Salinity Resilience and Sustainable Crop Production Under Climate Change (Earth and Environmental Sciences Library) 3031485416, 9783031485411

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Earth and Environmental Sciences Library

Hassan Auda Awaad

Salinity Resilience and Sustainable Crop Production Under Climate Change

Earth and Environmental Sciences Library Series Editors Abdelazim M. Negm, Faculty of Engineering, Zagazig University, Zagazig, Egypt Tatiana Chaplina, Antalya, Türkiye

Earth and Environmental Sciences Library (EESL) is a multidisciplinary book series focusing on innovative approaches and solid reviews to strengthen the role of the Earth and Environmental Sciences communities, while also providing sound guidance for stakeholders, decision-makers, policymakers, international organizations, and NGOs. Topics of interest include oceanography, the marine environment, atmospheric sciences, hydrology and soil sciences, geophysics and geology, agriculture, environmental pollution, remote sensing, climate change, water resources, and natural resources management. In pursuit of these topics, the Earth Sciences and Environmental Sciences communities are invited to share their knowledge and expertise in the form of edited books, monographs, and conference proceedings.

Hassan Auda Awaad

Salinity Resilience and Sustainable Crop Production Under Climate Change

Hassan Auda Awaad Crop Science Department Faculty of Agriculture Zagazig University Zagazig, Egypt

ISSN 2730-6674 ISSN 2730-6682 (electronic) Earth and Environmental Sciences Library ISBN 978-3-031-48541-1 ISBN 978-3-031-48542-8 (eBook) https://doi.org/10.1007/978-3-031-48542-8 © The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland Paper in this product is recyclable.

Preface

Climate change is one of the most pressing and contemporary issues in the fields of agricultural sciences. Climate vulnerability threatens global food production systems, affecting people’s lives. Climate change also poses a threat to the capabilities and wealth of future generations. The Paris Climate Agreement (COP21) is one of the efforts to mitigate climate change to bring global temperature decrease below 2 °C and to follow efforts to limit it to 1.5 °C. The agricultural sector is one of most sensitive sector to climate change. Intergovernmental Panel for Climate Change showed that the developing countries agriculture would be affected by severe desertification, floods, salinity, drought, rising temperature, and extreme events. As a result, climate change may threaten food security which would necessitate coordinated efforts to ensure food security on a long-term basis. Worldwide agriculture is greatly affected by the three major abiotic factors, viz., high temperature, salinity, and water scarcity. Salinity is among the major stresses to food production, having been one of the causes of the ancient Mesopotamian great commercial losses of above 10 billion USD. In the context, this book tried to present the impact of salinity on Sustainable Crop Production. Understanding cultivar differences and genotypes controlling traits of adaptation to stress is one of the best options for adaptation and salinity conditions in light of the changing climate. Therefore, this book helps to give an understanding of impact of salinity on morpho-physiological, anatomical, biochemical, molecular structures, reactive oxygen species, germination, nodulation, growth vegetation, yield and quality of crop plants, and then sustainable crop production.

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Preface

The book also dealt with crop responses to salinity stress by activating protective mechanisms and salinity resilience-relevant traits, i.e., phenological, morphophysiological, anatomical, and biochemical as selection criteria. It may include employing breeding approaches and using molecular markers to design new adaptive genotypes more tolerant to salinity relying on selective criteria and plant characteristics, whether phenological, morpho-physiological, or biochemical, which are closely related to salinity tolerance, are among the effective options. So, the focus was on the utilization of genetic diversity and genetic analysis in breeding and biotechnology approaches for producing salinity resilience genotypes. Also, the author addresses on mitigation options toward sustainability via agricultural practices, and finally techniques and measurements of assessing genotypes. This book included 10 chapters in six parts focusing on cereals, legumes, oil, sugar, fiber and forage crops, whether they are glycophytes or halophytes. Part I is an introduction and contains Chap. 1 to introduce the book chapters to the interested audiences. Part II is titled “Impact of Salinity on Sustainable Crop Production Strategies” which is covered in one chapter. Chapter 2 is titled “Salinity and Its Impact on Sustainable Crop Production”. Part III came in two chapters and its title “Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions?” Chap. 3 is titled “Protective Mechanisms of Salinity Stress: How Do Plants Resilient Salinity Conditions?” and Chap. 4 under title “Fundamentals of Crop Resistance to Salinity: Plant Characters and Selection Criteria”. Part IV has been explored in three chapters and is titled “Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress”. Chapter 5 is titled “Genetic Variability and Genetic Resources for Salinity Tolerance”, Chap. 6 is titled “Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops”, while Chap. 7 titled “Breeding Efforts and Biotechnology”. Part V has been extrapolated into two chapters and titled “Management Options, Mitigation and Genotype Assessment Techniques”. Chapter 8 is about “Mitigation Options Towards Sustainability Via Agricultural Practices” and Chap. 9 titled “Techniques and Measurements of Assessing Genotypes for Salinity Tolerance”. Part VI includes Chap. 10, for the general conclusions and recommendations of the chapters under each theme are existed. This book has been prepared and supported by recent references and statistics with tables and colorful figures to deliver recent advances to the audience of graduate students and researchers at universities and research centers in the fields of crop breeding and production, physiology, genetics, molecular biology and biotechnology, and allied fields such as agroecology, sustainable agriculture, and climate-resilient

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agriculture. The book provides a comprehensive review of the rapidly expanding. It includes in-depth discussions on salinity resilience, sustainable production under climate change, how do plants resilient salinity conditions? Beside genetic diversity and inheritance of resistance to salinity. Furthermore, it covers a vast array of special topics and applications illustrating the wide use recent approach of techniques and measurements of assessing genotypes for salinity resilience.

Zagazig, Egypt July 2023

Hassan Auda Awaad

Acknowledgments

The author wishes to express his thanks for all who contributed to make this high-quality book a real source of knowledge and latest findings in the field of Salinity Resilience and Sustainable Crop Production Under Climate Change. Acknowledgments must be extended to include all members of the Springer team who have worked long and hard to produce this book and make it a reality for researchers, graduate students, professionals, and scientists worldwide. The author appreciates the advices and encouragement of Dr. Abdelazim M. Negm, Professor of Water and Water Structures Engineering Department, Faculty of Engineering, Zagazig University, Egypt, the editor of the earth and Environmental Science Library Book Series. The author is highly grateful and appreciates the efforts made by his wife, Dr. Azza Hesssen Emam in accomplishing this book. Also, the author gives great thanks to Dr. El-Sayed Mansour El-Sayed, Assistant Professor, Department of Crop Science, Faculty of Agriculture, Zagazig University, Egypt and Prof. Ehab Saudi Moustafa, Desert Research Center, El-Matarya, Cairo, Egypt, for approval to use some specific tables and figures in this book. The book author would be happy to receive any comments to improve future editions. The email of the author can be found inside the book at the end of the preface. Zagazig, Egypt July 2023

Hassan Auda Awaad

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Contents

Part I 1

Introduction

Introduction to “Salinity Resilience and Sustainable Crop Production Under Climate Change” . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.1 Concept of Saline Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.2 Concept of Sodic Soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.3 Concept of Saline-Sodic Soils . . . . . . . . . . . . . . . . . . . . . . 1.1.4 Concept of Salt Resilience . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.5 Concept of Salt Resistance . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.6 Concept of Salt Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . 1.1.7 Concept of Agricultural Production Sustainability . . . . . 1.2 Purpose of the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3 Scope of the Book . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4 Themes of the Book and Contribution of the Chapters . . . . . . . . . 1.4.1 Impact of Salinity on Sustainable Crop Production Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.4.2 Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? . . . . . . . . . . . . . . . . . . . . . . 1.4.3 Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress . . . . . . . . . . . . . . . . . . . . . . 1.4.4 Management Options, Mitigation and Genotype Assessment Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3 3 4 5 5 5 6 6 6 14 15 16 17

17

18 20 21

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Part II 2

Impact of Salinity on Sustainable Crop Production Strategies

Salinity and Its Impact on Sustainable Crop Production . . . . . . . . . . 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Salinity, Its Causes, and Classes . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.1 Classes of Soil Salinity and Plant Growth . . . . . . . . . . . . 2.2.2 Salt-Affected Lands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3 Saline Irrigation Water and Its Validity . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Specific Ion Effect . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Ion Concentration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Evaluation of Validity of Irrigation Water . . . . . . . . . . . . . 2.3.4 Salinity Assessing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Levels of Crop Tolerance to Salinity . . . . . . . . . . . . . . . . . . . . . . . . 2.5 Salinity and Its Relationship to Field Crop Productivity . . . . . . . . 2.6 Summary of Adverse Effects of Salinity on Crop Plants . . . . . . . . 2.6.1 Effect of Salinity on the Production of Reactive Oxygen Species . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.2 Effect of Salinity on Photosynthetic Pigments and Quantum Yield of Photosystem-II . . . . . . . . . . . . . . . 2.6.3 Effect of Salinity on Physiological and Plant Water Relations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.4 Effect of Salinity on Biochemical Components . . . . . . . . 2.6.5 Effect of Salinity on Seed Germination and Its Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.6.6 Effect of Salinity on Nodulation Process . . . . . . . . . . . . . 2.6.7 Effect of Salinity on Vegetative Growth . . . . . . . . . . . . . . 2.6.8 Effect of Salinity on Yield and Quality . . . . . . . . . . . . . . . 2.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.8 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

29 29 31 32 32 34 35 36 41 41 42 45 55 57 60 62 63 66 67 67 69 83 83 83

Part III Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? 3

Protective Mechanisms of Salinity Stress: How Do Plants Resilient Salinity Conditions? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 3.2 Nature and Mechanism of Plant Resistance to Salinity . . . . . . . . . 97 3.2.1 Salinity Resistance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 3.2.2 Salt Avoidance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 3.2.3 Salt Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 104

Contents

Adaptive Mechanisms of Crop Genotypes to Salinity Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.1 Control of Absorption of Ions . . . . . . . . . . . . . . . . . . . . . . 3.3.2 Ion Management System in the Plant . . . . . . . . . . . . . . . . 3.3.3 Selectivity of Ion Passage . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3.4 Maintaining Ionic Equilibrium . . . . . . . . . . . . . . . . . . . . . . 3.3.5 Ion Homeostasis and Salt Tolerance . . . . . . . . . . . . . . . . . 3.3.6 Compartmentalization of Toxic Ions and Osmolytes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Phytoremediation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.6 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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3.3

4

Fundamentals of Crop Resistance to Salinity: Plant Characters and Selection Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Phenological Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2.1 Germination and Seedling Growth Ability . . . . . . . . . . . . 4.2.2 Early Maturity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3 Morphological Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.1 Leaf Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.2 Root System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.3 Shoot: Root Ratio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.3.4 Salt Glands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4 Anatomical Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Physiological Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Chlorophyll Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Stomata and Transpiration Rate . . . . . . . . . . . . . . . . . . . . . 4.5.3 Photosynthesis Efficiency . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.4 Relative Water Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Leaf Water Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.6 Osmotic Potential . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.7 Cell Membrane Stability . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Biochemical Characters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.1 Primary Metabolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.6.2 Secondary Metabolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

108 108 109 109 110 111 112 113 113 114 114 119 119 121 121 123 125 126 127 128 129 130 131 131 133 134 136 137 139 141 143 143 162 167 168 168

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Contents

Part IV Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress 5

6

7

Genetic Variability and Genetic Resources for Salinity Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Genetic Variability and Genetic Resources for Salinity Tolerance in Crop Plants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.1 Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.2 Barley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.3 Rice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.4 Maize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.5 Sorghum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.6 Faba Bean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.7 Chickpea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.8 Lupine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2.9 Cowpea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

189 189 190 190 193 194 196 197 198 198 199 200 214 214 214

Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2 Genetic Behavior of Salinity Tolerance in Crop Plants . . . . . . . . . 6.2.1 Wheat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.2 Barley . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.3 Rice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.4 Maize . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.5 Sorghum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.6 Faba Bean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.7 Cowpea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.8 Soybean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.9 Cotton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2.10 Canola . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

223 223 224 224 226 227 228 229 230 230 231 231 234 240 241 241

Breeding Efforts and Biotechnology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2 Classical Breeding Approaches for Salinity Tolerance . . . . . . . . . 7.2.1 Introduction and Gene Banks . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Phenotypic Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

247 247 248 249 251

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7.2.3 Recurrent Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.4 Hybridization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.5 Mutations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3 Recent Approaches in Breeding for Salinity Tolerance . . . . . . . . . 7.3.1 Molecular and DNA-Markers . . . . . . . . . . . . . . . . . . . . . . . 7.3.2 Gene Transfer Technology to Improve Salt Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.3 Tissue Culture Technology . . . . . . . . . . . . . . . . . . . . . . . . . 7.3.4 Epigenetic and Methylation of DNA . . . . . . . . . . . . . . . . . 7.3.5 Proteomic Approaches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.4 Transcriptional Regulation and Gene Expression in Relation to Salinity Stress Tolerance . . . . . . . . . . . . . . . . . . . . . . 7.4.1 Genes up or Down Regulated by Salinity . . . . . . . . . . . . . 7.5 Transformation and Tolerance to Salinity . . . . . . . . . . . . . . . . . . . . 7.6 Role of Cellular Signal Transduction in Salinity Tolerance . . . . . 7.6.1 Cell-Specific Signaling . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.7 Problems in Breeding for Salinity Resistance . . . . . . . . . . . . . . . . . 7.8 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.9 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part V 8

9

254 254 256 257 257 268 272 276 277 277 278 281 282 285 286 287 287 287

Management Options, Mitigation and Genotype Assessment Techniques

Mitigation Options Towards Sustainability Via Agricultural Practices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2 How to Deal with Salinity Problem: Role of Agricultural Practices in Improving Crop Tolerance to Salinity . . . . . . . . . . . . . 8.2.1 Application of Leaching Irrigations Process Pre-planting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.2 Application of Gypsum . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.2.3 Choosing Crop Species and the Cultivar . . . . . . . . . . . . . . 8.2.4 Applied of Proper Agricultural Practices . . . . . . . . . . . . . 8.3 Environmental Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4 Improvement of Salinity Tolerance by Exogenous Treatments with Metabolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.6 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

303 303 304 304 306 307 308 320 321 325 325 326

Techniques and Measurements of Assessing Genotypes for Salinity Tolerance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 333 9.2 Evaluation Methods of Crop Genotypes . . . . . . . . . . . . . . . . . . . . . 334

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9.2.1 Lysimeter Micro Plots . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.2 Laboratory Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.3 Phytotron Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.4 Growth Chamber Conditions . . . . . . . . . . . . . . . . . . . . . . . 9.2.5 Greenhouses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.6 Pots in Glasshouse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.7 Pots in Lath House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.8 Pots in Net-House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.2.9 Vinyl House . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.3 Evaluation at Tissue Culture Level (In-Vitro) . . . . . . . . . . . . . . . . . 9.3.1 Growth and Seeding Survival Ability . . . . . . . . . . . . . . . . 9.3.2 In-Vitro Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.4 Evaluation Under Field Conditions (In-Vivo) . . . . . . . . . . . . . . . . . 9.4.1 Nonsaline Filed with Saline Irrigation . . . . . . . . . . . . . . . 9.4.2 Saline Field with Saline Irrigation . . . . . . . . . . . . . . . . . . . 9.4.3 Evaluation in Screening Microplots . . . . . . . . . . . . . . . . . 9.5 Measurements and Scoring Systems of Salinity Tolerance . . . . . . 9.5.1 Cell Viability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.2 Germination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.3 Dry Matter Accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.4 Leaf Ion Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.5 Leaf Necrosis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.6 Root Growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.7 Osmoregulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.8 Yield . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.5.9 Tolerance Indices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9.7 Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Part VI

334 335 337 338 338 346 348 349 349 349 350 350 352 353 354 356 356 357 357 357 358 358 358 358 358 361 365 365 366

General Conclusions and Recommendations

10 Update, General Conclusions and Recommendations of “Salinity Resilience and Sustainable Crop Production Under Climate Change” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.2 Update . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3 General Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.2 Impact of Salinity on Sustainable Crop Production Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.3.3 Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? . . . . . . . . . . . . . . . . . . . . . .

375 375 377 378 378 379

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10.3.4 Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress . . . . . . . . . . . . . . . . . . . . . . 10.3.5 Management Options, Mitigation, and Genotype Assessment Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4 General Recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.2 Impact of Salinity on Sustainable Crop Production Strategies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10.4.3 Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? . . . . . . . . . . . . . . . . . . . . . . 10.4.4 Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress . . . . . . . . . . . . . . . . . . . . . . 10.4.5 Management Options, Mitigation and Genotype Assessment Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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380 380 381 381 381

382

382 383 383

Abbreviations

ARC ATP Ca2+ CaCl2 cDNAs cDNA-SSH CEC CID Cl– CO2 COP21 CSSRI DH population DNA DW ECe ECiw Enoyl-ACP reductase ESP FAO GCV GGE biplot Glutamyl-tRNA GPDH GSASmap GSP-FAO H2 O2 HNO3

Agriculture Research Center Adenosine triphosphate Calcium cation Calcium chloride Complementary DNA Complementary DNA-suppression subtractive hybridization Cation exchange capacity Carbon isotope discrimination Chloride anion Carbon dioxide Twenty-First Session of the Conference of the Parties Central Soil Salinity Research Institute Doubled haploids population Deoxyribonucleic acid Dry weight Electrical conductivity of a saturated soil-paste extract Electrical Conductivity of irrigation water Enoyl-acyl carrier protein reductase Exchangeable sodium percentage Food and Agriculture Organization Genetic coefficient of variation Genotype Main effect (G) plus Genotype by Environment interaction (GE) biplot Glutamyl-transfer RNA Glyceraldehyde 3-phosphate dehydrogenase Global Map of Salt-affected Soils Global Soil Partnership—Food and Agriculture Organization Hydrogen peroxide Nitric acid xix

xx

ICBA IRRI ISSR ITPS K+ MDA Mg2+ miRNAs mRNA Na+ NAC TFs NaCl P2 O5 PCV pH POX PS-II PUFA QTL RAPD-PCR RNA ROS SAR SCA SPAD SSR TDS UDP UDP-glucose UPGMA USDA

Abbreviations

International Center for Biosaline Agriculture International Rice Research Institute Inter-Simple Sequence Repeats Intergovernmental Technical Panel on Soils Potassium cation Malondialdehyde Magnesium cation MicroRNA Messenger RNA Sodium cation NAC transcription factors Sodium chloride Phosphorus pentoxide Phenotypic coefficient of variation Potential hydrogen Peroxidase Photosystem II Polyunsaturated fatty acid Quantitative trait locus Random Amplified Polymorphic DNA—Polymerase Chain Reaction Ribonucleic acid Reactive oxygen species Sodium adsorption ratio Specific combining ability Soil Plant Analysis Development Simple Sequence Repeat Total dissolved solids Uridine diphosphate Uridine diphosphate glucose Unweighted pair group method with arithmetic mean United States Department of Agriculture

Symbols AhABI4 ci /ca GmMYB173 GmMYB173S59A GmMYB173S59D HAL1 HKTs

Arachis hypogaea L. abscisic acid insensitive 4 The ratio of internal to atmospheric CO2 concentration Transcription factor Phospho-ablative (GmMYB173S59A ) version of GmMYB173 Phospho-mimic (GmMYB173S59D ) version of GmMYB173 Yeast gene responsible for salt tolerance High-affinity K+ transporters

Abbreviations

PIP r

ScPIP1-1

xxi

Plasma membrane intrinsic proteins Correlation coefficient is a statistical measure of the strength of a linear relationship between two variables. Its values can range from −1 to +1 Sugarcane plasma membrane intrinsic proteins gene 1

Variables and Units µS/cm dS m−1 Feddan Fv/Fm Hectare kDa kg/fed kg/ha mg/L−1 mmhos/cm mS/cm mS/m ppm

MicroSiemens per centimeter DeciSiemens per meter Equivalent to 4200.83 m2 Ratio of variable to maximum fluorescence 10,000 square meters Kilodalton Kilogram per feddan Kilogram per hectare Milligrams per liter Millimhos per centimeter MilliSiemens per centimeter MilliSiemens per meter Parts per million

Part I

Introduction

Chapter 1

Introduction to “Salinity Resilience and Sustainable Crop Production Under Climate Change”

1.1 Background Under the conditions of climate change threats and its impacts on the agricultural sector, salinization is one of the major challenges of contemporary agriculture. Consistent with the FAO, the global salt-affected area covers 424 million hectares of topsoil (0–30 cm) and 833 million hectares of subsoil (30–100 cm) according to 73% of the land mapped so far (FAO 2021). In this context, all over the world, approximately 20–50% of irrigated land areas are affected by salt stress (FAO 2021). Thus, global agricultural production’s sustainability is threatened by abiotic stresses (Hasanuzzaman et al. 2020; Yadav et al. 2020). Salt-affected areas are increasing by about 10% annually and if the problem is not overcome, by 2050 about 50% of arable land will be salinized (Butcher et al. 2016). Worldwide, soil salinity has affected 20 and 33% of total cultivated and irrigated agricultural lands, respectively, causing a loss of 27.3 billion USD (Qadir et al. 2014; Egamberdieva et al. 2019). Salinity is one of the most important abiotic stresses limiting the growth and productivity of crop plants in many regions worldwide, especially with the increased use of poor-quality water for irrigation and the high level of soil salinity in light of climate changes. Plant acclimatization and salt stress tolerance include physiological, biochemical and molecular features that regulate adaptation to salt stress in crop plants. A comprehensive understanding of how plants respond to salinity stress at different levels and an integrated approach combining molecular tools with physiological and biochemical techniques is important to produce salt-tolerant crop varieties grown in salinity-affected areas. Therefore, salt tolerance is an important feature in irrigated lands in semi-arid regions where the problem of soil salinity is widespread over hundreds millions of hectares. Every minute, the world loses at least ten hectares of arable land, five hectares due to soil erosion, three hectares owing to soil salinization, one hectare caused by various soil degradation processes, and one hectare as a result of nonagricultural uses (Buringh 1977). Soil salinity is projected to affect 3,230,000 km2 in © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_1

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Fig. 1.1 Global map of salt-affected soils (GSASmap) (FAO 2015)

over 100 nations around the world, and these figures steadily increase as illustrated in Fig. 1.1 (FAO 2015; Shahid et al. 2018). In areas where sprinkler irrigation is practiced, saline sprinkler water may cause significant damage because of leaf burn, whether the soil is saline or not. Also, salt accumulation in the root zone is a common problem in irrigated areas, which leads to partial or complete loss of soil productivity (Hasanuzzaman et al. 2014). To overcome the economic losses, appropriate techniques should be followed to cultivate salt-affected lands to achieve sustainable agriculture by cultivating salttolerant glycophyte crop varieties or halophyte plants. Numerous researchers have seen the possibility of increasing the salt tolerance of major food crops through breeding and molecular biology-based procedures along with improving the plant environment through adequate agricultural procedures (Mujeeb-Kazi et al. 2019; Saade et al. 2020; Hassan et al. 2021).

1.1.1 Concept of Saline Soils Saline soils are defined as the soils that usually have ECe ≥ 4 dS m−1 , the pH less than 8.5, and exchangeable sodium percentage (ESP) < 15%. Saline soils often are in normal physical condition with good structure and permeability. It is characterized by irregular plant growth and salty white crusts on the soil surface. The salts are usually sulfates and/or chlorides of calcium and magnesium. Electrical conductivity, abbreviated EC, is the ability of a soil solution to carry electrical current, and salts increase this ability (Chinchmalatpure 2017). Soil salinity is the salt content in the soil whereas, salinization is defined as the process of increasing the salt content in the soil. Salts occur naturally within soils and water. Salinity can result from natural processes such as mineral weathering, the gradual withdrawal of an ocean, or artificial processes such as irrigation and road salt.

1.1 Background

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Table 1.1 Salt-affected soil classification (Omuto et al. 2020) Classification

Electrical conductivity (mS/cm)

Soil pH

Exchangeable sodium percentage

Soil physical condition

Saline

>4.0

4.0

15

Normal

1.1.2 Concept of Sodic Soils Sodic soils have exchangeable sodium percentages of more than 15% of the soil’s cation exchange capacity (CEC). The pH is greater than 8.5, and the electrical conductivity is less > 4 mS/cm. .The combination of high levels of sodium and low total salts leads to disperse soil particles, making sodic soils poor tillable. These soils are sticky when wet, almost impermeable to water and has a slick look. As they dry, they become hard, cloddy, and crusty. Davis et al. (2014) explained that sodic soils harm most plants’ growth. They can be reclaimed, but it might be slow and costly due to the lack of a stable soil structure, which slows water drainage.

1.1.3 Concept of Saline-Sodic Soils Saline-sodic soils comprise large amounts of total soluble salts and more than 15% exchangeable sodium. The pH is generally less than 8.5 and the electrical conductivity is less than 4 mS/cm. Physical properties of these soils are good as long as there is an excess of soluble salts. Table 1.1 show the classes: saline, sodic and saline-sodic. Understanding the variances is critical for the reason that these factors determine how the soils should be managed and reclaimed.

1.1.4 Concept of Salt Resilience The concept of resilience provided insight and a new approach to the traditional perspective of agricultural management by emphasizing the need to maintain a variety of coping mechanisms with environmental changes. It means endurance or adaptive capacity, which is the ability of a variety to adapt and restore balance when faced with environmental stresses and exposure to high salinity levels. These include sensitivity or tolerance to increased salinity, the ability to recover from salinity damage, and the ability to change to other systems if salinity increases.

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1.1.5 Concept of Salt Resistance The ability of crop genotype to survive and produce harvestable yields under salt stress is defined as salt resistance. Salt resistance is a complex phenomenon, and plants manifest a variation of adaptations at subcellular, cellular, and organ levels, for instance, stomatal regulation, ion homeostasis, hormonal balance, stimulation of the antioxidant protection system, osmotic regulation, and maintenance of water status in the tissue to grow well under salinity.

1.1.6 Concept of Salt Tolerance Salinity tolerance can be defined as the ability of a genotype to maintain growth in an environment containing sodium chloride or a mixture of salts. Salt tolerance of crops is also defined as the maximum salt level a crop tolerates without losing its productivity. However, it is affected negatively at higher levels. The salt level is often taken as the salinity of the soil or the salinity of irrigation water.

1.1.7 Concept of Agricultural Production Sustainability Sustainability is an environmental term that describes how biological systems remain diverse and productive over time. Meanwhile, ustainability for humans is the ability to preserve the quality of life we live in the long term, which in turn depends on the conservation of the natural world and the responsible use of natural resources. At first, “sustainability” meant using only natural and renewable resources so that people could continue to rely on their crops for the long term. The United Nations Commission on Environment and Development, also known as the Brundtland Commission, founded in 1983, defined the term “sustainability” sustainable development as development that “meets the needs of the present without compromising the ability of future generations to meet their own needs.” The three pillars of sustainability are economy, society and environmental factors. The relationship between the “three pillars of sustainability”, in which both economy and society are constrained by environmental limits is illustrating Fig. 1.2. A different vision of sustainability has been developing since the 1990s. Where sustainability is not seen in terms of meeting human aspirations to increase wellbeing, rather the environmental and social dimension must be taken into account, as a systematic view of these aspirations (Capra 2015). Under this concept, the following interrelated pillars define sustainability: environment, economic and social. Also called the “triple bottom line,” the three dimensions are equivalent, and the goal is to balance between them. These three pillars are interrelated; in the long run, none can exist without the other. Sustainability can also be defined as a socio-environmental

1.1 Background Fig. 1.2 A diagram indicating the relationship between the “three pillars of sustainability”, in which both economy and society are constrained by environmental limits (drawn by the author H A Awaad)

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Sociality

Economy

Environment

process characterized by the pursuit of a common ideal. The goal is to conserve this balance, so available resources must not be depleted faster than natural resources. Figure 1.3 shows a brief description of sustainability. Negacz et al. (2022) stated that the total area of salt-affected lands worldwide equals 17 million km2 . Most promising saline soils for saline agriculture total to 2 million km2 . Also, water availability is the most restrictive factor limiting the potential area for saline agriculture. Therefore, Future mapping should focus on high-populated areas with favorable socio-economic conditions. Basics of Agricultural Production Sustainability FAO projections indicate that 80% of the additional food required to meet food demand in 2050 must come from land already under cultivation. There is not much room for expansion in agricultural area, except in some parts of Africa and South America. This is because much of the additional land available is not suitable for agriculture, and the environmental, social and economic costs of bringing it into production would be very high. Therefore, it was necessary to consider some of the following facts: • The Food and Agriculture Organization report (2011) indicated that 33 percent of the lands are moderately to severely degraded due to erosion, salinization, compaction, and chemical contamination of the soil. • Drought and desertification also cause the loss of about 12 million hectares of land every year (United Nations Convention to Combat Desertification 2013). • Over the past decade, about 13 million hectares of forest have been converted to other land uses, especially agriculture, at the expense of a myriad of ecosystem services (FAO and Joint Research Centre 2012).

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Fig. 1.3 A brief description of sustainability (drawn by the author H A Awaad)

• An agroecosystem and food systems perspective are essential to understanding sustainability. The transition of agroecosystems from individual fields to farms to ecoregions in the broader sense is also important. • Food systems, which include agroecosystems as well as components of food distribution and consumption, extend from farmers to the local community to the global population. A systems perspective provides a comprehensive view of agricultural production and distribution institutions and how they impact human societies and the natural environment. A systems-based approach also gives the tools to assess the impact of human society and its institutions on agriculture and its environmental sustainability. Agricultural sustainability is based on the need to meet the needs of the present without compromising the ability of future generations to meet their own needs. • The long-term management of natural and human resources is equally important for short-term economic gains. Human resource management involves considering social responsibilities such as working and living conditions for workers, the needs of rural communities, and consumer health and safety now and in the future. Land and natural resource management involves maintaining or improving

1.1 Background

• •

•

•

•

•

9

the quality of these resources and using them in ways that allow for their renewal in the future. Concerns regarding animal welfare in agricultural establishments must be taken into account (Brodt et al. 2011). Under stress biotic and abiotic conditions, it is worth noting that different types of natural and human systems are highly resilient, adaptable and have great diversity, especially under conditions of climate change, multiple pests, political contexts, etc. Adaptability is a key component of resilience, and the agroecosystem regains its precise form and function in the face of disturbances and changing conditions. Diversity often helps confer adaptability, because the more diversity within a food system, whether in terms of crop types or cultural knowledge, the more tools and methods the system has to adapt to change. The agri-food ecosystem approach also includes multifaceted efforts in research, education and action by researchers, farmers, workers, retailers, consumers, policy makers and others with a stake in agricultural and food systems, to move toward greater agricultural sustainability. Therefore, achieving sustainability in food and agriculture is an ongoing process that depends on the balance between the social, economic and environmental objectives of agriculture, as well as between agriculture and other sectors of the economy. Hereby, Developing community values and knowledge is important in how sustainability goals are put into practice. With the application of advanced technologies such as the use of mechanization, chemical fertilizers, specialization and government policies, the productivity of food and fiber crops increases and hence more food and fiber are produced at lower prices. This reduces many risks in agriculture, but also has significant costs. However, on the other hand, there are many negatives, namely the depletion of topsoil, groundwater pollution, air pollution, greenhouse gas emissions, the decline of family farms, neglect of living and working conditions for agricultural workers, and the emergence of new threats to human health and safety due to the spread of pathogens, and also economic threats.

Sustainable agriculture and environment natural resource management Achieving a balance between food and fiber production while reducing harmful impacts on ecosystems without compromising the ability of future generations to produce and prosper is an important goal of sustainable development. And so. The permaculture approach seeks to use natural resources in a way that enables them to replenish their productive capacity, as well as reduce harmful impacts on ecosystems even beyond the boundaries of the field. This is achieved by taking advantage of existing natural processes, and designing biologically integrated agroecosystems that rely more on internal cycling of nutrients and energy, to maintain an economically viable production system. Farmers sometimes seek to achieve a higher level of environmental sustainability by reducing their use of toxic pesticides through the following natural processes:

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1 Introduction to “Salinity Resilience and Sustainable Crop Production …

1. Planting fences along the edges of fields. 2. ground covers between the rows, thus providing a habitat for beneficial insects and birds that prey on pests. 3. Growing a more diverse mix of crops that confuse or deflect pests. 4. Maintaining a high degree of genetic diversity through the largest possible number of crop varieties and animal breeds will provide more genetic resources necessary for breeding programs for resistance to diseases and pests. 5. Use environmentally friendly pesticides and fertilizers. • Taking care of the soil and maintaining its integrity as a complex and highly organized entity containing mineral particles, organic materials, air, water, and living organisms is vital to long-term sustainability because healthy soil promotes the health of crops and livestock. Maintaining soil performance is achieved through: 1. Maintaining and increasing organic matter in the soil, as it serves as a primary source and sink for nutrients, as a substrate for microbial activity, and as a barrier against fluctuations in acidity, water content, and pollutants. 2. The accumulation of soil organic matter helps mitigate the increase in carbon dioxide in the atmosphere and hence climate change. 3. Organic matter builds better soil structure, which leads to improved water penetration, reduced surface runoff, enhanced drainage, increased stability, and therefore reduced wind and water erosion. • Improving the efficiency of fertilizer use and relying on organic nutrient sources (animal and green manure) are important elements of sustainable agriculture. Nutrient recycling is considered through diversified agriculture in which livestock and crop production are more spatially integrated. Hence, large-scale mixed croplivestock systems, especially in developing countries, can contribute significantly to future agricultural sustainability and global food security. • Several parts of the world suffer from shortages and/or poor quality of water for agriculture. Excessive withdrawal of surface water affects human activities and irrigation capabilities in the future. Salinization, nutrient overload, and pesticide contamination are also widespread water quality problems. Selecting and breeding more drought- and salt-tolerant crop varieties and hardier livestock breeds, using low-volume irrigation systems, and managing soil and crops to reduce water loss are all ways to use water more efficiently within sustainable agroecosystems. • Modern agriculture relies heavily on non-renewable energy sources, and sustainable farming methods aim to reduce external energy inputs and replace nonrenewable energy sources with renewable ones (such as solar energy, wind energy, biofuels from agricultural waste, or, where economically possible, animal or human labor.( There are many aspects of environmental sustainability, including good management of the systems and natural resources on which farms depend. This includes (David 2022):

1.1 Background

1. 2. 3. 4. 5. 6.

11

Build healthy soil and prevent erosion Manage water wisely Reducing air and water pollution Carbon storage on farms Increased ability to adapt to harsh weather conditions Promoting biodiversity.

An economically and socially sustainable agricultural system: Establishing an economic system on sound foundations helps enables farms of all sizes to be profitable and contribute to their local economies. Such a system supports the next generation of farmers, deals fairly with its workers, promotes equality and justice, achieves access to healthy food for all, and prioritizes people and communities over corporate interests. There are many research fields to achieve these goals for instance; ecological agriculture, the science of managing farms as ecosystems. By working with nature rather than against it, farms can avoid harmful environmental impacts without sacrificing productivity or profitability. By prioritizing science that addresses the interconnections between environmental, economic and social factors, can create a sound sustainable system. It is worth noting that the long-term sustainability of agro-ecosystems without the knowledge, technical competence and skilled labor necessary to manage them effectively is a futility. Given the ever-changing nature of agriculture, sustainability requires a diverse and adaptable knowledge base, using both formal and empirical science and the local knowledge of farmers on the ground. Social institutions play a moral role in educating farmers and encouraging researchers to innovate. Partnerships between farmers and researchers also enhance agricultural productivity as well as long-term sustainability. From an economic perspective, social justice in discussions of sustainable agriculture is an important point in terms of: 1. Agricultural labor wages are so low in most industrialized countries that their agricultural sectors rely heavily on migrant labor from poor countries, leaving farmers vulnerable to changing immigration policies and placing burdens on government social services. 2. The questionable illegal status of many workers contributes to their overall low wages and standard of living, job insecurity, lack of opportunities for advancement, and exemptions from occupational safety protections. 3. Pooling resources among many farmers to provide better housing, sharing labor between farms with different crops to balance the seasonality of employment opportunities, sharing shares in farm profits, and directing workers to own and operate their own farms. 4. Find innovative ways to provide affordable health insurance services and educational opportunities for employees to increase employment equality and social justice.

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1 Introduction to “Salinity Resilience and Sustainable Crop Production …

5. Banding together in production, processing or marketing cooperatives is one way in which farmers can increase their relative economic power. 6. Producing specialized crops of higher value, building direct marketing opportunities that bypass intermediaries, and searching for specialized markets, are other ways that help farmers obtain a greater share of the economic value of what they produce, and provide farmers with protection for farmers in the long term. 7. Economic development policies and tax structures that encourage more diversified agricultural production on family farms play an essential role for healthier rural economies. Within the confines of market structure, consumers can also play a role; Through their purchases, they send powerful messages to producers, retailers and others in the system about what they believe is important, including environmental quality and social justice. The FAO report sets out five key principles that balance the social, economic and environmental dimensions of sustainability: 1. 2. 3. 4. 5.

Improving efficiency in the use of resources. Conserving, protecting and enhancing natural ecosystems. Protecting and improving rural livelihoods and social well-being. Enhancing the resilience of people, communities and ecosystems. Promoting good governance of both natural and human systems.

These five principles provide a basis for developing national policies, strategies and programs that will guide the transition to highly productive, economically viable and environmentally sound agriculture, grounded in principles of equity and social justice. Consequently, the vision of sustainable agriculture is to make food available to all, by managing natural resources in a way that maintains ecosystem functions to support current and future human needs. Also, that farmers, herders, fisher folk, foresters, and other rural people have the opportunity to actively participate and benefit from economic development, enjoy decent working conditions, and work in an environment with fair prices, and that these communities live in security, control their livelihoods, and have equitable access to the resources they use effectively. Innovative governance and technologies to increase sustainable agricultural production Governance systems and innovative technologies are considered innovative fashions to increase sustainable agricultural production, and this is achieved through the following means (FAO 2014): 1. Genetically diverse group of varieties 2. Conservation agriculture 3. Judicious use of organic and inorganic fertilizers, improved soil moisture management 4. Improved water productivity and precision irrigation 5. Integrated pest management (IPM) 6. Genetically diverse base of breeding programs.

1.1 Background

7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

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Improved resource use efficiency. Balanced and precision animal feeding and nutrition Integrated animal health control Sustainable management of natural and planted forests Forest area increase and slowing deforestation 3. Improved efficiency of use of wood-based energy Development of innovative renewable forest products. Tree improvement to support productivity and resilience Aquafeed management Integrated multi-trophic aquaculture Robust biosecurity/aquatic animal health Use of best management practices (BMPs), good aquaculture practices (GAPs) and codes Domestication of aquaculture species Aquaculture certification for animal health and welfare, and food safety Implementing the Ecosystem Approach to Aquaculture (EAA).

Sustainable agricultural practices Many agricultural practices have proven effective in achieving sustainability and improving crop productivity, especially when used together (FAO 2014): 1. Rotating crops and embracing diversity. Growing a variety of crops brings many benefits, in terms of maintaining and improving soil fertility and improving pest control. As well as crop diversity in the intercropping system and crop rotation for several years. 2. Plant cover crops and perennials. Cover crops such as clover, lupine, vetch or rye, are planted and these crops protect and build soil health by preventing erosion, replenishing soil nutrients, and controlling weeds, reducing the need for fertilizers and herbicides. 3. Reducing or eliminating tillage. Conventional plowing (tillage) prepares fields for planting and prevents weed problems but can cause soil loss. No-till or reduced-till methods, which involve introducing seed directly into undisturbed soil, can reduce erosion and improve soil health. 4. Applying integrated pest management (IPM). The use of mechanical and biological control methods systematically keeps pest populations under control while reducing the use of chemical insecticides. 5. Integrating livestock and crops. A growing body of evidence shows that intelligent integration between crop and livestock production can make farms more efficient and profitable.

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6. Adopting agroforestry practices. By mixing trees or shrubs into their operations, they help provide shade and shelter that protects animals and water resources, and additional income from fruit or nut crops. 7. Managing whole systems and landscapes. Landscape vegetation alongside streams, or strips of prairie vegetation in or around crop fields, can help control erosion, reduce nutrient runoff, and support bees, other pollinators, and overall biodiversity.

1.2 Purpose of the Book The current work is devoted on how crop plants treaty with salinity stress conditions under fluctuations in climate conditions through improving novel cultivars more adapted to salinity environments. Hence, it was worthwhile discussing the impact of salinity on sustainable crop production from the perspective of the negative effects on morphology, physiology, biochemistry and crop production. In addition, this scientific work aims to identify the different protective mechanisms of resilience to salinity stress and the importance of genetic variances among crop germplasm in salinity resilience-relevant traits. In order to devise new salinity-tolerant cultivars, it is necessary to identify the inheritance and the nature of the gene action controlling salinity tolerance and the suitable breeding methods and biotechnology, beside, management options, mitigation and genotype assessment techniques in different crops i.e. cereal crops, legumes, oil crops, fiber crops, sugar crops and forage crops. The suggested strategies in improving salinity stress resilience include, breeding methods, marker assisted selection, gene transfer and tissue culture are deliberated a modern approaches helping the breeder in releasing novel cultivars more adapted to salinity stress environments. Beside, mitigation options towards sustainability through appropriate agricultural practices. Therefore, this manuscript will discuss the association between crop production and the impact of salinity stress conditions on crop plants. With a global population expected to reach 10 billion people by 2050, and hence an increased demand for food, more effort must be made to cultivate marginal soils that suffer from various problems, including salinity. Hence, this book provides essential information in the frame of climatic changes and how to mitigate the effects of salinity stress on the quantity of production and quality of crops to reduce the food gap and ensure food security in Egypt and the world.

