 4:1:100 Bordeaux in the early spring, before pollination, and then applying a mixture of 6:2:100 Bordeaux between the middle of May and the middle of June.

10.7.3.3 Powdery Mildew

10.7.3.3.1 Damage Symptoms

On both the leaves and the nuts, the symptoms take the form of a powderylike growth that is characteristically found on the surface. The most obvious sign of powdery mildew is when a white, fuzzy growth appears on the surface of the nuts.

10.7.3.3.2 Favorable Condition

There is a possibility that pecan trees could become afflicted after a prolonged period of high humidity and subsequent cool summer nights that restrict airflow through the canopy.

10.7.3.3.3 Mode of Spread and Survival

The powdery mildew fungus overwinters on fallen or clinging infected leaves. In early spring, after rain, the fungus releases spores into the air, which are then carried to the tree’s new leaves and buds.

10.7.3.3.4 Management

Complete harvest residue must be collected and disposed. Symptomatic trees need to be treated with sulfur based fungicides.

10.7.3.4 Zonate Leaf Spot

10.7.3.4.1 Damage Symptoms

Pecan leaves upper surface is covered in grayish brown spots, while the lower surface is covered in concentric ring formations that stand out more clearly. Light brown spots on the underside of a leaf become darker around its edges.

10.7.3.4.2 Favorable Condition

Zoneate leaf spot is caused by overly wet soil, high relative humidity, and inadequate ventilation.

10.7.3.4.3 Mode of Spread and Survival

The fungus rests dormant as sclerotia throughout the winter. The fungus can only flourish when the leaves are damp, and this is also when its growth rate is highest.

10.7.3.4.4 Management

Treatment with copper hydroxide or thiophanate-methyl at the first sign of disease is highly effective.

10.7.3.5 Brown Spot

10.7.3.5.1 Damage Symptoms

Lesions start out as small dots on the undersides of leaves, which grow and turn reddish-brown as they age. However, older spots often turn gray and form concentric rings.

10.7.3.5.2 Favorable Condition

Brown spot is most common in orchards that haven’t been cared for in places with a lot of rain or high humidity.

10.7.3.5.3 Mode of Spread and Survival

Brown spot-causing fungus spends the winter in dead leaves. The spores of fungi become alive and spread through the air and raindrops.

10.7.3.5.4 Management

A single application of Bordeaux mixture 6:2:100 in May, and June, or July will provide effective control.

10.7.3.6 Liver Spot

10.7.3.6.1 Symptoms

Liver spot is characterized by the presence of reddish brown (liver-colored) circular spots on the underside of leaflets, ranging in size from one-eighth of an inch to five-eighths of an inch in diameter. During prolonged wet periods, liver spot can cause severe defoliation.

10.7.3.6.2 Favorable Condition

Disease thrives in environments that are warm, damp, and dreary.

10.7.3.6.3 Mode of Spread and Survival

However, when the wet and warm weather returns in the spring, the fungus resumes its activity and produces a new crop of spores, which then inoculate the leaves of the current year’s growth.

10.7.3.6.4 Management

One application of Bordeaux mixture, 6–2–100, at any time during May, preferably after the middle of the month, will furnish very satisfactory protection to the foliage.

10.7.3.7 Vein Spot

10.7.3.7.1 Damage Symptoms

If the petiole or rachis of the leaf sustains significant damage, the leaflets and often the entire leaf will fall off prematurely. Alternatively, the petioles of the leaflets may become girdled, which causes the leaflets to die and remain attached to the tree for a period of time.

10.7.3.7.2 Favorable Condition

Conditions that are hot and humid are ideal for the fungus that causes vein spot.

10.7.3.7.3 Mode of Spread and Survival

The fungus over winters on the dead leaves and produces spores that are released into the air during the early spring. The spores land on the newly emerging leaves in the month of April and cause them to become infected.

10.7.3.7.4 Management

Vein spot can typically be controlled commercially by applying Bordeaux mixture 4:1:100 prior to pollination, followed by one or two applications of Bordeaux mixture 6:2:10.

10.7.3.8 Anthracnose

10.7.3.8.1 Damage Symptoms

Lesions on the leaves, shucks, and green fruit that are initially shiny and dark brown may eventually coalesce to cover the entire fruit; in wet weather, pink fungal masses may form on the lesions, and the crops yield may decrease.

10.7.3.8.2 Favorable Condition

Disease emergence is favored by warm temperatures and heavy precipitation.

10.7.3.8.3 Mode of Spread and Survival

The spores are dispersed by spring and early summer precipitation. The incidence of diseases in the autumn is proportional to the frequency of rainfall in the autumn.

10.7.3.8.4 Management

To reduce inoculum, remove and destroy infected plant material, such as mummified fruit and infected branches; avoid cover crops, which are an alternative host for the fungus.

10.7.3.9 Bacterial Leaf Scorch

10.7.3.9.1 Damage Symptoms

At first, necrotic lesions of a brownish-tan color appear on the tips or margins of leaves. The entire leaf eventually turns necrotic and falls off the tree.

10.7.3.9.2 Mode of Spread and Survival

Insects that feed on xylem, such as sharp-shooters and spittle bugs, or infected graft wood spread the bacterium.

10.7.3.9.3 Management

By providing adequate irrigation and thinning the trees, the disease should be controlled by minimizing the stress they experience.

10.7.3.10 Crown Gall

10.7.3.10.1 Damage Symptoms

The most noticeable sign is the appearance of wart-like growths or tumors on the roots or, more commonly, at the base of the trunk close to the soil line. If galling is severe and girdles the trunk, it weakens young trees by cutting off their blood supply.

10.7.3.10.2 Favorable Condition Moist soil favors bacterium.

10.7.3.10.3 Mode of Spread and Survival

The bacteria have been shown to survive in the soil for extended periods of time. They enter through cuts made by insects, grafting tools, or human cultivation in pecan roots and stems near the soil line.

10.7.3.10.4 Management

The antagonistic bacterium A. radiobacter strain K84 can be used for biological control of crown gall, but it can only be used for preventative purposes because the roots of healthy trees must be dipped in a solution of the bacterium before planting.

10.7.4 Nematodes

Criconemella rucium, also referred to as the ring nematode, is known to cause necrosis on pecan roots when Pythium irregular and Fusarium solani are present.

10.8 Major Pests Of Chilgoza Nut Crops

10.8.1 Economic Importance

Chilgoza pine is primarily found in the western Himalayan region, including parts of Afghanistan, Pakistan, India (particularly in the states of Jammu and Kashmir and Himachal Pradesh), and Nepal (Kumar and Negi, 2018). The major insect pests of chilgoza nut crops are given inTable 10.7.

Table 10.7 Major Pests of Chilgoza Nut Crops⏎

Sl. No | Common Name | Scientific Name | Order | Family
 1. | Coneborer | Dioryctria abietella | Lepidoptera | Pyralidae
 2. | Seed bug | Leptoglossus corculus, Tetyra bipunctata | Hemiptera | Coreidae
|  |  |  | Pentatomidae
 3. | Lepidopteron borer | Homaloxestis cholopis | Lepidoptera | Lecithoceridae
 4. | Wood inhibiting fungi | Ganoderma lucidum, Ganoderma applanatum | Polyporales | Ganodermataceae

10.8.2 Insect Pests

10.8.2.1 Coneborer

The coneborer, Dioryctria abietella (Lepidoptera: Pyralidae) causes huge significant economic losses in seeds and cones of different pine species. The attacks on Chilgoza pine were about 100% at Kalpa, Himachal Pradesh.

10.8.2.1.1 Life Cycle

About 12–14 hours after emerging, female moths lay eggs. The average incubation time is between 3 and 7 days. Between 16 and 32 days pass during the larval stage. The prepupal stage is 8–11 days long, while the pupal stage lasts 8–17 days. The entire life cycle takes 42 and 65 days from egg to adult (Pawan and Vikrant, 2011).

10.8.2.1.2 Damage Symptoms

Additionally, the resin gathers in the emptied shells of consumed seeds, which quickly dry out and take on a white, gleaming appearance (Pawan and Vikrant, 2011).

10.8.2.1.3 Management

Neem powder has been shown to be the most efficient in preventing chilgoza seed damage, hence seeds intended for consumption should only be treated with it or another biopesticides (Pawan and Vikrant, 2011).

10.8.3 Diseases

10.8.3.1 Ganoderma, Wood Inhibiting Fungi

Ganoderma is a parasitic organism that sustains itself saprophytically by deriving nutrients from decaying organic matter found in stumps and roots. It is postulated that the aforementioned disease has the potential to induce mortality in approximately 80% of plantings, occurring at the midpoint of their economic life span (Roslan et al., 2012). The fungus Ganoderma, which exhibits white-rot characteristics, belongs to the taxonomic class Agaricomycetes and the family Ganodermataceae. Upon encountering a conducive environment, the basidiospores undergo development into monokaryotic vegetative mycelia. The formation of a dikaryotic mycelium occurs through the process of nuclear exchange and migration, leading to its subsequent invasion and establishment within the host plant. Under optimal environmental conditions, the dikaryotic mycelia subsequently initiate the development of the fruiting body.

10.8.3.1.1 Damage Symptoms

The primary indications of Ganoderma wilt are characterized by the discoloration and wilting of the outermost cluster of leaves. Subsequently, a process ensues wherein a reddish brown liquid is exuded through fissures located at the lower portion of the tree’s main stem, with the resulting oozing gradually extending in an upward direction.

10.8.3.1.2 Management

The stem’s bleeding patches can be treated by chiseling them and applying tridemorph (5% Calixin) as a protective measure, followed by the application of hot coal tar. For root feeding, a solution consisting of 2 grams of copper sulfate and 1 gram of copper sulfate dissolved in 100 mL of water was administered. For soil drenching, it is recommended to apply 40 L of Bordeaux mixture at a concentration of 1%, evenly distributed around the base of the tree within a radius of 1.5 meters.

10.9 Conclusion

Insect pests and disease management is an effective strategy for eradicating pests and diseases, and an expert must have in-depth knowledge of insect pests, nematodes and pathogens in relation to their bioecology, phenology, biotic agents, economic injury level, forecasting system, and other mortality factors in order to develop the strategy. When using biological control in conjunction with other techniques of control, insecticide use must be kept to a minimum and done so carefully and in a way that does not negatively impact the populations of biotic agents. In reality, to limit the disruption of the agroecosystem, emphasis is placed in pest management on the coordinated, wise, and timely use of selective or broad spectrum pesticides in a precise fashion at a decreased rate. Even if there are chemical controls for the main pests and illnesses of temperate nut crops, efforts must be made to create IPM techniques.

KEYWORDS

bioecology

biotic agents

insect pests

nematodes

nut crops

pathogens

phenology

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Chapter 11 Pre-Harvest Factors Influencing the Production and Quality Attributes in Fruit Crops

LAKHWINDER SINGH¹, HARJINDER KAUR², and AB WAHEED WANI²

¹Faculty of Agriculture, Guru Kashi University, Talwandi Sabo, Bathinda, Punjab, India

²Department of Horticulture, School of Agriculture, Lovely Professional University, Phagwara, Punjab, India

* Corresponding author

Abstract

Fruit crops constitute a crucial component of global agriculture, supplying essential nutrients, flavors, and economic value. The intricate journey from flower to mature fruit is governed by a complex interplay of pre-harvest factors that significantly influence both production and quality attributes. Environmental factors, encompassing abiotic elements such as temperature, light, and humidity, and biotic components like pests and diseases, lay the foundation for fruit development. These factors interact to shape growth rates, nutrient uptake, and overall plant health, thus directly impacting fruit size, color, texture, and taste. Plant physiology plays a pivotal role as hormones orchestrate processes such as flowering, fruit set, and ripening. The balance between auxins, cytokinins, and ethylene regulates the timing and extent of maturation, influencing aroma, flavor, and shelf life. Concurrently, nutrient availability and uptake contribute to the nutritional content and structural integrity of fruits. Human interventions, embodied in cultural practices and genetics, further shape pre-harvest conditions. Cultural practices encompass irrigation, fertilization, and canopy management, while genetic traits establish inherent qualities such as disease resistance and sensory attributes. Understanding the interaction between these genetic traits and pre-harvest conditions is key to realizing desired qualities. While insights into these preharvest factors offer opportunities for optimizing fruit crop production and quality, challenges such as climate change and emerging pests require adaptive strategies. This review underscores the complexity and significance of pre-harvest factors in shaping the trajectory of fruit crops, laying a foundation for informed decisions and holistic approaches in fruit crop management.

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Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

11.1 Introduction

Fruit crops have long been integral to human sustenance, serving as a source of essential nutrients, vitamins, and gustatory delights. The journey from flower to fully matured fruit is a complex trajectory governed by a myriad of factors. Among these, pre-harvest influences play a decisive role in determining not only the yield but also the quality attributes of fruit crops. Understanding these pre-harvest factors and their intricate interactions is of paramount importance in ensuring a bountiful harvest of high-quality produce that meets the demands of an ever-growing global population (Hidalgo and Almajano, 2017). The production of fruit crops is an intricate dance between nature’s whims and human stewardship. From the moment a flower blooms to the point of harvest, a dynamic interplay of environmental, physiological, and management factors shapes the destiny of each fruit. The quest for maximum yield and optimal quality has driven researchers and farmers to explore the multifaceted tapestry of influences that converge on the pre-harvest stage. As we delve into the heart of this review, we uncover the multifarious dimensions that pre-harvest factors encompass and how they orchestrate the final composition and characteristics of fruit crops (Feliziani et al., 2016). Pre-harvest factors encapsulate the broad spectrum of elements that collectively sculpt the trajectory of fruit crops from conception to culmination. These factors encompass both abiotic and biotic components, each weaving its own thread into the intricate fabric of fruit development. Abiotic factors such as temperature, light, humidity, and soil quality lay the foundational groundwork for growth, while biotic factors like pests, diseases, and pollinators are the unseen conductors of this symphony. Beyond the realm of natural influences, human interventions in the form of cultural practices and technological advancements add yet another layer of complexity to the pre-harvest narrative (Davuluri et al., 2005; Limera et al., 2017, Mezzetti, 2013;). The environment serves as an overarching architect of fruit crop development. Temperature fluctuations, precipitation patterns, and sunlight availability imprint their signatures on the growth rate, metabolic processes, and ultimately, the quality attributes of fruits. The delicate balance between these factors can sway the outcome of the harvest, as extreme conditions might result in physiological stress, influencing factors such as fruit size, color, texture, and taste. Furthermore, the delicate equilibrium between abiotic elements can reverberate across the biotic realm, affecting the interactions between pests, diseases, and the fruit crop itself (Cordenunsi et al., 2002). The inner workings of a plant’s physiology further amplify the impact of pre-harvest conditions on fruit quality attributes. Hormones, those molecular messengers, regulate pivotal processes like flowering, fruit set, and ripening. The intricate dance between auxins, cytokinins, and ethylene can determine the timing and extent of fruit maturation, impacting attributes like aroma, flavor, and shelf life. In parallel, the availability and uptake of essential nutrients—nitrogen, phosphorus, potassium, and others—serve as foundational building blocks for fruit composition. Deficiencies or imbalances in these nutrients can manifest as irregular growth patterns, altered nutritional content, and compromised structural integrity (Milošević et al., 2016). In the ongoing quest to optimize fruit crop production and elevate quality attributes, human intervention emerges as a powerful factor. Cultural practices encompass a gamut of activities, from irrigation and fertilization to pruning and training. These practices bear the potential to fine-tune pre-harvest conditions, influencing water availability, nutrient uptake, and light exposure (Balducci et al., 2016; Capocasa et al., 2008; Vagiri et al., 2016, Diamanti et al., 2012). Moreover, the genetic makeup of fruit crops establishes a blueprint for potential qualities, influencing aspects such as disease resistance, shelf life, and sensory characteristics. The intersection of these genetic traits with pre-harvest factors charts the course for the realization of inherent qualities within each fruit. In this review, we embark on a journey through the intricate landscape of pre-harvest factors that wield influence over the production and quality attributes of fruit crops (Vagiri et al., 2016; Uleberg et al., 2016). By exploring the amalgamation of abiotic and biotic elements, physiological intricacies, and the harmonizing touch of human stewardship, we unravel the interconnected web that culminates in the final harvest. As we delve into the subsequent sections, we will delve deeper into the nuances of specific pre-harvest factors and their synergistic roles in shaping the fruitful narrative of fruit crop cultivation. In doing so, we hope to illuminate pathways towards sustainable practices and novel insights that uphold the legacy of nourishment and delight that fruit crops offer to humankind (Rouphael et al., 2017).

11.1.1 Fruit Plant Yield Efficiency

Plant yield refers to the quantity of commercially valuable fruits obtained from each production cycle. Growers typically prioritize this factor when deciding whether to cultivate a new plant variety. Additionally, the efficiency of the harvesting process plays a significant role, as it can impact labor expenses—a major cost component for fruit production. Equally crucial is the plant’s ability to thrive in various soil and climate conditions, while also resisting pests and diseases. These qualities take precedence in minimizing resource inputs and maximizing yield efficiency. These aforementioned attributes hold greater suitability for assessing yield efficiency. Notably, fruit size stands out as a particularly significant characteristic in selecting new genetic strains. This characteristic is substantially influenced by the growing atmosphere. When working with a sizable number of kids, the parental contribution to fruit size becomes quantitative (Gilbert, 1967). Species differences in preferred commercial fruit size are a natural occurrence. Selective breeding has led to substantial increases in fruit size, to the extent that some varieties produce unnaturally large primary fruits, a feature not always favored by consumers due to its perceived artificiality. Nonetheless, growers opt for these sizes to significantly lower harvesting expenses.

11.1.2 Fruit's Organoleptic Quality

Known evaluation techniques that have been fully documented and characterized are used to examine sensory and organoleptic qualities. Fruit form is often assessed with descriptors that aid in fruit identification, as it is strongly linked to specific varieties. Fruit color is a fundamental characteristic critical for attracting consumer attention and must accurately reflect the species. Generally, consumers prefer brighter-colored fruits over paler ones, and a neophobic attitude toward unconventional fruit appearances has been observed, such as with yellow-fleshed kiwifruit (Raudenbush et al., 1998; Jaeger et al., 2002). For larger red fruits, both background color and the amplification of red and orange hues during ripening enhance aesthetic appeal. Typically, fruit color transitions directly from green to red, orange, blue, or purple during ripening, while some cultivars may turn from white to red, retaining a white throat. Although genetics plays a key role, environmental factors and the fruit’s developmental stage significantly impact color. In addition to external appearance, the color of fruit flesh is increasingly valued due to pigments like anthocyanins, which correlate with pulp color. Firmness, both of the outer peel and inner flesh, is a crucial attribute indicating resistance to mechanical injury, essential for harvesting, transportation, and post-harvest processing. Consumer preferences favor firmer, crisper fruits over softer, juicier ones. Beyond visual and tactile attributes, taste is critical in assessing fruit quality, requiring the evaluation of acidity, sweetness, sourness, and bitterness. Sweetness, expressed in °Brix as Total Soluble Solids (TSS), is highly preferred by consumers and is often a focus of breeding programs. High fructose levels in fruits also make them suitable for diabetic individuals (Nile and Park, 2014). Acidity, measured as Total Acidity (TA), is another key determinant of organoleptic quality.

These characteristics work together to create a fruit’s sweet-acid equilibrium, which is measured by the Sugar/Acid (S/A) ratio. This ratio determines the fruit’s relative content of sugars and acids; a fruit with a balance between the two is considered to have the greatest consumer appeal. To provide a desired flavor profile, this equilibrium takes into account variables such a minimum TSS and maximum TA (Manning, 1996). Last but not least, flavor is a fundamental quality that consumers respect highly and has a considerable impact on how well-liked fruits are in general. Volatile organic compounds (VOCs) are thought to be responsible for the aromatic properties of fruits, and there are a lot of these molecules that have been found in the scientific literature (Latrasse et al., 1991; Ulrich and Olbricht, 2013).

11.1.3 Fruit's Nutritional Quality

In recent times, the remarkable nutritional value of these fruits has garnered significant attention and led to heightened consumer demand, in addition to the agronomic and sensory attributes mentioned earlier. The concept of nutritional quality precisely pertains to the presence of advantageous bioactive constituents within the fruit’s composition. Yet, in some instances, it has been described as a fusion of nutritional components, such as antioxidants, vitamins, and so forth, along with sensory components like color, sweetness, acidity, and aroma. This blend is often supported by the fact that specific bioactive compounds, including phenolic substances, not only contribute to the fruit’s sensory aspects but also contribute to its health-promoting attributes. According to Tomás-Barberán and Espín (2001), the astringency in fruits and raspfruits is largely attributed to ellagitannins, potent antioxidant compounds. In a similar vein, phenols enhance color stability while subtly tempering the brilliance of fruit color in processed fruit purees (Diamanti et al., 2015; Mazzoni et al., 2017; Scalzo et al., 2005a). Notably, the significant dietary fiber content, including fruit pectin, plays a pivotal role in regulating intestinal functions (Ramadan et al., 2008). Vitamins A, C, E, and those from the B complex are abundant in fruits, acting as antioxidants that bolster the immune system (Pantelidis et al., 2007). Furthermore, fruits stand as excellent sources of both macro- and micronutrients. Among the essential minerals found in fruits, potassium, phosphorus, magnesium, calcium, manganese, iron, copper, sodium, and aluminum hold notable significance. These substances are crucial for numerous physiological and biochemical processes, essential for bone and teeth development, muscle growth, and other biological activities. Fruits with red, blue, or purple hues tend to contain anthocyanins, a subclass of flavonoids responsible for imparting colored pigments. Anthocyanins are potent antioxidants, acknowledged for their positive effects on urinary tract health, blood vessels, anti-cancer properties, and anti-aging benefits (Manach et al., 2005; Arts et al., 2000; Moyer et al., 2002; Xue et al., 2002). Cyanidin-3-glucoside, a prevalent anthocyanin, is identified across multiple fruits (Paredes-López et al., 2010). Another significant flavonoid, catechin, is present in diverse forms and offers beneficial nutritional effects (Cieslik et al., 2006). Abundant in various fruits, quercetin serves as a potent antioxidant with an array of pharmacological, biological, and medicinal advantages (Beekwilder et al., 2005; Xue et al., 2002). A noteworthy compound, ellagic acid, is found abundantly in several fruit species. It occurs as ellagitannins (glucose esterified) or in free form (glucoside), constituting 51% of all phenolic compounds found in fruits (Nile et al., 2014). In certain studies (Paredes-López et al., 2010), the ellagitannin content in fruits has been reported to be up to 15 times higher than that in other fruits and nuts, surpassing even pecans and walnuts by threefold (Bushman et al., 2004; Hannum, 2004). Stilbenes, a category of minute phenolic compounds, are found in notable quantities in fruits. Among them, resveratrol and its analogues exhibit diverse properties like anti-allergenic, algicidal, antitumoral, anti-inflammatory, anti-aging, and antimutagenic effects, with pterostilbene emerging as a potent anticarcinogen and antioxidant (Wang et al., 2002). Phenolic acids are principal phenolic constituents within fruits, often existing in esterified forms alongside organic acids and carbohydrates (Paredes-López et al., 2010). Fruits also contain proanthocyanidins, a condensed non-hydrolyzable tannin type. Hydrolyzable tannins manifest as gallic acid and ellagic acid esters (Seeram et al., 2001). The capacity of fruits to accumulate bioactive compounds is markedly influenced by their genetic makeup, particularly true for fruits where genotype, species, and variety collectively exert a significant impact on their nutritional content (Hakala et al., 2003). Different fruit types exhibit varying nutrient profiles; for instance, blackcurrants and honey fruits surpass raspfruits, goosefruits, and fruits in terms of vitamin content (Oszmianski et al., 2004). Notably, blackcurrants and fruits are particularly rich in water-soluble ascorbic acid (Pantelidis et al., 2007). The macro- and micronutrient content of honey fruits is very abundant (Nile et al., 2014).

Extensive research has focused on analyzing the phenolic content of various fruit species, particularly anthocyanins, with a notable emphasis on those belonging to the genera Vaccinium, Rubus, and Ribes (Nile and Park, 2014). While red grapes often contain malvidin glycosidic derivatives and species like elderfruits and black chokefruits contain cyanidin, the principal anthocyanin found in multiple fruits is cyanidin-3-glucoside (Lyons et al., 2003; Pappas and Schaich, 2009). Another phenolic compound, catechin, varies based on genotype and is particularly prominent in cranfruits. Certain fruit varieties, including deerberry, blueberry, cowberry, and lingonberry, harbor stilbenes like resveratrol, pterostilbene, and piceatannol (Wang et al., 2002a). Specifically, flavonols such as quercetin and kaempferol are abundant in cranfruits, bilfruits, and chokefruits, while raspfruits contain quercetin in glucuronide form (Paredes-López et al., 2010). The concentration of hydroxy-cinnamic derivatives varies across different fruit types, with bluefruits and chokefruits presenting high levels, while blackfruits and honey fruits contain lower amounts (Shahidi and Naczk, 2004; Scalzo et al., 2005a). Conversely, hydrolysable tannins are present in smaller amounts in fruits, raspfruits, and blackfruits, making them less common (Tamir and Alumot, 2006; Nile and Park, 2014). Although fruits are recognized for their high Total Antioxidant Capacity (TAC), variations exist across different species and cultivars. Notably, TAC differs significantly among high-bush blueberry varieties (Connor et al., 2002). Fruits, in particular, exhibit remarkable antioxidant capacity compared to other fruits such as peaches, grapes, oranges, apples, pears, kiwifruit, and tomatoes (Scalzo et al., 2005b). This pattern aligns with studies indicating that both cultivated fruit varieties like raspfruits, fruits, blackfruits, and bluefruits, and wild fruits (F. vesca), possess potent antiradical activity (Halvorsen et al., 2001; Scalzo et al., 2005a). Subsequent research supported these findings (Moyer et al., 2002), underscoring that, in most cases, wild germplasm exhibited higher antioxidant levels than cultivated cultivars. The distinction between domesticated and wild species presents a compelling subject. Wild species often possess improved nutritional qualities but sometimes at the cost of essential sensory attributes (e.g., fruit size and firmness) (Diamanti et al., 2014). To enhance fruit nutritional quality, wild germplasm is invaluable as a genetic resource (Crespo et al., 2010; Wang and Lewers, 2007). This notion is exemplified by the behavior of wild fruits (F. vesca), which are gaining popularity due to their beneficial nutritional and sensory characteristics. Importantly, prior studies have indicated that sugar concentrations in F. vesca fruits are two to three times higher than those found in cultivated Fragaria x ananassa fruits (Zugic et al., 2014). The value of another wild species, F. virginiana glauca (FVG), as a source of bioactive compounds within the context of fruits has been established (Scalzo et al., 2005b; Deighton et al., 2003). Plant age may also be a genetic factor influencing fruit quality (Figure 11.1) (Milivojevic et al., 2011).

Figure 11.1 Major phenolic compounds present in fruit crops. ⏎

11.2 Environmental And Agronomic Factors Affecting Fruit Quality

Major fruits’ genetic make-up, in combination with environmental conditions, growing techniques, and other factors, ultimately determines their full potential in terms of productivity and quality (Kosar et al., 2004). To achieve the best possible production efficiency and fruit quality, each new cultivar must be paired with the appropriate pedoclimatic conditions and cultivation methods (Wang et al., 2000).

11.2.1 Environmental Factors And Fruit Quality

What actually distinguishes fruits is their incredible capacity to survive in a variety of climatic conditions, ranging from exceedingly hot to unusually cold environments (as indicated in Table 11.1). However, some soil characteristics, such as high pH levels, may pose significant challenges for some fruits, most notably bluefruits (Tulipani et al., 2011).

Table 11.1 Principal Environmental Elements Affecting Fruit Quality ⏎

Environmental Factor | Parameter Affected | References
Growing location | Acidity overall, TSS, and dry matter concentration of ascorbic acid, sweetness, and anthocyanins | Krüger et al. (2012)
Harvest season | Fruit weight, TSS, titratable acidity, total phenols, vapor-phase volatile aromatic component concentrations, pH, and color | Ulrich et al. (2014)
| Vitamin C concentration, sucrose concentration, nitrate concentration, and antioxidant capacity, Plant yield | Wold et al. (2007)
Light exposition and radiation | Flavonoids content | Spayd et al. (2002)
Temperature | Firmness, Soluble Solids, Titratable Acidity, TPH, ACY, Vitamin C, and pH Carotenoids | Remberg et al. (2014) Zoratti et al. (2015)

11.2.1.1 Growing Location

Some fruit species are remarkably adaptable to a range of pedoclimatic situations. In such cases, the particular geographic region where they are grown can have a significant impact on the quality of their fruits, particularly when grown in open field. Environmental conditions have been shown to be crucial in determining the yield and nutritional quality of fruits. This was discovered by Krüger et al. (2012). Similar to this, research on fruits produced in various Italian locations showed the complex interactions between genetics, climatic factors, production techniques, and location, which significantly influenced numerous fruit quality parameters. For example, fruits grown in southern Italy were shown to have higher levels of sweetness, ascorbic acid, and anthocyanins (Cocco et al., 2015).

11.2.1.2 Harvest Season

Different years and seasons bring forth varying environmental conditions that can influence cultivation cycles and harvest timing. Ulrich and Olbricht (2014) conducted research on the concentrations of VOCs in strawberry fruits, discovering that fragrance levels differed among three strawberry genotypes over three distinct years. These variations in fragrance concentrations were attributed to irregular weather conditions affecting strawberry growth and subsequently altering volatile patterns. The decline in fragrance concentrations observed from the first to the third year was linked to these changing environmental factors (Ulrich et al., 2014). In a separate study centered on bluefruits, the impact of ripening year and harvest date on multiple fruit quality attributes was investigated. Among the “Bluecrop” cultivar, fruit weight decreased across the first to fourth harvests due to interactions between harvest year and harvest date. Across several harvest dates, only the “Duke” cultivar showed changes in solids that dissolve concentration. Additionally, it was discovered that both the season of harvest and harvest year had an impact on total phenolic content (Milivojevi et al., 2016). The effects of two different culture phases on the quality of the fruit of hydroponically produced alpine fruits (F. vesca) were the subject of a fascinating experiment. Compared to the autumn-spring cycle, the longer summer-spring cycle resulted in improved plant yields, fruits with higher levels of ascorbic acid and sucrose, and fruits with lower nitrate content (Caruso et al., 2011). Similar trends were observed in commercial fruits, where attributes such as soluble solids, pH, TA, color, and particularly fruit size were influenced by both the ripening season and harvest year. However, these factors did not impact the quantity of ascorbic acid or the antioxidant activity (Wold and Opstad, 2007).

11.2.1.3 Light Exposure and Radiation

The exposure to light constitutes an additional environmental aspect influencing fruit quality. In cases where sunlight is scarce, the suppression of genes in the flavonoid pathway tends to occur, resulting in diminished flavonoid levels in both climacteric and non-climacteric fruits (Cortell and Kennedy, 2006). Studies focused on grapes have revealed that elevated light exposure leads to the upregulation of genes linked to flavonoid biosynthesis in the fruit’s skin, irrespective of environmental temperature (Azuma et al., 2012; Spayd et al., 2002). This genetic response ultimately elevates the content of anthocyanins and flavanols (Fujita et al., 2006; Koyama et al., 2002). Similar favorable impacts of light on flavonoid production have been observed in other fruits like bilfruits (Uleberg et al., 2012), raspfruits (Wang et al., 2009), Chinese bayfruits (Niu et al., 2010), and fruits (Kadomura-Ishikawa et al., 2013). However, it’s worth noting that not all these fruit species necessitate extensive light exposure to produce significant quantities of flavonoids. For example, bilfruits thrive in shaded environments yet exhibit high levels of anthocyanins (Jaakola et al., 2004). It’s pertinent to recognize that, akin to grapevines, different cultivars react differently to light-induced stimulation of flavonoid synthesis (Matus et al., 2009). Certain white fruit cultivars, featuring genetically modified flavonoid pathways, do not exhibit increased anthocyanin production in response to light. This phenomenon can be observed in fruits (Salvatierra et al., 2010), bilfruits (Jaakola et al., 2002, 2010), grapefruits (Walker et al., 2007), and Chinese bayfruits (Zoratti et al., 2014 a), among others, which have undergone such alterations (Zoratti et al., 2014b).

11.2.1.4 Temperature

Temperature is a fluctuating environmental factor influenced by seasonal changes, akin to the impacts of light quality, and it can profoundly influence fruit quality. Various fruit species have been subject to examination to unravel how temperature shapes fruit quality. In a study conducted in 2009, Diamanti et al. scrutinized four distinct strawberry cultivars over four years, investigating the interplay of genotype and environmental temperature on quality. Notably, varying temperatures prevailed throughout these years, leading to inconsistent outcomes concerning fruit quality. While some parameters, such as fruit total acidity and firmness, displayed a degree of sensitivity to temperature fluctuations, deciphering the specific effects of temperature on other measured attributes like TEAC, TPH, soluble solids (SS), and color proved challenging in an open field setting. Recent investigations by Remberg et al. (2014) and Uleberg et al. (2016) explored the quality of red raspfruits, black currants, and highbush bluefruits in Norway spanning 2002–2008. Notably, only soluble solids content in red raspfruits exhibited a favorable correlation. The apparent lack of connection between temperature variation and other assessed qualitative metrics could be attributed to the potential masking influence of ambient radiation and precipitation in open field studies. An extensive study by Karppinen et al. (2016 a) delved into the influence of climatic factors on Vaccinium fruit, with a specific focus on secondary metabolite synthesis. Noteworthy findings, such as those by Zoratti et al. (2015a,b), indicated that lower temperatures decelerated fruit ripening and anthocyanin accumulation in highbush bluefruits, while higher temperatures facilitated enhanced anthocyanin buildup. This pattern also extended to bilfruits, aligning with earlier research by Uleberg et al. (2012) that highlighted how lower temperatures (12°C) resulted in higher quantities of flavonols and hydroxycinnamic acids compared to higher temperatures (18°C). Elevated temperatures negatively impacted black currant quality by hampering anthocyanin production and altering fruit color. While optimal levels of total anthocyanins and total phenolics were observed at 18°C, vitamin C concentration declined as temperatures ascended from 12°C–24°C (Woznicki et al., 2015). In an investigation by Remberg et al. (2012) concerning the “Glen Ample” red raspberry cultivar, the influence of post-flowering temperatures (12, 18, and 24°C) was explored. Across all temperatures during the harvest period, higher temperatures expedited fruit weight reduction, prompting earlier fruit maturation and harvesting as temperature increased. As temperatures decreased closer to harvest, metrics such as dry matter, soluble solids, total acidity, pH, and FRAP values also diminished. This was attributed to a coinciding elevation in moisture content accompanied by fruit weight (Martinussen et al., 2010).

11.2.2 Agronomic Factors and Fruit Quality

Studies on fruits show that cultivation practices have the capacity to significantly affect the phytochemical content of fruits (Mezzetti et al., 2016; Giampieri et al., 2012; Josuttis et al., 2012; Fan et al., 2011; Oszmianski and Skupien, 2004). To efficiently manage the growth of a specific fruit species, a variety of parameters in the cultivation techniques can be changed (Table 11.2).

Table 11.2 Primary Agricultural Factors That Impact the Quality of the Fruit ⏎

Agronomic Factor | Parameter Affected | References
Organic farming | Ellagic acid, flavonols, total phenolics, antioxidant activity, and sugar content | Hakala et al. (2006)
Salinity | Dietary supplements and micronutrients | Li et al. (2013)
Management of water | Phenol concentration, antioxidant capacity, lipid peroxidation, TSS, acidity, firmness, plant production, and fruit weight | Lobos et al. (2016)
Plant nutrition | Weight of fruit and diameter of fruit, pH level, TPC, micronutrient content, and TSS are all factors that affect the quality of the fruit | Rupp et al. (2000)
Biostimulants and microbial inoculants | Anthocyanins, polyphenols, and ascorbic acid | Singh et al. (2010)
Mulching | Ellagic acid | Wang et al. (2002)
| Fruit height, width, and weight | Kumar et al. (2012)
| Yield of plant | Ahmad et al. (2008)
| Contents of an ingredient include sugar, total acidity, ascorbic acid, crude protein, and anthocyanins |
Soil management | Anthocyanins, flavonoids, and phenols | Wang et al. (2009)
| Fructose, glucose, ascorbic acid, flavonoids, and antioxidant activity of sugars and acids | Hakala et al. (2003)
Fruit harvest | Tensile strength, TPC, Vitamin C content, and antioxidant capability | Beekwilder et al. (2005)
| Titratable acidity, Soluble sugars | Wang et al. (2000) Shin et al. (2008)

11.2.2.1 Conventional and Organic Farming

It is possible to make a preliminary comparison of organic and conventional production techniques because there are differences between them in terms of nutritional and sensory qualities (Weibel et al., 2000). Notably, Olsson et al. (2006) claimed that as compared to conventionally produced fruits, organic fruits have a greater amount of total phenolics, ellagic acid, and flavonols. Numerous researchers have noted this tendency in a variety of fruit species (Del Amor et al., 2008). Similar results addressing the influence of organic cultivation on the nutritional makeup of bluefruits were also found by Ochmian et al. (2015). In this investigation, a number of cultivars from organic orchards showed higher polyphenolic content (Carbonaro and Mattera, 2001). In particular, delphinidin-based anthocyanins showed wide diversity, with delphinidin-3-galactoside being particularly abundant in organic fruits (Lombardi-Boccia et al., 2004). The examined cultivars also displayed considerable quantities of chlorogenic acid, which were unaltered by the style of culture, even though flavonoid levels were equivalent across conventional and organic practices. In contrast, Conti et al. (2014) highlighted how organic farming improves the amount of vitamin C, beta-carotene, fruit dry matter, sucrose, malic acid, and mineral components in organic fruits. But Hakkinen and Torronen (2000) found no differences in antioxidant levels between conventional and organic strawberry farming. Additionally, replacing inorganic fertilizers with organic amendments had no effect on the total antioxidant capacity or sugar content of the fruit (Hargreaves et al., 2008). In this regard, Hakala et al. (2002) showed that the sensory qualities, sugar content, and acidity of fruits cultivated conventionally and organically were equivalent. However, Ochmian et al. (2015) discovered that organic fruits had higher acidity, less soluble solids, and less firmness than conventional fruits. Regarding plant yield productivity, Conti et al. (2014) revealed that organic strawberry plants produced less overall than their conventional counterparts, despite an increase in average fruit weight. According to Ochmian et al. (2015), organic bluefruits also showed this trend.

11.2.2.2 Management of Water and Salinity

In general, plants possess a defense mechanism that triggers the synthesis and storage of phytochemicals, particularly phenols, as a response to stress-inducing factors like low salinity and reduced water availability. The levels of micronutrients and nutraceutical components in fruits have been shown to be impacted by extended exposure to salt stress (Keutgen and Pawelzik, 2007). However, it’s important to exercise caution in not excessively stimulating this stress-induced system, as it could lead to the formation of undesirable substances such as allergens. Hepaksoy et al. (2006) demonstrated that grapes cultivated without salt stress exhibited lower acidity compared to those subjected to saline treatment in sensory evaluations. Moreover, the Soluble Solids/Acidity Ratio indicated that acidity moderately decreased under saline conditions. Conversely, Li et al. (2013) found that the overall acidity of grapes increased in correlation with the quantity of sodium chloride applied, notably concerning tartaric and malic acid content. At low salt levels, soluble solids such as glucose and fructose also rose, but this positive trend reversed at higher salinity levels, which also influenced anthocyanin content. Moderate salt levels improved fruit firmness, yet fruit aroma was notably sensitive to low salinity, resulting in a distinct reduction in the quantity and composition of volatile components. In contrast, Hepaksoy et al. (2006) discovered that saline treatment led to reduced plant productivity compared to non-saline conditions. Researchers have also investigated the impact of deficit irrigation on fruit phenol content (Terry et al., 2007), finding that fruits exhibited heightened antioxidant activity (Valentinuzzi et al., 2015). Recent studies indicate that the severity of drought stress affects the positive outcomes of water scarcity. For bluefruits, severe water deficit treatment has been shown to restrain vegetative growth and negatively influence several fruit quality parameters, including average fruit weight, plant yield, titratable acidity, and soluble solids. Moreover, significant water deficit elevates lipid peroxidation and fruit oxidative stress. The remarkable concentrations of anthocyanins, phenolics, and antioxidant capacity found in wild fruit species are thought to be attributed, among other factors, to environmental stress conditions (Trethewey, 2004).

11.2.2.3 Plant Nutrition

The nutritional value of cultivated fruits can be influenced by the fertilization schedule. Recent investigations (D’Anna et al., 2012) have revealed that both low and high nitrogen application rates can yield comparable results, generating larger, and high-quality fruits with enhanced characteristics like total soluble solids, vitamin C content, and phenolic concentration. Conversely, studies have shown that decreasing iron and phosphorus intake can enhance strawberry quality (Castellanos-Morales et al., 2010; Valentinuzzi et al., 2015). In particular, a deficiency in iron disrupts the micronutrient balance in fruits, resulting in higher accumulation of zinc and copper without affecting taste, acidity, or firmness (Valentinuzzi et al., 2015). However, this shortage of iron affects the composition of bioactive components in fruits, leading to increased levels of total phenols and anthocyanins. When compared to the control group, fruits grown in iron-deficient soil experienced a significant 40% increase in pelargonidin-3-glucoside concentration (Valentinuzzi et al., 2015). Anthocyanins, known for their effective scavenging of reactive oxygen species, can be induced by various stimuli including UV and gamma radiation, temperature fluctuations, and chemical elicitors (Cantos et al., 2003; Eichholz et al., 2011; Liu et al., 2005). This rise in anthocyanins is often associated with a stress response mechanism (Valentinuzzi et al., 2015). In response to phosphorus deficit, the calcium concentration in fruits increased, indicating a positive correlation between calcium content and fruit firmness. This suggests that increased fruit hardness is also an outcome of phosphorus scarcity. Although insufficient phosphorus, similar to iron deficiency, negatively affected total soluble solids, it led to higher quantities of beneficial compounds in fruits (Valentinuzzi et al., 2015). According to Miloevi et al. (2018), the effects of nitrogen, phosphorus, and potassium fertilization on bluefruits had minimal impact on the fruit’s soluble solids content, titratable acidity, juice pH, or certain leaf mineral levels (Angeletti et al., 2010; Rupp and Tränkle, 2000).

11.2.2.4 Microbial Inoculants and Biostimulants

Utilizing bioregulators entails using hormones like auxins, gibberellins, and cytokinins to lessen the effects of biotic and abiotic stressors. This strategy boosts output and enhances the physical and chemical characteristics of crops. By boosting root activity, increasing water and nutrient absorption, and boosting crop resistance against environmental stressors, microbial biostimulants offer a possible route for sustainable agriculture, leading to higher yields and better product quality (Singh et al., 2010). Usually, microbial inoculants applied to soil contain advantageous fungus and/or bacteria. Although this technique is less frequently used to increase the quality of fruits, it has been shown to be effective in improving strawberry fruit quality in a study including the bio-inoculation of several bacteria and fungus.

11.2.2.5 Soil Management

Implementing enclosed soilless systems proves advantageous in mitigating the environmental impacts associated with greenhouse crop cultivation. Nevertheless, a significant challenge that arises within this cultivation context pertains to the accumulation of ions in the recycled nutrient solution, resulting from plants either incompletely absorbing or entirely failing to uptake certain ions. Signore et al. (2016) investigated potential solutions for this issue in tomato cultivation. They explored the effects of electrical conductivity values within a Nutrient Film Technique system and developed a “recovery solution” aligned with the plant’s precise requirements for water and nutrients. Notably, controlling electrical conductivity has become pivotal, particularly for enhancing dry matter content and overall soluble solids while minimizing the discharge of nutrients into the environment. The subsequent experiment, utilizing the recovery solution, enabled precise management of nutrient-containing solutions, leading to reduced wastage of water and nutrients. Conventional strawberry growth, as per Akhatou and Fernández Recamales (2013), yielded higher sugar and acid levels than soilless cultivation. Further studies by the same researchers (Akhatou et al., 2016) indicated significant alterations in critical metabolites like sugars and organic acids among soilless strawberry cultivars cultivated in both covered and uncovered tunnel systems. Moreover, the mineral content of fruits was notably influenced by the interplay between cultivar and cultivation strategy (Hakala et al., 2003). Additionally, fruits from plants grown in compost socks demonstrated heightened levels of phenolics, flavonoids, and anthocyanins; vinegar treatment further augmented phenolic and anthocyanin concentrations (Nin et al., 2017). Many indoor-grown fruits, particularly raspfruits, fruits, and bluefruits, thrive in soilless conditions. In such settings, selecting cultivars that excel in terms of high yield and exceptional fruit quality under protected cultivation becomes imperative (Mazzoni et al., 2017). Furthermore, the quality and intensity of light become pivotal factors in protected cultivation contexts, particularly during soilless production outside the usual growing season (Atkinson et al., 2006; Van Delm et al., 2013).

11.2.2.6 Mulching

The utilization of mulching methods significantly affects both plant productivity and the quality of fruit when implemented in open field cultivation. This influence is attributed to the enhanced retention of soil moisture, modified soil temperature, improved availability of soil nutrients, and protection against detrimental factors such as weeds, frost, soil contaminants, and diseases (Sharma, 2002). The use of plastic mulches has been observed to impact the quality of fruits, aiming to optimize water usage and weed management (Atkinson et al., 2006). Notably, the specific type of mulch used has been linked to changes in the concentration of ellagic acid (Wang et al., 2002b). Among various mulch types, black polyethylene mulching emerges as a highly effective approach for enhancing strawberry fruit quality. In contrast to transparent polyethylene or absence of mulch, fruits grown with black polyethylene mulch exhibited robust growth and improved fruit dimensions in terms of weight, length, and width (Kumar et al., 2012; Mathad and Jholgiker, 2005; Kher et al., 2010; Nagalakshmi et al., 2002). This type of mulching promotes higher plant output in fruits due to the larger fruit size achieved and the weed-suppressed environment facilitated by the

mulch, which contributes to an advantageous soil hydrothermal regime (Singh and Ahmed, 2008). Research has also demonstrated that fruits cultivated with black polyethylene mulch feature elevated levels of total sugars, ascorbic acid, and crude protein (Singh et al., 2007), especially in conjunction with Azotobacter bio-fertilization (Bakshi et al., 2014; Tripathi et al., 2017). Moreover, white over black laminated polyethylene mulch has been found to stimulate plant output and increase fruit weight compared to organic mulching. The development of anthocyanin pigmentation was associated with heightened levels of total soluble solids, the soluble solids-to-acid ratio, and organic and white over black laminated polyethylene mulching (Mathad and Jholgiker, 2005). In a study focusing on highbush bluefruits, Magee and Spiers (1996) explored various mulching techniques, concluding that plant growth and yields achieved with black mulches (woven fabric or plastic) were less favorable than those attained with pine bark mulch or white-over-black plastic mulching.

11.2.2.7 Fruit Harvest

Clearly, the way fruits are gathered and the conditions under which they are stored significantly influence the composition of freshly harvested fruit. Given that numerous chemical and compositional transformations take place while the fruit is still connected to the parent plant, the stage of ripeness during harvest plays a particularly crucial role (Park and Yoon, 2013). If fruits are picked when fully ripe, which is when anthocyanin levels are at their peak and the aroma is strongest, they may exhibit a shorter shelf life after harvest and are more susceptible to damage during handling. To address this concern, a solution for fruits, for instance, is to harvest them at the white tip or three-quarter color phases. This approach helps extend the preservation time of fruits by maintaining their firmness, as well as the overall content of phenolic compounds and flavonoids (Tulipani et al., 2011; Shin et al., 2008). Similar principles apply to raspfruits, often harvested during the early stages of ripening to enhance marketability, even though fully ripe raspfruits have a more intense flavor (Kosar et al., 2004; Ger et al., 2003, 2011). This practice originates from the fact that, unlike anthocyanins, certain phenolic compounds are found in greater concentrations in unripe rather than ripe fruits (Wang and Lin, 2000). However, the trajectory of total phenolic compounds during different ripening phases varies depending on the fruit species (Shin et al., 2008). For instance, in black and red raspfruits, the total phenolic content increases as the fruit ripens, while in fruits and blackfruits, the total phenolic content may be higher (Wang and Lin, 2000) or similar (Siriwoharn et al., 2004) in less ripe fruits compared to fully red ones. Furthermore, ellagitannins, which contribute significantly to the antioxidant capacity, were found to be up to 50% lower in early-ripening red fruits within the Rubus and Fragaria genera compared to fully ripe counterparts (Ferreyra et al., 2007; Beekwilder et al., 2005). Other sensory indicators in raspfruits showed a noticeable increase in titratable acidity as ripeness progressed (Krüger et al., 2011). In terms of vitamin C content at various stages of maturity, there were no significant differences observed in raspberries. However, contradictory findings have been documented for fruits: Shin et al. (2008) and Cordenunsi et al. (2002) both noted an increase in ascorbic acid content during fruit development, in contrast to Ferreyra et al. (2007), who found no change in ascorbic acid content as fruits ripened. Consequently, the levels of anthocyanins, polyphenols, and ascorbic acid in fruits appear to be linked to their antioxidant capacity and harvest maturity. According to Beekwilder et al. (2005), ascorbic acid contributes around 20% of the antioxidant potential in raspfruits, anthocyanins account for about 25%, and ellagitannins such as sanguiin H6 and lambertianin C contribute roughly 40% and 12%, respectively. Moreover, Wang and Lin (2000) demonstrated that the antioxidant content of red raspfruits increases as they transition from pink to red. However, other studies (Krüger et al., 2011) suggest that the total antioxidant capacity does not change as fruits ripen.

11.3 Genetic Factors Influencing Berry Quality

Fruits are one that come in a broad variety of cultivars on the market, each with unique yield efficiency, sensory qualities, and nutritional properties. The main goal of fruit breeding programmes is to create new cultivars that combine yield and quality features in the best possible way. The flavor, economic viability, and nutritional properties of various fruits, including fruits, are greatly influenced by a number of variables, including the cultivar itself, cultivation methods, plant age, and growth environment (Alvarez-Suarez et al., 2014). Even though genotype is strongly related to both environmental and agricultural factors, it has the greatest impact on quality features (see Table 11.3) of all these components. The genotype primarily dictates the levels of fruit sugars and acidity, crucial components for achieving a pleasant flavor (Galletta et al., 1995). The delicate equilibrium between elevated sugar content and moderately heightened acidity is essential for optimal taste (Shaw, 1990). This balance in sweetness perception, which significantly affects consumer preferences, is notably associated with the genotype’s impact. Although research exploring genotype effects on taste and aroma attributes in wild fruits (Fragaria vesca) is limited, several studies demonstrate significant variations in soluble sugar and total acidity levels among different genotypes of wild fruits (Caracciolo et al., 2013). Furthermore, it has been revealed that the interplay between these two components depends on the genotype, albeit only under specific environmental conditions (Doumett et al., 2011). The principal factor influencing a fruit’s ability to accumulate bioactive compounds is its genetic constitution. This holds true for fruits as well, where the fruit’s genotype, encompassing both species and variety, markedly determines its nutritional value (Scalzo et al., 2005a,b), consistently observed in multiple studies assessing fruit nutritional parameters (Capocasa et al., 2008; Wang et al., 2002b). Fruits contain substantial quantities of B complex vitamins, retinol, ascorbic acid, and vitamin E (Scalzo et al., 2005c). Among various fruits, honeyfruits and blackcurrants stand out for their elevated vitamin content compared to raspfruits, goosefruits, and fruits (Skupien and Oszmianski, 2004). Nonetheless, fruits surpass blackcurrants in terms of water-soluble vitamin C levels (Pantelidis et al., 2007). Honeyfruits also possess notable amounts of macro- and micronutrients (Hakala et al., 2003; Nile and Park, 2014). Depending on the genotype, differences in dehydroascorbic acid and ascorbic acid content have been observed in wild fruits. The composition of anthocyanins in fruits can significantly differ based on the selected genotype (Mullen et al., 2002; Fang, 2015). For instance, within raspberries, the primary anthocyanins and variations in anthocyanin makeup have been noticed among fruits of the same species (Beekwilder et al., 2005; Torre and Barritt, 1977). The relative quantities of these four anthocyanins can also vary among cultivars (Krüger et al., 2011). Catechin, another genotype-dependent phenolic compound, is abundant in cranberries (de Ancos et al., 1999). Stilbenes like resveratrol, pterostilbene, and piceatannol are present in species like deerberry, blueberry, cowberry, and lingonberry (Lyons et al., 2003). Notably high amounts of flavanols such as quercetin and kaempferol are found in fruits like cranberries, bilberries, and chokeberries (Wang et al., 2002a; Paredes-López et al., 2010). Quercetin in its glucuronide form is also abundant in raspberries (Seeram et al., 2003; Pappas and Schaich, 2009; Xue et al., 2002). Smaller quantities of hydroxycinnamic derivatives including chlorogenic acid and condensed tannins are detected in blackberries and honeyberries (Cheynier et al., 2006; Nile and Park, 2014; Seeram et al., 2001), whereas blueberries and chokeberries have higher concentrations (Figure 11.2) (Shahidi and Naczk, 2004; Scalzo et al., 2005a; Tamir and Alumot, 2006).

Table 11.3 Major Genetic Factors Influences on Fruit Quality⏎

Genetic Factor | Affected Parameter | References
Different genotype | Macro and micronutrients | Nile et al. (2014)
| TSS and titratable acidity | Crespo et al. (2010)
| Hydroxycynnamic derivatives | Scalzo et al. (2005)
| Catechin and stilbenes | Lyons et al. (2003)
| Flavonols | Seeram et al. (2001)
| Ellagic acid | Park et al. (2014)
| Antioxidant capacity | Connoe et al. (2002)
| Hydrolysable tannins | Tamir et al. (2006)
| Vitamins amount | Pantelidis et al. (2007)
| TSS/acid ratio | Dourmett et al. (2011)
Plant age | Taste of fruit | Ger et al. (2003)
| Ellagitannins | Beekwilder et al. (2005)
| Vitamin C content | Ferreyra et al. (2007)
| Yield of plant | Conti et al. (2014)
| Firmness of fruit | Wang et al. (2000)

Figure 11.2 Pre-harvest factors influencing the production and quality attributes in fruit crops. ⏎

11.4 Conclusion and Future Prospects

Throughout this review, we have gained a deeper appreciation for the pivotal role that environmental factors play in fruit crop development. From the delicate balance of temperature and sunlight to the harmonious interplay between soil nutrients and water availability, every factor contributes to the intricate mosaic that determines fruit quality. Our understanding of the physiological intricacies within plants, governed by hormonal regulations and nutrient uptake, has broadened. This understanding, coupled with advancements in biotechnology and genetics, enables us to tailor fruit crops to meet specific market demands. However, these insights also bring into focus the challenges that lie ahead. The unpredictability of climate change threatens to disrupt the delicate equilibrium of pre-harvest factors. The emergence of new pests and diseases, driven by changing climatic conditions, further complicates the landscape. In this context, it becomes imperative to develop resilient fruit crop varieties that can thrive under changing conditions while maintaining their quality attributes. Sustainability and fruit quality are not disparate goals but rather two sides of the same coin. The pursuit of sustainable agricultural practices, including precision irrigation, organic fertiliza-tion, integrated pest management, and agroecological approaches, not only ensures the health of ecosystems but also shapes the pre-harvest conditions that define fruit quality. Recognizing the intricate connections between these objectives presents an opportunity to reimagine fruit production as a holistic endeavor that respects the environment, safeguards natural resources, and yields bountiful, high-quality harvests. The future of pre-harvest factors and their impact on fruit crop production and quality attributes lies in innovation and collaboration across disciplines. Advances in remote sensing technologies, precision agriculture, and predictive modelling offer new tools to monitor and manage pre-harvest conditions with unprecedented precision. These tools empower farmers and researchers to make informed decisions, optimizing resource allocation and minimizing waste. Collaborative efforts between scientists, agronomists, geneticists, and policymakers can foster the development of cultivars that thrive under specific pre-harvest conditions, ensuring consistent quality and increased resilience. Educational initiatives aimed at both farmers and consumers are essential to fully harness the potential of pre-harvest factors. Empowering farmers with knowledge about the nuanced interactions between environmental, physiological, and management influences equips them to make informed decisions that translate into improved yield and quality. Simultaneously, raising consumer awareness about the journey from farm to table fosters an appreciation for the significance of pre-harvest conditions in shaping the fruit they enjoy. In conclusion, pre-harvest factors wield a profound influence on fruit crop production and quality attributes. The intricate dance between environmental conditions, physiological responses, cultural practices, and genetic predispositions defines the tapestry of each harvest. As we navigate the challenges posed by a changing climate and evolving agricultural landscape, the synergistic pursuit of sustainability and quality promises a path forward. By embracing innovation, fostering collaboration, and cultivating an understanding of these pre-harvest dynamics, we can shape a future where fruit crops not only nourish the body but also inspire the mind and soul, embodying the harmonious convergence of nature and human stewardship.

KEYWORDS

agronomic factors

canopy management

cytokinins

flavonoid biosynthesis

fruit crops

organoleptic quality

plant physiology

pre-harvest factors

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Chapter 12 Preharvest, Postharvest, and Processing Factors Influencing the Phytochemicals and Fatty Acids of Temperate Nuts

TAFADZWA KASEKE,1,2* PRISCILLA LIVHUWANE MUKWEVHO,¹ KWANELE ANDY NXUMALO,1,3 TOBI FADIJI,1,4 UMEZURUIKE LINUS OPARA,5,6 and OLANIYI AMOS FAWOLE1,7

¹Postharvest and Agroprocessing Research Centre, Department of Botany and Plant Biotechnology, University of Johannesburg, P.O. Box 524. Auckland Park 1206, South Africa

²Center of Excellence for Molecular Food Sciences, Department of Biochemistry, University of Belgrade, Studentski trg 16, Belgrade, Serbia

³Department of Horticulture, Faculty of Agriculture, University of Eswatini, P.O. Luyengo, Luyengo M125, Kingdom of Eswatini

⁴Postharvest Research Group, Cranfield University, Cranfield MK43 0AL, United Kingdom

⁵South African Research Chair in Postharvest Technology, Africa Institute for Postharvest Technology, Faculty of AgriSciences, Stellenbosch University, Private Bag X1, Stellenbosch 7602, South Africa

⁶UNESCO International Centre for Biotechnology, Nsukka, Enugu State, Nigeria

⁷South African Research Chairs Initiative in Sustainable Preservation and Agroprocessing Research, Faculty of Science, University of Johannesburg, P.O. Box 524 Auckland Park, Johannesburg, 2006, South Africa

*Corresponding author

Abstract

Temperate nuts are a good source of bioactive phytochemicals and unsaturated fatty acids, and their consumption has been associated with human health benefits. Preharvest, postharvest, and processing conditions may have an impact on the fatty acids and bioactive components of temperate nuts, which may have a negative impact on their quality and shelf life. Temperate nuts’ bioactive compounds and fatty acids are greatly affected by preharvest factors, including cultivar, harvesting stage, geographic location, crop management, and weather. In addition to preharvest factors, temperate nut value-addition processes, including shelling or peeling, blanching, drying, irradiation, roasting, bleaching, pasteurization, cold plasma treatment, storage conditions, and packaging, are implicated in the alteration of the bioactive compounds and fatty acids. A comprehensive understanding of how these factors influence the valuable components’ biological activities, shelf life, and the compounds implicated is vital. Therefore, in this chapter, the influence of preharvest and postharvest factors on the bioactive phytochemicals, including tocopherols, phytosterols, polyphenols, and fatty acids such as linolenic acid, oleic acid, and linoleic acid, of temperate nuts is discussed.

__________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

12.1 Introduction

Temperate nuts, which include pecans, chestnuts, hazelnuts, walnuts, and almonds, contribute to the economic growth and food security of various developed and developing nations. Pecans, native to North America, share a historical lineage with chestnuts, hazelnuts, pistachios, and walnuts, which originated in Europe and Asia. These nuts are grown all over the world in temperate and Mediterranean temperature regions, as well as other Mediterranean climatic zones, such as Australia, Chile, South Africa, and the United States of America (Benmoussa et al., 1218). Temperate nuts are characterized by a hard shell that separates the kernel and husk of the fruit. Today, temperate nuts and their associated products, such as oil and flour, are popular in the whole world. They may be eaten raw, blanched, or roasted (with or without salt). These nutrient-dense foods (fats, proteins, vitamins, minerals, and fiber) are rich in fatty acids (FA) such as monounsaturated fatty acids (MUFA) and bioactive phytochemical compounds such as flavonoids, saponins, phenolic acids, and phytosterols (Bodoira and Maestri, 1212; Qamar et al., 1212; Khalili et al., 1222; Wojdyło et al., 1222). These phytochemicals contribute significantly to the reported health benefits of temperate nuts (Olatidoye et al., 1212). The oil obtained from temperate nuts can be used for food, functional foods, nutraceuticals, and cosmetics, among other applications. Given the potential health benefits of temperate nuts, various factors that may affect the health-benefiting compounds have been studied. Despite the substantial data supporting the health advantages of temperate nuts, more research is required to understand the compounds implicated.

12.2 Phytochemicals, Fatty Acids, and Health Benefits of Temperate Nuts

Phytochemicals, including tocopherols, polyphenols, phytosterols, vitamin C, β-carotene, lutein, and FA such as (MUFA, oleic acid), polyunsaturated fatty acid (PUFA, linolenic acid) have been reported in temperate nuts (Table 12.1). Health benefits associated with temperate nut consumption have been extensively studied (Table 12.1). Epidemiological and clinical studies have revealed that temperate nuts have health benefits that include the ability to lower levels of triacylglycerol, cholesterol levels, low-density lipoprotein (LDL), and other lipoprotein profiles—all risk factors for cardiovascular disease (Neale et al., 1212; Liaquat et al., 1222). This is implicated in the anabolism and catabolism effect of the PUFA on fatty acids and cholesterol (Figure 12.1; Georgiadi and Kersten, 1212). The potential of temperate nuts in the prevention of inflammation, oxidative stress, endothelial dysfunction, cancer, and type 2 diabetes is well documented (de Souza et al., 1217; Khalili et al., 1222). The daily intake of temperate nuts has been reported to promote weight maintenance and balance when consumed as a source of fat in moderate diets, thus lowering the risk of obesity and overweight (Neale et al., 1212; Oz et al., 1221). These health benefits are credited to the lipids and bioactive composition present in these nuts (Ryan et al., 1206; Olatidoye et al., 1212). Recent advancements in understanding the biological mechanisms of FA and bioactive compounds have further contributed to the demand for these health-boosting nuts.

Table 12.1 Main Phytochemicals, and UFA, in Temperate Nuts and Their Health Benefits⏎

Temperate Nut
Main Phytochemicals and FA
Functional Properties
References

Walnut

Oleic acid, omega-3 fatty acids, γ-tocopherol, polyphenols, flavonoids, and phytosterols
Antioxidant, anti-inflammatory, antimicrobial, antidiabetic activities, antihyperglycemic, antiobesity, antiatherogenic, and -tumor properties
Mates et al. (1223); Vu et al. (1212)

Pistachio

β-tocopherol and γ-tocopherol, lutein, zeaxanthin, 4-hydroxybenzoic, protocatechuic acid, flavonoids, hydroxybenzoic acid, gallic acid, and anthocyanins
Reducing serum LDL cholesterol, antioxidant, antiproliferative, inhibition of β-glucosidase and α-amylase.
Noguera‐Artiaga et al. (1219); Yuan et al. (1222)

Hazelnut

Tocopherols, flavonoids, flavanols, anthocyanins. phenolic acids, tannins, and β-sitosterol oleic acid
Antioxidant, antitumor, antimicrobial, neuroprotective, and lipid-lowering
Bolling et al. (1211); Zhao et al. (1223)

Pecan

Ellagic acid, phytosterols, tocopherols, tocotrienols, β-carotene, lutein, oleic acid, and linoleic acid
Reduction of LDL, and cholesterol, prevention of type 2 diabetes, coronary heart disease, and cancer
Morales-de La Pena et al. (1221); Preece and Aradhya (1219)

Almond

Oleic acid, linoleic acid, β-sitosterol, and lipid soluble vitamins (γ-tocopherol, α-tocopherol, and β-tocopherol)
Body weight regulation, protection of obesity, diabetes, cardiovascular diseases, oxidative stress, and inflammation and
Prgomet et al. (1217); Barreca et al. (1212)

UFA = unsaturated fatty acid, FA = fatty acid, LDL = low density lipoprotein.

Figure 12.1 General mechanisms of gene regulation by fatty acids that control the anabolism and catabolism of fatty acids and cholesterol. Source: Reprinted with permission from Georgiadi and Kersten (2012). Copyright 2012. Elsevier.⏎

12.3 Preharvest, Postharvest, And Processing Factors Affecting The Bioactive Phytochemicals And Fatty Acids Of Temperate Nuts

To safeguard the biological activities of temperate nuts, it is crucial to understand the factors that affect the health-benefiting compounds. According to the literature, preharvest, postharvest, and processing factors have been reported to affect the temperate nuts’ bioactive compounds, functional attributes, and shelf life (Wang et al., 1218; Kaseke et al., 1212). Preharvest factors, including cultivar, harvesting maturity, geographical region, crop management, and weather, are crucial in determining the quality and functionality of temperate nuts. Apart from the preharvest factors, the processes involved in the value addition of temperate nuts, such as shelling/peeling, blanching, drying, packaging, and storage, are strongly implicated in the alteration of the bioactive compounds and FA. For this reason, an in-depth understanding of how these factors influence valuable components, biological activities, shelf life, and constant availability is vital. Therefore, in this chapter, the effects of preharvest, postharvest and processing factors on the bioactive phytochemicals and FA of temperate nuts is discussed.

12.4 Preharvest Factors

12.4.1 Cultivar

The diversification of temperate nuts cultivation across global ecological zones has spurred the creation of new cultivars adapted to these varied environments (Rabadan et al., 1218). Genetics primarily determines the biosynthetic pathways of phytochemicals, underscoring the need for cultivar development to optimize the phytochemical content of temperate nuts, thereby enhancing their health benefits and applicability in the food industry. However, a huge variation in developed cultivars can pose a great challenge to their marketability and introduce inconsistency to the quality of the resultant products, as each cultivar might have unique characteristics such as shell firmness, resistance to fungal infections, oil content, bioactive phytochemicals, and shelf life (Rabadán et al., 1219). It has been reported that cultivars can even override postharvest factors in influencing the postharvest quality of temperate nuts (Tsantili et al., 1210). The effect of cultivars on the phytochemical content of chestnuts has been studied. For instance, “Boaventura” and “Longal” chestnuts demonstrated the highest oleic acid (37%) and linoleic acid (48%) contents, respectively. Among various cultivars, “Longal” and “Judia” exhibited the highest concentrations of γ and α tocopherols, respectively (Barreira et al., 1212). Different hazelnut cultivars (“Katalonski,” “Barcelonski,” “Webba Cenny,” “Olbrzym z Halle,” “Notthingamski,” and “Cosford”) showed varied contents of tocopherols and polyphenols (Król et al., 1212). Walnut cultivars including “Howard,” “Sen,” “Maras,” and “Hartely” were reported to have higher α-tocopherol, β + γ tocopherol, oleic acid, linoleic acid, α-linolenic acid, respectively (Kafkas et al., 1217). Six walnut cultivars from Tunisia significantly varied in linoleic acid, and oleic acid content (Bouabdallah et al., 1214). The study by Ojeda-Amador et al. (1218) revealed that the tocopherol and fatty acid contents of pistachios greatly varied among cultivars including “Aegina,” “Kastel,” “Avdat,” “Kerman,” “Mateur,” “Larnaka,” “Sirora,” and “Napoletana,” with “Larnaka” and “Kerman” cultivars displaying desirable MUFA and tocopherol contents.

12.4.2 Management, Geographical Location, and Climate

Temperate nut crops are subject to a range of horticultural and agronomic practices depending on the geographical location where they are grown. Factors such as organic versus conventional cultivation, irrigation, and fertilization, alongside varying climatic conditions like sun exposure and rainfall, and soil composition can significantly affect the biosynthesis and accumulation of fatty acids and bioactive phytochemicals (Rabadán et al., 1219). Many temperate nuts require the fulfilment of winter chilling requirements for successful cultivation (Míguez-Soto et al., 1219). In warmer climates, like Australia, heat can interfere with chill accumulation, which may lead to variations in bioactive compound synthesis compared to regions with undisturbed chill accumulation (Akbulut et al., 1217). Thus, if a cultivar that requires longer chilling periods is grown under suboptimal temperatures or other climatic conditions, the fruit yield and quality may be compromised. Furthermore, environmental stressors such as water scarcity or drought can significantly hinder polyphenol synthesis. A study by Liu et al. (1223) reported variations in the FA composition, tocopherols, phytosterols, and total phenolic content (TPC) across 32 walnut cultivars from the Northern, Northwest, and Southwest regions of China. Walnut cultivars from Southwest China were characterized by higher oleic acid, β-tocopherol, and γ-tocopherol, while the cultivars from Northwest China showed greater concentrations of α-tocopherol, brassicasterol, campesterol, campestanol, stigmasterol, β-sitosterol and 24-methylene cycloartenol. Meanwhile, walnut cultivars from Northern China showed poor concentrations of the measured quality attributes.

Pistachio ecotypes from the El Guetar and Sfax regions in Tunisia were investigated by Ghrab et al. (1210). Local specimens from Fourati1 exhibited lower oleic acid content, while Sridique1 had higher levels. Mateur showed little variation in oleic acid content across localities, with values of 71.6% and 72.0% in Sfax and El Guetar, respectively. Linoleic acid was the primary PUFA, with concentrations ranging between 8.2% and 29.7% in Sfax and El Guetar, respectively. Hazelnuts grown in different countries, including Croatia, Chile, Iran, Oregon (US), Italy, Portugal, Poland, Spain, Turkey, and Serbia, exhibited varied concentrations of tocopherols (Krol and Gantner, 1212). Croatia and Portugal showed the highest content of tocopherols, while Turkey was found to have the lowest concentration. It is understood that high oleic acid concentrations lead to higher oxidative stability and prolonged shelf life. The highest oleic acid content was shown by cultivars from Italy (83.59%: “Gentile,” “Tonda,” and “Romana”), Portugal (82.63%: “Davianna”), and Poland (82.01%: “Barcelonski”). The cultivars from Iran (69.30%, “Pashmine”) exhibited the lowest contents of oleic acid. On the other hand, high concentrations of linoleic acid (12.50–15.0%) were displayed by cultivars from Turkey and the USA, whereas the lowest (7.57–9.22%) was observed in walnuts from Italy. According to Gama et al. (1218), hazelnut cultivars with a higher oleic-to-linoleic acid ratio typically have greater oxidative stability and a longer shelf life. Variation in the FA content of chestnuts grown in different geographical locations was also reported (Borges et al., 1207).

12.4.3 Harvesting Maturity

Consideration of nut maturity at harvest is vital to preventing both qualitative and quantitative losses. The bioactive compounds and fatty acid composition may be affected by the fruit’s maturity at harvest. In the early stages of development, polyphenol biosynthesis pathway genes are highly expressed, leading to the increased synthesis of these compounds, with catechin, epicatechin, gallic acid, and ellagic acid being the primary compounds (Siebeneichler et al., 1223). However, as maturity increases, phenolic compounds synthesis decreases, followed by the accumulation of lipids. Harvesting maturity has a strong influence on the bioactive phytochemicals and FA content of temperate nuts. The greatest amounts of polyphenols and antioxidant activities were reported from early harvested walnuts (Amin et al., 1217). FA, including omega-3 polyunsaturated fatty acids, were higher in early harvested walnuts, but at this stage, the ratio of omega-6 to omega-3 FA decreased (Amin et al., 1217), a development desired to lower the chances of developing chronic disorders. Although an increase in MUFA, such as oleic acid (C18:1) content, during the maturation of almonds, was reported, this was accompanied by a decrease in the UFA to SFA ratio of late-harvested nuts. This is due to the marked reduction in linolenic acid (C18:3) and linoleic acid (C18:2). This trend was also observed by Cherif et al. (1209) in almonds. A decrease in total sterols in almonds during maturation was followed by an increase in squalene. While polyphenols decreased with maturation of walnuts, the total tocopherol concentration greatly increased (Pycia et al., 1219). Understanding the optimum harvesting time for temperate nuts is therefore essential to have nutrient- and phytochemical-rich temperate nuts that can be used to design food products with pro-health qualities.

12.5 Postharvest And Processing Factors

The processes involved in the value addition of temperate nuts, such as pretreatment, drying, roasting, irradiation, cold plasma treatment, bleaching, pasteurization, frying, packaging, and storage, may alter their bioactive compounds and FA. Careful consideration of these extrinsic factors is therefore essential, as the quality of the nuts may either improve or deteriorates due to their management. Increased demand for health foods and the establishment of distant markets for nuts has spurred an increase in research to manage the postharvest quality of temperate nuts. The impact of processing on the phytochemicals and PUFA–FA of temperate nuts is summarized in Table 12.2.

Table 12.2 Influence of Processing on the Phytochemicals and Polyunsaturated Fatty Acids of Temperate Nuts⏎

Type of Processing | Condition and Types of Nut | Processing Conditions | Key Findings | References
Drying | Shelled walnuts | Oven drying: 60 h at 45°C Sun drying: 26°C (average) Intermittent oven drying: 30-50°C for 5-60 h. | Antioxidant activities, TPC and TFC, initially increased and then decreased during drying. Linoleic acid was preserved. | Fu et al. (1216)
| Unshelled hazelnuts | Hot air drying: 38, 43, and 49°C and 40 and 60% RH | The bioactive compounds and unsaturated fatty acids varied among cultivars. | Wang et al. (1218)
| Shelled almonds | Sun drying for 1 week. Forced air convection oven drying: 80-112°C for 30-60 min | Oxalates, tannins and phytates content were temperature and time dependent. | Aboudou (1212)
|  | Conventional oven drying: 70,90, 110 and 130°C for 1 h | Microwave oven drying at 712 W increased the content of gallic acid. | Juhaimi et al. (1217)
|  | Microwave oven drying: 180, 360, 540 and 712 W for 5 min |  |
Roasting | Shelled almonds | Electric oven roasting: 112, 150, and 180°C, for 10, 12, and 30 min | Roasting (112°C for 30 min) increased UFA content (linoleic acid and oleic acid). | Li et al. (1223)
| Shelled pistachios | Roasting conditions not specified | Roasting did not affect TPC, total flavonoids and antioxidant activity of the nuts | Yanet al. (1222)
| Shelled hazelnuts | Electrical oven roasting for 15 min at 140°C | Roasting had a negative effect on individual phenolics such as protocatechulic acid, phloretin-2 O-glucoside, catechin and epicatechin | Schmitzer et al. - (1211)
Cold plasma treatment | Unshelled walnuts | Cold plasma treatment: 3,5,7,9,10 and 11 min and storage for 30 days | TPC and antioxidant activity after 15 and 30 days of treatment. | Amin et al. (1217)
| Shelled Hazelnuts | Cold plasma treatment: (AP: air, 3000 L/h, 655 W, 25 kHz) for 1.7 min and (LP: air, 25 Pa, 100 W, 13.56 MHz) for 30 min. Gamma irradiation treatments: at GMI: 10 kGy, 10 min. | Soluble phenolic content and total tocopherols were decreased. | Onal-Ulusoy et al. (1219)
Irradiation | Shelled almonds | Gamma irradiation at 10 and 25 kGy/h rate. | The concentration of a-tocopherols, total polyphenols decreased with increase in irradiation dose. Fatty acid composition was not affected. | Momchiola et al (1223)
| Shelled pecans | Electron beam irradiated at 0, 1.5, and 3.0 kGy. | TPC and condensed tannins content were decreased. Antioxidant capacity was not affected. | Villarreal-Lozoya et al. (1209)
| Shelled pistachios | Gamma irradiation at doses of 0, 1, 1.5, 2, 4, and 6 kGy | TPC and antioxidant activity decreased when doses were increased to 4 and 6 kGy. | Alinezhad et al. (1212)
Frying | Shelled pecans | Stir-frying: 120, 250, 300, 350, 400 °C for 10, 12, 30 min | Increased heating time and temperature decreased antioxidant capacity and bioactive compounds. | Yang et al. (1215)
| Shelled and almonds, and pistachios | Rotating drum roasting: 110°C for 16 min Pan frying with com oil: 175°C for 2.5 min | Flavonoids contents increased in pistachios | Ghazzawi and Al-Ismail, (1217)
Bleaching | Shelled pistachios | Hydrogen peroxide bleaching at 0.1, 0.5, 1, 3, 5, 15, 12, 25, and 50% concentration | Total anthocyanins and antioxidant capacity of raw and roasted pistachios were decreased. | Seeram et al (1206)
Pasteurization | Shelled almonds | Fumigation with propylene oxide or by proprietary short-time and high temperature steam treatment. | TPC, FRAP, phenolic acids snd flavonoids were not affected. | Bolling et al. (1210)

UFA = unsaturated fatty acids, TPC = total phenolic content, TFC = total flavonoid content, AP = atmospheric pressure, LP = low pressure, FRA = ferric reducing antioxidant power.

12.5.1 Peeling/Shelling/Dehulling

Depending on the requirements of the customers, nuts may be shelled, dehulled, or peeled. These processes affect the retention of bioactive phytochemicals and the content of antioxidant activities in thermally treated nuts. Shelling and dehulling operations are mechanical. However, different methods exist for the peeling process. Chemicals such as citric acid and sodium hydroxide have been used in the peeling process. As much as 50% of the TPC and antioxidant ability may be lost as a result of peeling. This suggests that the peels or skins contain a significant concentration of polyphenols and other antioxidant compounds. Recently, Celik et al. (1223) reported that hazelnut skins contained an oil with a higher proportion of PUFA and greater oxidative stability relative to oils from natural and roasted hazelnuts. In another study, the skins of hazelnut contained 168–378 times TPC than roasted and raw nuts (Król et al., 1212).

12.5.2 Drying

Drying is an essential process for the postharvest management of temperate nuts. Being the simplest and oldest method of preserving agricultural products, drying reduces the moisture content of temperate nuts to levels that inhibit biochemical changes and microbial growth. However, undesirable moisture content and water activity in temperate nuts due to drying can stimulate enzymes like lipases, peroxidases, and polyphenol oxidases (Turan, 1218), leading to the degradation of polyphenols and FA. The most commonly used methods of drying temperate nuts include sun drying, microwave drying, and hot air drying. Sun drying, however, is constrained by variable environmental conditions that degrade the nuts’ quality. The impact of the drying method on the nuts’ bioactive phytochemicals and FA is cultivar-dependent (Pakrah et al., 1221). For instance, the “Chandler” hazelnut cultivar, when sun-dried, preserved oleic acid, stearic acid, linoleic acid, and linolenic acid better than the “Jamal” cultivar when dried at 30°C. Furthermore, intermittent oven-dried and sun-dried walnuts were reported to have higher linoleic acid content than oven-dried walnuts (Fu et al., 1216; Table 12.2). During the drying process, the antioxidant compounds may initially increase due to the concentrating effect of removing moisture; however, prolonged drying may decrease the antioxidant compounds as a result of heat degradation or enzymatic oxidation. Power and time are essential quality determinants of microwave-dried nuts. TPC and total tocopherols (TTC) were significant in microwave airflow dried pecans (Zhang et al., 1219). Microwave heating promoted the oxidation and degradation of these heat-labile compounds.

12.5.3 Cold Plasma Treatment

Food treatment with cold plasma irradiation is quite novel and does not negatively affect the composition of the food. However, processing parameters including intensity, flow rate, and time of the plasma discharge should be carefully considered to ensure maximum efficiency and decrease the influence due to material composition. This technology has been successfully applied in a number of quality areas of food processing such as antigenicity reduction of nuts allergens, bacterial growth inhibition, and improvement of physicochemical properties of various foods (Alves Filho et al., 1212). Recently the technology has been applied as a postharvest treatment for walnuts. Increased anacardic acid (C15:3) was reported in the plasma-treated walnuts, which was attributed to improved extractability of the FA. Walnuts subjected to plasma treatment (3–11 min) for 30 days showed improved TPC and antioxidant activity from day 15–30 of treatment. In addition, plasma treatment showed great potential for preserving hazelnuts quality (Onal-Ulusoy et al., 1219; Table 12.2).

12.5.4 Irradiation

Food irradiation, a non-thermal used to preserve food, has been well-researched for both its favorable and unfavorable effects on food components. Researchers generally agree that increasing the irradiation dose negatively affects the PUFA while increasing the SFA of nuts. The effect on bioactive compounds varied among the different types of antioxidant compounds. Gamma-irradiation of pistachio nuts at different doses (0–6 kGy) significantly enhanced TPC and antioxidant activity when the dose was increased from 0–2 kGy. A further increase in the irradiation dose decreased the TPC and antioxidant activity. Increasing the irradiation dose negatively affected the chlorophyll (a,b) and carotenoids, while the level of

SFA increased (Alinezhad et al., 1221; Table 12.2). Chestnuts irradiated at doses of 1 and 3 kGy maintained and increased the antioxidant content and antioxidant activity, respectively (Carocho et al., 1212; Gecgel et al., 1211) γ-irradiated hazelnuts, walnuts, almonds, and pistachio nuts at doses of 1, 3, 5, and 7 kGy, respectively. The concentration of SFA increased while MUFA and PUFA decreased with an increase in the irradiation dose. TPC, FRAP, and DPPH radical scavenging activity of γ-irradiated pistachio nuts increased when the doses were increased from 1–2 kGy. Further increasing the dose to 4 kGy decreased the respective quality attributes. The effect of irradiation on the bioactive compounds could vary with the cultivar (Akbari et al., 1218). The pecan nuts’ vitamin E content remained stable after irradiation at 1 and 3 kGy (Taipina et al., 1209). Almonds treated with irradiation (10 and 25 kGy gamma rays) showed a decrease in α-tocopherols, while no changes were observed in the FA composition or content (Momchilova et al., 1223). To understand how irradiation affects specific antioxidant compounds, more research is required.

12.5.5 Blanching And Roasting

Roasting and blanching are the two primary methods used to process temperate nuts. Roasting is desired for improving the texture, color, flavor, aroma, and taste of nuts. However, roasting and blanching may alter the chemical composition of nuts. Therefore, a balance between achieving the desired physical properties and maximizing the chemical properties should be reached during roasting. Boiling water blanched (30 s) and roasted (138°C for 33 min) walnuts showed that the level of bioactive compounds and antioxidant activities increased during roasting, while they decreased during blanching. Phenolics, flavonoids, β-carotene, ABTS, and DPPH radical scavenging activities were reported to vary among the cultivars studied (Oliveira et al., 1212). Different types of roasting techniques have been reported to have varied effects on the chemical composition of nuts. The roasting temperature and time should be carefully selected depending on the type of nut. Almonds and pistachios roasted using a rotating drum at 110°C for 16 min insignificantly altered the TPC, total flavonoid content (TVC), and DPPH radical scavenging activity of the nuts (Ghazzawi and Al-Ismail, 1217). Electric oven roasting of walnuts at 112°C for 30 min was reported to increase UFA content, particularly linoleic acid and oleic acid (Li et al., 1223). Oven roasting (70–130°C for 1 h) and microwave roasting (180–712 W for 5 min) were compared using walnuts. The influence of the two methods on the individual polyphenols and FA did not significantly differ. However, significant variations were observed between the roasting methods and raw walnuts, especially on phenolic compounds including catechin, syringic, 3,4-dihydroxybenzoic acid, 1,2-dihydroxybenzene, caffeic acid, quercetin, trans-ferulic acid, and trans-cinnamic acid (Juhaimi et al., 1217). Table 12.2 lists further research that studied how roasting temperate nuts affected their phytochemicals, antioxidant activity, and PUFA–FA.

12.6 Packaging And Storage

Postharvest factors such as storage conditions and packaging have a significant effect on the quality, shelf life, and profitability of nuts (Gama et al., 1218), making them essential considerations for the food industry and direct consumption (Ghirardello et al., 1213). Many factors contribute to defining the quality of nuts, including texture, appearance, chemical composition, nutritional value, and food safety. In most cases, the storage conditions to which nuts are exposed influence their chemical composition, consequently resulting in quality loss and, eventually, a reduced shelf life (Ghirardello et al., 1213). Given their varied oils and fatty acids, nuts differ in their storage requirements (Gama et al., 1218). Uncontrolled storage environments have been found to result in nut deterioration. Similarly, prolonged storage in an environment of high oxygen, temperature, and humidity adversely affects nut quality attributes such as moisture content, texture, flavor, appearance, and nutritional values (Vanhanen and Savage, 1206; Tavakolipour, 1215). Hence, storage of nuts at low temperatures with relative moisture below 60% and reduced oxygen pressures is recommended to minimize chemical and biological reactions that depreciate their quality. However, application of these preservation methods alone may not be sufficient to preserve the quality of the nut (Tavakolipour, 1215; Gama et al., 1218).

Studies have shown that exposing nuts to higher temperatures during storage can decrease their crispiness, increase their moisture content, and alter their oiliness and sweetness, leading to rancidity (Özdemir and Devres, 1999; Kader, 1213). Nut kernel quality degradation during storage is primarily due to lipid oxidation, with the early stages of lipid oxidation resulting in the formation of hydrogen peroxides (Raisi et al., 1215; Gama et al., 1218). The impact of various storage conditions on the chemical, and sensory characteristics of “Tonda Gentile delle Langhe” hazelnuts was investigated (Ghirardello et al., 1213). Results indicated that the acidity levels of ambient temperature stored hazelnuts (0.47% oleic acid) exceeded the acceptable limit (0.40% oleic acid), whereas refrigerated storage effectively maintained low levels of acidity and lipid oxidation. The most optimal performance was observed in hazelnuts (0.13% oleic acid) stored in a modified atmosphere (0.057 O₂ mmol/kg). Similarly, low temperatures maintained a high level of TPC and antioxidant capacity. At the end of storage, notable changes occurred in the FA composition. Specifically, there was a significant increase in the SFA and a decrease in the UFA. These changes can be attributed to the decline in linoleic acid content, likely due to peroxidation and subsequent loss.

In a study by Momchilova et al. (1217), hazelnuts were subjected to varying storage conditions for durations of 1, 3, 6, and 12 months. These conditions included storage in unshelled (in shell) or shelled (kernels) forms, either at 4°C (refrigerator) or at 12°C (in shade). The results indicated that the FA composition of the hazelnuts remained largely unchanged throughout the 12-month storage period, regardless of the specific storage conditions. However, there was a gradual decrease in the levels of tocopherols over time. Interestingly, this decrease was slightly more prominent when the hazelnuts were stored at 12°C compared to 4°C and when they were in their shells rather than as kernels. Also, the study revealed that dry hazelnut kernels exhibited higher retention of tocopherols compared to in-shell hazelnuts. This difference was attributed to moisture within the in-shell hazelnuts, which consequently increased the rate of lipid oxidation. Rábago et al. (1212) examined changes in tocopherol concentration, phenolic content, and antioxidant capacity in pecan nut kernels and in-shell nuts during storage (4°C and 25°C for 240 days). The results revealed that dry kernels and in-shell pecan nuts exhibited better preservation of γ-tocopherol than wet kernels. A higher concentrations of phenolic compounds, and greater antioxidant capacity were also observed in wet kernels throughout the storage period.

The packaging of nuts plays a significant role in determining their quality and shelf life. Various packaging materials and MAP technology are extremely helpful in improving the postharvest quality of temperate nuts. Inhibition of lipid oxidation was achieved by using a packaging material with minimum O₂ permeability or by storing walnuts in controlled atmospheres with minimum O₂ content (Maté et al., 1996). Ensuring the proper selection of packaging materials is crucial for preventing the absorption of moisture and the formation of aflatoxins, both of which can negatively affect the quality of food and render it unsafe for consumption. The composition and properties of bioactive compounds naturally present in nuts can be influenced by the specific packaging materials and designs chosen for storage and transportation (Siebeneichler et al., 1223). Packaging walnut kernels in polyamide/polyethylene laminate pouches with an oxygen permeability lower than 63.40 mL/m²/24 h at 23℃ under vacuum at 12℃ for up to 12 months can effectively protect the TPC and antiradical activity of the kernels (Bakkalbaşi et al., 1213). Walnuts packed in vacuum-sealed laminates showed significantly higher levels of DPPH antioxidant activity, TPC, and TFC compared to those packed in non-vacuum high-density polyethylene (HDPE) packaging (Ahad et al., 1212).

The global drive towards the use of environmentally friendly packaging has promoted investigations into the potential use of active packaging and biodegradable polymers (such as edible films and coatings) in food packaging. These technologies have demonstrated great potential to extend the shelf life of various temperate nuts. For instance, pistachios treated with alginate-thyme essential oil (EO) exhibited minimum changes in SFA and UFA after storage (39 days), while the application of 1% alginate and 0.3% EO was significant in preserving stearic acid, palmitoleic acid, linolenic acid, oleic acid, and linoleic acid (Hashemi et al., 1212). Similarly, walnuts coated with a walnut protein-based coating enriched with walnut phenolics showed lower deterioration of UFA, carotenoid, and -tocopherol content (Grosso et al., 1212).

12.7 Conclusion

Preharvest, postharvest and processing factors affecting the bioactive compounds and FA in temperate nuts have been discussed. Temperate nuts contain bioactive compounds such as phytosterols, tocopherols, polyphenols, tocotrienols, and UFA, including linoleic acid, oleic acid, and linolenic acid, which are responsible for the functional properties such as anti-tumor antioxidant, antimicrobial, anti-inflammatory, and antidiabetic properties. These valuable compounds are affected by cultivar, geographical location, and stage of fruit harvest. Cultivar may override postharvest factors in influencing the quality of temperate nuts and has been prioritized in breeding more economically valuable and nutritious cultivars. Geographical location, or crop-growing region, has attracted the interests of many researchers as it encompasses other factors such as cultivation practices and climate. However, detailing the conditions of the areas studied, for instance, the climatic conditions, agricultural practices, and soil type may help to improve the design of future studies. The interrelationship between cultivar and geographical location is noteworthy because the same cultivar can exhibit different chemical compositions when cultivated under varied environmental conditions. The synthesis of bioactive compounds and fatty acids also varies with the stage of fruit development, highlighting the importance of timely harvesting. After harvesting, the nuts are subjected to different value-added processes that also influence their bioactive compounds and fatty acids. Such processes include shelling or peeling, blanching, drying, roasting, irradiation, cold plasma, packaging, and storage. The application of irradiation and cold plasma to preserve temperate nuts’ quality during storage is relatively novel, necessitating further studies, particularly involving a wide range of irradiation doses. Similarly, the application of cold plasma on different types of temperate nuts requires further exploration. For thermal processes, the management of temperature and time is critical, as these can significantly degrades the quality of temperate nuts. The type of packaging and storage factors, such as oxygen concentration, temperature, and relative humidity, should be carefully considered to minimize quality deterioration. Given the global drive towards eco-friendly packaging, novel technologies in packaging temperate nuts such as edible coatings and films, require more investigation.

Keywords

bioactive phytochemicals

cold plasma treatment

cultivar

fatty acids

pasteurization

phenolic acids

phytosterols

saponins

temperate nuts

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Chapter 13 Genetic Diversity, Breeding Challenges, and Achievements of Temperate Nut Crops

RAHUL R. RODGE* and RAJNI RAJAN

Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

*Corresponding author

Abstract

Due to their high economic returns and high nutritional value, nuts are being produced and consumed more frequently worldwide. The importance of nuts such as walnuts, hazelnuts, pistachios, pecans, almonds, and chestnuts in a balanced diet and their advantages for human health have led to an increase in the breeding of nut species. Since consumers demand products with unique, fresh, and up-to-date qualities, breeding is an important innovation part in fruit production around the world. There are very few options available to producers in India for well-known nuts, despite the country’s vast genetic diversity. To achieve the primary breeding goals, it is essential to attain a reduction in the necessary chemical inputs for pest, disease, and disorder control, alongside an enhancement in yield, quality, and the variety of harvest timings. Additionally, biodiversity has caused a rich and diverse nut genetic variety to spread across the majority of the world, particularly in mountainous and forested places with a temperate temperature the major genetic variation within the species and its plasticity in adapting to various pedoclimates are important variables in the development of numerous distinct ecotypes and varieties in the wild. This chapter discusses the genetic diversity of nuts, including walnuts, hazelnuts, pistachios, pecans, almonds, and chestnuts, as well as the challenges and achievements of their breeding program.

__________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

13.1 Introduction

Nut crops encompass a diverse Assortment of plants originating from diverse botanical families. but share the common characteristic of having a nut-like fruit. They are grouped together due to similarities in harvesting, postharvest processing, nutritional value, and marketing traits. A nut typically consists of a tough outer shell protecting an edible kernel. While various dry seeds are colloquially referred to as nuts, botanically, a nut specifically refers to a seed or kernel enclosed in a hard shell or covering. nuts are often pollinated by wind and produce ample pollen, usually in specialized male inflorescences, to ensure fertilization of female flowers. nuts can be categorized as monoecious (e.g., walnut and pecan nut) or dioecious (e.g., pistachio). Additionally, there are types known as protandrous and protogynous, referred to as heterodichogamy. walnut and pecan nut belong to the Juglandaceae family and share a close relationship, yet they are not compatible for crossbreeding or grafting.