1.3 Scope of the Book

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1.3 Scope of the Book This work aims to raise awareness of the nature of salinity stress to which crop plants are exposed under climate change. Recent research has identified different adaptive responses to salinity stress at molecular, cellular, metabolic, physiological, biochemical as well as pheno-morphological-levels as illustrated in Fig. 1.4, although the mechanisms underlying salinity tolerance require a more complete understanding and more relevant research. This investigation comprehensively reviews different major mechanisms regulating plant adaptation and tolerance to salinity stress. Reports indicate that 10 million hectares of agriculture land destroyed each year because of the salinity of the soil (Pimentel et al. 2004). This number is likely to rise in the future because of increasing land salinization due to polluted artificial irrigation, weather change, and inappropriate land management. Where, the range of salt concentrations in irrigation water ranges from 0.6 to 1.7 dSm−1 (Valifard et al. 2017). Globally, it is assessed that approximately 6% of all land is affected by salt, with around 22% of the cultivated fields and 33% of the irrigated fields used for agriculture (Munns and Tester 2008; Shrivastava and Kumar 2015). Now, nearby 30 crop plants offer 90% of plant-based human nutrition and the majority of these crops are even salt-sensitive, named glycophytes (Zörb et al. 2019). These crops have had great yield losses under moderate salinity (EC 4–8 dSm−1 , around 40–80 mM NaCl) (Koyro et al. 2008). Under global climate change, this rate is likely to increase through increasing in sea water level, excessive use of groundwater for irrigation, increasing use of low-quality water for irrigation and poor drainage (Zahida et al. 2017; Isayenkov and Maathuis 2019). So, salinity-induced osmotic stress inhibits photosynthesis by reducing subcellular organelle structures and metabolic processes (Arif et al. 2020) and decreased crop productivity by about 50% by disturbing the metabolic balance (Abdul Majeed and Muhammad 2019; Awaad 2022). Fig. 1.4 A comprehensive reviews of different adaptive responses to salinity stress tolerance (drawn by the author H A Awaad)

Molocular & Cellular

Metabolic

Adaptation to Salinity

Physiological & Biochemical

Phenological & Morphological

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1 Introduction to “Salinity Resilience and Sustainable Crop Production …

Plants are classified in this respect into two main types; halophytes (which can tolerate salt) and glycophytes (which do not tolerate salt and finally die), and the majority of major crop types belong to this second category. But, crop genotypes differed significantly in their adapted to salinity stress and showed different levels of tolerance to salinity stress (Souana et al. 2020; Zahra et al. 2022; Mansour et al. 2021; Soni et al. 2022). The selection of nutrient-efficient, salt-tolerant genotypes is an important strategy in the field of salinity tolerance (Iqbal et al. 2015). Therefore, improving the genetic adaptation of crop varieties to support genotypes to grow under salt-affected soils along with following appropriate agricultural procedures and exploiting the compatibility between the improved variety and its environment are important strategies in dealing with the problem of salinity. Crop varieties have several salt tolerance strategies that help them grow in saline soils by activating a multifaceted signaling and response network and inducing the production of a range of compounds that help to reduce the effects of soil salinity and preserve cellular homeostasis (Zhu 2016; Zhao et al. 2020). Primary metabolites are involved in plant growth and development, however secondary metabolites alter the hydrological balance of the soil between the water used from irrigation and water used through crop variety, and both play key roles in plant adaptation to salinity stress tolerance (Manchanda and Garg et al. 2008; Kumari et al. 2015; Ashraf et al. 2018). Molecular markers and genetic engineering offers opportunities to improve salt tolerance in crops by activating different signaling pathways involved in stress perception, signal transduction, osmotic regulation as well as production of antioxidant enzymes (Ishaku et al. 2020). Besides, treating crops with priming agents helps in activating various physiological and biochemical processes, activating defense responses and improving salinity tolerance (Savvides et al. 2016; Singh et al. 2020).

1.4 Themes of the Book and Contribution of the Chapters Over and above the introduction (Current Chapter, Introduction) and the conclusions and recommendations (Latest Chapter), the book comprises of 6 themes. The second theme is titled “Impact of Salinity on Sustainable Crop Production Strategies” which is covered in one chapter. Chapter 2 is titled “Salinity and its Impact on Sustainable Crop Production”. The third theme came in two chapters and its title “Protective Mechanisms and Salinity Resilience-relevant Traits", How do Plants Resilient Salinity Conditions?”. Chapter 3 is titled “Protective Mechanisms of Salinity Stress” and Chap. 4 under title “Fundamentals of Crop Resilience to Salinity, Plant traits and Selection Criteria “. The fourth theme has been explored in three chapters and is titled “Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress”. Chapter 5 under title “Genetic Variability and Genetic Resources for Salinity Resilience”, Chapter 6 under title “Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops”, while Chap. 7 titled “Breeding Efforts and Biotechnology”. The fifth theme has been extrap-

1.4 Themes of the Book and Contribution of the Chapters

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olated into two chapters and titled “Management Options, Mitigation and Genotype Assessment Techniques”. Chapter 8 under title “Mitigation Options towards Sustainability via Agricultural Practices” and Chap. 9 titled “Techniques and Measurements of Assessing Genotypes for Salinity tolerance”. In the next subdivision, the main technical elements of the chapters under each theme are presented.

1.4.1 Impact of Salinity on Sustainable Crop Production Strategies Chapter 2 is suggested to introduce significant information on salinity and its impact on sustainable crop production under climate change, on terms of salinity, saltaffected lands, toxicity effect and others. Also discusses the levels of crop tolerance to salinity in relation to yield in numerous crop plants. As previous studies have shown that, the response to salinity stress is a polygenic phenomenon, due to the multiplicity of processes involved in the tolerance mechanism including compatible solutes/osmolality, polyamines, antioxidant defense mechanism, ion transport and harmful ion compartmentalization (Mudgal et al. 2010; Naeem et al. 2020). Previous investigators revealed that amount of yield reduction when irrigating crop plants with saline water depends on several factors comprising soil nature, drainage, frequency, system and time of irrigation. Nevertheless, crop varieties differ significantly in their resilience to saline stress (Hussain et al. 2021; Sarah et al. 2021; Kamoura 2022). This chapter also highlights on evaluation of the suitability of irrigation water, salinity assessments, nature and origin of the salt-affected lands and their relationship to crop growth. The harmful effects of salinity on crop plants are also discussed from the following aspects i.e. production of reactive oxygen species in plant tissues, germination assessments, nodulation process, physiological and water relationships, biochemical characters as well as yield attributes and quality (Hailu et al. 2020; Abbas et al. 2021a, b; Hozayn et al. 2021; Mansour et al. 2021).

1.4.2 Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? Chapter 3 highlights the different Protective Mechanisms of Salinity Stress tolerance in crop plants, which regulate cell-to-plant level adaptation to salt stress conditions in a lot of cereal, legumes, fiber, oil, sugar, fodder, halophyte crops, and others from the aspects of plant physiognomies. Where, Isayenkov (2012) showed that crop genotypes respond to salinity stress through a series of physiological and metabolic modifications to overcome the harmful effects of osmotic shock and ion toxicity. Research results showed that mechanisms responsible of the adaptation to salinity

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including avoidance, tolerance and salt resistance. Crop genotypes ability to resist toxic effects of salinity relay on genetic make-up of crop cultivar or variants in physiobiochemical process which include degree of ion exclusion, osmotic stress tolerance and tissue tolerance (Ashraf et al. 2008; Naeem et al. 2020; Ouertani et al. 2021). This chapter also emphasized the importance of maintaining satisfactory osmotic regulation as a key physiological mechanism and mitigating oxidative stress. Chapter 4 is proposed to highpoint an importance of fundamentals of crop resistance to salinity from the sides of plant characters and selection criteria associated with salt stress resistance i.e. phenological, morphological, physiological and biochemical characteristics. It deals with the potential of plant crops that manifest under salt stress to protect their life cycle by rapid growth, early flowing and maturity. For example in soybeans, seed vigour as a key feature of efficient germination and shoot development helped to improve growth and yield of soybeans, particularly under biotic and abiotic stress conditions (Mangena 2021), germination speed in alfalfa (Mbarki et al. 2020) and acceleration of flowering by an average of 3.3 days in barley (Saade et al. 2016). Biologists reasoned that salt tolerance’s physiological and molecular components should be transferred to crop varieties to adapt to the salt environment (Munns and Gilliham 2015; Arzani and Ashraf 2016). Also, in halophytes plants, Al-Muwayhi (2020) recorded considerable variants in physiological, morphological and anatomical modifications as a result of salinity in Mediterranean saltbush Atriplex halimus and giant saltbush Atriplex nummularia. Finally, the authors explained the role of accumulate organic osmolytes, activation of antioxidants to scavenge reactive oxygen species ROS, down-regulating electron transport through photosystems to reduce generation and improve salt tolerance in crop breeding program (Ashraf 2004; Iqbal et al. 2019; Hasanuzzaman et al. 2021).

1.4.3 Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress Chapter 5 A glycophyte is considered as salt-sensitive crop, but substantial genetic variability is pre-requisite for any specify physiological feature, based on which screening or selection can be implemented. Accordingly, the primary objective of the present chapter is to identify genotypes and sources of salt tolerance. Moreover, it aims to map the differences between crop varieties for salt stress tolerance based on phenological, morph-physiological, biochemical and yield tolerance measurements traits that can be used as selective criteria. Literature indicated that salt tolerance varies with species, cultivars within the same species, plant developmental stage which makes it more complex (Saade et al. 2020). For example, it is well known that hexaploid wheat is more salt tolerant compared to tetraploid wheat, they did not differ over about 10 days of salinization (Munns et al. 1995). Significant variances has been detected among canola cultivars owing to the interactions with magnetically treated

1.4 Themes of the Book and Contribution of the Chapters

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brackish-irrigation water led to positive effect on all yields and yield components compared to irrigation with brackish water (Hozayn et al. 2021). Atriplex halimus and giant saltbush Atriplex nummularia are true xerophyte species varied in their reaction to salt stress based on genetic makeup (Al-Muwayhi 2020). The salt-tolerance genetic resources of crop genotypes have been discussed in this chapter in detail. Chapter 6 highlights the genetic analysis and inheritance of salinity resilience. As the decision-making on the effective breeding method is mainly dictated by the type of gene action and heritability. Thus, the genetic information obtained from biometrical models gives detailed information about types of gene action and genetic system that control the deliberated traits correlated with salinity tolerance. Numerous genetically analyses models were conducted for estimating nature of gene action and heritability of them Cavalli (1952), Warner (1952), Hayman (1954), Kempthorne (1957), Hayman (1958), Jinks and Jones (1958) and Mather and Jinks (1982), Falconer (1993) and Kearsey and Pooni (1996). However, since salinity tolerance is a quantitative trait governed by multi genes, endeavors to adopt some methods that use both classical and novel approaches to improve salt tolerance are of interest. According to Hüttner and Strasser (2012) and Souleymane et al. (2017), salt tolerance is a quantitative inherited character controlled by multiple genes, with the additive and dominant effects. The genetic parameters could have important implications for the quantitative genetics and development of salt-tolerant cultivars in field crops (Omrani et al. 2022). Chapter 7 is proposed to integrate with Chaps. 5 and 6 and contains detailed information about breeding efforts and biotechnology for producing salt-tolerant genotypes for sustainable crop production in areas sensitive to the effects of climate change and soil salinity. Therefore, this chapter came to highlights on classical breeding procedures with recent approaches. Using DNA molecular markers not only introduces tolerant cultivars beneficial for hybridization and breeding programs, but also detect DNA regions involved in the mechanism of salinity tolerance. Nationally, under Egyptian conditions, crop breeders released through selection and hybridization numerous salt tolerant cultivars in wheat, barley, rice, maize, sorghum, faba bean, chickpea, lupine, peanut, soybean, sunflower, sesame, cotton, canola, sugar cane, alfalfa and quinoa (Anonymous 2023). Internationally, selection is an important method for producing more salt-tolerant varieties in different crop plants i.e. in rice, variety Line SS1-14 (Ma et al. 2018); wheat variety Harmonija (Stojšin et al. 2022); cotton genotypes NIAB-135, NIAB-512, and FH-152 (Munawar et al. 2021); Alfalfa, variety Naimat or GR-722 (Jabbar et al. 2021). Hybridization is useful in transferring foreign input genes to sensitive cultivars, and developed salinity stress tolerant durum and bread wheat lines called Nax1 and Nax219, respectively (Munns et al. 2000), elite Indian rice variety Naveen (Ramayya et al. 2021). Incorporated crop breeding, molecular techniques, marker assisted selections, gene transfer, proteomics as technology approaches to enhancing salt tolerance are also discussed (Singer et al. 2021; Hasan et al. 2022).

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1.4.4 Management Options, Mitigation and Genotype Assessment Techniques Chapter 8 emphasizes optimizing inputs management for mitigating salinity stress under climate change. In the present chapter, the authors discuss the importance of how to treat with salinity problem from an agricultural perspective. First of all, leaching is an important process for removing harmful elements from the soil (Gupta and Abrol 2016; Bashir et al. 2023). This chapter also sheds light on the importance of choosing suitable agricultural practices under salinity conditions and climate change, for instance sowing methods, cultivating a suitable type of crop, and tolerant variety, and exploiting the best nutrient tactics and appropriate fertilization programs, all of them play vital roles in enhancing salinity tolerance. So, previous studies tried to find out the effect of agricultural practices viz. raised bed system, fertilizer rates and seed soaking, on enhancing fertility of saline soil and its productivity on faba bean (Amer et al. 2018). Also, the influence of deficit furrow irrigation with diverse salinity levels and planting methods in-furrow and on-ridge was studied as approaches for managing with water and salinity stress on wheat yield and quality (Mosaffa and Sepaskhah 2019). Several studies showed the vital role of organic amendments in reducing salt stress by modifying ionic homeostasis (Khalilzadeh et al. 2017; Alamer et al. 2022; Hoque et al. 2022; Imran et al. 2022). In addition, improving salt tolerance through exogenous treatments with metabolites have discussed in this manuscript. From the perspective of assessing techniques and measurements of appraising genotypes, Chapter 9 came to focus on screening techniques and parameters used to test genotypes for salt tolerance as another uphill task. The interaction between salinity tolerance and environmental factors reduces the effectiveness of the selection process for salinity tolerance. These variables related with salt damage that are improbable to control under field screening techniques (Pathan et al., 2007; Lee et al. 2008; Khan et al. 2022). So, the breeding program’s success depends on the proper evaluation of the salinity tolerance of the various genotypes. Negrao et al. (2017) attempted to measure salinity’s effect on different crop plant traits. Therefore, it becomes clear the importance of identifying and separating random environmental effects from genetic effects to allow the development of salt-tolerant varieties. Numerous screening techniques have focused on evaluating crop genotypes for salt tolerance under Lysimeter micro plots, laboratory conditions, greenhouses, hydroponic culture and field conditions. Tolerance indices were discussed on determining the degree of tolerance of crop genotypes. This current chapter topic has been discussed in several recent reviews that highlight its importance and urgency.

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Iqbal M, Ahmad M, Mustafa G (2015) Impact of farm households’ adaptation on agricultural productivity: evidence from different agro-ecologies of Pakistan. Online at https://mpra.ub.unimuenchen.de/72863/ MPRA Paper No. 72863, posted 08 Aug 2016 08:23 UTC Iqbal M, Athar H, Ibrahim M, Javed M, Zafar zu, Ashraf M (2019) Leaf proteome analysis signifed that photosynthesis and antioxidants are key indicators of salinity tolerance in canola (Brassica napus L.). Pak J Bot 51(6):1955–1968 Isayenkov SV (2012) Physiological and molecular aspects of salt stress in plants. Cytol Genet 46:302–318 Isayenkov SV, Maathuis FJM (2019) Plant salinity stress: many unanswered questions remain. Fronti Plant Sci Ishaku GA, Tizhe DT, Bamanga RA, Afolabi ET (2020) Biotechnology and drought stress tolerance in plants. Asian J Plant Sci 5:34–46 Jabbar A, Zubair M, Basit A, Shah AU, Minhas R, Hussain A, Aslam M, Ahmad G, Ahmad Khan A, Bazmi MSA (2021) The development of distinctive multi-cut a new alfalfa variety “naimat or gr-722” performs well in salt-affected soils. Egypt J Agron 43(3):347–355 Jinks JL, Jones RM (1958) Estimation of the components of heterosis. Genetics 43(2):223–234 Kamoura ME-SSA (2022) Verification of varietal purity in wheat. Ph.D. Thesis, Agron Depart, Fac of Agric, Zagazig Univ, Egypt Kearsey MJ, Pooni HS (1996) The genetical analysis of quantitative traits. Chapman and Hall, London Kempthorne O (1957) An Introduction to Genetic Statistics. John Wiley and Sons Inc, Landon, New York Khalilzadeh R, Seyed SR, Jalilian J (2017) Growth, physiological status, and yield of salt stressed wheat (Triticum aestivum L.) plants affected by biofertilizer and cycocel applications. Arid Land Res Manag 32(4):71–90 Khan MY, Nadeem SM, Sohaib M, Waqas MR, Alotaibi F, Ali L, Zahir ZA, Al-Barakah FNI (2022) Potential of plant growth promoting bacterial consortium for improving the growth and yield of wheat under saline conditions. Front Microbiol 13:1–12 Koyro HOW, Lieth H, Said S (2008) Salt tolerance of Chenopodium quinoa Willd, grains of the Andes, influence of salinity on biomass production, yield, composition of reserves in the seeds, water and solute. Tasks Vegetation Sci 43:133–145 Kumari A, Das P, Parida AK, Agarwal PK (2015) Proteomics, metabolomics, and ionomics perspectives of salinity tolerance in halophytes. Front Plant Sci 6:537 Lee JD, Smothers SL, Dunn D, Villagarcia M, Shumway CR, Carter TE, Shannon JG (2008) Evaluation of a simple method to screen soybean genotypes for salt tolerance. Crop Sci 48(6):2194–2200 Ma NL, Che Lah WA, Abd Kadir N, Mustaqim M, Rahmat Z, Ahmad A, Lam SD, Ismail MR (2018) Susceptibility and tolerance of rice crop to salt threat: physiological and metabolic inspections. PLoS ONE 13(2):e0192732 Majeed A, Muhammad Z (2019) Salinity: a major agricultural problem-causes, impacts on crop productivity and management strategies. In: Plant abiotic stress tolerance, pp 83–99 Manchanda G, Garg N (2008) Salinity and its effects on the functional biology of legumes. Acta Physiol Plant 30(5):595–618 Mangena P (2021) Analysis of correlation between seed vigour, germination and multiple shoot induction in soybean (Glycine max L. Merr.). Heliyon 7(9):1–8 Mansour E, Moustafa ESA, Abdul-Hamid MIE, Ash-shormillesy SMAI, Merwad AMA, Wafa HA, Igartua E (2021) Field responses of barley genotypes across a salinity gradient in an arid Mediterranean environment. Agric Water Manage Elsevier 258(C):107206 Mather K, Jinks JL (1982) Introduction biometrical genetics, 3rd edn. Chapman and Hall London, p 396 Mbarki S, Skalicky M, Vachova P, Hajihashemi S, Jouini L, Zivcak M, Tlustos P, Brestic M, Hejnak V, Khelil AZ (2020) Comparing salt tolerance at seedling and germination stages in

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local populations of medicago ciliaris L. to Medicago intertexta L. and Medicago scutellata L. Plants (Basel) 9(4):526 Mosaffa HR, Sepaskhah AR (2019) Performance of irrigation regimes and water salinity on winter wheat as influenced by planting methods. Agric Water Manage 216(C): 444–456 Mudgal V, Madaan N, Mudgal A (2010) Biochemical mechanisms of salt tolerance in plants: a review. Int J Bot 6:136–143 Mujeeb-Kazi A, Munns R, Rasheed A, Ogbonnaya FC, Ali N, Hollington P, Dundas I, Saeed N, Wang R, Rengasamy P, Saddiq MS, De León JLD, Ashraf M, Rajaram S (2019) Breeding strategies for structuring salinity tolerance in wheat. Adv Agron 155:121–187 Munawar W, Hameed A, Khan MKR (2021) Differential morphophysiological and biochemical responses of cotton genotypes under various salinity stress levels during early growth stage. Front Plant Sci 12:622309 Munns R, Gilliham M (2015) Salinity tolerance of crops-What is the cost? New Phytol 208:668–673 Munns R, Tester M (2008) Mechanisms of salinity tolerance. Annu Rev Plant Biol 59:651–681 Munns R, Schachtman DP, Condon AG (1995) The significance of a two-phase growth response to salinity in wheat and barley. Aust J Plant Physiol 22(4):561–569 Munns R, Hare RA, James RA, Rebetzke GJ (2000) Genetic variation for improving the salt tolerance of durum wheat. Crop Pasture Sci 51(1):69–74 Naeem M, Basit A, Ahmad I, Mohamed H, Wasila H (2020) Effect of salicylic acid and salinity stress on the performance of tomato plants. Gesunde Pflanzen 72(4):393–402 Negacz K, Malek Ž, Vos AD, Vellinga P (2022) Saline soils worldwide: identifying the most promising areas for saline agriculture. J Arid Environ 203:1–9 Negrao S, Schmockel SM, Tester M (2017). Evaluating physiological responses of plants to salinity stress. Ann Botany119(1):1–11 Omrani S, Arzani A, Moghaddam ME, Mahlooji M (2022) Genetic analysis of salinity tolerance in wheat (Triticum aestivum L.). PLoS One 17(3):e0265520 Omuto CT, Vargas R, Viatkin, K, Yigini Y (2020) Global soil salinity map—GSSmap. Lesson 4—Spatial modelling of salt–affected soils. FAO, Rome Ouertani RN, Abid G, Karmous C, Chikha MB, Boudaya O, Mahmoudi H, Mejri S, Jansen RK, Ghorbel A (2021) Evaluating the contribution of osmotic and oxidative stress components on barley growth under salt stress. AoB Plants 13(4):plab034 Pathan MS, Lee JD, Shannon JG, Nguyen HT ((2007) Recent advances in breeding for drought and salt stress tolerance in soybean. In: Advances in molecular breeding toward drought and salt tolerant crops. Springer Dordrecht the Netherlands, pp 739–773 Pimentel D, Berger B, Filiberto D, Newton M, Wolfe B, Karabinakis E, Clark S, Poon E, Abbett E, Nandagopal, (2004) Water resources: agricultural and environmental issues. Bio Science 54(10):909–918 Qadir M, Quillérou E, Nangia V, Murtaza G, Singh M, Thomas RJ, Drechsel P, Noble AD (2014) Economics of salt-induced land degradation and restoration. Nat Resour Forum 38(4):282–295 Ramayya JP, Vinukonda VP, Singh UM, Alam S, Venkateshwarlu C, Vipparla AK, Dixit S, Yadav S, Abbai R, Badri J (2021) Marker-assisted forward and backcross breeding for improvement of elite Indian rice variety Naveen for multiple biotic and abiotic stress tolerance. PLoS ONE 16(9):e0256721 Saade S, Maurer A, Shahid M, Oakey H, Sandra M, Schmöckel NS, Pillen K, Tester M (2016) Yieldrelated salinity tolerance traits identified in a nested association mapping (NAM) population of wild barley. Sci Rep 6:1–9 Saade S, Brien C, Pailles Y, Berger B, Shahid M, Russell J, Waugh R, Negrão S, Tester M (2020) Dissecting new genetic components of salinity tolerance in two-row spring barley at the vegetative and reproductive stages. PLoS ONE 15:e0236037 Sarah S, Ola G, Ramadan E, El-Fadly G (2021) Genetic and molecular evaluation of rice (Oryza sativa L.) genotypes for salinity tolerance at seedling stage. Fresenius Environ Bull 30(11A):12204–12214

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Savvides A, Ali S, Tester M, Fotopoulos V (2016) Chemical priming of plants against multiple abiotic stresses: mission possible? Trends Plant Sci 21(4):329–340 Shahid SA, Zaman M, Heng L (2018) Soil salinity: historical perspectives and a world overview of the problem. In: Guideline for salinity assessment, mitigation and adaptation using nuclear and related techniques. Springer International Publishing, pp 43–53 Shrivastava P, Kumar R (2015) Soil salinity: A serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation. Saudi J Biol Sci 22(2):123–131 Singer SD, Laurie JD, Bilichak A, Kumar S, Singh J (2021) Genetic variation and unintended risk in the context of old and new breeding techniques. Crit Rev Plant Sci 40(1):68–108 Singh AK, Dhanapal S, Yadav BS (2020) The dynamic responses of plant physiology and metabolism during environmental stress progression. Mol Biol Rep 47(2):1459–1470 Soni S, Nirmala S, Naresh K, Charu L, Ashwani K, Anita M (2022) Varietal variation in physiological and biochemical traits of durum wheat genotypes under salinity stress. Indian J Agric Res 56(3):262–267 Souleymane O, Salifou M, Hamidou M, Manneh B, Danquah E, Ofori K (2017) Genes action in salinity tolerance and the implication in rice breeding. J Plant Breeding Genet 5(3):115–120 Souana K, Taïbi K, Leila AA, Amirat M, Achir M, Boussaid M, Mulet JM (2020) Salt-tolerance in Vicia faba L. is mitigated by the capacity of salicylic acid to improve photosynthesis and antioxidant response. Scientia Horticulturae 273:109641 - cR KD (2022) Stojšin MM, Petrovi´c S, Banjac B, Zeˇcevi´c V, Nikoli´c SR, Majstorovi´c H, Ðordevi´ Assessment of genotype stress tolerance as an effective way to sustain wheat production under salinity stress conditions. Sustainability 14(12):1–19 United Nations Convention to Combat Desertification (2013) White Paper 1: Economic and Social Impacts of Desertification, Land Degradation and Drought. 2nd UNCCD Scientific Conference, 9-12 April 2013. https://www.unccd.int/sites/default/files/documents/12112014_Invisible%20f rontline_ENG.pdf Valifard M, Mohsenzadeh S, Kholdebarin B (2017) Salinity effects on phenolic content and antioxidant activity of Salvia macrosiphon. Iran J Sci Technol 41(2):295–300 Warner JN (1952) A method for estimating heritability. Agron J 44:427–430 Yadav S, Modi P, Dave A, Vijapura A, Patel D, Patel M (2020) Effect of abiotic stress on crops. In Sustainable Crop Production; Hasanuzzaman M, Filho MCMT, Fujita M, Nogueira TAR, Eds, IntechOpen: London, UK:3–24 Zahida Z, Hafiz FB, Zulfiqar AS, Ghulam MS, Fahad S, Muhammad RA, Hammad HM, Naseem W, Shahid M (2017) Effect of water management and silicon on germination, growth, phosphorus and arsenic uptake in rice. Ecotoxicol Environ Saf 144:11–18 Zahra N, Wahid A, Hafeez MB, Lalarukh I, Batool A, Uzair M, El-Sheikh MA, Alansi S, Kaushik P (2022) Effect of salinity and plant growth promoters on secondary metabolism and growth of milk thistle ecotypes. Life 12:1530 Zhao C, Zhang H, Song C, Zhu JK, Shabala S (2020) Mechanisms of plant responses and adaptation to soil salinity. Innovation 1(1):100017 Zhu JK (2016) Abiotic stress signaling and responses in plants. Cell 167(2):313–324 Zörb C, Geilfus CM, Dietz KJ (2019) Salinity and crop yield. Plant Biol 21(S1):31–38

Part II

Impact of Salinity on Sustainable Crop Production Strategies

Chapter 2

Salinity and Its Impact on Sustainable Crop Production

2.1 Introduction Salinity is among the major pressures affecting food production, having been one of the causes of the ancient Mesopotamian great commercial losses of above 10 billion USD (Qadir et al. 2014). Salt stress is one of the detrimental abiotic stresses which greatly reduce crop growth and productivity (Wang and Huang 2019). The General Assembly of the Global Soil Partnership survey revealed that more than 70% of the countries have varied aspects of salt problems and data for mapping salt-affected soils (Fig. 2.1) (GSP-FAO 2018). Abiotic stresses are strictly linked with climate change and obstruct crop plant growth, development, yield and quality. All over the world, approximately 20–50% of irrigated land areas are affected by salt stress (FAO 2021). Thus, global agricultural production’s sustainability is threatened by abiotic stresses (Hasanuzzaman et al. 2020; Yadav et al. 2020a). Low rainfall, poor drainage, high evaporation and irrigation using saline water are among the reasons for the salinity of the land in Egypt (Kotb et al. 2000). Besides, with climatic changes, soil salinity increases further due to reduced salt leaching and increased evapotranspiration with higher temperatures and lower precipitation (Chen and Mueller 2018; Attia et al. 2021). Salt tolerance is the ability of a plant to tolerate higher concentrations of salt that can be measured in terms of maintenance of vigor, sustained growth and yield of crop genotypes. The area of saline lands worldwide is estimated by approximately 955 million hectares, while the irrigated lands are estimated at about 230 million hectares, and the area affected by salinity is estimated at about one-third, or about 77 million hectares (Metternicht and Zinck, 2003; Parihar et al. 2014). And 33% of irrigated lands, causing estimated yield losses of 20% worldwide (Ashraf and Akram 2009; Jamil et al. 2011). Therefore, with a global population expected to reach 10 billion people by 2050 and an increased demand for food, more effort must be made to cultivate marginal soils suffering from various problems, including salinity. © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_2

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Fig. 2.1 Survey results on country-level data availability for mapping salt-affected soils (GSP-FAO 2018)

It is interesting to mention that the mechanism of stress tolerance and genes controlled in the stress signaling network is essential for crop development. Growth reduction was recorded as a major morphological effect of salinity due to several biochemical mechanisms of the plant. The increase in salts delays water absorption and reduces growth through the osmotic effect. The adverse effects of salts on growth result from the toxicity of specific ions, raised osmotic stress, or increased alkalinity that constrain water availability and affect cell physiology and metabolic pathways (Alharby et al. 2021). The response to salinity stress is a phenomenon controlled by polygenes due to the multiplicity of processes involved in the tolerance mechanism including compatible solutes/osmolarity, polyamines, reactive oxygen species, antioxidant protection mechanism, ion transport, and compartmentalization of harmful ions (Mudgal et al. 2010). Several in vitro and in vivo studies have indicated the potent impact of salinity stress on different traits of various field crops i.e. production of Reactive Oxygen Species in plant tissues (Meloni et al. 2003; Vaidyanathan et al. 2003; Nigam et al. 2022); germination assessments (Aflaki et al. 2017; Mhamdi and Van Breusegem 2018); nodulation process (Mudgal et al. 2009; Khan et al. 2019); vegetative growth (Hussain et al. (2021; Sarah et al. 2021; Abbas et al. 2021); Physiological and water relations (Hussain et al. 2021; Altunta¸s et al. 2020; Alharby et al. 2021); biochemical characters (Sandhu et al. 2017; Kholghi et al. 2018; Abbas et al. 2021) and yield attributes and quality (Hailu et al. 2020; Mansour et al. 2021; Hozayn et al. 2021). Therefore, this manuscript focused on discussing the significant effect of salinity on germination, growth, and various physiological and biochemical characteristics of plant, in addition to yield and quality.

2.2 Salinity, Its Causes, and Classes

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2.2 Salinity, Its Causes, and Classes Salinity arises as a result of dissolving salts from the primary rocks and not leaching them sufficiently due to the scarcity of rain. It is also formed due to an increase in the evaporation rate with high temperatures in arid and semi-arid regions. Salinity also occurs in irrigated areas with poor drainage or when using low-quality irrigation water as well as unregulated use of chemical fertilizers. So, the most common sources of salts in the soils are listed below: • Inherent soil salinity as weathering of rocks or parent material • Brackish and saline irrigation water • Seawater seepage into the coastal lands and into the aquifer as a result of excessive extraction and overuse of fresh water • Restricted drainage and a rising water-table • Surface evaporation and plant transpiration • Sea water mist, condensed vapors that fall on the soil as rainfall • Wind-borne salts produce saline fields • Overuse of fertilizers i.e. chemical and farm manures • Unregulated use of soil amendments such as lime and gypsum • Use of sewage sludge and/or treated wastewater • Dumping of industrial brine onto the soil. Salinity is defined as the state of increasing the level of salts in the soil and increasing the osmotic pressure of the soil solution, which requires the plant to exert more effort and energy to extract its needs of water and nutrients, and this is at the expense of its growth and production, in addition to the accompanying effects of toxicity of ions and imbalance of elements. Saline soils: the definition of saline soils refers to the soils that usually have electrical conductivity (ECe) in the saturated extract ECe ≥ 4 dS m−1 at a temperature of 25 °C, the pH less than 8.5, and exchangeable sodium percentage (ESP) < 15. Saline soils often are in normal physical condition with good structure and permeability. It is characterized by white, salty crusts on the surface of the soil and irregular plant growth. Salts of sulfate and/or chlorides of calcium and magnesium predominate. Salinization: salts occur naturally within soils and water. Salinization can be initiated by natural processes for instance mineral weathering or by gradual ocean retreat or through artificial processes for example irrigation and road salt. Soil salinity is the content of salt present in the soil. The process of increasing the salt content is known as salinization. The ions responsible for salinization are; Na+ , K+ , Ca2+ , Mg2+ and Cl− (Sverdrup and Warfvinge 1988). Plant salinity tolerance results from the contributions of three components; exclusion of sodium from the shoot, tissue tolerance of accumulated sodium, and tolerance of osmotic stress imposed by elevated external sodium concentrations (Munns and Tester 2008).

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Table 2.1 Classes of saline lands and their relationship to crop growth (USSL Staff 1954) No

Class of saline lands

Electrical conductivity ECe (dSm−1 )

Effect on crop growth

1

Non-saline

≤2

Salinity effects mostly negligible

2

Very slightly saline 2–4

Yields of very sensitive crops may be restricted

3

Slightly saline

4–8

Yields of many crops are restricted

4

Moderately saline

8–16

Only salt tolerant crops exhibit satisfactory yields

5

Strongly saline

>16

Only a few very salt tolerant crops show satisfactory yields

2.2.1 Classes of Soil Salinity and Plant Growth Often in saline soils, there is a crust of salt on the surface, and the salts usually increase in the surface layer and decrease in the lower layers before cultivation and then after cultivation and irrigation, the situation changes. The soil particles are usually agglomerated and the earth has good permeability. The electrical conductivity of the soil saturation extract (ECe) is the standard measure of salinity. The general relationship of ECe and plant growth has described by USSL Staff (1954), in which saline lands were divided on the basis of the degree of salinity, the type of salts present, their natural characteristics, their geographical distribution, and their biological effects on growing plants into five classes as shown in Table 2.1.

2.2.2 Salt-Affected Lands Nature and Origin of the Salt-Affected Lands Salt-affected lands contain a high proportion of soluble salts, exchangeable sodium percentage or together, and obstruct plant growth of crop varieties for most of the period, which negatively affects agricultural production. These lands are expressed as productive and satisfying lands. The salt-affected lands are generally spread in the arid and semi-arid regions with less than 10–20 inches annual rainfall. The distribution of salt-affected land is determined by environmental influences for instance climate, geology, geochemistry and environmental conditions. The composition of diverse types of salt-affected land in irrigated regions is directly associated with the concentration of chloride, sulfate and bicarbonate. In Egypt, the total cultivated area is increased to 9.7 million feddans nationwide in 2021, compared to 8.9 million feddans in 2014, which depends entirely on irrigation.

2.2 Salinity, Its Causes, and Classes

33

The area of salt-affected soil is 2 million feddans, at a proportion of 35% of the total area, distributed as follows: 60% of the lands of the North Delta, 25% of the lands of the Central and South Delta and 25% of the lands of Upper Egypt (Fig. 2.2). The salt-affected lands in Egypt are focused in the north, east and west of the Delta, as well as some further areas in Wadi El-Natrun, El-Tal El-Kabeer, Al-Wahat and Fayoum. Sodium chloride salt is considered the major cause of salinity. Besides, the soil with sea water, lakes and salt lakes for a lengthy period is the reason behind the occurrence of salinity. The occurrence of sulfate salts and magnesium chloride are the highest basis of salinity in Lake Manzala. Whereas sodium chloride salts are widespread in the lands of Apis and south of Lake Mariout. Chloride and sodium sulfate salts are dominated in the areas of Mariout and Al-Tal Al-Kabeer. Sodium carbonate and sulfate salts predominate. Moreover, the main cause of the alkalinity problem is the bio reduction of sulfate, and the emergence of salinity in that area is due to sodium chloride salts and irrigation with saline water of 5000 ppm. The problem of saline lands is associated with the presence of dissolved salts in excess concentrations, especially chlorides. There are insoluble salts such as calcium sulfate, calcium carbonate and magnesium. Calcium and magnesium cations are the main cations present, and there is no problem with excess sodium exchange. The saline lands contain large quantities of salts dissolved in the water, which are white salts, chemically neutral, and most of them are chlorides, carbonates, or nitrates

Fig. 2.2 Salt-affected soils in Egypt. Source https://www.un.org/esa/sustdev/sdissues/desertificat ion/beijing2008/presentations/hussein.pdf

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2 Salinity and Its Impact on Sustainable Crop Production

of calcium, magnesium, sodium and potassium. And usually absent sulfates and sometimes nitrates and bicarbonates and dissolved carbonates.

2.3 Saline Irrigation Water and Its Validity The quality of irrigation water affects the performance, growth and productivity of crop genotypes and is determined by pH, electrical conductivity, water content of dissolved solids, and the concentration of different ions, namely calcium, sodium, magnesium, carbonate, bicarbonate, chlorides, and sulfates. Carbonates are found when the pH is more than 8.5 and there is a relationship between the degree of electrical conductivity of the soil and the total dissolved salts in the soil. Whereas, water that contains 640 mg/L of salts has an electrical conductivity of about 1.0 dS m−1 . The presence of some ions in varying concentrations in irrigation water such as chloride, sodium, boron … etc. causes a toxic effect, reducing crop growth and affecting its production. However, this damage depends on the resistance of crops to these ions, as a certain concentration of an ion may be harmful for a specific crop without another. While the toxicity of some ions appears on a crop without affecting its growth and production, the growth and production of another crop growing under the same conditions is affected without the signs of toxicity appearing on it until late. The toxic effect of some ions depends on the sensitivity of the crop, the amount of accumulated ion, weather conditions and ion concentration in irrigation water, water needs, irrigation method and salt leaching, and the availability of drainage system or not. Among the other ions that determine irrigation water quality are boron, selenium and lithium, which are found in very moderate proportions but are toxic to plants at certain levels. Where, the recommended maximum concentrations of trace elements in irrigation waters were 1000 µg L−1 for boron (Bañuelos et al. 1999); 20 µg L−1 for selenium (Gupta and Gupta 2017) as well as 2500 µg L−1 for Lithium (Malan et al. 2015). Irrigation water also contains phosphates PO4 , nitrates NO3 , and potassium K. Nitrates are useful for plants but dangerous if water is used for drinking. In general, the Nile River is Egypt’s main irrigation source. The Nile water contains dissolved salts of 250 ppm at the source (Aswan) and gradually increases until it reaches 750 ppm downstream (Mediterranean Sea). There is a close relationship between salinity stress and moisture stress. An increase in moisture stress and water deficiency lead to salinization. Also, salinity stress increases the negative effects of moisture stress and the amount of energy required for the crop plant to attain its water and nutritional needs. Water at the field capacity is held by a force of 1/10–1/3 bar. It represents the maximum moisture availability in the soil, and here the plant must make a little effort to absorb water from the soil at the field capacity, gradually increasing until it reaches the minimum moisture availability at wilting. With an increase in the salt concentration of more than 4 mm (saline soil), the moisture stress at the field capacity will increase to more

2.3 Saline Irrigation Water and Its Validity

35

than 1/10–1/3 bar due to the increase in the osmotic component, affecting crops’ growth. A crop, for example, wheat cannot grow and produce at −0.6 bar.

2.3.1 Specific Ion Effect The specific effect of an ion is defined as the effect of an increased concentration of a certain ion on the various physiological processes in a particular crop. Some crops tolerate a higher concentration of a certain ion than other crops. Rice and beet plants tolerate an increase in sodium concentration, as they can use it instead of potassium in construction processes, but they are sensitive to an increase in chloride concentration. The tomato plant tolerates an increase in chloride concentration and does not tolerate an increase in sodium concentration. Maize plants tolerate CaCl2 , while leguminous crops are severely affected, which is a special effect rather than a general effect. There is no doubt that increasing the sensitivity of the plant to a particular ion in the case of its presence in a high concentration leads to an effect on the physiology of the plant and may reach the level of toxicity. The saline irrigation water affects plant growth in two ways; the effect of salinity and the effect of toxicity. Salinity tolerance depends on a combinations of several mechanisms that work together to overcome ion toxicity and mineral nutrient deficiency. In conditions of moderate salt stress, the leaves are smaller, thicker and appear dark green. Upon salinization, sodium first movements to the old leaves, shielding the young leaves (Yeo and Flowers 1982). The effect of NaCl on rice causes an increase in salt concentration in older leaves, which may result from the exclusion of a specific ion from the xylem vessels of younger leaves (Yeo 1998). It has been revealed that Nax2 is an essential gene for reducing root-to-shoot transfer of Na+ in durum wheat, whereas Nax1, is vital for lowering root-to-shoot Na+ transfer, and also involved in sequestering Na+ into the leaf sheath, keeping Na+ levels in the leaf blade low (James et al. 2006). Salinity decreases sugar beet growth by instigating osmotic, which results in ionic imbalance due to high accretion of sodium (Na+ ) and chlorine (Cl− ) ions, causing specific ions cytotoxicity (Dadkhah and Rassam 2017; Makhlouf et al. 2022). Under saline circumstances, seedlings of Atriplex canescens accumulated more Na+ ion in both plant tissues and salt bladders, and maintained K+ in leaf through the selective transport of K+ over Na+ from stem to leaf and from leaf to bladder (Pan et al. 2016). The exclusion mechanism of Na+ can protect the plant from specific-ion toxicity, the low Na+ absorb would be related with high uptake of K+ and Ca2+ , as adequate levels of these ions play a perfect role in osmotic regulation, without the energy cost required in the synthesis of the compatible organic process (Munns and Tester 2008; Tavakkoli et al. 2010; El- Hendawy et al. 2017).