The disparity in yield between walnuts and pecans is notable, mainly because walnuts have a higher performance. This is because walnuts can produce nuts not only from terminal buds but also from lateral buds on one-year-old wood. While most nut seeds naturally separate from their shells as they mature, hazelnuts and chestnuts are exceptions, as they have sturdy shell walls and develop from compound ovaries. In terms of climate, walnuts, pecans, hazelnuts, chestnuts, and pistachios are categorized as temperate nuts (Mir et al., 2023).

Production of nuts worldwide in 2022 are almond 1,643.84 metric tons, walnut 996.08 metric tons, pistachios 759.3 metric tons, hazelnut 545.15 metric tons, pecans 129.51 metric tons (Shahbandeh, 2022). Production of nuts India in 2022 are almond 10,000 Ha area production 11,000 metric tons, walnut 10,900 Ha area production 282,000 metric tons (NHB, 2022).

13.2 Walnut1

13.2.1 Genetic Diversity

The significance of genetic diversity in crop enhancement cannot be over-stated as it allows for the combination of genetic elements from different origins, demonstrating superior traits compared to closely related species. The success of plant breeding hinges on the availability of substantial genetic variation, enabling the realization of crops’ maximum genetic yield potential. Efficient selection for improvement depends on the exploitation of this diverse genetic pool (Martin et al., 2005).

Walnut (Juglans regia L.) holds great importance as a dried fruit and belongs to the Juglandaceae family. Its main cultivation areas include China, USA, Iran, and India. Within India, the key states for cultivating walnuts are AR, J&K, HP and UK. Notably, J&K stand out as the leading region for walnut production, being the principal walnut growing state and the main supplier of dry fruits. The walnut is widely utilized in India for preparing nutritious dishes, bakery products, confectionery, and oils, making it a crucial source of livelihood for numerous farmers (Fatima et al., 2022; Lone et al., 2023).

In India, walnut cultivation primarily occurs in four major states: AR, J&K, HP and UK. The state of J&K stands out as the most significant contributor, accounting for over 95% of the country’s total walnut production, cultivated on more than 85% of the total walnut-growing area. Out of the entire 1,08,000 hectares dedicated to walnut cultivation in India, a substantial 89,000 hectares are located within the Union Territory of J&K. When considering the overall production figures, the nation’s total output of 2,99,000 metric tonnes is dominated by Jammu and Kashmir, which alone produces 2,75,000 metric tons (Hassan et al., 2021).

The genetic variation among 82 walnut genotypes that are well-suited to the North region of J&K was investigated using 13 SSR primers. The research highlighted a considerable level of genetic diversity in the populations, with each locus displaying a range of one to five alleles, indicating the presence of multiple genetic variations. The similarity among the genotypes ranged from 12%–79%, with an average of 49%. Upon analyzing the data, a dendrogram was constructed, illustrating all the collected samples fell into four primary clusters, each exhibiting various degrees of sub-clustering within them (Ahmed et al., 2012).

The research utilized microsatellite markers to examine the genetic variation and distribution of walnut populations in parts of China. The results revealed a moderate degree of genetic variety within these populations, with each genetic location showcasing full polymorphism (100% variability) and effective alleles per location spanning from 1.75 to 3.35. The expected heterozygosity within each population varied from 0.389–0.687. Discrepancies within the populations contributed to around 18.6% of the complete genetic variation. Through the utilization of the unweighted pair group method with arithmetic averages (UPGMA) for clustering and the Mantel test, researchers identified a notable association between the genetic dissimilarities among the nine populations and their geographic spread (Wang et al., 2008).

In India, the walnut populations exhibited significant genetic variation, as indicated by differences in morphology and the use of RAPD and Simple Sequence Repeat (SSR) markers. (Ahmed et al., 2012). At present, SSR markers are gaining popularity as molecularly characterizing various plant species (Gupta and Varshney, 2000).

The study was to assess the genetic diversity present in populations of walnuts in Iran by analyzing their phenotypic and morphological traits and exploring potential relationships based on these characteristics. The researchers selected 31 walnut accessions and evaluated them using 18 qualitative and 3 quantitative vegetative parameters.

Using straightforward correlation analysis, the researchers uncovered significant positive and negative associations among several important variables. To discern essential characteristics and establish the number of primary factors, they utilized factor analysis. This approach led them to identify six primary factors that collectively explained 80.78% of the total variance. The primary connections were established between nut and kernel characteristics, measurements like fruit weight with husk, nut dimensions (length, width, thickness), and kernel dimensions (length, width). Leveraging cluster analysis, the walnut varieties were categorized into six distinct clusters. Notably, the scatter plot of the walnut genotypes clearly exhibited distinct separations, validating the findings from the cluster analysis (Norouzis et al., 2013).

The primary goal was to assess the genetic diversity and interconnections among 12 distinct groups of Persian walnut within in Iran. To carry out this analysis, scientists utilized the physical traits of the walnuts. The findings revealed significant genetic variation among the walnut samples, particularly concerning their physical characteristics (Karimi et al., 2014).

In Iran, a research effort was conducted to explore the genetic variety and arrangement of natural groups of Juglans regia L. This was achieved by investigate 11 microsatellite markers. The investigation encompassed 105 individuals from seven separate populations. The results revealed a noteworthy degree of genetic diversity among these groups, with the count of alleles per genetic location (A) spanning from 3–11 (with an average of 5.73). Remarkably, all scrutinized locations displayed variability (100%), and the projected heterozygosity ranged from 0.598–0.848 (with an average of 0.707). Around 12% genetic variations among the populations accounted for the entirety of the diversity observed the clustering analysis categorized the seven populations into two primary clusters (Karimi et al., 2010).

The exploration of genetic diversity and connections of 31 walnut genotypes obtained from Iran, with four foreign cultivars, The use of SSR markers facilitated the execution of the process. In this SSR analysis, nine primer pairs were utilized, leading to the identification of 39 alleles. The number of alleles per primer varied from 2–8, with an average of 5.10 alleles per primer. Notably, the Iranian genotypes exhibited considerable diversity at their SSR loci. Interestingly, the foreign cultivars (“Serr,” “Vina,” “Franquette,” and “Lara”) formed a distinct cluster, while also showing a close association with the Iranian genotypes (Table 13.1) (Ebrahimi et al., 2011).

Table 13.1 Different Walnut Species and Their Genetic Diversity⏎

Species | Common Name | Origin | Genetic Diversity | Use
J.regia | English or Persian walnut | Mediterranean region and central Asia | In India, major walnut growing states are J & K, HP, UK, and AR. | Medicinal plant
J. cinerea | Butternut or White Walnut | United States and southeast Canada | Eastern forests of North America | Timber and Nut
J.ailantifolia | Japanese walnut | Japan and Sakhalin | Eastern United States and Canada | Nut
J.cathayensis | Chinese Walnut | East Asia | Southern china | Nut and Wood
J.mandshurica | Manchurian walnut | Northeast China | China, Korea, Siberia, Japan, India, and Russia | wood
J.nigra | Black Walnut | North America | Ontario, Canada, as far west and east, respectively, as Kansas and New Jerseys (with scattered occurrences up into Vermont), and south to northern Florida | Timber and Nut production
J. sigillata | Iron walnut | China | Yunnan | Wood and Nut

13.3 Breeding Challenges and Achievements

Walnut cultivation in India faces numerous challenges, including low productivity, inadequate fruit quality, limited availability of suitable rootstocks and superior scion stock, insufficient knowledge of standard propagation techniques, and limited understanding of cultural practices. Additionally, walnuts have a prolonged pre-bearing age, exhibit significant variability in vigor, and have high shell and kernel ratios (Sajwan et al., 2020).

In early walnut breeding, the main focuses were nut size and kernel color. However, researchers also sought traits such as more kernel percentage, easy removal of the kernel, and thinner shells. As walnut breeding progressed into the mid-twentieth century, increasing emphasis was placed on lateral bearing, a crucial factor contributing to yield. This led to the introduction of the Chandler cv. Apart from lateral bearing, other commonly targeted traits in walnut breeding programs include disease resistance against blight and anthracnose, as well as late leafing date.

Certain characteristics involved in the improvement of walnut varieties are influenced by the specific growth location and prevailing climatic conditions (Avanzato et al., 2014). For instance, in regions like France, Iran, and Turkey, where late-spring frosts are common, the trait of late leafing holds significant importance in walnut breeding. This delayed leafing is beneficial as it serves as a preventive measure against walnut blight, caused by Xanthomonas arboricola pv. juglandis, which tends to spread during the spring rainy season. On the other hand, in the United States, an essential breeding trait is an early harvest date. This characteristic aims to extend the harvesting period and circumvent potential damage caused by autumn rains (Bernard et al., 2018; Ebrahimi et al., 2015; McGranahan, 2014).

The present and forthcoming breeding goals prioritize considerations of climate change and worldwide temperature increase. This includes developing rootstocks that can withstand abiotic stresses, specifically drought, while also possessing resistance to diseases.

Walnut growing faces numerous challenges stemming from the lack of suitable propagation methods and other related factors. One of the primary issues is the inadequacy of vegetatively propagated plants, which affects the overall quality and quantity of walnut production. Moreover, the absence of standard rootstocks and cultivars further compounds the problem, hindering the industry’s growth.

Re-establishing nursery plants in the orchard is yet another hurdle, as this process requires careful attention and expertise. Specific climatic requirements and pollination behavior add complexity to the cultivation process, making it essential to find suitable pollinizers to ensure successful reproduction.

Additionally, walnuts have a long juvenile period, which means it takes a considerable amount of time before they start bearing fruit. This prolonged maturation period affects the overall turnaround time for harvesting and commercial viability.

Furthermore, incompatibility between rootstocks and scions poses a significant challenge, as it can lead to poor grafting success rates and compromised plant health. The distinct heterodichogamous characteristic of walnuts, wherein male and female flowers reach maturity at separate intervals, requires precise preparation and supervision to guarantee effective pollination.

Finally, walnut trees are susceptible to various diseases such as Phytophthora root rot, crown gall, and anthracnose, which can significantly impact their health and productivity if not effectively managed.

Addressing these issues and developing better propagation methods, resistant cultivars, and improved management practices is crucial to overcome the challenges and foster a thriving walnut industry.

13.4 Breeding Challenges for Scion

The main focus for growers in the cooler regions of the State is the creation of scion varieties that can resist cherry leafroll virus, the primary cause of blackline disease, which poses a significant concern for them due to its high prevalence in those areas.

13.5 Breeding Challenges Rootstock

The most important characteristics sought in rootstocks are their vigor, ability to Capable of enduring the blackline virus and exhibiting resistance to crown gall, nematodes, as well as Phytophthora root and crown rots. A top priority for the industry is to develop economically feasible methods for propagating rootstocks clonally, enabling nurseries to move away from their current reliance on unimproved seedlings to instead use improved, cloned rootstocks (Leslie et al., 2004).

The introduction of various walnut varieties has significantly contributed to the diversity and productivity of walnut cultivation. Some of these introduced varieties include Opex Culchery, Nugget, Chenovo, Franquette, Lake English, Eureka, Hartley, Ashley, Chico, Paynee, Colby Blackmore, Turtle 16, Fernette, Howard, Turtle 31, Nielson, Chandler, Orth, Serr, and Natra Attiro.

An example of an introduced variation is called Chandler, which was developed by the institute of California in the year 1979. Chandler is a cultivar that is harvested late in the season and is known for its high productivity, producing large nuts of outstanding quality. The nut has a strong shell seal and a remarkable kernel color when exposed to 90% light. The tree has a medium size and grows in a semi-upright pattern, and it can undergo cross-pollination with Scharsch Franquette or Cisco. Chandler has demonstrated to be an incredibly fruitful variety with superior nut quality, showcasing lateral and bud fruitfulness that ranges from 80% to 90%.

Forde, a variety introduced by the University of California in 2004, stands out due to its remarkable productivity in young trees, boasting high yields. It usually reaches maturity around 5 days earlier than the Chandler variety and impressively exhibits 100% lateral fruitfulness. Vina and Sexton are both considered as potential pollinators for the Forde trees. The nuts from this variety are characterized by an oval to round shape, featuring a secure seal. Moreover, the sizeable kernels are predominantly light and extra light, constituting approximately 54% of the total weight of the nut.

Fredrick, a cultivar introduced by Burchell Nursery in 2004, stands out for its early blooming and spreading growth pattern. The nuts it produces are tightly sealed and boast an impressive crack-out ratio. Fredrick’s harvest time arrives slightly ahead of Serr’s. Moreover, this variety shows promising signs of having low susceptibility to blight and has consistently demonstrated high yields. Burchell Nursery is actively gathering more information about this exceptional new cultivar.

In 1999, the University of California introduced the Robert Livermore, an exceptional type of walnut resulting from crossing the Howard and Juglans purpurea varieties. Notably, it made history as the first patented red-kernel walnut. The Robert Livermore tree shares a similar leafing date with the Chandler, typically occurring in mid-April, and its nuts are ready for harvest around the first week of October. The tree has a lateral fruiting habit and produces a moderate to high quantity of medium to small, round nuts with a securely sealed shell. Thanks to its unique characteristics, the Robert Liver-more variety is highly sought after in specialized markets. Anyone interested in cultivating the Robert Livermore variety must pay a royalty fee of $1.50/tree.

Eureka, another walnut variety, is best harvested early to mid-season. Its leafing date typically follows Payne’s by approximately 4–5 days. The nuts are medium-sized, elongated, and possess a good shell seal. The Eureka tree is notably large with a somewhat spreading growth habit. However, it is no longer widely planted in commercial applications.

On the other hand, the Howard walnut variety is usually harvested in the mid-season. It exhibits 80%-90% lateral bud fruitfulness and leaves 15 days after Payne. The nuts are large with a good seal, and their kernel is 90% light in color. The Howard tree is relatively small to medium-sized with a semi-upright growth pattern. However, the nuts are susceptible to blight due to the tree’s late leafing. Pollinizers for the Howard variety include Scharsch Franquette or Cisco.

13.5.1 Selection

13.5.1.1 Cith Walnut-1

Conducted a selection process for Export purposes to enhance the quality of a bold-sized nut variety. (Kumar et al., 2023) This particular variety originated as a chance seedling from the natural population in the Kashmir valley. The trees display medium vigor, with semi-erect and open branches that are well-spaced, dense, stout, and exhibit a brown to grey and healthy appearance. The twigs are medium to long, brown, and slightly covered in fine hairs. Buds primarily appear on new growth and also on the tips of one-year-old shoots. At the age of 40, each tree bears approximately 60 kg of nuts, and the plant starts producing fruit in the fourth year with an initial yield of 48 nuts (Verma et al., 2011).

13.5.1.2 Cith Walnut-2

The variety is predominantly protogynous, with early-season blooming and terminal bearing characteristics. The nuts are substantial, weighing about 21.90 grams, with a medium-sized kernel of approximately 11.24 grams. It boasts good kernel recovery, reaching 51.27%, and a higher yield of 60 kilograms per tree. The kernels are semi-soft, well-filled, plumy, and have a light color simplifying the process of detaching complete kernel halves. The crop demonstrates resilience to pests in the field, with the exception of the white grub. The CITH released this variety in the year 2009, as noted by Verma et al., (2010) and Sofi et al., (2010).

13.5.1.3 Cith Walnut-3

The nut weight is exceptionally high at 18.3 g, accompanied by a very large size and a soft shell with a light color and smooth texture. The seal is intermediate. The kernel weight is also remarkable, reaching 10.0 g, with a kernel recovery rate of 55% (Shikha Jain et al., 2022). This variety, identified as a chance seedling from the natural population of Kashmir valley, exhibits medium-vigorous trees with semi-erect growth and open, well-spaced, dense, and sturdy branches. The bark appears brown to grey and remains healthy. Twigs are medium to long, brown, and slightly covered in fine hair. The buds are sharp-pointed, primarily borne on fresh growth and one-year-old shoot tips. The leaves are compound, medium-sized, elliptic, with an entire leaf margin, green, and slightly pubescent. The inflorescence is protogynous, showing a moderate abundance of light catkins and green stigma coloration (Verma et al., 2010).

13.5.1.4 Cith Walnut-4

This is a description of a chance seedling that was selected from a natural population in the Kashmir valley. The trees are strong and vigorous with open branches, well-spaced, dense, and healthy, displaying a brown to grey appearance. The twigs are medium to long, brown, and slightly covered in fine hairs. The buds are pointed and primarily develop on new growth and one-year-old shoot tips. The leaves are compound, medium-sized, elliptic to broad elliptic in shape, with smooth edges, dark green color, and a slight fuzz on the surface. The inflorescence is protandrous, with a moderate number of green catkins and stigma. According to Verma et al., (2011), this variety exhibits protogynous flowering, both terminal and lateral bearing (16%), and a late maturity period. The nuts are relatively large, weighing about 18.33g, with medium-sized kernels (10 g) and a high kernel recovery rate (54.55%). It produces a higher yield of approximately 40 kg per tree, and the kernels have a good flavor, full appearance, and light color. The shell can be moderately removed to extract the kernel halves. However, it is vulnerable to moisture stress and pests, except for white grub. The variety was released by CITH in the year 2009, as noted by Verma et al., (2010) and Sofi et al., (2010).

13.5.1.5 Cith Walnut-5

This is a randomly grown seedling from a natural population found in Kashmir valley. The trees exhibit robust growth, with spreading, open branches that are well-spaced and dense. The branches are sturdy, brown to grey in color, and in good health. Twigs are medium to long, brown, and slightly covered with fine hairs. The buds are pointed and mainly appear on new growth and one-year-old shoots at the tips. The leaves are compound, medium-sized, broad elliptic, with smooth edges, green, and slightly covered with fine hairs. The inflorescence follows a protandrous pattern, with a moderate abundance of light green catkins and green stigma color. The nuts are large and ovate, with a smooth shell texture and light colored outer shell. The shell has moderate sealing and strength, ensuring complete integrity. The kernels have a satisfactory flavor and are well-filled, with a plume-like appearance, making it moderately easy to remove the kernel halves. The kernel itself has a light color (Verma et al., 2011).

13.5.1.6 Cith Walnut-6

The kernels have a moderate weight of 12.2 grams, with a kernel recovery rate of 51%. They possess a light color, making them easy to separate into halves. Additionally, the kernels are plump and well-filled.

13.5.1.7 Cith Walnut-7

The kernels have a medium weight of 12.4 grams, and the kernel recovery rate is 50%. They exhibit a light color and can be easily separated into halves. Furthermore, the kernels are plump and well-filled.

13.5.1.8 Cith Walnut-8

The kernels have a light color and can be easily split into halves. Moreover, they are plump and well-filled.

13.5.1.9 Cith Walnut-9

The kernels have a moderate weight of 10.8 grams, with a kernel recovery rate of 51%. They have a light color and are simple to separate into halves. Additionally, the kernels are plump and well-filled.

13.5.1.10 Cith Walnut-10

According to (Shikha et al., 2022), the nuts have an exceptionally high weight of 20.0 grams and are characterized by a long trapezoid shape, light color, and rough texture. The nuts have an intermediate seal. As for the kernels, they exhibit a medium weight of 11.2 grams, with a kernel recovery rate of 56%.

13.5.2 Hybridization

Through a hybridization technique designed to produce novel varieties of walnut trees (Juglans regia) Indian walnut (Figure 13.1) that display enhanced productivity, fruit quality, and side branch bearing, a fresh cultivar named “Leto” was effectively created. This newly developed cultivar emerged from the crossbreeding of the “Gustine” and “Pedro” varieties. Throughout a continuous period of ten years, the fundamental phenotypic and fruit-related traits of the “Leto” cultivar were evaluated according to the standards outlined in the IPGR (1994) and UPOV-TG/125/6 (1999) guidelines. When compared to its parent cultivars and “Chandler,” “Leto” demonstrated an impressive high lateral bearing rate of 90% and yielded satisfactory harvests upon reaching full maturity. The size of the “Leto” tree is smaller than that of its parent plants and “Chandler,” and it produces female flowers between April 11 and April 22, with male flowers blooming from April 3 to April 6. The “Leto” nuts are harvested in late September and are characterized by easily removable hulls and a high kernel percentage (Figure 13.2, Figure 13.3, Figure 13.4 and Figure 13.5) (Manthos et al., 2021).

Figure 13.1 Indian walnut J. regia.⏎

Figure 13.2 Black walnut J. nigra.⏎

Figure 13.3 Japanese walnut (Juglans ailantifolia).⏎

Figure 13.4 Butter nut or white walnut J. cinerea.⏎

Figure 13.5 Manchurian Walnut J. mandushurica.⏎

UC Wolfskill originates from a successful cross between the Chandler and Solano walnut varieties. Notably, it stands out due to its early harvest date and impressively abundant yield. The kernels it produces are consistently light in color. Moreover, during the intense heat wave in September 2022, UC Wolfskill demonstrated exceptional performance under stressful conditions. Across various trial locations throughout the state, it displayed remarkable resilience, with over 85% of its kernels classified as light or extra light.

13.5.3 Varieties Developed By Hybridization

The varieties which are developed by hybridization are:

Tehama: Waterloo × Paynee

Leto: Gustine × Pedro

Wolfskill: Chandler × Solano

Vina: Franquette × Paynee

Biotechnology has seen extensive applications in the realm of walnut cultivation, as highlighted in a recent review by Dandekar et al. (2005). Nevertheless, in comparison to agronomic crops, walnuts are yet to fully embrace these advancements. The implementation of gene transfer techniques for walnuts dates back to 1988, as demonstrated by McGranahan et al., (1998). Currently, mature transgenic walnut trees are undergoing testing in continuous field trials. These trials aim to assess the effectiveness of specific genes, such as Bt derived from Bacillus thuringiensis, which grants insect resistance (Leslie et al., 2001). Efforts to modify tree architecture using the rol ABC genes from A. rhizogenes were made, but the desired enhancement in root ability was not accomplished, as observed by Vahdati et al., (2002).

13.6 Chestnut Genetic Diversity

The north-western Himalayan area sustains a wide range of economically valuable temperate fruit plants, displaying remarkable and varied genetic diversity. Among these plants, Chestnut (Castanea sativa Mill.) is particularly well-regarded due to its high productivity, easy harvestability, simple Chestnut is valued for its suitability for consumption, low fat content, and the ability to be used in various ways. Despite these advantageous characteristics, Chestnut suffers from a lack of genetic diversity. A collection of 150 different chestnut varieties or genotypes has been identified in the Kashmir valley, varying in age from 80 to 100 years. Out of these, the genotypes H-26, H-27, H6-30, H-6, H5-39, and H-9 have particularly stood out as the most favorable choices (Pandit et al., 2007).

13.6.1 Water Chestnut (Trapa Natans L.)

The north-western region of the Himalayas is home to a wide variety of economically significant temperate fruit plants, boasting abundant and diverse genetic traits. Chestnut (Castanea sativa Mill) is especially valued for its remarkable productivity, convenient harvestability, simple preparation for consumption, low fat content, and other beneficial attributes. its versatility in various applications. However, the genetic diversity of Chestnut is found to be relatively poor. In the Kashmir valley, researchers have identified 150 different chestnut selections/genotypes, all within the age range of 80–100 years (Crow and Hellquist, 2000). The water chestnut, also known as singhara, is a noteworthy fruit crop that thrives in aquatic settings and is scientifically referred to as Trapa natans var. bispinosa Roxb. Belonging to the Trapaceae family, this crop holds great potential for cultivation in water-logged areas and is widely cultivated in different Indian states, such as UP, BR, TN, WB, AS, OD, J&K on an annual basis (Chakor et al., 1974). The water chestnut varieties have been identified as ideal choices for profitable commercial farming in the Lucknow region. Their exceptional attributes, such as big fruit size, attractive appearance, and superior fruit quality, make them stand out from other varieties. As a result, these selected cultivars offer more significant financial rewards to farmers in the area (Dwivedi et al., 2010). The genetic diversity and arrangement of populations of the water chestnut, which serves as a case study for an annual aquatic plant that is currently being closely monitored for conservation purposes, have experienced an impact. This particular species has faced a decline in Europe dating back to at least the early 19th century (Jaggi, 1883; Hegi, 1926). Presently, the water chestnut has become a rarity and has experienced regional extinction. The exact reasons for its decline remain unclear, although some factors have been linked to human-induced freshwater eutrophication and destruction (Lansdown, 2013). Additionally, the examination of various sub-fossil fruits of Trapa L. revealed that climatic fluctuations, along with the loss of natural habitats due to vegetation changes over time, had already diminished its geographical range since the conclusion of the Holocene thermal maximum (Gams, 1927; Apinis, 1967).

Clusters of T. natans plants that are tall and easily noticeable have been linked to eutrophication caused by human activities, particularly in areas beyond its original habitat where it is deemed invasive (Hummel and Kiviat, 2004). Similarly, within the Insubric region, prominent populations of water chestnut are thriving in shallow lakes that have high levels of nutrients and are susceptible to eutrophication (Limno, 2017).

The sweet chestnut (Castanea sativa Mill), commonly known as the European chestnut, traces its origins back to Europe. It belongs to the Castanea section and is a prominent species in the region. The tree’s common name, “European or sweet chestnut,” alludes to its delicious, edible nuts. These nuts have been cherished and cultivated in orchards across Europe, Asia Minor, and even North Africa.

Tree shape and structure exhibit considerable variability. Castanea dentata and C. sativa are characterized by their upright, tall, and slender growth, while certain species display a smaller size with rounded foliage and branches originating from the base. Additionally, some species exist as dwarf shrubs Figure 13.6.

Figure 13.6 Important chestnut species.⏎

In Europe, two types of chestnut were recognized: C. sativa and C. latifolia Sord (Paganelli, 1997). After the last glaciation period (Würmian period), as indicated by pollen charts, only C. sativa successfully endured. Nowadays, C. sativa remains the only indigenous species found in the Mediterranean and Central European areas (Table 13.2).

Table 13.2 Different Chestnut Species and Their Genetic Diversity⏎

Species | Common Name | Origin | Selection | Genetic Diversity | Use
Trapa natans | Water chestnut | Eurasia and Africa | Castanea | In India, this crop is cultivated in the regions of BR, MP, UP, WB, OD, JH, KA, J&K. | Nut
C. sativa Mill | European or sweet chestnut | Europe | Castanea | Europe, Asia Minor, North Africa | wood
C. crenata Sieb. et Zucc. | Japanese chestnut | Asia | Castanea | Japan, Korea | Nut
C. pumila Mill. var. pumila | Allegheny chinkapin | America | Balanocastanon | Southeast USA | Nut

In Europe, the distribution of C. sativa spans from Turkey to Portugal and Spain. The Azores archipelago serves as the farthest western location for C. sativa, while its southernmost point is marked by the Canary Islands. As we move northward, chestnut fruit production can be observed in latitudes situated just south of the United Kingdom, northern Germany, Poland, and Ukraine.

In the early 1800s, European settlers brought C. sativa to Chile, introducing it to South America. Since then, it has predominantly thrived in the Andes Mountain Range region (Bounous, 2002).

C. sativa is a majestic tall tree with a striking appearance, known for its vigorous growth, capable of surpassing 30 meters in height and living up to 400 years. Some of the century-old specimens boast a girth measuring 6–7 meters. The nut, weighing between 10–30 grams, contains a white-cream pulp and may have pellicle intrusions into the kernel.

In Europe, the gene pool of C. sativa displays considerable variety, comprising a broad spectrum of genetic differences. Nevertheless, there is a significant concern about genetic depletion regions (Bounous et al., 2001). To protect the invaluable biodiversity of C. sativa, it is crucial to conserve the most valuable genetic resources that have been carefully selected and cultivated for centuries. The existence of numerous cultivar names for chestnuts makes it essential to tackle the matter of synonymous or homonymous designations to ensure precise identification and effective conservation endeavors (Botta et al., 2001).

The Japanese chestnut (Castanea crenata Sieb. Zucc.) is a species native to Asia, specifically found in regions like Japan and Korea. Belonging to the Castanea genus, this tree is commonly known as the “Japanese chestnut.” The species is primarily cultivated for its nuts, which are a valuable food source and hold cultural significance in these regions. In Japan and Korea, orchards are dedicated to the cultivation of this species.

The ideal conditions for its growth include a gentle summer climate, moderate winter temperatures, and significant summer rainfall ranging from 1,200–1,400 mm per year. In Japanese Islands, where winters are mild and summers receive abundant rainfall, C. crenata can thrive up to an altitude of 1,300m. However, compared to its American and Chinese counterparts, it is less tolerant to cold temperatures (Rutter et al., 1991) the plant’s tendency to bloom early increases its vulnerability to frosts occurring in late spring (Breisch, 1995). The nuts of C. crenata exhibit significant variation from one tree to another; certain nuts are the largest among the species, weighing over 30 g. The hilum scar is notably wide, extending to the center of the chestnut. These nuts are typically not sweet, occasionally astringent, and possess a pellicle that sticks firmly to the kernel, making it challenging to detach (Tanaka and Kotobuki, 1992).

In France, the germplasm of C. crenata has been extensively employed in breeding with the aim of developing trees that are resistant to Phytophthora, a plant pathogen (Salesses et al., 1993). This species gets its name from the abundant fine hair (pubescence) commonly found across the country. C. mollissima flourishes in a wide range of regions, including sub-tropical, temperate-continental, and temperate-maritime areas, which are known for their mild winters and hot summers. The average annual rainfall in these areas is approximately 1,000 mm, with most of it occurring during the summer.

The Chinese chestnut (Castanea mollissima) has been recently introduced to numerous countries due to its ability to adapt to different pedoclimates. It displays thriving growth across a broad range of latitudes, from Jilin Province near Korea, extending northwards to Hainan Island. Within China, it flourishes in various regions, including other parts of China. Additionally, in Korea, both C. mollissima and C. crenata are found, with the former being more prevalent in northern Korea and the latter predominantly found in the southern regions, which serves as the primary production area (Kim et al., 2005). The growth of this chestnut species can be observed at altitudes ranging from 50–2,800 meters, thriving under diverse climatic conditions.

Many different types and regional variations of the Chinese chestnut have been recognized, and around 50 of them are under cultivation (Liu, 1993). Chinese chestnut is a medium sized tree, typically reaching a height of 12 meters and featuring trunk diameters that can measure up to 75–80 centimeters. The leaves of this tree have large, irregular serrations that are not very distinct and end with a hairy, pointed tip called a mucronate point. The upper surface of the leaves (adaxial surface) appears bright green, while the lower surface (abaxial surface) is characterized by a whitish-grey or velvety appearance due to the presence of fine hairs (pubescence).

The species is Castanea pumila Mill. var. pumila, commonly known as Allegheny chinkapin, and it originates from America. The specific selection of this variety is referred to as Balanocastanon, and It is mainly cultivated in orchards situated in the southeastern part of the US.

13.7 Breeding Challenges and Achievements of Chestnut

In recent years, there has been a notable acceleration in temperate nut tree breeding programs due to the growing demand for their production. The primary focus of these breeding efforts is to develop cultivars that exhibit increased productivity, desirable kernel traits, and immunity to diseases. However, emerging challenges like global warming and climate change have led to the inclusion of new objectives in these programs, such as reduced chilling requirements and enhanced tolerance to late spring and early autumn frosts. To achieve these breeding goals, a combination of traditional and modern techniques is employed. Conventional strategies, including the utilization of genetic resources and targeted hybridization, play a significant role in developing temperate nut tree varieties. Additionally, molecular breeding techniques complement these conventional methods, resulting in an accelerated and more efficient breeding process (Vahdati et al., 2023).

In recent decades, significant advancements have been achieved in rootstock breeding for tree nut crops, including chestnuts. Alongside this, considerable efforts have been dedicated to breeding the nut species themselves. Although the main emphasis of fruit breeding initiatives has centered on improving the genetic makeup of the upper plant part (scion), the integration of regionally suited grafted rootstocks has displayed its own benefits in boosting the yield and excellence of tree fruit yields. Grafting, a traditional method in gardening, has been effectively used in nut cultivation to control scion traits and production, effectively addressing challenges posed by living organisms and environmental factors. The goals of cultivating rootstocks are multifaceted, encompassing a range of physiological and molecular facets concerning the interplay between rootstocks and scions, specifically within the realm of nut cultivation.

13.8 Breeding for Disease Resistances

In recent, focus on breeding and biotechnological advancements to tackle the main ailments afflicting chestnut trees: chestnut blight, caused by Cryphonectria parasitica, and ink disease, caused by Phytophthora cinnamomi. These dedicated efforts have primarily aimed at discovering ways to combat ink disease and chestnut blight by creating chestnut varieties that are resistant or tolerant to these pathogens.

Developing resistance to pathogens is crucial to ensure viability of chestnut trees in Europe and the United States. To achieve this, various genomic methods have been applied to create a hybrid population by crossing the European species researchers have successfully identified potential genes that play a role in conferring resistance to ink disease (Santos et al., 2016). The process of reintroducing blight resistance into the American chestnut involves using traditional plant breeding techniques. After hybridization with resistant species, the resulting offspring are assessed for blight resistance by directly exposing them to the blight fungus. depending on their resistance levels, the screening occurs when the trees are 3 or 4 years old for moderately resistant ones and 1 or 2 years old for highly resistant trees. The growth of these trees is carefully managed through intensive horticultural methods. Unlike similar programs for crop plants, this breeding initiative stands out due to the vast areas used for tree cultivation and the focus on restoring genetic diversity rather than creating improved cultivars. Successful recovery of highly blight-resistant offspring has been observed from intercrossing various generations, indicating the potential to reintroduce blight resistance into the American chestnut species (Hebard et al., 2006)

The start of chestnut breeding in Europe involved developing hybrids that were resistant to ink disease, which is triggered by Phytophthora spp. These hybrids were intended to replace the native species while safeguarding European chestnut orchards from the disease threat. Between 1917 and 1940, for this purpose, seedlings from Asian species C. crenata and C. mollissima were introduced (Elorrieta et al., 1949). Despite being confirmed as disease-resistant, these hybrids presented several drawbacks when compared to the European species C. sativa. These included reduced vigor, inferior nut quality, limited compatibility with local cultivars, susceptibility to early spring frosts and summer droughts, and challenges in adapting to specific European climatic conditions in certain regions (Elorrieta, 1949).

In 1989, a fresh initiative was initiated with the aim of identifying hybrid clones that exhibited potential in terms of wood output, nut yield, or their suitability as rootstocks (Pereira-Lorenzo and Fernández-López, 1997; Pereira-Lorenzo and Fernández-López, 2001).

Due to two serious disease, chestnut trees in Europe and North America have suffered greatly. Chestnut blight is one among them, and it’s brought on by the ascomycete fungus Cryphonectria parasitica (Murr.). The other disease is Phytophthora root rot, also known as ink disease, primarily caused by the soil-borne oomycetes Phytophthora cinnamomi Rands and P. cambivora (Petri) Buisman. Consequently, a major priority for breeders is to develop resistance against these two ailments. Through breeding efforts, the quality of chestnut fruit and crop yields have improved dramatically throughout eastern Asia. Meanwhile, by using molecular markers and other genomic tools to help in the selection process, researchers in all areas where chestnuts are produced have successfully improved disease resistance (Rita Costa et al., 2011).

In France, the germplasm of C. crenata has been extensively utilized in breeding programs aimed at obtaining trees resistant to Phytophthora infection (Salesses et al., 1993).

Two destructive illnesses have had significant consequences for chestnut trees in both Europe and North America. One of these conditions is chestnut blight, which originates from the ascomycete fungus Cryphonectria parasitica (Murr.) Barr. The other affliction is Phytophthora root rot, also known as ink disease, primarily caused by the soil-borne oomycetes Phytophthora cinnamomi Rands and P. cambivora (Petri) Buisman. Consequently, a major area of focus in breeding endeavors is directed towards developing resistance against these two ailments. In eastern Asia, chestnut breeders have made impressive progress in enhancing.

In all areas where chestnuts are grown, scientists have made significant advancements in enhancing the quality of chestnut fruits and increasing crop yields. Additionally, they have successfully enhanced disease resistance by utilizing molecular markers and genomic techniques to aid in the selection process. (Craddock et al., 2019).

Chestnut blight arises from Cryphonectria parasitica (formerly known as Endothia parasitica [Murr.] And.). This fungus has emerged as a significant threat to chestnut trees, primarily due to the susceptibility of C. dentata and, to a lesser extent, C. sativa to its impact. The blight inflicts damage by attacking the bark and cambium, leading to branch or tree mortality when the disease encircles these areas (Anagnostakis 1987; Heiniger and Rigling 1994 ) In 1938, the initial outbreak of this phenomenon was observed in Genoa, Italy. Although it had a lower impact in the Southern UK, the Netherlands, Central and Southern Spain, as well as the Canary Islands, the disease spread quickly throughout Italy and several other European nations (Robin and Heiniger, 2002). The European chestnut (C. dentata) is showing indications of recovery despite the American chestnut (C. dentata) being badly blighted and having dsRNA hypovirulence-carrying CHV1 as a natural hypovirus (Allemann et al., 1999) were able to isolate five different subtypes of this CHV1 virus. In Europe, biological control measures have been implemented using hypovirulent strains of the hypovirus, which are encouraged to grow on cankers through Grente method (Grente and Berthelay-Sauret, 1978).

Cryphonectria parasitica resistance in C. sativa, C. mollissima, and C. crenata is attributed to only two specific genetic locations, as identified in their genetic material (Sisco et al., 2005). The primary source of resistance against blight can be traced back to Asian species, with C. mollissima being particularly significant (Hebard and Stiles, 1996). To revive the American chestnut C. dentata, A backcross breeding program has been started by the American Chestnut Foundation. Through three backcrosses, the resulting offspring demonstrate an average of 96% American genetic background, eventually displaying completely American traits in subsequent generations (Diskin et al., 2006).

13.9 Breeding for Pest Resistance

The gall wasp hasn’t received as much attention as other mentioned pathogens because it doesn’t directly kill the trees. Nonetheless, its unchecked spread could undo the progress made in breeding and sustaining European and American chestnut trees, leading to reduced nut production. Additionally, the galls it forms could serve as entry points for CP (presumably a type of pathogen), which may escalate branch mortality (Meyer et al., 2015)

The primary insect pest that poses a severe threat to Castanea (chestnut) trees tolerate this pest has spurred the creation of gall-resistant chestnut cultivars. To capitalize on the abundant genetic diversity within the genus, interspecific hybridization presents a promising opportunity to blend the most desirable traits and introduce them into locally-adapted populations through introgression (Craddock et al., 2019).

To tackle the vulnerabilities found in each type of chestnut species, researchers have undertaken interspecific hybridizations. For instance, in Europe, they conducted crossbreeding between C. sativa and C. crenata, incorporating genes that provide resistance against ink disease, canker blight, and chestnut gall wasp (Pereira-Lorenzo et al., 2012; Santos et al., 2015). In the USA, backcross breeding was employed to introduce blight resistance from C. mollissima into C. dentata (Hebard et al., 2006). These hybridization endeavors aimed at bolstering the overall strength and ability of chestnut trees to withstand the various threats they encounter.

Certain cultivars displayed an intriguing resistance to gall wasps, showcasing a promising trait. Nonetheless, hybrid cultivars suffer from a perceived drawback in terms of nut organoleptic quality compared to C. sativa cultivars, primarily attributed to the inferior quality of Japanese chestnuts. Nevertheless, C. crenata serves as a significant repository of genes responsible for pest and pathogen resistance or tolerance. Identifying these valuable genes can pave the way for incorporating them into breeding programs, as discussed by Torello Marinoni et al., (2020).

13.10 Breeding Challenges for Scion

The profitability of chestnut growers is significantly influenced by the weight of the nuts they produce. Nevertheless, chestnut breeding faces a notable challenge in selecting desirable traits during the early developmental stages due to the prolonged juvenile phase of chestnut trees. This issue was addressed by Kang et al., (2019).

The majority of current fruit breeding efforts have been directed on enhancing scions’ genetic characteristics. However, including locally adapted grafted rootstocks has been shown to be beneficial, leading to greater crop quality and productivity in tree fruit harvests. In order to efficiently manipulate scion traits, increase output, and address problems brought on by biotic and abiotic challenges, grafting, a traditional horticultural practice, has been widely used in nut crops. According to the discussion by Vahdati et al., (2021), rootstock breeding is a complicated procedure that has a number of objectives and entails examining the physiological and molecular interactions between rootstocks and scions in nut crops.

The nuts of Asian species achieve maturity at an earlier stage, typically in early September, while C. sativa takes a longer time to mature, usually around late October. This early harvest trait observed in Asian species has been inherited in interspecific hybrids due to genetic transmission (Pereira-Lorenzo and Fernandez-Lopez, 2002). Spanish cultivars show significant genetic variability due to selective breeding. In Southern Spain, the harvest includes cultivars collected during the latter half of September as well as those gathered in October. In Northern regions, there are cultivars such as “Negral,” which are harvested at the starting of October, deviating from the more common harvest period towards the end of that month.

Regarding Spanish cultivars, (Pereira-Lorenzo et al., 2006) there was significant differences in the makeup of chemicals among different cultivars and regions, which can be attributed to substantial genetic diversity between these cultivars. Environmental parameters showed weak correlations, suggesting that the observed dissimilarities between regions were primarily a result of varietal distinctions rather than environmental factors. In Spain, certain cultivars exhibited lower moisture content due to the limited summer rainfall in those areas. Additionally, cultivars from Galicia and Extremadura demonstrated the lowest fiber content and were the most easily digestible. Although there were no differences in Fe, Zn, and Cu content, it’s worth noting that the Zn content in Spanish chestnuts was reported value for European chestnuts.

Japanese chestnuts are known for yielding the largest nuts compared to other species of the Castanea genus, occasionally surpassing 30 g in weight. The size of the nuts is a crucial aspect, and modern cultivars are often developed to have nuts weighing between 25–30 g. However, a challenge lies in the fact that the thick outer skin (pellicle) is frequently deeply embedded into the nuts, making the peeling process arduous. Consequently, Japanese chestnut breeding programs prioritize the development of cultivars with easily peelable kernels as a significant objective.

13.11 Hazelnut Genetic Diversity

The Corylus genus, commonly known as hazelnuts, is a group of 13 species that belongs to the Betulaceae family in the Fagales order. These hazelnut species in various temperate regions of the Northern hemisphere and can be categorized into four subsections. Some of them are leafy husked shrubs like the European hazel (C. avellana), American hazel (C. americana), Yunnan hazel (C. yunnanensis), Guizhou hazel (C. kweichowensis), and Siberian hazel (C. heterophylla). Another group includes bristle husked shrubs like the California hazel (C. californica), Beaked hazel (C. cornuta), and C. sieboldiana. Additionally, certain species grow as single-trunked trees, such as the Turkish tree hazel (C. colurna), Chinese tree hazel (C. chinensis), Indian tree hazel (C. jacquemontii), and Paperbark tree hazel (C. fargesii). Lastly, the only chestnut-like, spiny husked tree in this genus is the C. ferox (Botta et al., 2019).

The exact historical beginnings of hazelnuts in human civilization remain ambiguous. Nonetheless, there is a belief that hazelnuts were utilized as a food source by Mesolithic tribes approximately between 10,000–6,000 B.C. Subsequently, their popularity saw a rapid expansion during the post-glacial era (Boccacci et al., 2009). The Indian hazelnut (Corylus jacquemontii Decne.), which belongs to the Betulaceae family, is considered synonymous with the Turkish hazelnut (C. colurna L.). Indian hazelnut exists in various forms, ranging from 10–15 ft bushes to medium-sized trees reaching 70–80 ft. These trees are scattered across the North-western temperate Himalayas, from Kashmir to Kumaon, and thrive at altitudes between 1800–3300 m. In their native environment, these hazelnuts are frequently discovered growing alongside oak, fir, spruce, deodar, betula, maple, and walnut trees. Although not widely recognized in India, except among the high Himalayan regions, where locals, grazers, and tribes (Pangwal and Bhot) depend on it as a source of sustenance (Gupta et al., 2019).

Hazelnut cultivation is still at its initial phase in India, with wild seedling trees spread across the hilly areas of Shimla, Kinnaur, and Chamba districts in Himachal Pradesh, a state in the northwest. Recently, efforts have been made to conduct surveys of these seedling tree populations to identify more favorable and superior varieties of this valuable nut (Sharma et al., 2000).

The European hazelnut (Corylus avellana) is a diploid plant, possessing 22 chromosomes (2n = 22). It exhibits monoecious characteristics; wherein male and female flowers coexist on the same plant and relies on wind pollination. Its nuts are highly sought after, leading to widespread cultivation. Notably, Turkey occupies the dominant position as the world’s leading hazelnut producer, contributing a substantial 70–80% to global hazelnut exports. The primary region for cultivating hazelnuts is the Black Sea Region, where clonal propagation serves as the primary method for plant maintenance (Gürcan et al., 2010).

In Spain, hazelnuts are predominantly grown in Catalonia, specifically in the province of Tarragona, which contributes to 88% of the country’s total hazelnut plantations. The local variety known as Negret is the most prevalent, making up nearly 80% of the production in Tarragona, while other cultivars are cultivated to a lesser degree. Some less common cultivars are present in older orchards, farmyards, and gardens, and efforts have been made to collect and preserve them. To aid hazelnut germplasm conservation and parent selection in breeding programs, researchers analyze 18 minor hazelnut cultivars from northeastern Spain using 16 SSR markers, and the obtained results proved to be valuable (Boccacci et al., 2008).

Turkey’s main focus on hazelnut cultivation lies in the areas encompassing the Black Sea and Eastern Marmara regions. Specific provinces like Ordu, Trabzon, Giresun, Samsun, Duzcce, and Sakarya have 90% of the total hazelnut production (Table.13.3) (Sezer et al., 2017).

Table 13.3 Hazelnut Species and their Genetic Diversity⏎

Species | Common Name | Genetic Diversity
C.avellana | European hazel | Europe, Caucasus, western Asia
C.americana | American hazel | Eastern North America
C.heterophylla | Siberian hazel | Northeast China, Japan, Korea, Russian, far east
C.Kweichowensis | Guizhou hazel | Middle southern China
C. Yunnanensis | Yunnan hazel | China
C.cornuta | Beaked hazel | Appalachian Mountains (USA) to Gaspe Peninsula to central British Columbia
C.californica | California hazel | Southern British Columbia (Canada)
C.colurna | Turkish tree hazel | Balkans, Turkey
C.Jacquemontii | Indian tree hazel | Northern India and Pakistan
C.chinensis | Chinese tree hazel | Middle southern China
C.fargesii | Paperbark tree hazel | Middle southern China
C.ferox | Tibetan hazel | South central china

13.12 Breeding Challenges

Hazelnut, derived from species within the Corylus genus, particularly the Corylus avellana variety, is a nut associated with the hazel plant. Ranking as the second most costly nut, it thrives in cold and hilly regions, requiring a few days of sub-zero temperatures. Consequently, regions such as HP, J&K, UK, and the North-Eastern states are ideal locations in India for its cultivation (Dobhal et al., 2018).

Hazelnut is widely known as a crop with low environmental impact and minimal input requirements. It has been predominantly cultivated in regions where major profitable crops like cereals or high-value fruits cannot grow due to unfavorable environmental factors such as unsuitable soil types, lack of irrigation possibilities, or hilly terrain. However, there is potential to further enhance hazelnut production by embracing innovative and sustainable cultivation methods. This includes utilizing hazelnut cultivars that are more resilient to environmental limitations, as well as addressing challenges posed by significant pests and pathogens. To attain these goals while maintaining both quality and yield, it would be greatly beneficial to combine biotechnological methods and an enhanced comprehension of hazelnut genetics with conventional approaches (Botu et al., 2009).

The breeding endeavors is to optimize the quantity and quality of nuts produced while minimizing vulnerability to diseases like Eastern Filbert Blight (EFB). Additionally, efforts are being made to improve characteristics such as resistance to bud mites and EFB, early maturity, the ease of harvesting nuts that naturally detach, achieving a round nut shape, reducing the number of nut and kernel defects, obtaining a high percentage of kernels, facilitating easy kernel blanching, and ultimately increasing overall yield (Botta et al., 2019).

13.13 Breeding Achievement

13.13.1 Selection

Three hazelnut cultivars (“Emoa 1,” “Emoa 2,” and “Emoa 3”) are well-suited for organic cultivation in the Netherlands due to their outstanding yield potential and desirable quality attributes, including size, shape, taste, and easy pellicle removal (Schepers et al., 2005).

In the Black Sea Region of Turkey, a total of 17 different hazelnut varieties are grown. These varieties include “Acı,” “Cavcava,” “C¸akıldak,” “Fosa,” “Incekara,” “Kalınkara,” “Kan,” “Karafındık,” “Kargalak,” “Kus,” “Mincane,” “Palaz,” “Sivri,” “Tombul,” “Uzunmusa,” “Yassıbadem,” and “Yuvarlakbadem (Köksal et al., 2006).

13.13.1.1 Italy

The Torino university introduced five new selections derived from various crossings. Four of these selections (Daria, UNITO 101, UNITO 119, and UNITO 3L) originated with while the fifth selection (UNITO G1) resulted from the crossing of Payrone with Tonda Romana. These new cultivars are suggested as both cultivars and pollinators for cv. Tonda Gentile delle Langhe, and they produce nuts of comparable quality, as documented by(Valentini and Me (1999). Additionally, there is one more selection (UNITO L35) specifically recommended for the in-shell market, which was derived from crossing (Valentini et al., 2001).

13.13.1.2 France

The INRA Bordeaux breeding initiative commenced during the 1960 and concluded in the early 1990. As part of this program, three varieties were introduced. These include Fercoril-Corabel (also known as Fertile de Coutard o.p.), which was cultivated specifically for the in-shell market, as detailed by Germain et al., (1989). Additionally, there were Ferwiller, a pollinizer resulting from the cross of Hall’s Giant and Tonda Romana, and Feriale, derived from the cross between Imperiale de Trebizonde (also known as Kargalak) and Butler, intended for the kernel market.

13.13.1.3 Turkey

Tsssswo new cultivars were developed and named Giresun Melezi and Okay 28. Furthermore, they introduced a cultivar called Allah Verdi, which either originated from a chance seedling or through a local selection process. Currently, the institute is actively conducting evaluations of 14 clones of Tombul in replicated trials to assess their characteristics and potential for cultivation.

13.13.1.4 China

Hybridization efforts between different species began in 1980 in the North region of China. The main goal was to develop plants that combined the cold resistance of Corylus heterophylla with the increase productivity (Xie et al., 2005). Subsequently, starting from the year 2000, China identified and selected 14 distinct variations of these hybrids for widespread cultivation. The Ping’ou hybrids have garnered attention for their remarkable frost resistance and more yields (Wang et al., 2018). Ongoing efforts focus on acquiring cold-tolerant pollenizers and developing hybrids suitable for southern regions through the combination of C. kweichowensis and C. avellana breeding techniques.

The utilization of genomic resources to enhance breeding endeavors is exemplified by the “Jefferson’s” genome and transcriptome assembly, as well as the examination of genetic variations among seven additional accessions. The progress of molecular markers for breeding programs will particularly benefit from identifying polymorphisms associated with gene coding regions (Rowley et al., 2014).

The American hazelnut (Corylus americana) serves as the native host for A. anomala and, despite its small, thick-shelled nuts, holds significant promise as a valuable resource for EFB resistance and adaptation to different climates. Scientists have been studying interspecific hybrids (Corylus americana and C. avellana) for almost a century, seeking to merge EFB resistance with broader adaptability and larger nuts (Revord et al., 2020).

13.14 Almond

13.14.1 Genetic Diversity

Long ago, humans introduced the almond tree to regions bordering the Mediterranean, extending its presence to North Africa, Southern Europe, and other global locations, with California being a prominent example. In India, almond cultivation is primarily limited to hilly states like J&K, HP, and UK. Despite its significant value as a nut crop, the commercial cultivation of almonds is not widely practiced Figure 13.7. This limited adoption can be attributed to the scarcity of suitable almond genotypes. Most plantations consist of chance seedling selections, whose genetic background or origin remains unknown, thus posing obstacles to breeding endeavors aimed at developing genetically improved varieties.

Figure 13.7 Almond varieties grown in India.⏎

Almond (Prunus dulcis Mill.) is grown primarily for its nuts and has a long history of domestication, making it one of the earliest cultivated plants. Its self-incompatibility system, which is genetically controlled, contributes to a high level of genetic diversity in the species. To assess this diversity, various marker techniques such as morphological characteristics, isoenzyme detection, and molecular markers have been utilized, aiding in estimation and study (Szikriszt et al., 2011). Almond cultivation in India is primarily focused in the hilly regions of J&K, HP, and UK. Among these areas, Kashmir holds the special status of being the country’s almond heartland. The dry fruits from the Kashmir valley, especially almonds, have gained global recognition and are exported to various parts of the world (Hajam et al., 2022). Around 430 species are spread across the northern temperate regions on a global scale. The almond tree and its related species are originally from the Mediterranean climate region in the Middle East, which includes countries such as Turkey, Pakistan, and Syria. Almonds have a rich history and are considered among the earliest fruit trees cultivated in both Asian and European territories, with records of cultivation dating back to approximately 2000 B.C. Prunus dulcis (Almond) is a remarkably nutritious nut crop. Due to a genetically controlled self-incompatibility system, almonds demonstrate considerable genetic diversity, which can be evaluated using various morphological characteristics, molecular markers, and isoenzymes, employing an extensive range of marker techniques. Among the DNA based molecular markers, the SSR techniques, involving RFLP or SNP, are the most widely utilized methods (Sana et al., 2021).

It is notable for being the foremost global tree nut crop in production and is remarkable as one of the most genetically varied types of fruit. Moreover, it has a significant function as a nut-bearing crop in the moderate climates of India. It is mainly grown as a rain-fed crop in the Kashmir valley. originating in the Mediterranean region, it is considered one of the ancient trees globally and shares a close evolutionary connection with the peach, likely stemming from a common ancestral species in South Central Asia. The expansion of its cultivation from Central Asia to the Mediterranean region is believed to have been facilitated by the Phoenicians or Greeks (Godini et al., 2005). During the 16th century, Persian settlers brought saffron to Kashmir, India. Despite its significant potential in the region, the crop did not achieve the same commercial success as apples.

The genetic variation was studied among several almond genotypes, namely CITH-Almond-23, CITH-Almond-22, CITH-Almond-09, CITH-Almond-01, CITH-Almond-15, CITH-Almond-02, CITH-Almond-19, and CITH-Almond-06. These genotypes demonstrated superior nut quality when grown in the northwestern Himalayan region of India. It is suggested that these selected genotypes be propagated and tested in various temperate regions of India to improve productivity. Additionally, they could serve as valuable parent plants in almond breeding programs aimed at developing desirable traits. (Dinesh et al., 2018)

The spread of cultivated almonds took place in three distinct stages: the Asiatic, Mediterranean, and California phases. In the Asiatic phase, almonds were initially domesticated and gradually disseminated across central and southwestern Asia, tracing ancient trade routes. Their distribution covered a vast area from present-day Iran to western China in the east, and extended southeast to India and northern Pakistan. Moving northwestward, almonds spread through Turkey and continued southwest-ward into the uplands and deserts of central Israel and Syria. There is evidence of almonds being mentioned in Hebrew literature as early as 2000 BCE. Today, almond cultivation continues in the Asiatic region, where traditional dryland, subsistence agricultural practices are still used in many areas, resembling the methods employed thousands of years ago (Gradziel et al., 2013).

Almond breeding programs encounter numerous challenges because of the limited genetic diversity present in commercial cultivars. To overcome these limitations, modern plant breeding seeks to utilize native plants as valuable gene pools for crossbreeding. By incorporating traits from wild almond species, which are distributed in the mountains and deserts of Central Asia from western China to Iran and Turkey, new and desirable characteristics can be introduced into commercially grown almond varieties (Rahemi et al., 2012).

Iran serves as a hub for the genetic diversity of almonds, boasting the presence of approximately twenty wild almond species documented in its arid and semi-arid regions (Sorkheh et al., 2009). Iran displays diverse environmental conditions across its different regions. The southern areas experience a subtropical climate, while the north enjoys a temperate climate. The central parts consist of vast deserts. These environmental variations facilitate the presence and distribution of various wild species, like almonds. Notably, the Zagros region in Iran, comprising both mountainous and plain sub-regions within different ecological zones, relies heavily on wild almond germplasm as a predominant plant species. In these areas, where the annual precipitation exceeds 100 mm, wild almonds flourish and contribute significantly to the ecosystem (Sabeti et al., 1994).

In the North West Himalayan region of India, 23 indigenous almond (Prunus amygdalus) genotypes were studied, namely CITH-Almond-01, CITH-Almond-02, CITH-Almond-04, CITH-Almond-6, CITH-Almond-8, CITH-Almond-09, CITH-Almond-15, CITH-Almond-19, CITH-Almond-21, CITH-Almond-22, and CITH-Almond-23. The research revealed that these selected almond genotypes exhibited significant genetic diversity concerning the chosen horticultural traits (Dinesh et al., 2018).

13.15 Breeding Challenges

The successful adaptation of almond to anticipated future warmer climates will rely on the development of climate-resilient varieties capable of completing endodormancy under these changing and more unpredictable conditions. A significant obstacle in breeding such varieties lies in effectively identifying and selecting superior seedlings from extensive breeding populations. To tackle this challenge, advanced techniques like genomics, transcriptomics, and epigenetics offer valuable tools to enhance breeding strategies. These methods prove especially beneficial when evaluating complex traits such as endodormancy and ecodormancy, which may be costly or time-consuming through traditional means.

Late flowering and self-compatibility have been enabling profitable almond cultivation in colder regions. As a result, new extra-late flowering cultivars have expanded the boundaries of almond cultivation even into extremely cold areas that were previously unsuitable for almond farming.

One crucial aspect that breeders are focusing on in the development of these new cultivars is early maturation. The ability to mature early will be an essential trait in adapting to these new environments and ensuring successful almond production.

However, with the expansion of almond cultivation into new territories, a new set of challenges arises, particularly concerning resistance to pests and diseases. As almond trees encounter different environments and climates, breeders must prioritize developing varieties that can withstand and fend off various threats from pests and diseases.

A key goal for the breeders is to optimize production costs and promote environmentally-friendly agriculture practices. This approach not only benefits the almond industry financially but also contributes to a healthier environment and the production of more wholesome almonds.

The soaring demand for almonds has led to the convergence of prices across different cultivars. In this highly competitive market, productivity emerges as the primary trait that breeders emphasize above all other characteristics. A high-yield almond cultivar, capable of producing more than 2000 kg of kernel per hectare, holds immense value and significance for the industry.

As the almond cultivation landscape evolves and expands into colder areas, the development of new cultivars with early maturation, disease resistance, and high productivity becomes critical to meet market demands and sustain the almond industry’s growth.

Presently, almond commercial cultivars cultivated worldwide exhibit a rather limited genetic diversity, posing a significant obstacle to almond breeding endeavors. Consequently, there is a growing emphasis on incorporating local cultivars and carefully chosen genotypes, potentially carrying unique genes or gene combinations, as a means to augment the genetic variation in almonds (Sorkheh et al., 2007).

13.16 Breeding Achievement

Throughout history, almonds have served as a significant food source for countless years, found in cultivated orchards and even as untamed, wild seedlings. Local farmers in different regions carefully chose the finest wild seedlings to propagate, while natural selection constantly pushed for better adaptation to local conditions, including protection against region-specific diseases and pests. The self-sterile characteristic of almonds ensured an ongoing intermingling of cultivated and wild germplasm, sometimes even encompassing related species (Socias i Company, 2002).

In these areas, natural almonds are collected and consumed, which has led to the discovery and promotion of superior varieties. Many modern almond types found in Asia, the Mediterranean region, and even California can be traced back to carefully chosen seedlings from the past. Over centuries, through numerous clonal propagations, a continuous process of selection has identified and refined sources for numerous well-established cultivars. This selection process has resulted in genetic enhancements, including deletions, point mutations, aneuploidy, and other beneficial factors.

In regions where wild almonds are gathered for consumption, unique variations are identified and deliberately grown. Many contemporary almond varieties in Asia, the Mediterranean region, and more recently in California can be traced back to these well-tested wild seedling choices. Over the course of centuries and through numerous clonal propagations, these widely established cultivars have undergone further refinement, leading to improved clonal sources. Various types of changes, such as genetic alterations (e.g., deletions, point mutations), aneuploidy (as observed by Martínez-Gómez and Gradziel, 2003), chromosomal modifications (such as translocation, as mentioned by Jauregui et al., 2001), and epigenetic shifts (gene activation/silencing, etc.), all undergo the process of selection. However, the specific nature of inheritance is seldom analyze due to the vegetative propagation methods used in subsequent selections.

During the early 1900s, formal efforts were implemented in major regions of plant production to accelerate the process of selective breeding through controlled crosses and genetic manipulations. While these initiatives aimed to improve overall yield and production efficiency, specific breeding goals varied across regions due to differences in environmental conditions, diseases, and pest challenges. At the same Over time, the international almond market has established more stringent criteria for acceptable qualities of almond kernels and shells. Despite challenges such as the considerable size of the plants and a lengthy generational cycle of at least four years, controlled breeding efforts have led to the development of numerous commercially successful varieties in recent years. Note-worthy instances include the French almond types Ferragnes, Ferraduel, and Ferrastar; Californian varieties like Butte, Ruby, Sonora, Padre, and Winters; as well as the Spanish type known as Guara. A comprehensive assessment of localized almond breeding initiatives and their primary goals can be noted by Kester et al., (1996).

In almond breeding, it is essential to account for various external factors, such as environmental interactions, spanning several years to decades. Attributes such as evaluating the time when flowering occurs and the ability of flowers to self-pollinate need to be monitored for a minimum of three years after the seedlings have matured. Because of these limitations, becomes a necessary component within breeding initiatives. The success of a particular almond variety in a specific environment depends heavily on the prevailing environmental conditions, which also shape the breeding objectives and overall sustainability. Additionally, the ability of new almond varieties or designs to withstand changing climatic conditions is closely linked to their winter cold adaptability (Campoy et al., 2011). For rootstocks, their compatibility with various soil conditions is also a critical factor to consider. Eskandari et al., (2009) examined the vegetative and pomological attributes of specific maternal and pollen donor varieties.

13.16.1 Maternal Varieties

13.16.1.1 Azar Or Ah50

This particular type, referred to as Azar or AH50, demonstrates a strong and sizable structure, characterized by gracefully curved branches. It can be easily pruned and has a flowering period that coincides with, or slightly precedes, the Ferragnes variety. The fruit develops on branches that are two to three years old, resulting in a high productivity level. Unlike certain other varieties, it does not follow a biennial bearing pattern, and its kernel-to-fruit ratio falls between 40% and 42%. The occurrence of double kernels is extremely low, ranging from 0% to 2%. Azar or AH50 is well-suited for mechanical harvesting and shows notable resistance to foamy canker. It originated from a past hybridization initiative at the Azar-Shahr Horticulture Research Station.

13.16.1.2 Ferragnes

Ferragnes, which has its roots in France, is known for its rapidly growing tree with erect branches and delayed blossoming. The fruit develops on flower buds found on both spurs and branches that are two years old. It boasts a kernel-to-fruit ratio of around 38% and does not yield double kernels. The fruit it produces is not only flavorful but also well-formed, making it convenient to gather during harvest. Although it may occasionally exhibit some biennial bearing tendencies, such occurrences are relatively infrequent.

13.16.2 Pollen Donor Varieties

13.16.2.1 Yalda (Ne. Plus Ultra)

Yalda, a robust American cultivar, is characterized by its sturdy and adaptable tree that thrives in various climatic conditions. Despite not yielding a surplus of flowers, it has a prolonged flowering period. The incidence of foamy canker in its kernels is relatively mild, occurring in approximately 7%–9% of cases. The kernel-to-fruit ratio stands at 50%, with the fruit being elongated and broad. Yalda’s fruit emerges on branches that are 2–3 years old.

13.16.2.2 Nonpareil

Hailing from America, Nonpareil suffers from bud failure syndrome and is considered a medium-built tree. It exhibits late flowering and offers very high fruit quality. The kernel-to-fruit ratio ranges from 55%–60%, with a thin and appealing kernel shape. Nonpareil performs exceptionally well, ripening its fruit very early, though it is highly susceptible to kernel-consuming pests.

13.16.2.3 Shoukofeh (Ah3)

This type displays a moderately sized posture and has a wide-spreading and open tree structure. It blooms a few days after the Azar variety. Fruits grow on branches that are two to three years old, leading to a kernel-to-fruit ratio of approximately 55%–60%. Occasionally, double kernels are noticed, making up around 2% of the fruit. While the harvesting process can be a bit challenging, it may show some biennial bearing tendencies and is susceptible to foamy canker. Similar to Azar or AH50, it was developed as part of a previous hybridization program at the Azar-shahr Horticulture Research Station.

13.16.2.4 Sahand Or L62

Sahand, also known as L62, is a native cultivar of Iran with a unique growth pattern characterized by fewer branches and sub-branches. This variety can be easily pruned and starts bearing fruits in its third year. The majority of fruit production takes place on spurs. Like Ferragnes, Sahand experiences late flowering and does not exhibit biennial bearing tendencies. However, its kernel-to-fruit ratio is relatively low, typically ranging from approximately 25%–28%. Notably, this cultivar shows a significant occurrence of double kernels, approximately 15%–20%, which contributes to its high productivity.

13.16.2.5 Managga

The Managga variety, originally from Iran, distinguishes itself with its robust form and excellent fruit quality. While it blooms quite early, its delicate fruit is vulnerable to damage during the cold spring in the Azarbaijan province. The kernel-to-fruit ratio for Managga is approximately 50%–55%.

13.16.2.6 A200

Originating from Spain, A200 displays late flowering and a high productivity rate. While its fruit quality is good, the kernel-to-fruit ratio is around 32%. However, the occurrence of double kernels is less than 2%.

13.16.2.7 A230

Another Spanish variety, A230, exhibits late flowering and a remarkable productivity level. The fruit quality is excellent, with a kernel-to-fruit ratio of around 33%. Interestingly, the occurrence of twin kernels is negligible, and the tree itself is very robust.

13.16.3 Almond Breeding Methods

13.16.3.1 Introduction

Almond (Prunus dulcis) an important nut crop, is planted extensively for its edible nuts. The goals of almond breeding are to increase the crop’s productivity, quality, and resistance to disease. Selection, hybridization, polyploidy, mutation, and biotechnological methods are some of the strategies used in breeding.

13.16.3.2 Selection

Identifying individuals who have desirable characteristics and using them as parents for the next generation is the process of selection. In almond breeding, features including high yield, quality, and disease resistance are selected for. Many almond varieties, including the Nonpareil cultivar, known for its higher-quality kernels, have been created through selection.

13.16.3.3 Hybridization

Through a way in order to produce offspring with desirable features, two genetically distinct almond varieties are crossed through hybridization. Embryo rescue, open pollination, and controlled pollination are some of the hybridization methods used in almond breeding. Hybridization has been used to create a number of almond cultivars, including the Carmel cultivar, which is known for its high production and superior kernel quality.

13.16.3.4 Polyploidy

When an organism has more than two sets of chromosomes, it is said to be polyploid. Chemicals like colchicine can be used in almond breeding to create polyploidy. With the increased vigor and production that polyploid plants frequently show, this procedure can be utilized to create new almond cultivars that have desired characteristics. An example of a polyploid cultivar created in almond breeding is the “Texas” almond cultivar.

13.16.3.5 Mutation

Mutation involves inducing changes in the genetic makeup of the plant. Mutation can be induced using chemicals or radiation. In almond breeding, mutation breeding is used to introduce new traits into the crop, such as disease resistance, improved yield, and kernel quality. Several new almond cultivars have been developed using mutation breeding, such as the “Mission” cultivar, which is known for its high yield and disease resistance.

13.16.3.6 Biotechnological Approaches

In biotechnological methods, the genetic makeup of the plant is altered using genetic engineering methods. Using biotechnological methods, almond breeding involves the application of strategies including genetic engineering, gene editing, and RNA interference. Almond cultivars with desirable characteristics, such as disease resistance, increased yield, and superior kernel quality, can be created using these procedures. The “Marcona” cultivar of almonds, which is famous for its premium kernels, was created using biotechnological methods.

13.17 Genetic Diversity

13.17.1 Pecanut

The Punjab government brought pecans from the USA to India in 1937. At the Government Fruit Farm in Palampur, HP, eight cultivars were planted, and this location became a significant source of planting material in the Himalayan region. Presently, pecan nuts are one of the crucial temperate nuts cultivated in India, primarily in J&K and HP. The total cultivation area of pecan nuts is expanding due to their favorable economic returns and their ability to adapt well to the intermediate zone of Jammu. (Rani et al., 2018). In India, pecan cultivation is restricted to mid-hill regions such as HP, J & K, UK, and areas with similar climates in the North-Eastern states and Nigiri hills of TN. The significance of this cultivation lies in the nuts, which have a relatively thin shell, making them easy to crack. Additionally, the kernel boasts high nutritional value, containing over 11%–12% protein, 70% fat, a good amount of phosphoric acid, and a high calorific value. The introduction of pecan nuts to J&K was carried out by the State Horticulture Department from HP. In the Jammu region alone, there are approximately 464.68 hectares of pecan nut plantations, producing about 104.03 metric tonnes in 2015–16. The highest pecan nut cultivation is found in Rajouri district, with an area of 163.0 hectares yielding 62.00 metric tonnes, followed by Poonch, which has 125.0 hectares (Anonymous et al., 2016).

The pecan tree, scientifically known as Carya illinoinensis, holds significant economic importance. This genus belongs to the walnut family called Juglandaceae and encompasses a total of 20 species. The southern USA and northern Mexico together account for over 98% of the global annual pecan production. Pecan trees are diploid (n = 16), long-lasting, and monoecious, indicating that they have separate male and female flowers on the same tree. They primarily undergo cross-pollination due to their heterodichogamy, leading to a high genetic diversity but showing signs of inbreeding depression when self-pollinated. During the 19th century, commercial pecan orchards were established. Among the 13 Carya species native to the USA, pecan stands as one of them. Recognizing the value of this underutilized resource, the was founded in 1984. This repository is dedicated to preserving over 300 pecan cultivars, landraces, and species accessions to safeguard their diversity and characteristics. (Thompson et al., 2012).

Pecan nut holds significant importance as one of the key temperate nuts cultivated in India. Its primary cultivation areas in the country are J&K, as well as HP. The production of pecan nut is expanding, thanks to its favorable economic returns and successful adaptation to the intermediate zone of Jammu. Currently, most pecan nut plantations consist of scattered seedling trees, leading to the production of nuts with varying qualities. However, breeders have capitalized on this variation among the seedlings, selecting superior genotypes with desirable traits over the years (Ravindran et al., 2006).

13.18 Major Breeding Challenges

Pecans encompass a variety of essential horticultural attributes, such as features related to the tree, fruit, and nuts. regarding the tree, these attributes consist of the timing of bud break, fruiting patterns, dichogamy (separate male and female flower maturation), leaf characteristics like size, orientation, color, and retention, the overall structure, size, and shape of the tree, patterns of alternate bearing (yielding in alternating years), precocity (early fruiting), and prolific bearing (abundant fruiting), cluster size, length, and density of fruiting shoots, and the ability to retain fruits on the tree.

Key attributes of nuts include the period when the nuts mature, the characteristics of their outer covering (shell), markings on the shell, size and shape of the nut, color of the kernel, the presence of grooves, plumpness, and oil percentage, as well as the thickness of the shell. Additionally, their suitability for mechanical harvesting, how easily they can be cracked and shelled mechanically, and their capacity for storage are also important factors to consider.

Insect pests such as aphids, bud moth, leaf phylloxera, casebearer, bark beetle, and borers are present. nevertheless, when choosing cultivars, insect resistance is not a primary concern. on the contrary, disease resistance, especially against leaf and fruit scab, holds significant importance in the selection process. Another crucial aspect is resistance to winter injury, as it dictates the suitable geographic regions for cultivating a specific cultivar (Sparks et al., 1992).

Improved pecan varieties offer a range of resistance levels to scab and aphids, and breeding efforts concentrate on creating new cultivars that possess both strong resistance and favorable horticultural qualities (Thompson et al., 2012).

13.18.1 Breeding Achievement

Pecan is a diploid plant with a chromosome count of 16 (n = 16). It relies on wind pollination (anemophilous) and possesses both male and female flowers on the same tree (monoecious) but exhibits an interesting phenomenon known as heterodichogamy, where either male or female flowers mature first. This peculiarity leads to almost complete cross-pollination, resulting in high genetic diversity (heterozygosity). However, if self-pollination occurs, the plant experiences inbreeding depression due to the heterodichogamy trait. The species has naturally evolved to display hybrid vigor, as observed in previous studies (Thompson et al., 2012). Pecan germplasm offers varying degrees of resistance to scab, a common fungal disease. Nonetheless, only a few cultivars have enough resistance to eliminate the need for fungicide applications, and these cultivars often lack other desirable nut quality traits required for commercial cultivation. Moreover, certain esteemed varieties like “Stuart” and “Desirable” are increasingly prone to scab infection (Thompson et al., 1994).

13.19 Pistachio Nut

Iran possesses a diverse collection of pistachio germplasm, resulting in a remarkable variety and quantity of Iranian pistachio cultivars that are unparalleled globally. This genetic diversity plays a vital role in the sustainable utilization and preservation of genetic resources (Mahdavi et al., 2021).

13.20 Concluding Remark And Future Prospects

The current chapter makes an effort to investigate the genetic diversity, breeding difficulties, and breeding successes of temperate nuts such walnuts, hazelnuts, pistachios, pecans, almonds, and chestnuts globally. For ex. Highest genetic diversity of walnut, Almond in Iran, chestnut in China, hazelnut in Turkey, Georgia, and Azerbaijan. Despite being economically viable, nut farming is impeded by several kinds of location-specific limitations for climatic conditions. we have already achieved some kind of good yield, Disease resistance, fruit quality but primary breeding issue is to create a variety that can be cultivated in tropical and subtropical areas also in diff climatic condition and will be beneficial for meeting future demand of nuts.

Keywords

breeding challenges

dioecious

genetic diversity

hybridization

Juglandaceae family

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Chapter 14 Advancement in the Micropropagation of Temperate Nut Crops

JAGVEER SINGH,¹ KULDEEP PANDEY,¹ PRAMOD VERMA,² VISHAL SHARMA,³,* POPAT GAIKWAD,⁴ ANKUSH SHARMA,⁵ and PRABHAT KUMAR¹

¹Department of Fruit Science, College of Horticulture and Forestry, Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

²Department of Fruit Science, College of Horticulture, Dr. Yashwant Singh Parmar University of Horticulture and Forestry, Nauni, Himachal Pradesh, India

³School of Biotechnology, Faculty of Applied Sciences and Biotechnology, Shoolini University of Biotechnology and Management Sciences, Solan, Himachal Pradesh, India

⁴School of Agricultural Biotechnology, Punjab Agricultural University, Ludhiana, Punjab, India

⁵Plant Genome Mapping Laboratory, University of Georgia, Athens, Georgia, USA

* Corresponding author

Abstract

India, being one of the primary centers of origin for nut crops, holds the top position as the world’s leading producer of these crops. The coastal regions within 400 kilometers from the coastline, along with some non-coastal states, contribute significantly to nut production in the country. With strong international cooperation, India envisions a promising future for nut breeding programs, particularly through the application of cutting-edge biotechnology techniques. Remarkable progress has been made in the micropropagation of nut trees in India. Various methods, such as axillary shoot proliferation, adventitious shoot initiation, micrografting, somatic embryogenesis, and meristem tip culture techniques, have been extensively studied over the past three decades, both in India and globally. The successful techniques have now been put into commercial use, and numerous certified nurseries produce micro-grafted and micro-propagated saplings. However, a significant challenge faced by the nut crops industry is the prevalence of viral infections in almost all nut crops. These viruses can be transmitted to subsequent generations, particularly through propagules. In contrast, seeds from virus-infected plants generally do not carry the virus, making sexual progeny usually virus-free, except in cases of new infections. To keep up with the changing demands and advancements in propagation technology, it is recommended to establish modern nut crop orchards using new cultivars and rootstocks. Professional consultants and scientists are actively advising and contributing to this process. The distribution of micro-propagated nut crop production across the globe can quickly change in response to production shifts and technological advancements. This chapter aims to evaluate the present status and progress of micrografting and micropropagation techniques for nut crops. Although specific details regarding methods, challenges, and prospects for nut crops will be extensively discussed, the overall focus remains on the advancements made in this field in India and beyond.

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Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan,and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

14.1 Introduction

Since the late 1970s, micropropagation has played a crucial role in the commercial production of fruit and nut crops. Over the past three decades, extensive research has explored various grafting and tissue culture procedures, such as micropropagation and somatic embryogenesis, leading to the successful commercialization of effective approaches. Currently, authorized nurseries offer commercial grafted and micropropagated plants of walnut, pistachio, and other nut crops. Initially, micropropagation was used primarily for small fruit crops and rootstocks of tree fruits, but with advancements in techniques and experience, its application expanded to various crops. Italy and the USA are among the largest producers of micropropagated temperate zone fruit and nut crops, though the distribution can change rapidly based on demand and technological advancements.

A nut is a specific kind of fruit characterized by a durable or resistant outer shell that safeguards a consumable inner kernel. Although the culinary interpretation encompasses an extensive range of desiccated seeds, from a botanical standpoint, a nut pertains to seeds possessing shells that do not naturally split open. Nuts and seeds are abundant in protein content, akin to that found in meat, fish, and poultry. They are enjoyed in various forms, including raw, roasted, or processed into oil, which is frequently utilized in baking and culinary preparations. Among temperate nut crops produced in India, walnut (Juglans regia) holds significant importance. Other temperate nuts grown in India include the European chestnut (Castania sativa), ornamental horse chestnut (Aesculus indica), and Filbert or European hazelnut (Corylus avellana). These nuts offer various nutritional benefits and play a vital role in combating cardiovascular diseases.

Traditional vegetative propagation methods, such as grafting and cutting, have drawbacks, such as slow multiplication rates and high plant costs. Micropropagation offers a solution by allowing cost-effective production of superior planting material throughout the year, without seasonal limitations. Fruit plants have been micropropagated through axillary shoot proliferation, adventitious shoot initiation, and somatic embryogenesis. Axillary shoot proliferation, producing plants with genotypic and phenotypic fidelity, is widely used in commercial micropropagation of fruit plants. Adventitious shoot initiation, though less desirable due to potential variants, has been explored for certain crops. Somatic embryogenesis has been studied in chestnuts, hazelnuts, and other nut crops, offering potential benefits in propagation.

Tissue culture techniques have been employed to improve various temperate nut crops, including in vitro propagation, organ culture, in vitro mutagenesis, somatic embryogenesis, in vitro shoot tip grafting, and cryo-preservation for long-term storage. The research on these techniques for chestnuts, hazelnuts, pecan nuts, pistachios, and walnuts has led to significant progress in the micropropagation of these nut crops. Organ culture, although less explored, has shown promise for certain nut crops. In vitro mutagenesis has been used to produce tetraploid walnut cultivars, and in vitro shoot tip grafting has been investigated for improving shoot multiplication rates. Micropropagation has revolutionized the commercial production of fruit and nut crops, offering cost-effective and efficient ways to produce high-quality planting material. Advances in tissue culture techniques have significantly contributed to the improvement and propagation of various temperate nut crops, bringing about substantial benefits in their cultivation and nutritional value. This review assesses the current status of micropropagation for fruit crops, highlighting its potential and challenges for specific nut crops.

14.2 Micropropagation Methods

Various methods for in vitro propagation have been used. Out of these, major are micropropagation by proliferation of axillary shoots, initiation of adventitious shoots, and somatic embryogenesis.

14.2.1 Axillary and Terminal Shoot Proliferation

The described technique ensures a higher likelihood of maintaining both the genotypic and phenotypic characteristics consistent with the original clone. Presently, this method is extensively utilized for the commercial micro-propagation of almost all fruit plants.

14.2.2 Adventitious Shoot Regeneration

In vitro propagation from adventitious shoots is often regarded as less desirable due to the possibility of producing plants with variant phenotypic or genotypic characteristics. These adventitious shoots can originate from basal callus or stem tissue when the basal part of a shoot cluster is recultured, as observed in apple (Nasir and Miles, 1981). The occurrence of such shoots is more likely when cytokinin concentrations exceed the optimal levels, as demonstrated with TDZ on apple (Van Nieuwkerk et al., 1986). Frequent subculturing, performed every two weeks with strawberries, stimulates the formation of adventitious buds on leaf margins (R.H. Zimmerman, unpublished data). Additionally, certain crops, like blueberries, exhibit the formation of adventitious shoots on leaves that come into contact with the proliferation medium (Zimmerman and Broome, 1980).

14.2.3 In Vitro Culture of Temperate Nuts

Plant tissue culture is a versatile technique that encompasses various strategies aimed at enhancing different plant species. These strategies can be categorized as follows.

14.2.3.1 In Vitro Propagation

This involves the aseptic culture of plant tissues, leading to the generation of multiple plantlets from a single explant. In vitro propagation enables the production of a huge number of plants with desirable traits.

14.2.3.2 Somatic Embryogenesis

Somatic embryogenesis is the process of inducing somatic cells to form embryos, bypassing the typical reproductive pathway. This technique allows for the production of multiple plantlets from somatic cells, offering a valuable tool for mass propagation.

14.2.3.3 Organ Culture

Organ culture involves excising and culturing plant organs, such as endosperm, ovary, anther, pollen, and embryos, to stimulate their development into complete plants. This technique is useful in generating new plants from specific plant parts.

14.2.3.4 In Vitro Mutagenesis

In vitro mutagenesis is the application of mutagenic agents to plant tissues in a controlled environment. This method induces genetic mutations, which can lead to the development of new varieties with improved characteristics.

14.2.3.5 In Vitro Shoot Tip Grafting

In vitro shoot tip grafting involves the joining of shoot tips from one plant onto the in vitro-cultured shoots of another plant. This technique is used to combine desirable traits from different plant varieties.

14.2.3.6 Cryopreservation For Long-Term Storage

Cryopreservation is the process of preserving plant tissues or cells at ultra-low temperatures. This method allows for the long-term storage of valuable genetic resources.

In the realm of temperate nut crops, various co-workers have employed plant tissue culture techniques to improve commercially important species. For further details and specific examples, refer to Table 14.1.

Table 14.1 Different Approaches Encompass in vitro Propagation, Somatic Embryogenesis, Organ Culture, in vitro Mutagenesis, in vitro Shoot Tip Grafting, and Cryopreservation for Long-Term Storage Reported by Various Authors ⏎

Sl. No. | Temperate Nuts | Plant Tissue Culture/Micropropogation Method | References
1 | Carya illinoinensis | Micropropagation | Wood (1982)
2 | C. illinoinensis | Somatic embryogenesis, somaclonal variations | Vendrame and Wetzstein (2020)
3 | Castanea spp. | In vitro propagation | Vieitez et al. (1986, 1983); Vieitez and Vieitez (1980)
4 | Castanea spp. | In vitro regeneration | Chevre et al. 1983
5 | Castanea spp. | Callus culture | Vieitez et al. (1978); Jacquiot (1950)
6 | Castanea spp. | STG | Fernandez Lorenzo and Fernandez-Lopez (2005)
7 | Castanea spp. | Micropropagation, micrografting, organogenesis | Merkle et al. (2020)
8 | Corylus spp. | Direct regeneration | Perez et al. (1985); Anderson (1983)
9 | Corylus spp. | Callus culture | Kai et al. (1984)
10 | Corylus spp. | Somatic embryogenesis | Wetzstein et al. (1989); Merkle et al. (1987)
11 | Juglans spp. | Direct and indirect regeneration | Payghamzadeh and Kazemitabar (2011)
12 | Juglans spp. | Somatic embryogenesis | Tulecke et al. (1988); Tulecke and McGranahan (1985)
13 | Juglans spp. | Endosperm culture | Tulecke et al. (1988)
14 | Juglans spp. | Somaclonal variation | Yajima et al. (1997)
15 | Juglans spp. | Callus culture | Cummins and Ashby (1969)
16 | Juglans spp. | Direct and indirect regeneration, somatic embryogenesis, genetic transformation, cryopreservation | Brown et al. (2020)
17 | P. vera L. | Direct regeneration | Tilkat et al. (2013)
18 | P. vera L. rootstock UCB-1 | In vitro shoot tip necrosis | Kermani et al. (2017)
19 | P. vera L | Micropropagation | Delijam et al. (2016)
20 | P. vera L. cv. “Siirt” | In vitro STG | Onay et al. (2003)
21 | P. vera L. | Somatic embryogenesis | Ghadirzadeh-Khorzoghi et al. (2019)
22 | P. vera L. rootstock UCB-1 | Tissue culture propagation | Pour et al. (2019)
23 | P. vera L. rootstock | In vitro propagation | Gabr and Hassanen (2012)
24 | P. vera L. | In vitro selection-salt tolerance | Raoufi et al. (2021)
25 | P. vera L. | Direct shoot organogenesis | Tilkat and Onay (2009)
26 | P. vera L. | In vitro shoot tip grafting | Onay et al. (2016); Marín et al. (2016); Garcia et al. (2012); Can et al. (2006); Onay et al. (2003, 2004a); Abousalim and Mantell (1992)
27 | P. vera L. | Micropropagation, STG, somatic embryogenesis, organogenesis, somaclonal variations, cryopreservation, genetic transformation | Onay et al. (2020)

14.2.4 In Vitro Propagation

Chestnut cuttings have proven to be challenging to root (Vieitez, 1974), which prompted early research to explore tissue culture as an alternative propagation technique. Many studies have been published, primarily using seedling material, to investigate the initiation and maintenance of shoot proliferation. Vieitez et al. (1986) conducted a comprehensive review on chestnut tissue culture, and they were successful in micropropagating mature plants from this refractory species by utilizing stump sprouts as explants (Vieitez et al., 1983).

In their research, Vieitez and Vieitez (1980) encouraged shoot proliferation using 3-month-old seedlings and nodal explants on MS media. After testing various macro- and micro-nutrient basal media, they found Blayde (1966) medium, Heller’s (1953) medium with 1mM NH₄NO₃, and Lepoivre’s (Quoirin and Lepoivre, 1977) medium with 0.1–0.5 mg/l (0.4–2.2 pM) BA to be suitable. However, there were still challenges encountered with mature explants. One of the issues observed was explant browning during the establishment process. To address this problem, explants were soaked in sterile water after surface sterilization and before transfer to the medium. Additionally, rooting in adult material could only be achieved to a limited extent using auxin dips followed by transfer to hormone-free media. Further-more, different cultivars exhibited significant variations in their responses to shoot proliferation and root formation (Jacquiot, 1950; Vieitez and Vieitez, 1980; Chevre et al., 1983; Vieitez et al., 1983). These variations added to the complexity of the micropropagation process for chestnuts. In the case of Hazelnuts, the use of basal explants instead of shoot tips has shown to improve shoot multiplication (Anderson, 1983). Additionally, Perez et al. (1985) found that optimal shoot initiation in Hazelnuts was achieved by growing seedling shoot and cotyledonary node segments on Cheng’s media.

Pecans, native to the southern region of United States and Mexico, have proven to be challenging to grow in vitro with limited success. However, attempts have been made using seedlings to create cultures, and the pre-treatment of seedlings was found to be crucial (Hansen and Lazarte, 1984). Explants from stock plants did not proliferate well, while those from stock plants maintained in a greenhouse with a 16-hour photoperiod exhibited satisfactory proliferation. Nodal explants were promoted to grow shoots using woody plant medium (WPM) (Wood, 1982; Hansen and Lazarte, 1984). In Italy and Spain, a technology for in vitro propagating the rootstock Pistacia integerrima has been developed and is currently being evaluated in the field (Martinelli, 1988). Moreover, progress has been made in the micropropagation of P. atlantica and various cultivars of P. vera. However, after transplantation to soil in a greenhouse, rooted shoots of P. vera cultivars failed to develop successfully (Martinelli, 1988). In their comprehensive review, Payghamzadeh and Kazemitabar (2011) provided a detailed analysis of in vitro propagation techniques for various Juglans species, including walnuts. The review covered a wide range of topics, such as different sterilization techniques employed for explants, most commonly used hormones and culture media for micropropagation, various solidifying agents, and different conditions utilized by researchers in their studies. The authors also explored the use of different sterilizing agents, media concentrations, plant growth hormones combinations, and solidifying agents in the in vitro propagation methods of pistachio, pecan nut, walnut, and chestnut, as extensively reviewed by other researchers (Onay et al., 2020; Merkle et al., 2020; Vendrame and Wetzstein, 2020; Brown et al., 2020). The review provided valuable insights into the state-of-the-art practices and advancements in in vitro propagation techniques for these temperate nut crops.

14.2.5 Somatic Embryogenesis

In chestnuts, callus formation has been successfully achieved using cambial tissue and cotyledons (Jacquiot, 1950; Vieitez et al., 1978). In hazelnuts, Kai et al. (1984) found that IBA at a concentration of 0.1 mg/liter (0.5 pM) was the most preferable for inducing callus, as higher auxin concentrations led to increased callus formation. Merkle et al. (1987) described the development of somatic embryogenesis from pre-mature zygotic embryos, and Wetzstein et al. (1989) demonstrated that a series of media significantly enhanced the rate of embryogenic response. For Juglans spp. (walnuts), early research aimed to initiate roots from callus as a solution to the challenges of rooting cuttings. Jacquiot (1951) noted the absence of callus formation on J. regia (English walnut) explants when employing media devoid of auxins. In contrast, the utilization of White (1963) medium containing naphthaleneacetic acid (NAA) and kinetin led to the generation and maintenance of callus from stem tissue of J. nigra (black walnut), albeit without subsequent differentiation (Cummins and Ashby, 1969). Notably, greater achievements have been attained with the hybrid rootstock “Paradox” (J. hindsii x J. regia). Driver and Kuniyuki (1984) demonstrated that WPM or B-5 media outperformed MS or Cheng (1978) media in various assessments. Additionally, somatic embryogenesis has shown promise in yielding walnut plants, and successful field-grown plants have been produced (Tulecke and McGranahan, 1985).

Furthermore, different authors have thoroughly reviewed somatic embryogenesis approach and regeneration of pecan nut, pistachio, chestnut, and walnut, compiling and covering all the previous reports on these subjects (Onay et al., 2020; Merkle et al., 2020; Vendrame and Wetzstein, 2020; Brown et al., 2020). The reviews provide a comprehensive understanding of the advancements in these important nut crops and their potential applications in tissue culture techniques.

14.2.6 Organ Culture

Organ culture is a plant tissue culture method that involves excising and culturing a specific plant organ on various media to stimulate the development of a complete plant. This technique encompasses various types of organ cultures, such as anther, pollen, endosperm, ovary, and embryo culture. However, when it comes to temperate nut crops, relatively little work has been done on organ culture compared to other tissue culture techniques. In the case of American chestnuts, embryogenic culture initiation has been achieved using immature seeds as explants. Embryogenic cultures of American chestnut were successfully induced on a modified WPM (Lloyd and McCown, 1980). This represents a significant step in the tissue culture of American chestnut and offers potential applications for propagation and conservation. In walnut species, the embryogenic process has been utilized to produce triploid plants (3n = 48) from walnut endosperm. Tulecke et al. (1988) reported successful induction of embryogenic cultures from the endosperm of cultivars like “Payne,” “Early Ehrhardt,” and “Manregian.” In fact, triploids derived from the endosperm of “Manregian” walnuts are currently maintained in the Juglans germplasm collection at the University of California, Davis.

Though organ culture remains relatively less explored in temperate nut crops, the successful induction of embryogenic cultures in both American chestnuts and walnuts represents promising advancements in tissue culture techniques for these valuable nut crops.

14.2.6 In Vitro Mutagenesis

In a study conducted by Yajima et al. (1997), a tetraploid variety of the “Mitsuru” walnut was developed through colchicine treatment. This tetraploid “Mitsuru” walnut was then compared to the diploid “Mitsuru” walnut, and various pollen properties, including size, germination rate, and fertility, were examined. The “Mitsuru” walnut is a cultivar known as the Shinano variety, which was created through a cross between J. regia var. orientis Kitamura (Teuchi walnut) and the Persian walnut (J. regia L.). The use of colchicine treatment led to the development of the tetraploid version of this cultivar, which has twice the number of chromosomes compared to the diploid version.

The examination of pollen properties in the tetraploid and diploid “Mitsuru” walnuts aimed to understand the impact of ploidy on reproductive characteristics. Such studies are essential for gaining insights into the potential advantages and disadvantages of utilizing tetraploid plants in breeding and cultivation programs for improved walnut varieties.