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2.3.2 Ion Concentration The sensitivity of some genotypes of crops to salinity is due to the plants’ failure to exclude Na+ and Cl− ions from the cytoplasm of plant tissues. Salinity damages seem on the leaves of sensitive crop varieties with the increase in the concentration of ions in the apoplast and the effect of toxic ions on the metabolic processes. As plants are under salt stress conditions, they have to absorb more nutrients and prevent the uptake of toxic ions under low water stress compared to normal conditions. Hence, the importance of discuses the aspects of the osmotic effects of salts under salt stress conditions.

Osmotic Effect Effects of salinity on crop plants are, in general, summarized as water stress, salt stress and ionic misbalance stress. Water stress rises as a result of evaporation water used by plants and the accumulation of salts. Excess amounts of soluble salts in soil solution limit the availability of water to plants. A decrease in plant water potential must be matched by a decline in osmotic potential through increasing solute content to maintain turgor potential. Salinity decrease sugar beet growth through instigating osmotic, which results in ionic imbalance as a result of high accretion of sodium (Na+ ) and chlorine (Cl− ) ions, causing specific ions cytotoxicity (Dadkhah and Rassam 2017; Makhlouf et al. 2022). Mechanisms of salt tolerance in of Atriplex canescens as excellent resistance to salinity was investigated by Pan et al. (2016). The impact of Na+ to leaf osmotic potential (Ψs) was increased from 2% under control to 49% under 400 mM NaCl. Atriplex canescens under saline stress is capable of preserving K+ homeostasis in leaves, increase the accumulation of Na+ in tissues and salt bladders, and exploit compatible solutes and inorganic ions for osmotic adjustment to improve state of water in plant tissue.

Salinity Effect The roots of plants absorb moisture through the membranes in the root cells through osmosis, where water passes via a semi-permeable membrane. Water moves from a solution with lower levels of dissolved salts to a solution with higher levels of dissolved salts. This process continues until the plant cells are filled with water. If the irrigation water is moderately saline, the plant makes more effort to absorb water from the soil, and growth slows down, with reduced yields. In the case of using highly saline irrigation water, the osmosis process can be reversed. When the concentration of the solution outside the roots of the plant is higher than those in the root cells, water will move from the roots into the surrounding solution. At this point, the plant loses moisture and becomes stressed. This explains why the symptoms of high salt damage are similar to those of high moisture stress.

2.3 Saline Irrigation Water and Its Validity

37

The harmful effect of salt could be caused by the toxicity of a particular ion and the effect on water availability and thus cell physiology and metabolic pathway. One of the most damaging effects of salt stress is the disruption of the plant’s ionic balance mechanisms. The similar radii of Na+ and K+ make it problematic for passage proteins to discriminate between both ions. So, in situations of high sodium, there is significant uptake of Na+ through transporters or K+ channels (Blumwald et al. 2000). Salinity comprises two main features: an osmotic component and an ionic component interrelated with the accumulation of toxic ions at high (Na+ and Cl− ) concentrations (Lefèvre et al. 2001). Hyperosmotic stress initiated by excessive salt is involved for the primary stress signals. Whereas, secondary signals are created by ions and their toxicity effects on cells. They comprise oxidative stress and damage to cell membrane lipid layer, proteins and nucleic acids (Zhu 2016). In confirmed with Munns (2002), the reduction in germination in saline conditions was generated from the accumulative effect of osmotic and ionic influences. The cations component of total soluble salts in soils contain Na+ , Ca2+ and Mg2+ and the anions are Cl− , SO4 2− and carbonates (CO3 2− , HCO3 − ). So, the contribution of different soil ions to growth reduction under salt stress is clear less understood than that of Na+ in crops. In the case of Salicornia europaea L., Orlovsky et al. (2016) observed good germination of large seeds happened at NaCl between 0.5 and 2%, under Na2 SO4 and 2NaCl+ KCl+ CaCl2 between 0.5 and 3%, and at 2Na2 SO4 + K2 SO4 + MgSO4 between 0.5 and 5%. Fatemi et al. (2019) indicated that salinity stresses by potassium chloride was more toxic than sodium chloride, and the K+ ion affected plant growth more than the Na+ ion. Valdez-Aguilar et al. (2011) proved that plant growth diminished when irrigated with increasing concentrations of NaCl+ CaCl2 .

Toxicity Effect Excess sodium and chloride ions concentrations in irrigation water lead to plant toxicity. These ions are absorbed either by the roots or by direct contact with the leaves. The damage is greater due to direct absorption through the leaves.

Chloride Chloride moves in the soil freely as it does not enter into ion exchange reactions with the soil complex. In addition, it is not considered a nutrient for crops. Chloride accumulates in the leaves of the plant and its toxicity appears on sensitive crops when its percentage exceeds 0.3–1.0% of the dry weight of the leaves. There are medium restrictions on the use of sprinkler irrigation water if it contains chloride with a concentration of more than 3 mg/l and the rate of sodium adsorption SAR between 3 and 9.

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2 Salinity and Its Impact on Sustainable Crop Production

Table 2.2 Chloride and sodium concentrations in irrigation water causing damage to leaves Sensitivity level

Chloride (mg/L) Sodium (mg/L) Affected crop

Sensitive

458

Cotton, safflower, sesame, sorghum, sunflower, Cauliflower

Source https://www.agric.wa.gov.au/water-management/water-salinity-and-plant-irrigation

Crop varieties absorb chloride ion through plant roots and accumulate in leaves. Excessive accumulation causes burning of leaf tips or margins, bronze, and early yellowing of leaves. Most fruit trees are sensitive to chloride, while most vegetable, forage and fiber crops are less sensitive. Crops, and even varieties and strains, vary greatly in their tolerance to chloride and sodium. Fruit leaves generally suffer from toxicity when the dried leaves contain more than 0.2% sodium or 0.5% chloride. The damage is more severe in hot dry weather, where evaporation leads to the concentration of salts on the leaf surfaces and the direct adsorption through leaves occurs. Table 2.2 shows the chloride and sodium concentrations in irrigation water that will damage the leaves of some crops. Leaf damage depends on agricultural and environmental factors, for example, winds, humidity, speed of rotation of sprinklers and timing and frequency of watering.

Sodium Typical symptoms of sodium toxicity are leaf scorch, scalding, and dead tissue along the outer edges of the leaves. Whereas symptoms of chloride toxicity initially appear at the tip of the leaves. High concentrations of sodium in irrigation water lead to calcium and potassium deficiency in soils poor in these nutrients and crops respond to fertilization with these nutrients. Another effect of sodium is that if sodium is high in relation to calcium and magnesium, waterlogging may result from deterioration of well-regulated soils. Table 2.3 shows the degree of sensitivity or tolerance of crop plants to sodium concentrations in irrigation water. Sodium toxicity appears when it accumulates at a concentration more than 0.25– 0.5% of the dry weight of leaf tissue. There are restrictions on the use of water for sprinkler irrigation when it contains more than 3 mg/l of sodium and the sodium adsorption ratio between 3 and 9, in addition to the indirect effect of increasing sodium exchange rate on the deterioration of land properties and lack of porosity and thus the effect on the growth of crops. The exchange sodium percentage (ESP) is used as a measure of sodium toxicity for some crops. However, sodium is necessary for halophytic plants, which collect salt in the vacuoles to maintain the turgor pressure and growth. The beneficial effect of sodium

2.3 Saline Irrigation Water and Its Validity

39

Table 2.3 Tolerance of crop plants to sodium Class

Sodium adsorption ratio (SAR*) of irrigation water

Crops

Sensitive

8–18

Beans

Moderately tolerant

18–46

Clover, oats, tall fescue, rice

Tolerant

46–102

Barley, beets, Lucerne, wheat, tomatoes

“A high SAR indicates there is potential for sodium to accumulate in the soil. This can degrade soil structure by breaking down clay aggregates, which results in waterlogging and poor plant growth.” (Source https://www.agric.wa.gov.au/water-management/water-salinity-and-plant-irrigation)

Table 2.4 The ability to absorb sodium in different crops

High

Medium

Low

Very low

Fodder beet

Cotton

Barley

Black wheat

Sugar beet

Lupine

Flax

Maize

Table beet

Oats

Millet

Ray-grass

Swiss chard spinach

Potato

Rape seed

Soybean

Mangold

Cabbage

Wheat

Suaeda

Coconut Rubber Turnip

on plant growth was observed under lowland conditions in the potassium content, where the sodium ion Na+ partially replaces the potassium ion K+ . The crops were classified according to their ability to absorb sodium in the following sections (Table 2.4).

Boron Boron is one of the elements necessary for plant growth, but it becomes toxic when it is present in irrigation water at a concentration of more than 1–2 mg/l. Moreover, the toxicity of boron on plants appears when its concentration in the leaf blade reaches 250–300 mg/kg dry weight. The analysis of soil and irrigation water is useful in confirming the negative effect of boron. There are restrictions on the use of water for sprinkler irrigation when it contains more than 0.7 mg/L and the sodium adsorption ratio (SAR) is between 3 and 9. The restrictions are higher if its concentration exceeds 3 mg/l and the rate of sodium adsorption exceeds 9. The crops of wheat, barley, sunflower, sesame, lupine, beans and cowpeas are among the crops sensitive to boron, while sugar beet, alfalfa and maize are considered resistant to boron toxicity, whereas cotton is one of the highly resistant crops to the element. Table 2.5 shows the permissible limits of boron mg/liter or ppm.

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2 Salinity and Its Impact on Sustainable Crop Production

Table 2.5 Limits of boron in irrigation water (Der Leeden et al. 1990)

Permissible limits of boron mg/liter or ppm Crop group Class of water

Sensitive

Moderate

Resistant

Excellent

>0.33

>0.67

>1.0

Good

0.33–0.67

0.67–1.33

1.0–2.0

Permissible

0.67–1.0

1.33–2.0

2.0–3.0

Doubtful

1.0–1.25

2.0–2.5

3.0–3.75

Unsuitable

>1.25

>2.50

>3.75

Table 2.6 Maximum concentration of micronutrients and heavy metals in irrigation water Element

Concentration mg/liter

Element

Concentration mg/liter

Aluminum

5.0

Beryllium

0.1

Iron

5.0

Chromium

0.1

Zinc

2.0

Cobalt

0.05

Copper

0.2

Lead

0.5

Manganese

0.2

Lithium

2.5

Arsenic

0.1

Nickel

0.2

Cadmium

0.01

Selenium

0.02

Boron

1.0

Vanadium

0.1

Molybdenum

0.01

Chloride

1.0

From Ayers and Westcot (1985)

Trace Elements in Irrigation Water Ordinary irrigation water contains a very small percentage of trace elements, less than 100 µg/liter. Groundwater contains more concentrations than surface water. Sewage and polluted water comprise high concentrations of trace elements. Although some trace elements are necessary for plant growth, such as manganese, iron, zinc, copper, cobalt, and molybdenum, but their increased accumulation in plant tissues becomes toxic. In addition, heavy metals such as cadmium, arsenic, lead, chromium, nickel and zinc are found in irrigation water due to industrial pollutants and leading to harm plants, animals and humans alike. Table 2.6 shows the maximum concentration of some heavy metals and microelements in irrigation water that does not cause damage to agricultural crops.

2.3 Saline Irrigation Water and Its Validity

41

Table 2.7 Classification of sprinkler irrigation water salinity in Australia Chloride (mg L−1 )

Sodium (mg L−1 )

Affected crop

458

Cotton, safflower, sesame, sorghum, sunflower, Cauliflower

Source https://www.agric.wa.gov.au/water-management/water-salinity-and-plant-irrigation

2.3.3 Evaluation of Validity of Irrigation Water Irrigating crop varieties by saline water may result in yield loss and reduced its quality. Crop varieties differ significantly in their tolerance to saline water. The amount of yield reduction when irrigating crop plants with saline water depends on several factors comprising soil nature, drainage, frequency, system and time of irrigation. It has been possible to develop a guide to assess the suitability of irrigation water for use based on observations and detailed studies of the problems that arise from the use of water with certain characteristics in the long term on the basis of salinity, toxicity and other problems. This guide was used to assess the suitability of water for agricultural use and was applied to water. The classification of sprinkler irrigation water salinity in Australia is given in Table 2.7.

2.3.4 Salinity Assessing Water salinity is usually assessed from its electrical conductivity (EC), which might be transformed to total dissolved solids (TDS). The EC provides a fairly reliable indicator of salinity problems. Table 2.8 presents a general salinity classification of water. EC is measured in milliSiemens per meter (mS/m) in DPIRD. Table 2.8 General salinity classification of water Status

EC (mS cm−1 , dS m−1 or mmhos cm−1 )

EC (mS m−1 )

Approximate total dissolved solids (mg L−1 or ppm)

Low salinity

0–0.80

0–80

0–456

Moderately salty

0.80–2.50

80–250

456–1425

Salty

2.50–5.00

250–500

1425–2850

Very salty

>5.00

>500

>2850

Source https://www.agric.wa.gov.au/water-management/water-salinity-and-plant-irrigation

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2 Salinity and Its Impact on Sustainable Crop Production

To convert mS m−1 to milliSiemens per centimeter (MS cm−1 ), deciSiemens per meter (dS m−1 ) or millimhos per centimeter (mmhos cm−1 ), multiply by 0.01. To change mS m−1 to microSiemens per centimeter (µS cm−1 ), multiply by 10. To convert EC to milligrams per liter (mg/L) or parts per million (ppm) of TDS, multiply an amount in mS m−1 by 5.7, or an amount in mS/cm or dS m−1 or mS/cm by 570. These conversion estimates are approximate, proper for EC readings of less than 1000 mS/m and of the common salts that existed in WA irrigation water.

2.4 Levels of Crop Tolerance to Salinity Different crops can tolerate different levels of salinity in irrigation water. Crop plants vary extensively in their response to saline soils. Several crops show reduced growth and yield rates, while others, for instance Atriplex amnicola, reach an optimum growth rate under a moderate salt level (Aslamw et al. 2006). Depending on crop sensitivity to saline soils, plants can be divided into two major groups i.e. the saltsensitive glycophytes, which are comparatively easily damaged by salt; and the salttolerant halophytes which can tolerate and might even need high salt concentrations in the soil. Many reference studies have been conducted, which aimed at classifying irrigated crops according to their tolerance to salinity, commonly into many divisions. The degree of salinity tolerance of crop plants can be expressed using the following equation (Maas 1990): Yt = 100 − b (ECe −a).

(2.1)

where Yt: the percentage of the yield of the cultivar grown under saline conditions compared to the yield of the same variety grown under non-saline conditions, with other factors remaining constant. a: The threshold level of soil salinity at which the yield is not affected, and after this level the yield begins to decrease (Table 2.9). b: the percentage of yield decrease per unit increase in salinity above the threshold level value (a). ECe: salinity of saturated soil paste extracts (dS m−1 ). Threshold salinity level is defined by YS100 : it is the maximum salinity level at which there is no decrease in the yield of the cultivar, and it ranges from 1 dS m−1 in the case of legumes to 8 dS m−1 in the case of barley and cotton. While YS50 : is defined, the level of salinity at which a 50% decrease in the yield of the crop cultivar occurs, and it ranges from 4 dS m−1 for legumes to 15 dS m−1 for barley and cotton (Table 2.10). Salinity usually does not affect the yield unless the salinity level exceeds a certain concentration that varies according to the plant species, and this particular concentration is what is called the threshold level of salinity. In general, the yield of most plants decreases with increasing salinity. Maas and Hoffman (1977) divided crop

2.4 Levels of Crop Tolerance to Salinity Table 2.9 Tolerance of some crops to salinity

Crop

43

Critical limit for salinity (dS m−1 )

b (Tolerance)

Cereal, fiber and oil crops Barley

8.0

T

Maize

1.7

MS

Cotton

7.7

T

Peanut

3.2

MS

Rice

3.0

S

Rey

11.4

T

Sorghum

6.8

MT

Soybean

5.0

MT

Wheat

6.0

MT

Grasses and forage crops Alfalfa

2.0

MS

Red clover

1.5

MS

Tall Fescue

3.9

MT

Orchard grass

1.5

MS

Vetch

3.0

MS

b: These data are used as a guide to infer the degree of tolerance of different crops to salinity T = salinity tolerance, MT = moderate salinity tolerance S = salinity sensitive, MS = moderate sensitivity to salinity (From: Maas 1990) Significant variances were established between crops in their resistance to salinity in the form of YS50 and YS100 Table 2.10 Differences in the level of resistance to salinity in different crop plants Crop

Threshold salinity level (YS100 )* (dS m−1 )

(YS50 ) ** ( dS m−1 )

Legumes

1

4

Onion

1

4

Barley

8

15

Cotton

8

15

Sugar beet

8

15

Wheat

3

9

YS100 *: the maximum salinity level at which there is no decrease in the productivity of the crop variety YS50 **: The level of salinity at which the yield of the crop variety decreases by 50%

44

2 Salinity and Its Impact on Sustainable Crop Production

Fig. 2.3 Divisions for classifying crop tolerance to salinity. From Maas and Hoffman (1977)

plants into five classes according to the degree of their tolerance to salinity on the basis of the degree of electrical conductivity of the saturated soil paste extracts as illustrated in Fig. 2.3. The results in Table 2.11 apply to soils where chloride is the prevalent anion. As a result of the dissolution of CaSO4 when preparing saturated-soil extracts, the ECe of gypsiferous (non-sodic, low Mg2+ ) soils will be 1–3 dS m−1 greater than that of non-gypsiferous soils exhibiting the same soil water conductivity at field capacity. The extent of this dissolution relies on the exchangeable ion composition, CEC and solution composition. Hence, crops cultivated on gypsiferous soils will tolerate ECe s about 2 dS m−1 greater than those registered in Table 2.11. The latest column offers classifications of qualitative salt tolerance which is useful for classifying crops in general. Figure 2.3 shows the limits of these categories. Some crops have only a qualitative classification because the experimental data are insufficient for computing the threshold and slope. Maas and Hoffman classified crops into four clusters based on their tolerance to salinity into; (1) relatively tolerant crops, (2) resistant crops, (3) semi-sensitive crops, and (4) sensitive crops (see Table 2.11). In 1985, Food and Agriculture Organization published a revised version of Irrigation and Drainage Paper No. 29. This publication included an extensive list of crop salt tolerance data. Meanwhile, Maas and Grattan (1999) published updated lists of salt tolerance results (Table 2.12). This appendix reproduces these data together with the introductory sections.

2.5 Salinity and Its Relationship to Field Crop Productivity

45

Table 2.11 Tolerance to salinity in some important crops (Maas and Hoffman 1977) Crop

Salinity level threshold (dS m−1 )

Crop

Salinity level threshold (dS m−1 )

1-Relatively tolerant plants

2-Resistant plants

Cowpea

4.9

Sugar beet

7

Soybean

5

Cotton

7.7

Wheat

6

Barley

8

Durum wheat

5.7

Chicken

6.9

Sorghum

6.8

Wheat grass

7.5

3-Semi-sensitive plants

4-Sensitive plants

Alfalfa

2

Bean

1

Corn

1.7

Carrot

1

Rice

3

Orange

1.7

Tomato

2.5

Peach

1.7

Sugarcane

1.7

Apricot

1.6

Lettuce

1.3

Plum

1.5

Pasture and fodder crop tolerance to salinity One way to address high soil salinity is to produce more salt-tolerant crop germplasm. However, salt stress is a complex process, and there are varying degrees of tolerance between and within species (Flowers et al. 2010; Turner et al. 2013). Salt tolerance is an independently evolved trait that can arise from completely unrelated mechanisms. However, genetic diversity within crops can be used to release germplasm with ideal traits, including salt tolerance (Al-Ashkar et al. 2020). Table 2.13 show pasture and fodder crop tolerance to irrigation with saline water of loamy soil.

2.5 Salinity and Its Relationship to Field Crop Productivity Yield, correlation, regression, path coefficient and principal component analyses are among the important selection indices that are preferred to be estimated in breeding programs for salinity tolerance. The selection for the average yield is basically the selection of the highest varieties in the yield. As for the selection through analysis of correlation, regression, path coefficient and principal component, it depends on the stable performance of the variety under a wide range of environments. Reaching higher yields is one of the important strategies in breeding programs. Thus, the efforts of breeding through hybridization and selection are important for isolating genotypes more tolerant to salinity stress. Undoubtedly, salinity has effects on the amount of yield and the associated traits in different crop species based on the genetic makeup of the variety and its interaction with the adjacent environmental conditions.

46

2 Salinity and Its Impact on Sustainable Crop Production

Table 2.12 Salt tolerance of herbaceous crops Crop Common name

Salt tolerance parameters Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Fiber, grain and special crops Artichoke, Jerusalem

Helianthus tuberosus L.

Tuber yield

0.4

9.6

MS

Barleyd

Hordeum vulgare L.

Grain yield

8.0

5.0

T

Canola or rapeseed

Brassica campestris L. [syn. B. rapa L.]

Seed yield

9.7

14

T

Canola or rapeseed

B. napus L.

Seed yield

11.0

13

T

Chickpea

Cicer arietinum L.

Seed yield

–

–

MS

Cornf

Zea mays L.

Ear FW

1.7

12

MS

Cotton

Gossypium hirsutum L.

Seed cotton yield

7.7

5.2

T

Crambe

Crambe abyssinica Hochst. ex R.E. Fries

Seed yield

2.0

6.5

MS

Flax

Linum usitatissimum L.

Seed yield

1.7

12

MS

Guar

Cyamopsis tetragonoloba (L). Taub

Seed yield

8.8

17

T

Kenaf

Hibiscus cannabinus L.

Stem DW 8.1

11.6

T

Millet, channel

Echinochloa turnerana (Domin) J.M. Grain Black yield

–

–

T

Oats

Avena sativa L.

Grain yield

–

–

T

Peanut

Arachis hypogaea L.

Seed yield

3.2

29

MS

Rice, paddy

Oryza sativa L.

Grain yield

3.0g

12g

S

Roselle

Hibiscus sabdariffa L.

Stem DW –

–

MT

Rye

Secale cereale L.

Grain yield

11.4

10.8

T

Safflower

Carthamus tinctorius L.

Seed yield

–

–

MT

Sesameh

Sesamum indicum L.

Pod DW

–

–

S

Sorghum

Sorghum bicolor (L.) Moench

Grain yield

6.8

16

MT (continued)

2.5 Salinity and Its Relationship to Field Crop Productivity

47

Table 2.12 (continued) Crop

Salt tolerance parameters

Common name

Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Soybean

Glycine max (L.) Merrrill

Seed yield

5.0

20

MT

Sugar beeti

Beta vulgaris L.

Storage root

7.0

5.9

T

Sugar cane

Saccharum officinarum L.

Shoot DW

1.7

5.9

MS

Sunflower

Helianthus annuus L.

Seed yield

4.8

5.0

MT

Triticale

X Triticosecale Wittmack

Grain yield

6.1

2.5

T

Wheat

Triticum aestivum L.

Grain yield

6.0

7.1

MT

Wheat (semi-dwarf)j

T. aestivum L.

Grain yield

8.6

3.0

T

Wheat, Durum

T. turgidum L. var. durum Desf

Grain yield

5.9

3.8

T

Alfalfa

Medicago sativa L.

Shoot DW

2.0

7.3

MS

Alkali grass, Nuttall

Puccinellia airoides (Nutt.) Wats. & Coult

Shoot DW

–

–

Tc

Alkali sacaton Sporobolus airoides Torr

Shoot DW

–

–

Tc

Barley (forage)d

Hordeum vulgare L.

Shoot DW

6.0

7.1

MT

Bent grass, creeping

Agrostis stolonifera L.

Shoot DW

–

–

MS

Bermuda grassf

Cynodon dactylon (L.) Pers

Shoot DW

6.9

6.4

T

Bluestem, Angleton

Dichanthium aristatum (Poir.) C.E. Hubb. [syn. Andropogon nodosus (Willem.) Nash]

Shoot DW

–

–

MSc

Broad bean

Vicia faba L.

Shoot DW

1.6

9.6

MS

Brome, mountain

Bromus marginatus Nees ex Steud

Shoot DW

–

–

MTc

Brome, smooth

B. inermis Leyss

Shoot DW

–

–

MT (continued)

48

2 Salinity and Its Impact on Sustainable Crop Production

Table 2.12 (continued) Crop

Salt tolerance parameters

Common name

Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Buffel grass

Pennisetum ciliare (L). Link. [syn. Cenchrus ciliaris]

Shoot DW

–

–

MSc

Canary grass, reed

Phalaris arundinacea L.

Shoot DW

–

–

MT

Clover, alsike

Trifolium hybridum L.

Shoot DW

1.5

12

MS

Clover, Berseem

T. alexandrinum L.

Shoot DW

1.5

5.7

MS

Clover, Hubam

Melilotus alba Dest. var. annua H.S.Coe

Shoot DW

–

–

MTc

Clover, ladino Trifolium repens L.

Shoot DW

1.5

12

MS

Clover, Persian

T. resupinatum L.

Shoot DW

–

–

MSc

Clover, red

T. pratense L.

Shoot DW

1.5

12

MS

Clover, strawberry

T. fragiferum L.

Shoot DW

1.5

12

MS

Clover, sweet

Melilotus sp. Mill

Shoot DW

–

–

MTc

Clover, white Dutch

Trifolium repens L.

Shoot DW

–

–

MSc

Corn (forage)e

Zea mays L.

Shoot DW

1.8

7.4

MS

Cowpea (forage)

Vigna unguiculata (L.) Walp

Shoot DW

2.5

11

MS

Dallis grass

Paspalum dilatatum Poir

Shoot DW

–

–

MSc

Dhaincha

Sesbania bispinosa (Linn.) W.F. Wight [syn. Sesbania aculeata (Willd.) Poir]

Shoot DW

–

–

MT

Fescue, tall

Festuca elatior L.

Shoot DW

3.9

5.3

MT

Fescue, meadow

Festuca pratensis Huds

Shoot DW

–

–

MTc

Foxtail, meadow

Alopecurus pratensis L.

Shoot DW

1.5

9.6

MS (continued)

2.5 Salinity and Its Relationship to Field Crop Productivity

49

Table 2.12 (continued) Crop

Salt tolerance parameters

Common name

Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Glycine

Neonotonia wightii [syn. Glycine wightii or javanica]

Shoot DW

–

–

MS

Gram, black or Urd bean

Vigna mungo (L.) Hepper [syn. Phaseolus mungo L.]

Shoot DW

–

–

S

Grama, blue

Bouteloua gracilis (HBK) Lag. ex Steud

Shoot DW

–

–

MSc

Guinea grass

Panicum maximum Jacq

Shoot DW

–

–

MT

Harding grass Phalaris tuberosa L. var. stenoptera (Hack) A. S. Hitchc

Shoot DW

4.6

7.6

MT

Kallar grass

Leptochloa fusca (L.) Kunth [syn. Diplachne fusca Beauv.]

Shoot DW

–

–

T

Lablab bean

Lablab purpureus (L.) Sweet [syn. Dolichos lablab L.]

Shoot DW

–

–

MS

Love grassl

Eragrostis sp. N. M. Wolf

Shoot DW

2.0

8.4

MS

Milkvetch, Cicer

Astragalus cicer L.

Shoot DW

–

–

MSc

Millet, Foxtail Setaria italica (L.) Beauvois

Dry matter

–

–

MS

Oat grass, tall Arrhenatherum elatius (L.) Beauvois ex J. Presl & K. Presl

Shoot DW

–

–

MSc

Oats (forage)

Straw DW

–

–

T

Orchard grass Dactylis glomerata L.

Shoot DW

1.5

6.2

MS

Panic grass, blue

Panicum antidotale Retz

Shoot DW

–

–

MSc

Pigeon pea

Cajanus cajan (L.) Huth [syn. C. indicus (K.) Spreng.]

Shoot DW

–

–

S

–

–

MTc

Avena sativa L.

Rape (forage) Brassica napus L Rescue grass

Bromus unioloides HBK

Shoot DW

–

–

MTc

Rhodes grass

Chloris Gayana Kunth

Shoot DW

–

–

MT

Rye (forage)

Secale cereale L.

Shoot DW

7.6

4.9

T (continued)

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2 Salinity and Its Impact on Sustainable Crop Production

Table 2.12 (continued) Crop

Salt tolerance parameters

Common name

Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Ryegrass, Italian

Lolium multiflorum Lam

Shoot DW

–

–

MTc

Ryegrass, perennial

Lolium perenne L.

Shoot DW

5.6

7.6

MT

Ryegrass, Wimmera

L. rigidum Gaud

–

–

MT*

Saltgrass, desert

Distichlis spicta L. var. stricta (Torr.) Bettle

Shoot DW

–

–

Tc

Sesbania

Sesbania exaltata (Raf.) V.L. Cory

Shoot DW

2.3

7.0

MS

Sirato

Macroptilium atropurpureum (DC.) Urb

Shoot DW

–

–

MS

Sphaerophysa Sphaerophysa salsula (Pall.) DC

Shoot DW

2.2

7.0

MS

Sudan grass

Sorghum sudanense (Piper) Stapf

Shoot DW

2.8

4.3

MT

Timothy

Phleum pratense L.

Shoot DW

–

–

MSc

Trefoil, big

Lotus pedunculatus Cav

Shoot DW

2.3

19

MS

Trefoil, narrowleaf birdsfoot

L. corniculatus var tenuifolium L.

Shoot DW

5.0

10

MT

Trefoil, broadleaf birdsfoot

L. corniculatus L. var arvenis (Schkuhr) Ser. ex DC

Shoot DW

–

–

MS

Vetch, common

Vicia angustifolia L.

Shoot DW

3.0

11

MS

Wheat (forage)j

Triticum aestivum L.

Shoot DW

4.5

2.6

MT

Wheat, Durum (forage)

T. turgidum L. var durum Desf

Shoot DW

2.1

2.5

MT

Wheatgrass, standard crested

Agropyron sibiricum (Willd.) Beauvois

Shoot DW

3.5

4.0

MT

(continued)

2.5 Salinity and Its Relationship to Field Crop Productivity

51

Table 2.12 (continued) Crop

Salt tolerance parameters

Common name

Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Wheatgrass, fairway crested

A. cristatum (L.) Gaertn

Shoot DW

7.5

6.9

T

Wheatgrass, intermediate

A. intermedium (Host) Beauvois

Shoot DW

–

–

MTc

Wheatgrass, slender

A. trachycaulum (Link) Malte

Shoot DW

–

–

MT

Wheatgrass, tall

A. elongatum (Hort) Beauvois

Shoot DW

7.5

4.2

T

Wheatgrass, western

A. smithii Rydb

Shoot DW

–

–

MTc

Wildrye, Altai Elymus angustus Trin

Shoot DW

–

–

T

Wildrye, beardless

E. triticoides Buckl

Shoot DW

2.7

6.0

MT

Wildrye, Canadian

E. canadensis L.

Shoot DW

–

–

MTc

Wildrye, Russian

E. junceus Fisch

Shoot DW

–

–

T

Bean, common

Phaseolus vulgaris L

Seed yield

1.0

19

S

Bean, lima

P. lunatus L

Seed yield

–

–

MTc

Bean, mung

Vigna radiata (L.) R. Wilcz

Seed yield

1.8

20.7

S

Cassava

Manihot esculenta Crantz

Tuber yield

–

–

MS

Beet, redi

Beta vulgaris L.

Storage root

4.0

9.0

MT

Corn, sweet

Zea mays L.

Ear FW

1.7

12

MS

Cowpea

Vigna unguiculata (L.) Walp

Seed yield

4.9

12

MT

Gram, black or Urd bean

Vigna mungo (L.) Hepper [syn. Phaseolus mungo L.]

Shoot DW

–

–

S

Pea

Pisum sativum L.

Seed FW

3.4

10.6

MS

Pigeon pea

Cajanus cajan (L.) Huth [syn. C. indicus (K.) Spreng.]

Shoot DW

–

–

S (continued)

52

2 Salinity and Its Impact on Sustainable Crop Production

Table 2.12 (continued) Crop

Salt tolerance parameters

Common name

Botanical namef

Tolerance Thresholda Slope Rating based on (EC e ) %per b dS dS m−1 m−1

Potato

Solanum tuberosum L.

Tuber yield

1.7

12

MS

Sweet potato

Ipomoea batatas (L.) Lam

Fleshy root

1.5

11

MS

Tepary bean

Phaseolus acutifolius Gray

–

–

MSc

Winged bean

Psophocarpus tetragonolobus L. DC

–

–

MT

Shoot DW

These data serve only as a guideline to relative tolerances among crops. Absolute tolerances vary, depending upon climate, soil conditions, and cultural practices a In gypsiferous soils, plants will tolerate an EC about 2 dS m−1 higher than indicated e b Ratings are defined by the boundaries in Fig. 2.3. Ratings with an c are estimates d Less tolerant during seedling stage, EC at this stage should not exceed 4 or 5 dS m−1 e e Unpublished U. S. Salinity Laboratory data f Grain and forage yields of DeKalb XL-75 grown on an organic muck soil decreased about 26% per dS m−1 above a threshold of 1.9 dS m−1 (Hoffman and Genuchten 1983) g Because paddy rice is grown under flooded conditions, values refer to the electrical conductivity of the soil water while the plants are submerged. Less tolerant during seedling stage h Sesame cultivars, Sesaco 7 and 8, may be more tolerant than indicated by the S rating i Sensitive during germination and emergence, EC should not exceed 3 dS m−1 e j Data from one cultivar, “Probred” k Average of several varieties. Suwannee and Coastal are about 20% more tolerant, and common and Greenfield are about 20% less tolerant than the average l Average for Boer, Wilman, Sand and Weeping cultivars. Lehmann seems about 50% more tolerant (Modehied after, FAO 1985; Maas and Grattan 1999)

It is worth mentioning that, more land area on the planet is being lost to high salinity at the rate of ~1.5 million hectares yearly. This show an indication that about 50% of arable lands will be saline by 2050 (Hasanuzzaman et al. 2014a, b). Salinity is the major environmental stress that constrains sustainable agricultural productivity in arid and semiarid regions by reducing germination, seedling establishment, growth and crop production worldwide, due to the most of the cultivated plants are salt-sensitive glycophytes. The salts commonly found in irrigation water are sodium chloride salt, calcium and magnesium bicarbonates, chlorides and sulfates. This varies in different areas, both coastal and pastoral. Crop yields can be significantly reduced before visual symptoms of salinity damage become apparent. The degree of effect of salinity on plant growth depends on several factors, including climate, soil conditions, agricultural procedures, irrigation management, crop type and stage of growth. Meanwhile, world farming is faced with a lot of difficulties such as creating 70% more nourishment for an extra 2.3 billion individuals by 2050 (FAO 2009). It is of

2.5 Salinity and Its Relationship to Field Crop Productivity

53

Table 2.13 Pasture and fodder crop tolerance to irrigation with saline water under loamy soil conditions* Crop

0% yield loss EC (mS m−1 )

10% yield loss EC (mS m−1 )

25% yield loss EC (mS m−1 )

Birds foot trefoil

330

400

500

Cocksfoot

100

210

370

Couch

270–635

–

–

Kikuyu grass

270–635

–

–

Love grass

130

210

330

Paspalum dilatatum

270–635

–

–

Perennial ryegrass

370

460

590

Phalaris

310

380

530

Puccinellia

635–2365

–

–

Red clover

100

160

240

Rhodes grass

270–635

–

–

Saltwater couch

635–2365

–

–

Strawberry clover

100

160

240

Sub clover

100

110

240

Tall fescue

260

390

570

Tall wheat grass

500

660

900

White clover

90

–

–

Barley (hay)

400

490

630

Lucerne

130

220

360

Maize

110

170

250

Sorghum

450

500

560

– Indicate no data available Absolute tolerances vary depending on climate, soil conditions and cultural practices. *Source https://www.agric.wa.gov.au/water-management/water-salinity-and-plant-irrigation

utmost concern that 7% of the total world area (930 million hectares) is affected worldwide. Also about 1.5 million of the productive land is affected every year by salinity stress (Munns 2002; Pitman and Läuchli 2002; Munns and Tester 2008). The occurrence of salinity stress on the crop also causes a chain of changes in crop metabolic pathways and nutrient uptake comprising disruption in the uptake of mineral ions. Alarmingly, salinity stress affects crop growth and development through, decreased water potential makes the osmotic stress which cause a cellular imbalance with interference in the uptake of vital ions such as potassium, calcium, and nitrates. Lastly, leads to ion toxicity due to Na+ and Cl− (Tavakkoli et al. 2011). Crop genotypes respond to salinity stress through a series of physiological and metabolic modifications to overcome the harmful effects of osmotic shock and ion toxicity (Isayenkov 2012). Soon after the plant is exposed to salinity, plant root and shoot metabolism changes, resulting in hyperosmotic shock and ionic imbalance

54

2 Salinity and Its Impact on Sustainable Crop Production

Leaves turn bluish green

Stunted of plant growth

Symptoms of salinity on crop plants

Toxic levels, burn the tips and edges of old leaves

The death and fall of the leaf and finally the plant dies

Fig. 2.4 Symptoms of salinity on crop plants (drawn by the author)

leading to secondary stresses, for instance, nutritious imbalance and pathological outcomes (Isayenkov 2012; Hasegawa et al. 2000). Meinzer (2002), Cochard et al. (2002) evidenced that stomatal regulation of vapor loss is very sensitive to shortterm salinity stress. Then, salinity stress reduced net carbon dioxide uptake rates with deterioration in photosynthetic pigments and non-stomatal agents similar Jmax and Vcmax (Mugnai et al. 2009; Flexas et al. 2014). Furthermore, the photosynthetic rate decreases with the long-term salinity stress in plants of crop genotypes (Parida and Das 2005; Chaves et al. 2009). Salt stress affects plant growth and the appearance of the following symptoms (Fig. 2.4). The effects of salinity on plant growth are a complex phenomenon responsible for various modifications at the level of a whole plant. Salinity as abiotic stress cause changes in morphological, physiological, biochemical and molecular plant processes. Increasing soil salinity is one of the most serious obstacles to increasing crop yield and quality. Generally, the adverse effects of saline soil comprise ion toxicity, nutrient constraints, osmotic stress and oxidative stress, as illustrated in Fig. 2.5. The effects of salinity also occur because of the participation of one or more of these factors, which leads to a disturbance of the biochemical and physiological processes that revolve around the plant’s rhizosphere. The effect of osmotic stress is effective in the beginning (several hours to a few days) of exposure to salinity, and the effects of toxicity ions become clear on plant growth with the length of exposure.

2.6 Summary of Adverse Effects of Salinity on Crop Plants

Ion toxicity

55

Nutrient constraints Adverse effects of soil salinity

Osmotic stress

Oxidative stress

Fig. 2.5 Possible adverse effects of soil salinity (drawn by the author HA Awaad)

2.6 Summary of Adverse Effects of Salinity on Crop Plants Increasing soil salinity leads to desertification of previously productive agricultural lands, loss of vegetation cover and loss of biodiversity and ecosystem. Crop varieties suffer greatly under salinity conditions due to increased moisture pressure, which requires the plant to have more energy to meet its water and nutrient requirements. In general, the adverse effects of salinity on crop plants can be summarized and illustrated in Fig. 2.6 in the following topics: 1. Production of peroxides and active oxygen species that lead to the destruction of lipids, pigments, protein and DNA in plants. 2. Reverse chromatin assembly and blocking the DNA transcription and translation process. 3. Increased chromatin viscosity in epidermal nuclei and cortex cells. 4. Inhibition of meristematic activity and disruption of chromosomes in the Anaphase in root cells. 5. Decreased numbers of mitochondria and hypertrophy of Golgi bodies and endoplasmic membranes. 6. Loss of the plasma membrane integrity and damage to the cell membrane due to shock of the membranes at high osmotic concentrations associated with high salinity in the environment surrounding the plant. 7. Reduced the efficiency of the enzyme Ribulose-bis-phosphate carboxylase, oxygenase, nitrate reductase, and the decreased ascorbic acid and cytokinin content. 8. The lack of availability of nutrients, the decrease in the water content of the plant, and the occurrence of physiological changes, including the effect on the rate of elongation and cell division.

56

2 Salinity and Its Impact on Sustainable Crop Production

Salinity

Osmotic effect

Increase the concentration of organic

Disturbance of water relations

Specific ion effect

Unbalance of mineral nutrition

Toxicity

Sodic

Fig. 2.6 The effect of salinity and alkalinity on crop plant. Modified after, Lauchli and Epstein (1990)

9. Salinity indirectly affects the net photosynthesis per unit leaf area as a result of stomata closure, in addition to the direct effect on the disturbance of the photosynthesis system. 10. Salinity affects the leaf extension rate and photosynthetic activity, thus decreasing dry matter production. 11. Decreased growth of the primary roots, the degree of their branching, the super in accumulating process of hypodermis and the endodermis. 12. Rolling of leaves, yellowing and burning of their tops. 13. Increasing the darkening of the leaf color, increasing the pubescence, decreasing growth, and the small size of the plant. 14. Excess salinity affects moisture stress, due to the increase in the osmotic component, so the plant depletes energy compounds from ATP, ADP, AMP, UTP, UDP-glucose in order to absorb its requirements of water and nutrients, which affects the growth and yield of the plant.