14.2.7 In Vitro Shoot Tip Grafting (Stg)

In the context of European chestnuts, a method encompassing the stepwise micrografting process of in vitro shoot tips sourced from mature trees onto in vitro shoots arising from juvenile plants has yielded enhanced rates of shoot multiplication. Notably, the transfer of elongated scions onto a multiplication medium has yielded a discernible augmentation in shoot multiplication, particularly evident in one of the two mature clones that underwent testing. Regrettably, the application of this micrografting technique did not yield improvements in in vitro rooting outcomes (Fernandez Lorenzo and Fernandez-Lopez, 2005). This method shows promise for enhancing shoot multiplication in certain mature clones of European chestnuts. In the realm of pistachio cultivation, micrografting has been the subject of thorough exploration both within and outside the laboratory setting. A multitude of micrografting methodologies have been documented by various researchers, such as Onay et al. (2016), Marín et al. (2016), Garcia et al. (2012), Can et al. (2006), Onay et al. (2003, 2004a) and Abousalim and Mantell (1992). The research on micrografting techniques in pistachios aims to develop efficient methods for propagating and multiplying desirable pistachio varieties, contributing to the improvement of pistachio cultivation practices.

14.3 Applications Of Micropropagation

Indeed, micropropagation techniques for fruit and nut crops have been extensively studied and documented in numerous reviews and original research papers. These techniques encompass various methods such as axillary shoot proliferation, adventitious shoot initiation, somatic embryogenesis, and in vitro grafting, among others. The focus of these studies is often on optimizing the protocols for successful micropropagation, ensuring genotypic and phenotypic fidelity of the propagated plants, and improving the efficiency of the propagation process. While the technical aspects of micropropagation have been well-covered in the literature, the emphasis in recent research has shifted towards exploring the practical applications of these techniques and the outcomes achieved so far. Researchers and horticulturists are keen on understanding how micropropagation can be effectively integrated into large-scale commercial production systems to meet the demands of the fruit and nut industry.

Some key areas of application for micropropagation in fruit and nut crops include:

Rapid Propagation of Elite Cultivars: Micropropagation allows for the rapid multiplication of high-quality plant material with desirable traits, such as improved fruit yield, disease resistance, and better fruit quality. This aids in the commercialization of superior cultivars.

Germplasm Preservation and Conservation: In vitro techniques offer a means to preserve and maintain valuable genetic resources of fruit and nut crops, safeguarding biodiversity and providing a backup against potential losses.

Disease Elimination and Virus-Free Planting Material: Micro-propagation offers the opportunity to produce virus-free planting material, reducing the risk of propagating diseases to subsequent generations and ensuring healthy orchards.

Rootstock Production: Micropropagation facilitates the mass production of uniform and disease-free rootstocks, enabling improved fruit tree performance and graft compatibility.

Crop Improvement Through Genetic Transformation: Advanced biotechnology methods, such as genetic transformation and gene editing, can be applied to improve fruit and nut crops for various agronomic and consumer traits.

The results obtained from these applications are crucial in shaping the adoption and implementation of micropropagation techniques in the fruit and nut industry. By evaluating the success and challenges in real-world scenarios, researchers and practitioners can fine-tune the techniques to maximize their practical benefits and support sustainable agricultural practices. The continuous exploration of micropropagation applications paves the way for improved crop productivity, enhanced fruit quality, and greater resilience in the face of changing agricultural challenges.

14.3.1 Walnut (Juglans SPP.)

In recent times, new micropropagation techniques for walnut under protected conditions have shown promising results in various studies worldwide. Two such techniques are the hot callusing method and epicotyl grafting, which have been demonstrated to be highly effective in producing healthy walnut plants. Erdogan (2006) reported an average graft take success rate of 82% and significantly increased mass multiplication of walnut, yielding up to 20,000 plants in a year using the hot callusing cable technique. This method involves applying controlled heat to facilitate callus formation, which is crucial for successful grafting. Gandev (2009) explored the propagation of walnut under controlled temperature conditions using omega bench grafting, hot callus, and epicotyl grafting methods. Among these techniques, epicotyl grafting demonstrated the highest graft-take success rate of 77.5%, followed closely by the hot callus method with a graft success rate of 74.20%. The controlled temperature of 27°C proved to be conducive to callus formation and successful grafting. Soleimani et al. (2010) studied different grafting techniques for walnut (J. regia L.) and found that the modified hot callusing cable (MHCC) system with the saddle method of grafting achieved the highest grafting success rate of 87.52%, along with the lowest loss rate of 13.4%. This indicates the effectiveness of the MHCC system in promoting successful grafting outcomes.

In another study by Gandev and Arnaudov (2011), they investigated the impact of the timing of grafting on the percentage of grafting success in walnut propagation using epicotyl grafting under protected conditions. Grafting performed at the end of March resulted in higher graft take-success compared to grafting done at the end of April. They concluded that the epicotyl grafting method under protected conditions is not only successful in propagating walnut trees but also holds potential for commercial applications. Overall, these recent advancements in micropropagation techniques for walnut under protected conditions have shown remarkable success rates and hold promise for enhancing walnut cultivation and production practices on a larger scale. These techniques offer a reliable means to multiply and propagate walnut trees efficiently and contribute to the sustainable development of the walnut industry.

Recently, the epicotyl grafting technique has been successfully developed in India by Quershi et al. (2014) for walnut nursery plant production in the Kashmir valley region under open field conditions. The study involved grafting at different heights (0, 2, 4, and 6 cm) on rootstocks of various ages (15, 30, and 45 days) using scion wood from different parts of the shoot. The highest graft-take success rate (68.88%) and scion sprouting (41.12%) were achieved at the point of attachment of cotyledons. Moreover, the interaction between the point of attachment of cotyledons and 15-days-old rootstocks resulted in higher scion take (67.70%) and scion sprouting (38.95%) compared to other combinations of treatments.

In contrast, Ladon et al. (2020) conducted a study to assess the feasibility of using epicotyl grafting for walnut propagation in the mid-hills of Himachal Pradesh under protected conditions. Their aim was to reduce the nursery production period from two years to one year. They performed three methods of epicotyl grafting (cleft, wedge, and tongue) on 15, 30, and 45-days-old epicotyls. Among these methods, cleft grafting on 15-days-old epicotyls showed the highest percentage of bud-sprouting (94.66%), followed by wedge grafting with 90% success, resulting in saleable-sized plants within one year. The study recommended using the wedge method of grafting on 15-days-old epicotyls for commercial multiplication of walnut nursery plants within a year under protected conditions. The tissue culture of walnut was reviewed by McGranahan et al. (1987) and has seen significant progress since then. Successful techniques for micropropagation of walnut rootstocks and cultivars have been developed (Driver and Kuniyuki, 1984; McGranahan et al., 1988). Commercial scale production of approximately 20,000 walnut plants per year, including both rootstock (Paradox) and self-rooted cultivars, has been achieved in one laboratory (Driver, personal communication). Trees of the self-rooted cultivars are showing promising signs of precocious fruiting. However, further testing and field performance over a longer period will be necessary to determine their commercial viability. Additionally, walnuts can also be produced through somatic embryogenesis, and field-established plants from this technique have been reported (Tulecke and McGranahan, 1985; Tulecke et al., 1988). However, further evaluation is needed before recommending the widespread use of somatic embryogenesis-derived plants.

Micropropagation is indeed a highly efficient method for propagating plants on a large scale. It allows for the production of healthy and disease-free plants and is particularly useful for multiplying genotypes with desirable characteristics. In the case of J. regia (walnut), various plant parts such as mature embryos, immature cotyledons, nodal segments, ovules, and meristems can be utilized for in vitro propagation (Avıĺes et al., 2009; Vahdati et al., 2004). In the micropropagation process, the number of axillary shoots that emerge from microshoots is found to be highest in dwarf and semi-dwarf cultivars when compared to highly vigorous cultivars. Additionally, there is a positive relationship between the rooting ability of the micropropagated shoots and the cultivar’s vigor. However, there are some challenges associated with micropropagation, including the stabilization of the shoot tips formed during in vitro culture, a decrease in the multiplication rate, difficulty in root proliferation, and low success rates during plant adaptation.

Over the past decade, progress has been made in overcoming some of these challenges, especially in the rooting and acclimatization of various walnut cultivars (Nacheva, 2012). Despite these advancements, micropropagation of walnut is not yet widely adopted for large-scale industrial production of planting material due to the remaining obstacles and uncertainties. As such, additional research and improvements are needed to establish micropropagation as a reliable and commercially viable method for walnut propagation. Physiological and morphological irregularities are commonly observed in plantlets cultivated through traditional tissue culture techniques. However, researchers have identified certain factors that can improve the growth and development of plantlets in vitro. For instance, forced ventilation has been found to be beneficial for the formation of leaf wax and survival of plants in vitro (Zobayed et al., 2001). Natural ventilation has also been shown to improve the majority of growth parameters in Persian walnut (Hassankhah et al., 2014). Sucrose is commonly used as a carbon source in plant culture media, and the concentration of sucrose can significantly impact plantlet health. Hassankhah et al. (2014) found that using 15 g/L sucrose resulted in healthy plantlets, while Vahdati et al. (2004) reported that increasing the sucrose concentration in root induction medium improved rooting.

The mineral composition of the culture medium assumes a pivotal role in shaping morphogenic processes. A notable example is the cultivation of explants on mDKW media, which resulted in the absence of deficiency symptoms and facilitated the development of elongated stems and an increased number of auxiliary buds (Ashrafi et al., 2010). Furthermore, the presence of elevated concentrations of specific minerals, such as Cu and myoinositol, has been demonstrated to exert an influence on the growth rate and the percentage of rooting of explants (Najafian-Ashrafi et al., 2009). Abiotic factors, such as plant hormones, also have a significant impact on micropropagation success. Optimal germination treatments containing 2 mg/L abscisic acid have been shown to result in a 41% transition of embryos into plantlets (Vahdati et al., 2008). Moreover, sucrose has been found to play a role in increasing the number of secondary embryos.

By carefully controlling these environmental and nutritional factors, researchers can enhance the success rate and overall health of plantlets produced through tissue culture techniques, making micropropagation a more reliable method for large-scale plant propagation.

14.3.2 Pecan (Carya Illinoensis)

During the organogenesis process, meristemoids are formed, which are specialized centers with meristematic activity. These meristemoids give rise to unipolar structures, such as shoots or roots, from non-meristematic cell aggregates or plant tissues. Organogenesis is a plant-specific phenomenon and can be induced under specific conditions in tissue culture. In the case of cotyledon segments, Obeidy and Smith (1993) observed that by using a medium containing 50 mM NAA, they could stimulate organogenesis to generate adventitious roots. Furthermore, they successfully induced extensive auxiliary shoot development from the embryonic axis without the occurrence of cotyledon abscission. This achievement was attained through the application of a regeneration medium containing concentrations of 20 and 5 M IBA (indole-3-butyric acid).

In a separate investigation conducted by Payghamzadeh and Kazemitabar (2010), immature pecan embryos were employed as the primary explants for organogenesis experiments. The initial step involved disinfection of the immature fruits, followed by their cultivation on a modified DKW basal medium with the aim of initiating the process of organogenesis. Organogenesis is a valuable technique in plant tissue culture as it allows the production of new shoots or roots from non-meristematic tissues, and it has been successfully applied in various plant species for the propagation and regeneration of plants in vitro. In tissue culture, the development of callus is a common phenomenon that occurs due to the use of phytohormones such as auxins and cytokinins. Callus is an undifferentiated mass of tissue composed of thin-walled parenchyma cells that arise from proliferating cells in the parent tissue. It can be generated from a small percentage of plant tissue by culturing it on modified basal media supplemented with specific concentrations of phytohormones. The combination of 1 mg/L BAP (benzylaminopurine), 0.05 mg/L IBA, and 2 mg/L GA3 (gibberellic acid) in dark culture conditions has been found to induce a high frequency of plantlets in tissue cultures of immature embryos.

Callus cultivation is an important technique in tissue culture and has various applications, including the establishment of clonal populations, plant regeneration, and genetic modification. Both monocotyledonous and dicotyledonous plants can produce callus in response to the presence of specific phytohormones. In the case of pecan (Carya illinoinensis), researchers Rodriguez and Wetzstein (1994) used immature seeds to stimulate embryogenesis. They found that the type and concentration of auxin used influenced the formation of callus, with higher levels of auxins (such as 2,4-D) leading to more callus formation compared to lower levels (such as NAA). Similarly, Payghamzadeh and Kazemitabar (2010) studied organogenesis in pecan using immature seeds as explants. They observed that varying concentrations of BAP and IBA promoted callus development, but the addition of GA3 to the culture medium suppressed callus formation.

Callus development is a crucial step in various tissue culture techniques and plays a significant role in the successful propagation and regeneration of plants in vitro. Somatic embryogenesis is a significant advancement in the field of tissue culture and has found various applications in the industry. It involves the development of embryos from somatic cells, allowing for mass clonal propagation, genetic transformation, and research on embryo development. In the case of pecan (Carya illinoinensis), somatic embryogenesis has opened up possibilities for establishing clonal rootstocks with specific genes of economic importance. These genes may confer traits such as dwarfing for size control, improved nutrient uptake, control of alternate bearing, tolerance to saline conditions, resistance to pests, and growth uniformity.

The study by Merkle et al. (1987) was one of the pioneering works in somatic embryogenesis of pecan. They formed somatic embryos using undeveloped nuts as explants, marking an important milestone in this technique’s application. For successful somatic embryogenesis, the stage of the explant is crucial. Wetzstein et al. (1989) found that collecting immature pecan seeds at 15 weeks after pollination resulted in an embryogenic frequency of 85%, indicating that this stage is optimal for inducing embryogenesis. Rooting of somatic embryos is another critical step for successful plantlet development. For improving rooting in somatic embryos, Wetzstein et al. (1990) used a combination of cold treatment followed by desiccation treatment. The embryogenic response and success of somatic embryogenesis can vary between different pecan cultivars. Yates and Reilly (1990) observed that the embryogenic response differed among eight pecan cultivars and was influenced by the genotype of the plant material.

Somatic embryogenesis in pecan offers immense potential for producing genetically improved and clonally propagated rootstocks with desirable traits, contributing to the advancement of pecan cultivation and breeding practices. Propagation of pecan through in vitro techniques has indeed faced challenges, and success rates have been relatively limited. Experiments using explants from pecan seedlings showed low proliferation rates in culture, as observed in studies by Wood (1982), Phillips and Ramirez (1983), and Hansen and Lazarte (1984). The rooting of shoots proved to be a challenging step, but some plants were successfully transferred to soil in the study by Hansen and Lazarte (1984).

Somatic embryogenesis, reported by Merkle et al. (1987), offered an alternative approach to propagate pecan in vitro. However, achieving a high rate of embryogenic response required a sequence of media, as demonstrated by Wetzstein et al. (1989). Although plantlets were produced from the somatic embryos, their continued growth after transfer to soil was difficult to achieve, suggesting some challenges in acclimatization and establishment in the field. The limited success in in vitro propagation of pecan highlights the complexities and intricacies of this technique for this particular species. Further research and refinement of the culture protocols and acclimatization methods are required to improve the success rates and overall efficiency of pecan micropropagation. Understanding the factors that influence the success of in vitro techniques and optimizing the culture conditions will be crucial for advancing the application of tissue culture in pecan propagation and production.

14.3.3 Almond (Prunus Amygdalus)

In vitro culture of almond has been the subject of several reviews by Rugini (1986b), Kester et al. (1986), and Skirvin (1984). These reviews likely provide comprehensive insights into the techniques and methodologies used for micropropagation of almond. Although limited quantities of almond cultivars have been micropropagated in Italy (E.R.S.O., unpublished data) and California (1. Driver, personal communication), the full-scale results of field trials with these micropropagated cultivars are not yet available. Field trials are essential to assess the performance and adaptability of micropropagated plants in real-world conditions. The use of in vitro culture for almond propagation holds promise for producing a large number of clonal plants with desirable characteristics. However, successful commercial implementation and widespread adoption will depend on the performance of these micropropagated plants under field conditions, including their growth, yield, and overall plant health.

It is likely that ongoing research and field trials will provide valuable insights into the potential of in vitro propagation as a practical and efficient method for almond propagation, and may pave the way for its broader application in almond cultivation.

14.3.4 Pistachio (Pistacia Spp.)

The selection of the right explant is indeed crucial for the success of tissue culture. It ensures that the tissue has the potential to regenerate into a whole plant. Contamination is a significant concern in tissue culture, and using appropriate sterilization methods, such as mercuric chloride or sodium hypochlorite, can help reduce the risk of contamination.

Tissue browning is a common issue encountered during in vitro culture, and it is caused by oxidation of the plant tissues. This can be managed through proper subculturing techniques, which involve transferring the plant material to fresh media regularly to maintain healthy growth and development. Overall, tissue culture and micropropagation are valuable tools for plant propagation and research, but careful attention must be given to explant selection, sterilization, and subculturing to ensure successful outcomes and minimize potential issues. Ongoing research and improvement in techniques will continue to enhance the efficiency and reliability of tissue culture methods for various plant species, including pistachio.

Rooting is indeed a critical phase in the success of micropropagation as it determines the ability of the plantlets to establish and survive in soil after their transfer from in vitro conditions. However, the ability to induce adventitious root formation can vary significantly between herbaceous and woody species. In the case of pistachio (Pistacia vera), successful rooting has been achieved using both in vitro and ex vitro methods. The application of the auxin hormone IBA has been found to be effective in promoting rooting. Different studies have reported varying responses to rooting in pistachio using different concentrations of IBA, ranging from 1 mg/L to 35,000 mg/L, depending on the type of cutting and the growth conditions.

Media composition, particularly the presence of plant growth regulators (PGRs), plays a crucial role in tissue differentiation and growth during micropropagation. The use of meta-topolin (mT), a cytokinin-like PGR, has been shown to be effective in promoting axillary shoot proliferation in vitro in pistachio. Media supplemented with mT and activated charcoal have been found to enhance plantlet elongation during micropropagation. Overall, the rooting phase in pistachio micropropagation requires careful optimization of the media composition, including the type and concentration of PGRs, to achieve successful rooting and acclimatization of the plantlets for their successful establishment in the field. Ongoing research and refinement of these techniques will continue to improve the success rates of micropropagation in pistachio and other woody species.

Light is an important micro-environmental factor that can significantly influence the culture response in in vitro plant growth. The intensity and duration of light exposure can affect various aspects of plant development, including internode and leaf length. Studies have shown that plants grown under moderate light conditions tend to have longer internodes and leaves compared to those grown under intense light conditions. The specific light intensity that provides the best results can vary depending on the plant species and growth conditions. In the case of Pistacia vera seedlings, it was found that a light intensity of 40 mol/m2/s resulted in the most favorable growth outcomes. In terms of micropropagation of Pistacia species, progress has been made in developing techniques for micropropagating the rootstock Pistacia integerrima, as well as P. atlantica and several cultivars of P. vera. However, some challenges have been encountered in the successful transfer of rooted shoots of P. vera cultivars to soil in a greenhouse.

Although some commercial production of pistachio through micropropagation has been reported in Italy, there are limited published details about the specific micropropagation techniques used in commercial laboratories. The commercial application of micropropagation techniques is likely focused on producing rootstocks for pistachio cultivation. Overall, light and other micro-environmental factors play a crucial role in the success of in vitro micropropagation, and ongoing research and development will continue to improve the efficiency and reliability of these techniques for pistachio and other plant species.

14.3.5 Chestnut (Castanea Spp.)

Vieitez and colleagues have made progress in micropropagation techniques for chestnut using explants obtained from mature plants. They have utilized stump sprouts and partially etiolated shoots from the crown of mature trees as sources of explants for successful establishment and proliferation of cultures. It is important to note that tissue culture techniques and research continue to evolve over time, and new developments might have occurred since the last review in 1986. For the latest advancements and details on tissue culture of chestnut, it would be best to refer to more recent and up-todate publications in the field.

14.3.6 Hazelnut

Micropropagation, as described for hazelnuts, is indeed an effective and efficient method for the mass production of genetically similar plants. Compared to traditional propagation methods like seed germination or cuttings, micropropagation allows for precise control over the growth conditions and nutrient supply, leading to higher success rates and consistent results. The process involves several key steps, starting with the establishment of aseptic cultures, followed by shoot proliferation, root development, and finally, the acclimatization of the plantlets to field conditions. The growth media used in micropropagation provides essential nutrients, carbohydrates, and plant growth hormones necessary for the growth and development of the hazelnut plantlets. The success of micropropagation relies on various factors, including the condition of the explants (source of the shoots), the specific hormones and substances used in the growth media, and the overall culture conditions. Researchers have found that shoots taken in the spring from dormant plants tend to perform well in large-scale multiplication. Additionally, the proportion and type of plant growth hormones used in the artificial medium play a crucial role in determining the success rate.

For instance, in one study, treating hazelnut shoots with a specific concentration of IBA for a short duration and using a growth medium with peat pellets resulted in an impressive 97% success rate within just three months. Overall, micropropagation offers significant advantages for the propagation of hazelnut plants and has become an important tool for enhancing agricultural practices and producing high-quality, genetically uniform plant populations.

14.3.7 Miscellaneous Nut Crops

Indeed, micropropagation techniques have been developed for several other nut crops as well, and seedling material is often used as the source of explants in these methods. Researchers have explored the potential of micropropagation for various nut crop species to achieve mass propagation and genetic uniformity. For filbert (hazelnut, Corylus avellana), around 2,000 plants were produced in Italy in 1988 using micropropagation techniques. These plants were likely intended for field trials to assess their performance and adaptability under different environmental conditions.

Micropropagation offers numerous advantages for nut crop propagation, such as the ability to produce a large number of genetically identical plants, disease-free propagation, and the potential to select and propagate desirable traits. It has become an important tool in modern agriculture for enhancing crop production, improving cultivars, and maintaining genetic diversity. However, successful implementation of micropropagation requires careful attention to various factors, such as the choice of explants, growth media composition, and environmental conditions during the culture process.

14.4 Perspective

Micropropagation has indeed become a reliable and commercially important technique for propagating fruit and nut crops. Certain crops, like almond and hazelnut, are likely to see continued growth in the use of micropropagated plants in the future. The advantages of increased plant vigor, early and heavy cropping, and the availability of disease-free plants outweigh the slightly higher cost associated with micropropagation. As more experience is gained and techniques are refined, the use of micropropagation is expected to become more widespread across various fruit crops. In the future, micropropagation will be considered as just one of several techniques available for propagating fruit crops, and decisions on its use will be based on a variety of factors, including the specific cultivar or crop being propagated. The adoption of micropropagation will vary among different crops, with small fruit crops likely to see widespread use sooner, followed by some tree fruits and nut crops. Each crop will reach this stage of adoption at different times, depending on the accumulated experience and success in micropropagating that specific crop. Overall, the future of micropropagation in fruit and nut crop propagation looks promising as its benefits become increasingly apparent and its techniques become more refined.

Keywords

in vitro mutagenesis

in vitro propagation

micropropagation

organ culture

shoot tip grafting

somatic embryogenesis

temperate nuts

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Chapter 15 Omics Technology for Elite Temperate Nut Crop Development

GAURAV Y. RAKHONDE,1,* NAMBURI KARUNAKAR REDDY,¹ POOJA PURUSHOTHAM,¹ SHIVANI JHA,² M. L. SUPRIYA,¹ FAROOQKHAN,¹ SHALAKA AHALE,³ and ANANYA DESHKAR⁴

¹ Department of Plant Pathology, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

² Division of Plant Pathology, Indian Agriculture Research Institute, New Delhi, India

³ Department of Plant Pathology, Punjab Agricultural University, Ludhiana, Punjab, India

⁴ Department of Horticulture, University of Agricultural Sciences, GKVK, Bangalore, Karnataka, India

*Corresponding author

Abstract

Various “omics” tactics have emerged as effective technologies in recent for utilization of wild and other neglected species harboring desirable natural allelic diversity. These tactics are vital to advance climate resilient with improved abiotic and biotic tolerance, nutritive with desirable traits. NGS advances have paved a new era of omics. Combination different omics reveals relationship among crop genomes and phenotypes under various physiological and environmental situations. Multi-omics technologies in nut crop breeding research and their integration will provides opportunities in improvement. Possible hurdles to multi-omics integration were gene functions and their networks, with the creation of prospective characteristics for nut crop improvement. Panomics stage permits the usage of complicated omics to build models to predict complex features. Integration of biology and multiomics helps in understanding of molecular regulator for crop development. Use of “phenotype to genotype” and “genotype to phenotype” integrate whole omics. Combining multi-omics approaches with modern breeding along with genetic engineering tactics safeguards all-inclusive method to develop nutritive and climate resilient crop to encounter present and future nutritive food in a sustainable and sufficient manner.

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Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

15.1 Introduction

Temperate nuts play a substantial part in global agriculture, contributing to the economy, medicine, and nutrition. They are widely consumed worldwide and have gained importance in the international market (Rather et al., 2023). In the United States, the edible nuts market was valued at US$24 billion in 2020, accounting for a significant portion of the global market. Nuts, which are dry edible fruits or seeds, are rich in fat, protein, fiber, and oil. There are a wide variety of nut crops available, including almonds, pistachios, hazelnuts, walnuts, chestnuts, pecans, and chilgozas. However, the nut sector faces challenges from several biotic and abiotic influences causing significant economic losses (Nazir et al., 2023).

Traditional methods of commercial propagation and genetic enhancement for temperate nuts can be difficult and time-consuming. To address these challenges, temperate nut breeding projects are being developed, particularly those utilizing modern techniques. These tactics possesses great potential for future of nut production and may provide solutions to mitigate the impact of diseases on nut crops (Mirzadi Gohari and Feechan, 2023).

Advancements in the molecular biology, including genetic transformation, CRISPR-Cas9, NGS, high-throughput genotyping, and genomics-based tactics like genomic selection and genome-wide association studies, have paved the way for significant advancements in temperate nut improvement. In past few decades, the breeders in nut crop have effectively utilized these modern techniques to delve into the genetic foundation of desirable traits, leads to innovative nut varieties and rootstocks (Sharma et al., 2023). Challenges such as persistent pests or adaptability to specific environments have been key factors behind rootstock development for nut crops. The utilization of interspecific hybrids as rootstocks has also emphasized the role of genetic diversity in optimizing orchard profitability while addressing site-specific limitations.

The omics technology such as proteomics, transcriptomics and now, metabolomics, are fascinating approaches and employed in plant response to environmental fluctuation, diseases and pests, nutrient deficiencies of temperate nut crops. They can thoroughly analyze a changes at the transcriptional as well as translational levels when utilized in conjunction. Researchers are familiar with transcriptomics or quantitative gene expression profiling along with microarrays, which have been commonly employed. The usage of proteomics was potentially to a lesser extent because of lack of knowledge about genome sequences. The advancement in genome sequencing helped to overcome this to some level. The untargeted characterization of entire metabolites in specified system is the focus of metabolomics, the latest of these approaches.

The progress of innovative crop via genetic and molecular path modification has recognized highly beneficial against several biotic and abiotic stress responses (Muthamilarasan et al., 2019). Understanding functions of various genes is possible by analyzing transcriptome, metabolome, and proteome profiles. Additionally, it aids to identify and quantify transcripts, non-coding RNAs, and paths related to fruit traits like sugar metabolism, maturation, development, shelf life, quality traits, and resistance against physiological along with environmental stresses (Zheng et al., 2021).

Overall, the collaborative omics tactics, including genomics, transcriptomics, metabolomics, and proteomics provide further prospective for genetic amendment through GE tools like CRISPR and RNAi to enhance fruit quality and productivity by speeding up lengthy breeding programme (Mathiazhagan et al., 2021). In a general variety of crop species, GAB (genomics-assisted breeding) is currently extensively used to address higher quality, production and many stress resistances (Wani et al., 2022). Additionally, numerous omics platform employment has been practicing for various fruit enhancements and have the potential in temperate crop development.

15.2 Genomics For Elite Nut Crop Improvement

Genomics has revolutionized crop improvement, including the enhancement of nut crops, by providing powerful tools and techniques. Through genomics technologies, researchers can gain a comprehensive understanding of the genetic composition of nut crops, identify crucial genes of desirable traits, and employ various strategies to develop improved varieties via breeding programs or genetic engineering. The following strategies demonstrate how genomics can contribute to enhancing elite nut crops:

15.2.1 Genomic Sequencing

The first step in genomics is to sequence the genome of the nut crop of interest. This provides a complete blueprint of the plant’s genetic information, including genes, regulatory sequences, and repetitive elements. The genomes of various nut crop species, including almond, walnut, pistachio, and pecan, have undergone sequencing. The accessibility of genomic sequences enables researchers to find genes linked with important traits. Genomic sequencing allows researchers to exploit the genetic diversity within a nut crop species. Understanding the genetic variability is crucial for breeding programs as it helps to identify diverse gene pools used to develop improved varieties with enhanced yield, disease resistance with quality. Genomic sequencing also provides the foundation for genome assembly and annotation, where sequence data is organized and analyzed to identify genes, regulatory elements, and other functional elements. This helps researchers to understand the genetic architecture of nut crops and find candidate genes held responsible for desirable traits. Candidate gene identification allows exploring traits responsible for nut size, yield, flavor, pests and diseases confrontation and environmental adaptation. Once these potential genes have been discovered, researchers will be able to investigate their activities and alter them to promote desired features in nut crops. In walnut breeding, genomic sequencing has been instrumental in identifying genes related to vital traits such as disease resistance, nut quality, and tree architecture. Whole-genome sequencing enables to recognize genes associated with resistance against Colletotrichum gloeosporioides causing walnut anthracnose (Feng et al., 2021). This information can guide breeders in selecting resistant genotypes and developing disease-resistant varieties. Genetic basis of kernel bitterness in peach almonds was explored by studying the genomes of bitter and sweet almond varieties where single gene was accountable (Werner and Creller, 1997). This knowledge allows breeders to select for non-bitter varieties more efficiently, improving the consumer experience. Breeding efforts aided in the understanding the important traits along with genetic diversity of pistachio where genomic sequencing was utilized to investigate genetic variety and structure of cultivated and wild pistachio accessions (Mahdavi et al., 2021). This information helps breeders develop improved varieties by identifying diverse genetic resources and understanding the dealings between different pistachio populations. The genetic basis of commercially relevant cashew including nut production and nut quality was investigated by finding potential genes related with these qualities (Sika et al., 2015). Breeders can employ MAS to hasten progress of high-yielding and superior-quality cashew varieties. The genomic sequencing has proven invaluable in elite nut crop improvement and enable genetic basis of desirable characters. This knowledge empowers breeders to develop improved varieties with enhanced yield, quality, disease resistance, and other important characteristics.

15.2.2 Trait Mapping

Genomic approaches such as GWAS and QTL mapping, help to recognize particular areas in nut crop genome, linked with characters. By correlating genomic variation with phenotypic variation, scientists will pinpoint genetic markers linked to desirable characters, like nut yield and quality and against disease and drought. Such markers will be employed to select and develop improved nut varieties more efficiently.

The initial step in trait mapping is collecting phenotypic data on the traits of interest. For nut crops, it includes traits like yield, nut quality, disease resistance, shell thickness, oil content, and other agronomic or horticultural traits. The phenotypic data is typically collected from a diverse population of nut trees or cultivars. Next, a set of genetic markers, like SSRs and SNPs are developed across genome of nut. These markers serve as signposts in the genome and allow to identify genetic areas accompanying with traits of interest. Phenotypic and genotypic data from the genetic markers are analyzed statistically to see relationship between certain markers and the traits of interest. This step involves constructing a linkage map, which shows the relative locations of genetic markers on the chromosomes of the nut crop species. Linkage mapping helps to recognize areas of genome allied with expression of the target traits. As the linkage map is constructed, QTL analysis is performed to categorize specific genomic areas, or QTLs, allied with targeted traits. QTL investigation involves statistical methods that calculate probability of a genetic marker being accompanying to specific trait. The analysis determines the effect and location of QTLs in the genome. These identified QTLs are further validated in different populations and environments to ensure their consistency and stability. Integration of QTLs from multiple studies or populations helps build a more comprehensive knowledge of genetic control of the targeted traits. By employing trait mapping multiple QTLs were recognized using genetic markers as well as phenotypic data from a diverse almond population. These QTLs were linked with kernel bitterness, architecture, nut size and kernel quality in walnut (Bernard et al., 2020) providing actual events into the genetic control of particular trait tree. This information can guide almond breeders in selecting parental lines with low bitterness and developing non-bitter almond varieties. Similarly, the genetic resistance to Eastern Filbert Blight (EFB) in hazelnuts was developed using trait mapping, employing molecular markers along with phenotypic data from a hazelnut population with varying levels of EFB resistance. The identified QTLs linked with resistance to EFB, provided valuable information for hazelnut breeders working to develop EFB-resistant varieties (Mehlenbacher et al., 2006). Trait mapping, combined with the usage of genetic markers along with phenotypic data, helps to identify genomic areas associated with important traits in elite nut crops. This information assists breeders in development of improved varieties with improved traits, such as reduced bitterness, improved tree architecture, larger nuts, better kernel quality, and increased disease resistance.

15.2.3 Marker-Assisted Selection (Mas)

Once the genetic markers associated with desired traits are identified and employed in MAS. MAS allow breeders to select plants with the desired traits at an early stage, grounded on the presence or absence of specific markers, rather than relying solely on phenotypic evaluations. This accelerates the breeding process by minimizing the time for multiple generations of selection. First, markers accompanying with target traits are identified and developed. Common genetic markers used in MAS include SSRs, SNPs, and InDel markers. Such markers are typically dispersed throughout genome of nut crop. The breeding population or germplasm collection is evaluated for target desirable traits. Phenotypic data is collected to assess the expression of the traits. Simultaneously, the population is genotyped using the developed markers to identify individuals carrying the desired marker alleles linked with the target traits. Statistical methods are applied to analyze the association between the genetic markers and the target traits. This analysis determines the strength of the correlation between specific markers and expression of the desired traits. It helps to identify markers consistently associated with the traits across different environments or populations. Depending on markertrait association analysis, individuals carrying the promising marker alleles associated with the target traits are selected for further breeding. These individuals will exhibit the desired traits, increasing the efficiency of selection compared to traditional phenotypic selection alone. Selected individuals are employed as parents in subsequent breeding cycles to grow new populations or cultivars. The breeding process emphases on retaining promising marker alleles while improving other important traits includes yield, disease resistance and nut quality. The performance of selected individuals is evaluated in multiple environments to validate the effectiveness of MAS in improving the target traits. The breeding process continues with repeated cycles of selection and evaluation. As more data on marker-trait associations and phenotypic performance become available, the accuracy of selection increases, and breeding programs can make more informed decisions in selecting parent trees for subsequent generations. The employment of MAS and SSR markers associated with traits like nut size, kernel percentage and kernel color focused on the usage of MAS for improving pistachio nut quality traits. The selected parent trees with favorable marker alleles, crosses were performed to develop new pistachio populations (Kafkas et al., 2017). The offspring from MAS had significantly improved nut quality traits compared to the control population, demonstrating the effectiveness of MAS in enhancing nut quality in pistachio breeding. Similarly, MAS has been used to select self-compatible almond genotypes based on molecular markers associated with self-compatibility. The selected genotypes were crossed with commercial almond cultivars, resulting in self-compatible progeny. This approach allowed breeders to rapidly introgress self-compatibility into almond cultivars, reducing dependency on manual pollination and increasing almond production efficiency. MAS was employed for disease resistance in walnuts against Xanthomonas arboricola pv. Juglandis. DNA markers associated with resistance were developed and used for MAS. The selected walnuts showed significantly higher resistance to walnut blight compared to non-selected individuals (Preece et al., 2012). This demonstrated the effectiveness of MAS in accelerating advance of walnut cultivars with enhanced disease resistance. MAS can be successfully applied in elite nut crop improvement by using genetic markers associated with desirable traits and breeders can select parent trees with the desired alleles and incorporate those traits more efficiently into new populations or cultivars. MAS enables more targeted and effective breeding, leading to the advance of improved nut crop varieties with enhanced traits like nut quality, disease resistance, self-compatibility, and more.

15.2.4 Functional Genomics

It is a field aims to understand role and gene interaction within an genome. It involves the comprehensive analysis of gene expression, protein function, and regulatory networks to give insights into how genes contribute to various biological processes. In elite nut crop improvement, functional genomics have a vital role in identifying genes associated with important traits, understanding their functions, and accelerating the breeding process. Functional genomics can be employed to enhance elite nut crops by employing flowing approaches like;

Transcriptomics: Transcriptomics involves studying whole set of RNA transcripts shaped by the genome, providing insights into gene expression patterns. Through techniques like RNA-seq (RNA sequencing), researchers can utilize transcriptomes of nut crops during diverse developmental phases, environmental or in specific treatments (Wang et al., 2022). Transcriptomic data can identify differentially expressed genes accompanying traits of interest.

Proteomics: Proteomics focuses on to identify and characterize proteins produced by an organism. By analyzing the entire complement of proteins in nut crops, researchers can identify key proteins involved in important biological processes. Proteomic studies can help unravel the molecular mechanisms underlying traits such as disease resistance, seed development, and stress responses (Baya et al., 2007). Understanding protein functions can guide in progression of choice of candidate genes for further investigation.

Metabolomics: It involves inclusive examination of minor molecules, referred as metabolites, existing in cells or tissues. By profiling the metabolite of nut crops, researchers can gain insights into the metabolic pathways and chemical composition associated with specific traits. Metabolomics studies can identify metabolites linked to nut quality, flavor, aroma, and nutritional value (Lipan et al., 2019). This information can aid in the selection of breeding lines with desirable metabolic profiles.

Gene Function Analysis: Functional genomics techniques allow researchers to investigate the functions of specific genes. This can be done through gene knockout or gene overexpression studies using techniques such as CRISPR-Cas9 or RNAi (Liu et al., 2021). By manipulating the expression of target genes, researchers can assess the effects on nut crop traits and gain a deeper understanding of gene function and regulation.

Regulatory Network Analysis: Functional genomics can unravel the regulatory networks that control important biological processes in nut crops. Through techniques such as transcription factor binding analysis and chromatin immunoprecipitation (ChIP), researchers can identify the regulatory elements and transcription factors that control gene expression (Shi et al., 2022). Understanding these regulatory networks provides insights into molecular mechanisms in trait variation and guide breeding efforts.

Data Integration and Systems Biology: Functional genomics data, including proteomics, transcriptomics and metabolomics, can be integrated through genetic and phenotypic data to construct comprehensive models of nut crop biology. By applying systems biology approaches, researchers can gain a holistic understanding of how genes, proteins, and metabolites interact and contribute to complex traits (Liang et al., 2023). This integrated approach can help identify key genetic targets for breeding and assist in the prediction of trait performance.

15.2.5 Genetic Engineering

It is a powerful means allows modification of an organism’s genetic material to introduce specific traits. In prospective of elite nut crop improvement, genetic engineering techniques can be employed to enhance desirable traits, such as increased yield, improved quality, enhanced nutritional content, disease resistance, or environmental adaptability. Genetic engineering able to enhance elite nut crops that include the following ways;

Gene Introduction: Genetic engineering enables the introduction of specific genes from other organisms into nut crop plants. These genes can encode for desired traits, such as improved pest or disease resistance, increased nutrient content, or improved tolerance to environmental stresses (McGranahan et al., 1988). The introduced genes can come from same species or from other related or unrelated species.

Gene Silencing: Genetic engineering can be employed to silence or suppress expression of specific genes in nut crops. This technique, known as RNA interference (RNAi), involves introducing RNA molecules that target and degrade specific messenger RNAs (mRNAs) of target genes (Wang et al., 2021). Gene silencing can down regulate the expression of genes accountable for undesirable traits or to alter metabolic pathways for desired traits.

Modification of Metabolic Pathways: Genetic engineering techniques can be used to modify the metabolic pathways in nut crops, leads to fluctuations in the production of specific compounds. For example, genes involved in the biosynthesis of specific flavor compounds, antioxidants, or essential nutrients can be manipulated to enhance their production levels or alter their composition, thereby improving the nutritional value or sensory qualities of the nuts (Di Guardo et al., 2021).

Disease and Pest Resistance: Genetic engineering can confer resistance to pests, diseases, and pathogens in nut crops. This is accomplished by incorporating genes encoding insecticidal proteins (e.g., Bacillus thuringiensis toxins) or genes that produce antimicrobial peptides, which enhance the plant’s ability to defend against pathogens. Genetic engineering has ability to improve tolerance to specific pests (Rodriguez et al., 1994) or diseases (Shah et al., 2018) through the modification of genes having role in defense.

Abiotic Stress Tolerance: Nut crops often face challenges from various stresses, such as salinity, drought, extreme temperatures and nutrient deficiencies. Genetic engineering can introduce genes that confer tolerance or resistance to these stresses. For instance, genes accompanying with drought or nutrient utilization introduced to enhance the plant’s ability to withstand adverse conditions (Guney et al., 2021).

The employment of genetic engineering in enhancement of nut crops is subjected to regulatory frameworks and public approval. Extensive testing and risk assessments are typically conducted to confirm the safety of genetically engineered nut crops before they are released for commercial cultivation. Overall, genetic engineering provides a commanding means for targeted modification of nut crop plants, allowing for the introduction or suppression of specific genes to enhance desirable traits. The use of genetic engineering in elite nut crop enhancement offers the potential to speed up the production of new varieties with superior characteristics, higher productivity, and greater resistance to biotic and abiotic challenges.

15.3 Transcriptomics

It is to quantify the transcriptome with a comprehensive set of transcripts in cells and their profusion for a specific development phase or physiological state (Wang et al., 2009). The capability to compare different mRNA aids in examining quantity and quality deviations in gene expression. It has a substantial impact on the study of temperate nut crops and contributes significantly to the understanding of pests and diseases and other abiotic stress impacts, aiding in their improvement. This has substantially improved gene expression in the infection process and expression profiling under an extensive array of in vitro stress conditions. As tissues and fruits mature, there is a great deal of diversity in how genes are expressed (Xie et al., 2013). Based on comparative transcriptome analysis of distinct apple varieties, the anthocyanin concentration of apples, which is allied to their ideal look, is regulated by 34 genes (El-Sharkawy et al., 2015). Though sequence-based methods like Serial Analysis of Gene Expression (SAGE) and other comparable methods are popular with the advancement of NGS, microarrays have historically been the preferred platform for many transcriptome research studies.

GS-FLX, SOLiD, and Genome Analyzer are examples of NGS technologies employed for transcript profiling with the potential to dramatically enhance sequencing throughput at a lower cost. Additionally, they have a lot of benefits over microarrays, such as higher sensitivity with a wider dynamic range. The microarray will deliver gene expression data characterized on the array; sequence-based techniques are likewise impartial with regard to the assessment of gene expression. To create the array for a microarray, wide sequence data is also needed, often a genome sequence. Commentary on the impending doom of microarrays has been drawn to the shortcomings of the array-based method as compared to sequence-based tactics (Ledford et al., 2008). Still, high-throughput sequencing approaches have certain downsides, requiring a skilled bioinformatician to efficiently analyze and interpret the data, which adds considerably to the cost. SOLiD and Genome Analyzer will generate numerous, significantly smaller sequences, which may provide more of a challenge.

15.3.1 Microarrays

Microarrays have played a crucial role in temperate nut crop improvement with gene expression profiling and genomic studies. They have been employed to investigate various aspects of nut crop biology, leading to advancements in breeding, disease resistance, and understanding molecular mechanisms. Microarray technologies have revolutionized high-throughput applications by allowing parallel hybridization of carrier-bound DNA probes (Nowrousian, 2007). The prominent applications of microarrays are gene expression profiling, employed in various biological studies (Breakspear and Momany, 2007). Microarrays have become a well-established platform for investigating gene expression, particularly in the era of genome sequencing. The availability of genomic sequences has provided a valuable resource for designing probes and studying molecular-level interactions and disease processes.

Microarrays have greatly updated to understand of disease processes by enabling gene expression during infection in nut crop during various stress conditions. They have significantly enhanced knowledge of diseases at the molecular level. The microarray gene expression profiling was initially applied in Magnaporthe oryzae, causing rice blast disease. Researchers learned about the pathogen’s gene expression ways during infection by using microarray analysis.

15.3.2 Sage (Serial Analysis Of Gene Expression)

Multiple transcripts can be identified simultaneously using the effective method known as SAGE. This method depends on sequencing, quantification, and matching of 14 bp oligotags to genome sequences or EST databases to see corresponding expressed genes. The current advancements in gene expression investigations in phytopathogens have not utilized up to its full potential of SAGE due to certain challenges. One such challenge is the difficulty in identifying a gene with a 14-bp tag in the absence of a genome sequence. However, current advancement has addressed these limitations, making SAGE and related techniques promising tools for gene expression studies in future (Velculescu et al., 1995) . With the ability to directly count and quantify SAGE tags without the need for a genome sequence and the decreasing cost of sequencing technologies, quantitative comparisons across different cDNA populations have become feasible. As a result, SAGE and similar means are anticipated to have a significant impression on gene expression investigations in phytopathogens moving forward (Velculescu et al., 1995).

Environmental stress tolerance is a complicated attribute regulated by several genes in woody plants. Both transcriptome and proteomic investigations show that the activation of genes and proteins in reply to biotic and abiotic stress is highly overlapping. In temperate nut crop development, SAGE has been useful to know gene expression changes during key developmental stages such as flowering, fruit development, and seed maturation. By profiling the transcriptomes of specific tissues or developmental stages, researchers can identify genes specifically expressed or upregulated during these critical periods. This information helps in unraveling the molecular mechanisms underlying important developmental processes and can guide breeding efforts aimed at improving yield, fruit quality, and other desirable traits.

15.3.3 Expressed Sequence Tags (Ests)

ESTs are short single read sequences obtained through partial sequencing of a large pool of mRNA. It provides a snapshot of the transcriptome during sample collection and offer insights into gene expression patterns. EST sequencing is particularly useful for functionally annotating genome sequences as it provides information on intron and exon boundaries and other features. However, many EST developments in plant pathogen research have been limited in scope, lacking the depth necessary for quantitative gene expression studies. The lack of sequence depth hinders the discovery of unusual transcripts (Bouck and Vision, 2007).

In nut crop research, ESTs have played a crucial role in discovering and characterizing genes accompanied to specific metabolic production with pathways. By analyzing EST data, researchers can identify genes governing biosynthesis of important compounds such as fatty acids, antioxidants, and flavor components. This improves the nutritional value and sensory qualities of nut crops. ESTs have been particularly valuable in identifying genes related to color pathways, impacting chlorophyll breakdown and carotenoid production. Additionally, ESTs have helped in identifying genes accompanying with different stages of fruit softening (Crowhurst et al., 2008). By generating and analyzing EST libraries, researchers can obtain a comprehensive view of active genes in specific contexts, laying molecular basis of significant traits and processes.

15.4 Proteomics

Proteomics provides a complementary approach to understand the protein profile of an organism. The transcriptomics offers a valuable information of global gene expression but lacks comprehensiveness (Zhu et al., 2003). Recent advancements in genome sequencing and cDNA have made mass spectrometry-based proteomics is possible. This technique involves provides mass spectra from proteolyzed protein spots and compared with reference protein dataset.

Mass spectrometry (MS)-based proteomics has revolutionized investigation of fungal proteomes. Procedures such as 2-DE (two-dimensional gel electrophoresis) coupled with MS or gel-free methods like MudPIT (Multidimensional Protein Identification Technology) have empowered researchers about protein composition of fungal phytopathogens. Through these techniques, proteins involved in various aspects such as morphogenesis, host interactions, signaling pathways, and overall protein composition of an organism have been identified.

The kernel pellicle tissues of two high-quality walnut cultivars proteomic investigation were done to identify proteins having role in secondary metabolism playing a vital role in determining nut quality. This underlying the pigmentation control in walnuts (Zaini et al., 2020). A network analysis and transcriptomics was employed to unravel the regulatory mechanisms affecting acid accumulation and citrate content in sweet oranges. These factors significantly influence fruit quality and flavor. By fit in protein interaction networks and gene expression data, the researchers identified key control mechanisms involved in these processes (Huang et al., 2016).

15.4.1 Gel-Free Proteomics In Temperate Nut Crops

Previously, proteins were separated through isoelectric focusing and MS on polyacrylamide gel. However, this method has undergone variations, with many now relying on LC-MS for protein or peptide separation. LC-MS based techniques typically involve protein tryptic digestion, two dimensional LC assortment of peptides with subsequent MS analysis, such as MudPIT (Washburn et al., 2001). While having a genome sequence is ideal to find comprehensive protein, demonstrated that other tactics, such as cross-genome matching, ESTs and novel sequencing can also be utilized. Proteomics has proven effective in aiming for genetic and functional analyses. The 2-DE approach combined with MS is still favored due to its simplicity and compatibility with MS. In recent developments, rutheniumbased fluorescent SYPRO Ruby technique compatible with MS, allowed for multiplexing with other fluorescent dyes to identify post-translational changes (Lopez et al., 2000).

Post-translational modification should be focused more as their role is not clear. It can be challenging to use 2-DE to detect proteins with severe pI values, low molecular weight with less abundance and lower solubility (Celis and Gromov, 1999). Gel free MS based approaches were identified like MudPIT to evaluate proteomes (Washburn et al., 2001). Additionally, the usage of metabolic labelling and isotope tags (such as iCAT, iTRAQ, and SILAC) has made it possible to effectively quantify proteins in the MS-based proteomics. MudPIT, DIGE (2D-difference gel electrophoresis), SILAC (stable isotope labelling by amino acids in cell culture), iTRAQ (Isobaric tag for relative and absolute quantitation), ICAT (isotope coded affinity tags) as well as LOPIT (localization of organelle proteins by isotope tagging) are gel-free protein separation approaches. Using this method, 37 proteins with varying abundances in papaya ripening process were identified and analyzed using MS (Nogueira et al., 2012).

15.5 Metabolomics

The recent technique being employed in functional genomics is metabolomics, employed to identify and quantify untargeted metabolome. Quantitative low-molecular complement metabolites in cell in specific set of physiological conditions is known as the metabolome (Kell et al., 2005). It is common to see metabolomics used in conjunction with functional genomics methods, including as transcriptomics and proteomics. The metabolome and phenotype are closely connected. Further, the gene expression, posttranscriptional with post-translational developments control metabolic changes. The metabolome has a greater impact on phenotype than moreover transcripts or proteins have. Further, modifications to the metabolome frequently have a greater impact than those on transcriptome or proteome (Hollywood et al., 2006). Metabolomics revealed environment impact, like temperature, water availability, nutrient status and metabolism, allowed to identify metabolic pathways intricate in stress and adaptation. A metabolomics examination of peach found a correlation between galactinol, mannitol, and raffinose, with raffinose accumulation was higher in freezing stress (Brizzolara et al., 2018). Naturally, this makes metabolomics appealing to scientists or researcher particularly to one without a genomic sequence. It is accepted that over several decades, a different approach has been practiced for targeted metabolite classes (such as mycotoxins), to monitor or detect a particular metabolite.

15.5.1 Gc-Ms (Gas Chromatography-Mass Spectrometry)

Proteomics provides a complementary approach to understand protein profile of an organism (Zhu et al., 2003). Recent advancements in genome sequencing and cDNA have made mass spectrometry-based proteomics possible. This includes production of mass spectra from proteolyzed protein spots and compare to a reference protein dataset.

15.5.2 Direct Infusion Electrospray-Mass Spectrometry (Esi-Ms)

It enables study of complex compounds without prior chromatographic separation. It involves injecting samples of extracted metabolites directly into MS. The metabolites are ionized using electrospray and the atmospheric pressure chemical ionization, and resulting profiles of ion intensity are used to identify and group the detected ions using multivariate statistical analysis. ESI-MS eliminates the necessity of prior chromatography, which can introduce biases to identify. ESI-MS has certain limitations as it cannot differentiate between chemical isomers with identical masses unless they are first separated. Ion suppression issues may come during ESI, where certain components are ionized to varying degrees, resulting in substantial reduction in observed response when analyzing complex mixtures (Koulman et al., 2007).

15.5.3 Nmr (Nuclear Magnetic Resonance) Based Fingerprinting

The usage of metabolomics began with NMR based fingerprinting in biochemistry (Dunn et al., 2005). As a spectroscopic technique, NMR distinguishes atom-atom bonds in particular, which makes it fundamentally different from the MS-based approaches. NMR requires few samples preparation because it is unbiased and non-destructive. With NMR, high-throughput fingerprinting is also possible, enabling to enhance the sample analysis ability. NMR, in contrast to MS-based techniques, has a severe limitation called sensitivity. NMR is half as sensitive as MS, making it unable to detect low abundance metabolites (Sumner et al., 2003).

NMR spectra of kiwi and peach aqueous extracts of indicate a distinct set of primary metabolites that are nearly common, as well as some chemicals that are distinctive to type of fruit and can may be called “markers” of product. Using 1D and 2D trials, the NMR approach may identify primary and secondary metabolites. NMR methods are crucial to characterize fruit as it provides a thorough metabolic profile of samples, direct structural information about every present metabolite in mixture, along with water state in tissue. NMR based metabolic profiling will be beneficial method for differentiating different fruit kinds, studying nutritional qualities, monitoring fruit development, and determining the best harvesting time (Capitani, 2013).

15.5.4 Other Approaches

LC-MS is frequently applied in metabolomics. The sample preparation is mandatory for LC-MS, which employed when GC-MS is not physible. Still, LC is challenging and necessitates the usage of significant quantities of solvents of MS grade. LC-MS has not been exploited metabolomics study of phytopathogens in temperate nut crops and employed to screen secondary metabolites (Nielsen and Smedsgaard, 2003). Additional evolving technique is mass spectrum imaging (MSI) that offer the community studying of plant pathogens interactions. In a sample, MSI enables in-vivo distribution of molecules. It is possible to ascertain how metabolites are distributed spatially on an infected host (Rubakhin et al., 2005).

15.6 Ionomics

Ionomics is a field, emphases on the ionome, which denotes to overall composition of nutrients and trace elements in biological systems (Satismruti et al., 2013). It involves quantitative assessment of elemental configuration and variation in mineral configuration induced by several physiological responses, genetic alterations and developmental factors involved. Ionomics provides a dynamic tool for investigating gene and gene network activity that characterizes the ionome for physiological and environmental stress (Baxter, 2010).

In ionomics, numerous analytical strategies have been practiced for high throughput profiling of elements in plants, includes inductively coupled plasma-mass/optical emission spectroscopy (ICP-MS/OES), neutron activation analysis (NAA), and X-ray crystallography. The researchers have applied ICP-MS to investigate the leaf and grain ionomes of rice, enabling the preparation of genetic maps, identification of QTLs and exploration of genetic diversity in mineral elements (Pinson et al., 2015). Ionomic profiling examine the nutritional status in various fruits, including apples, oranges, kiwifruit, mangos, and blueberries, highlighting the importance of ionomics research in crop development and responsiveness to abiotic and biotic challenges (Parent et al., 2013).

The combination of ionomics along with other omics disciplines, presents a capable path to recognize potential genes and gene networks associated with enhanced nut crop resilience under stresses (Guo et al., 2017). By combining ionomics with genomics or metabolomics, researchers can understand molecular interactions underlying ionomic responses and their influence on nut crop performance.

15.7 Phenomics

Phenomics involves the inclusive study of phenotypes at an organism-wide level, utilizing high-dimensional phenotypic data. The phenome represents the entirety of a phenotype and is influenced by interactions between the genome (G), environment (E), and management (M) factors (Großkinsky et al., 2018). Specific phenotyping is crucial for gene and QTL mapping to uncover the roles of specific traits in genetic crop plant improvement (Kumari et al., 2015). Automated high-throughput imaging technology enables to identify best germplasm lines. One such technique is red, green, and blue (RGB) imaging, which uses visible light to evaluate canopy and root systems, plant vigor, disease symptoms, and stress responses. This tactic permits for rapid and non-destructive phenotyping of large plant populations. Infrared thermography is another imaging technique employed in phenomics to study stomatal conductance under salt stress. By measuring the infrared radiation emitted by plants provides insights into plant responses to environmental stresses. Additionally, chlorophyll fluorescence imaging helps in examine the efficiency of photosynthesis and plant stress responses (Yang et al., 2021).

Phenotyping procedures are essential for analyzing crops in field conditions and offer valued insights that may not be captured in greenhouse or laboratory settings. In the field, various agronomic traits can be determined using multispectral and hyperspectral method (Rascher and Pieruschka, 2008). The LIFT (laser-induced fluorescence transient) approach assesses the crop photosynthetic efficiency directly in the field and provides vital data that can be exploited in breeding programs. To analyze phenotyping data, several platforms are available, like artificial neural networks (ANNs), support vector machines (SVMs) and principal component analysis. These tools facilitate investigation and complex phenotype interaction datasets (Yang et al., 2009).

Crop Sight, an Internet of Things (IoT)-based technology, was utilized to assess crop phenotyping along with genotype-environment interactions (GxE). The use of high-throughput applications (HTP) with new generation sensors in next generation phenomics gives great promise for enhancing yields, stress tolerance, and future management (Roitsch et al., 2019). Phenomics is vital in crop breeding strategies by integrating with other omics disciplines. This integration allows a comprehensive understanding of the intricate interactions between the phenome, genome, and environmental factors, ultimately benefiting crop management. However, a significant challenge in plant phenomics has been the establishment of effective information systems for the storage and retrieval of phenotyping and trait datasets, enabling their reanalysis to generate novel insights and ideas (Cabrera‐Bosquet et al., 2012).

15.8 Role Multi Omics In Nut Crop Improvement

Single omic technologies have contributed significantly to understand plant biology and management. In past decades, numerous “omics” strategies have evolved as effective tactics for plant systems. A new generation of diverse omics has been made possible by advancements in NGS (Yang et al., 2021). They are certain limitations when it comes to addressing the multifaceted interactions between biotic as well as abiotic factors influencing plants viz., incomplete view of biological system, neglecting epigenetic and post-translational modifications, limited functional annotations, inability to capture dynamic responses and lack of integration and system level understanding (Crandall et al., 2020). Genes, transcripts, proteins, metabolites, and other macro and micro molecules collaborate to perform complex biological functions. The incorporation of omic technologies is necessary to understand of the complex biological interactions occurring in plants. By combining multiomics approaches, a more comprehensive and detailed picture can be obtained regarding the dynamic interplay between plants and their biotic and abiotic environments (Figure 15.1) This multi-omics approach surpasses the limitations of relying solely on a single omic technology, allowing for a deeper exploration of the multifaceted interactions and providing valuable insights into plant responses and adaptations.

Figure 15.1 Multiomics in crop improvement.⏎

15.8.1 Integration Of Genomics And Phenolics

Sequencing technology have undergone significant revision and development during last few decades and high quality reference genome sequence for a variety of crop have been refined and maintained. Re-sequencing of crop accessions based on these reference genomes can yield millions of genetic variations along with functional genes for trait throughout crop domestication and improvement (Wang et al., 2020). Use of high throughput tools like restriction-site associated DNA sequencing (RAD-seq), genotypingby-sequencing (GBS), bulked segregant analysis sequencing (BSA-seq), and specific locus amplified fragment sequencing (SLAF-seq) will help in QTL mapping (Bundo et al., 2022). A GWAS could deconstruct complicated features and find candidate genes with natural variations based on millions of SNPs by combining genetic differences (genotype) and phenotype (Fang et al., 2017).

With standardization and good reproducibility, genotyping accompanying high-throughput phenotyping will yield useful genetic information for complex traits in crop plants (Zhang et al., 2017). This can be achieved by using hyperspectral imaging with UAV (unmanned aerial vehicles) (Yang et al., 2020). The integration of phenotyping techniques with a deep learning platform offers a precise and efficient means of acquiring information related to various stressors. This approach is particularly valuable for perennial nut crops, as continuous phenomic data can facilitate the detection of disease initiation and pest infestations. By utilizing this information, early prediction of impending endemic diseases and pests becomes feasible, enabling proactive measures for effective management.

15.8.2 Integration Of Genomics And Transcriptomics

Genomic data analysis is instrumental in identifying QTLs and candidate genes that are pivotal in triggering defense mechanisms against various pests and diseases. However, merely identifying these genes is insufficient to comprehend the actual interaction. To gain a deeper understanding, gene expression studies conducted at various time intervals after pathogen infection delivers insights into heightened defense response and specific gene responsible for its upregulation. These studies allow us to unravel the molecular mechanisms behind the enhanced defense and genes involved in orchestrating immune response (Khalid et al., 2019).

15.8.3 Combination Of Genomics, Transcriptomics, And Metabolomics

Metabolomics based study genome-wide association (mGWAS) is another excellent supplementary approach for phenotypic trait mapping, often applied in crop improvement (Zhu et al., 2018). Metabolites with its pathways having genetic differences might reveal metabolome diversity and their connection to complex phenotypes for metabolomics-related crop breeding programmes (Chen et al., 2021). Cohesive metabolomics and transcriptomics creates a metabolite gene correlation system to identify candidate genes responsible for metabolic pathways (Wen et al., 2014).

15.8.4 Genomics, Epigenomics, And Transcriptomics Combination

The epigenetic variations primarily rely on environmental factors, including biotic as well as abiotic ones. These environmental cues reprogram the transcriptome and ensure genomic stability, enabling adaptation to ever-changing surroundings. The resulting epigenetic diversity has the capacity to generate novel heritable phenotypes, expanding the pool of genetic along with phenotypic variations. As a result, this offers significant promise for improving agricultural attributes and aiding crop improvement initiatives (Hou and Xiangyuan, 2021). Leveraging epigenetic variations helps to reprogramme transcriptomes to achieve a fine balance among essential agronomic traits. In prospective of crop breeding programs, embracing epigenetic diversity becomes imperative to effectively enhance crop performance and optimize desired traits.

15.8.5 Genomics, Transcriptomics, And Microbiomics Combination

The plant associated microbiome serves as foundation for plant growth and stress resilience, encompassing vital aspects of drought and disease resistance. Within this microbiome, the rhizospheric microorganisms act as intermediary in roots and soil. These microorganisms not only facilitate the absorption of indispensable mineral nutrients by plants but also aid in fortifying plants against pathogen attacks.

The metagenomic analysis combined with the transcriptome profiling offers insights into soil microbiome contributing to higher yield of rice (Zhong et al., 2020). According to metagenomic and meta transcriptomic on various watermelon cultivars, it was indicated that the microbiome closely associated with the fruit could potentially exert significant influence on the carbohydrate metabolism during ripening (Saminathan et al., 2018). So, these kind of integrated omic technology helps us to explicate the influence of microbiome, which are accountable for improving yield and superior fruit quality in nut crops.

15.8.6 Integration Of Transcriptomics And Proteomics

The transcriptomics and proteomics have emerged as valuable tools for investigation at genetic and protein-level responses to both biotic and abiotic stresses. These comprehensive analyses enable a deeper understanding of global deviations occurring in crops to provide insights into various potential mechanisms involved. Transcriptomics and proteomics explore the symbiotic relationship between soybeans and arbuscular mycorrhizal fungi (AMF). This investigation insights on molecular mechanisms of disease resistance (Zhang et al., 2020). Similarly, transcriptomics along with proteomics screening techniques identify small secreted proteins (SSPs) that play a role in regulating rice immunity against rice blast. Transcriptome and proteomic study of temperate nut crops is crucial for unraveling the precise role of AMF in disease resistance. These analyses will enable us to investigate factors such as small SSPs, which are major contributors to the immune response.

15.8.7 Role Of Bioinformatics For Crop Omics Analysis

Bioinformatics plays a vital part in crop omics analysis by providing advanced computational tools and methodologies for processing, analyzing, and interpreting large-scale omics datasets. Some of bioinformatics’ specialized roles in crop omics analysis viz., data management and preprocessing, Data integration, Sequence analysis and annotation, identification of candidate genes and molecular markers and predictive modeling with data visualization.

Bioinformatics have been extensively employed in crop science to analyze multi-omics approaches. The tools utilize diverse software packages and have become increasingly valuable attributable to the remarkable expansion and advancements in omics platforms. These developments have enabled the utilization of multi-dimensional exploration in plant science. The computational things have played a pivotal role by facilitating storage, cataloging, and available data. Moreover, they have provided user-friendly access to databases, making it easier for researchers to retrieve information. As a result, several multi-omics databases and multi omics integration specifically tailored for crop sciences have been developed to support research endeavors in this field. Multi-omics integration is the combining and analyzing data from omics disciplines.

15.8.8 Software And Websites For Multiomics

By integrating these different layers of biological information, investigators gain a more comprehensive and holistic inspection of complex biological systems (Jamil et al., 2020).

In summary, bioinformatics is indispensable in multiomic approaches, providing the computational infrastructure, analytical tools, and expertise providing to gain expressive information from various omics datasets. It enables the integration, analysis, and interpretation of multiomics data, ultimately enhancing our understanding of complex biological process and driving scientific advancements (Table 15.1).

Table 15.1 Multiomics Platforms Tools⏎

Software | Supported Omics Platform | Functionality | Website
IMPaLA (Integrated molecular pathway level analysis) | Proteomics Transcriptomics Metabolomics | Enrichment Pathway analysis | http://impala.molgen.mpg.de/
COBRA (Constraint based reconstruction and analysis) | Transcriptomics Proteomics Metabolomics | Genome modeling | https://opencobra.github.io/cobratoolbox/stable/index.html
KBCommons (Knowledge Base Commons) | Genomics Epigenomics Transcriptomics Proteomics Metabolomics Phenomics | Data organization and retrieval supervision | https://kbcommons.org/
MapMan4 | Transcriptomic Metabolomics Proteomics | Enrichment study Visualization of expression statistics | https://mapman.gabipd.org/
mixOmics | Metagenomics Transcriptomics Proteomics Metabolomics | Data integration Similarity relationship | http://mixomics.org/
VANTED (Visualization and Analysis of Network) | Metagenomics Transcriptomics Metabolomics Proteomics | Metabolic mappings Correlation networks investigation | https://www.cls.unikonstanz.de/software/vanted/ (Not accessible as of [27/06/2025])
Regulomics | Epigenomics Transcriptomics | Data mining, Functional characterization, upstream regulators retrieval, | http://bioinfo.sibs.ac.cn/plantregulomics/ (Not accessible as of [27/06/2025])
PathVisio 3 | Proteomics Transcriptomics Metabolomics | Pathway editor and data interpretation Pathway study | https://pathvisio.org/

15.9 Challenges

The omics have revealed prodigious potential in temperate nut crop improvement. Still, it faces some challenges in their employment. Some of these challenges are discussed below.

15.9.1 Data Analysis and Interpretation

Omics techniques create complex huge data and challenging to analyze and interpret. Effective data analysis methods, including bioinformatics tools and statistical approaches, are vital to have information from omics data to identify relevant patterns, associations, and candidate genes or metabolites.

15.9.2 Integration Of Omics Data

Integrating data from diverse omics approaches can provide a precise understanding of nut crop biology. However, integrating diverse datasets from various omics platforms pose a challenge due to differences in data formats, measurement techniques, and data normalization methods. Developing strategies to effectively integrate and analyze multi-omics data is crucial for harnessing the full potential of omics techniques.

15.9.3 Sample Heterogeneity

Nut crops, like other plant species, can exhibit substantial genetic and phenotypic variation within populations. This heterogeneity can pose challenges in omics studies, as the sampled individuals may possesses different genetic makeup, developmental stages, or responses to environmental conditions. Careful sampling strategies and experimental designs are required to account for and minimize the impact of sample heterogeneity on the interpretation of omics data.

15.9.4 Validation Of Omics Findings

Omics techniques deliver valued understandings into genetic and molecular underlying desirable traits in nut crops. However, the identification of candidate genes, proteins, or metabolites through omics approaches needs to be validated using functional studies, such as genetic transformation, gene editing, or biochemical assays. Validating omics findings helps to establish causal associations between the identified targets and the desired traits, ensuring their utility in breeding programs.

15.9.5 Availability Of Genomic Resources

Omics techniques heavily rely on accessibility of high-quality resources, such as reference genomes and gene annotations, for the target nut crop species. Developing and improving genomic resources for lesser-studied nut crops can be challenging, requiring substantial investment in sequencing technologies, data analysis pipelines, and expert annotations.

15.9.6 Translating Omics Findings Into Breeding Programs

The ultimate goal of employing omics techniques in nut crop improvement is to have improved cultivars with enhanced traits. However, translating the findings from omics studies into practical breeding programs and developing new varieties is a complex process, involves integration with traditional breeding approaches, consideration of regulatory and commercial aspects, and extensive field testing.

Addressing these challenges requires collaborations among researchers, advancements in analytical tools and methodologies, and continued investment in omics research for temperate nut crop improvement. Overcoming these obstacles will unlock the full potential of omics techniques in fasttracking the breeding of improved nut varieties with enhanced productivity, quality, and sustainability.

15.10 Conclusion

In conclusion, omics techniques have emerged as powerful tools in temperate nut crop development. These techniques will revolutionize the genetic and molecular basis of desirable traits mechanism, providing valuable insights into nut crop biology and enables the progress of improved varieties.

Genomic sequencing has allowed to find candidate genes associated with important traits. Transcriptomics has provided a comprehensive gene expression pattern, aiding to identify genes involved in specific developmental processes and stress responses. Proteomics has shed light on the protein profiles and post-translational modifications associated with nut quality, pathogen interactions, and stress responses. Metabolomics has exposed the metabolic pathways and biochemical markers accompanying with flavor, nutritive value, and tolerance to stress in nut crops.

However, the successful employment of omics techniques in nut crop development is not without challenges. Data analysis, integration of multiomics data, sample heterogeneity, validation of findings, availability of genomic resources, and translation of omics findings into breeding programs are some of the challenges that need to be addressed. To overcome these challenges, a continued advancements in analytical tools, bioinformatics, and data integration approaches will be required. Collaborative efforts among researchers, breeders, and industry stakeholders are crucial for successful plan of omics techniques in breeding agendas. By harnessing power of omics, development of improved nut crop with enhanced yield, quality, disease resistance, and adaptableness to environment stresses can be accelerated.

Overall, omics techniques offer marvelous potential opportunities for temperate nut crop improvement, paving for more efficient and targeted breeding strategies that address the demands of the industry, consumers, and sustainable agriculture practices. The ongoing advancements in omics research will continue to contribute to develop resilient, productive, and nutritionally superior nut crops for the benefit of growers and consumers alike.

Keywords

ionomics

metabolomics

nut crop biology

omics technology

phenomics

proteomics

transcriptomics

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Chapter 16 Genetic Manipulation and Genome Editing in Temperate Nut Crops

KULDEEP PANDEY,1,* JAGVEER SINGH,¹ REENA PRUSTY,² RAJNI RAJAN,³ MANISH SRIVASTAV,⁴ and AVDHESH KUMAR¹

¹Department of Fruit Science, CHF, Acharya Narendra Deva University of Agriculture and Technology, Ayodhya, Uttar Pradesh, India

²ICAR-Central Institute of Temperate Horticulture, Srinagar, J&K

³Department of Horticulture, Lovely Professional University, Phagwara, Punjab, India

⁴ICAR–Indian Agricultural Research Institute, New Delhi, India

*Corresponding author

Abstract

Tree nuts are a popular fruit crop grown in temperate climates. They offer a wealth of good fats, excellent sources of plant-based dietary protein and fiber, and other health-promoting nutrients. Improvement of nut crops has always been a time-consuming and challenging task due to its perennial nature, long juvenile phase, high degree of heterozygosity, and so forth. However, problems associated with conventional breeding can be overcome through Genetic manipulation/genetic transformation which provides an alternative and direct delivery of desired characters into targeted genotype. Recent developments have made genetic manipulation possible for plant species that are recalcitrant to tissue culture. These techniques possess broad applicability in the enhancement of tree fruit crops, particularly in the context of tissue culture, which is inherently a complex undertaking. Additionally, the enhancement of nut crop efficiency can be augmented through the application of genome-editing methodologies such as zinc finger nucleases (ZFNs), transcription activatorlike effector nucleases (TALENs), and clustered regulatory interspaced short palindromic repeat (CRISPR)/Cas-based RNA-guided DNA endonucleases. This chapter will explore in detail specific techniques, issues, and potential futures in an effort to examine the current situation and advancement in the field of genetic modification and genome editing for nut crops.

______________________

Temperate Nut Crops: Cultivation, Science, and Innovation, Ab Waheed Wani, Rajni Rajan, and Faheem Ahmad (Eds.)

© 2026 Apple Academic Press, Inc. Co-published with CRC Press (Taylor & Francis)

16.1 Introduction

Tree nuts are a common fruit crop cultivated in temperate climates. They provide a wealth of health benefits, including good fats, excellent sources of plant-based dietary protein, fiber, and other health-promoting nutrients. Traditional breeding limits the genetic improvement of nut crop trees because of its lengthy juvenile duration and costly and time-consuming assessment of horticultural traits in the field. Linkage of undesired genes with beneficial ones has always been the most prominent drawback of conventional breeding. Typically fruit tree breeding takes 20–40 years for the creation of new varieties. This is mostly owing to the time required to backcross desirable selections with existing commercial verities in order to develop a new commercial variety with excellent fruit attributes (Ibáñez et al., 2011)

However, genetic transformation can speed up conventional breeding by quickly introducing desirable genes into selected cultivars. Specifically with tree fruit species that are extremely heterozygous, take a long time to mature, and require a substantial amount of area in hybridization. Beneficial genes might be employed to improve fruit and growth qualities, or they could code for pesticides, diseases, or resistance to insects. Furthermore, majority of varieties commercially being grown deficient in one or two traits, inserting the gene of interest can improve the varieties’ efficiency while preserving its true character (Figure 16.1).

Figure 16.1 Targeted traits via genetic engineering in nut crops. ⏎

Genetic transformation, also known as genetic engineering or transgenic technology, involves the introduction of a single gene or a limited number of genes from a species of foreign origin using recombinant DNA technology. The incorporation of foreign DNA into an organism’s genome can be classified into two main categories: direct approaches, which involve nonbiological systems of transgene integration such as physical and chemical procedures, and indirect methods, which involve biological systems of transformation. Electroporation, lipofection, microinjection, sonication, particle bombardment/biolistic, silicon carbide fiber-mediated gene transfer, and laser microbeam-induced gene transfer represent direct techniques employed in genetic manipulation. In the context of biological gene transformation, the utilization of Agrobacterium, a naturally occurring genetic engineer, is employed. In this process, Agrobacterium undergoes transformation by the utilization of a binary vector (as shown in Figure 16.2), which harbors a transgene within its T-DNA region (Saifi et al., 2020). One of the major drawbacks of Agrobacterium-mediated transformation is that it requires a well-developed in vitro regeneration protocol. However, the regeneration of tree nut crops is always challenged by excessive phenolic exudation postexcision of explants, culture media discolorations, deep-seated microbial contamination; and slow in vitro response of explants. Problems associated with Agrobacterium-mediated transformation can be solved through tissue culture-independent in planta transformation technology. The aforementioned technique has several advantages, particularly its cost-effectiveness, ease of implementation, and ability to yield a significant amount of transformants within a brief timeframe (Pandey et al., 2023; Saifi et al., 2020).

Figure 16.2 T-DNA of binary vector pCAMBIA1302 and pCAMBIA2301. ⏎

In recent times, notable advancements have been achieved in the realm of efficient regeneration systems for perennial fruit and nut crops (Dandekar et al., 1988; Archilletti et al., 1995; Scorza et al., 1994; Corredoira et al., 2004; Hegde et al., 2005; Ramesh et al., 2006; Pandey et al., 2023). Various types of explants have been employed in different nut crops for the purpose of transformation. Nevertheless, it was shown that walnut somatic embryos had the highest rate of transformation (Escobar et al., 2000; Tang et al., 2000). Similarly, that leaf was found suitable explant for almonds (Miguel et al., 1999). The utilization of genome editing tools has facilitated advancements in nut crop improvement, allowing for the deliberate introduction of mutations at specific places. This is achieved by targeting a distinct and specific sequence using a guided nuclease. Various genome editing tools, such as meganucleases, Zinc Finger Nucleases (ZFN), Transcription Activator Effectors (TALENs), and Clustered Regularly Interspaced Short Palindromic Repeats/Cas (CRISPR/Cas), are used to alter the genome by deleting, adding, or silencing any gene within the cell without external interference (Alvarez et al., 2021).

16.2 Genetic Manipulation of Temperate Nut Crops

The English or Persian walnut (Juglans regia L.) (2n = 2x = 32), is considered to be one of the most notable temperate nut crops within the Juglandaceae family which is indigenous to central Asia. The walnut is an excellent dietary source of important fatty acid Omega 3, as well as vitamin E. Additionally, it contains riboflavin, niacin, thiamine, pantothenic acid, vitamin B6, and folate/B9 (Şen et al., 2015). Trees belongs to genus Juglans are monoecious in nature in which male flower (catkin) born separate to female (spike) flower. Flowering in walnut exhibit mix-dichogamy; protandry (male part matures first) and protogyny (female part matures first) which promotes outcrossing. Walnut was the very first temperate nut crop among all the perennials fruit crops which was genetically transformed using Agrobacterium (Dandekar et al., 1988; McGranahan et al., 1988).

The introduction of the S65T synthetic green fluorescent protein (GFP) gene into walnut somatic embryos resulted in the successful development of walnut plants and embryos expressing GFP, exhibiting normal growth and development. The utilization of this marker has the potential to yield substantial reductions in labor, cost, and time within the walnut somatic embryogenesis-based transformation system (Escobar et al., 2000). Rezaei et al. 2021 transformed Somatic embryos of the walnut cultivar “Chandler” with Agrobacterium strain LBA4404 and the plasmid pBI121 containing a BADH gene for salt and drought tolerance. Results revealed regeneration efficiency was 5.5%, and plants transformed with the BADH gene can tolerate osmotic stress levels up to 8% of PEG and salinity up to 200 mM NaCl. Alteration in the walnut genome via introgression of the BADH gene will be useful in breeding varieties for salt and drought-prone. The influence of genotype on genetic transformation is a significant constraint, as demonstrated by Wang et al. (2009) who devised a procedure for Agrobacterium-mediated genetic transformation of “Vlach,” a hybrid of Paradox (Junglans hindsii × Junglans regia). The walnut rootstock is a crucial component in the cultivation of walnut trees. Sheikh et al., 2016 transformed somatic embryos of walnut with fld gene obtained from a cyanobacteria. Transformants expressing specific cyanobacterial protein exhibits greater tolerance to salinity and osmotic stress.

The only Prunus species cultivated for its edible seed (kernel) is almond (Prunus amygdalus Batsch). Almonds originated in mountainous regions of Central and South-West Asia. Self-incompatibility trait of almond is regulated by a multi-allelic codominant S-locus. (Dicenta and García, 1993). Almond is the earliest-blooming deciduous fruit tree in winter/spring. Prune dwarf virus and prunus necrotic ringspot virus are among the most significant viral diseases posing a threat to almond production due to their quick spread throughout the orchard, even with proper management. Genetic manipulation could be one of the most powerful tools for control of viral diseases. The insertion of the CP gene into the genome has the potential to confer resistance to viruses in plants. The almond leaf fragments were subjected to transformation using Agrobacterium tumefaciens strain LBA 4404. The successful integration of neomycin phosphotransferase II and g-glucuronidase genes, which were carried by pBinGUSint, was validated using Southern blot analysis and enzyme activity assays conducted on the transformed explants (Archilletti et al., 1994). Nut crops have been genetically modified using genes either for standardization of transformation protocols (marker genes) or genes against biotic and stresses (Table 16.1).

16.3 Genetic Manipulation Regulations in India

In India, the Ministry of Environment, Forest, and Climate Change (MoEFCC) regulates all GMOs, including GE plants, in accordance with the Environment (Protection) Act of 1986. Guidelines and protocols exist for evaluating the safety of genetically modified commodities. The Food Safety and Standards Authority of India (FSSAI) is responsible for regulating GM commodities under the Food Safety and Standards Act of 2006. The Rules of 1989 have established the notification of six competent authorities (as depicted in Figure 16.3), outlining their organizational structure and delineating their respective roles. The Review Committee on Genetic Manipulation (RCGM) and the Genetic Engineering Appraisal Committee (GEAC) establish several subcommittees and expert groups on a situational basis. The composition of these committees consists of individuals who possess expertise in many disciplines and are employed by public sector organizations. Their job is to formulate and review different guidelines and biosafety data. Central Compliance Committees (CCC) are also set up to keep an eye on GE plants that are controlled and are being tested in confined fields. Figure 16.4 depicts the procedure for requesting approval for restricted field trials and the release of GE plants.

Figure 16.3 The regulatory structure pertaining to genetically engineered or modified (GE/GM) plants in India. ⏎

Figure 16.4 Steps for approval; enclosed trials and open field trials of GE/GM plants. ⏎

16.4 Genome Editing

In the realm of new breeding tools (NBTs), molecular breeding and genome editing technologies have become a form of evolution that closes the gap in traditional breeding and pushes breeding objectives to yet another level in order to accomplish the aforementioned. Various genome editing tools, including mega nucleases, ZFN, TALENs, and CRISPR/Cas, are employed to modify the genome by manipulating genes within a cell without external intervention. These tools enable the deletion, addition, or silencing of specific genes. Compared to RNAi and RNA antisense, which were created to lessen the number of gene transcripts, these genome editing technologies have a variety of advantages. CRISPR/Cas is the third-generation genome editing tool that offers enormous potential value in gene function research, germplasm innovation, and genetic enhancement in plants (Min et al., 2022). With its high efficiency, simplicity of use, versatility in genome editing, and capacity to cleave methylated sites, CRISPR/Cas has recently gained popularity among other genome editing techniques.

16.5 Principle of Crispr/Cas

The discipline of molecular breeding has witnessed a significant transformation in plant breeding due to the advent of genome editing techniques. Genome editing involves the utilization of specific site-directed nucleases (SDNs) to induce double-stranded breaks (DSBs) at predetermined sites within the genome. The main advantage of SDNs is in their ability to selectively induce DNA damage and use biological mechanisms to facilitate the required modifications during the subsequent repair processes. The DSBs are repaired with imprecision by the cellular DNA repair mechanism, leading to the occurrence of insertion and deletion (indels) mutations throughout the gene of interest. These mutations do not involve the addition of any foreign elements into the genome.

The CRISPR DNA fragment is characterized by the presence of brief, discontinuous DNA repeats that are interspersed with short, variable sequences referred to as “spacers.” The discovery of cas genes in the genome of Escherichia coli was initially reported in 1987 by Ishino et al. This finding is significant as cas genes are commonly discovered in close proximity to a CRISPR locus. Subsequently, Jansen et al. (2002) postulated a correlation between CRISPR-associated (cas) genes and the CRISPR locus. The year 2005 witnessed a noteworthy development in our comprehension of the functioning of CRISPR, with the identification of spacers originating from invasive viruses and plasmids serving as a pivotal milestone (Pourcel et al., 2005). This discovery provided a suggestion that CRISPR/Cas could potentially play a role in the adaptive immunity of prokaryotes. Subsequently, the mechanism was derived from the adaptive immunity exhibited by bacteria and archaea in response to viruses and plasmids (Wiedenheft et al., 2012). The CRISPR/Cas9 editing system requires two essential components: the single endonuclease-CAS protein and a synthetic single-guide RNA (sgRNA) (Barrangou et al., 2007). The trans-activating CRISPR RNA (tracrRNA) and the CRISPR RNA (crRNA) are coalesced to generate the single guide RNA (sgRNA). The sgRNA normally consists of a distinct 20-base pair sequence accompanied by a brief DNA sequence, often ranging from 2 to 6 base pairs in length, which is essential for its function and referred to as the “protospacer adjacent motif” (PAM) (Deveau et al., 2008). The single guide RNA (sgRNA) exhibits specificity in identifying and binding to the designated target sequence. Subsequently, the Cas nuclease induces a DSB in the DNA region of interest. The cellular systems responsible for repairing damaged DNA strands are activated upon the production of DSBs. These mechanisms proceed to repair the resulting DSBs using either non-homologous end joining (NHEJ) or high-fidelity homology-directed repair (HDR). The CRISPR/Cas system that is most commonly employed in practical applications consists of an effector nuclease known as Cas9. This particular Cas9 enzyme belongs to class II and type II and is derived from the bacterium Streptococcus pyogenes, as documented by Chylinski et al. (2014). In addition, other advanced Cas9 nucleases, along with additional categories of nucleases including Cas12a (formerly known as Cpf1) (classified as class II and type V) and Cas13 (classified as type VI), have been recently utilized.

16.6 Crispr/Cas Application In Temperate Nut Crops

There has been relatively little documented work on genome editing in temperate nut crops. Accelerating breeding progress hinges on the pivotal accessibility of whole genome sequencing for the specific crop of interest. This breakthrough empowers the development of molecular markers that can be effectively correlated with desired phenotypic traits, substantially streamlining the evaluation process for novel genotypes. Consequently, this transformative approach minimizes the time and resources needed to assess new crop varieties, expediting the breeding cycle significantly. It was conceivable to induce specific mutations into temperate nut crops in order to investigate genetic alterations and add new capabilities. Among temperate nut crops, the CRISPR/Cas genome editing was reported only in two crops, that is walnut and chestnut. Since whole-genome sequencing from walnuts was readily available, it provided a base to conduct the gene editing through CRISPR/Cas. As of right now, the cultivars “Chandler” and “Serr” of Juglans regia and Juglans macrocarpa have entire genome sequences. Whole genome sequencing offers a significant improvement in correctly comprehending the gene/marker repertoire and chromosomal organization from an ordered perspective. In Walnut, only 2 reports regarding CRISPR/Cas were reported, one with pds gene and the other for the WOX gene.

Walnut is a valuable multipurpose plant for its high-value timber and nut production. In 2019, a groundbreaking attempt to apply CRISPR/Cas genome editing to the walnut cultivar Chandler focused on targeting the phytoene desaturase (PDS) gene, as reported by Walawage et al. This gene, responsible for phytoene biosynthesis, plays a crucial role in the production of carotenoids, influencing various essential aspects of the plant’s physiology. Carotenoids not only contribute to plant coloration but also have significant impacts on crucial processes such as photosynthesis, photoprotection, and cell signaling, as documented by Wang and Fu (2016). Within the carotenoid biosynthesis pathway, phytoene desaturase (pds) acts as a pivotal enzyme, following phytoene synthase, to initiate the conversion of phytoene into other essential carotenoids, as highlighted by Foudree et al., (2010) and Koschmieder et al., (2017). This pioneering research opens up promising avenues for enhancing walnut traits through targeted genetic modifications, offering potential benefits to the agricultural and horticultural industries. Herbicides containing norflurazon, which interfere with chloroplast activity and cause a bleached phenotype, can prevent pds (Arias et al., 2006). In their CRISPR study focusing on the pds gene, researchers opted to employ secondary embryos from the walnut cv. Chandler as their experimental subjects. By selecting secondary embryos as the starting material, scientists aimed to harness the power of CRISPR/Cas genome editing to precisely target and modify the pds gene. In this study, the binary vector pDM17.0101.01 was employed to transform 40 small (2–5 mm) white, intact walnut somatic embryos. The successful transformation was verified by cultivating the embryos in a hygromycin-rich medium. Among the six resulting transgenic lines, researchers conducted a comprehensive analysis using both phenotypic observations of developing embryos and sophisticated molecular techniques like PCR and Sanger sequencing. Remarkably, the findings revealed intriguing outcomes from the transformed lines. Approximately 18.5% of germinated embryos exhibited green shoots and displayed phenotypic traits indistinguishable from those of the non-genetically transformed parental line. These transformants retained their original characteristics, implying a minimal impact on the plant’s overall development and morphology. On the other hand, 6.5% of the transformed embryos produced albino shoots, exhibiting a unique and visually distinct trait. Additionally, 7% of the transgenic lines displayed variegated leaves, suggesting a diverse range of phenotyping alterations induced by genetic transformations.

The induction of adventitious roots poses a significant challenge in the propagation and reproduction of perennial woody fruit crops. This intricate biological process involves the formation of roots from tissues other than the primary root, with stems and leaves being the primary sources. This phenomenon can occur spontaneously or in response to diverse stressors, such as injury, flooding, or other environmental stresses (Steffens and Rasmussen, 2016). The ability of plants to undergo somatic developmental plasticity plays a vital role in this context. This remarkable adaptability allows plants to respond and adjust to changing environmental conditions, effectively coping with stressful situations, and even recovering from severe injuries. By exhibiting such flexibility, plants can generate adventitious roots, which, in turn, hold the potential to facilitate propagation and aid in the survival and regeneration of these perennial fruit crops. CRISPR/Cas9-mediated gene editing was done to edit the walnut plants for changes in plant architecture. Immature embryo was used as explants for this experiment. Immature embryos from the fruits of walnut cv. “Zhonglin 6” (ZL6) gathered approximately 8 weeks after pollination was used for the induction of the somatic embryos (Chang et al., 2022). The somatic embryos were used as initial material for the CRISPR study targeting knock out of WUSCHEL-related homeobox 11 (JrWOX11) to study its impact on plant architecture. In the field of plant genetics, WOX proteins play a pivotal role as a family of transcription factors containing homeodomains. These proteins are instrumental in regulating the development of various plant organs by controlling critical processes like cell proliferation and differentiation (Jha et al., 2020). In a recent experiment, researchers employed Agrobacterium-mediated genetic transformation to investigate the functionality of multiplexing CRISPR/Cas9 vectors containing three single-guide RNAs (sgRNAs). These sgRNAs were specifically designed to target the walnut WUSCHEL-related homeobox 11 (WOX11) gene in a model somatic embryo (SE). The primary objective of this study was to understand the potential effects of WOX11 gene deletion on the development of the transformed plants. The results of the transformation revealed that the majority of the genetic changes induced were minor indels, with small insertions or deletions in the DNA sequence. However, significant fragment deletions of 26 nucleotides were also observed in some cases. Out of the transformed plants, only four exhibited successful deletion of the WOX11 gene. Interestingly, these plants demonstrated distinct phenotypic alterations. The reduction in micro-shoot formation, vegetative growth, and adventitious rooting were noticeable effects associated with the deletion of WOX11. These findings shed light on the functional significance of WOX11 in plant development, particularly in micro-shoot formation, vegetative growth, and root development. The study’s outcomes hold promise for enhancing our understanding of the molecular mechanisms governing plant organogenesis, and may pave the way for targeted genetic modifications in crop improvement and horticulture. Pavese et al., (2021) published the first study on the use of the CRISPR/Cas gene editing technology in chestnut. Embryogenic line CI-3 maintained by secondary embryogenesis from zygotic embryo of Castanea Sativa Mill. (European chestnut) was used for this gene editing. They have targeted pds gene whose mutation results in clear visibility of albino plants. Globular and early torpedo-stage somatic embryos were co-cultured with a CRISPR/Cas9 construct for five days in order to target two conserved gene areas of pds. Following that the embryos were cultured on a selection medium containing kanamycin and genotyping through Sanger sequencing resulted in successful gene editing with four kanamycin-resistant embryogenetic lines.

Chestnut proved to be a pioneering nut crop in the realm of CRISPR/Cas applications, where researchers, as reported by Pavese et al. in 2022, achieved successful gene modifications in protoplasts without the use of transgenes. This breakthrough highlighted the potential of CRISPR/Cas technology as a powerful tool for precision genome editing in chestnut and other nut crops. Traditionally, the introduction of CRISPR/Cas into plant genomes was accomplished through techniques like Agrobacterium tumefaciens or particle bombardment. However, these methods have drawbacks, particularly concerning the prolonged activity of the Cas9 enzyme and the guide RNA, which can lead to off-target effects. To address these concerns, researchers have explored an innovative approach using the CRISPR/Cas9 construct in the form of ribonucleoproteins (RNPs). This RNP approach provides a distinct advantage by minimizing or even preventing the stable integration of recombinant DNA. By doing so, the risk of transgene integration is significantly reduced, making it a desirable strategy for precise genetic modifications without the introduction of foreign DNA (Woo et al., 2015). The RNP-based approach is effective because it works on the target site right away without the need to activate the transcription process, and RNPs are quickly degraded after that. Embryogenic calli regenerated from immature seeds of Castanea sativa were used as an explant for the isolation of protoplast. For protoplast transfection capability testing, the plasmid pAVA393 containing the GFP gene using 35SCaMV promoter and the Nos terminator was employed (Ochatt et al., 2005). Pds gene was selected as a reported gene for setting up a transformation prototype using CRISPR/Cas RNP as this is the first-ever application report of genome editing in chestnut without the use of transgene. Both the study provides the protocol and reference for further study and genomic improvement in chestnut.

16.7 Advantages Crispr-Cas9 System

The CRISPR-Cas9 system facilitates a diverse array of modifications to be implemented on the structure and functionality of specific DNA sequences. These modifications encompass the insertion and deletion of genetic material, the replacement of genes, the introduction of new genetic elements, the disruption and stimulation of transcription processes, as well as the alteration of epigenetic patterns in native genes. Furthermore, the utilization of the CRISPR-Cas9 system in conjunction with fluorescence molecules facilitates the visualization of the genome’s structural arrangement, commonly referred to as genome imaging. Consequently, the deduction of gene expression, recombination, and the functionality of a genomic site can be achieved. The CRISPR/Cas9 system possesses the capability to generate comprehensive collections of mutant genomes, which are essential for conducting highthroughput functional genomics studies. Additionally, it enables the simultaneous editing of many genes, a process known as multiplexing (Sattar et al., 2021).