2.6 Summary of Adverse Effects of Salinity on Crop Plants

57

15. Occurrence of plant toxicity, in case of accumulation of ions at a level that exceeds the critical limit of tolerance. 16. The appearance of vegetation-free spots in the field and a decrease in the yield per unit area. So, the development of organized programs to release new varieties of field crops characterized by tolerating salinity conditions and high-yielding capacity is one of the important approaches for plant breeders in breeding programs. There are three important parameters that should be taken into consideration in the issue of salinity tolerance of crops: 1. The ability of the crop variety to survive under saline soil conditions. 2. Quantity of the cultivar’s production when grown in saline soil. 3. Quantity of the yield obtained from the cultivar as a percentage of its normal yield on normal or non-saline soil. It is interest to note that the third issue is the most acceptable. The crop cultivar is considered tolerant to salinity and can be grown in economic terms in saline soil if it is possible to obtain 50% of its yield in normal soil. If we assume that the productivity of a rice cultivar is 4 tons in normal land, then this cultivar is considered a salinitytolerant if it is produced 2 tons in saline soil (>4–8 mmose cm−1 ). Where, Rao et al. (2008) showed that under sodic conditions aat pH 9.8, a decrease in rice grain yield of 25%, 37% and 68% was recorded for tolerant, semi-tolerant and senstive rice cultivars, respectively. The negative impact on crop physiology and biochemical pathway could be occurred by irrigation of crops with water with high EC levels enclosing high sodium chloride and other salts concentrations (Bre´s et al. 2022). In detail, salinity stress affects plant growth and development in three steps: firstly, reduced water potential creates osmotic stress which leads to a cellular imbalance with interference in the uptake of essential ions like calcium, potassium and nitrates; finally, it leads to the ion toxicity (sodium Na+ and chloride Cl− ) (Tavakkoli et al. 2011). Therefore, the intensity of growth suppression is directly associated with the concentration of salt exposed to the crops. After the osmotic stress and ion toxicity occur in the chain, there is a higher chance of detrimental effects causing cessation of growth and ultimate death of the crop (Munns and Tester 2008). In general, the effects of salinity on crop plants can be discussed from the following perspectives.

2.6.1 Effect of Salinity on the Production of Reactive Oxygen Species Salt stress, like other abiotic stresses, can also lead to oxidative stress through the increase of Reactive Oxygen Species (ROS), such as singlet oxygen (1 O2 ), hydrogen peroxide (H2 O2 ) and hydroxyl radicals (OH¯), which are extremely reactive and may cause cellular injury through oxidation of lipids, proteins and nucleic acids (Pastori

58

2 Salinity and Its Impact on Sustainable Crop Production

and Foyer 2002; Apel and Hirt 2004). For example, exposure of rice plants to salinity for approximately 24 h increased the up-regulation of glutathione-S-transferase and ascorbate peroxidase, that play an effective role in the elimination of reactive oxygen species ROS resulting from salinity stress (Kawasaki et al. 2001). Furthermore, oxidative damage to different cellular components, for example, proteins, lipids and DNA, interrupts vital cellular functions that occurs in plants has been production as reactive oxygen species due to salinity stress. It has been revealed that salinity induces oxidative stress in plant tissues and lipid peroxidation has frequently been used as an indicator of oxidative stress when plants are subjected to salinity, as recorded in cotton (Meloni et al. 2003) and rice (Vaidyanathan et al. 2003). Mittova et al. (2002) detected an increase in the activities of the antioxidative enzymes i.e. ascorbate peroxidase, catalase, guaicol peroxidase, glutathione reductase and superoxide dismutase under salt stress as a reaction against the production of ROS. Osmotic stress imposed around the root reduced plant growth. Osmotic stress in the preliminary phase of stress results in various physiological modifications, such as disruption of membranes, nutrient imbalance, impairment of the detoxification capacity of reactive oxygen species (ROS), variations in antioxidant enzymes, decreased photosynthetic activity and a decrease in stomatal opening (Munns and Tester 2008; Rahnama et al. 2010). On soybean, Osman et al. (2021) showed that MDA increased by 47 and 75 and H2 O2 augmented by 42 and 50% under 75 and 150 mM NaCl for 56 days in soybean cultivar Giza 111. Whereas, Nigam et al. (2022) revealed that the 100 ppm salt triggered more severe effects than 50 ppm salt on soybean cultivars. Salt stress-induced H2 O2 generation and MDA accumulation, developed ionic imbalance, increased electrolyte leakage, and decreased biomass and yield. Bybordi et al. (2010) investigated the effects of increasing salinity stress on five cultivars of canola (SLM046, Okapi, Fornax, Licord and Elite). Salt stress was applied on 30-day-old cultivars through five different levels of NaCl (0, 50, 100, 150 and 200 mM). Under salinity stress, the Elite cultivar displayed a higher Na: K ratio than the others. The activities of reactive oxygen species scavenging enzymes and reduced glutathione content were higher in the leaves of SLM046. However oxidized glutathione content was higher in the leaves of Elite cultivar compared to the other cultivars. Thus, comprising oxidative damage in five canola cultivars, revealed lower levels of lipid peroxidation and H2 O2 concentration in SLM046 cultivar under salt stress situations. Salinity stress produces reactive oxygen species, such as hydroxyl radicals (OH− ), superoxide radicals, and hydrogen peroxide (H2 O2 ), all highly oxidizing compounds that are detrimental to cell integrity. Antioxidant metabolism, comprising antioxidant enzymes and non-enzymatic compounds, plays an important role in the detoxification of reactive oxygen species caused by salinity stress in crop plants (Groß et al. 2013). Generation of ROS is part of the signaling process in crop plants at lower stress, but at sever stress, ROS cause oxidative stress. Osmotic and ionic stress caused by salinity lead to ROS overproduction, oxidative damage to cell organelles and membrane

2.6 Summary of Adverse Effects of Salinity on Crop Plants

59

components, and cell and plant death. The antioxidant defense system protects the plant from salt-induced oxidative damage by detoxifying ROS. Various plant hormones and genes are also linked to the signaling defense system and antioxidants to protect plants when they are under salt stress (Hasanuzzaman et al. 2021). Salinity caused a significant increase in electrolyte leakage due to production of ROS, which is indicated by an increase in the degree of electrical conductivity. Thus, genotypes with low electrical conductivity had higher viability and vigour than the high-EC genotypes. Kamoura (2022) performed electrical conductivity test on four sub-samples of 50 seeds of each cultivar were weighed to 0.001 g, placed into plastic cups with 250 ml of distilled water, and held at 25 °C after 24 h, the electrical conductivity of the leachates was determined using Ec meter. The electrical conductivity test is based on the premise that the cell membranes become less rigid and more solute as seed deterioration progresses, allowing soluble cell materials to scape. These exudates increase the electrical conductivity of the soaking solution. Results in Table 2.14 indicated significant differences between wheat varieties i.e. Misr1, Gemmeiza11, Giza168 and Sids12 in the 1st season and the combined. Sids 12 and Giza 168 verified the lowest EC values, respectively. However, the highest EC values were recorded by Gemmeiza 11 and Misr1 ones. This result indicated that low-EC genotypes have a higher viability and vigour percentage than the high-EC genotypes. Meanwhile, the results indicated insignificant differences between wheat genotypes in the second season for EC values. The effect of wheat seed categories on EC values was insignificant through two seasons and its combined. Table 2.14 Mean performance for electrical conductivity (µScm−1 g−1 ) for some wheat cultivars under three seed categories during two successive seasons (2015–2016 and 2016–2017) and their combined (Kamoura 2022) Main effect and interaction

Electrical conductivity (µScm−1 g−1 ) 2015–2016

2016–2017

Combined

Misr 1

12.61 ab

11.86

12.23 ab

Gemmeiza 11

13.36 a

12.61

12.98 a

Giza 168

12.14 b

11.76

11.95 b

Sids 12

12.05 b

11.41

11.73 b

F-test

*

N.S

*

Basic seeds

12.36

11.77

12.07

Certified seed

12.71

12.11

12.41

Farmer seed

12.54

11.84

12.19

F-test

N.S

N.S

N.S

Interaction

N.S

N.S

**

Cultivars

Seed categories

N.S,* and ** indicated insignificant and significant at 0.05 and 0.01 level, respectively

60

2 Salinity and Its Impact on Sustainable Crop Production

Table 2.15 Electrical conductivity (µScm−1 g−1 ) of wheat as affected by the interaction between cultivars and seed categories (Combined) (Kamoura 2022) Seed categories Basic Certified Farmer seeds

Cultivars Misr1

Gemmeiza 11

Giza 168

Sids 12

D

AB

BCD

BC

10.44

13.59

11.81

12.43

A

BCD

CD

CD

14.62

12.21

11.36

11.45

BCD

ABC

ABC

CD

11.63

13.14

12.68

11.32

The influence of interaction between wheat cultivars and seed categories on EC value (Table 2.15) was highly significant in combined data. The high value of EC 14.62 was achieved by Misr 1 cultivar with certified seed category followed by Giza 168 cultivar with basic seed category 13.59. While the lowest value of EC 10.44 was recorded by Misr1 cultivar with the Basic seed category.

2.6.2 Effect of Salinity on Photosynthetic Pigments and Quantum Yield of Photosystem-II Salt stress reduced the net CO2 assimilation rates alongside a decline in photosynthetic pigments and non-stomatal factors such as J max , and V cmax (Urban et al. 2008; Mugnai et al. 2009). Furthermore, the photosynthetic rate drops with several stomatal and non-stomatal limitations like electron transport rate and inhibition of Calvin Cycle enzymes, for instance, Rubisco, phosphoenolpyruvate carboxylase, ribulose-5-phosphate kinase, glyceraldehyde-3-phosphate dehydrogenase or fructose-1,6-bisphosphatase can occur in the long-term salt stress in the plant (Parida and Das 2005; Chaves et al. 2009). In this respect, Munns et al. (2006) showed that photosynthesis per unit leaf area was not initially decreased by salinity in the more salt-tolerant Entry 455, as the chlorophyll per unit area was higher in saline than nonsaline situations. However photosynthesis per plant was reduced due to the leaves were smaller in area. With time, photosynthesis per unit area reduced in both genotypes due to reductions in stomatal conductance, and later there were non-stomatal limitations associated with a build-up of Na+ and Cl− in the whole tissue above 250 mM. Chlorophyll fluorescence parameters indicated that the efficacy of PSII photochemistry in Entry 455 was unaffected. But, in Entry Wollaroi, the potential and actual quantum yield of PSII photochemistry began to decrease with age of the leaf and the increase in thermal energy dissipation of excess light energy (NPQ). This coincided with high concentrations of Na+ and Cl− in the leaf at 250 mM and with chlorophyll degradation, showing that the later reduction in CO2 assimilation in Entry Wollaroi was due to the direct toxic ion effect. Other than NPQ, the

2.6 Summary of Adverse Effects of Salinity on Crop Plants

61

fluorescence parameters were no more sensitive than chlorophyll itself. The fluorescence parameter F v /F m declined only when chlorophyll content decreased. The physiological mechanism of salinity tolerance in Entry 455 was to delay the onset of non-stomatal effects on photosynthesis, probably by delaying the time at which Na+ or Cl− reached a critical toxic level. The salt-sensitive crop genotypes can respond to salinity by suppressing water potential between the apoplast and symplast, causing a reduction in the turgor pressure with reduced photosynthetic activity (Isayenkov 2012), this causes growth inhibition due to cell dehydration (Taiz et al. 2015). In durum wheat, salinity stress decreased significantly photosynthetic level (Hussein and Abd El Hady 2014). Salt stress caused reduction in total chlorophyll content and quantum yield of PSII significantly in the deliberated wheat cultivars. The salt-stressed plants of wheat cultivar MH-97 produced maximum decrease in total chlorophyll (SPAD values) in the leaves, followed by Kohistan-97. On the contrary, wheat cultivars S-24 and LU-26S gave the reverse trend. Similar trend of salt-induced decrease in quantum yield of PSII was detected in last wheat cultivars by Hussain et al. (2021). Photosynthesis appeared to be well-linked within different salt concentrations, as growth stage, stomatal conductance, genotypes, time of the day and duration of salt exposure in wheat (Maha et al. 2017). Whereas, Sarah et al. (2021) indicated a differential effect of salinity stress on rice genotypes regarding physiological characters. Results indicated that the mean performance of SPAD value was increased by 12.49% over the grand mean under salt stress. Meanwhile, in maize, Chlorophyll synthesis was inhibited by reductions in the expression levels of Mg-Ch under stress. However, to enhance stress tolerance, the application of a protective compound for instance Mg2+ (Zhou et al. 2011) and exogenous proline could improve leaf photosynthesis (Altunta¸s et al. (2020) In fiber crops, the salinity stress effect might be due to stomata closure as a result of osmotic pressure or salt-induced injury to photosynthetic apparatus in cotton (Brugnoli and Lauteir 1991). Altered chloroplast products and mitochondrial metabolism through stress cause oxidative damage to various cellular compounds comprising proteins, membrane lipids and nucleic acids. Razaji et al. (2020) revealed that drought and salinity stresses, caused major reduction in plant growth, chlorophyll content and photosynthesis in two cotton varieties, with the major visible effect under combined stress. In canola genotypes, Rameeh (2012) reported that the potassium (K+ ) ion content reduced as salinity increased, whereas calcium (Ca2+ ) and sodium (Na2+ ) ion contents increased, declining the photosynthetic level. However, in alfalfa, Sandhu et al. (2017) showed that salinity not affected net photosynthetic rate and transpiration rate. Whereas, salinity increased chlorophyll content in most alfalfa genotypes. Moreover, in fodder shrub, Pan et al. (2016) investigated the influence of salt stress on the A. canescens of C4 perennial fodder shrub as excellent resistance to salinity. They treated 5-week-old seedlings with diverse levels of external NaCl (0–400 mM). The results demonstrated significant stimulation for the growth of A. canescens seedlings at moderate salinity (100 mM NaCl) compared to high salinity

62

2 Salinity and Its Impact on Sustainable Crop Production

(200 or 400 mM NaCl). Likewise, A. canescens seedlings displayed greater photosynthetic ability at NaCl treatments, excluding 100 mM NaCl, with significant rises. It was showed that Na+ facilitates some biochemical processes in C4 pathway photosynthesis such as converting pyruvate into phosphoenolpyruvate, improving photosystem II activity and enhancing water use efficiency and net photosynthetic rate. Salinity induced a significant increase in leaf electrolyte leakage in four halophytes, with the maximum increase in the two green-leaved genotypes, A. hortensis green (+131%) and A. halimus (+105%). The three C3 A. hortensis genotypes exhibited a similar (−33‰ on average) and statistically lower (more negative) δ 13 C rather than the C4 A. halimus genotype. The 360 WS encouraged a δ 13 C alteration towards less negative estimates in the three A. hortensis genotypes with non-effects, instead, in A. halimus. After seven days of salt stress initiation, the two genotypes displaying the highest photosynthetic activity under Ctrl, i.e., A. hortensis scarlet and green, where those registered the highest photosynthetic activity drop at salinity (−32% and −29%, correspondingly), whereas the remaining two genotypes were milder (Calone et al. 2021).

2.6.3 Effect of Salinity on Physiological and Plant Water Relations Usually, high salt concentrations cause osmotic stress by decreasing water potential within the cells, and ionic stress owing to inhibition of metabolic processes (Heidari 2012). Physiological and water relations reduction in the genotypes of salinized crop depended on the effects of leaf water, stomatal conductance, transpiration rate, osmotic potential, proteins, relative leaf water content and biochemical components for instance, photosynthetic pigments, soluble carbohydrates and reduction of available CO2 by stomatal closure. The net photosynthesis rates were greatly decreased by salinity. Under high salt stress, the photosynthesis, respiration, chlorophyll fluorescence and chlorophyll contents extensively decreased in wheat (Kafi 2009). Moreover, Shtaya et al. (2019) showed that salinity stress decreased relative water content, whereas leaf chlorophyll content, fresh weight and dry weight were unaffected. Wheat genotype “Norsi” may be deliberated as the most tolerant landrace, meanwhile, it exhibited the lowermost reduction % in leaf relative water content at 50 and 100 mM NaCl. Salinity stress significantly affected plant water relations of wheat genotypes. Furthermore, Hussain et al. (2021) showed that salt stress significantly decreased leaf water potential (ΨW), osmotic potential (ΨS) and leaf relative water content (RWC). However, an insignificant influence on turgor potential (ΨP) has been detected in all the studied wheat genotypes due to salt stress. The salt-tolerant wheat genotypes had greater leaf water potential (ΨW) and osmotic potential (ΨS)

2.6 Summary of Adverse Effects of Salinity on Crop Plants

63

than those of salt-sensitive ones. Conversely, both tolerant and sensitive wheat genotypes did not diverge significantly in turgor potential (ΨP). Between salt-sensitive wheat genotypes, leaf water potential (ΨW) and osmotic potential (ΨS) were the lowest in genotype MH-97. Leaf relative water content (RWC), also decreased in all wheat genotypes under saline environments. The reduction percentage in leaf relative water content (RWC) was greatest in salt-sensitive wheat genotypes rather than the salt-tolerant ones. Whereas in barley, Liu et al. (2014) found differences of gas exchange and stomatal characters in response to salinity stress. In 200 mM NaCl treatment, salt-tolerant CM72 was larger stomatal opening compared to salt-sensitive Gairdner. Ma et al. (2018) evaluated salt effect on physiological and metabolites assessments of rice genotypes. At a lower rate of sodium ion accumulation, the tolerant genotype (SS114) managed to maintain their water when compared to the sensitive (SS2-18) one. Under salt stress in maize, Jiang et al. (2017) revealed that respiration process affects the balance of photosynthates within plants and net photosynthesis. In maize, Altunta¸s et al. (2020) added that the reduction in chlorophyll biosynthesis, nutrient unavailability, and enhanced chlorophyllase activity might occur due to salinity’s depressing effects on leaf chlorophyll contents. Excess salt in the growing region of soybean adversely affects protein synthesis, uptake and transportation of water and nutrients, translocation of assimilates, cytosolic and mitochondrial responses, and some other metabolic pathways (Alharby et al. 2021). Moreover, Pan et al. (2016) investigated the influence of salt stress on the A. canescens of C4 perennial fodder shrub as excellent resistance to salinity. They found that stomatal conductance and transpiration rate were unaffected by 200 and 400 mM NaCl, this might be due to the C4 properties of A. canescens. Under high salinity, the Na+ might improve photosynthetic process of A. canescens seedlings and thus increase water use efficiency. Furthermore, Yadav et al. (2020b) stated that reduced grain dry matter in pearl millet-wheat was appeared attributable to the low translocation of assimilates under salinity and drought stress environments.

2.6.4 Effect of Salinity on Biochemical Components Salinity stress leads to fundamental changes in the biochemical components of plant cells in crop varieties. During the primary stages of salinity stress, the capability of root systems to absorb water is decreased and water loss from leaves is accelerated because of the osmotic stress of high salt accumulation in soil and plants as hyperosmotic stress (Munns 2005). So, salinity stress is considered as hyperionic stress. One of the most harmful effects of salinity stress is the accumulation of sodium and chloride ions in plant tissues exposed to soils with high concentrations of sodium chloride. The high sodium concentration results in inhibiting the uptake of essential elements for growth and development, likewise potassium ions, which causes lower productivity and plant death in bread wheat (James et al. 2011). Likewise, oxidative

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damage to various cellular components for instance proteins, lipids and DNA, interrupting vital cellular functions that occurs in plants has been produced as reactive oxygen species due to salinity stress. Wu et al. (2013) showed that the sodium accumulation in vacuoles and in the cytoplasm of distinct root zones was explored for six salt-tolerant and sensitive wheat cultivars by using a sodium-sensitive fluorescent dye. Unpredictably, cells of root meristem in the salt-tolerant cultivars exhibited a higher Na+ in their cytoplasm compared to the salt-sensitive cultivars. Increased salt stress in the growth environment caused a significant decrease in total soluble proteins. However total free amino acids were significantly increased in three salt-tolerant; S-24, LU-26S and Pasban-90 and salt-sensitive i.e. four; MH97, Kohistan-97, Inqilab-91 and Iqbal-2000 wheat varieties. But, the decrease in total soluble proteins or increase in total free amino acids were less significant in the three salt-tolerant wheat genotypes compared to in salt-sensitive ones. Likewise, salt-sensitive both MH-97 and Kohistan-97 had the lowermost total soluble proteins at saline situations. Moreover, highest rise in amino acids has been detected in salt-stressed wheat genotype MH-97. However the lowest increase was perceived in wheat genotype S-24. Accumulation of proline in the leaves of salt-stressed wheat genotypes significantly increased, and S-24 and LU-26S exhibited maximum accumulation of proline, whereas the opposite trend was found in Kohistan-97 (Hussain et al. 2021). Salt stress increased the total soluble sugars in the tested wheat cultivars. Due to salt stress, salt-sensitive genotypes MH-97, Kohistan-97 registered about 60% reduction in total carbohydrates. However ~40% reduction in total carbohydrates was recorded in salt-tolerant genotypes S-24, LU-26S and Pasban-90. Starch content in leaves decreased in all wheat varieties as a result of salt stress. The decrease in starch content was lesser (~26 to 27%) in salt-tolerant genotypes than in salt-sensitive wheat ones (~45 to 55%). Total soluble sugars increased substantially in all wheat genotypes subjected to salinity stress of 150 mm NaCl. The increase in total soluble sugars was much higher (~143 to 152%) in salt-sensitive wheat genotypes compared to salt-tolerant ones (~74 to 87%). They added that accumulation of Na+ in the leaves of wheat genotypes significantly increased attributable to salt stress, while K+ , N, and P accumulation was decreased significantly. However, Na+ accumulation was larger in salt-sensitive genotypes than that in salt-tolerant ones. The genotype S-24 accumulated the highest K+ in the leaves of salt-stressed genotypes, whereas genotypes MH-97 and Kohistan-97 were the least in K+ accumulation in leaves. Both N and P content in leaves were reduced in all wheat genotypes. Salt-tolerant genotypes had higher accumulation of N and P in their leaves under salt-stress environments. A combination of salinity and high phosphorus rather than low phosphorus is more harmful to the growth of maize. Tang et al. (2019) showed that both phosphorus deficiency and salinity significantly reduced the growth of maize. Nevertheless, phosphorus deficiency had a more noticeable effect on shoot growth. The combination of phosphorus deficiency and salinity treatments had a more marked effect on the density of tissue mass, leaf proline and soluble sugars rather than individual treatment of either low phosphorus or NaCl. In legumes, high salt uptake interrelated to the uptake of other nutrient ions, mainly K+ caused K+ deficiency. In faba bean and Chickpea Mudgal et al. (2009) showed

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that increased levels of NaCl induces an increase in Na+ and Cl¯ and a decrease in Ca++ , K+ and Mg++ . In leaves of chickpea, Mudgal (2004) study the effect of salt stress on amino acids contents. They revealed a marked decrease in the arginine and aspergine with rise in salinity. Whereas, threonine display a significant increase in the content at 4 dS m−1 EC then it decrease with rise in salinity. Furthermore, isoleunine, leucine, aspartic acid and proline exhibited a continuous improvement up to 16 dS m−1 EC. The Nitrate Reductase Activity decrease in root and shoot of pea plants leading to accumulation of NO3 ¯ and NH4 + nitrogen (Garg et al. 2001). In oil crops, on five soybean genotypes subjected to three salinity levels (0, 0.25 and 50 mM NaCL), EL Sabagh et al. (2013) found a relationship between salt tolerance of cultivar and each of proline content, Na+ accumulation in the leaves and germination percent. Whereas, Abbas et al. (2021) recorded a significant increase in Na+ and proline accumulation in peanut genotypes Ismailia1 and Samnut 22, while Ca++ , Mg++ and K+ declined dramatically in peanut under salinity conditions in all genotypes. In the leaves of five salinity-stressed canola cultivars, Bybordi et al. (2010) showed that ROS-inhibitors, Superoxide dismutase, Catalase, Monodehydroascorbate reductase, Glutathione reductase were higher than in non-stressed ones. Meanwhile, Saadia et al. (2012) detected an accumulation of proline in the roots of salt-resistant canola varieties and the shoots of salt-sensitive ones. But, when Kholghi et al. (2018) exposed 14 canola genotypes to three salinity levels 0, 150, and 350 Mm to evaluate their effect on biochemical attributes. Aggravated salinity stress caused a significant effect in all estimated parameters. Salinity stress increases lead to reduce chlorophyll content, RWC and K+ content of shoots and roots. Whereas, proline content, shoot and root Na+ content and electrolyte leakage were enhanced by salinity stress. In fodder and forage crops, under saline environments, Pan et al. (2016) detected more accumulated of Na+ in both plant tissues or salt bladders of A. canescens seedlings, also reserved fairly constant K+ in leaf tissues and bladders by increasing the selective transport capability for K+ more than Na+ . The impact of K+ to Ψs exhibited a significant reduction from 34% (control) to 9% at 400 mM NaCl. Amusingly, compatible solutes concentrations of betaine and free proline revealed a significant increase in the leaves of A. canescens seedlings, offered up to 12% of contribution to Ψs at high salinity. Thus, under saline environments, A. canescens is capable to keep relative K+ homeostasis in leaves, improve photosynthetic capability, enhance Na+ accumulation in tissues and salt bladders and utilize compatible solutes and inorganic ions for osmotic adjustment to improve water status in plant tissue. Otherwise, Sandhu et al. (2017) showed that salinity increased chlorophyll content and antioxidant capability in most alfalfa genotypes. Conversely, neither parameter correlated well with salinity tolerance index.

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2.6.5 Effect of Salinity on Seed Germination and Its Measurements Germination and seedling growth is critical one. Germination under saline environments is commonly affected due to high osmotic pressure of the soil solution. Because of the capillary increase of salts, the concentration of salts is more at seed depth than at lower levels in soil. One associated report came from studies of Pirasteh-Anosheh et al. (2015) showed that salinity disturbs the germination and growth of the plant at all developmental stages, due to its effects on photosynthesis, respiration protein synthesis, and others (Volkmar et al. 1998; Jaleel et al. 2008; Shahbaz et al. 2011),. Moreover, ROS are correlated with some biological processes in plants such as germination and root, shoot, flower and seed development (Mhamdi and Van Breusegem, 2018). In this respect, in wheat, Aflaki et al. (2017) found that with increasing salinity levels, germination %, germination rate, seed vigor, coefficient of germination rate, coleoptile to plumule ratio, and daily germination mean decreased. Whereas, ratio of radicle: plumule and mean of germination time increased. However, Hamada and Khalaf (2010) verified forty-one diverse barley landraces under three salt treatments, viz, (1) control, (2) 8000 ppm and (3) 12,000 ppm. Results revealed highly significant differences in seedling indicators; seeding height, fresh weight and dry weight among 41 entries in their response to salinity stress. The height of seeding decreased as a result of higher salinity levels. The decrease in height under 8000 ppm. was 19.37 when compared with the control. Plant height diminished statistically with increasing salinity levels at the highest two levels in all landraces. Increasing salinity levels caused remarkable decreases in fresh and dry weight. Dry weight production under 8000 ppm ranged from 0.11 to 0.44 with an average of 0.24, and under 12,000 ppm ranged from 0.09 to 0.25 with an average of 0.15, while the control ranged from 0.26 to 0.80 with an average of 0.49. Mudgal (2004) revealed that salinity has been shown to affect time and rate of germination in chickpea. Whereas, in faba bean, a significant decrease in emergence %, survival plants at harvest % was observed with an increase in the average soil salinity from 1.95, 2.95 to 4 mmose/cm (Darwish et al. 2003). Soil salinity may affect the germination of soybean seeds either by inducing an osmotic potential external to the seed stopping water uptake, or the toxic effects of Na+ and Cl− ions on germinating seed (Khajeh-Hosseini et al. 2003). Salt and osmotic stresses are responsible for both inhibiting or delaying seed germination and seedling establishment (Almansouri et al. 2001). Moreover, to determine the influence of three salinity levels (0, 25 and 50 mM NaCL) on some physiological parameters during germination in five soybean genotypes, EL Sabagh et al. (2013) conducted an experiment at plant nutritional physiology laboratory, Graduate school of Biosphere science, Hiroshima University, Japan. Seeds were irrigated by defined saline water near the field capacity. Three weeks old seeding grown in plastic pots, plants was harvested and the various measures were recorded. Results revealed a large variability within the soybean cultivars for salt tolerance at the early growth stages.

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Germination percentage was significantly decreased with increasing salinity levels in all cultivars. The Japanese cultivars (TSU) and the Egyptian cultivar (Giza111) are the most tolerant ones during germination stage and that there is a association between salt tolerance of the cultivar and germination percent, proline content and Na+ accumulation in the leaves.

2.6.6 Effect of Salinity on Nodulation Process Several studies indicate that salinity obstructed with the nodule initiation in chickpea, cowpea and mung bean and decreased number, weight and nitrogen-fixing efficiency of nodules (Balasubramanian and Sinha 1976). Salinity causes a significant decrease in the content of leghaemoglobin as compared with control up to 125 DAS which decline with aging of nodules, probably due to irreversible oxidation of leghaemoglobin. Nitrogen fixation process is also affected by salinity. The formation of root nodules and nitrogen fixation in chickpeas, were reduced with the increase in salinity levels from zero, 50, 75 to 100 mM sodium chloride. A significant decrease in the root, stem and individual plant weight, and the effect on the formation of root nodules and nitrogen fixation was detected in sensitive cultivars (Singh et al. 2003). Salt stress reduces total number of nodule per plant, nodule weight, shoot and root dry weight in faba bean and chickpea (Mudgal 2004). Although nodules were detected in inoculated plants grown at 6 dS m−1 , nitrogen fixation was completely inhibited. The findings specify that symbiosis is more salt sensitive than both rhizobiun and host plants. Salinity inhibits nitrogen fixation by decreasing nodulation and nitrogenase activity in chickpea (Mudgal et al. 2009). Dehydration of cell and toxic ion accumulation happen when the rhizobia-legume symbiosis process is hampered in particular. The presence of excess salt in the growing region of soybean adversely affects the quality and quantity of seed, growth and nodulation process) Khan et al. 2019).

2.6.7 Effect of Salinity on Vegetative Growth Salinity is one of the most prevalent abiotic stresses that destructively affect soil fertility and field crop production (Moustafa et al. 2021a, b). High salinity levels in the plant’s external medium are recognized to affect various physiological and metabolic processes which lead to growth reduction. High salinity levels cause ion imbalance and osmotic stress in numerous crop varieties (Maggio et al. 2000). Accordingly, of these primary effects, secondary stresses, for instance, oxidative damage occur (Zhu 2001). In this regard, Hussain et al. (2021) screened 40 wheat varieties at 150 mMNaCl stress. A highly significant decrease in shoot dry weight was recorded in the deliberated wheat varieties under saline hydroponic conditions as compared to the

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control. Salt stress significantly decreases both shoot and root fresh and dry biomass, plant height and flag leaf area of all wheat genotypes. Shoot fresh and dry biomass was decreased to ~50% in MH-97 and Kohistan-97 under saline circumstances. However salt-induced fresh and dry biomass reduction by 20–30% in S-24, LU-26S and Pasban-90 genotypes. Likewise, reduction in fresh and dry biomass of root varied from 47 to 52% in Kohistan-97 and Inqilab-91, whereas reduction in root fresh and dry weight was different from 28 to 37% in Pasban-90, LU-26S and S-24 genotypes. Stem height was reduced significantly as a result of salt stress. The highest reduction was perceived in Kohistan-97 with value of (37%), while, LU-26S was the lowest. Flag leaf area affected significantly by Salt stress and was reduced by 71 to 75% in genotypes MH-97 and Kohistan, but in varieties S-24 and LU-26S, flag leaf area was reduced by 46 to 49%. These variances in the reduction ratio indicate the difference between genotypes in salinity tolerance genes. In a important study carried out in rice, Minh et al. (2016) determined a correlation between salinity stress and growth and phenolic compounds and showed that salinity stress led to a significant reduction in shoot length, and both fresh and dry weights of rice varieties. Sarah et al. (2021) indicated a differential effect of salinity stress on rice genotypes of all morpho-physiological characters. Results showed that the most affected traits by salinity were K+ /Na+ ratio, root dry weight, shoot fresh weight, shoot length and shoot dry weight which were reduced by 35.2, 22.6, 16.6, 15.2 and 14% compared with control, respectively. The estimated traits showed a decrease in mean performance under salt stress, except root/shoot length ratio and SPAD value which increased by 18.64 and 12.49% over the grand mean. In maize, Sümer et al. (2004) confirmed the toxicity of sodium to vegetative growth during the first phase of salt stress. They showed that under moderate salinity stress, a hang-up in lateral shoot development becomes apparent over weeks, as well as over months, there are effects on reproductive development, for instance, early flowering or a decreased number of florets. During this period, a number of old leaves might die. Conversely, the production of younger leaves remains. The decrease in leaf development is primarily attributable to the osmotic effect of the salt stress. Likewise, 20 maize genotypes with contrasting root systems exposed to NaCl for 10 days (0, 50 mM or 100 mM NaCl). The more salt-tolerant genotypes such as Jindan 52 had less growth reductions, lower shoot Na+ contents and higher shoot K+ / Na+ ratios under salt stress (Wang et al. 2020). In legumes crop genotypes, EL Sabagh et al. (2013) concentrated on the influence of three salinity levels (0, 0.25 and 50 mM NaCL) on five soybean genotypes. The results revealed a large variability within the cultivars for salt tolerance. Increasing salinity levels significantly reduced chlorophyll content, water uptake, leaf number, and plant height. The Japanese cultivar (TSU) and the Egyptian cultivar (Giza 111) were less affected by salinity stress than the other cultivars. A significant reduction in plant height, number of leaves, water uptake, chlorophyll content, water content, fresh and dry weight of root and stem, were found in all cultivars. While, salinity stress induced a significant increase in leaf sodium (Na+ ) in deliberated cultivars. In groundnut, Mensah et al. (2006) revealed decreases in plant height and vigour with increases in salinity. Also, there was a decline in the leaves number/plant with

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increasing salinity levels. Whereas, Nokandeh et al., (2015) showed that increasing salinity reduced the size of morphological traits of the seedlings of three varieties of peanut. Furthermore, Abbas et al. (2021) revealed a reduction in peanut growth parameters, i.e., plant height, number of shoots/plant, number of leaves/plant and leaf area with increasing NaCl concentration from 0 up to 1000 and 3000 mg L−1 . Moreover, Bybordi et al. (2010) inspected the effects of increasing salinity stress on plant growth in five cultivars of canola on 30-day-old through five diverse levels of NaCl (0, 50, 100, 150 and 200 mM). The shoots of Elite showed greater reduction in fresh weight, dry weight and water content when compared with the remaining cultivars with increasing salt stress. In salt-sensitive genotypes of canola, with increasing salinity levels, decline in chlorophyll concentration led to lower dry weight and leaf weight, however in saltresistant canola cultivars, the reduction in the leaf weight and plant height does not occur (Kamrani et al. 2013). Meanwhile, Kholghi et al. (2018) found that exacerbating salinity stress caused a significant reduction in fresh and dry masses of shoots and roots. In cotton, salt stress harmfully affects biomass production, i.e. decreased leaf area, stem thickness, shoot and root weight. Cheng et al. (2018) revealed that plant height, stem thickness, shoot and root weight and expansion of leaves size phenotypically, sternly affect the yield of cotton and influenced by salinity stress. Whereas, Liu et al. (2017) showed that enhanced K+ /Na+ ratio and low Na+ uptake are important as markers for salinity tolerance. Moreover, Farooq et al. (2019) irrigated cotton genotypes with nutrient solution with an electrical conductivity of 10 dS m−1 and 15 dS m−1 since 10 day seedlings stage to 40 days. Results indicated significant differences between genotypes under control and both salinity levels. Salinity harmfully affected the root length, shoot length, fresh root weight, fresh shoot weight, dry shoot weight, and dry root weight in comparison to chlorophyll content. The magnitude of sodium under NaCl stress increased several folds and a reduction in potassium was also witnessed in the leaves. In sugar beet, salinity harmfully affects the growth and survival via induction of osmotic and drought stresses, which results in ionic misbalance due to high accretion of sodium (Na+ ) and chlorine (Cl− ) ions, which leads to specific ions cytotoxicity (Dadkhah and Rassam 2017; Abd-Elrahman et al. 2022; Makhlouf et al. 2022).