16.8 Challenges of Genome Editing Application in Nut Crops

Despite the fact that genome editing has been developed and used to improve plant immunity and development over the last ten years, there are still numerous challenges to overcome before genome editing systems can be improved. The following six significant barriers typically prevent the use of genome editing in fruit crops:

SgRNA and Cas delivery systems are still inefficient;

The expression of Cas protein derivates and enzyme activity are not fully optimized;

The specificity of genome editing in plants requires improvement;

Time-consuming regeneration process of gene-edited plantlets;

Persistence throughout the gene-edited plant and in subsequent generations;

Transgene dissemination to other plants and mutation reversion via horizontal transfer;

Execution challenges in woody plants and long life cycles;

Genotypic chimerism;

Strict GMO restrictions are all factors to consider;

Another significant challenge, particularly for these polyploid crops, is transgene-free genome editing (Lino et al., 2018).

Many of these hurdles can be effectively managed through meticulous avoidance of incorrect gRNA design, meticulous selection of the most suitable Cas protein variant, refinement of the expression cassette which encompasses a promoter, embracing a remarkably efficient DNA delivery approach, and precision targeting of specific tissue types. The innovative Fast-TrACC-driven meristem induction strategy has achieved successful gene modifications in grape plants without the need for labor-intensive tissue culture. This pioneering technique holds substantial promise as a futuristic solution to the challenges associated with plant gene manipulation. In parallel, the gene gun technology and virus vector delivery techniques continue to showcase their remarkable efficacy and user-friendliness in the realm of gene editing for model plants and herbs, as highlighted by Min et al., (2022) in their study.

16.9 Conclusion

The advancement of NBTs marked by precision, strong selection capabilities, and accelerated breeding, notably exemplified by CRISPR-Cas and its contemporary counterparts such as Base Editors (BE) and Prime Editors (PE), stands as a promising avenue to effectively tackle the growing concerns surrounding global food security. Beyond these innovations, diverse strategies like chimaeras have also emerged, aimed at mitigating the challenges of off-target effects and other constraints associated with NBTs in tree species.

The utilization of CRISPR-mediated tree breeding holds remarkable potential for significantly enhancing agricultural output while minimizing the demands for labor and financial investment. A particularly innovative method involves the incorporation of nanomaterial-based delivery systems into CRISPR/Cas systems. This integration not only facilitates the creation of genetically modified plants devoid of transgene integration but also enables the strategic selection and deployment of these modifications based on the distinctive properties of nano-materials. While CRISPR-mediated gene editing has been explored in a variety of nut crops, such as walnut and chestnut within temperate regions, a myriad of studies has unveiled the versatile utility of CRISPR/Cas targeting a wide spectrum of traits, spanning qualitative and quantitative attributes, as well as conferring biotic and abiotic stress tolerance. Although the successful application of GE has been evident in multiple field crops, its adaptation for tree breeding necessitates a thorough identification of key breeding characteristics, an endeavor best achieved through comprehensive stakeholder consultations.

KEYWORDS

Agrobacterium

CRISPR/Cas systems

genotypic chimerism

novel breeding techniques

plasmid

temperate nut crops

transgenics

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Index

A

Abdomen, 295, 357

Abiotic

challenges, 245, 454, 526

constraints, 272

elements, 377, 379

stress, 111, 187, 247, 265, 436, 538

tolerance, 526

Abscisic acid (ABA), 110, 111, 113, 114, 119, 120, 237, 238, 497

Acarina, 322, 338

Acclimatization, 163, 169, 496, 499, 501, 502

Acetate, 205

Acetylcholine (ACh), 151

Acetylcholinesterase (AChE), 151

Acidity, 347, 381, 385, 387–392, 395–397, 421

Actinobacteria, 203

Adequate irrigation, 367

Adontomerus amygdali, 322

Adult female weevils, 333

Adventitious

roots, 227, 497, 558

shoot initiation, 484, 485, 493

Aflatoxigenic species, 215

Aflatoxin, 206, 207, 214, 215, 319, 421

B1 (AFB1), 206, 207

testing, 214

Aged plants, 262, 274

Aglycone, 134

Agonoscena pistaciae, 348, 349

Agricultural

activities, 22, 110

landscapes, 14

production, 5, 6, 183, 184

sector, 7, 40, 101

Agriculture, 1, 2, 7, 13, 14, 21, 31, 32, 37, 39, 112, 164–166, 175, 176, 178, 181, 183, 199, 216, 218, 377, 392, 398, 464, 503, 518, 543

industry, 1, 2, 39

Agrobacterium, 309, 316, 318, 330, 357, 551–553, 558, 559, 562

tumefaciens, 309, 318, 330, 331, 357, 553, 559

Agroforestry systems, 8, 32

Agronomic

crops, 445

factors, 384, 388, 399

features, 171

measures, 293, 296, 299

practices, 412

Alcidodes porrectirostris, 294

Alkyl phenols, 127, 128, 141, 142, 153

Alkylation, 141

Allelopathic effects, 142

Almond

breeding methods, 468

consumption, 9–12

crops, 317

cultivars, 469, 500, 523

genetic diversity, 460

genotypes, 460, 462, 463, 523

milk, 6, 24, 34, 40

pests, 325

production, 28, 31, 272, 463, 523, 553

seeds, 152

skin polyphenols, 150

Alpha-linolenic acid (ALA), 9

Alternaria sp., 206, 214

alternata, 208

Alternate bearing (AB), 69, 114, 119, 197, 268, 273, 377, 471, 499

Alzheimer’s disease (AD), 151

Ambrosia beetle, 298, 299, 343, 344

Amyelois transitella, 317, 319

Amygdalus, 57, 60, 61, 128, 258, 463, 553

Anacardiaceae family, 142, 272

Anacardium occidentale, 142, 215

Anemophilous species, 83

Antagonistic effects, 111

Anthesis, 54–56, 61, 63, 67, 69, 78–80, 83, 86, 102, 112

Anthocyanidins, 132, 135

Anthocyanin, 127, 133, 135, 380, 382, 383, 385–391, 393–396, 410

Anthracnose, 324, 336, 366, 436, 437, 520

Anti-arthritis, 133

Antibacterial, 142, 152

Anticancer, 26, 132, 133, 137, 138, 142, 144, 150, 225, 247, 382

properties, 137, 138, 150, 382

Anticarcinogenic activities, 141

Anti-diabetic, 133, 247

activities, 151, 225, 410

effects, 133, 135

Antifungal, 142, 152, 207

peptides (AFPs), 207

Anti-inflammation, 129, 132

Anti-inflammatory, 6, 12, 13, 26, 127, 128, 131–134, 137, 138, 141, 144, 149, 150, 216, 382, 410, 422

activity, 149, 150

properties, 6, 26, 131, 132

Antimicrobial

activity, 152

properties, 152

Antioxidant, 4–6, 10–13, 25, 26, 32, 127, 128, 131–135, 137, 138, 141–144, 148, 149, 228, 241, 267, 274, 381, 382, 383, 385, 386, 389–391, 395, 410, 414–418, 421, 422, 526, 529

activity, 135, 142, 143, 149, 386, 389, 391, 414–418, 422

content, 12, 395, 417

defenses, 148, 149

enzymes, 149

properties, 12, 13, 26, 132, 143

Antioxidation, 129, 132

Anti-proliferation, 132

Antiproliferative, 127, 138, 410

Antitumor, 132, 133, 141, 150, 410

Aphalaridae, 348, 349

Aphid, 267, 287, 288, 294, 295, 307, 311, 342, 471, 472

nymphs, 295

Aphididae, 309, 338, 356

Apical

bud dominance, 111, 112, 114, 167, 246, 334

dominance, 111, 114

Apigenin, 130, 134, 139, 140, 201

Apis mellifera, 80

Apoptosis, 133, 134, 150, 152

Apple mosaic virus (ApMV), 264, 287

Aprostocetus bucculentus, 322

Arbuscular mycorrhizal fungi (AMF), 211, 538, 539

Archaea, 198, 199, 215, 556

Archaeological evidence, 15

Armillaria

mellea, 211, 290, 309, 338

root rot, 287, 288, 290, 291, 309, 344, 338

Aromatic

acids, 130

hydrocarbon, 129

ring, 130, 132

Artificial

intelligence (AI), 100, 163–166, 169, 175, 178–181, 185–188

classification, 165

systems, 164–166, 179

work horse, 166

neural networks (ANNs), 163, 164, 169, 187, 535

pollination, 271

selection, 266

Ascomycota, 207, 292, 309, 317, 318, 332, 338, 348, 357

Aseptic cultures, 502

Asexual (clonal)

micropropagation, 242

propagation, 225, 245

Aspergillus, 205–207, 209, 214, 215, 319

ochraceus, 214

species, 214

Atherosclerosis, 138, 146, 148, 153

Atopy, 216

Automated high-throughput imaging, 534

Auxiliary shoot development, 497

Auxin, 98, 111, 112, 114, 117–119, 233, 239, 240, 244, 246, 377, 379, 489, 491, 498, 501

concentrations, 118, 491

cytokinin interactions, 114

protectors, 119

Axillary

buds, 114, 237, 340

meristem (AM), 92, 167, 246

shoot, 237, 486, 496

proliferation, 484, 485, 493, 501

staminate, 92

Azoxystrobin, 290, 324–327, 329

B

Bacillales, 205

Bacillus

atropheus, 199

licheniformis, 200

pumilus, 200

thuringiensis, 319, 342, 343, 445, 526

Bacterial

blight, 263, 287–289, 300, 307, 338

canker, 331

diversity, 216

growth, 152, 416

leaf scorch, 357, 367

pathogens, 319

Bacteroidaceae, 204

Bacteroidales, 205

Bacteroidetes, 203

Banksia, 80

Basal

callus (BC), 167, 486

portions, 119

Base editors (BE), 561

Basidiomycota endophytes, 207

Beauveria bassiana, 294, 312, 333, 340

Benzene rings, 138

Benzyladenine (BA), 110, 113, 114, 117, 119, 244, 274, 489

Benzylaminopurine (BAP), 110, 118, 119, 498

Bifidobacteria, 209, 210

Bifidobacteriaceae, 203, 204

Bifidobacterium spp., 205

Binucleate pollen grains, 83

Bioactive

components, 391, 408

compounds, 6, 10, 11, 33, 153, 163, 381, 382, 384, 396, 408, 409, 411, 414, 416, 417, 422, 423

phytochemicals, 149, 265, 408, 411, 412, 414, 415, 423

Biocontrol agents, 210, 211, 218, 275, 349

Biodiversity, 1, 8, 13, 14, 32, 40, 171, 198, 431, 448, 494

conservation, 13, 14

promotion, 14

Bioecology, 370, 371

Biofertilizers, 218

Bioinformatics, 539

tools, 541

Biological

activities, 128, 132, 133, 141, 382, 408, 409, 411

control, 21, 275, 291, 293–295, 297, 323, 368, 370, 453

information, 539

mechanisms, 555

process, 539, 558

studies, 528

Biomarker, 150

Biomolecules, 149

Bionectriaceae, 292

Bioregulators, 113, 392

Biostimulants, 392

Biotechnological tools, 266

Biotechnology, 167, 200, 398, 484, 494

techniques, 484

Biotic

agents, 370, 371

challenges, 534

components, 377, 378

pollination, 51

stress, 111, 172, 264, 268

tolerance, 517

Bisexual, 61, 65, 78

Black pecan aphid, 357

Black sea region, 75, 298, 338, 456–458

Blackened mush, 310

Blanching, 408, 411, 417, 423, 458

Bleaching, 130, 408, 414

Blister-like swellings, 296

Blood

cholesterol, 148

glucose, 151

sugar, 5, 10, 51

vessels, 9, 382

Body mass index (BMI), 9, 202

Botryosphaeria panicle, 355

Brassinosteroids (BRs), 111

Breast cancer, 133

cells, 138, 150

Breeding, 8, 22, 23, 32, 36, 37, 39, 40, 51, 56, 64, 67, 73, 75, 76, 86, 88–90, 163, 170–173, 231, 242, 258, 259, 261, 264–267, 269, 270, 272, 276, 277, 307, 315, 380, 381, 395, 422, 431–433, 436, 449–455, 457–460, 462–466, 468, 469, 472, 473, 483, 492, 499, 517–520, 522–525, 527, 529, 534, 535, 537, 538, 541–543, 549, 550, 553, 555–557, 561, 562

achievement, 458, 464, 472

challenges, 431, 435, 437, 450, 454, 457, 463, 471, 473

cycles, 522

difficulties, 472

endeavors, 452, 458, 460, 464

methods, 22, 32, 36, 37, 172, 173

objectives, 466, 555

population, 463, 522

process, 23, 37, 450, 522–524

programs, 8, 32, 36, 37, 75, 163, 170, 171, 173, 231, 267, 269, 270, 381, 436, 450, 452, 454, 455, 457, 460, 462, 519, 520, 523, 534, 538, 541, 542

strategies, 36, 463, 535, 543

successes, 472

Bronchitis, 25

Bud, 53, 54, 61–63, 67, 78, 82, 86, 89, 90, 92, 94, 95, 98, 112–114, 227, 231, 232, 235, 237, 241, 273, 294, 310, 314, 333, 334, 336, 339, 340, 342, 344–347, 349, 351, 354, 355, 362, 363, 432, 440, 441, 466, 486, 497

break, 61, 84, 113, 114, 119, 353, 471

dormancy, 78, 111

drop, 349

Bugs, 273, 287, 288, 297, 298, 307, 329, 342, 343, 348, 367

Bulked segregant analysis sequencing (BSA-seq), 536

Burkett, 144, 214

Butyrate, 204, 205

C

Caffeic acid (CA), 130, 131, 139, 140, 418

Callaphis juglandis, 294

Callus, 117, 229, 235, 236

growth, 117

Campesterol, 139, 140, 144, 145, 413

Cancer, 5, 10, 12, 26, 128, 129, 133, 135, 137, 138, 141, 143, 144, 146, 149, 150, 153, 203, 225, 228, 247, 319, 382, 409, 410

cell growth, 133, 137

Candida species, 152

Candidate genes, 200, 520, 524, 536, 537, 539, 541, 542

Canker, 176, 289, 292, 307, 315, 331, 335, 336, 338, 344, 356, 453, 454, 466, 467

Canopy, 3, 20, 62, 84, 180, 185, 259, 269, 270, 296, 300, 328, 337, 355, 359, 363, 377, 399, 534

management techniques, 259, 269, 270, 377, 399

Carbohydrates, 26, 112, 151, 203, 204, 241, 245, 382, 502

Carbon

dioxide, 15

sequestration, 14, 15, 264

Carboxylic group, 131

Carcinogenic

mycotoxins, 215

toxins, 319

Carcinogens, 150

Cardiac function, 133

Cardiovascular

benefits, 9

conditions, 141

disease (CVD), 5, 9, 10, 12, 128, 129, 135, 138, 143, 144, 146, 148, 151, 153, 409, 410, 485

health, 6, 8–10

risk factors, 148

system, 133

Carob moth, 325

Carotenoids, 26, 127, 128, 143, 149, 151, 153, 204, 242, 385, 416, 557

Carposphere, 200

Carya

carolinae-septentrionalis, 88, 89

illinoensis, 238, 258, 497

species, 82, 88, 470

Cashew nut, 113, 116, 142, 214–216, 225

plant-microbiome association, 215

Castanea spp., 210, 231, 488, 502

crenata, 65, 66, 239, 274, 448, 449, 452–454

mollissima, 65, 274, 449

sativa, 65, 66, 119, 128, 239, 258, 274, 445–447, 448, 452–455, 560

Castanopsis, 65

Catechin, 130, 133, 136, 137, 139, 140, 149, 151, 152, 382, 383, 396, 397, 414, 418

Catkin, 61, 62, 64, 65, 67, 70, 73, 74, 77, 82–84, 94, 97, 114, 440, 441

primordia, 61

shedding pollen, 64

Cedidophyopsis vermiformis, 338

Cell

cycle, 150

division, 111, 112

elongation, 111, 114, 115

Central

Asia, 16, 56–58, 93, 241, 244, 462

Compliance Committees (CCC), 554

Europe, 448

Ceratobasidiaceae, 211

Chameamygdalus, 57, 60

Chemical

composition, 208, 417, 418, 423, 524

inputs, 218, 431

reactivity, 142

spraying, 287

Chestnut, 1, 2, 39, 61–68, 76, 89, 110, 119, 128, 130, 131, 133, 135, 138, 139, 150–152, 210, 211, 225, 231–233, 239, 243, 258, 261, 274–276, 307, 308, 332–337, 408, 412, 413, 431, 432, 445–456, 472, 485, 489–493, 502, 518, 557, 559, 560, 562

blight, 66, 275, 334, 335, 451, 452

breeding challenges, 450

crops, 332

cultivars, 63, 232

cultivation, 211, 261, 274, 275

cuttings, 489

fruit production, 448

genetic diversity, 445

growers, 454

microbiome (metagenomic) analysis, 210

pollen, 64

shells, 133, 150, 152

Chilgoza, 271, 307, 308, 368, 369

nut, 271, 368

Chinese chestnut, 62, 63, 65, 66, 274, 449, 450

Chinkapin, 65–67, 448, 450

Chlorogenic acids, 131, 139, 149, 150, 390, 396

Chlorophyll, 116, 128, 143, 144, 153, 416, 529, 534

Chloroplast, 112, 276, 557

Chlorpyrifos, 312

Cholesterol, 5, 6, 9, 128, 143, 144, 148, 241, 409–411

Chromaphis juglandicola, 294–296, 309

Chromatin immunoprecipitation (ChIP), 525

Chromatographic separation, 532

Chronic

conditions, 149

diseases, 4, 5, 10, 12, 129, 132, 141, 146, 153

inflammation, 12

venous, 133

Chrysolepis, 65

Circadian rhythms, 112

Citrus canker, 176

Cladosporium, 206, 214, 318, 357

sp., 206, 214

Clonal

propagation, 118, 225, 228, 233, 238, 244, 261, 456, 465, 499

rootstocks, 230, 242, 243, 247, 258, 499

Clonostachys, 206, 207, 209

Clostridiales, 203

Clustered regularly interspaced short

palindromic repeats/Cas (CRISPR/Cas), 39, 173, 277, 518, 519, 524, 550, 552, 555–562

DNA fragment, 555

genome, 557

principle, 555

RNA (crRNA), 556

systems, 562

technology, 173

Codling moth, 3, 291, 292

Cognitive function, 5, 11, 25, 33, 151

Colchicine treatment, 492

Cold

plasma treatment, 408, 414, 416, 423

pressed macadamia nut oil (CPMO), 265

temperatures, 86, 449

Coleoptera, 309, 317, 332, 338, 348, 353, 356

Colletotrichum sp., 214

Colon, 137, 138, 143, 144, 209, 210, 352

Colonic enterococci, 210

Colorectal cancers, 133

Commercial

cultivation, 460, 472, 526

production systems, 493

significance, 55

use, 484

Computational techniques, 163, 170

Computer

techniques, 163

tools, 166, 167

vision, 174, 175, 179

Condensed tannins, 128, 135, 136, 396

Coneborer, 368

Consumer

awareness, 4, 29

demand, 29, 33, 225, 381

preferences, 4, 33–35, 268, 395

satisfaction, 38

trends, 33

Controlled pollination, 22, 72, 87, 469

Conventional

breeding, 266, 549, 550

management methods, 287

methods, 167, 233, 450

Convolutional neural network (CNN), 175, 176, 181

Coreidae, 317, 338, 368

Coronary heart disease (CHD), 143, 148, 149, 410

Corylobium avellanae, 72, 75, 76, 208, 209, 229, 338, 455, 460

Corylus, 18, 67, 69, 72, 75–77, 128, 207, 228, 229, 258, 262, 264, 265, 455–457, 459, 460, 485, 488, 503

avellana, 18, 69, 75, 128, 207, 228, 258, 262, 264, 265, 456, 457, 485, 503

colurna, 72, 229, 264

species, 67, 69, 75, 264

Cotyledon, 118, 236, 275, 490, 495, 496

abscission, 498

segments, 497

Coumaric acid, 130–132, 139, 140

C-reactive protein (CRP), 12

Criconemella rucium, 368

Crop

breeding, 172

development, 36–39, 174, 175, 378, 398, 518, 519, 528, 534, 542

domestication, 170, 536

genetic variety, 170

genomes, 517

growth, 170, 180, 181

health, 2, 31, 37, 184

height, 114

improvement, 172, 173, 518, 519, 521, 523, 525, 527, 536–538, 540, 542, 543, 552, 559

management, 3, 37, 176, 185, 276, 378, 408, 411, 535

monitoring, 184

omics analysis, 539

productivity, 3, 8, 21, 39, 52, 184, 188, 198, 218, 494

quality, 454

regions, 179

wild relatives (CWR), 163, 170–173

yields, 35, 37, 176, 181, 184, 312, 452

Cross pollination, 63, 69, 78, 80, 96, 97

Cryopreservation, 167, 485, 487–489

Culinary

applications, 1, 6, 34

innovation, 27

staples, 27

techniques, 19

texts, 18

traditions, 15, 18, 19, 23, 24, 27

uses, 23–25, 29, 40

versatility, 1, 2, 34

Cultivation, 1, 2, 7, 8, 13–17, 19–23, 28, 29, 31, 36, 38–40, 52, 75, 99, 119, 167, 211, 218, 227, 238, 258–263, 265, 266, 271–275, 288, 290, 367, 379, 385, 386, 388, 389, 392, 393, 395, 411, 412, 422, 433, 435–437, 445, 446, 449–451, 456–464, 470–472, 485, 492, 493, 495, 497–500, 502, 526, 553

environment, 167

methods, 39, 40, 385, 395, 458

practices, 1, 2, 38, 259, 271, 388, 422, 493

techniques, 19–23, 388

Cultural

browning, 167

celebrations, 27

conditions, 168, 246, 498, 500, 503

exchange, 19

media, 163, 167, 169, 246, 490, 497, 551

practices, 2, 3, 52, 262, 274, 287, 289–291, 316, 377, 378, 399, 436

systems, 167, 233

Curculio nucum, 263, 338

Curculionidae, 292, 332, 338, 348, 353, 356

Cyanidin, 135, 140, 149, 383

Cydia

latiferreana, 338

pomonella, 3, 291

Cytokinin, 111–114, 117, 118, 120, 377, 379, 392, 399, 486, 498, 501

therapy, 113

Cytotoxic actions, 209

D

Daidzein, 134

Data

analysis, 186, 537, 541, 542

collection, 181, 184, 187

integration, 525

interpretation, 540

normalization, 541

preprocessing, 182

sensing system, 178

De novo domestication, 173

Decision

making layer, 178–180

support systems, 176, 185

Deep

convolutional neural network (DCNN), 176

learning, 164, 175, 181, 188, 536

root systems, 13, 14

Defense mechanism, 129, 390, 537

Defoliation, 114, 290, 324, 331, 335, 349, 357, 365

Dehulling, 260, 415

Delphinidin, 135, 390

Dementia, 151

Demethylation inhibitor (DMI), 326

Deoxyribonucleic acid (DNA), 149, 152, 242, 266, 461, 523, 528, 536, 550, 551, 555, 556, 559–561

damage, 149, 555

markers, 266, 523

probes, 528

repair mechanism, 555

synthesis, 152

Dermatopathy, 133

Design of experiment (DoE), 163, 167–169

Desirable

alleles, 172

traits, 20, 22, 32, 37, 52, 171, 173, 227, 238, 264, 454, 462, 471, 487, 493, 499, 503, 517–520, 522, 523, 525, 526, 529, 541, 542

Desired

characters, 549

traits, 2, 23, 39, 522, 525, 538, 541

Destructive fungus, 292

Detoxification properties, 129

Diabetes, 5, 8, 10, 12, 128, 129, 133, 137, 143, 146, 149, 151, 153, 204, 209, 210, 259, 409, 410

Diabetic retinopathy, 151

Diabetogenic effect, 209

Dichlorvos, 310, 312

Dichogamous, 69, 70

Dieback, 114, 293, 336

Dietary

advantages, 39

antioxidants, 149

fiber, 5, 26, 204, 241, 262, 382

pistachios, 210

Difenoconazole/cyprodinil, 324, 328

Difference gel electrophoresis (DIGE), 531

Digalloylglucose, 136, 140

Digestive enzymes, 137, 151

Digital information, 177

Dihydrochalcone (DHC), 133, 134, 139

Dilactone form, 135

Dinitro-o-cresol (DNOC), 93

Dioecious plant, 92, 242, 432, 473

Diphenolic compounds, 141

Diptera, 295

Disease

almond

kernel shrivel, 330

leaf scorch, 329

alternaria leaf spot, 323

anthracnose, 313, 324

armillaria root rot, 314

brown rot blossom blight, 324

control, 2, 3, 101, 185, 287, 290, 291

crown gall, 315, 329

emergence, 366

free plants, 236, 504

green fruit rot, 326

hull rot, 325

management, 21, 176, 291, 370

phytophthora

crown, 328

root, 315

powdery mildew, 314

prevention, 8, 10, 215, 216

processes, 528

resistance, 2, 3, 8, 22, 32, 36, 37, 52, 172, 227, 276, 377, 379, 436, 451, 452, 464, 469–471, 493, 520–525, 527, 538, 539, 543

shot hole, 326

symptoms, 534

verticillium wilt, 327

walnut blight, 316

Disorder control, 431

Distant markets, 414

Diverse datasets, 541

Divine

intelligence, 17, 24

protection, 18

Domain, 163, 165, 182, 184, 185, 208

Domestic markets, 39

Domestication processes, 15, 56, 75, 163, 170, 173, 266, 460, 536

Double-stranded breaks (DSBs), 555, 556

Drip irrigation, 3, 21

Drought-tolerant, 7, 13, 22, 31, 198, 553

rootstocks, 31

Dwarf walnut, 237

E

Early

harvest date, 436, 445

larval instars, 358

Ease of kernel removal (EKRN), 174

Eastern filbert blight (EFB), 37, 75, 76, 230, 263, 458, 460, 522

Eco-climatic drivers, 175

Eco-friendly methods, 295

Ecological

footprint, 14

functions, 129

sustainability, 197, 217

Economic

benefits, 1, 5–7, 13, 19

damage, 273, 349

importance, 28, 470, 499

losses, 298, 308, 368, 518

opportunity, 1, 2, 7, 39

prosperity, 1

returns, 274, 431, 470, 471

thresholds, 287

value, 6, 7, 51, 291, 377

viability, 395

Ecosystem, 1, 8, 14, 32, 40, 197, 291, 308, 463

services, 1, 8, 32, 40

stability, 14

Ectomyelois ceratoniae, 325

Edible plant microbiome, 200

Effective pollination, 96, 266, 437

Efficient

irrigation systems, 21

regeneration systems, 552

Electrospray-mass spectrometry (ESI-MS), 532

Elite nut crop, 519, 526

Ellagic acid, 130, 131, 135–140, 149, 150, 152, 274, 382, 389, 393, 397, 410, 414

Ellagitannins, 135, 136, 139, 140, 150, 381, 382, 395

Embryo, 62, 117, 167, 236–238, 246, 487, 491, 496, 497–499, 552, 553, 557–559

development, 69, 499

sac development, 70

Embryonic axis, 497

Emericella, 205–207, 209

Endophytic fungi (EF), 207

Endothelial function, 9

Enterobacteriaceae, 210, 216, 217

Entomopathogenic

fungus, 340

nematode (EPN), 300, 321, 333

Environmental

adaptability, 525

benefits, 28

challenges, 13, 173

conditions, 37, 55, 101, 130, 172, 173, 181, 186, 198, 227, 244, 287, 292, 311, 369, 384, 386, 396, 399, 415, 423, 463, 465, 466, 503, 541, 558

considerations, 38, 101

factor, 52, 171, 173, 209, 211, 242, 380, 385–387, 398, 451, 455, 458, 501, 502, 535, 537

impacts, 3, 20, 21, 31, 38, 392

situations, 517

stress, 111, 391, 533

Epicatechin, 130, 133, 136, 137, 139, 140, 414

gallate (ECG), 133, 139, 140

Epicoccum nigrum, 208

Epicotyl grafting methods, 494

Epigallocatechin gallate (EGCG), 150

Epigenetic patterns, 560

Equilibrium, 379, 381, 395, 398

Eriodictyol-7-O-glucoside, 134, 135, 152

Eriophyes erinea, 296

Eriophyidae, 338

Erwinia herbicola, 199

Erysiphe corylacearum, 290

Escherichia coli, 152, 210, 555

Essential

nutrients, 5, 215, 225, 377–379, 502, 526

oil (EO), 320, 422

Ester, 139, 143

Ethephon treatment, 63, 110, 113, 115

Ethrel, 116

Ethyl gallate, 152

Ethylene, 110–115, 138, 246, 377, 379

moiety, 138

production, 115

Euamygdalus, 57, 60

Eulecanium pruinosum, 296

Eupenicillium crustaceum, 199

European

chestnut, 65, 66, 447, 451, 453, 455, 485, 492, 493, 559

red mite, 296, 297

Eurotium, 205–207, 209

Ex vitro, 501

Exarate type, 310

Exceptional performance, 445

Excessive defoliation, 114

Exogenous hormones, 116

Expressed sequence tags (ESTs), 529, 530

Ex-situ, 167, 170, 188

External conditions, 114

Extreme

gradient boosting (XGBoost), 182

weather events, 13, 23, 39

Extremophiles, 198, 200, 218

F

Fagus, 65, 274

Farming system, 7, 8, 164, 211

Fatty acid (FA), 5, 11, 13, 25, 26, 128, 144, 151, 204, 205, 209, 241, 320, 407–419, 421–423, 529

Fecal microbiota, 209, 210

Female

floral growth, 113

flowers, 61, 63, 67, 70, 86, 92, 96, 112, 113, 275, 432, 437, 442, 456, 470, 472

reproductive organs, 116

weevil, 310, 333

Fertilization, 3, 4, 54, 70, 71, 97, 178, 228, 265, 275, 299, 377, 379, 391, 392, 394, 398, 412, 432

Fertilizer management, 269, 270

Ferulic acid, 130, 131, 139, 140, 418

Fiber, 4–6, 9, 10, 26, 33, 151, 204, 241, 262, 267, 382, 408, 455, 518, 549–551

Field surveys, 175

Filbert worm, 300, 341

Financial well-being, 163

Firmicutes, 203, 204, 318

Flavanols, 127, 132–135, 387, 396, 410

Flavanones, 132–134

Flavones, 132

Flavonoid, 6, 127–130, 132–134, 139, 149–153, 204, 382, 385, 387, 389, 393, 394, 408, 410, 417

biosynthesis, 387, 399

Floral

biology, 51, 52, 61, 67, 82, 94, 102

bud development, 52, 82, 92, 113, 114, 340, 355

initiation, 112, 113

organ, 95, 112

patterns, 259, 277

repressor, 113

Flower

bud, 53, 54, 62, 95, 310, 333, 334, 466

clusters, 72, 73, 78, 87, 95

development, 52, 70, 86

initiation, 86, 113

production, 78

quantity, 51

Fluorescence

microscope, 73

molecules, 560

Flurprimidol, 116

Focused identification of germplasm strategy (FIGS), 171

Foliar treatments, 116

Food

components, 416

industry, 412, 418

irradiation, 416

metabolism, 112

plant cultivars, 200

quality, 170

Safety and Standards Authority of India (FSSAI), 418, 553

source, 14, 449, 456, 464

Foreign exchange, 7, 257, 308

Forest plants, 65

Formononetin, 134

Fragaria virginiana glauca (FVG), 384

Franquette cultivar, 142

Free radicals, 132, 149, 150, 228

Frotcher cultivar, 214

Fruit

crop development, 63, 247, 377–379, 384, 398, 399, 446, 484, 486, 504, 549, 550, 552, 558, 561

detection, 179

development, 111, 112, 175, 263, 377, 378, 395, 423, 529, 533

growers, 163

harvest, 179, 394, 422, 454

nutritional quality, 381

organoleptic quality, 380

picking, 180

plant yield, 380

production, 380, 398, 431, 448, 468

quality, 51, 52, 111, 186, 379, 381, 384–388, 391–393, 398, 435, 442, 446, 467, 468, 473, 493, 494, 519, 529, 530, 538

ripening, 111, 388

set management, 2, 52, 54, 71, 72, 80, 96, 97, 111, 114, 270, 377, 379

size, 111, 377, 379, 380, 383, 386, 393, 446

species, 227, 269, 382, 383, 385, 387–389, 391, 394, 550

trees, 116, 228, 235, 245, 308, 461

Functional

attributes, 409

genes, 536

Fungal

community, 208, 209, 211

diversity, 205, 207–209

fruiting bodies, 314

genera, 205

growth, 138, 290

infection, 267, 290, 412

populations, 211

richness, 207, 211

species, 207, 211, 215

Fungi, 135, 152, 206–209, 211, 215, 292, 294, 315, 319, 330, 333, 336, 343, 361, 364, 368, 538

Fungicide, 186, 290, 294, 363

treatments, 291

Furrow irrigation, 21

Fusarium, 201, 208, 214, 368

equiseti, 208

fujikuroi, 208

Future potential, 28, 31

Fuzzy logic (FL), 163, 168, 169, 188

G

Galactoside, 134, 135, 140, 151, 390

Galangin, 130, 140

Gall wasp, 276, 333, 453, 454

Gallic acid, 130–133, 135, 139, 140, 150, 152, 274, 382, 410, 414

Gallotannins, 135, 136, 139

Gamma

irradiation, 416

radiation, 391

Gas chromatography-mass spectrometry (GC-MS), 532, 533

Gastrointestinal (GI) diseases, 133

Gathering procedure, 232

Gene

editing techniques, 39, 262, 277, 470, 494, 541, 557–559, 561, 562

expression, 519, 523–525, 527–531, 537, 542, 560

function, 517

analysis, 524

research, 555

manipulation, 561

mapping, 277

modification, 559, 561

networks, 534

pool, 242, 448, 462, 520

silencing, 261, 525

transcripts, 555

Generations, 170, 173, 291, 292, 297, 357, 451, 453, 484, 494, 522, 523, 561

Genetic, 271, 377, 380, 385, 398, 458, 558

algorithms, 163, 169

crop plant improvement, 534

diversity, 20, 32, 52, 172, 173, 242, 243, 265, 270, 273, 431–435, 445, 446, 448, 451, 454, 455, 457, 460–464, 470, 472, 473, 503, 518, 520, 534

engineering, 22, 23, 227, 270, 276, 469, 518, 519, 525, 526, 550, 551

Appraisal Committee (GEAC), 554

enhancement, 465, 518, 555

factors, 240, 395

heterogeneity, 231, 239

improvement, 22, 36, 265, 550

make-up, 384

manipulation, 465, 549, 551, 553

markers, 37, 521–523

reservoir, 170

resources, 52, 56, 65, 75, 80, 88, 93, 98, 171, 259, 264, 270, 276, 448, 450, 472, 487, 493, 520

preservation, 52, 472

transformation, 488, 489, 494, 499, 518, 541, 549, 550, 553, 558

variation, 170, 431, 433–435, 460, 462, 464, 536

Genetically

control yield, 266

improved varieties, 460

similar plants, 502

Genistein, 134, 140

Genome, 39, 163, 170–173, 188, 266, 270, 277, 460, 517–524, 527–530, 532, 534–537, 541, 549–553, 555–557, 559–561

analysis, 266

editing

application, 172, 173, 550, 552, 555–557, 559–561

technologies, 555

tools, 552, 555

imaging, 560

sequencing, 39, 170, 270, 519, 520, 528, 530, 532, 556, 557

projects, 39

technology, 170

wide association studies (GWAS), 266, 518, 521, 536

Genomic, 172, 198, 261, 270, 276, 277, 463, 518–520, 523–525, 531, 534, 540, 560

assisted breeding, 519

databases, 171

epigenomics, and transcriptomics combination, 537

resources, 541

selection, 23, 37, 518

sequencing, 520, 521

site, 560

studies, 527

transcriptomics, 537, 538

Genotype, 56, 127, 167, 171, 173, 214, 229, 231, 233, 237, 238, 240, 244–246, 271, 382, 383, 386, 387, 395–397, 433–435, 445, 446, 460, 462–464, 471, 496, 499, 518, 520, 523, 535, 536, 549, 553, 556

environment interactions (GxE), 535

Genotypic chimerism, 561, 562

Genotyping, 170, 171, 518, 536, 559

Geographic

information systems (GIS), 37, 176, 177

location, 408

Geographical

areas, 214

region, 411

Geosmithia morbida, 292, 293

Germination, 55, 85, 87, 96, 97, 111, 163, 169, 229, 237, 238, 243, 260, 261, 273, 492, 497, 502

Germplasm, 32, 53, 76, 88, 166, 167, 170–173, 231, 242, 259, 263, 265, 266, 270, 383, 449, 452, 457, 463, 464, 472, 492, 522, 534, 555

banks, 167, 231

collection, 492, 522

innovation, 555

lines, 534

Gibberellic acid (GA3), 63, 110, 112–116, 119, 120, 199, 246, 498

Gibberellin, 98, 111, 112, 246, 392

Glaciation period, 448

Glansreginin A, 136, 139, 140, 152

Global

agriculture, 377, 518

database, 171, 293

demand, 7, 28, 35

economy, 5

market, 1, 5, 33, 35, 36, 40, 518

dynamics, 33, 35

plant microbiome, 200

positioning systems (GPS), 37, 176–178

production, 6, 28, 29, 35, 308, 317

Glucose, 135–137, 140, 147, 148, 151, 382, 389, 390

homeostasis, 148

levels, 147, 151

Glucoside, 133–135, 138–140, 150–152, 330, 382, 383, 391

Glucuronidase, 553

Glycemic control, 10

Glycitein, 134

Glycoproteins, 152

Gonocerus acuteangulatus, 338, 342

Good

agricultural practices (GAPs), 290

fats, 549, 550

horticultural practices (GHP), 258, 277

luck, 18, 25

Graft

connections, 229

success rates, 231

union, 231

Grafting, 2, 20, 64, 225, 226, 229–236, 238, 240, 241, 243–245, 247, 260, 261, 264, 269, 270, 274, 275, 316, 347, 367, 432, 437, 451, 454, 484, 485, 487–489, 493–495, 504

Gram-negative

bacteria, 152, 216

types, 152

Green

fluorescent protein (GFP), 552, 560

fruit rot, 326

gold, 272

Greenhouse gas emissions, 15, 64, 232, 233, 235, 241, 392, 490, 502, 534

Grevillea, 80

Growth

media, 502, 503

phases, 175

promoters, 218

rates, 230, 237, 246, 377

regulating chemicals, 109, 110

Grub, 310, 333, 334, 359, 439, 440

Guided nuclease, 552

Guilford, 89

Guillain-Barré syndrome (GBS), 536

Gut

microbiome, 201, 202, 204, 205, 216

microbiota, 11, 12, 200, 203–205, 209, 210

Gypsy moth, 310

H

Hakea, 80

Halobacillus sp., 200

Halophiles, 198, 218

Halyomorpha halys, 297

Hardwood cuttings, 226, 239, 244, 247

Harvesting

optimization, 185

stage, 408

Hatching, 320, 341

Haustoria, 314, 345

Hazelnut, 1, 2, 5–9, 12, 13, 15, 18, 19, 23–29, 33–37, 39, 67, 69, 70, 72, 74, 75, 81, 128, 130–134, 136–138, 141–145, 148, 151, 207–209, 214, 225, 228–231, 258, 260, 262–265, 274, 287, 288, 290, 297, 298, 300, 307, 308, 338, 339, 341–344, 346, 347, 408, 412, 413, 415–418, 421, 431, 432, 455–458, 460, 472, 485, 490, 502, 503, 518, 522

crops, 288, 290, 338

cultivation, 29, 288, 290, 456, 457

genetic diversity, 455

grafting, 230

orchards, 263–265, 298, 342

plantations, 75, 297, 457

production, 29, 35, 228, 263, 341, 457, 458

rootstock materials, 229

skins, 134

supply, 264, 338

trees, 229, 298

Healing properties, 25

Health

benefits, 4–6, 8–12, 25, 26, 29, 32, 33, 36, 128, 129, 131, 132, 148, 241, 258, 272, 408, 409, 412, 550

conscious consumers, 33

foods, 414

production, 225

promoting nutrients, 549, 550

Heat treatments, 293

Heavy precipitation, 366

Hemiptera, 309, 317, 348, 349, 352, 353, 356, 357, 368

Hepatoprotection, 135

Herbaceous plants, 55, 290

Herbicide, 234, 557

applications, 228

Hermaphrodite flowers, 53, 98

Herpes simplex virus type, 152

Hetero dichogamy, 82, 86

Heterocyclic ring, 132

Heteroptera, 338

Heterorhabditis bacteriophora, 333, 340

Heterozygosity, 231, 433, 434, 472, 549

Hexahydroxydiphenic acid (HHDP), 135

glucose, 136

Hibernacula, 299

Hicoreae, 88

High

nutritional value, 1, 40, 431, 470

density

planting (HDP), 258, 270

polyethylene (HDPE), 422

dimensional phenotypic data, 534

quality inputs, 272

throughput

phenotyping (HTP), 535, 536

stress phenotyping (HTSP), 174

Historical

cultivation, 19

data, 170, 181, 184

roots, 15, 16, 18, 19

significance, 1, 23

Homogamous, 69

Homogamy, 71

Homology-directed repair (HDR), 556

Homoptera, 338

Honeydew, 294, 342

Hormonal regulations, 398

Hormone, 109, 111, 112, 115, 116, 244, 377, 392, 490, 497, 502, 503

therapy, 117

Horticultural

crops, 51, 176, 186, 228

plants, 177

practice, 277, 454

Horticulture, 1, 51, 109, 164, 177, 188, 197, 225, 227, 231, 245, 257, 259, 264, 377, 407, 431, 466, 467, 470, 483, 517, 549, 559

Horticulturists, 493

Host

plants, 290, 291, 329

species, 200

Hot callus, 236, 494

Human

centered AI (HCAI), 165

health, 5, 8, 11, 146, 147, 153, 201, 216, 258, 408, 431

intelligence, 166, 178

neuroblastoma cells, 151

Humidity, 73–75, 84, 85, 87, 96, 97, 205, 227, 230, 235, 236, 264, 266, 345, 354, 362–364, 377, 378, 418, 423

Hybrid, 58, 75, 80, 230, 233, 243, 451, 452, 455, 459, 460, 518

seeds, 72, 73

Hybridization, 60, 90, 173, 259, 264, 277, 442, 445, 450, 451, 454, 459, 466–469, 473, 528, 550

Hydrocarbon, 129, 143

Hydrogen cyanamide (HC), 93, 113, 114

Hydrolysable tannins, 128, 130, 135, 136, 383

Hydroxybenzoic acid, 130, 131, 139, 140, 152, 410

Hydroxycinnamic acid (HCA), 130, 131

Hydroxyl, 128, 131, 135, 138, 144

Hypercholesterolemia, 148

Hyperglycemic toxicity, 209

Hyperhydricity (H), 167

Hyperoside, 133

Hyperspectral imaging (HIS), 176, 536

Hypertension, 146, 148, 149, 153

Hypocreales, 292

Hypolipidemic, 147

I

Image-processing techniques, 177

Immature

cotyledons, 236, 496

pecan embryos, 498

Immunity, 211, 450, 538, 556, 560

In vitro, 55, 85, 97, 117–119, 137, 163, 167–169, 205, 211, 236, 237, 246, 263, 485–490, 492, 493, 496–502, 504, 527, 551

cultivation, 119

culture, 168, 169, 486, 496, 500

grafting, 493

multiplication, 167, 263

mutagenesis, 485, 487, 492, 504

procedures, 163

propagation, 246, 485–490, 496, 499, 500, 504

shoot tip grafting (STG), 487–489, 492

In vivo, 85, 97, 137, 205, 211

Indigenous species, 448

Individual crops, 228

Indole-3

acetic acid (IAA), 110, 112, 115, 117–119, 199, 239

butyric acid (IBA), 98, 110, 113, 117–119, 232, 233, 240, 244, 246, 264, 491, 498, 501, 503

Inducible nitric oxide synthase (iNOS), 150

Inductively coupled plasma-mass/optical emission spectroscopy (ICP-MS/OES), 533

Industrial robotic process, 165

Ineffective pollination, 266

Infected

graft wood, 367

plant

material, 366

surfaces, 290

Inflammation, 5, 12, 128, 129, 132, 146, 149, 150, 152, 153, 409, 410

Inflammatory

biomarkers, 148

markers, 12, 150

mediator molecules, 149, 150

Inflorescence, 61, 79, 98, 275, 356, 432

emergence, 98

Infrared

radiation (IR), 264, 534

thermography, 534

Inositol phosphates (InsPs), 142

Insect, 14, 21, 62–64, 80, 98, 115, 135, 275, 292, 300, 309, 316, 322, 343, 352, 355, 358, 367, 550

issues, 308

pests, 37, 287, 288, 308–310, 317–322, 332, 338, 339, 348, 356, 368, 370, 371

almond borer and fruit wasp, 321, 322

leaf footed bug, 322

longhorn beetle, 321

navel orangeworm, 319

poplar lacewing, 320

pollination, 275

species, 14

Insecticidal treatments, 293

Insecticides, 3, 186, 187, 292, 295, 321, 335, 358, 360, 361

In-situ, 166, 170, 188

Instars, 297, 333, 349, 358

Insulin

metabolism, 151

resistance, 10, 151

sensitivity, 10

Integrated pest management (IPM), 3, 21, 268, 287, 289, 370, 398

Intensive breeding, 170

Inter simple sequence repeats (ISSR), 242

Interleukin

4 (IL-4), 205

6 (IL-6), 12

International

cooperation, 483

markets, 6, 29, 39, 233

Internet of things (IoT), 187, 535

Inter-retrotransposon amplified polymor-phism (IRAP), 242

Intestinal microbiota composition, 209

Ionomics, 533, 534, 543

Iron-deficient soil, 391

Irrigation, 2–4, 14, 20–22, 28, 31, 37–39, 176, 178, 180, 184, 186, 228, 268, 269, 276, 308, 316, 327, 355, 367, 377, 379, 391, 398, 412, 458

practices, 22, 31, 268

techniques, 4, 14, 22, 31

technology, 28

Ishikawa diagram, 167

Isobaric tag for relative and absolute quanti¬tation (iTRAQ), 531

Isoflavones, 127, 130, 132–134, 139

Isorhamnetin, 130, 133, 134, 139, 140

Isotope coded affinity tag (ICAT), 531

J

Jaccard index, 208

Japanese

beetle, 334

butternut, 99

chestnut, 65, 274, 448, 449, 454, 455

walnut, 99

Jasmonic acid (JA), 113

Jejunum, 210

Jewish holiday, 27

Joyful gatherings, 25

Joyous occasion, 27

Judaism, 24

Juglandaceae family, 267, 432, 433, 473, 552

Juglandis, 289, 293–295, 300, 309, 436, 523

Juglans, 2, 16, 88, 97–100, 102, 117, 118, 128, 236, 237, 258, 270, 288, 308, 317, 433, 434, 438, 442, 443, 485, 488, 490–492, 552, 557

ailantifolia, 99–101

cinerea, 97

mandshurica, 97

nigra, 117

poilanei, 88

regia, 2, 16, 98, 118, 128, 236, 237, 258, 269, 288, 308, 317, 433, 434, 442, 485, 552, 557

spp., 494

Juglone (5-hydroxy-1,4-naphthoquinone), 142, 152

Justifying phenomena, 56

Juvenility, 109, 245, 269

K

Kaempferol, 130, 133, 134, 139, 140, 152, 383, 396

3-O-glucoside, 134, 139

Kaltenbach, 294

Kashmir valley, 439, 440, 446, 460, 461, 495

Kernel/nut proportion, 25, 56, 58, 62, 63, 66, 69, 70, 81, 82, 89, 90, 95, 97, 115, 131, 132, 136, 138, 142, 144, 145, 149, 174, 206, 214, 228, 238, 241, 259, 261–263, 268, 289, 292, 294, 296, 298, 299, 310, 318, 319, 323, 337, 339, 341–343, 349, 359–361, 408, 418, 421, 422, 432, 434, 436, 438–442, 445, 448–450, 455, 458, 459, 464–471, 485, 520–523, 530, 553

color, 436, 438, 523

dry weight accumulation, 63

filling, 115, 349

percentage, 70, 174, 436, 442, 523

quality, 228, 521

Key

factor, 113, 293

genes, 39, 173

metabolic activities, 111

production regions, 28, 35

Kinetin, 117, 118, 491

Korea, 65, 101, 274, 297, 435, 448, 449, 457

L

Labor cost, 22, 259, 263, 274

Lachnospiraceae, 203, 204

Lactobacillales, 205

Lactobacilli populations, 210

Lactobacillus spp., 203, 205

Large-scale grafting, 231

Lariciresinol, 139, 141

Larva, 288, 291, 312, 321, 333, 334, 341, 352, 359

Larvae, 291–294, 296, 299, 300, 310, 312, 321, 322, 333, 339–341, 343, 350, 351, 358–360