2.6.8 Effect of Salinity on Yield and Quality The crop variety, agricultural procedures, and adjacent environmental conditions play an essential role in salt tolerance during its cultivation in a saline location. Alqahtani et al. (2019) explained that the cultivar that shows a yield reduction below fifty percent is considered better for the farmer than the cultivars which showa higher reduction of more than fifty percent. Wheat (Triticum aestivum) is a moderately salt-tolerant crop. In the field, where the salinity rises to 100 mM NaCl (about 10 dS m−1 ), rice (Oryza sativa) will die

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before maturity, while wheat will produce a reduced yield. Even barley (Hordeum vulgare), the most-tolerant cereal, dies after extended periods at salt concentrations more than 250 mM NaCl (equivalent to 50% seawater). Durum wheat (Triticum turgidum ssp. durum) is less salt tolerant than bread wheat (Triticum aestivum), as are maize (Zea mays) and sorghum (Sorghum bicolor) (Maas and Hoffman 1977; USDA-ARS 2005). Pirasteh-Anosheh et al. (2015) showed that abiotic stress is accountable for the loss of crop yield and 17% and 20% of crop loss is assessed by drought and salinity stress, correspondingly. A rise in salinity in the soil has several deleterious effects on plant growth and development. Salt stress obstructs the uptake of several vital nutritional elements associated directly or indirectly with plant metabolic responses. In wheat, genotypes differ in their response to salinity, and the separation of the components of the phenotypic variance of genotypes reflects that about 60% of the variance in grain yield, biological yield and harvest index is due to salinity levels and genotypes. The results also indicate that higher grain yield under saline stress conditions is a better selection criterion than biological yield, harvest index or stress sensitivity index (Jafari-Shabestari et al. 1995). Salinity tolerance is associated with an increase in the yield of spike grain weight (Singh and Rana 1985), and the decrease in the number of productive tillers is the most common component of yield reduction under saline conditions (Maas et al. 1996). The results indicated that the grain yield of main stem of wheat appears to be less affected by salinity in tolerant varieties such as the Anza variety, which yielded about 10% more than the Yecora Roja variety with an increase in salinity level from—0.05 Mpa to—0.65 Mpa and twice as much at high salinity level—0.85 Mpa. Instead, the tillering capacity and the number of productive tillers are affected by salinity. Therefore, increasing the plant density of wheat may play an important role in compensating grain yield under saline conditions (Grieve et al. 1992). Experimental studies indicated that when evaluating the performance of six wheat cultivars under salinity levels of 12, 9, 6, and 4 dS m−1 , Chopra and Chopra (1997) found that the average values of the yield components decreased significantly in all cultivars with an increase in the salinity levels of irrigation water. The average decrease in yield reached 46.2% at the high salinity level compared to the control. Both cultivars Kharchia 65 and HD 2189 gave the highest yield, while WD 416 cultivar produced the lowest yield. The decrease in yield at 12 dS m−1 was the lowest in the wheat cultivar Kharchia 65 compared to WD 416 one. The linear regression equation showed that the two cultivars Kharchia 65 and HD 2189 were distinguished by the lowest slope and the lowest decrease in yield for every one unit increase of salinity, as well as at the highest degree of salinity of irrigation water (ECiw) which caused a 50% decrease in yield. This is in agreement with the results of Al-Dakheel et al. (2022) showed that Lulu and Barhi varieties, are characterized by high-yielding with high salinity tolerance, where average salinity level at 50% yield reduction was 12 dS m−1 ECw. Under Ras-Sudr, two field trials were carried out by Farag et al. (2020). The first was irrigated by saline water with 3900 ppm and the second with 6300 ppm on 19 durum wheat lines. The three wheat lines, ACSADs: 1487, 1566 and 1567, exhibited

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the maximum grain yield, its relevant characters and straw yield/plant. Positive and significant phenotypic association was registered between grain yield/plant and each of spike length, number of spikelets/spike, number of grains/spike, 1000-grain weight and straw yield/plant, showing their important on grain yield under stress. The first group of cluster analysis include 6 lines displayed close association with wheat grain yield, its relevant characters and tolerance indices excluding stress sensitivity percentage index, likewise their great grain yield at both 3900 ppm and 6300 ppm levels. Correlation and the path coefficients studies have confirmed the importance of number of spikes/plant, strawweight and grain weight of the main stem in wheat grain yield variation. Hence, they can be used in selection for the higher yield under salt affected soils (Ahmad et al. 2006). The relationship between agronomical and physiological traits in wheat under salinity stress conditions was computed by Mansour et al. (2020) through principal component analysis PCA. The first two PCAs accounted 87.31% of variation. The first and second PCA explaining 79.24% and 8.07% of the total variation between measured traits, respectively (Fig. 2.7). The measured traits were allocated into three groups. The first group enclosed the yield attributes parameters i.e. plant height, spike length, number of spikes per square meter, number of grains per spike, 1000-grain weight, and grain yield per hectare, along with containing eight out of 18 physiological and biochemical traits i.e. net photosynthetic rate, transpiration rate, stomatal conductance, relative water content, membrane stability index, K+ content, and K+ /Na+ ratio with an acute angle between the vectors of these traits. The second group contained non-enzymatic-enzymatic osmolytes viz. soluble sugar, free proline content, and ascorbic acid, as well the activities of three enzymatic antioxidants i.e. superoxide dismutase, catalase, peroxidase with an angle less than 90° between the vectors of these parameters and those of the yield traits, and with the previous eight physiological and biochemical traits. The third group comprised malondialdehyde and toxic ion viz. electrolyte leakage, Cl− and Na+ with a straight angle between the vectors of these traits and all the above-mentioned parameters. A strong positive relationship was perceived among the traits involved in the same group. Moreover, a positive relationship was observed between the second and third groups. Otherwise, a negative relationship was detected between the first and third groups. Hence, these traits can be used as selective criteria to assess the salt tolerance of wheat genotypes under field conditions. Hussain et al. (2021) showed that imposition of salt stress significantly reduced yield and yield attributes in all wheat genotypes. But, wheat genotypes differed in yield attributes under salt stress circumstances. The three salt-tolerant wheat varieties S-24, LU-26S and Pasban-90 had better grain yield and thousand-grain weight than those of four salt-sensitive cultivars i.e. MH-97, Kohistan-97, Inqilab-91 and Iqbal2000. While, wheat genotypes did not vary in spike length at saline circumstances, the salt-sensitive genotype Iqbal-2000 exhibited greatest decrease in spike length. In the same way, the number of tillers were the maximum in salt-tolerant genotype S-24. However the opposite was right in salt-sensitive genotype MH-97 one. Furthrmore, De Santis et al. (2021) showed that salinity and drought conditions affect the rate of carbon and nitrogen accumulation during grain filling, and starch and storage protein

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Fig. 2.7 Biplot of the principal component analysis for the first two principle components of agronomic and physiological traits at three salinity levels. PH is plant height, SL is spike length, NSm is number of spikes per square meter, NGS is number of grains per spike, TGW is 1000-grain weight, GY is grain yield, Chl is total chlorophyll, Pn is net photosynthetic rate, E transpiration rate, Gs is stomatal conductance, RWC is relative water content, MSI is membrane stability index, Sug is soluble sugars content, Pro is free proline content, AsA is ascorbic acid, SOD is superoxide dismutase, CAT catalase, POD peroxidase, MDA is malondialdehyde, EL is electrolyte leakage, Cl is chlorine content, Na is sodium content, K is potassium content, and K/Na is K/Na ratio (Mansour et al. 2020)

amount and composition in durum wheat caryopsis, thus affecting production and quality characteristics. Stress conditions affect grain protein content, composition, and technological and health quality. Stress conditions also affect the accumulation and formation of starch, dietary fiber and accumulation of health-related grain micronutrient accumulation, for instance Fe and Zn. In barley, most of the world’s barley-producing countries are influenced by the salinity problem containing but not limited to the following Russian Federation, Australia, Bangladesh, USA, China, Egypt, Turkey, India, Mexico, Iran, Syria, Iraq and Pakistan (Hossain 2019). Three cultivars i.e. Giza 2000, Giza 123 and Giza 129 were treated with 50, 100, 150, 200 and 250 mM NaCl. Salinity stress up to the level of 150 mM NaCl stimulated the production of dry matter of barley cultivar Giza 2000, whereas total carbohydrates content was decreased under sever salinity in that cultivar, while stimulated in Giza 129 and not affected in Giza 123. Proteins content showed enhancement in Giza 2000 and Giza 123, but reduced in Giza 129 especially at higher salinity levels. Giza 2000 was the most amino acid accumulator followed by Giza 123, while Giza 129 failed to accumulate amino acids particularly at higher salinity levels. Proline increased significantly in Giza 2000 followed by Giza 123,

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while reduction rather than stimulation recorded in barley cultivar Giza 129 (Saleh et al. 2017). Under three saline fields (7.72 dS m−1 ) were irrigated with well water of three salinity levels i.e. low (5.25 dS m−1 ), moderate (8.35 dS m−1 ), and high (11.12 dS m−1 ). Mansour et al. (2021) showed that at the genotypic level, although the barley genotype factor accounted for the major contribution in grain yield variation, the genotypes exhibited relevant rank variations according to their yield performance under the tried salinity levels. Genotypes G4 and G14 displayed the highest ranks of grain yield and better ranks for biological yield and harvest index at the three salinity levels. This is attributed to the ability of the genotypes to produce more spikes across salinity levels, greater grains number/spike and to maintain a relatively respectable their grain weight and harvest index. On the contrary, genotypes G1 and G10 displayed that the order of grain yield, biological yield and harvest index improved with increased salinity, which is indicative of salinity tolerance. This improvement is attributed to the spikes number/m2 , grains number/spike and grain filling. In contrast, the increase in salinity led to a severe decrease in the yield of G16 and G17. Their yield was good at low salinity level, and they showed a sharp decrease in grain yield with increasing salinity. This decrease was due to decreasing spikes number/m2 , grains number/spike and 1000-grain weight with increasing salinity level. Moreover, correlations for each trait between different salinity levels were calculated and presented in Table 2.16. It was noted that the correlation was significant between low and intermediate levels, as well as between intermediate and high levels, but it was lower between the lowest and highest levels. Strong positive relationships were noticed between 1000-grain weight and grain yield as well as plant height, harvest index and grains number/spike. While, spikes number/m2 displayed a slight positive correlation with grain yield. Hereby, under salinity conditions, 1000grain weight and grains number/spike could be utilized as good parameters for grain yield. However number of spikes/m2 is less important for this purpose. Also, a significant relationship was found between grain yield and plant height under the three salinity levels. At Ras-Sudr of salinity condition, Moustafa (2021) tested 45 advanced barley lines grown in natural salty soil (5000 ppm) and irrigated by naturally saline water at 9000 ppm across 3 seasons (2016–2019). For determining the interrelationship among yield traits, principal components (PCs) were computed over the three generations (Fig. 2.8). The first two principal components (PC1 and PC2) accounted the most of variance 84.25% (72.87 and 11.38% for PC1 and PC2, respectively). Therefore, they were used in the biplot. The traits are represented by parallel or closely vectors that show a strong positive association, whereas the vectors approximately close (at 180°) display a very negative association. Besides, the vectors toward sides had expressed slight association. Results of PC-biplot displayed that number of tillers/ plant, number of spikelets/spike, number of grains/spike, grain weight/spike, spike length and biological yield had a close and consistent positive association with grain yield. The results are consistent with the findings of genotypic and phenotypic correlations. Path analysis also shows the importance of these traits in improving barley grain yield under salinity stress conditions.

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Table 2.16 Linear correlation coefficients between the three salinity levels for each agronomic trait of barley (Mansour et al. 2021) Trait

5.25 and 8.35 dS m−1

8.35 and 11.12 dS m−1

5.25 and 11.12 dS m−1

Days to heading

0.98**

0.96**

0.93**

Plant height

0.94**

0.86**

0.75**

Spikes

number/m2

0.82**

0.84**

0.82**

Grains number/spike

0.96**

0.96**

0.90**

1000-grain weight

0.93**

0.93**

0.86**

Grain yield (kg/ha)

0.78**

0.78**

0.60**

Biological yield (kg/ha)

0.73**

0.68**

0.68**

Harvest index

0.76**

0.86**

0.65**

** ,

indicate highly significant at 0.01 probability level

Fig. 2.8 Biplot of agronomic traits for fifty-two barley genotypes under salinity conditions. DH is days to heading, PH is plant height, NTP is number of tillers/plant, SD is stem diameter, SL is spike length, NSS is number of spikelets/spike, NGS is number of grains/spike, GWS grain weight/spike, TGW is 1000-grain weight, GY is grain yield (kg/fed), BY is biological yield (kg/fed) (Moustafa 2021)

Salinity drastically reduced plant growth and yield in rice, particularly at seedling stage. Rice yield loss under saline soil conditions (>6 dS m−1 ) reaches 50–100%. A salinity stress of 8 dS/m at the panicle emergence stage reduced rice yield by 50% (Rad et al. 2012). Meanwhile, Hasanuzzaman et al. (2009) showed that the yield of salt-tolerant rice varieties in Bangladesh decreased by 30% at a salinity level of 10 dS/m. Grain yield per plant, chlorophyll content, fertility %, number of productive tillers, panicle length and number of primary braches per panicle of the studied

2.6 Summary of Adverse Effects of Salinity on Crop Plants

75

genotypes were reduced significantly by salinity (Ali et al. 2004)). Additionally, rice genotypes Jhona-349 × Basmati 370, NR-1, DM-59418, DM-63275, DM-64198 and DM-38-88 revealed better salinity tolerance than the others. Influence of salinity on yield components indicated that percent increase over control for number of primary braches per panicle ranged from 17.07 to 21.66; number of productive tillers per plants 22.64 to 42.45; panicle length 8.44 to 20.27 and fertility % from 9.05 to 24.54 in the six genotypes. All genotypes were graded as salt tolerant with respect to yield components compared to the others. The reduction in yield, leaf area and yield components in rice might be due to the decrease in cell contents, reduced cell differentiation and development, disturbed nutrition, injury of membrane and malfunction of the avoidance mechanism. The reduction in leaf area, yield and its attributes under saline environments were due to decrease growth rate due to reduced water absorption, toxicity of sodium and chloride in stem cell and decreased photosynthesis activity. Furthermore, salt stress decreased fructose-2,6-bisphosphatase levels in salt-stressed rice leaves, increasing sucrose accumulation, which regulated cell osmolarity and thus improved salt tolerance (Udomchalothorn et al. 2009). Whereas, in maize, salt stress during the reproductive stage, decreases the number and weight of grains, resulting in significant reductions in grain yield (Schubert et al. 2009). Salinity stress causes an increase in phytotoxic ions and oxidative stress through increased reactive oxygen species production and ionic effect in the cytosol. Iqbal et al. (2020) added that salinity obstruct respiration, photosynthesis, transpiration and stomatal functioning. Also, salinity negatively affects hormone regulation, seed germination, and dormancy and water relation of maize plants, reducing plant growth and yield production. Hailu et al. (2020) showed that plant height, shoot fresh and dry weight of sorghum appeared to be decreased with increasing salinity levels of NaCl of all sorghum lines and varieties. This agrees with Abida et al. (2012), who showed that as the concentration of soil salinity level increases, plant height, shoot fresh and dry weight of sorghum varieties decline. Meanwhile, Derevyanchuk et al. (2015) found that salinity induces the formation of many proteins in maize e.g. heat shock proteins and late embryogenesis abundant proteins that protect cell membranes, structural proteins, and enzymes from Na+ toxicity and Na+ -induced dehydration. Under normal and soil salinity stress conditions, the cotton genotypes varied significantly in most traits in both years. Mahdy et al. (2021) showed that the variances between genotypes are significant in one year and in the combined analyses under saline soil for seed cotton yield/plant, lint yield/plant, seed index, number of seeds/boll, plant height and pressley index. The highest performance was registered in genotypes “G 90 × Aus”, G95, G 90, G 80 and G 83 for seed cotton yield/ plant, lint yield/plant, Lint% and number of seeds/boll. Whichever, under normal and saline soil, reduction% resulted from salinity was detected for plant height (55.92%), lint yield/plant (52.21%), seed cotton yield/plant (48 75%), number of bolls/plant (32.47%), lint index (5.68%), Micronaire reading (11.22%), Pressley index (6.63%) and upper half mean length UHM (0.89%). The results showed wide range in days to the first flower (67.83 to 80.00) under normal soil. However it was narrow (58.17 to 60.67) under saline soil. Giz 90 × Aus followed by Giza 90 were the best tolerant to salinity stress.

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2 Salinity and Its Impact on Sustainable Crop Production

In legumes, it was observed, a significant decrease in survival plants of faba bean at harvest % and the seed yield/plot with an increase in the average soil salinity from 1.95, 2.95 to 4 mmose/cm, where Darwish et al. (2003) recorded a decrease in faba bean seed yield reached 50% at the moderate level and 70% at the high level. The effect of salinity on the performance of different traits was greater than the effect of genotypes or their interaction with salinity levels. The studied cultivars exhibited different behavior in seasons or locations and under different salinity levels. This indicates the importance of expanding the genetic base of varieties that can be recommended for cultivation in different environments by devising synthetic varieties that secure productivity through a buffering effect under the effects of salinity and other adverse environmental conditions. Also, taking into account the need to improve the saline environment through agricultural practices that can reduce the harmful effects of salinity on the plant. Under NaCl stress, Nasrallah et al. (2022) recorded a marked accumulation in amino acid during all growth stages. Salt stress induced proline accumulation and increased soluble sugar content. In Chickpea, Turner et al. (2013) conducted three experiments in a glasshouse in Perth, Western Australia, in which up to 55 genotypes of chickpea were exposed to 0, 40 or 60 mM NaCl added to the soil. Results revealed that when genotypes were grown in soil with 40 mM NaCl, a 27-fold range in seed yield was recorded between the 55 chickpea genotypes. The increased salt tolerance was positively correlated with greater pod and number of seeds, and greater shoot biomass, in the non-saline treatment. In the salt-sensitive genotypes, pod abortion was higher. However pollen viability, in vitro pollen germination as well as in vivo pollen tube growth has not been influenced by salinity in each of the salt-tolerant or salt-sensitive genotypes. The sodium and potassium ions concentrations in the seed were significantly higher in sensitive than in tolerant genotypes. Hence selections of genotypes with great numbers of pods and seeds in which low concentrations of salt accumulate in the seed are favorable. In addition, Kaur et al. (2022) evaluated salinity tolerance in 10 chickpea genotypes including CSG-8962 (Karnal Chana-1), as salt tolerant check under control and salinity ECiw 6 dS m−1 and ECiw 9 dS m−1 during 2018–19 and 2019–20. Results indicated that saline irrigation water decreased the number of pods per plant by 21.29% at ECiw 6 dS m−1 and 53.29% at ECiw 9 dS m−1 . Saline water of 6 dS m−1 caused a 36.1–65.0% reduction in seed yield, which additionally increased to 81.0– 98.5% with saline water of 9 dS m−1 . Genotypes S7 and ICCV-10 had seed yield reductions of 36.13% and 41.24%, separately. However salt tolerant check attained a reduction of 46.94% at ECiw 6 dS m−1 . In oil crops, Azevedo Neto et al. (2020) indicated that the most salt-tolerant sunflower genotypes was BRS323 and the most salt-sensitive was AG967. Salinity reduced leaf dry mass by (43%), stem dry mass (56%), root dry mass (52%), and total dry mass (50%) of AG967 compared to control situations. The dry mass yields of both genotypes were comparable under control situations. Conversely, in salt stress, the leaf dry mass, stem dry mass, root dry mass and total dry mass of the BRS323 genotype were, 37, 87, 67, and 61%, respectively, higher than AG967. Principal component analysis (PCA) revealed that PC1 and PC2 explained 94.17% of the total variance. PC1 described the major variance detected (79.29%). However PC2

2.6 Summary of Adverse Effects of Salinity on Crop Plants

77

accounted for 14.88% of the total variance. The leaf K+ content and total dry mass were positively associated, whereas leaf Na+ content, exhibited a negative correlation with dry mass yield. Hierarchical cluster analysis and Principal component analysis clarifying that the degree of salt-tolerance in sunflower is correlated with Na+ and K+ concentrations of leaves. The genotypes BRS323 and AG967 placed on the extreme sides of the PC1 axis, were involved in assay 2 as the most salt-tolerant and the most salt-sensitive cultivars, correspondingly. Flagella et al. (2004) showed that sunflower seed yield decrease percent per unit increase of irrigation water electrical conductivity was higher at 1 ETc (7%) than at 1.5 ETc (5.8%). Oil yield showed a significant decrease from 38.3 to 3.4 g per head on increasing salt stress and a marked increase of about 50% with the higher saline level. Fatty acid oil compositions, showed no differences between the two treatments. At higher level, only a slight decrease in linoleic and gadoleic acid and an increase in arachidic acid were observed. Significant differences among saline treatments were observed for oleic and linoleic acid. Oleic acid showed an increase from 82.8% at the control to 86.8% at the highest salinity treatment. Conversely, a progressive decrease from 6.9 to 2.8% was detected in linoleic acid with increasing salinity levels. Hereby, a possible inhibition of oleate desaturase happening under salt stress. Exposure of canola to environmental stress leads to an abundance of antioxidant enzymes. Islam et al. (2001) found that high salt concentrations in the root zone impair the growth and production of canola and mustard plants by affecting the water-nutrient balance. The reduction in seed yield of Brassica under salinity stress is attributed to the effect on lower stomatal conduction, nutrient uptake, more ion toxicity, and an imbalance in nutrient access. Under saline field conditions, Hassan and Abo-El-Haleem (2013) recorded high positive association between seed yield/ plant and each of number of branches/plant, number of pods/plant and seed oil content of canola for both Serw 4 and Serw 6 cultivars treated by gamma rays. Under the Sinai region of Egypt, irrigation with groundwater has different salinity degrees that prevent cultivated crops from reaching full yield. Hozayn et al. (2021) tried three canola cultivars; Pactol, Serw-4 and Serw-6 under three irrigation water treatments: (i) Brackish-water (BW), (ii) Magnetic-BW1; brackish water after magnetization through passing a three-inch static-magnetic unit, 3.75 mT and (iii) Magnetic-BW2; brackish water after magnetization through passing a threeinch static magnetic unit, 0.75 mT. The results showed that irrigation with M-BW1 or M-BW2 surpassed irrigation with BW in dry matter of leaves, stem and total plant and chemical analysis for mineral content i.e. N, P, K, Mg, Fe, Cu, Zn at 85 days after sowing (DAS). Overall both magnetically brackish-water treatments over tried three canola varieties, the percent of improvement compared to irrigation with brackish-water ranged between 28.33–31.76% for dry matter of plant; 15.58– 80.81% for leaf; 10.71–63.88% for stems and 2.42–54.48% for mineral content of leaves at 85 DAS. Na+ and proline contents were increased under both magnetic brackish water managements by 66.08 and 43.75%, individually. In general, the three tested canola varieties showed a positive response under magnetic brackish water treatments reflected improvement in canola yield and its components. The percent of improvement ranged between 9.35 and 35.98 for yield components and

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2 Salinity and Its Impact on Sustainable Crop Production

reached 1.29,19.66 and 21.30% in seed oil percentage, seeds and oil yield (kg fed−1 ), respectively compared to brackish water. Under Ras Sudr, Egypt conditions, Moustafa (2006) showed that increasing the levels of water irrigation salinity from 2000 ppm, 4000, 6000 to 8000 ppm decreased both the number of days to the first flower (Table 2.17) and the appearance of first open boll in all studied genotypes. These reductions were 9 and 4% in the first season and 13 and 6% in the second one. Cotton plants grown under high salinity levels try to protect their life cycle by early flowing and opening bolls. The highest reduction were observed in cotton cultivars Giza 89 and Dandara in the first season as well as Giza 85 and Giza 89 in the 2nd one; while the lowest reductions were attained in Ashmoni and Giza 70 in the first season also, Dandara and Karsheneski-2 in the 2nd one for days to first flower and first open boll, respectively. A significant decrease was observed in lint and seed cotton yields/feddan, number of fruiting branches, the number of bolls/plant, boll weight, seed index and oil percentage with an increase in salinity levels. Moustafa (2006) added that the decrease percentage in seed cotton/feddan in some cases was more than 50% (Table 2.18), where, the reduction in vegetative growth was reflected on lower number of flowers, open bolls as well as lower boll weight. Results varied from genotype to another, Giza 70, Giza 80 and Giza 83, Giza 86 and Giza 89 attained the lowest reduction in the first season and Giza 80, Giza 83 and Dandra in the second one. The result referred to Giza 70 and Giza 80 in the 1st season and Giza 83 and Dandra in the 2nd one were the most tolerant cotton genotypes which had lowest reduction % and (SI > Table 2.17 Performance of days to first flower for ten cotton genotypes under different salinity levels (Moustafa 2006) Season

Season 2001

Genotype

Treatment

Season 2002

2000

4000

6000

8000

2000

4000

6000

8000

Giza 45

75.50

73.50

72.40

65.60

78.50

76.40

75.50

65.80

Giza 70

75.70

71.80

66.90

66.90

74.60

71.20

66.00

65.70

Giza 80

77.70

75.90

73.30

73.30

81.70

81.70

78.50

75.10

Giza 83

75.00

69.00

68.20

66.50

79.40

71.70

68.90

67.50

Giza 85

74.40

74.20

68.10

67.50

73.30

67.30

58.70

58.50

Giza 86

76.70

75.40

71.70

71.30

84.90

78.60

72.00

69.10

Giza 89

77.90

75.40

67.90

65.50

69.20

68.50

60.70

56.90

Dandara

69.10

65.70

64.50

63.80

69.00

67.00

65.30

64.70

Ashmoni

68.70

68.60

68.50

65.70

69.10

67.70

67.60

64.20

Karshenseki-2

62.70

61.50

60.70

59.70

58.20

54.90

54.70

51.70

X=

73.30

71.10

68.20

66.60

73.80

70.50

66.80

63.90

F-test

**

**

**

**

**

**

**

**

LSD0.05

3.84

3.95

3.77

1.96

0.95

1.28

1.45

0.88

** ,

indicate highly significant at 0.01 probability level

2.6 Summary of Adverse Effects of Salinity on Crop Plants

79

1). These differences confirmed the presence of significant genetic variability among cotton genotypes with reduction in seed cotton yield due to increasing salinity levels. Moreover, Mohamed et al. (2018) showed that the decrease in yield was due to a reduction in the number of bolls and can led to early maturing cotton. At quality level, Moustafa (2006) indicated that fiber length exhibited genetic differences and tended to decrease with elevation of salinity levels from 2000 to 8000 ppm. This reduction in fiber length reaches to 7% overall genotypes. Using saline irrigation water could affect cell wall formation of cotton fibers and decreasing fiber length. The maximum reduction due to salinity stress was noticed in cotton cultivars Giza 45 and Giza 70, while Giza 83, Giza 85, Dasndra and Ashmouni showed the minimum reduction in both seasons (Table 2.19). Whereas, elevating salinity levels from 2000 to 8000 ppm, increased micronaire reading of all studied genotypes by 15% in the first season and 20% in the second one. It well established that the variation in fiber fineness is caused by variations in fiber maturity and intrinsic fineness. In other words, Peng et al. (2016) showed that while cotton is categorized as a salt-tolerant crops, with a salinity threshold of 7.7 dS m−1 , the fiber strength, micronaire value, maturity ratio, and maturity percentage are severely reduced with rise in salinity (Zhang et al. 2013). Fiber yield and fiber quality are the main criteria for cotton production and are negatively affected by soil salinity. Oil content of seeds depends upon climate and soil factors prevailing during the maturation period of bolls. As shown in Table 2.20, Moustafa (2006) shows that Table 2.18 Performance of seed cotton yield/fed Season

Season 2001

Genotype

Treatment 2000

4000

Season 2002 8000

RD%

Giza 45

643.35 392.55 253.65 86.85

6000

8000

38.98 594.75 371.70 209.55 85.20

37.50

Giza 70

580.80 520.05 147.45 126.45 10.46 572.10 274.95 104.10 85.20

51.94

Giza 80

524.55 426.00 113.25 103.80 18.79 535.20 370.50 108.15 88.50

30.77

Giza 83

849.45 594.45 233.10 181.80 30.02 638.55 576.00 259.65 196.50 9.80

Giza 85

645.60 430.95 160.05 153.75 33.25 645.30 229.65 107.70 101.55 64.41

Giza 86

608.55 508.35 255.00 67.20

Giza 89

634.35 531.60 217.80 123.60 16.20 676.05 330.30 222.90 112.50 51.14

Dandara

753.90 540.90 226.20 153.75 28.25 647.40 490.95 237.90 131.40 24.17

Ashmoni

876.60 423.90 282.75 118.95 51.64 850.65 433.65 307.05 107.40 49.02

Karshenseki-2 728.85 423.00 288.45 83.10

RD% 2000

4000

6000

16.47 643.50 285.75 156.15 61.65

41.96 680.55 328.35 222.15 73.05

X=

684.60 479.18 217.77 119.93

648.41 369.18 193.53 104.30

F-test

**

*

**

**

*

**

**

**

LSD0.05

65.25

14.09

5.28

2.06

32.25

7.71

4.82

2.14

55.59

51.75

(kg) for ten cotton genotypes under different levels of salinity (Moustafa 2006) One feddan = 4200 m2 , * and **, indicate significant and highly significant at 0.05 and 0.01 probability levels, respectively

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2 Salinity and Its Impact on Sustainable Crop Production

Table 2.19 Performance of fiber length for ten cotton genotypes under different levels of salinity (Moustafa 2006) Season

Season 2001

Genotype

Treatment

Season 2002

2000

4000

6000

8000

RD% 2000

4000

6000

8000

RD%

Giza 45

33.60

32.81

31.74

29.36

12.62 33.89

32.67

31.71

30.33

10.50

Giza 70

33.91

33.55

31.82

30.26

10.76 33.92

33.09

31.87

30.55

9.94

Giza 80

29.73

28.98

28.16

27.67

6.93

29.30

29.73

28.14

27.69

5.49

Giza 83

29.36

28.54

28.84

28.13

4.19

30.04

29.76

28.21

28.16

6.26

Giza 85

28.20

28.03

27.83

27.17

3.65

28.77

28.42

28.04

27.16

5.60

Giza 86

31.47

30.63

29.72

29.24

7.09

31.67

30.84

29.70

29.21

7.77

Giza 89

31.27

31.11

29.14

28.84

7.77

31.56

30.52

30.11

29.67

5.99

Dandara

29.26

29.03

28.39

28.04

4.17

29.63

29.20

29.06

28.42

4.08

Ashmoni

29.43

29.11

28.78

28.15

4.35

29.99

29.25

29.11

29.06

3.10

Karshenseki-2 30.91

30.57

29.59

29.08

5.92

31.67

30.54

29.81

29.56

6.66

X=

30.714 30.236 29.401 28.594

31.044 30.402 29.576 28.981

F-test

**

**

**

**

**

**

**

**

LSD0.05

0.21

0.18

0.19

0.11

0.32

0.25

0.19

0.17

** ,

indicate highly significant at 0.01 probability level

salinity levels adversely decreased seed oil percentage to 19% in the 1st season and 17% in the 2nd one by elevating salinity levels from 2000 to 8000 ppm. Giza 83 cotton cultivar exhibited the highest reduction ( 0.8) between the control and saline conditions in seven barley traits i.e. days to flowering, days to maturity, number of ears per plant, number of grains per ear, dry mass per m2 , yield and harvest index. Negatively

Fig. 4.2 Biplot of the first two principal components for agronomic traits of 39 wheat genotypes over three growing seasons under salinity stress (Moustafa et al. 2021)

4.3 Morphological Characters

125

correlation between flowering time with yield, yield components, and yield-derived traits, suggests that salinity speed up flowering by an average of 3.3 days related to higher salinity tolerance based on genetic base. A few quantitative trait loci (QTL) governing the flowering time with different effects under control versus saline conditions, suggesting that these loci effect salinity tolerance. Furthermore, Sayed et al. (2021) found that days to heading was associated negatively and significantly with all yield attributes under two salinity levels, except with harvest index, which was non-significant. In chickpea, Katerjia et al. (2005) found early flowering in the genotypes watered with two salt solution levels of NaCl and CaCl2 viz. 4 and 8 dS m−1 EC, rather than the plants irrigated with freshwater without salt. Cotton genotypes were evaluated under four levels of water salinity i.e. 2000, 4000, 6000 and 8000 ppm. Moustafa (2006). The results showed that increasing levels of water irrigation salinity from 2000 to 8000 ppm resulting in a decrease in both number of days to the first flower and the appearance of the first open boll in ten genotypes, with earliness percentages 9 and 4% in the first season and 13 and 6% in the second one. The highest reduction was observed in cotton cultivars Giza 89 and Dandara in the 1st season as well as Giza 85 and Giza 89 in the 2nd one for days to first flower and first open boll, respectively. It well established that variations in fiber maturity and intrinsic fineness cause the variation in fiber fineness. In the same framework, Mahdy et al. (2021) revealed that salinity stress reduced yield of cotton by reducing the number of bolls and causing early maturity. Salinity enhanced flowering since the mean days to the first flower decreased under normal soil from 76.51 to 59.82 under saline soil. The earliest cultivars were Giza 90 under normal soil and Giza 95 under saline soil and more tolerant to salinity. In canola, Hassan and Abo-El-Haleem (2013) under saline field conditions and irrigation water salinity, identified seventeen early promising mutants by 15 Kr Serw 6 were earlier in flowering than the parent, ranging from 7 to 27 days. The promising mutants are considered the support of future breeding programs for earliness and economic qualities of canola under saline conditions. In light of previous findings, the role of early ripening in the escape of crop varieties from salt stress is evident.

4.3 Morphological Characters Crop varieties tend to self-adapt through many morphological changes to maintain life potential during salinity stress conditions.

126

4 Fundamentals of Crop Resistance to Salinity: Plant Characters …

4.3.1 Leaf Properties Leaf area is an indicator of plant photosynthetic capability and mainly involved for stress tolerance for a certain period. A larger leaf area per plant is related with higher photosynthetic assimilate production and higher dry matter production. The wheat salinity-tolerant cultivars, like Yakura Rojo, Strain 1 and Strain 3 have good leaf characteristics i.e. leaf area, green viability, and rate of photosynthesis (Sallam and Afiah 1998). The same was observed in transgenic tobacco plants, characterized by a high chlorophyll content under salinity conditions (Sumesh et al. 2003). Nevertheless, Udovenko and his co-workers (1974) showed that the change in photosynthetic pigments contents in response to salinity was irregular in the plant leaves. Moreover, ten wheat genotypes were tested in their reaction of morphological traits to different levels of salt stress (0, 50, 100, 150 and 200 mM NaCl) by Al-Khaishany et al. (2018). The tolerant genotype Shebam 8 exhibited better leaf area compared to the sensitive genotypes Maaya, Pawni, Samra and Mesri. Hussain et al. (2021) found a relationship between leaf characteristics in wheat and salinity tolerance. Flag leaf area affected significantly by salt stress and decreased by 46– 49% in varieties S-24 and LU-26S, but it decreased more by 71–75% in genotypes MH-97 and Kohistan, respectively. Further, leaf area accounted the most part of the total variation in the yield of cultivars under salinity conditions. In rice, Zeng et al. (2003) recorded a positive and significant correlation between leaf area index, yield and its components in all salinity rice-tolerant and sensitive genotypes. Whereas, Ali et al. (2004) showed that rice genotypes DM-63275, Jhona-349 × Basmati-370, DM-59418, DM-38-88, DM64198 and Basmati-370 × NIAB-RICE-1 showed minimum percent reduction for leaf area. While, maximum percent reduction over control was noted in NIABIRRI9, NIAB-Rice-1, DM-25 × NIAB-IRRI-9, DM-5-89 and super basmati, attributed to suppressed cell division. The better leaf growth and leaf water content, detected in salt-tolerant maize were associated with greater antioxidant activity with higher accumulation of polyphenols under salinity conditions (Kaya et al. 2010). In sorghum, the increase in the number of green leaves at harvest and the delay in aging are unique traits that sustenance crop genotypes to tolerate salinity conditions. The parental genotypes ICSA-14, ICSA-47, ICSA-88015, ICSA-88015 × ICSR-91022, ICSA-14 × ICSR-91022 were characterized by an increase in the number of green leaves (>11 leaves) able to survive until harvest number of green leaves (El-Menshawi et al. 2003). Twelve faba bean genotypes were verified under two levels of salt stress (100 mM and 200 mM) and the control. Afzal et al. (2022) showed that the most important characteristics that contributed to the salinity response of faba bean genotypes are leaf fresh weight, leaf dry weight, leaf area, Na+ , K+ , and Na+ /K+ . Meanwhile, EL Sabagh et al. (2013) showed that Japanese soybean cultivar (TSU) and the Egyptian soybean cultivar (Giza 111) were greater in leaf number and considered as most tolerant to salinity than the other cultivars.

4.3 Morphological Characters

127

With increasing salinity levels, Kamrani et al. (2013) recorded a decline in chlorophyll concentration led to lower leaf weight and dry weight, but in salt-resistant canola varieties, the reduction in the leaf weight does not happen. In respect to sugarcane, Dwivedi (1994) revealed that sugarcane cultivars with high dry matter partition in old leaves recorded less dry matter yield reduction and greater tolerance to sodium stress, while sensitive cultivars recorded an opposite trend. Recently, da Silva et al. (2022) tested ten cultivars and two sugarcane species i.e. IM76-228 (S. robustum) and IN84-82 (S. spontaneum) under two levels of sodium chloride (NaCl), control (naturally in the soil used: EC with 0.083 dS m−1 ) and soil enriched with NaCl: EC of 7.2 dS m−1 . Cluster analyses classify sugar cane genotypes to three distinct groups concerning salinity tolerance on biomass-basis. The cultivars RB855156, SP80-1842, SP80-1816 and species IM76-228 showed no reduction in leaf dry matter and shoot dry matter. Nonetheless, the cultivars SP803280, RB928064, RB92579 and species IN84-82 were impaired by salinity. The cultivar SP80-1816 displayed the highest biomass accumulation and the highest tolerance index. Reinforcing the important role of leaf properties in salt-tolerant genotypes.

4.3.2 Root System Root architecture is influenced by soil water content and plays an important role under different soil stress conditions. The root is a determining factor for the tolerance of crop genotypes to extreme influences (Tang et al. 2011). Root growth depends on the amount of water absorbed from the soil. Crops varieties differ in their growth habit, development, distribution, strength and depth of the root pattern. Crop varieties with a strong root system are characterized by the ability to absorb water from the soil to maintain the water balance within the plant, and of course, this is reflected in the level of crop production. Salt, through its osmotic effects, is reported to reduce root epidermal cell division and rate of elongation, which reduces primary root growth. However initiates lateral root development in wheat and Arabidopsis (Jung and McCouch 2013; Rahnama et al. 2011). This would help plants in mining nonsaline zones for minerals and water until exploitation of saline regions become necessary. Roots of Arabidopsis exposed to a high NaCl band in sterile culture show negative halotropism that is they grow away from salt (Galvan-Ampudia et al. 2013). Fang et al. (2017) showed that root system assists aerial growth and is important for yield. Root morphological characters comprise root length, surface area, and root volume affect the spatial arrangement of underground roots, whereas root diameter is associated with the ability to penetrate strong soil and stress tolerance, besides the root tip is the most active portion of the root system (Bai et al. 2019; Kabir et al. 2015; Maccaferri et al. 2016). The number of embryonic roots and number of crown roots and their distribution in wheat crops are considered as selection criteria for drought and salinity tolerance.

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4 Fundamentals of Crop Resistance to Salinity: Plant Characters …

These traits are associated with the cultivar’s ability to survive and produce a yield under harsh environmental conditions. The high yield of the best varieties of winter wheat was attributed to the continuous selection of root characters (Xu et al. 2021). Besides in rice, Kakar et al. (2019) observed superiority of salinity-tolerant genotypes (BR47 and Geumg) was due to the numbers of root tips, root forks and root crossings. Thus, salt-tolerant genotypes develop extensive root systems. The salt sensitive genotype (75-1-127) showed the least previous characters under salinity stress. Whereas, strong root growth in maize under saline conditions is one of the mechanisms of resistance by preserving cell osmotic regulation (Maiti et al. 1996). Salt tolerance was positively correlated with shoot height, shoot dry weight and primary root depth, but negatively associated with shoot Na+ content at 100 mM NaCl. Primary root depth is important for recognizing salt reactions in maize genotypes as a selection criterion for screening salt tolerance during early growth. The selected salttolerant genotypes have the potentials for cultivation in saline soils and improving high-yielding salt-tolerant maize crosses in prospect breeding programs (Wang et al. 2020). The selection for dry weight of root system, shoot system, root size and the seedling root length are considered important indicators in the screening sorghum genotypes to salinity tolerance during seedling stage before the tests of evaluating the yield under field conditions (Hassanein and Azab 1993). Abdelraouf et al. (2016) recorded significant interaction between the salinity and faba bean cultivars on root dry weight. The highest mean relative decreases in root dry weight under all salinity levels were 42.30, 41.44, 33.65, 24.10 and 8.95% compared to the control of Giza 843, Nubaria1, Giza3, Itay1, and Lozodo cultivars, respectively. Thus, the root dry weight of Giza 843 was the highest sensitive to salinity. However, Lozodo was tolerant. Root system characteristics frolicked an important role in the salinity tolerance of sugarcane, as the tolerant cultivars were distinguished by highly porous roots and a greater number of aeriferous parenchyma compared to the sensitive ones. Dwivedi (2000) used this property to screen sugarcane germplasm to tolerate Soddy soils’ stress. Bishopp and Lynch (2015) have shown that improving root growth leads to more efficient water and nutrient uptake and improved yield levels.

4.3.3 Shoot: Root Ratio Salinity affects the growth of the shoot system to a greater degree than the growth of the root system. The growth and extension of the roots, as is the case in the elongation of the stems, depends on the turgor pressure of the cells. The small and thin lateral roots are more sensitive to salinity than the old and thick roots of the original root system. Wheat cultivars varied in their degree of tolerance to salinity under 10, 15, 20 and 25 mmohs/cm. Tolerant cultivars showed the least significant decrease in seedling rate, seedling length, shoot dry weight, root length and dry weight compared to sensitive cultivars (Raiz et al. 1998). The number of wheat

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grains per unit area, number of grains/spike and plant biomass were lower in wheat genotypes with shorter root lengths, compared to genotypes with longer roots that had higher biomass and grain yield (Xie et al. 2017). Al-Khaishany et al. (2018) indicated that genotype Shebam 8 was obvious as salt tolerance showed better shoot fresh weight and shoot dry weight than the other genotypes. Yecora Rojo, KSU106, Samma, Sonalika and Gemmeiza 9. So, Shahzad et al. (2012) showed that based on association and heritability, it transformed into supposed that lengths of root and shoot, their fresh and dry weights, have positive associations and high heritability, so they can be exceptionally gainful norms for settling on salt tolerant genotypes. Ouertani et al. (2021) revealed better performance of the salt-tolerant barley Barrage Malleg genotype over the salt-sensitive Saouef genotype for leaf dry weight, root dry weight and root length. The salt-tolerant Barrage Malleg genotype had superior osmoprotection against salt stress compared to the salt-sensitive Saouef genotype. On the other hand, in rice, the ratio of shoot weight the root mass was also associated with seedling strength 30 days old in rice under saline conditions (Zayed et al. 2004). Sarah et al. (2021) indicated differential tolerance to salinity stress in rice genotypes based on morphological characters. Results indicated that mean performance of root/shoot length ratio was increased by 18.64 over the grand mean under salt stress. Rice genotypes FL478, RBL-236, RBL-238 and RBL-252 exhibited the best performance of root length, shoot length, root: shoot length ratio, root fresh weight, shoot fresh weight, root dry weight, shoot dry weight, root: shoot dry weight ratio, SPAD value and K+/Na+ ratio under salt stress. According to principal component analysis, root fresh weight, shoot fresh weight, root dry weight, shoot dry weight, root: shoot length ratio, root: shoot dry weight ratio and K+ /Na+ ratio were promising traits of salt tolerance in rice. In faba bean cultivars, Abdelraouf et al. (2016) showed that salt levels of 50 and 100 mM NaCl improved shoot/root ratio of fresh and dry weight, while 25 mM NaCl salt level had decreased but not significantly shoot/root ratio on fresh and dry weight basis of faba bean cultivars. The highest value has been found in Nubaria 1 and the lowest in Giza 843.

4.3.4 Salt Glands Salt glands are found in numerous halophytes. They work by moving salt into apoplastic space where it accumulates and is pushed out of the leaf by bulk flow of water by reason of the negative osmotic potential generated by the Na+ increase. This process is generally found in salt marsh plants where water is not a limiting factor, and has also been observed in grasses containing two-celled glands that secrete salt (Amarasinghe and Watson 1989; McWhorter et al. 1995). A wild type of rice, Porteresia coarctata, can develop and mature on 25% seawater and contains fine hairs that secret salt (Flowers et al. 1990). Results showed that a mutant of the common ice plant lacking epidermal bladder cells was more sensitive to salt than the wild type, where the epidermal bladder cells play a significant role as water reservoirs as well

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as in the sequestration of Na+ (Agarie et al. 2007). Some halophytes overcome the problem of using bulk flow to expel accumulated Na+ by using “salt hairs,” that accumulate salt and water and then die, thus decreasing transpiration losses. Otherwise, hydathodes, which release water by grasping during periods of low transpiration, may be adapted to saline through the transformation of particular cell types by Na+ transporting genes. Salt Glands in the Poaceae family and their association to salinity tolerance was deliberated by Céccoli et al. (2015). Species within this family display a very wide difference in salinity tolerance. Salt secretion through the saline glands plays an important role in regulating ion equilibrium, which contributes to salt tolerance. Histological sacks are illustrious from salt glands in the plant families. In Atriplex, completely 200 species exhibited salt bags. The salt solution is transmitted from mesophilic cells to glandular trichomes through stem cells against the gradient concentration. The salt accumulates in the central vacuolar glandular trichomes, eventually rupturinged and ireleased onto the leaf surface. Salts accumulated in the leaf surface, reduce transpiration rate and increase light reflection. Glandular trichomes can remove over 80% of sodium chloride inflowing the Atriplex leaves (Akbar et al. 1972; Hairmansis et al. 2017).