Larval

development, 333

instar, 358

Laser-induced fluorescence transient (LIFT), 534

Late

leafing, 58, 436, 439

spring frost (LSF), 268, 269

Lateral/axillary buds, 114

bearing, 436, 440, 442

roots, 229

Layering, 225, 226, 229, 231, 240, 245–247

Leading producer, 241, 258, 262, 483

Leaf

curling, 294

length, 501

petioles, 310, 352, 361

yellowing (LY), 167

Leaflets, 116, 296, 311, 357, 365

Learning capability, 163

Legacy effects, 211

Legumes, 142

Lepidoptera, 291, 309, 317, 338, 348, 350, 356, 359, 368

Lepidopteran pests, 319

Leptoglossus clypealis, 322

Leptopus, 57, 60

Lesions, 289, 317, 323, 328, 329, 354, 355, 361, 362, 366, 367

Leto, 442, 445

Life

cycle, 207, 288, 290, 291, 342, 369, 561

generations, 292

Light

exposure, 379, 387, 501

quality, 387

Lignans, 127–129, 139, 141, 153

Lipid metabolism, 203, 205

Lipoprotein cholesterol, 148

Livelihoods, 7, 257

Local

economy, 7, 15, 257

farmers, 464

LOD (limit of detection), 214

Long

breeding cycles, 259, 277

juvenile

period, 269, 436

phase, 549

juvenility, 109

season cultivars, 63

term organic management, 211

LOPIT (localization of organelle proteins by isotope tagging), 531

Lovely blossoms, 116

Low

density lipoprotein (LDL), 6, 9, 138, 143, 144, 148, 409, 410

cholesterol, 9, 410

fertile soils, 269

nut yield, 266

productivity, 259, 261, 274, 435

LOQ (limit of quantification), 214

Lung cancers, 133

Lutein, 26, 143, 144, 151, 242, 272, 409, 410

Luteolin, 135, 139, 140

Luteoxanthin, 143

Lycioides, 57, 60

Lymphocytic leukemia, 133

M

Macadamia, 71, 78, 80–82, 258, 261, 265–267

flowers, 79

germplasm, 265, 266

integrifolia, 77, 80, 81, 258, 265

jansenii, 82

nut, 71, 81, 82, 258, 265–267

orchards, 266

species, 265

ternifolia, 82

tetraphylla, 80–82, 265

Machine learning (ML), 163–167, 169, 171, 173–176, 180–188

algorithms, 163, 167, 173

analytics, 183

community, 166

employment, 171

Major insect pests, 308, 348, 356, 368

Male flowers, 62, 63, 72, 92, 95, 112, 442

Maleic hydrazide (MH), 112

Malus domestica B, 112

Management practices, 3, 20, 21, 23, 28, 31, 39, 101, 181–185, 211, 259, 261, 264, 269, 276, 289, 437

Marker

alleles, 522, 523

assisted selection (MAS), 22, 37, 173, 261, 266, 520, 522, 523

Market

demand, 7, 398, 464

developments, 34

drivers, 33

dynamics, 1, 2, 4, 33, 35, 39, 40

trends, 28

Mass

production, 494, 502

spectrometry (MS), 530, 532

spectrum imaging (MSI), 533

Matairesinol, 141

Matrix effects, 214

Mature

embryos, 236, 496

explants, 489

plant material, 231, 232, 489, 502

Mean

absolute error (MAE), 183

squared error (MSE), 183

Measurement techniques, 541

Mechanical methods, 115

Mechanization, 21, 38, 40, 263

Mechanized harvesting, 272

Medicinal

features, 262

plants, 200, 201

properties, 16, 18, 25

Medieval period, 19

Mediterranean, 2, 13, 15, 16, 24, 28, 53, 56, 65, 93, 208, 244, 263, 347, 408, 435, 448, 460–462, 465

countries, 65, 263

region, 16, 56, 93, 347, 435, 461, 462, 465

Mega nucleases, 555

Megagonoscena viridis, 348, 349

Meganucleases, 552

Meiosis, 94, 228

Meloidogyne incognita, 331

Membrane structure, 152

Menopausal symptoms, 133

Mental

acuity, 17

health disorders, 151

Mercuric chloride, 500

Meristem tip, 118, 484

culture, 484

Meristematic activity, 497

Meristemoids, 497

Meristems, 118, 167, 236, 246, 496

Messenger RNAs (mRNAs), 525

Meta-analysis, 9, 10

Metabolic

activity, 150

processes, 119, 203, 379

Metabolites, 128, 137, 205, 209, 393, 519, 524, 525, 531–533, 535, 541

Metabolomics, 270, 519, 524, 525, 531–534, 537, 540, 542, 543

genome-wide association studies (mGWAS), 537

Metagenome analysis, 211

Metal ions, 149

Metarhizium anisopliae, 333, 340

Meta-topolin (mT), 501

Methodology, 180

Methyl jasmonate (MeJA), 243

Micro propagation, 246

Microarrays, 519, 527, 528

Microbial

alterations, 209

colonization, 197

communities, 197, 200, 201, 204, 210, 215, 217, 218

diversity, 197, 198, 215–218

habitats, 200

inoculants, 389, 392

passage, 216

population, 209, 211

profiles, 211

proteins, 152

shifts, 209, 210

species, 204, 210, 216

Microbiome, 197, 200–202, 205, 215, 216, 218

analysis, 197, 198, 200–202, 204, 205, 210, 214–218, 538

association, 198, 209, 217, 218

diversity distribution, 207

spatial distribution, 207

Microenvironments, 210

Micrografting, 484, 488, 492, 493

Microhabitats, 200, 216

Microirrigation systems, 14

Micronutrient balance, 391

Microorganisms, 11, 197, 198, 200, 201, 204, 209, 214–216, 218, 331, 538

Micro-propagated saplings, 484

Micropropagation, 117, 163, 166, 167, 169, 226, 228, 231, 236, 237, 242, 245–247, 259, 263, 264, 274, 483–486, 490, 493–497, 500–504

applications, 493

methods, 167, 486

research, 163, 167

techniques, 246, 259, 484, 493–495, 502, 503

Micro-sprinklers, 21, 354

Mineral nutrient, 167

Ministry of Environment, Forest, and Climate Change (MoEFCC), 553

Miscellaneous nut crops, 503

Mitigation, 13, 15

Moderate climate, 1, 2, 67, 205, 461

Modern

breeding, 172, 518

cultivation, 20, 21

Modified

atmosphere packaging (MAP), 38

hot callusing cable (MHCC), 495

Moisture

content (MC), 243, 388, 415, 418, 455

distribution, 21

Molecular

biology, 112, 518

breeding, 22, 32, 37, 259, 450, 555

level interactions, 528

mechanisms, 524, 525, 527, 529, 537, 538, 559

techniques, 36, 37, 259, 557

Monoculture, 258, 273, 308, 338

Monoecism lifecycle, 295

Monomeric flavanols, 134

Monoterpenes, 152

Monounsaturated

fat, 5, 26, 209, 262, 408

fatty acids (MUFA), 209, 408, 409, 412, 414, 417

pentadecenyl cardanols, 142

Morphological

characteristics, 290, 460, 461

structure, 111

Mother plants, 232, 290

Moths, 287, 288, 291, 292, 300, 310, 319, 359, 369

Mountainous regions, 553

Mucus layers, 210

Mulching materials, 23, 393, 394

Multidimensional Protein Identification Technology (MudPIT), 530, 531

Multi-omics, 277, 517, 518, 535, 539, 541

approaches, 539

data, 539, 541

software and websites, 539

Multi-spectral

photography, 177

sensing, 176

Mummified fruit, 319, 325, 366

Murashige Skoog (MS), 117–119, 489, 491, 530–533

Mutant genomes, 560

Mutation, 465, 468, 469, 487, 552, 555, 557, 559, 561

breeding, 469

Mutualistic interactions, 51

Mycelia growth, 291

Mycelium, 290, 314, 344, 345, 369

Mycobiome, 205, 207

Mycotoxin, 201, 214, 215, 263, 531

producing microorganisms, 214

Myricetin, 133, 139, 140, 152

3-O-glucoside, 134

Myzocallis coryli, 338

N

Naphthaleneacetic acid/naphthyl acetic acid (NAA), 110, 116–119, 232, 233, 246, 491, 497, 498, 533

Naphthoquinone compound, 142

Naringin, 130, 134, 139, 140

Narthecius simulator, 293

National economies, 110, 119

Natural

enemies, 296, 319, 343, 353

population, 439, 440

selection, 464

variations, 536

Necrosis, 12, 167, 209, 323, 329, 342, 368, 488

Necrotic lesions, 354, 367

Neisseriales spp., 205

Nematodes, 51, 300, 307–309, 317, 318, 330, 331, 333, 356, 368, 370, 371, 437

lesion nematode, 330

pin nematodes, 331

root knot nematode, 331

Neocalosoter, 293

Neoxanthin, 143

Nepovirus, 331

Nervous system, 133

Neural networks, 163, 164, 169, 175, 188

Neurodegenerative

diseases, 128, 129, 149, 153

issues, 151

Neuronal structures, 134

Neuroprotection, 135

Neuroprotective, 11, 25, 132, 133, 147, 151, 152, 410

activity, 151

effect, 151

Neutron activation analysis (NAA), 533

New

breeding tool (NBT), 555, 561, 562

genetic elements, 560

Niacin, 552

Nitric oxide (NO), 150, 489

Nitrogen application rates, 391

Nodal

explants, 118, 489

segments, 236, 496

Non-alcoholic

fatty liver disease (NAFLD), 137

steatohepatitis (NASH), 137

Non-destructive phenotyping, 534

Non-embryogenic calluses (NECs), 117

Non-homologous end joining (NHEJ), 556

Non-meristematic cell, 497

Non-rooted cuttings, 119

Norflurazon, 557

Novel

breeding techniques, 562

crops, 266

genes, 170

Nuclear

magnetic resonance (NMR), 532, 533

polyhedrosis virus (NPV), 311

Nursery production systems, 227

Nut

breeding programs, 267

consumption, 4, 9, 10, 13, 29, 148, 409

crop, 1–40, 51, 52, 101, 109, 110, 115, 119, 120, 127, 153, 163, 164, 166, 167, 169, 171, 173–178, 181–188, 197–202, 212, 217, 218, 225, 227, 239, 246, 247, 257–260, 262, 265, 272, 276, 287–290, 292, 294–298, 307, 308, 317, 348, 356, 368, 370, 371, 377, 407, 412, 431, 432, 450, 454, 460, 461, 468, 483–486, 488, 490–494, 503, 504, 517–529, 533, 534, 536, 538–543, 549–553, 556, 557, 559, 562

biology, 525, 527, 541–543

breeding, 39, 517

cultivation, 21–23, 31, 36, 52, 218, 259

genome editing application, 560

improvement, 518, 519, 521, 523, 525, 527, 535, 540, 542, 543, 552

production, 3, 4, 14, 22, 28, 31, 32, 37–39, 52, 164, 181, 184, 276, 484

species, 197, 503, 520, 521

deterioration, 418

drop, 63, 261, 288, 310, 339, 341, 342, 359

farming, 216, 473

fruits, 292, 296, 299, 316

genetic variety, 431

maturity, 76, 113, 414

orchards, 14, 15, 37, 177, 274

processing, 33, 38

producers, 32, 35, 36, 38

production, 2, 36, 63, 101, 113, 174, 227, 261, 263, 266, 268, 273, 353, 453, 483, 518, 520, 557

quality, 3, 8, 22, 32, 36, 38, 55, 227, 239, 259, 261, 265, 273, 418, 438, 452, 462, 472, 520, 521, 523, 524, 530, 542

rot, 337

size, 58, 116, 174, 238, 436, 520, 521, 523

species, 2, 52, 431, 450

trees, 8, 14, 20, 22, 23, 117, 215, 216, 226, 234, 259, 273, 292, 484, 521

weevil, 338

weight, 440

yield, 259, 260, 263, 266, 267, 294, 296, 452, 521

Nutrient, 5, 11, 12, 14, 20, 33, 116, 149, 167, 186, 215, 225, 228, 270, 345, 360, 369, 377–379, 392, 393, 398, 447, 502, 526, 533, 538, 549, 550

acquisition, 198, 218

cycling, 14, 20, 180, 215

databases, 127

dense seeds, 110

density, 29

levels, 184

management, 3, 184, 276

supply, 502

uptake, 184, 216, 274, 377, 379, 398, 499

Nutritional

benefits, 1, 2, 4, 5, 7, 16, 33, 485

content, 52, 186, 200, 377, 379, 382, 525

enhancement, 32

importance, 225, 258

profiles, 22, 32, 33

quality, 173, 266, 381, 383, 385

value, 1, 4, 8, 17, 19, 23, 24, 28, 29, 33, 40, 381, 391, 396, 418, 431, 432, 470, 524, 526, 529

Nymphal

diapause, 349

instars, 349

Nymphs, 294, 295, 311, 340, 342, 349, 352, 357, 361

O

Oak, 65, 456

Obligate biotrophic, 290

Oceanobacillus iheyensis, 200

Oligomeric flavanols, 134

Olympic athletes, 17

Omega-3 fatty acid, 5, 9, 11, 13, 25, 26

Omics, 277, 517–519, 534, 535, 539–543

data, 541

findings, 541, 542

techniques, 541

technology, 517, 519, 543

One factor at a time (OFAT), 168

Open field setting, 387

Operational taxonomic units (OTUs), 201–203, 205, 207

Optimal irrigation, 184

Oral microbiomes, 205

Orchard

border, 178

level, 180, 181

management, 20, 23, 28, 182, 184, 269

sanitation, 3, 293

Organ culture, 485, 487, 488, 491, 492, 504

Organic

compounds, 141, 381

management, 211

matter, 8, 14, 15, 20, 369

plots, 211

systems, 211

versus, 412

Organisms, 8, 198, 242, 451, 525, 534

Organogenesis, 83, 118, 264, 488, 489, 497, 498, 559

Organoleptic quality, 381, 399, 454

Osmophiles, 198, 218

Outer bud scales, 86

Ovary, 53, 54, 62, 67, 69, 70, 78, 79, 81, 86, 92, 94, 95, 97, 487, 491

development, 70

Overwintering larvae, 299

Ovoid, 310

Ovules, 53, 55, 56, 78, 87, 96, 236, 496

Oxidative

biomarkers, 148

stress, 6, 12, 137, 149, 150, 152, 391, 409, 410

P

Paclobutrazol (PBZ), 93, 115, 116

Pallor, 294

Palomena prasina, 338, 342

Panonychus ulmi, 296

Pantothenic acid, 552

Parasitic wasps, 295, 358

Parasitoid, 295, 312, 322, 323, 334, 341, 349, 352

Paratrichodorus lobatus, 331

Paratylenchusma crodorus, 331

Parent plant material, 232

Parkinson’s disease (PD), 151

Pasteurization, 130, 408, 414, 423

Pathogen, 3, 37, 118, 129, 135, 138, 186, 187, 198, 201, 202, 211, 215–217, 230, 242, 243, 261, 275, 288–291, 308, 313–316, 319, 326, 330, 343, 370, 371, 449, 451, 453, 454, 458, 526, 528, 529, 533, 537, 538, 542

Pathogenic

microbial agents, 218

species, 211

p-coumaric acid, 131, 132, 139, 140, 150

Peanut, 205–207, 209, 268

allergic participants, 205

consumption, 205

Pecan, 26, 74, 82, 83, 85–89, 109, 113–117, 128, 130, 131, 133–137, 140–145, 150, 174, 175, 214, 215, 225, 238–240, 258, 260, 267–269, 273, 307, 308, 356–363, 367, 368, 382, 408, 410, 416, 417, 421, 431, 432, 470–472, 485, 490, 491, 497–500, 518, 520

axillary buds, 114

blossoms, 117

cultivars, 86, 144, 214, 471, 499

genotypes, 214

kernels, 144, 214

nut, 74, 113, 116, 134, 150, 214, 215, 225, 238, 258, 260, 267, 268, 307, 356, 358, 417, 421, 432, 470, 471, 485, 490, 491

stem cuttings, 240

Pedoclimatic conditions, 385

Peeling/shelling/dehulling, 408, 411, 415, 423, 455

Pellicle, 66, 142, 152, 260, 275, 337, 448, 449, 455, 458, 530

intrusions, 448

Pendulous racemes, 77

Penicillium, 199, 205–207, 209, 214

citrinum, 199

sp., 214

Pentatomidae, 297, 338, 348, 368

Perennial

fruit crops, 558

nature, 15, 549

Perfect blossoms, 116

Perianth lobes, 78

Pest, 21, 23, 37, 51, 115, 129, 181, 184, 186, 187, 243, 261, 263, 265, 267, 268, 273, 275, 276, 287–289, 291, 296, 297, 299, 307–309, 317–319, 325, 332, 338, 339, 348, 349, 356, 360, 368, 370, 371, 377–380, 398, 439, 440, 458, 464, 467, 471, 499, 518–520, 526, 527, 537

detection, 184

management, 3, 20, 37, 185, 268, 287–289, 300, 370, 398

resistance, 22, 287, 453

Petaloid sepals, 77, 81

Petiole, 310, 365

pH levels, 211, 385

Phenolic, 129, 130, 242, 388, 389, 391, 393, 422

acids, 127–132, 150, 152, 153, 382, 408, 410, 423

compounds, 6, 128–131, 141, 142, 149–153, 167, 382, 384, 394, 414, 418, 421

concentration, 391

profile, 130, 131

Phenology, 52, 174, 186, 370, 371

Phenols, 128, 130, 141, 153, 208, 381, 385, 389–391

Phenome, 534, 535

Phenomics, 534, 535, 540, 543

Phenotype, 264, 517, 518, 531, 534–537, 557

Phenotypic

data, 521, 522, 525, 534

evaluations, 522

fidelity, 485, 493

traits, 556, 558

Phenylpropanoid, 132, 141

derivatives, 132

Pheophytins, 143

Pheromone traps, 21, 293, 300

Phloem sap, 349

Phloridzin, 133, 139

Phosphorus, 12, 26, 142, 215, 241, 379, 382, 391, 392

intake, 391

Photoperiod, 349, 490

Photoperiodism, 112

Photosynthetic activity, 116, 294

p-hydroxybenzoic acids, 131, 139

Phyllactinia guttata, 290, 309, 338, 348

Phylloquinone, 262, 272

Phyllospheres, 197

Phylum, 204, 207

Physical properties, 417

Physiological

disorders, 168, 259

functions, 129

intricacies, 379, 398

Phytate/phytic acid, 127, 128, 142, 143, 153

contents, 142, 143

Phytoalexins, 138

Phytochemical, 6, 127–129, 147–150, 152, 153, 265, 272, 390, 408, 409, 411, 412, 414, 415, 418, 423

compounds, 128, 141, 408

Phytoene desaturase (PDS), 557

Phytohormone, 109–112, 119, 120, 498

inhibitors, 114

Phytophthora

cambivora, 211, 332

root rot, 261, 275, 336

Phytoptys avellanae, 338

Phytosterol, 6, 10, 127, 128, 144, 145, 149, 153, 242, 272, 408–410, 413, 422, 423

content, 145

Phytotoxicity, 113

Piceatannol, 138, 139, 383, 396

Pigmentation, 129, 394, 530

Pigments, 143, 144, 380, 382

Pinoresinol, 139, 141

Pinostrobin, 134, 140

Pinus gerardiana, 271

Pistachio

dietary elements, 210

ecotypes, 413

kernels, 142, 144

nut, 74, 92, 118, 142–144, 209, 210, 241, 258, 272–274, 308, 348, 353, 354, 416, 417, 472, 523

psyllids, 349

skins, 134

supplementation, 210

trees, 116, 242, 273, 349–351, 353

vera, 349

weevil, 353

Pistacia, 93, 94, 128, 167, 169, 241, 242, 244, 246, 258, 347, 352, 490, 501, 502

integerrima, 94, 490, 502

khinjuk, 94

narbonensis, 93

species, 167, 501

spp, 167, 242, 244, 500

vera, 93, 128, 241, 246, 258, 272, 347, 352, 501

Pistil, 65, 78, 81, 94, 95

Pistillate

clusters, 72

floral bud primordia, 92

flowers, 61–65, 67, 70, 72, 73, 75, 85, 86, 94–96, 98

inflorescence, 61, 82, 85, 92, 98

receptivity, 62

Pityophthorus juglandis, 292, 293, 295

Pivotal factors, 169, 393

Plant

biotechnology, 167

culture media, 163, 169, 497

debris, 299

diseases, 175, 201

growth

hormones, 490, 502, 503

regulator (PGR), 109–112, 114–116, 119, 120, 167, 175, 187, 198, 237, 246, 331, 394, 490, 501–503, 538

health, 38, 96, 215, 218, 377, 437, 500

hormones, 111

kingdom, 132

microbiome, 216

multiplication, 236

nutrition, 389, 391

pathogens, 215, 288, 290, 533

phenolic compounds, 128

physiology, 377, 399

reproduction, 51, 227

sap flow sensors, 37

species, 14, 52, 112, 135, 144, 167, 170, 208, 239, 342, 434, 463, 486, 498, 501, 502, 541, 549

stunning, 294

tissues, 114, 208, 311, 487, 497, 500

varieties, 176, 487

vigor, 291, 504, 534

Plantations, 66, 75, 238, 297, 340, 349, 350, 352, 353, 457, 460, 470, 471

Plasmid, 552, 560, 562

Pollen, 55, 62–64, 72, 73, 75, 79, 82, 84, 85, 87, 96, 97

charts, 448

dehiscence, 84, 87, 96

donor, 466, 467

grains, 97

shed, 62, 64, 65, 67, 69, 73, 83, 84

tubes, 55, 69, 70, 73, 79, 97

viability, 61, 64, 85, 96, 102

Pollination, 14, 22, 51–56, 60, 62–65, 69, 70, 72, 73, 78–80, 85–87, 92, 93, 96, 97, 101, 102, 238, 240, 259, 261, 263, 264, 266, 269, 271, 272, 274, 275, 277, 362, 363, 366, 436, 437, 456, 469, 470, 472, 499, 523, 558

difficulties, 269

management, 259, 277

services, 14

techniques, 64

Pollinators, 14, 38, 51, 52, 96, 258, 266, 269, 378, 438, 459

population, 258

Pollinizers, 96, 258, 436

Polyethylene mulching, 393, 394

Polyhydric alcohols, 135

Polymeric procyanidins, 130

Polyphenolic

compounds, 132, 135, 137, 149

content, 389

Polyphenols, 10, 12, 32, 83, 127, 130, 136, 138, 141, 148–151, 204, 389, 395, 408–410, 412, 414, 415, 418, 422

Polyploidy, 468, 469, 561

Polyunsaturated

fatty acid (PUFA), 151, 409, 413–419

hydrocarbon, 143

Postharvest, 266, 408, 409, 411, 412, 414–416, 421, 422, 432

conditions, 130

factors, 408, 412, 422

heat treatment, 333

management, 261, 273

technology, 38

Potassium (K), 26, 113, 199, 242, 272, 273, 320, 379, 382, 392

nitrate, 113

Powdery mildew, 287, 290, 363

Practical applications, 493, 556

Pre-bearing age, 436

Precise control, 21, 502

Precision

agriculture, 31, 37, 176, 178, 398

irrigation

systems, 31

techniques, 4, 14

Preharvest

factors, 377–379, 397–399, 408, 411

cultivar, 411

interval, 326

management, 412

Premature

defoliation, 349

fruit drop, 333

nut dropping, 310

Prevotella, 205

Primary explant, 498

Prime editors (PE), 561

Proactive measures, 23, 537

Proanthocyanidins, 127, 128, 130, 135–137, 139, 140, 150, 153, 382

Probiotics, 216

Processed data, 179

Processing

conditions, 131, 408

equipment, 38

factors, 409, 411, 422

Procyanidin, 136, 151

B2, 135, 139

Production

challenges, 32, 259

constraints, 271

efficiency, 385, 465, 523

practices, 3, 28, 36, 52, 495

Productive phase, 92

Prolonged juvenile phase, 454

Promalin treatments, 114

Pro-oxidant enzymes, 149

Proper timing, 87

Propionate, 205

Prostate cancers, 133, 144

Protea spp., 79

Proteaceae, 80, 265

Proteobacteria, 202, 203

Proteomics, 270, 519, 524, 525, 529–532, 538, 540, 542, 543

Protocatechuic acid (PCA), 131, 132, 139, 140, 152, 410

Protogynous, 69, 82, 83, 86, 432, 439, 440

cultivars, 83, 86

Protogyny, 71, 72, 82, 552

Protospacer adjacent motif (PAM), 556

Pruning, 3, 31, 38, 69, 185, 228, 259, 269, 270, 275, 293, 299, 322, 329, 335, 344, 347, 379

Prunus

amygdalus, 500

avium, 246

bucharica, 56

communis fritsch ., 58

dulcis, 2, 15, 128, 227, 272, 317, 460, 461, 468

fenzliana, 56

kumarica, 56

Pseudomonas spp., 210

syringae, 199, 331, 338

Pterostilbene, 139, 382, 383, 396

Pupation, 294, 312, 333

Pyrogallol, 152

Q

Quality

attributes, 377–379, 386, 397–399, 413, 417, 418, 458

loss, 418

Quantitative trait loci (QTL), 521, 534, 536

Queensland nut, 81, 82, 265

Quercetin, 130, 133, 134, 138–140, 149–152, 382, 383, 396, 418

3-β-D-glucoside, 151

glycosides, 134, 150, 152

Quercus, 65, 274

Quinone, 142

group, 142

outside inhibitor (QoI), 326

reductase (QR), 138, 150

R

Radiation, 385, 386, 388, 391, 469

Randomized controlled trials (RCTs), 9, 10

Rapid alert system for food and feed (RASFF), 214

Raspfruits, 381, 383, 387, 388, 393–396

Reactive

nitrogen species (RNS), 149

oxygen species (ROS), 138, 149, 152, 391

Recommended practices, 308

Red, green, and blue (RGB), 177, 187, 534

Reference genome, 170, 536, 541

Refractory species, 489

Regeneration medium, 498

Region convolutional neural network (R-CNN), 175, 181

Regulatory network analysis, 524

Related species, 432, 461, 464

Relative humidity (RH), 74, 84, 85, 87, 96, 205–207, 243, 264, 266, 364, 423

Renal failure, 151

Reproducibility, 536

Resistant cultivars, 259, 268, 295, 437

Resource

allocation, 184, 185, 398

management, 38

Respiratory

conditions, 25

health, 25

pathologies, 149

Resting spores, 314, 345

Restriction-site associated DNA sequencing (RAD-seq), 536

Resveratrol (RV), 127, 130, 138–140, 382, 383, 396

Retrotransposon-microsatellite amplified polymorphism (REMAP), 242

Review committee on genetic manipulation (RCGM), 554

Rhinitis, 133

Rhizogenesis, 119, 163

Rhizomorphs, 344

Rhizopus, 205–207, 209, 318, 325

spores, 325

Rhizosphere, 197, 200, 331

Riboflavin, 552

Ribonucleoproteins (RNPs), 559, 560

Ripened fruits, 179

Ribonucleic acid (RNA)

interference (RNAi), 470, 519, 524, 525, 555

sequencing (RNA-seq), 524

Ripening time, 62, 63, 111, 112, 164, 185, 377, 379, 380, 386, 388, 394, 395, 467, 531, 538

Roasting techniques, 127, 130, 141, 274, 408, 414, 417, 418, 423

Robotic, 31, 38, 40

competence, 180

crop harvesting, 178

motion, 180

Root

development, 236, 240, 502, 559

infections, 211

mean squared error (RMSE), 183

systems, 3, 8, 13, 14, 229, 242, 267, 534

zone, 21, 201, 328

Rootstock, 2, 20, 31, 60, 66, 76, 99, 168, 169, 225, 226–231, 233, 235, 236, 238–245, 247, 258–261, 263, 264, 270, 272–274, 435–437, 450–452, 454, 466, 484, 488–491, 494–496, 499, 501, 502, 518, 553

breeding, 261, 450, 454

propagation, 238, 242

seeds, 242

Roseburia spp., 203

Rotting root pieces, 314

Rough-shell type, 80

Ruminococcaceae, 203, 204

Ruminococcus spp., 203

Rural

development, 1, 7, 15, 40

households, 338

Rutin, 133, 139, 140, 152

S

Salicylic acid, 113, 131

Salinity, 243, 389

Salt stress, 199, 390, 534

Sanitation, 3, 293–295

Saponins, 408, 423

Saprophytic fungi, 319

Scab, 214, 238, 239, 307, 327, 361, 362, 471, 472

disease, 238

Secoisolariciresinol, 139, 141

Secondary

active metabolite, 151

metabolites, 128, 209, 533

symptoms, 290

Seed, 35, 72, 73, 79, 110, 113, 133, 152, 167, 225, 226, 228, 234, 238–240, 242, 247, 268, 342, 368, 369, 432, 484, 485, 491, 498, 499, 518, 560

germination, 111, 163, 169, 502

propagation, 20, 227

Seedling, 63, 117, 118, 211, 226, 229, 236, 238–240, 244, 247, 330, 437, 452, 463–466, 471, 489, 490, 499, 501

material, 489, 503

rootstocks, 226, 235, 242, 247

selections, 460

Self-incompatibility (SI) system, 69, 460, 461, 464

Semi-dwarf genotypes, 237

Senile orchards, 258, 259, 262, 274

Sensor, 31, 37, 38, 164, 178, 184–187, 535

technologies, 37, 186

Sepals, 53, 77, 81, 92, 94, 95

Sequencing technology, 170, 207, 242

Serial analysis of gene expression (SAGE), 527–529

Serratia marcescens, 152

Sex

differentiation, 98

ratio, 116

Sexual

identity, 112

incompatibility, 51

propagation, 225

reproduction, 290

Shed pollen, 61, 74, 84

Shoot

growth, 61, 78, 115–117, 119, 246

proliferation, 484–486, 489, 490, 493, 501, 502

regeneration, 486

tip, 117, 440, 487, 490, 492, 496

grafting (STG), 485, 487–489, 492, 504

necrosis (STN), 167, 488

Short-chain fatty acids (SCFAs), 204, 205

Shriveled hazelnuts, 297, 300

Signal transduction pathways, 132

Signaling pathways, 112, 134, 530

Simple sequence repeat (SSR), 242, 433–435, 457, 461, 521–523

Sinapic acid, 131, 132, 140

Single-guide RNA (sgRNA), 556, 558

Site

directed nucleases (SDNs), 555

specific crop management (SSCM), 176, 177

Small secreted proteins (SSPs), 538, 539

Socioeconomic benefits, 15

Sodium hypochlorite, 500

Softwood cuttings, 232, 239, 244

Soil

carbon, 15, 264

characteristics, 182, 184, 385

erosion, 8, 14, 267, 275

fertility, 14, 20, 274, 276

health, 3, 8, 13, 14, 32

management, 211, 215, 392

moisture, 3, 31, 37, 39, 184, 393

nutrients, 186, 393, 398

pH, 211

structure, 8, 14

Solids-to-acid ratio, 394

Soluble solids (SS), 381, 385–388, 390–392

Somatic

embryo (SE), 167, 233, 237, 246, 484–489, 491, 493, 496, 498, 499, 504, 552, 553, 557–559

embryogenesis, 233, 484–491, 493, 496, 498, 499, 504, 552

Soothing effect, 25

Sooty mold, 294, 342

Spartioides, 57, 60

Species

diversity, 203, 216

specific diversity, 200

Specific locus amplified fragment

sequencing (SLAF-seq), 536

Specific phenotyping, 534

Sphingolipids, 127

Squalene, 128, 143, 153, 414

Stable isotope labelling by amino acids in

cell culture (SILAC), 531

Stamens, 53, 61, 78, 83, 92, 94

Staminate

catkins, 61, 67

flowers, 61, 63, 64, 83, 94

inflorescence, 83

primordia, 92

Staphylococcus aureus, 152

Statistical

approaches, 541

methods, 521, 522

Steinernema

carpocapsae, 321

feltiae, 333, 340

spp, 340

Stenocarpus, 80

Sterile pollen, 94

Sterilization, 217, 489, 490, 500, 501

methods, 500

Sterols, 145, 152, 414

Stigma/stigmatic area, 54, 55, 61, 65, 78–80, 82, 86, 87, 94–97, 324, 440, 441

colour, 86

maturity, 96

receptivity, 54, 79, 87, 96

surface, 97

Stilbenes, 127–130, 137–139, 153, 382, 383, 396, 397

Stink bugs, 273, 297, 307, 342, 343

Stomatal conductance, 534

Streptococcus mutans, 152

Streptozotocin (STZ), 209, 210

Subculturing techniques, 500

Suckering tendency, 229

Superoxide anion, 142

Superstitions, 18, 25

Support vector

machines (SVMs), 535

regression (SVR), 182

Sustainability, 4, 8, 13, 19, 21, 28, 31–33, 36–38, 40, 197, 217, 268, 276, 398, 399, 466, 542

Sustainable

agriculture, 1, 7, 13, 14, 164, 216, 392, 543

use, 266

utilization, 472

water management, 22

Symbiotic fungi, 211

Synergistic effects, 111

Synthetic

auxins, 239

chemicals, 111, 188

seeds, 167

Syringic acid (SA), 130–132

Systematic

plantation, 258

review, 9, 10

T

Tannin, 110, 120, 128–130, 135–137, 149, 151, 153, 208, 382, 383, 396, 397, 410

temperate nut crops, 153

Tebuconazole, 290

Technological advancements, 28, 31, 36, 37, 172, 261, 275, 378, 484

Temnochila chlorodia, 293

Temperate

climates, 208, 307, 549, 550

crops, 259

fluctuations, 387, 391

nut crop, 1–16, 18–40, 51, 101, 109, 110, 119, 120, 127, 153, 163, 166, 167, 169, 171, 173–176, 178, 180, 181, 183–188, 197, 225, 227, 239, 247, 257–260, 262, 265, 272, 276, 287, 288, 307, 308, 370, 377, 407, 412, 431, 483, 485, 488, 490–492, 517, 519, 527, 528, 533, 539, 540, 542, 543, 549, 552, 556, 557, 562

agricultural production, 183

contribution, 13

CRISPR/CAS application, 556

culinary traditions, 23

cultivation techniques, 19–23

development, 36–39, 174, 175, 528, 542

economic significance, 5

employing, 166

gel-free proteomics, 530

genetic manipulation, 552

health benefits, 8–12

historical roots, 15, 16, 18, 19

importance, 5

major disease, 289

nutritional significance, 5–8

production, 28, 31, 32, 181, 184

robotic crop harvesting, 178

scope, 28

Tephritidae, 295

Terpenoid, 143

Tetraploid, 84, 90, 485, 492

Tetraterpene, 143

Therapeutic benefits, 132

Thermal treatment, 292

Thermophiles, 198, 218

Thiamine, 552

Thidiazuron (TDZ), 115, 486

Thousand cankers disease (TCD), 292

Three-quarter color phase, 394

Tissue, 114, 142, 207–209, 296, 311, 327, 329, 487, 497, 498, 500, 524, 527, 529, 530, 558

culture, 109, 117, 119, 120, 227, 228, 233, 237, 240, 245, 246, 264, 484–486, 488, 489, 491, 492, 496–498, 500–502, 549, 551, 561

methods, 501

practices, 109, 119

Tocopherol, 151, 152, 226, 262, 408–410, 412–414, 416, 417, 421, 422

Tortricidae, 291, 338, 356

Total

acidity (TA), 381, 386–389, 396

antioxidant capacity (TAC), 383, 390, 395

cholesterol levels, 148

flavonoid content (TFC), 417, 422

phenolic

compounds, 130, 394

content (TPC), 130, 386, 389, 394, 395, 413, 415–417, 421, 422

phenols, 385, 391

soluble solids (TSS), 381, 385, 389, 391, 392, 394, 397

sterol concentration and content, 145

tocopherols (TTC), 416

Trade routes, 16, 19, 462

Traditional

breeding methods, 36, 37, 172, 173, 259, 542, 555

cuisine, 24

cultivars, 258

irrigation methods, 21

medicine, 25, 88

methods, 227, 272

planting systems, 269

propagation methods, 167, 246, 502

Trait mapping, 521

Trans-activating CRISPR RNA (tracrRNA), 556

Transcription

activator-like effectors nucleases (TALENs), 549, 552, 555

processes, 560

Transcriptomics, 270, 463, 519, 524–526, 529–531, 537, 538, 540, 542, 543

Transgenics, 562

Trans-p-coumaric acids, 131

Transplantation, 229, 490

Trans-resveratrol, 127, 138, 140

Treatment efficacy, 287

Tree

canopy, 62, 270, 300, 328, 355

fruit harvests, 454

growth retardants (TGRs), 115

nuts, 145, 175, 204

plants, 290

Tricarpelary superior ovary, 92

Triglyceride, 148

levels, 9, 143

Trigona spp ., 80

Trioxys pallidus, 295, 341, 342

Triterpene, 144

Trunk traps, 333

Tumor necrosis factor-alpha (TNF-a), 12, 132

Tunnel, 180, 321, 350–352, 358, 360, 393

Twig dieback, 114, 336

Two-dimensional gel electrophoresis (2DE), 530

Type 2 diabetes mellitus (T2DM), 137, 146, 151, 153

U

Ultraviolet (UV), 129, 138, 391

light, 138

radiation, 129

Unfavorable weather conditions, 54, 96, 185

Uniconazole (UCZ), 115, 116

Unipolar structures, 497

United Kingdom (UK), 214, 407, 448

United States (US), 6, 7, 28, 29, 66, 100, 101, 214, 230, 241, 258, 267, 273, 288, 331, 408, 435, 436, 451, 490, 518

Unmanned aerial vehicle (UAV), 175, 176, 536

Unsaturated fatty acids, 128, 241, 408

Unweighted pair group method with arith-metic mean (UPGMA), 434

Uzbekistan, 93

V

Vaccinium, 383, 388

Value

added product, 4–7, 32

addition processes, 15, 261, 276, 408, 411, 414

development, 38

Vanillic acid, 130–132, 139, 140

Vapor pressure deficit (VPD), 96

Varietal spectrum, 258

Vascular necrosis (VN), 167

Vectors, 292, 331, 335, 558

Vegetative

buds, 53, 54, 62, 67, 69, 78, 82, 92, 98, 112–114, 116, 225, 227, 228, 231, 233, 236, 238, 239, 245, 247, 259, 260, 263, 269, 290, 339, 340, 355, 369, 391, 434, 465, 466, 485, 559

condition, 98

phases, 225

propagation, 227, 228, 233, 247, 269, 465, 485

Vein spot, 357, 365, 366

Verrucomicrobia, 203

Versatile ingredients, 5

Vigor, 2, 86, 230, 237, 239, 247, 270, 273, 291, 436, 437, 439, 452, 469, 472, 496, 504, 534

Vigorous

growth, 238, 448

seedlings, 238

Vineyard diseases, 176

Violaxanthin, 143

Virus, 152, 245, 275, 484, 553, 556

free planting material, 494

Vision system, 174, 178, 179

Vitamin, 5, 26, 32, 33, 128, 149, 167, 246, 262, 267, 378, 381, 389, 396, 397, 408, 410

Viviparous females, 295

Vivipary, 62

Volatile organic compounds (VOCs), 381, 386

W

Walnut, 1–3, 5, 6, 8–13, 15–17, 19, 22–29, 31–37, 39, 77, 86, 94–100, 109, 116–118, 128, 130, 131, 133, 134, 136, 140–145, 150–152, 174, 199, 201–205, 214, 226, 233–237, 239, 243, 258, 260, 269–271, 287–289, 291–297, 300, 307–313, 316, 317, 382, 408, 410, 412–418, 421, 422, 431–439, 442–445, 456, 470, 472, 484, 485, 490–492, 494–497, 518, 520, 521, 523, 530, 552, 553, 557, 558, 562

aphid, 294, 311

blister mite, 296

clones, 118

consumption, 9–13, 202–205

crops, 96

cultivars, 95, 97, 142, 233, 234, 236, 270, 412, 413, 485, 496, 523, 530

cultivation, 271, 433, 435, 437, 445, 495

enriched diet phase, 202

genotypes, 237, 433–435

husk fly, 295, 312, 313

inflorescence, 98

intake, 11, 204

kernels, 145, 422

microbiome association, 202

micropropagation, 236

orchard systems, 271

pellicle extract (WPE), 152

plantings, 96

pollen, 96, 97

production, 29, 269, 271, 433, 436

rich diet, 12

somatic embryos, 552, 557

trees, 98, 174, 234, 269, 271, 289, 291, 292, 317, 437, 442, 445, 456, 495, 553

trunk borer, 312

twig beetle, 292

weevil, 294, 300, 309, 310

Warm temperatures, 74, 84, 349, 355, 366

Wastewater, 22

Water

application, 21

availability, 268, 328, 379, 390, 398, 531

chestnut, 446

conservation, 4, 13, 14, 21

distribution, 21

dynamics, 180

infiltration, 8, 14

loss, 3, 21

management, 3, 8, 14, 21, 22, 31

recycling, 22

resources, 31, 38, 258

runoff, 14

samples, 115

scarcity, 8, 14, 22, 38, 391, 413

soaked

lesions, 289

spots, 346

source, 315

supply, 20

use efficiency, 3, 14, 21, 22, 31, 38, 39

wastage, 14, 21

Weak root systems, 229

Wealth, 17, 25, 39, 153, 185, 549, 550

Weather, 13, 23, 37, 39, 54, 67, 94, 96, 166, 176, 182–186, 243, 267, 269, 290, 324, 326, 327, 344, 346, 365, 366, 386, 408, 411

conditions, 54, 96, 176, 182–185, 267, 386

events, 13, 23, 39

forecasting, 166, 185, 186

patterns, 184

stations, 37

Websites, 539

Weeding, 180

Weevils, 267, 275, 288, 294, 307, 310, 333, 338–340, 359

Weight

gain, 9

maintenance, 9, 409

management, 6, 8–10, 29, 33, 147

Weiser, 321

Well-rooted rootstocks, 231

Well-spaced, 439, 440

Western

Asia, 15, 93

Schley, 115

style diet, 203

Wet weather, 346, 366

White

callus, 118

cream pulp, 448

powdery

appearance, 290

patches, 290

rot roots, 290

Wichita, 85, 114–116

Wider adaptability, 272

Widespread

cultivation, 16, 238, 456, 459

utilization, 172

Wild

chestnut cultivation systems, 211

genes, 172

genetic diversity, 173

seedlings, 464

species, 56, 383, 384, 463

systems, 211

Wind pollination, 64, 96, 456, 472

Windbreaks, 8, 23

Windless day, 75

Winter, 2, 13, 53, 60, 61, 66, 67, 69, 72, 95, 98, 99, 176, 228, 232, 234, 236, 238, 272, 291, 293, 315, 319, 325, 327, 329, 333, 334, 339–341, 346, 347, 349, 358, 364, 366, 412, 449, 466, 471, 553

forms, 349

legume cover crops, 358

Wisdom, 17, 23–25, 165, 185

Wolfskill, 445

Wood, 3, 65, 67, 81, 82, 89, 92, 110, 245, 288, 307, 321, 345, 356, 362, 367, 432, 435, 448, 452, 495

Woody

plant

medium (WPM), 243, 490, 491

stems, 207

species, 244, 501

Worldwide machine-learning, 166

Worm-like shape, 341

Wound, 134, 246

healing properties, 134

Würmian period, 448

WUSCHEL-related homeobox 11 (WOX11), 558, 559

X

Xanthine oxidase (XO), 142

Xanthomonas, 260

arboricola pv pruni (Xap), 263, 289, 436, 523

Xanthophyll, 143, 144

carotenoid, 143

Xerophilic aspergillus spp., 215

Xerophytic, 56, 59

conditions, 59

environment, 56

Xiphinema americanum, 331

species, 331

X-ray

crystallography, 533

pictures, 174

Xyleborinus saxesenii, 298

Xyleborus dispar, 338

Xylella fastidiosa, 3, 318, 357

Xylem, 367

Xylosandrus germanus, 298

Y

Yaltsinki almond cultivar, 117

Yeast extract sucrose (YES), 206

Yellow

chlorotic haloes, 289

fleshed kiwifruit, 380

green anthers, 84

pistachio hard scale, 352, 353

pollen, 84

spots, 328, 362

sticky traps, 296

Yoghurt, 201

Z

Zagros region, 463

Zaomma lambinus, 352

Zarand seedling, 239

Zeatin, 199

Zeaxanthin, 26, 143, 242, 410

Zinc (Zn), 26, 267, 391, 455, 549

finger nuclease (ZFN), 549, 552, 555

Zonate leaf spot, 357

Zonatus, 317, 322, 323

Zoospores, 315, 337

Zygote, 97

Zygotic

embryo, 491, 559

selection, 62