4.4 Anatomical Characters Anatomical features play a vital role in salinity stress tolerance in crop plants. Anatomical parameters are considered an indicator that helps plant breeders select salinity tolerance in breeding programs. Indeed, barley over-expressing the HKT subfamily 2 gene, HvHKT2;1, had greater xylem and leaf Na+ content in plants grown in saline and was associated with increased salt tolerance (Mian et al. 2011). El-Emary et al. (2013) tested some genetic materials of rice included one variety sensitive to salinity Giza 177, four moderately salinity tolerance i.e., GZ 1368 and Sakha104, Sakha 101m (a) and Sk.101m (b) and four highly salinity tolerance i.e., Giza 159 GZ 6296, Giza 179 and Giza 178 with three levels of salinity concentration, 4000, 6000 and 8000 ppm of NaCl, as well as, the tap water for root parameters i.e. epidermis, cortex thickness, number and diameter of xylem vessels and diameter of the vascular cylinder, as well as, some yield traits were determined. Highly differences were found for diameter and numbers of xylem vessels in the vascular cylinder for the studied materials. Moreover, there are wider vascular shown in salinity tolerant varieties especially for Giza 159, GZ 6296, Giza 178 and Giza 179. Therefore, new rice variety Giza 179 could be considered promising under saline soil condition compared with Giza 178 one. Wankhade et al. (2013) recorded an optimistic correlation between salt stress tolerance and the thickness of rice epidermal cells. Moreover, Srivastava and Sharma (2022) showed salinity tolerance rice varieties exhibited developed dense trichomes and increased in size with the assistance of a layer of air trapped in trichomes to diminish water transpiration rate compared to sensitive varieties under differing levels of salt (40–160 mmol/l). Leaf ultrastructure changed

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and the plant tolerance to salinity varied in two rice species (Oryza sativa L.). The sensitive rice species (Jaya) showed variations in the chloroplast integrity in comparison to the tolerant species (Kogut). Especially, the majority of chloroplasts of Jaya displayed indicators of injury in response to raised NaCl. Whereas, Korgut tolerance chloroplasts genotype did not show any salinity impact. This reaction was accompanied by a 53% reduction in PN in Jaya, while no significant variation in PN was found in Korgut. Dolatabadian et al. (2011) showed that salt stress induces changes in anatomical characteristics such as increase of cutin synthesis on epidermal stem cells and alterations in xylem construction and lignification in soybean stems. Under Sinai region, Hozayn et al. (2021) tried three canola cultivars; Pactol, Serw4 and Serw-6 under three irrigation water treatments: (1) Brackish-water (BW), (2) Magnetic-BW1; brackish water after magnetization through passing a threeinch static-magnetic unit, 3.75 mT and (3) Magnetic-BW2; brackish water after magnetization through passing a three-inch static magnetic unit, 0.75 mT. The results showed that irrigation with M-BW1 or M-BW2 surpassed irrigation with BW in leaf anatomy i.e. midvein and lamina thickness, length and width of leaf vascular bundle and lower and upper epidermis thickness; stem anatomy i.e. stem diameter and thickness of cortex, xylem and phloem in addition pith diameter. Overall both magnetically brackish-water treatments over tried three canola varieties, the percent of improvement compared to irrigation with brackish-water ranged between 15.58 and 80.81% for leaf. Likewise, changes were recorded in the anatomical mechanisms to cope with salt stress in numerous crops, for example, in wheat (Nassar et al. 2020); barley (Kiliç et al. 2007); mung bean (Khan et al. 2021); soybean (Silva et al. 2021), Cynodondactylon (Hameed et al. 2010) and Salicornia europaea (Cárdenas-Pérez et al. 2022).

4.5 Physiological Characters Salinity stress leads to changes in several physiological processes depending on the intensity and duration of the stress and thus inhibits crop production (James et al. 2011; Rozema and Flowers 2008).

4.5.1 Chlorophyll Content Chlorophyll content, green viability and photosynthetic efficiency are characteristics of salt-tolerant cultivars. The cultivars and strains of wheat Yakura Rojo, Strain 1 and Strain 3 were higher in chlorophyll a + b content (Sallam and Afiah 1998). Chlorophyll content has been recommended as one of the attributes for salinity tolerance in wheat plants (El-Samad 1993; James et al. 2002). Physiological characteristics like photosynthesis and chlorophyll content are the mainly imperative ones for salts

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tolerance in a wheat (Iqbal et al. 2018). Whereas, more chlorophyll and carotenoid contents in wheat under control condition with compared salt stressed plants has been found by Khatkar and Kuhad (2000) and James et al. (2002). Khan et al. (2009) showed that maximum chlorophyll contents were maintained by wheat genotype Sarsabz and KTDH followed by Lu-26s were found to be tolerant on the basis of salinity measurement. These genotypes also maintained the higher proline content and K/Na ratio under saline conditions. Moreover, Hussain et al. (2013) found a relationship between chlorophyll content and salinity tolerance in wheat cultivars. They showed that both wheat genotypes ZAS 42 and ZAS 08 were less affected by salinity based on its higher chlorophyll content and were reported as salt tolerant. Whereas, genotype ZAS 70 registered the greatest loss in total chlorophyll content. Hussain et al. (2021) revealed that the salt-stressed plants of wheat cultivars S-24 and LU-26S produced maximum content in total chlorophyll (SPAD values) in the leaves followed by Kohistan-97. In contrast, MH-97 had a reverse trend. Wu et al. (2013) showed that Tibetan wild barley, XZ16 had higher chlorophyll content and compatible solutes than CM72. Whereas, the barley cultivar CM72 possibly improved its salt tolerance by increasing glycolysis and energy consumption, under high salinity environment. Therefore, the importance of barley salt tolerance Tibetan wild barley as genetic resource for developing novel barley cultivars high salt tolerance. Among 18 rice genotypes, Ali et al. (2004) showed that the most salt-tolerant rice genotypes DM-3-89, NIAB-Rice-1, Jhona-349 × Basmati-370 and NIAB-IRRI-9 × DM-25 were attained minimum reduction in chlorophyll content. Whereas, M64198, Basmati-370 and DM-5-89 displayed maximum reduction for total chlorophyll content and were classified as sensitive ones. Ma et al. (2018) assessed a comprehensive study of physiological and metabolite changes in rice genotypes from salinity stress in tolerant versus sensitive genotypes among 92 entries. They selected the most tolerant genotype (SS1-14) which maintains their water and chlorophyll contents compared to the sensitive line (SS2-18) at lower rate of sodium ion accumulation. Whereas, in maize Molazem (2022) detected significant positive correlations between chlorophyll a and chlorophyll b in normal and salt stress conditions. Under normal conditions, an intense positive association was attained between sodium concentration in leaves with yield. While, between chlorophyll b and maize grain yield, a significant positive correlation coefficient was observed under salinity conditions. At the same time, Ali et al. (2022) detected enhancement in values of chlorophyll a/b ratio and carotenoids in maize plants under salt stress. Faba bean genotypes exposed to salt stress leads to alterations in photosynthetic pigments, total carbohydrates. Where, Afiah et al. (2016) identified tolerant faba bean genotypes (NBL-Mar.3 and NBL-5) that exhibited high chlorophyll content compared to sensitive ones (Nubariya-1 and Misr-1). They added that seed yield/ plant showed wide range of variances between genotypes in stress conditions. In soybean under salinity stress, Do et al. (2019) indicated a significant linear association between four traits i.e. leaf scorch score, chlorophyll content ratio, leaf sodium content and leaf chloride content. Among these, correlation coefficients (r 2 ) of chlorophyll content ratio with the other traits were negative and ranged from −

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0.61 to −0.92. Conversely, the correlations between leaf scorch score, leaf sodium content and leaf chloride content were positive. Under salt environments, transformed canola produce more chlorophyll content and more production than wild-type ones (Sun et al. 2015). In sugar beet, using transcriptomic analyses of two contrasting genotypes. Geng et al. (2019) revealed that the salt-tolerant cultivar sugar beet (T710MU) revealed better growth and displayed a higher chlorophyll content compared to the salt-sensitive one (S710). In forage crop alfalfa, Farissi et al. (2013) demonstrated that the ability to maintain appropriate levels of chlorophyll and water content as well as high concentrations of proline in tissues under salinity stress have been suggested to be used as tolerance markers for alfalfa populations verified under diverse geographic locations of Morocco.

4.5.2 Stomata and Transpiration Rate Stomata are of great importance in the vital functions of energy storage and utilization, as well as a protective mechanism by reducing water lost by closing the stomata. The stomata closure is one of the most important lines of plant defense against salt and drought stress environments. Decreased uptake or loss of water from the guard cells alters the pressure of their turgor, reducing stomata opening. Since, the guard cells are always exposed to the external atmosphere, they lose water directly by evaporation, which reduces the turgor pressure, and the stomata close by a mechanism called Hydropassive closure. This mechanism occurs when water is rapidly lost from the guard cells and the stomata are closed to equalize the water moving to the guard cells from the epidermal cells. A second mechanism is called Hydroactive closure, stomata close when the leaf or roots are under stress. This mechanism depends on the metabolic processes in the guard cells. This process is considered a reversal of the mechanism of opening the stomta. Stomatal evolution can occur under the conditions of selection, as the behavior of stomata is under genetic control. Gas exchange is a determinant of productivity and a valuable tool as a physiological trait that can easily be used as a breeding criterion. Carbon pass and transpiration happen using open stomata, which both help to enhance photosynthesis and nutrient absorption from the growth environment. But, under saline environments, the stomata tend to close to avoid water loss as it is a scarce resource due to osmotic imbalance (Adem et al. 2014). Water potential measurements were essential to avoid variation in plant water status owing to differences in water loss through transpiration. El-Hendawy et al. (2017) showed that the increase in the transpiration rate in wheat variety Sakha 61 could significantly contribute to enhancing the inward water flow and consequently lead to an increase in the influx of toxic ions (Na+ and Cl− ) within the transpiration stream (Vysotskaya et al. 2010; Zheng et al. 2008).

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In barley, Liu et al. (2014), in response to salinity stress, the salt-tolerant barley genotype CM72 was characterized by significantly larger stomatal opening at 200 mM NaCl compared to salt-sensitive genotype Gairdner. Stomatal traits, for example, opening width/length were significantly correlated with grain yield at salt stress conditions. Genetic analysis of the population CM72/Gairdner showed the importance of stomatal characters-related to salt tolerance. In rice, stomata sensitivity and the rapid decrease in the degree of stomata conductivity and the low transpiration rate during the initial stages of exposure to salinity were characteristic of the salinity-tolerant rice varieties. While, the salinity-sensitive rice strains were delayed by a day or two before the gas exchange rate decreased significantly (Ismail and Moradi 2003). Whereas, in a preceding comparative study in sorghum, a relationship was recorded between the degree of stomata conductivity and photosynthetic rate under salinity stress. More salt-sensitive sorghum genotype displayed a significant decline in the actual photosystem II efficiency under higher salt stress rather than tolerant genotypes which negatively affected CO2 intake and transpiration rate (Sui et al. 2015). It was noted in faba bean that changes in the rate of transpiration under salinity conditions depend on the sensitivity of genotypes to stress. Moulay (2004) observed the occurrence of stomata closure as an expression of the cells’ ability to save water in light of changes in the current metabolites, osmotic protectors, and factors of plant resistance to stress. Also in quinoa, Cocozza et al. (2013) recorded a good resistance to moisture and salt stresses through stomatal responses and strict dependencies between relative water content and potential water components that caused the osmotic regulations. This is essential to maintain leaf turgor favorable to plant growth. In Atriplex, Calone et al. (2021) evaluated salinity tolerance in the perennial C4 species Atriplex halimus, and in the three cultivars of the annual C3 Atriplex hortensis: green, red, and scarlet subjected to water salinity ranged from zero to 360 mM NaCl. The degree of stomatal conductivity and transpiration rate were more affected by salinity in the C4 A. halimus compared to the C3 species A. hortensis, due to lower leaf water potential showing stronger osmotic adjustment, and higher relative water content related to more turgid leaves, in A. halimus than A. hortensis. The stomatal conductance and electrolyte leakage are negatively associated with the fresh weigh, which is positively associated with Na content and water use efficiency. The decreased gas exchange related to Na+ content contributed to enduring intrinsic water use efficiency under salinity condition.

4.5.3 Photosynthesis Efficiency Photosynthetic efficiency might be a major factor in determining plant tolerance to salt stress. Plants can sense stress when growing conditions are unfavorable and trigger an internal response at an early stage before external symptoms appear. When a high quantity of salt enters the plant cell, the membrane system and function of

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thylakoids in chloroplasts could be devastated and affect photosynthetic performance if the salt concentration is not regulated to optimum levels. Maintaining optimal photosynthesis and respiratory processes is crucial for salinity tolerance. Increased biomass of resistant spring wheat genotypes might be associated with their cap-potential to preserve a better photosynthesis rate over the sensitive ones (Ashraf and Ashraf 2012). Whereas, James et al. (2002) showed that organic solutes, sucrose and other sugar-related compounds; would impose a real carbon cost on the plant as it was observed that photosynthetic production in sensitive durum wheat genotypes may be reduced at 150 mmol NaCl by stomatal closure and smaller leaf area. Eighteen bread wheat genotypes were assessed under natural saline field conditions and under three levels of saline irrigation (5.25, 8.35, and 11.12 dS m − 1) extracted from wells. Based on yield index under three levels of salinity, the genotypes were categorized into four groups i.e. group A, tolerant (Gemmeiza-11); group B, moderately tolerant (Gemmeiza-9, Gemmeiza-10, Giza-171, Sids-14, Line-6083 and Line-6084)); group C, moderately sensitive (Giza-168, Gemmeiza-7, Sakha94, Sids-12, Misr-1, Line-6052, Line-6078, and Line-1208) and group D, sensitive, (Gemmeiza-12, Misr-2 and Shandawel-1). Mansour et al. (2020) indicated that net photosynthetic rate Pn showed a highly significant influence by salinity level, genotype group and their interaction (Table 4.1). The highest Pn rate was assigned for the genotype in group A. The salt-tolerant genotype Gemmeiza-11 in groups A maintained higher values of net photosynthetic rate. This physiological parameter reflects the tolerance of the wheat genotype to salt stress at the canopy, organ, tissue and cellular levels. Zhu et al. (2020) identified proteins that are associated with photosynthesis, reactive oxygen species (ROS) scavenging, and ATP synthase upregulated 12 proteins that were increased in response to salt stress in salt-tolerant barley genotype T46, but remained unchanged in N33S at 300 mM NaCl. In the salinity tolerant line, Table 4.1 Performance of four group wheat genotypes for net photosynthetic rate (Pn) under three salinity levels, S1 (5.25 dS m−1 , S2 (8.35 dS m−1 (and S3 (11.12 dS m − 1 ) (Mansour et al. 2020) Genotypes

Net photosynthetic rate (Pn) S1

S2

S3

Mean

Group A n = 1

12.72

10.14

6.89

9.92a

Group B n = 6

12.50

9.91

6.42

9.61b

Group C n = 8

11.24

9.18

6.07

8.83c

Group D n = 3

10.61

8.39

5.24

8.07d

Mean

11.77A

9.40B

6.169C

ANOVA

d.f

P-value

LSD

Salinity (S)

2

< 0.001

0.07

Group (G)

3

< 0.001

0.11

S×G

6

< 0.001

0.20

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increased abundance of photosynthesis-associated proteins, a PsbP family protein (spot 127), fructose-bisphosphate aldolase 2 (spots 251, 266), and the cytochrome b6 -f complex iron-sulfur subunit (spot 528) were only observed under salt stress. The previous four proteins were identified as functioning in photosynthesis i.e. spots 127, 251, 266, 528. ROS Scavenging, Photosynthesis, and ATP Synthase Related Proteins were Upregulated in salinity-tolerant lines. Oryza species have salt-tolerant and salt-sensitive genotypes; however, very few studies have investigated the genetic architecture responsible for photosynthetic efficiency under salinity stress in cultivated rice. Chlorophyll fluorescence analysis in diverse rice entries reveals a positive correlation between the seedlings’ salt tolerance and photosynthetic efficiency (Tsai et al. 2019). Rajhi et al. (2020) assessed salinity tolerance using 21 morphological, physiological, and photosynthetic traits in faba bean under control, moderate, and severe salinity environments. Principal component analysis showed that the most discriminating quantitative characters were related to plant biomass production and photosynthesis, especially the mass of fresh root, number of leaves, water-use efficiency, and the substomatal CO2 concentration. Results distinguished cultivar Najeh could survive under salinity conditions and conserve high productivity and photosynthetic activity. However, cultivar Chourouk was the most sensitive one. Under salinity stress among 22 cotton genotypes screened for salt tolerance, Munawar et al. (2021) found that photosynthetic rate was maintained in all the genotypes except of SITARA-16. The two sensitive genotypes i.e. IR-NIBGE-13 and 6071/16, accumulated more Na+ ion in leaves rather than K+ ion and an increase in Na+ /K+ ratio under salinity conditions. Whereas, the tolerant cotton genotypes NIAB135, NIAB-512 and FH-152 exhibited less significant accumulation of malondialdehyde (MDA) and higher activity of antioxidants, for example, superoxide dismutase, peroxidase, and ascorbate peroxidase compared to sensitive genotypes IR-NIBGE13 and 6071/16. Salt tolerance was associated with plant biomass maintenance, photosynthetic rate and ionic homeostasis K+ /Na+ ratio. In sugar cane, da Silva et al. (2022) showed that the limitations of the photosynthetic process are variable depending on the genotype, time of exposure and intensity of salinity stress. The tolerant cultivars RB855156 and SP80-1842 showed no reduction in net photosynthesis, while genotypes SP80-3280, RB855453 and RB928064 had the greatest limitations in photosynthesis and transpiration. Referring to the importance of photosynthetic efficiency in salinity tolerance.

4.5.4 Relative Water Content The leaf’s relative water content is one of the best indicators of the water state of the plant. The relationship of relative water content with cell size largely reflects the balance between leaf water supply and transpiration rate under stress conditions. Schonfeld et al. (1988) showed that, in wheat, leaf relative water content is an important selection criterion for breeding to tolerate water stress in wheat. They also

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indicated that the high relative water content is a mechanical resistance rather than a stress escape mechanism. It is believed to result from the high osmotic regulation or low elasticity of the tissues of the stress-resistant variety. Commonly, salinity leads to a significant decrease in the relative water content of wheat leaves, but the varieties differ in this regard. The salt-tolerant wheat cultivar Kharchia 65 showed the smallest decrease in water relations, growth and yield compared to C 306 under the effect of salinity because of the sensitivity of the latter to salinity (Sharma et al. 1994). Under three levels (0.0, 50.0 and 100.0 mM of NaCl), Shtaya et al. (2019) revealed that wheat landrace “Norsi” was considered as the most tolerant genotype, since it showed the lowest reduction percent in leaf relative water content compared to White heteyeh and Black heteyeh under 50 and 100 mM NaCl. Hussain et al. (2021) showed that salt stress significantly decreased relative water content in all wheat genotypes in saline environments. But the reduction percentage in relative water content was lowest in salt-tolerant wheat genotypes compared to the salt-sensitive ones. Vysotskaya et al. (2010) registered greater tolerance in ‘20–45’ barley genotype, characterized by less inhibition of leaf water content, leaf area, root fresh weight, and chlorophyll concentration than in salt-sensitive genotype ‘T-1’. Pour-Aboughadareh et al. (2021) revealed that the salt barley tolerant genotypes G6 (2.46%), G 8 (2.65%), G 15 (4.77%), G 1 (5.26%), G 16 (6.10%), and G 20 (7.74%) had the lowest reduction of relative water content relative to G3 (33.18%) and G4 (32.30%) showed the greatest reductions. At 100 mM salt concentration, Polash et al. (2018) showed that only 6.6% relative water content declined in the rice Pokkali variety compared to the varieties Mohini and BRRIdhan 29 displayed a decrease in relative water content valued 18.3 and 21.7%, respectively over corresponding control. In quinoa Cocozza et al. (2013) showed strict relationship between relative water content and components of potential water t involved in the osmotic regulations, which maintain leaf turgor favorable to plant growth under salt stresses. A high relative water content characterized the transgenic tobacco plants as a result of the role of Ectoine acid in maintaining the turgor pressure and preventing water loss and cell membrane stability under salinity conditions (Sumesh et al. 2003). Several studies reported that relative water content was associated with salinity tolerance in Brassica rapa ecotypes (Jan et al. 2016) and faba bean (Hussein et al. 2017).

4.5.5 Leaf Water Potential Leaf water potential denotes to the potential energy of water in relation to pure water, and hence regulates the direction of water movement, where water moves from a site with a higher water potential to a site with a lower water potential. Crop genotypes can decrease their water potential by reducing leaf osmotic potential by accumulating inorganic ions and synthesizing organic osmolytes (Nawaz et al. 2010; Singh et al. 2010).

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Cell growth depends on the pressure of its turgidity, that is, on its driving force, which is one of the important physiological characteristics related to salt tolerance. Estimates of relative turgidity pressure are useful in measuring the ability of a genotype to maintain yield levels under stress conditions. When studying the physiological responses to salinity in two selected strains of wheat, they differed in their tolerance to salinity below zero and 20% seawater salinity levels. Kingsbury et al. (1984) indicated that water absorption may start rapidly by leaf parts until the first 2–4 h (stage 1) and then begin to decrease at a rate closer to the constant at 4–6 h (stage 2) and then stabilize at 12 h. It became clear that in the first stage, water absorption was due to a lack of water in the tissues, which continued until the fourth hour. In the second stage, water absorption was attributed to growth requirements. The results indicate that both sensitive and resistant strains performed similarly under the control treatment, where the average relative turgidity was approximately 98%. As for the salinity treatment, the behavior of the two strains varied significantly, as the degree of relative turgidity in the resistant strain ranged from 94.7 to 98.3% with an average of 96%, which is slightly lower than the control, and at the same time higher than the sensitive strain, which ranged from 90 to 96.8% with an average of 93.10%. The variance in the behavior of the sensitive strain was attributed to the low values during the first three days of estimation. These results indicate that genotype that begins its day with a decrease in turgidity pressure or a decrease in full turgidity can suffer from an early and great deficiency of water on that day, and this leads to a decrease in photosynthesis activity because of an increase in stomatal resistance. This confirms that the resistant strain performs the osmotic regulation process more quickly under stress conditions compared to the sensitive strain. El-Hendawy et al. (2017) showed that the success of wheat genotypes in tolerating low soil water potential is related to their capacity to lower leaf water potential adequately to improve water uptake. Moderate salinity levels encouraged a significant reduction in leaf water and osmotic potentials, stomatal conductance, and photosynthesis, and transpiration rates. This also led to a greater leaf turgor pressure assessment than that recorded in the control. Conversely, the salt-tolerant cultivar Sakha 93 displayed lower leaf water potential, leaf osmotic potential, leaf turgor pressure and transpiration rate and greater stomatal conductance and photosynthesis rate compared to the salt-sensitive cultivar Sakha 61. Sakha 93 than Sakha 61 exhibited less negative estimates of leaf water and osmotic potentials, indicating that Sakha 93 cultivar might possess a better ability to preserve an equilibrium between water uptake and transpiration rate, to adjust osmotic pressure by the accumulation of more suitable inorganic ions like K+ and Ca2+ or compatible organic constituents, which play a significant role in the preservation of leaf water potential and turgor pressure under salinity stress (Atiq-ur-Rahman et al. 2014). Furthermore, Hussain et al. (2021) showed that the salt-tolerant wheat genotypes had greater leaf water potential (ψW) than salt-sensitive ones. Between salt-sensitive wheat genotypes, leaf water potential (ψW) was the lowest in genotype MH-97. On the other hand, Vysotskaya et al. (2010) showed that leaf water potential was similar in salt-tolerant ‘20–45’ and salt-sensitive genotype ‘T-1’ barley lines.

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Three soybean genotypes Galarsum, BD 2331 and BARI Soybean-6 were tested by Khan et al. (2015). They analyzed leaf water relationships, xylem exudation and proline accumulation under salt and water stress environments. At 75 mM NaCl, the decrease in leaf water potential, relative water content, and xylem exudation of soybean plants in salt and water stress environments were lesser in genotype Galarsum and registered 74.28% relative water content, 7 mg hr-1 xylem exudation rate and-1.03 MPa leaf water potential and accumulated greater amount of proline in leaves under salt and water stress environment. Thus, soybean genotype Galarsum was classified as more tolerant than BD 2331 and BARI Soybean-6 to salt stress under water deficit situations. Leaf water potential may differentiate between resistant and sensitive cultivars of different crops. Resistant genotypes displayed higher water potential under both of the stress conditions in maize (Azevedo Neto et al. 2004), in a grass (Xu and Zhou 2008), and in Quercus ilex leaves (Echevarrıa-Zomeno et al. 2009). Results also explained the importance of cell turgor in the tolerance of sugarcane cultivars to salinity compared to sensitive and moderate ones (Dwivedi 2004). Furthermore, a positive and significant mean general correlation was recorded between water potential and normalized difference vegetation index (r = 0.71). Revealing that a higher decrease in water potential increased the water availability to keep the plant leaf area alive and metabolically active in some crop species. The highest correlation coefficients were recorded in Bursera fagaroides, (0.844), Parkinsonia aculeata (r = 0.89), and Atriplex canescens (r = 0.71) (Gonzáles et al. 2021).

4.5.6 Osmotic Potential The ability to regulate osmosis is a vital component of resistance to salinity in genotypes and a selection criterion for stress tolerance in field crops. Osmotic regulation is the process by which the water potential of plant cells is adjusted without accompanying a decrease in cell turgor. It is known that the accumulation of salts in the soil affects the physiological state of the plant, as the water stress (ψw ) and the osmotic pressure (ψ p ) of the plant cells decrease. Salinity-tolerant crop varieties can secure themselves osmotically by increasing the concentration of organic solvents such as proline, glycine betaine and carbohydrates in addition to potassium and other nutrients to increase the ability of cells to regulate osmosis. Taiz and Zeiger (1991) defined osmotic regulation as the net increase in cell content regardless of changes in volume that result from water loss. During cell exposure to water deficit, an increase in the concentration of solutes in the cell sap occurs to cause osmotic regulation. The change in the water potential of the tissues occurs as a result of the change in the solution potential (ψs ) and the osmotic potential (ψ p ), and this is evident from the following equation: (ψw ) = (ψs ) * (ψ p ).

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The osmotic potential of the cell sap is alternated to maintain a constant water potential gradient between leaf and soil. Osmotic effects dominate when plant growth is associated to the osmotic potential of root medium that contains different combinations of salts. The reduced growth accompanying osmotic stress is attributed to the increase in osmotic pressure of plant cells to counteract the increased osmotic pressure of the rooting zone as turgor persists (Greenway and Gibbs 2003). But, leaves of genotypes that have the ability to balance osmosis maintain the cell turgidity at lower water status compared to those who lack this ability. Maintaining the turgidity state enables plant cells to continue to grow, elongate, and increase the degree of stomatal conductivity under stress conditions. Osmotic regulation can also occur in root meristems, which helps to maintain cell turgidity and the continued growth of roots and increase their ability to extract water from the soil. There are differences between crop varieties in the ability to regulate osmosis. Wheat cultivars vary in the degree of osmotic regulation, and the highly osmoticregulated cultivars are better in growth and production than the low osmotic-regulated cultivars under stress conditions. Where Morgan (1995) explained the importance of osmotic regulation in improving water use efficiency in plants in order to maintain the rates of photosynthesis and translocate of metabolic products to the grain and increase the harvest index. The yield of wheat cultivars with high osmoregulation increases with a range of 1–60% compared to cultivars with low osmotic regulation under stress conditions (Morgan et al. 1986). Some plant species respond to salinity stress environments by activating mechanisms, for example, ion inclusion and accumulation in organs of the endive plants (Helaly et al. 2016) and/or accumulation of osmotically active compounds to reduce the osmotic potential and consequently leaf water potential, thereby guaranteeing water uptake and plant survival (De Sedas et al. 2019). For this reason, the study of salinity responses has great biological and ecological significance. In this regard, some plant species avoid salt toxicity by synthesizing osmotically active complexes (Turner 2017). For instance, in wheat, proline, glycine betaine, glutathione, and others rised the osmotic pressure and reduced the osmotic potential and, consequently, leaf water potential (Argentel-Martínez et al. 2019). Moreover, Rajendran et al. (2009) revealed that the most tolerant wheat genotype based on relative growth rate under saline conditions was AUS 18755-4 compared to the other eleven tested genotypes. This variety had excellent osmotic tolerance and good tissue tolerance. They also observed a positive association between a plant’s total salinity tolerance and the sum of its ability in Na+ exclusion, osmotic tolerance, and tissue tolerance. Hussain et al. (2021) showed that the most salt-tolerant wheat genotypes had greater osmotic potential (ψ S ) than those of salt-sensitive ones. Between salt-sensitive wheat genotypes, osmotic potential (ψ S ) was the lowermost in genotype MH-97. While, the tolerant barley cultivar Numar tends to send more sodium Na+ to the shoot system through the transpiration stream and use it as a cheap osmoticum to preserve shoot turgor. Whereas, sensitive barley variety Naso Nijo delayed this process favoring sodium Na+ accumulation in the roots (Adem et al. 2014). Tolerant rice genotypes characterized by the genetic capability to retain osmotic potential under salt stress and accumulated higher biomass, while sensitive genotypes

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ionic toxicity induces a loss of cell turgor leading to leaf rolling and stomatal closure, so disrupting the photosynthesis activity (Yadav et al. 2021). Sugarcane cultivars differed significantly in their water equilibrium, which was accompanied by the accumulation of sodium, potassium and calcium ions with proline. The osmotic regulator was improved for the most stress-tolerant sugarcane cultivar COM 9516, which was better able to absorb potassium and was characterized by a higher content of proline (Panwar et al. 2003). Also, Geng et al. (2019) showed that the salt-tolerant sugar beet cultivar (T710MU) exhibited better growth and displayed greater levels of osmotic adjustment molecules compared to the salt-sensitive (S710) one. Atriplex canescens seedlings accrued more Na+ in both plant tissues and salt bladders under saline conditions but reserved constant K+ in leaf tissues and bladders. The contribution of Na+ to the leaf osmotic potential (ψs) was increased suddenly from 2% in control plants to 49% in plants exposed to 400 mM NaCl. Thus, under saline conditions, A. canescens is capable of increasing osmotic adjustment to improve water status in plant tissue (Pan et al. 2016).

4.5.7 Cell Membrane Stability Cell membranes are an important characteristic in improving crops to tolerate salinity. It represents natural barriers between the plant and its environment and between cellular structures and organelles within the plant’s organs of leaves and roots. Membranes have multiple functions in relation to salinity tolerance, as they regulate the process of transfer of ions between cells and the external environment, selective transfer of ions at the level of tissues and organelles, and the disposal of toxic ions across membranes. Selective permeability is one of the important properties of bio membranes, and this means allowing specific substances to pass through the membranes more easily and rapidly than other materials due to the fact that many regions of the cell membrane are mostly lipids. Salinity leads to a decrease in the degree of water conductivity in sensitive cultivars compared to tolerant ones due to a lack of membrane permeability to water or rooted suberin. However, water permeability, in general, decreases with increasing salt stress to varying degrees between sensitive and tolerant varieties. Plant cell membranes act as biological barriers, protecting the cell contents of organelles from salt stress. Alterations in membrane lipids have been detected in both halophytes and glycophytes in response to salinity, directly affect the activity of signal transduction pathways, adjusting the fluidity and permeability of membranes (Guo et al. 2019). Soluble sugars and sugar alcohols accumulate to regulate osmotic adjustment, protect cell membranes and salinity stress tolerance in crop plants (Ahanger et al. 2018; Slama et al. 2015). Cell membrane stability is one of the important physiological characteristics responsible for salt tolerance, as the tolerant varieties are characterized by a high degree of cell membrane stability, while the rate of electrolyte leakage increases in

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sensitive varieties. Mansour (1994) observed a decrease in the water permeability index with an increase in salinity in both barley and wheat after 7 days. However, the rate of deficiency was higher in sensitive cultivars than in tolerant ones. The difference between the varieties was attributed to the variation in the composition and content of the cell membrane. The importance of cell membrane stability in the tolerance cultivars to severe environmental conditions was assured by Pirayvatlou and Saidi (2002). Moreover, Al-Khaishany et al. (2018) investigated the effects of different levels of salt stress (0, 50, 100, 150 and 200 mM NaCl) on the different physiological and biochemical traits on ten wheat genotypes. The results indicate that among the ten genotypes, genotype Shebam eightwas obviously as salt tolerant as it showed better membrane stability index and leaf area. Whereas, genotypes Maaya, Pawni, Samra and Mesri were the sensitive ones. Eighteen bread wheat genotypes was tested under natural saline field conditions and under three saline irrigation levels (5.25, 8.35, and 11.12 dS m−1 ) and classified into four groups i.e. group A, tolerant (Gemmeiza-11); group B, moderately tolerant (Gemmeiza-9, Gemmeiza-10, Giza-171, Sids-14, Line-6083, and Line-6084)); group C, moderately sensitive (Giza-168, Gemmeiza-7, Sakha-94, Sids-12, Misr-1, Line6052, Line-6078, and Line-1208) and group D, sensitive, (Gemmeiza-12, Misr-2, and Shandawel-1). Mansour et al. (2020) indicated that the salt-tolerant genotype of group A (Gemmeiza-11) maintained desirable lower values in cell membrane stability index (CMSI) rather than the remaining groups (Table 4.2). Cell membrane stability index reveal the tolerance of the wheat genotype Gemmeiza-11 to salt stress. Changes in membrane lipids and fatty acid composition associated with salt-stress resistance were recognized by Chalbi et al. (2013). They showed that increased electrolyte leakage of membranes caused by salinity has been pronounced in roots of salt-sensitive barley genotypes. Adem et al. (2014) added that K+ cellular homeostasis is strongly associated with the sensitivity of plasma membrane transporters to ROS. Table 4.2 Performance of four group wheat genotypes for Cell membrane stability index (Pn) under three salinity levels, S1 (5.25 dS m−1 ), S2 (8.35 dS m−1 (and S3 (11.12 dS m−1 ) (Mansour et al. 2020) Cell membrane stability index (CMSI) Genotype

S1

S2

S3

Mean

Group A n = 1

60.78

49.01

36.22

48.67a

Group B n = 6

59.96

48.07

33.90

47.31b

Group C n = 8

55.45

44.35

32.60

44.13c

Group D n = 3

51.18

40.71

26.90

39.60d

Mean

56.84A

45.54B

32.40C

ANOVA

d.f

P-value

LSD

Salinity (S)

2

< 0.001

0.16

Group (G)

3

< 0.001

0.32

S×G

6

< 0.001

0.55

4.6 Biochemical Characters

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The high-tolerance barley cultivars have the ability to prevent the accumulation of hydroxyl radicals caused by salt stress in stressed tissues. In this respect, the salttolerant rice cultivar Giza 178 gave the lowest values in electrolytic leakage compared to the sensitive cultivar Giza 177 and the American strain M-201, which displayed highest values of electrolyte leakage and cell membrane damage (Zayed et al. 2004). The better leaf properties and cell membrane stability index detected in salt-tolerant maize were associated with higher antioxidant activity and more accumulation of polyphenols under saline environments (Kaya et al. 2010). In salt-affected soils in arid areas, Souana et al. (2020) evaluate two faba bean genotypes under several concentrations of NaCl and salicylic acid (SA). Salt tolerance of both genotypes was significantly improved by salicylic acid, which allowed the maintenance of cell membrane and photosynthetic process. Faba bean genotype Aguadulce performs better at 0.5 mM SA, whereas Histal shows greater performance with 1 mM SA. The sugarcane cultivars varied in the degree of cell membrane stability from 14 to 48%, and the damage to the cell membrane was less (13.8%) in the salttolerant cultivar Co 6304, while the sensitive cultivars Co 8202 and Co 5021 verified higher values of cell membrane damage amounting to 48.7 and 40.6%, respectively (Vasantha 2003). The same behavior was shown in tobacco-tolerant plants that gave high values of cell membrane stability index (Sumesh et al. 2003).

4.6 Biochemical Characters Plants can rapidly sense the type and intensity of salinity stress and then try to cope with the effects of stress through some modifications at the molecular level. By sensing the characteristics of various stresses, crop varieties inductee several types of alterations through molecular networks comprising signaling, initiation or termination of different pathways to improve short or long-term tolerance.

4.6.1 Primary Metabolites Primary metabolites originate through the primary metabolic processes of growth, photosynthesis and respiration of the cell. Examples of these metabolites are carbohydrates, amino acids, proteins, lipids, Nucleic acid DNA and RNA, Abscisic acid, alcohols, lactic acids and vitamins (Fig. 4.3). Organic solutions help crop plants to maintain their life, and secure themselves osmotically by enhancing the concentration of organic osmolytes substances such as sugars, proline, betaine, glycine, and others. These substances contribute to the osmotic balance and help protect the enzymatic activity in the presence of toxic ions. It is known that the ionic expulsion process protects many non-saline plants "Glycophytes" from the toxic effects of salinity, but it may also contribute to the

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Primary vs. Secondary Metabolites

Primary Metabolites

Biological role in the plant

Examples

Secondary Metabolites

Growth, development and reproduction.

Participates in adaptations to environmental stresses,

Performs a physiological Functions.

Defense reactions to biotic and abiotic stresses

Carbohydrates, Nucleic acids DNA and RNA, amino acids, lactic acids, proteins, lipids, Abscisic acid, alcohols and vitamins

Alkaloids, terpeniods, phenolics, sterols, steroids, essential oils, lignins, antioxidants, growth regulators.

Fig. 4.3 Primary versus secondary metabolites in relation to salinity stress (drawn by the author HA Awaad)

osmotic imbalance. The regulation of osmosis depends on the synthesis of osmotic regulators from the aforesaid organic molecules, and genotypes depend on them to facilitate the absorption of water into the plant. It is also a source of carbon, nitrogen and energy, which mitigates the impact of salt stress.

Carbohydrates Changes in the levels of metabolites linked with energy storage under salinity stress indicate that regulation of carbohydrate metabolism is critical for salinity stress tolerance in various crop plants. Several Up-Regulated Metabolites has been induced in response to salt stress. Carbohydrates, such as hexoses like fructose and glucose, disaccharides like sucrose and trehalose and oligosaccharides such as raffinose and stachyose are vital osmolytes in various halophytes and glycophytes plants (Slama et al. 2015; Ahanger et al. 2018). Sucrose and hexoses can act as signaling molecules and show a double function in gene expression regulation by downregulating stress-related genes and upregulating growth-related genes. Growth and stress-related genes are controlled

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145

by hexokinase (HXK)-dependent and/or HXK-independent pathways (Rosa et al. 2009). So, primary metabolites are necessary for the regular functioning of crop plants and are directly involved in photosynthesis and respiration, producing the energy and the signs required for the biosynthesis of macromolecules required for growing processes in crops (Kumar et al. 2017). Primary metabolites comprise sugars (mono-, di- and trisaccharides), polyols (i.e., sorbitol and mannitol) which could serve as osmoprotectants and osmolytes in plants under salinity stress (Gupta and Huang 2014). Soluble sugars, for instance, sucrose, trehalose and raffinose, and sugar alcohols, such as sorbitol and mannitol, accumulate to control osmotic stress levels and helping to stabilize cell membranes under salinity stress in various crop plants (Ahanger et al. 2018; Slama et al. 2015). The accumulation of sugar in the tolerant genotype increases with the increase in the salinity level, which was observed in many varieties of wheat, barley, rice, chickpeas, tobacco and others. The existence of sulfated polysaccharides between the crop species was limited to halophytes, signifying an association with salt stress resistance. Sairam et al. (2002) detected an increment in soluble sugars contents in wheat cultivars exposed to salt-stress compared to control cultivars. Moreover, under salt stress 8.6 dSm−1 , Guo et al. (2015) showed that an increase in soluble sugars increases the osmotic potential and protected wheat plants from oxidative stress via activating anti-oxidant enzymes. In this respect, Naz et al. (2022) showed that the salt-tolerant wheat variety Halberd accumulated more Na+ , B, and Cl− in its leaf sheath and saved the leaf blades free from these toxic ions compared to the sensitive variety Westonia. Water-soluble carbohydrate i.e., glucose, sucrose, fructose and fructans concentration augmented in reaction to single and combined effects of soil salinity and toxic Boron in the leaf blade in both tolerant and sensitive wheat varieties. However, the increase was greater in the tolerant variety rather than the sensitive one. Plants consume energy to obtain their needs of water and nutrients under salinity conditions. The level of carbohydrates and energy compounds needed in the phosphorylation processes in the cell is indicative of the plant’s ability to adapt with salinity stress. Sallam and Afia (1998) observed an increase in the total carbohydrate content in the stems of wheat cultivars, and the increase was more pronounced in the tolerant variety Yecora Rojo and Line 2 under the high salinity level (8000 ppm). The transfer of available carbohydrates and their utilization as a result of the lack of the required ATP energy compounds is due to the lack of absorption of inorganic phosphate under saline conditions or the plant employing ATP energy compounds to transport salts and store them in vacuoles. The salt-tolerant Egyptian bread wheat variety Sakha 8 was characterized by an increase in the accumulation of carbohydrates, especially soluble, reduced (glucose and fructose) and non-reducing (sucrose), which improves the optimal use of available water and increases the plant’s ability to regulate osmosis (Salib et al. 2003). Sairam et al. (2002) showed a rise in soluble sugars contents under salt-stress-induced cultivars compared to control ones. Moreover, salt stress causes an increase in the hydrolysis of starch or polysaccharides and is associated with salt-tolerant wheat cultivars (Athar et al. 2015). Furthermore, Hussain et al. (2021) showed that exposure of wheat varieties to salinity stress at 150 mM NaCl, cause an

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increase in total soluble sugars. Conversely, the increase in total soluble sugars was much higher (~143–152%) in salt-sensitive wheat cultivars than in salt-tolerant ones (~74–87%). In barley, under salinity stress conditions, wild and cultivated barley displayed different metabolic reactions in roots and leaves. Tibetan wild barley of Hordeum spontaneum characterized by a higher compatible dissolved content rather than cultivated barley H. vulgare and the latest exhibited increased glycolysis and energy consumption in greater salinity than wild barley (Wu et al 2013). While, in maize, Gavaghan et al. (2011) revealed an increase in carbohydrate i.e. sucrose in shoots under salt stress. Whereas, levels of carbohydrate i.e. sucrose, and amino acid alanine, other metabolites γ-amino-N-butyric acid, malic acid and succinate were increased in the roots. Physiological studies indicated the ability of salt-resistant rice cultivar Pokkali to accumulate sucrose, and the activity of sucrose-phosphate synthesis increased, meanwhile, the accumulation of reducing sugars such as glucose and fructose occurred, while the level of trehalose and enzymatic activity decreased in the sensitive cultivar Ikp. The spermidine content increased in the resistant cultivar and did not change in the salinity-sensitive one. The role of this amino acid in regulating the action of the enzyme sucrose-phosphate synthase (SPS) was demonstrated. In this respect, Lutts (2003) explained the importance of the genetic factor Rsus 2 in regulating the level of transcription of the enzyme Sucrose-phosphate synthase (SPS) and, thus resistance to salinity. Aquino et al. (2011) revealed that the sulfated polysaccharide concentration was positively associated with salinity. Exposing rice as a glycophyte to salt stress induces the biosynthesis of carboxylated polysaccharides. Thus, negatively charged cell wall polysaccharides play a significant role in managing with salt stress and the presence of sulfated polysaccharides in crop species helps adapt to salt environments. Whereas, Oliveira et al. (2020) registered reduced deposition of matrix polysaccharides, cellulose and lignin in seedling roots, as well as roots and stems of maize plants in response to salinity stress. Faba bean genotypes subjected under water and salt stress leads to alterations in total carbohydrates and starch (Afiah et al. 2016). A significant increase in total soluble sugar content with increasing the salt and water stress levels were detected in all genotypes. The tolerant genotypes (NBL- Mar.3 and NBL-5) displayed higher carbohydrates and starch content compared to sensitive ones (Nubariya-1 and Misr1). Likewise, in chickpea, an increase in sugar accumulation was observed in the tolerant genotypes with an increase in salinity concentrations from 0, 4 to 8 dS m−1 (Singh et al. 2003a). Also, Dias et al. (2015) in flower and pod of chickpea found an increase in the contents of some carbohydrate i.e. Gentiobiose, fructose, sucrose and erythritol. Furthermore, results showed an increase in other metabolites i.e. pipecolate, isocitrate, cis-aconitate, citrate, fumarate, malate, citrate and 2-oxoglutarate. As well, transgenic tobacco plants contained high levels of sucrose and TransABA with increased salinity levels. Results indicated the importance of ectoine acid in alerting, activating and understanding the genetics of tolerance to stress conditions (Begam et al. 2003).

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147

In oil crops, the tolerant sesame cultivars RT-54, RT-46 and RT-127 accumulate more sugars with increasing in salinity compared to the sensitive cultivar RT-125 in which the content of Malondiadehyde was increased as an indicator of salinity damage (Gehlot and Prohit 2003). In soybean, under severe salt stress (80 mM NaCl), soluble sugar and soluble protein which helpful in keeping osmotic adjustment are detected to decrease (El-Esawi et al. 2018). Whereas, an increment in concentrations of carbohydrate i.e. Lactitol and maltitol were found in soybean leaves (Lu et al. 2013). Nevertheless, the changes in content of sugar under salt-induced situations can differ based on soybean varieties. Tolerant genotype can display increased sugar content under salt stress to preserve turgor inside plant species (Parveen et al. 2020). On the other side, Azevedo Neto et al. (2020) showed that the levels of carbohydrates solute in the stressed roots of the tolerant sunflower genotype BRS323, were extensively higher than in salt-sensitive AG967 genotype under salinity stress. Sun et al. (2015) showed that transformed canola produced more product and high sugar content, compared to wild-type canola under salt environments. Sugarcane plants improve mechanisms to acclimatize with osmotic and ionic stresses caused by high salt, for example, osmotic regulation through the splitting of harmful ions and accumulation of compatible solutes like sugars (Patade et al. 2009; Plaut et al. 2000; Rhodes et al 2002; Vivekanand et al. 2015). Finally, Gong et al (2005) detected an increase in the contents of several carbohydrate i.e. fructose, sorbose, galactinol, glucose, glycerol, inositol, raffinose and trehalose, and in Thellungiella halophile under salt stress. In light of this, the role of carbohydrates in providing crop varieties with energy and the ability to tolerate salt stress is increasing.

Polyols Salinity induces an accumulation polyols, which help as compatible solutes, lowmolecular-weight chaperones and as scavengers of stress-induced oxygen radicals and maintain cell turgor and helping to stabilize cell membranes (Bohnert et al. 1995). Polyols are compounds with multiple functional hydroxyl groups of which sugar alcohols are a class of polyols as ROS scavengers. These compatible solutes act as a protector or stabilizer for enzymes or membrane structures sensitive to dehydration or ion damage. Penitol accumulates inside the plant cell when the plant is exposed to salinity stress. It also plays an important role in relieving stress (Ashraf and Foolad 2007; Matysik et al. 2002). In a study of Zhifang and Loescher (2003) developed salt-tolerant plants by means of introducing mannitol biosynthesis using M6PR to raise high level of salt tolerance through growing, completing normal development, flowering and producing seeds in developed transgenic plants with 300 mM NaCl in the nutrient solution. Accumulating of various solutes accretion comprising polyol in the plant cell is essential to maintain the osmotic potential in vacuoles against ions toxicity accumulated in cell compartments and protect the wheat plants against salt stress (Dos Reis et al. 2012; Khan et al., 2009). Under 65 mM, Trehalose maintained osmotic

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balance and increased relative growth rate, chlorophyll content, biomass production, K+ accumulation and K/+ Na+ ratio (Turan et al. 2012; Yan and Zheng 2016). Furthermore, polyols and sugar alcohols such as trehalose, sorbitol, and mannitol, etc. as osmotic protectors perform vital functions in osmotic regulation, as well as proteins and membranes stability, hence improved salt stress tolerance in wheat genotypes (Hasanuzzaman et al. 2017). Roots and leaves of wild and cultivated barley showed various metabolic responses under salinity stress. Wu et al. (2013) indicated that Tibetan wild barley was higher in compatible solutes compared to cultivated barley H. vulgare which exhibited increased glycolysis and energy consumption. In rice, trehalose-6-phosphate synthase (TPS) and trehalose-6-phosphate phosphatase (TPP) are important in enhancing the biosynthesis of trehalose. Overexpression of OsTPS1 improved salt tolerance of rice seedling by increasing trehalose and proline contents and up-regulating stress-related genes (Ouyang et al. 2011). Recently, an increase in trehalose was also recorded in the high-yielding rice cultivar IR64 to enhance salt tolerance under salinity and sodic conditions (Joshi et al. 2020). Both chickpea cultivars (Genesis 836 and Rupali) under saline stress, exhibited increased levels of sugar alcohols, including erythritol, xylitol, arabitol, mannitol, galactitol and inositol, displaying important roles of the previous molecules in salt tolerance (Dias et al. 2015). In sugar beet, the accumulation of arabinose, mannitol, gluconolactone, inositol, serine, proline and thymine was improved after 3 h and 14 days of salt stress. Whereas, the contents of galactose, putrescine, trehalose, sucrose, homocysteine, norleucine, cytosine, xylose and glycolate increased first in response to saline stress, but then dropped in the later time point of salt stress (Hossain et al. 2017). Polyols and polyamines, play an essential role in adjusting the tolerance of sugarcane to salinity at various growth stages (Patade et al. 2009; Plaut et al. 2000; Rhodes et al. 2002; Vivekanand et al. 2015). Finally, Bendaly et al. (2016) recorded enhancement in levels of carbohydrate i.e. myo-inositol and sucrose in seedling of Atriplex halimus.

Proline and Free Amino Acids Compatible solutes are a group of chemically different organic compounds that are uncharged, polar and soluble in nature and mainly include proline (Fig. 4.4) as primary metabolites is necessary for the regular functioning of crop plants and are directly involved in photosynthesis and respiration, producing the energy and the signs required for the biosynthesis of macromolecules required for growing processes in crops (Kumar et al. 2017). Amino acids are important for protein synthesis and other key cellular functions as they also act as essential osmolytes to equilibrium the cellular osmotic potential and regulator ion transport. They also function as scavengers of reactive oxygen species produced in plants under salinity stress (Rai 2002). Amongst the best famous compatible solutes, proline was described

4.6 Biochemical Characters

149

Fig. 4.4 Proline structure (Source https://collegedunia. com/exams/proline-chemis try-articleid-7744)

to increase significantly under salt stress (Munns 2002). Proline plays a significant role in many vital functions in tissues, which comprise osmotic regulation, carbon and nitrogen reserve for growth after stress tolerance, detoxification of excess ammonia, maintenance of cell membranes, protection of photosynthetic activity and mitochondrial functions, as well as scavenging of free radicals (Gupta and Huang 2014; Kavi-Kishore et al. 2005). At the physio-biochemical level, the synthesis and accumulation of organic solutes as compatible solutes or compatible osmolytes in crop plants cultivated under salinity is an acclimation mechanism that assists the conservation of turgor (Singh et al. 2015). The alleviation of toxicity could be initiated by regulating Na+ /K+ ratio and improving the accumulation of proline (Wu et al. 2017). Proline is synthesized in varying amounts between different crop species and their varieties. Accumulation of amino acid proline occurs in taxonomically different groups of plants. The concentration of compatible solutes inside the cell is maintained to protect the structure and maintain the osmotic balance inside the cell by a continuous flow of water (Hasegawa et al. 2000). ProDH and P5CS genes play important roles in salinity stress tolerance by regulating the proline synthesis (Nguyen et al. 2018). Salt-tolerant wheat cultivars such as Kharchia-69 were characterized by the ability to accumulate higher levels of proline, which agreed with an increase in the osmotic pressure of the cell sap compared to the sensitive cultivar J-405, with increased levels of salinity (Maliwal and sutaria 1992). Under salinity of irrigation water 2275 and 8000 ppm, wheat cultivars differed significantly in the green leaf content of proline during tillering and heading stages. The cultivars ICARDA 8, ICARDA 7 and Sakha 8 (Table 4.3) had the highest proline content and salinity tolerance, while the rest of the wheat cultivars attained different values in this regard as an indicator of their variation in salinity tolerance (Hassan 1996). Sairam et al. (2002) detected a higher proline content in wheat cultivars as a result of salt stress compared to control cultivars. Under salinity, proline can contribute for more than 39% of the osmotic regulation in the cytoplasmic compartments of older leaves in durum wheat seedlings (Carillo et al. 2008). Meanwhile, Khan et al. (2009) showed that wheat varieties preserving higher K/Na ratio are salt tolerant and displaying a positive association between grain yield and K+ /Na+ ratio. Results revealed that there is a positive association between

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Table 4.3 Performance of wheat genotypes for leaf proline content under salinity of irrigation water (Hassan 1996)

No.

Wheat genotypes

60 day

90 day

1

ICARDA-1

332.0 f

506.0 h

2

ICARDA-2

410.0 de

551.0 g

3

ICARDA-3

461.0 cd

592.0 f

4

ICARDA-4

439.0 d

633.0 e

5

ICARDA-5

651.0 b

767.0 c

6

ICARDA-6

379.0 e

517.0 gh

7

ICARDA-7

652.0 b

836.0 b

8

ICARDA-8

768.0 a

897.0 a

9

ICARDA-9

446.0 d

620.0 ef

10

ICARDA-10

396.0 e

625.0 ef

11

ICARDA-11

412.0 de

596.0 f

12

ICARDA-12

431.0 de

640.0 e

13

Sakha-8

620.0 b

874.0 ab

14

Sakha-69

496.0 c

666.0 e

15

Giza-155

445.0 d

714.0 d

16

Giza-163

425.0 de

520.0 gh

F. Test

**

**

**

Proline content (ppm)

denote highly significant at 0.01 probability level

proline accumulation and the performance of wheat genotypes in expressions of grain yield under salinity stress. In barley, several up-regulated metabolites like amino acids proline and glycine betaine in barley leaves has been induced in response to salt stress (Chen et al. 2007). Also, Wu et al. (2013) demonstrated the importance of changes in amino acids levels metabolism in plants under salt stress by testing four barley genotypes viz. CM72, Gairdner, XZ16 and XZ169. They found that proline levels increased in all four genotypes in response to salt stress, but changes in the levels of alanine, aspartate, glutamate, threonine and valine were genotype-dependent. In rice, Reddy et al. (2017) reported an increase in proline content in both leaves and roots of rice genotype BRS323 could be considered a biochemical indicator associated with salt stress tolerance. Forlani et al. (2019) estimated relationships with tolerance to excess salt in a group of 17 Italian rice genotypes, in which proline content was related to salt tolerance. Meanwhile, the accumulation of proline was increased and showed positively correlated with salinity tolerance in maize (Abdel Tawab 1997). In shoots of maize, Gavaghan et al. (2011) revealed an increase in amino acids alanine, glutamate and asparagine and other metabolites i.e. Glycine betaine. Whereas, levels of Alanine, other metabolites γ-amino-N-butyric acid, malic acid and succinate were increased in the roots. Furthermore, Ali et al. (2022) detected an

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improvement in levels of proline and lipid peroxidation in maize plants under salt stress. In chickpea, the accumulation of proline and protein, as well as the activity of catalase, amylase and peroxidase enzymes in seedlings of chickpea germplasm 8 days old, increased with an increase in salinity level from 0, 4 to 8 dS m−1 , where Singh et al. (2003c) recorded a positive and significant correlation between these chemical assessments and germination percentage. Dias et al. (2015) detected an increase in the contents of some amino acids i.e. arginine, glutamic acid, glycine, histidine, homoserine, hydroxyproline, isoleucine, leucine, lysine, methionine, proline, threonine, tryptophan and valine in chickpea with salinity stress. However, in some situations, higher accumulation of total free amino acids in salt-sensitive wheat genotypes did not assist in preserving plant water status and coping with adverse osmotic effects due to salt stress. Where, no relationship was recorded between the accumulation of total free amino acids and salt tolerance in some genotypes of sesame (Koca et al. 2007); sunflower (Ashraf and Tufail 1995); safflower (Ashraf and Fatima 1995) and in brassica species (Ashraf and Naqvi 1992). On the other side, Azevedo Neto et al. (2020) showed that in sunflower genotype BRS323, salinity increased leaf and root proline contents and root carbohydrates content and vice versa in salt-sensitive AG967 genotype. Thus, the leaves and roots of the BRS323 genotype possessed a more effective osmotic regulation mechanism to deal with salt stress compared with the salt-sensitive AG967. Whereas, in a comparable study of two varieties of Glycine max (C08) and Glycine soja (W05) under salt stress, distinguished that the alanine content declined in the seedling leaves of both genotypes, but serine and glycine levels increased in the W05 genotype only (Lu et al. 2013). Moustafa (2006) in cotton, confirmed the existence of a positive and significant association between proline content and seed cotton yield/plant during the 1st and 2nd seasons and with boll weight during the 1st season only under high level (800ppm) of salinity stress. But, a negative and significant correlation has been detected between proline content and salinity sensitivity index of seed cotton yield/plant in favor of salinity tolerance (Table 4.4). Sun et al. (2015) showed that transgenic canola by the 5-ALA-encoding gene, YHem1, produced high proline content, as well as more free amino acids compared to wild-type canola. Sugarcane plants develop mechanisms to adapt to osmotic and ionic stresses induced by high salt, such as osmotic regulation through accumulation of compatible solutes like proline (Patade et al. 2009; Vivekanand et al. 2015). On the halophytic species, Aeluropus lagopoides and Salicornia brachiata A. lagopoides revealed fluctuations in the levels of metabolites under salinity stress. The levels of proline, alanine, valine, asparagine, arginine, lysine, histidine, glutamine, phenylalanine, glycine, tyrosine, serine and cytosine increased (Sobhanian et al. 2010). Meanwhile, Gong et al. (2005) detected an increase in the contents of some amino acids i.e. aspartic acid, glutamic acid, proline, glycine, serine and threonine in Thellungiella halophile. Bendaly et al. (2016) recorded enhancement in levels of alanine, proline, arginine threonine, glycine, valine, leucine, phenylalanine and

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4 Fundamentals of Crop Resistance to Salinity: Plant Characters …

Table 4.4 Correlation coefficients between proline content and each of yield, boll weight and salinity sensitivity index (SSI) of cotton (Moustafa 2006) Character

Salinity level (ppm)

Proline content 1st season

Seed cotton yield/fed

2000 8000

Lint yield/fed

2000 8000

Seed cotton yield/plant Lint yield/plant Boll weight SSI of seed cotton yield/fed SSI of lint yield/fed SSI of seed cotton yield/plant SSI of lint yield/plant SSI of boll weight *

0.656* −0.009 0.668* −0.013

2nd season 0.328 0.350 0.472 0.388

2000

0.672*

0.193

8000

0.738*

2000

0.521

−0.164

8000

0.306

0.399

2000

0.512

0.066

8000

0.827**

2000

0.358

−0.129

8000

0.136

−0.326

2000

0.465

−0.138

8000

0.215

−0.278

2000

−0.401

−0.549

8000

−0.516

−0.914**

2000

0.237

−0.491

8000

−0.058

−0.375

2000

−0.186

−0.038

8000

−0.577

−0.286

0.899**

0.170

and ** Indicate significant and highly significant at 0.05 and 0.01 probability levels, respectively

tryptophan in seedling of Atriplex. halimus. Mishra et al. (2015) in succulent halophyte Salicornia brachiate, plants showed an increase in the contents of asparagine, valine, cysteine, proline, lysine, leucine, isoleucine, methionine and tyrosine under salinity stress. Furthermore, Pang et al. (2016) under salinity stress, in extracts of S. corniculata leaves, 19 metabolites were identified, out of nine amino acids i.e. valine, glycine, alanine, leucine, isoleucine, glutamine, glutamate, aspartate and threonine and three sugars i.e. sucrose, glucose and fructose, only sucrose and alanine revealed significantly different levels under salinity stress, but other metabolites displayed insignificant variances in their contents under salinity stress. Abbas et al (2021) tried application of NaCl concentration levels of (0,100, 200, 300, 400, 500, 600 and 700 mM) throughout 18 days in Parkia biglobosa suspension cells. They indicated that the rate of proline accumulation in Parkia biglobosa suspension cells was higher under moderate NaCl stress.

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Glycine Betaine Glycine betaine as a compatible solute is one of the most important soluble organic substances that accumulate in the cytoplasm of plant cells exposed to salt stress, leading to osmotic equilibrium events, protects the cell by osmotic regulation, stabilizes proteins, and protects the photosynthetic system from stress injury and increases the plant’s ability to salinity tolerance. Glycine betaine is an amino compound that is highly soluble in water (Fig. 4.5). Due to its unique structural properties, it interacts with both hydrophobic domains and macromolecules, for instance enzymes and protein complexes. Physiological studies have indicated that the tolerant plants halophytes contain high levels of betaine. Therefore, the accumulation of glycine betaine could be a selective guide for improved salinity tolerance. Although this trait alone is not considered a sufficient criterion if other traits attributed to salinity tolerance are not available (Munns 2002). The accumulation of glycine betaine in the leaves of crop genotypes was accompanied by an increase in their ability to tolerate salinity in cereals i.e. wheat cultivar Gogatsu, barley cultivars Jeoniju, Gondar 1, Haru-nanijou and rye plants under growth chamber conditions in response to salinity (Arakawa et al. 1992; Ishitani et al. 1993). An increase in glycine betaine content was determined in wheat cultivars under salt stress conditions compared to control cultivars (Sairam et al. (2002). Different solutes accretion containing glycine betaine, in wheat plant cell are the requisite to retain the osmotic potential in vacuoles against the ions toxicity accumulated in cell compartments (Dos Reis et al. 2012; Khan et al. 2009). Rahman et al. (2002) detected the positive effect of glycine betaine on the microstructure of rice seedlings when subjected to salt stress. Under stressful conditions (150 mM NaCl), glycine betaine played significant role in treating and preventing damages for example swelling of thylakoids, dissociation of grana and intergranular lamellae, disruption of mitochondria and pigment stability and increased rate of photosynthesis and growth (Ahmad et al. 2013; Cha-Um and Kirdmanee 2010). In conclusion, increases in synthesis of several compatible solutes as osmolytes for example glycine betaine, β-alanine betaine to survive against ionic, oxidative and osmotic stress were detected in various crop species. Glycine betaine improved the photosynthetic efficiency, cell membrane stability efficacy of PS-II and water use Fig. 4.5 Glycine betaine structure. Source https:// www.hairuichem.com/en/ 107-43-7.html)

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4 Fundamentals of Crop Resistance to Salinity: Plant Characters …

efficiency under salinity stress in cultivars of wheat (Tian et al. 2017); barley (Mian et al. 2011); canola (Bybordi et al. 2010; Lyer and Caplan 1998), sugarcane (Patade et al. 2009; Plaut et al. 2000; Rhodes et al. 2002) and Atriplex halimus (Fu et al. 2011; Martinez et al. 2005).

Polyamines Polyamines are small, low molecular weight aliphatic molecules that are widespread through the plant kingdom. Polyamines include putrescine diamine, triamine spermidine and spermine tetraamine (Shu et al. 2012). Polyamines play significant roles in normal growth and development for instance regulating cell proliferation, somatic embryogenesis, differentiation and morphogenesis, dormancy breaking and seed germination, flower and fruit development and senescence (Galston et al. 1997; Knott et al. 2007). It also plays a critical role in abiotic stress tolerance like salinity, where increases in polyamine level are associated with stress tolerance in plants (Gupta et al. 2013). Salt stress regulates polyamine biosynthesis and catabolism by acting as a cellular signal in hormonal pathways and thus regulating abscisic acid (ABA) in response to stress in the common ice plant (Shevyakova et al. 2013). The level of endogenous polyamine increases when the plant is exposed to salinity stress. The intracellular polyamine level is regulated by polyamine catabolism. Positive effects of polyamines have been correlated with maintaining membrane integrity, regulating gene expression for osmotically active solute synthesis, reducing ROS production, and controlling Na+ and Cl− ion accumulation in different organs (Yiu et al. 2009). Production of putrescine diamine, triamine spermidine and spermine tetraamine increases salt tolerance in rice, tobacco and Arabidopsis (Roy and Wu 2022). When Chai et al (2010) studied the effects of exogenous spermine on Sorghum bicolor during germination under salinity through exposing seedlings by 0.25 mM salt stress. They show an improvement in growth and a partial increase in peroxidase and glutathione reductase activity with a concomitant reduction in the level of lipid peroxidation. Sugarcane cultivars tolerant to salt stress are characterized by high polyamine levels (Gomathi and Thandapani 2005; Patade et al. 2009 Plaut et al. 2000; Rhodes et al 2002). Numerous studies illustrated that polyamines as antioxidant can also enhance protective mechanisms against salinity stress in many crops for instance, wheat (Khan et al. 2015; Rady and Hemida 2015), rice (Roychoudhury et al. 2011); maize (Panuccio et al. 2018); mung bean (Nahar et al. 2016); ginseng (Parvin et al. 2014), foxtail millet cultivars (Sudhakar et al. 2015); finger millet (Satish et al. 2018) and zoysia grass (Li et al. 2016).

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155

Fatty Acids The composition of fatty acids affects the cell membranes permeability which decreases with a decrease in the degree of saturation of phospholipids. Whereas, unsaturation significantly increases the negative permeability of potassium cation K+ over sodium Na+ . It was also observed that the leaves content of linoleic acid was higher than that of linolenic acid in salt-tolerant species such as sugar beet. Plants comprising wheat (Salama and Mansour 2015), Spartina patens (Wu et al. 2005), maize (Salama et al. 2007), canola (Zamani et al. 2010), buffalo grass (Lin and Wu 1996), displayed an increased concentrations of saturation or a decreased unsaturation of fatty acids in their cell membranes under salinity stress. Unsaturatedto-saturated ratio of fatty acids reduced in roots of salt-treated canola (Zamani et al. 2010). Otherwise, a decrease in lipid content under salt stress was also detected in a salt-sensitive cultivar of barley Hordeum vulgare L. Manel, while no change was perceived in a salt-tolerant wild species Hordeum maritimum. The ability to preserve lipid homeostasis in salt stress conditions sustained cell expansion and growth of saltstressed genotypes (Chalbi et al. 2013). However, Dooki et al. (2006) showed that enoyl-ACP reductase catalyze, the final enzyme in the de novo fatty acid biosynthesis cycle, was upregulated up to 42% of young rice panicles upon exposure to salinity. Increased enoyl-ACP reductase abundance was detected as a result of enhancing fatty acid synthesis as sustenance improved biosynthesis of cellular membranes to substitute the injury under salinity stress. Moreover, researches on fatty acids in saltsensitive crop genotypes or species, for example barley and maize, advised they were more saturated, on the contrary, fatty acids in salt-tolerant crop species were more unsaturated (Chalbi et al. 2013). This might reveal that there is a correlation between the degree of unsaturation of membrane lipid fatty acids and salinity tolerance. Lu et al (2013) found an increase in concentrations of fatty acid linolenic acid and other metabolites such as abscisic acid and caffeic acid under salinity stress in soybean leaves. Dwivedi (2000) showed that the tri-unsaturated fatty acid content was increased from 37.7 to 61.5% in the salt-tolerant sugarcane genotypes CoS 8118 and CoS 767, with the lowest reduction 25.9–38.5% in the dry matter. While, both cultivars CoJ 64 and Co 1148 contained 19.6 and 7.5% of tri-acids, with the maximum yield decrease and classified as moderate tolerant and sensitive to salinity, respectively. On the other hand, in halophyte Salicornia brachiate, Mishra et al. (2015) noticed an increase in the contents of some fatty acids i.e. tridecanoic acid, heptadecanoic acid, stearic acid, oleic acid, linoleic acid, α-linolenic acid, arachidic acid, heneicosanoic acid and lignoceric acid in shoots to cope salt stress environments.

Heat Shock Proteins Due to Salinity Stress Plant breeder’s objects to improve salinity tolerance and heat stress. One of the defense mechanism is the induction of molecular chaperones, heat shock proteins

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4 Fundamentals of Crop Resistance to Salinity: Plant Characters …

(HSP). Proteins play a pivotal role in salinity tolerance through modifications in the plasma membrane, cell cytoplasm, cytoskeleton, and the intracellular partition which contain modification in their impacts, for instance, cell- cytoplasmic affinity for water (Bogeat-Triboulot et al. 2007; Gygi et al. 1999). Crop plants responds to salt stress through a series of physiological, and metabolic changes to overcome the detrimental effects of osmotic shock and ion toxicity. After salinity is imposed on the plants, plant root and shoot metabolism changes, resulting in hyperosmotic shock and ionic imbalance causing secondary stresses such as nutritional imbalance and pathological outcomes (Isayenkov 2012). Preceding studies suggested an involvement of heat shock proteins HSPs in osmoprotection, ions transportation, scavenging of free radicals and embryogenesis. Heat shock proteins (HSPs), are universal group of conserved proteins, mainly generated in heat stress response (Al-Whaibi 2011). Lately, are known to be induced under a diversity of environmental stresses. Five major families of HSPs, HSP100, HSP90, HSP70, HSP60, and small HSP (sHSP) have been detected in crop plant cells (Kotak et al. 2007; Park and Seo 2015; Wang et al. 2004). HSPs maintain cellular homeostasis in both prokaryotic and eukaryotic cells (Lindquist and Craig 1988; Wang et al. 2004). HSPs support plants to tolerate stress by acting as molecular chaperones, aiding to avoid protein misfolding, and achieving proper folding of denaturated proteins and facilitating cell function and survival under stress (Hüttner and Strasser 2012; Wang et al. 2004). Research studies on HSPs showed that sti1 (protein) was up-regulated in tolerance to salinity stress in rice (Chen et al. 2010), Arabidopsis (Takahashi et al. 2003) and in canola (Banaei-Asl et al. 2016). In recent studies on wheat, Wang et al. (2020) found that T. aestivum HSP23.9 shows a significant upsurge in bread wheat HSP23.9 expression under abiotic stresses. Muthusamy et al. (2017) detected an upregulation in bread wheat HSP17.4, HSP17.7 and HSP19.1 genes under salinity stress conditions. Al Khateeb et al. (2020) showed that salt stress causing adverse effects on plant growth and development and the expression of heat shock proteins in five Jordanian durum wheat landraces. Plants were irrigated with tap water as control and 200 mM NaCl. They observed significant variances between five Triticum durum landraces in the expression of heat shock proteins genes. Salt stressed landraces demonstrated increased levels of Hsp17.8, Hsp26.3, Hsp70 and Hsp101 expression. Landraces T11and M23 displayed the highest growth, lowest levels of stress indicator parameters, with high expression of heat shock protein genes under NaCl stress. Otherwise, both landraces J2 and A8 exhibited the lowermost growth, maximum levels of stress indicator parameters and little expression of heat shock protein genes at salt stress. Moreover, Razzaque et al. (2019) detected an increase of heat shock protein in tolerant rice genotypes under salinity stress at 72 h. Acetyltransferase is responsible for transferase activity, while heat shock protein is a stress responsive protein. In maize, Wang et al. (2003) advocated the participation of HSPs in osmotic protection, ion transport, free radical scavenging, and embryogenesis in maize roots. Furthermore, in canola, families of HSP have been recognized in the leaf and expression of Hsp70 has been designated in the root (Banaei-Asl et al. 2016; Bandehagh et al. 2011).

4.6 Biochemical Characters

157

Nucleic Acid Content With the advancement of biotechnology and molecular biology techniques, the breeder’s work and interest with specialists in the field of genetic engineering breeding crops moved to the level of nucleic acids. Nucleic acid content indicates the plant’s biological activity level under stress conditions. A positive and significant association between wheat grain yield and the percentage of DNA, proline, sodium, soluble protein and reducing sugars, while the correlation was negative with the ratio of RNA and magnesium. The content of DNA and RNA was increased in the shoots and stems of the tolerant cultivar Yecora Rojo under the high salinity level (8000 ppm). Also, a significant increase in the RNA content was also observed in the tolerant genotypes, Strain 1, Giza 160 and Gemmeiza 1 at salinity level 4000 ppm and in tolerant cultivars Mixipac 69 and Sakha 92 at 8000 ppm (Sallam and Afiah 1998). The increase in DNA and RNA accumulation in the shoots of the cultivars was attributed to the salinity-inhibiting effect on RNase and DNase enzyme activity. However, with severe salinity stress, DNA and RNA synthesis decrease and the nucleic acid breakdown rate increases. In addition, Mehta et al. (2021) showed that salt stress induces saline stress-responsive genes represented by transcription factors, signaling and kinases, transporter, biosynthesis, DNA/RNA modification and antioxidants, respectively. Among 53 SSR markers screened, 10 cg-SSRs and 8 miR-SSRs were found to be polymorphic. Polymorphic information content between wheat varieties varied from 0.07 to 0.67, showing the extant of great genetic variation between the salt tolerant and sensitive varieties at the DNA level. Moreover, 102 DNA bands were recognized through six ISSR primers, out of which 72 bands (51 non-unique bands and 21 unique bands). Herby, Line1 was the best wheat genotype followed by Line 3 and Line 7 for tolerant to saline stress (El-Saber 2021). Razzaque et al. (2019) showed that rice sensitive genotypes had lower expression of glutamyl-tRNA synthase, RNA binding counts after 72 h of stress compared to 24 h. But, tolerant genotypes had higher expression counts at 72 h of stress rather than at 24 h. A gradual rise in gene expression over time was detected in the leaf tissues of tolerant genotypes, but was absent in sensitive ones. The induction of mRNA accumulation caused activations of photosynthesis shoots of maize and catalase activity under salt stress. Also, accumulation of superoxide dismutase transcripts enhanced (Menezes-Benavente et al. 2004). In white lupine under three different levels of salinity stress (2, 4 and 8 dSm−1 ), Mahfouze et al. (2019) utilized SRAP technique to identify regions of DNA and verified seven white lupine genotypes with eleven primers and recognized fifty-one alleles. Pi et al. (2018) evaluated the salt tolerance levels of transformed soybean roots overexpressing the 35S promoter-driven coding sequence and RNAi constructs of GmCHS5 and phospho-mimic (GmMYB173S59D). They stated that overexpression of GmMYB173S59D and GmCHS5 controlled salt stress tolerance through accumulation of flavonoid. Meanwhile, in canola, Zhong et al. (2012) identified two B. napus NAC TFs (BnNAC2 and BnNAC5) factors act in negative regulation of salinity and osmotic tension tolerance. Sixty NAC TFs were described in B. napus (Wang et al. 2015). Moreover, Jian et al. (2016) stated that more than

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4 Fundamentals of Crop Resistance to Salinity: Plant Characters …

340 miRNAs contribute in the post transcription mechanism of regulation of the salt-responsive genes. Furthermore, several salt-stress responsive genes with diverse cellular functions and miRNAs have been functionally validated for salt-stress tolerance in many crop plants including, wheat (Mehta et al. 2021), Sorghum bicolor (Katiyar et al. 2015), rice (Molla et al. 2015; Mondal and Chakraborty 2020) and Acacia (McLay et al. 2022).

Abscisic Acid Abscisic acid ABA is an energetic cellular signal that modulates the expression of a number of genes responsive to salt and water stresses (Fig. 4.6). Abscisic acid ABA is an important phytohormone that improves the tolerance against stress conditions. It is a hormone that is regulated by water deficiency in the soil around the rootstock, and salinity stress causes osmotic stress and water deficiency, which increases ABA production in branches and roots (He and Cramer 1996). ABA accumulation can attenuate the inhibitory effect of salinity on photosynthesis, growth, and translocation of mimetics (Jeschke et al. 1997). Positive relationship between ABA accumulation and salinity tolerance is at least in part attributable to the accumulation of K+ and Ca2+ and compatible solutes, such as polysaccharides in the vacuoles of the roots, which interfere with the uptake of Na+ and Cl− (Gurmani et al. 2011). In their research on wheat genotypes, Sairam et al. (2002) determined an increment in abscisic acid content under salt-stress induced cultivars compared to control ones. Pál et al. (2018) recorded an association, between polyamine metabolism and abscisic acid signalling leads to the governed regulation and preservation in the levels of polyamine and proline under osmotic stress situations in wheat seedlings. Schubert et al. (2009) showed that maize root tips under salt environment are the first to sense impaired water availability attributable to the osmotic effect, transfer a signal to shoots to regulate whole plant metabolism. Higher levels of abscisic acid in salt-tolerant maize help to decrease water loss and adjust growth promotion. Leaf growth sensitivity declines as abscisic acid levels increase under such environments. Results also explained the importance of abscisic acid as an effective signal at the ionic level (with an increase in the level of Na+ ) and the osmotic level in the tolerance to salinity in sugarcane cultivars Co 740, Up-5, CoS767 compared to sensitive cultivar CoJ 64 (Dwivedi 2004). Recently, Tang et al. (2021) detected constitutive expression Fig. 4.6 Abscisic acid structure. Source https:// www.researchgate.net/public ation/324330787_Phytoh ormones_and_Effects_on_G rowth_and_Metabolites_of_ Microalgae_A_Review/fig ures?lo=1

4.6 Biochemical Characters

159

of Te ScPIP2-1 gene in sugarcane tissues, and its transcript level was increased by ABA, under NaCl and PEG 6000 stress. In common ice plants, salt stress modulates polyamine biosynthesis and catabolism by acting as a cellular signal in hormonal pathways and thus regulating abscisic acid (ABA) in response to stress (Shevyakova et al. 2013). An upsurge in abscisic acid has been detected under salinity stress, in leaves of other several crop plants i.e. rice (Chen et al. 2022), Soybean (Lu et al. 2013), Brassica napus (Chen et al. 2012), tobacco and Arabidopsis cells (Sokol et al. 2007). Ethylene also known as stress hormone is released as a physiological reaction to various stresses. The accelerated production in plants can improve growth of plants under salt stress (Hontzeas et al. 2004). Previous results indicate the importance of biochemical components as useful estimates in breeding programs for salinity tolerance.

Antioxidants Upon exposure to salt stress, plants activate a defense mechanism that relies on biochemical and physiological responses to manage abiotic stress (Ul Hassan et al. 2021). Antioxidants play a vital role in protecting the biological system, enzymatic activity, biochemical components and physiological processes from the damages of active oxygen species. The degree of enzymatic activity determines the level of tolerance to environmental stress. Several studies have found differences in the expression levels or activity of antioxidant enzymes i.e. Shakeri and Emam (2017), Soni et al. (2020) and Ali et al. (2021). These variances are associated with a more tolerant genotype and sometimes a more sensitive genotype. Munns and Tester (2008) have suggested that variances in antioxidant activity between genotypes may be due to genetic variability in degrees of stomata closure or in other responses that alter the rate of carbon dioxide fixation and differences that lead to the processes that evade photoinhibition. Cunha et al. (2016) proposed that the activities of these antioxidants rely on the salinity threshold and period of salinity exposure. Antioxidant metabolism, comprising antioxidant enzymes and non-enzymatic compounds, plays an important role in the detoxification of reactive oxygen species caused by salinity stress in plants i.e. the hydroxyl radical (OH− ), the superoxide radical, and hydrogen peroxide (H2 O2 ) are all strongly oxidizing compounds and therefore possibly damaging for cell membrane integrity (Groß et al. 2013). It has been observed that plants with higher levels of antioxidant activity have greater resistance to oxidative injury (Elkahoui et al. 2005). It should be noted that the defense mechanism could be stimulated to resist stress through exogenous treatment with some stimulants such as radiation, high temperature and hydrogen peroxide, etc. Non-enzymatic antioxidants comprising ascorbate (AsA), GSH, tocopherol, phenolic combinations (PhOH), flavonoids, alkaloids, and nonprotein amino acids working in a coordinated way with enzymes antioxidants containing superoxide dismutase, catalase, peroxidase, polyphenol oxidase, ascorbate peroxidase, dehydroascorbate reductas, glutathione reductase, glutathione

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peroxidase, glutathione S-transferase, thioredoxin reductase and peroxiredoxin (Carocho and Ferreira 2013). Salt tolerance was positively correlated with the activity of antioxidant enzymes, such as superoxide dismutase, catalase, glutathione peroxidase, ascorbate peroxidase, glutathione reductase and the accumulation of non-enzymatic antioxidants compounds (Asada 1999; Gupta et al. 2005). Glutathione is interacting with superoxide radicals, hydroxyl radical, and hydrogen peroxide, thus acting as a free radical scavenger (Foyer et al. 1997). In this respect, Gill et al. (2013) have detected a couple of helicase proteins functioning in salinity tolerance by improving photosynthesis and antioxidant mechanism in plant. Superoxide dismutase activity is related to plants under stress and begins the first stage of protection, transforming oxygen into hydrogen peroxide and then reduction of H2 O2 (Del Río et al. 2018; Laxa et al. 2019). In the salinity-tolerant wheat cultivars an increase in the activity level of enzymes, Superoxide dismutase, Catalase, Glutathione reductase, Ascorbate peroxidase and Peroxidase was detected with an increase in salt stress from 5.4 to 10.6 dS m−1 compared to the sensitive cultivars in which the production of hydrogen peroxide and Thiobarbituric increased, as an indicator to destroy lipids, also decrease ascorbic acid content, pigments and cell membrane stability (Sairam et al. 2003a, b.( Also, a synergistic effect of these enzymes was observed as protective systems under salinity and boron stress conditions at seedling and maturity stages of wheat (Angrish et al. 2003). Soni et al. (2020) also showed that durum wheat genotypes exhibited a significant differential response, and the antioxidative enzyme activity increased in roots and shoots under mild and severe salinity. Recently, Laus et al. (2022) detected enhancement of antioxidant activity as an adaptive mechanism associated with tolerance to hyperosmotic stress in durum wheat. The levels of ascorbate–glutathione and the antioxidant enzymes viz. superoxide dismutase, catalase and peroxidases in durum wheat are enhanced in response to drought and salt stresses. Two diverse barley; salt-stress tolerant genotype Barrage Malleg (tolerant) and Saouef (sensitive) were subjected to 200 mM NaCl at early vegetative stages. Ouertani et al. (2021) discovered that the salt-tolerant Barrage Malleg genotype had better osmoprotection against salt stress compared to the salt-sensitive Saouef genotype, with a stronger antioxidant mechanism as supported by higher activities of Superoxide Dismutase, catalase and Ascorbate Peroxidase and more abundant Cu/ Zn-SOD transcripts, particularly in roots. In tolerant rice germplasm, the activity of the enzyme Superoxide Dismutase played a role in the protection against active oxygen species, and the two rice cultivars Pokkali and CSR-13 were more tolerant to salinity compared to the sensitive variety MI 48 (Singh et al. 2003b). The activity of the peroxidase enzyme was used as one of the important indicators in selecting the rice germplasm to salinity tolerance (Babu et al. 2003). Acetyltransferase is responsible for transferase activity. Upregulated acetyltransferase and serine/threonine-protein kinase have been detected in rice genotypes under salinity stress (Razzaque et al. 2019). In addition, the regulation of UDP-glucose pyrophosphorylase by salt has been seen pronounced in various crop varieties with antagonistic results. For example,

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levels of UDP-glucose pyrophosphorylase were reduced in rice roots by salinity (Yan et al. 2005), and exclusively upregulated in roots of tolerant barley genotypes rather than a sensitive ones (Mostek et al. 2015). Conversely, UDP-glucose pyrophosphorylase has detected as a regulator of sucrose and polysaccharides in salt-tolerant plants. Ma et al. (2018) performed comprehensive analysis of the physiological besides metabolite changes in rice plants from salinity stress among 92 genotypes. The antioxidant activities of ascorbate peroxidase and catalase were significantly higher in the sensitive genotype (SS2-18), whereas superoxide dismutase was higher in the tolerant line (SS1-14). Mishra et al (2013) discovered an increase in expression of Cu/Zn-SOD genes responsible for superoxide dismutase activity in a salinity-tolerant cultivar of O. sativa under prolonged salinity stress. Moreover, Rossatto et al. (2017) showed that gene OsCATB expression was improved in rice cultivar BRS AG, with the exposure duration (10, 15 and 20 day) of salt stress, which led to augmented activity of catalase. Meanwhile, Catalase, ascorbate peroxidase, and guaiacol peroxidase enzymes with superoxide dismutase have the uppermost hydrogen peroxide scavenger activity in both roots and leaves of salt-stressed maize cultivars (Azevedo Neto et al. 2006). Furthermore, Ali et al. (2021) detected relationship between antioxidants and salinity tolerance in maize, and identified changed antioxidant enzyme activities in scavenging ROS at two levels of NaCl viz. 80 mM and 160 mM in two Zea mays cultivars. They found that the enzyme activities SOD, POD, APX and CAT were 49, 43, 39 and 52% in cultivar P1574, as well as 67, 46, 47 and 61% in cultivar Hycorn-11, correspondingly, at 160 mM NaCl stress, as P1574 cultivar is more salt-tolerant than the Hycorn-11 cultivar. The relative efficacy of biochemical traits and stress tolerance indicators contributing to genotypic differences in salinity tolerance has been deliberated among 30 genotypes and 14 cultivars of sorghum. Shakeri and Emam (2017) showed that peroxidase and superoxide dismutase activity were higher under salinity environments in the sensitive and tolerant genotypes. Catalase activity was found to be promoted in tolerant genotypes. Proline accumulation did not appear to be related to salinity tolerance in sorghum. Thus, salinity tolerance in sorghum genotypes was not only related with Na+ exclusion from the shoot, but also with the enrichment of Catalase activity. In legumes, the activity of enzymes i.e. peroxidase, catalase, amylase, accumulation of proline, protein, sugar and phenol was increased, whereas protease activity decreased in salt-tolerant chickpea cultivars, and the correlation was positive between them with germination percentage. Singh et al. (2003a) indicated the importance of previous biochemical components as useful indicators in improving salinity tolerance. Also, in Pea plants grown under saline stress (150 mM NaCl) showed an enhancement of both Ascorbate Peroxidase and S-nitrosylated APX activity. BegaraMorales et al. (2014) indicated that Ascorbate mitigates the adverse effects of salinity stress in different plant species and promotes plant recovery from stress. Moreover, the glutathione content was increased in salinity and drought tolerant lupine and maize genotypes than the sensitive ones of soybean and millet which attained the lowest glutathione content (Tepe and Harms 1995). Whereas, Musa

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et al. (2015) examined the effect of long-term sodium chloride treatment in two peanut cultivars and the activities of antioxidant enzymes. It has been shown that the most important processes of protection against salt stress in peanut tissues are the activity of glutathione reductase and the level of proline. Quinoa’s tolerance to high levels of salinity in the early stages of seed germination depends on alterations primary metabolites and enzyme activity levels. (Adolf et al. 2013). Moreover, in canola Sun et al. (2015) found that transgenic genotypes under salt environments produce a larger antioxidant enzyme, compared to wild-type canola. Bandehagh et al. (2011) showed that H2 O2 might be transmuted into H2O with the enzyme activity, i.e., ascorbate peroxidase, catalase and glutathione peroxidase. Accumulation of superoxide dismutase has been described as a protective approach in response to salinity in canola. Furthermore, ascorbate and glutathione are plentiful antioxidants for detoxifying H2 O2 and xenobiotics (Foyer and Noctor 2011). Also beta carotene reacts with ROO radicals, OH and O2 caused diminished contents of cellular ROS (Kapoor et al. 2019). Geng et al. (2019) revealed that the salt-tolerant sugar beet cultivar (T710MU) characterized by better growth and displayed a higher antioxidant enzyme activity, in comparison to the salt-sensitive one (S710). It has been observed in alfalfa that, acid phosphatase activity was increased under saline conditions in the tolerant cultivar Yazdi compared to the sensitive Hamedani one (Ehsanpour and Amini 2003). Furthermore, in Marigold herb, glutathione and ascorbate were found to be effective in increasing plant height, number of branches, fresh and dry weight, content of carbohydrates, phenols, xanthophyll tincture and content of mineral ions when exposed to saline conditions (Eid et al. 2011). Latently, in Parkia biglobosa, an enhancement in the activity of peroxidase and glutathione peroxidase isozymes, was discovered at 500 mM NaCl concentration in the salttolerant genotypes (Abbas et al. 2021). Further international publications confirmed assured that antioxidant activities play an important role as ROS scavengers under salinity stress in crop plants, for instance, Lupinus termis cv. Gemmeiza (Nessem and Kasim 2019), sugarcane (Patade et al. 2009; Plaut et al. 2000; Rhodes et al 2002), Ricinus communis; Catharanthus roseus (Jaleel et al. 2007); Milk thistle Silybum marianum (Zahra et al. 2022), Chelidonium majus (Yahyazadeh et al. 2018); tobacco cells (Sachan et al. 2010); Solanum nigrum (Šutkovi´c et al. 2011); in selected fruits, vegetables and grain products (Velioglu et al. 1998); in halophytes and salt tolerant plants (Benjamin et al. 2019; Salah 2015).

4.6.2 Secondary Metabolites Secondary metabolites SMs create through the non-growth phase of the cell. Secondary Metabolites are deliberated to be necessary for the ordinary functioning

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of crop plants and protection from biotic and abiotic stresses. Crop species demonstrated great variability in the species and levels of SMs in response to environmental stresses. There are more than 100,000 SMs in crop plants (Wink et al. 2015; Zagorchev et al. 2013). The secondary metabolites participate in defense reactions are alkaloids, phenolics, sterols, steroids, essential oils and lignin’s (Fig. 4.3).

Alkaloids Alkaloids are a group of naturally exciting chemical compounds that mostly contain basic nitrogen atoms established in higher plants. More than 3000 different types of alkaloids were recognized in more than 4000 plant species. Ricinine alkaloids was detected in roots of Ricinus communis and was significantly depressed by salt stress. However it was augmented in shoots. Alkaloid accumulation induced in response to salinity conditions in crop varieties. Alkaloids contain a nitrogen atom in a heterocyclic ring, which are considered by antioxidant activities and play vital roles as ROS scavengers under salt stress (Sytar et al. 2018). Along with enzymatic and non-enzymatic components for instance GSH, ascorbic acid (Asc), α-tocopherol, flavonoids, carotenoids, alkaloids, phenolic acids as well as non-protein amino acids show an important role in protective the plant from ROS-induced oxidative stress and in improving stress tolerance (Hasanuzzaman et al. 2020). Jaleel et al. (2007) found an increase in the content of indole alkaloids compared to control plants in Catharanthus roseus at 80 mM NaCl, while Osman et al. (2007) found that in shoots of Catharanthus roseus plants that were exposed to 150 mM NaCl for two months, the content of vincristine accumulated significantly rather than the control. Also, Benjamin et al. (2019) recorded an increase in levels of some alkaloids i.e. 3, 6-dihydronicotine, portulacaxanthin II, papaviroxine and cyclopropene. However, the contents of alkaloids i.e. harmol and ricinine, reduced in the leaves of S. brachiata under salinity stress. They also treated leaves of Sesuvium portulacastrum with 200 mM NaCl, found an increase in the contents of cyclo-dopa 5-o-glucoside, Nformyldimiculcin and colchicine, whereas content of cyclo-acetoacetyl-L-tryptophan and kylerubin decreased. The levels of chelirubine, deoxypumiloside, 2-descarboxybetanidin and noscapine, were decreased in the roots of S. maritima under salinity stress.

Terpenoids Terpenoids in crop plants for instance, isoprene-C5, monoterpenes-C10, sesquiterpenes-C15, diterpenes-C20, and polyterpenoids-C5xn) are chemicals components, naturally occurring and have various functions in plant growth, development and ecological roles in the interactions between plants and environmental stresses (Mosadegh, et al. 2018; Zhou et al. 2020). In this connection, Vaughan et al. (2015) demonstrated that plant terpenoids i.e. zealexins and kauralexins accumulate

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in maize roots under environments of drought and high salinity, which advocates that they play an important role in osmotic stress tolerance. Experiments have shown that terpenes exhibit antioxidant activities and have important functions in overcoming oxidative stress. Valifard et al. (2019) exposed the leaves of Salvia mirzaiani plants to salt stress and found that the concentrations of terpenoids, for instance, 1, 8-cineole and linalyl acetate, increased, however bicyclogermacrene level reduced. They recognized the cineole synthase1 gene (SmCin1), which plays an important role in 1,8-cineole essential oil biosynthesis. They added that the expression of SmCin1gene was induced in the leaves through salt stress. Under salinity stress, Benjamin et al. (2019) perceived an increase in the levels of oleanolate 3-β-D-glucuronoside-28-glucoside, taxol and glycyrrhetinate terpenoids in the roots of S. brachiata, while in stressed leaves accumulations of sesquiterpenoids for example desoxyhemigossypol-6-methyl ether, heliespirunolide and 15-hydroxysolavetivone were decreased. Plant terpenoids viz., isoprene-C5, monoterpenes-C10, sesquiterpenes-C15, diterpenes-C20 and polyterpenoids-C5xn) are naturally happening chemicals and exhibited a variety of functions in growth and development of sweet basil (Mosadegh et al. 2018). Terpenoid might be involved in the scope of mangroves from salt stress (Basyunia et al. 2009; Oku et al. 2003). Similarly, terpene compounds from Arabidopsis thaliana showed positive responses against salinity (Zwenger and Basu 2007).

Phenolics Secondary metabolites of phenolics such as phenylpropanoids, flavonoids, tannins, coumarin and flavonoid lignin, isoflavones, flavonols, flavanones, proanthocyanidins, anthocyanidins, play vital roles in environmental stress tolerance in crop plants. Phenol compounds are a class of non-enzymatic antioxidant agents acting as free radical terminators (Boeckx et al. 2015; Hasanuzzaman et al. 2020). Studies indicated that diverse non-enzymatic antioxidants such as phenols, flavonoids and free proline catalyzed redox reactions (Al Kharusi et al. 2019). Phenolic acids are known as a major group of compounds that contribute to the antioxidant activities of crop species, as a result of their ability to scavenge free radicals attributed to their hydroxyl group (Tiong et al. 2013; Venkata Saibabu et al. 2015). Accumulation of phenolic compounds is a well-known phenomenon under environmental stress conditions, as the phenylpropanoid system produces different classes of phenolic acids depending on the type of stress to which crop plants are exposed (Weisskopf et al. 2006). Stojšin et al. (2022) recorded positive associations between wheat grain yield/ plant and biochemical parameters viz. radical scavenging activity and total phenolic content in all phenophases. This enables the selection of recombinations with high antioxidant activity and high yield capacity, even in the early stages of plant development. Lim et al. (2012) in buckwheat (Fagopyrum esculentum), found that various concentrations of sodium chloride initiated the accumulation of phenolic compounds, for example, rutin, orientine, isorentin and vitexin. Additionally, Xu et al. (2020)

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registered significantly higher contents of two flavonols, quercetin and kaempferol, in Apocynum venetum seedlings under salinity stress. Furthermore, the flavonol biosynthesis-related genes viz. flavonoid 3' -hydroxylase, flavanone 3-hydroxylase and flavonol synthase were up-regulated, but chalcone synthase, chalcone-flavonone isomerase and flavonol 3-O-galactosyltransferase were down-regulated under salinity stress. The contents of arabinoxylans decreased in the roots of salt-stressed seedlings and plants. Se nanoparticles increased total phenolic contents and reduced MDA activity in barley (Habibi and Aleyasin 2020). Meanwhile, in rice plants, Ferulic acid and p-coumaric acid and their derivatives are capable to be used as promising agents to decrease the negative effects of salt stress on rice production. Kim et al. (2013) showed that anthocyanins are a flavonoid that has been documented to accumulate in rice plants subject to salt stress to a large extent. Moreover, Minh et al. (2016) verified variations in chemical contents of phenolic compounds in rice cultivars under salinity stress. Levels of total phenolics and flavonoids and contents of vanillin and protocatechuic acid in tolerant varieties were intensely increased. However they were significantly decreased in the sensitive ones. In tolerance rice cultivars, Ferulic acid and p-coumaric acid were detected. Vanillin and protocatechuic acid might play a role. However ferulic acid and pcoumaric acid might be greatly responsible for the mechanical tolerance against salinity stress. Hichem et al. (2009) exposed two varieties of forage maize (Aristo and Arper) to 0, 34, 68 and 102 mM NaCl for 6 weeks under glasshouse conditions. They detected an increase in the major polyphenolic compounds in young leaves. The better performance of Arper salt-challenged leaves compared to Aristo, was associated with their higher water content and polyphenol content, principally anthocyanins as important in scavenging from Reactive Oxygen Species. Ali et al. (2022) detected enhancement in secondary metabolites i.e. phenol, flavonoids, and tannins in maize plants under salt stress conditions. In soybean, a significant increase in dihydroxy B-ring-substituted flavonoids, for instance, cyanidin 3-arabinoside chloride, luteolin 3' -methyl ether 7-glucuronosyl(1 → 2)-glucuronide, quercetin 3-(6'' -methylglucuronide), cyanidin 3-(6'' -succinylglucoside) and quercetin 3,3' ,7-tri-O-sulfate, has been detected in soybean roots under salinity stress by Pi et al. (2018). Whereas, Abbas et al (2021) experimented with NaCl concentration levels of (0,100, 200,300, 400, 500, 600 and 700 mM) for 18 days in Parkia biglobosa suspension cells. They indicated that phenolic constituents play a role in adaptation processes. By using HPLC, they separated the phenolic ingredients that governed tolerance of Parkia biglobosa to salinity stress such as gallic, caffeic, vanillic, ferulic, p-coumaric and salicylic acids, that could be used as markers for salt tolerance.

Phospholipids and Sterols Contents Changes in the content of sterols, phospholipids and glycolipids are associated with the accumulation of chloride ion Cl− and sodium ion Na+ under saline conditions.

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Cell wall structures with a high ability to control permeability are characterized by the presence of saturated phosphatidylethanol-amine, phosphatidlyglycerol and phosphtidylcholine phospholipids, which play vital role due to a good balance between the size of polar groups and the size of hydrophilic molecules. Significant increases in phospholipid content were recorded in the roots of salinity-tolerant species such as sugar beet and plantago, while it was less in the sensitive species. This was attributed to the effect of sodium and potassium ions on stimulating the activity of the enzyme ATPase. Salama and Mansour (2015) showed that salt stress raise the content of total phospholipid in either salt-tolerant or salt-sensitive genotypes in the plasma membrane of wheat roots. Chalbi et al. (2013) recorded a decrease in lipid content under salt stress in a salt-sensitive variety of barley Manel belong to Hordeum vulgare, but no change was detected in a salt-tolerant wild species Hordeum maritimum. Hereby, the capability to maintain lipid homeostasis under salt stress resulted in continued cell expansion and growth of salt-stressed genotypes. Membrane phospholipids are structural and signaling molecules in plant cells. Results indicated that there were changes in their quantity and species in the crop varieties exposed to salinity stress (Furt et al. 2011; Xue et al. 2009). In maize, an increase in phospholipids was detected in the root of the salt-tolerant plasma membrane variety by about 1.7 times higher than the sensitive variety, indicating a positive relationship between phospholipid content and salt tolerance (Salama et al. 2007). In addition, the higher phosphatidylcholine to phosphatidylethanolamine ratio in maize, are the prevailing phospholipids in cell membranes, have been closely related to greater salt tolerance (Omoto et al. 2016). In soybeans, an increased total membrane lipid concentration was observed due to the abundance of glycerolipids in salt-tolerant genotypes under salt stress (Yu et al. 2005). However, a reduction in phospholipid content was observed in various sensitive genotypes of crop species (Magdy et al. 1994; Lin and Wu 1996). In buffalo grass, the phospholipid content diminished under salt stress in both the salt-sensitive and the salt-tolerant cultivars, and the reduction in the sensitive strain was greater (Lin and Wu 1996). The composition of fatty acids in phospholipids affects the permeability of the membranes, so the permeability of phospholipids decreases with a decrease in the degree of saturation of phospholipids. Unsaturation leads to a significant increase in the negative permeability of potassium cation K+ over sodium Na+ . It was also observed that the leaves content of linoleic acid was higher than that of linolenic acid in salt-tolerant species such as sugar beet, which offers the ability to tolerate low temperatures as well. Whereas, found that the tri-unsaturated fatty acid content was high from 37.7 to 61.5% in the salt-tolerant sugarcane cultivars CoS 8118 and CoS 767, with the lowest reduction percentage 25.9–38.5% in the dry matter. Meanwhile, both cultivars CoJ 64 and Co 1148 contained 19.6 and 7.5% of tri-acids, with the highest yield decrease of 50.2 and 68.9%, and classified as moderate tolerant and sensitive to salinity, respectively. The ratio of sterols/phospholipids was higher in the salinity-resistant lines than in the sensitive ones. Plant tissues lose the ability to regulate the passage of ions through the membranes when this ratio is higher than the unit. On the other hand, glycolipids content in roots and stems of barley,

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sugar beet, sunflower, alfalfa and plantago decreases with salinity stress (Staples and Toenniessen 1984). Whereas, an increase in phosphatidylglycerol under salt stress was detected in leaves of Thellungiella halophila (Sui and Han 2014), in salt-tolerant buffalo grass (Lin and Wu 1996) and in epidermal bladder cells of the halophyte M. crystallinum (Barkla et al. 2018). Sterols play an effective role in regulating the stability of the plasma membrane, ion permeability and salt tolerance. Beck et al. (2007) detected modifications in sterol composition of the membranes as important to protective cell membrane from adverse environmental stress. Also, the salt-tolerant varieties of barley, sugar beet and beans were distinguished by a higher level of sterols than the sensitive ones (Staples and Toenniessen 1984). Total sterol levels under salt stress played a vital adaptive role in salt-tolerant wheat genotypes. Magdy et al. (1994) observed an increase in the sterol compounds Stigmasterol, brassisterol, cholesterol and a decrease in the content of phospholipids and phosphatidyl choline with salinity stress in wheat. In sensitive genotypes, the amount of sterol lipids was meaningfully reduced (Salama and Mansour 2015). Beta-sitosterol, stigmasterol and sterol were found to differ significantly between tolerant and sensitive rice lines. High accumulation of stigmasterols, beta-sitosterol, sterol, PUFA, alkyi chains, fatty acids, phosphotidylcholine, TAG and diglyceride were observed in the most salinity tolerant line (SS1-14) than the most sensitive line (SS2-18) (Ma et al. 2018). Higher plant cells comprise a vast species of sterols, especially 61 diverse sterols and pentacyclic triterpenoids were isolated and described from maize (Guo et al.1995). Apart from the total/individual sterol content and sterol/phospholipid ratios have also been associated as a marker of membrane remodeling under salt stress. The sterol/phospholipid ratio increased in the halophytes K. virginica and S. patens (Blits and Gallagher 1990; Wu et al. 1998). Conversely, the sterol/ phospholipid ratio was reduced in the plasma membrane of a salt-sensitive maize cultivar (Salama and Mansour 2015).

4.7 Conclusion This review provides a comprehensive outline of the response of the crop varieties to salinity stress. Morpho-phenological, anatomical, physiological and biochemical traits are involved in crop salinity tolerance. Resistant genotypes showed higher water potential, chlorophyll content, high levels of carbohydrates, proline, antioxidants, lipids, Nucleic acid and Abscisic acid, enabling the plant to maintain and survive under salt stress. Secondary metabolites SMs such as alkaloids, phenolics, sterols, steroids, essential oils and lignin’s participate in defense reactions from salinity stresses. There are more than 100,000 SMs in crop plants. Sterol and phospholipid has also been associated as a marker of membrane remodeling under salt stress to maintain cell integrity. In this review, we compile evidence on the salt stress responses of the different traits of crop varieties and species. The role of various

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traits for improving the tolerance of crop genotypes to salinity conditions was also presented and discussed.

4.8 Recommendations Based on the results of recent research in the arena of this chapter, if the plant breeder wants to raise the level of salinity tolerance in the recently developed varieties, he must focus on the following characteristics: early maturity, morphological, physiological and biochemical characteristics that have a strong correlation with salt tolerance. The transfer of these traits through selection or hybridizationbreeding programs to novel cultivars is significant for the possibility of expanding the cultivation of salt-affected soils.

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Part IV

Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress

Chapter 5

Genetic Variability and Genetic Resources for Salinity Tolerance

5.1 Introduction Rapid global warming associated with abiotic stresses, particularly salinity stress, directly poses a major challenge to present-day agriculture. In the era of climate change, decreased precipitation and increased evapotranspiration hinder crop production along with the soil salinity and poor ground water resource. Salinity is one of the most important abiotic stresses that negatively affect plant growth and productivity globally. Therefore, crop plants face many challenges under irrigated agriculture in arid and semi-arid regions. It is worth mentioning that between 7% (about 930 million hectares) and 10% (nearby 954 million hectares) of land areas are salt-affected. It is projected that more land will come to be affected by salinity owing to various causes viz. global warming, irrigation of land with salt-affected water, low precipitation, and evaporation of soil moisture (Grigore et al. 2014; Rokebul Anower et al. 2017). In order to produce crop varieties suitable for cultivation under salt-affected soils, the strategy of selecting salt-tolerant crop genotypes through breeding programs is of great importance. Wide genetic variation in crop varieties allows the successive breeding program to achieve its hoped-for goals of breeding new salt-tolerant varieties (Sakina et al. 2016). Plants provide over 80% of the human diet. There are 30.000 plants suitable for human nutrition, there are 7,000 plants that man cultivates or collects for food, and 30 crops feed the world. Five-cereal crops, namely rice, wheat, maize, millet and sorghum, provide 60% of the energy consumed in the world. About 7.4 million samples of genetic diversity are also sad in the 1700 gene banks worldwide. Crop improvement contributes about 50% of the world’s available food (FAO 2013). Germplasm is an appreciated natural resource that affords information about the genetic makeup of a species and is crucial for conserving plant diversity and improving economic characteristics. Plant breeding and habitat regeneration of ecosystems for crops are a few applications of germplasm protection and include PGRs for food and agriculture (PGRFA). Therefore, more attention should be paid © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_5

189

190

5 Genetic Variability and Genetic Resources for Salinity Tolerance

to the use of available genetic resources for crop improvement. Introgression of desirable genes from wild relatives to high-yielding cultivars is one way of developing climate-resilient crop genotypes that are better adjusted to particular growing conditions (Warschefsky et al. 2014). Germplasm accessions are indispensable tools for studying gene function and genetic improvement (Foster and Aranzana 2018). The presence of large genetic variability in a crop species is a prerequisite to begin an effective breeding program. The ability to tolerate salinity stress differs from one genus to another. For example, barley, cotton, sugar beet, alfalfa, quinoa and some oil crops such as rapeseed are more resistant to salinity than other crops such as faba bean, lentils and sesame. Also, species’ ability within the same crop genus to resist salinity varies according to the level of chromosomal polymorphism. Soni et al. (2020) showed that wheat genotypes exhibited a significant difference under mild and severe salinity. Hexaploids wheat is considered to be more resistant to salinity than the tetraploids and diploids wheat, and the tetraploids species of the genus Brassica is more tolerant to salinity than the diploids with substantial variation among their varieties (Hozayn et al. 2021). Also, crop varieties differ within the same species in their tolerance to salinity. Several applied studies registered genetic differences in salt tolerance across species and crop varieties within species. Barley is more salt tolerant than rice and wheat, while dicotyledons are very sensitive to salinity. However halophytes such as Atriplex sp. are more tolerant (Sai Kachout et al. 2014). Sugarcane cultivars differ genetically in their resistance to salinity. Breeding salttolerant genotypes can provide a foundation for sustainable crop production in regions that are sensitive to the effects of climate change (Stojšin et al. 2022). Finding salttolerant genotypes capable of producing under salinity stress is considered one of the promising strategies for managing with salinity problems. A general representation of global plant genetic resources is shown in Fig. 5.1. The present chapter aims to identify breeding and genetic peculiarities for salt tolerance in field crop genotypes and to identify effective genetic sources for improving salt tolerance.

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance in Crop Plants 5.2.1 Wheat Wheat (Triticum aestivum L.) is one of the most important crop plants worldwide and feeds a large number of people. However, wheat is classified as moderately tolerant to salinity, and the loss in its grain yield exceeds 60% under saline conditions (Khan et al. 2017). Research studies showed that the two imported wheat Strain PI 180988 and PI 78012 showed a high degree of salinity resistance, while the two Strain I 94353 and PI 94341 were more sensitive ones (Mansour et al. 1993). Sallam and Afiah (1998) found that the most tolerant genotypes to salinity were Strain 1, followed by Yakura Rojo, Strain 3, Strain 2, and cultivars Giza 160 and Mexibak 69. Further

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance … Fig. 5.1 Overall representations of global plant genetic resources (Modified after, Priyanka et al. 2021)

191

Crop wild relatives & Land races

Obsolete cultivars

Plant Genetic Resources for Food and Agriculture

Modern cultivars

Breeding lines & Genetic stocks

studies revealed that the Egyptian variety Giza 164 was more tolerant to salinity, followed by Sakha 8 and Sids 1, while wheat varieties Giza 165, Giza 168 and Sakha 93 were affected by salinity (El-kholy et al. 2004). By comparing the cultivars Sakha 8, Sahel 1 and Sids 1 in their tolerance to salinity, Sakha 8 was more tolerant to salinity than Sahel 1 and Sids 1 (Salib et al. 2003). The two exotic Strain K 9006 and KRL 1–4 recorded the lowest percentage of sodium: potassium in the tissues and were highly salt tolerant rather than the variety K 9644, which recorded the highest percentage of sodium: potassium (Parihar and Singh 2003). The cultivar Kharchia 65 was distinguished by its high tolerance to salinity, as it showed the smallest decrease in total dry matter and yield, the highest activity of antioxidants, osmotic regulation, potassium content, lower content of sodium and hydrogen peroxide H2 O2 , while the cultivars HD 2687, HD 2009, KRL 19 varied in the level of salinity tolerance (Sairam et al. 2003). High levels of genetic variances have been reported between wheat cultivars and Strains. The local bread wheat cultivars Gemmeiza 7, Gemmeiza 9, Gemmeiza 10, Sids 1, Sakha 8, and Sakha 93 are more salt tolerant compared to Giza 165 and Giza 168 cultivars (Anonymous 2021). Based on a framework of the genetic diversity among wheat genotypes of crop growth and development under salinity stress, a study by Hussain et al. (2013) showed that wheat genotypes ZAS 08, ZAS 34, and ZAS 42 were least affected at 50 mM NaCl concentration. While ZAS 67 revealed a moderate loss of the total chlorophyll at 50 mM NaCl concentration. Genotype ZAS 70 recorded a great loss in its total chlorophyll content. Al-Khaishany et al. (2018) carried out the effects of different levels of salt stress (0, 50, 100, 150 and 200 mM NaCl) on wheat germplasm. The results revealed that genotype Shebam 8 was obviously salt-tolerant among the ten genotypes. However, Yecora Rojo, KSU106, Samma, Sonalika and Gemmeiza 9 were

192

5 Genetic Variability and Genetic Resources for Salinity Tolerance

moderately tolerant and the rest genotypes Maaya, Pawni, samra and Mesri were the lowest tolerance to salinity. Genotype Shebam 8 showed better ionic homeostasis (higher K+ /Na+ and Ca2+ /Na+ ratios in plant leaves), membrane stability index, leaf area and chlorophyll content. Thus, the aforementioned parameters must be used as selection criteria for salt tolerance. At Toshka Agricultural Experiment Station of Desert Research Center, Aswan governorate, Egypt with soil ECe 2.26 dS m−1 on depth 0–15 cm and 2.03 dS m−1 on depth 15–30 cm, ten divergent parents of bread wheat and their five crosses were evaluated. Nassar et al. (2020) registered highly significant variances among F3 families for yield traits. Mean performance for the five F3 families and their parents revealed that selected plants of the 4th and 5th cross were the earliest in heading and had the highest values for all traits. Whereas, the assessments of genetic variance within selected plants were greater than those among families for most deliberated traits in the tested crosses. Moreover, at 150 mM NaCl stress at the seedling stage, Hussain et al. (2021) tested forty wheat genotypes. Salt-tolerant wheat i.e. three; S-24, LU-26S and Pasban-90 and salt-sensitive i.e. four; MH-97, Kohistan-97, Inqilab91 and Iqbal-2000 genotypes were also evaluated for growth, yield, biochemical and physiological characteristics. Genotypes Pasban-90, S-24 and LU-26S had the maximum shoot dry weight under salt stress situations. However genotypes Kohistan97, MH-97, Inqilab-91 and Iqbal-2000 were the lowest in the growth traits. Likewise, variation in the reduction of fresh and dry biomass of root ranged from 47–52% in Kohistan-97 and Inqilab-91, whereas reduction in root fresh and dry weight was less and fluctuated from 28 to 37% in Pasban-90, LU-26S and S-24 genotypes. At tissue culture level, the foreign wheat cultivars West Bred 911 and Yecora Rojo were the most tolerant to salinity, followed by the two local cultivars Giza 157 and Sakha 90 (Barakat and Abdel-Latif 1996). Also, the cultivar Nebraska of Agropyron desertorum and genotypes PI 297874 and PI 276399 of Agropyron elongatum were among the genetic resources that could be bred and selected for salinity tolerance (Flowers and Yeo 1995 and Shannon and Noble 1990). Identification salt tolerance differences among 15 wheat lines developed through doubled haploid (DHL) procedure was compared with Sakha 93 as a salt-tolerant check cultivar. Al-Ashkar et al. (2019) deliberated the performance of the genotypes at three levels of salinity (0, 100, and 200 mM NaCl). Significant variances were noticed for the studied characters. The salinity tolerance membership index relied on the three characters categorized one novel Line DHL21 and the check cultivar Sakha 93 as greatly salt-tolerant; DHL25, DHL26, DHL2, DHL11 and DHL5 as tolerant, as well as DHL23 and DHL12 as moderate. Discriminant function analysis and MANOVA suggested differences among the five tolerance groups; Sakha 93 is considered a donor to improve salinity tolerance during the seedling stage. The tolerated Lines DHL21, DHL25, DHL26, DHL2, DHL11, and DHL5 could be also recommended as novel genetic resources for improving wheat to salinity tolerance in breeding programs. Based on physiological characters i.e. relative leaf water content, chlorophyll content, plant fresh weight and plant dry weight, Shtaya et al. (2019) revealed that genotype “Norsi” could be deliberated as the most tolerant landrace compared to White Heteyeh 1 and

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance …

193

Black Heteyeh, where it exhibited the lowermost reduction % in leaf relative water content at 50 and 100 mM NaCl.

5.2.2 Barley Although barley (Hordeum vulgare L.) is considered salt tolerant among field crop plants, its growth and plant development is rigorously affected by ionic and osmotic stresses under salt-affected soils (Mahmood 2011). Indeed, barley genotypes exhibited different potentials to produce acceptable yields under salinity stress. In this respect, inclusive genetic difference has been verified by numerous researchers in available studies. For instance, the local barley cultivar Giza 123, American Beecher cultivar, newly developed Strain SU 12330, ICARDA Strain 4, 3, 2 and Oxidized 410 are characterized by stable yield and suitability for cultivation under high salt stress environments in the Egyptian deserts (Afiah et al. 2001). The Indian barley cultivars Karan 92, Karan 19 and the Danish cultivar Golden are important as sources for salinity tolerance (Finnie et al. 2004; Singh 2001). In addition to the foreign cultivar California Mariout was tolerant to salinity, whereas Morex was sensitive one (Mansour and Stadelman 1994). At four salinity levels i.e. 0, 100, 200, and 300 mM NaCl in Hoagland nutrient solution, 35 barley (Hordeum vulgare L.) entries have been tested for salt tolerance during germination and vegetative growth stages. Some entries displayed good salt tolerance at germination but were unsuccessful in surviving at the seedling stage. On the contrary, five genotypes i.e. Jau-83, Pk-30109, Pk-30118, 57/2D, and Akermanns Bavaria exhibited better tolerance to salinity (200 mM) at both growth stages (Mustafa et al. 2019). Moreover, Pour-Aboughadareh et al. (2021) showed that overall means of twenty-barley genotypes, cell membrane stability index fluctuated from normal to salinity stress with slight reduction (15.53% and 19.45%, respectively) under salinity conditions. Membrane stability index, indicated a slight increase in barley G5 (0.51%) and G18 (0.94%). However the lowest reductions were detected in genotypes G10 (5.52%), G3 (8.46%) and G16 (10.55%). The weighted average of the absolute scores index and the multi-trait genotype-ideotype distance index revealed that three genotypes G7, G14 and G16 can be recommended as novel genetic resources for improving and stabilizing grain yield in barley breeding programs for moderate climate and saline areas of Iran. Under physical and chemical properties of soil texture as sandy loam affected by salinity with soil EC of 8.54 dS m−1 and irrigation water EC of 7.94 dS m−1 at Ras Sudr Research Station, Egypt, Moustafa et al. (2019) indicated that three genotypes (G2), (G11) and (G14) verified the greatest grain yield with one or two of its components that can be exploited to improve barley production across environments. Meanwhile, the index of tolerance across the two stress treatments showed that the five genotypes G1, G6, G7, G8 and G15 on the 1st sowing date (12 November) and the two genotypes G9 and G12 on the 2nd sowing date (12 December) had the least stress sensitivity index for grain yield/m2 . The early genotype G2 and the

194

5 Genetic Variability and Genetic Resources for Salinity Tolerance

two high-yielding genotypes G11 and G14 were stable for yield and its components and could be used for cultivating directly under undesirable environments. Furthermore, Mansour et al. (2021) examine agronomic responses of 21 different barley genotypes to naturally occurring salinity in an arid Mediterranean climate. Three saline fields (with an average electrical conductivity of the soil water extract 7.72 dS m−1 ) were irrigated with well water of three increasing salinity levels, low (5.25 dS m−1 ), moderate (8.35 dS m−1 ) and high (11.12 dS m−1 ). They showed substantial genotypic variations under the three salinity levels. Increasing salinity levels declined the performance of the measured agronomic yield traits. Barley genotypes G4, G14, G1 and G10 exhibited high and stable salt tolerance and are suggested to grow commercially under saline regions, as well as parental genotypes in barley breeding programs for enhancing salt-tolerant cultivars. Genotypes as G15 were strongly affected by osmotic stress, with severe declines of biological yield and spikes number, but remarkable tolerance for later-determined components, like grains number/spike and 1000-grain weight at high salinity. Contrariwise genotypes G5, G8, G12, G16 and G17 showed good performance under low salinity levels but not at high salinity levels. As shown in Table 5.1, several response patterns were observed for grain yield and yield index at different salinity levels. G4 and G14 were the most tolerant ones and displayed the highest ranks of grain yield and yield index. The ranks of some genotypes improved with salinity viz. G18, G19 in a sustained manner from low to high salinity, whereas G10, G1, G9 and G11 improved only at the highest salinity level. Quite the reverse, ranks of G8, G5 and G12 declined rigorously with increasing salinity level, from the lowest to the highest level, whereas ranks of G17 and G16 declined at the highest salinity level only. These trends were also visible for each yield component.

5.2.3 Rice Rice a glycophyte is considered as salt-sensitive crop, and the growth and yield of rice are significantly affected by salinity. Prolonged exposure to saline conditions leads to stress and a significant decrease in grain production (Jenks et al. 2007). The response of rice to salinity varied with the growth stage. Commonly, rice displays tolerance to salt stress during germination, becomes sensitive during the early seedling stage, gains tolerance during vegetative growth, becomes sensitive again during the reproductive and pollination stage, and shows an increasing tolerance until maturity (IRRI 1967). Salinity risk is estimated to reduce worldwide rice production by 50%. Ma et al. (2018) surveyed 92 genotypes and identified the most salinity-tolerant Line (SS1-14) and most sensitive one (SS2-18) based on physiological and metabolites assessments. In general, rice can tolerate a small amount of saltwater without compromising growth and yield. But there is a difference in the degree of tolerance in their varieties to different levels of salinity. The Egyptian local rice cultivars Giza 159, Giza 178, Sakha 104, and Egyptian Hybrid 1 are distinguished for their ability to be

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance …

195

Table 5.1 Grain yield (kg/ha) and yield index of 21 barley genotypes under salinity conditions (averaged over the two growing seasons) (Mansour et al. 2021) Genotype Grain yield (kg/ha)

Yield index (YI)

5.25 dSm−1 8.35 dSm−1 11.12 dSm−1 5.25 dSm−1 8.35 dSm−1 11.12 dSm−1 G1

3814

2551

1519

1.13

1.06

1.16

G2

2793

1966

1209

0.83

0.82

0.93

G3

2649

1833

1175

0.78

0.76

0.90

G4

4315

3334

1921

1.28

1.39

1.47

G5

4108

2277

1161

1.22

0.95

0.89

G6

2184

1176

752

0.65

0.49

0.58

G7

3993

2125

1361

1.18

0.89

1.04

G8

3444

1626

1067

1.02

0.68

0.82

G9

2750

2346

1346

0.81

0.98

1.03

G10

3196

2842

1753

0.95

1.18

1.34

G11

2679

2465

1309

0.79

1.03

1.00

G12

3818

2326

1265

1.13

0.97

0.97

G13

2764

2357

1176

0.82

0.98

0.90

G14

4999

3872

1906

1.48

1.61

1.46

G15

3292

2629

1351

0.97

1.10

1.03

G16

4284

3028

1303

1.27

1.26

1.00

G17

4429

3673

1302

1.31

1.53

1.00

G18

2921

2121

1424

0.87

0.88

1.09

G19

2927

2227

1394

0.87

0.93

1.07

G20

2828

1977

913

0.84

0.82

0.70

G21

2713

1619

821

0.80

0.68

0.63

cultivated in newly reclaimed saline lands and when there are problems with irrigation water and its quality (Anonymous 2007 and Anonymous 2023). Studies have confirmed that CSR 10 Strain have a high level of salt stress tolerance compared to Type III, Pant Dhan 4, Pokkali, Pusa Basmati 1 and Basmati 370 (Shankhdar et al. 2000). Among the local and foreign cultivars, Giza 178 and IRAT 111 were considered to be salt tolerant and IR 47686-6-2-2-1 were moderately tolerant, while Giza 177 was sensitive one (Shehata 2004). The Belgian cultivar Pokkali was also considered salinity resistance, while the Ikp cultivar was sensitive (Lutts 2003). Strain ADT 39 and IR 20 ranked first in salinity tolerance, followed by cultivar TRY 1, while the two cultivars White Ponni, ADT 38 were more sensitive to salt stress (Djanaguiraman et al. 2003). The foreign cultivars Pokkali, CSR 10, CSR 11, CSR 27, IR 47 were tolerant to salinity. However Strain CSR 30 was moderately tolerant and Strain IR 28, MI 48 were sensitive ones (Ammar et al. 2007). Nine rice genetically diverse genotypes were appraised by EL-Emary et al. (2013). They planted four hundred rice seeds of each variety in 8 petri dishes with three levels

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of salt concentration, 4000 ppm, 6000 ppm and 8000 ppm of NaCL, and the tap water. The genetic materials used in this investigation included one sensitive variety to salinity Giza 177, four moderately salinity tolerance i.e., GZ 1368 and SaKha 104, SaKha 101 m (a) and Sakha 101 m (b) and four highly salinity tolerance i.e. Giza 159, GZ 6296, Giza 179 and Giza 178. Results showed that highly variances were found for the diameter and number of xylem vessels in vascular cylinder for the studied materials. Also, there are wider vascular in salinity tolerance varieties Giza 159, GZ 6296, Giza 178 and Giza 179. Furthermore, rice variety Giza 179 verified high desirable estimates for yield characters and might be expressed as a promising genotype under saline soil conditions. Moreover, Kakar et al. (2019) recorded a wide range of variability among rice genotypes for root traits under salt stress conditions. Salt stress response indices were used to categorize the 74 rice genotypes; 7 genotypes (9.46%) were celebrated as salt sensitive, 27 (36.48%) each as low and moderately salt tolerant, and 13 (17.57%) as highly salt tolerant. Genotypes FED 473 and IR85427 were recognized as salt-tolerant and salt-sensitive, correspondingly. Screening rice genotypes in their salinity tolerance has been implemented by Sarah et al. (2021). Analysis of variance represented highly significant variations between rice genotypes for morpho-physiological traits. Also, highly significant differences were detected among treatments for all traits, except root length. The highly significant interaction between genotypes and treatments was also recorded, indicating the differential effect of stress on a genotypic component of all traits. The salinity tolerance scores at the seedling stage showed that the 25 rice genotypes revealed diverse reactions for salinity varied from 2.5 to 8.0. The rice genotypes were rated as tolerant to salinity (scores varied from 2.5 to 4), except RBL-268, RBL-267 and RBL-268 which were moderately tolerant (salinity score of 5.3). While, genotypes IR72, IR29, and GZ10365-2-4-1-2 were classified as sensitive to salinity stress (salinity scores of 8.0, 7.7 and 6.8, correspondingly).

5.2.4 Maize Maize is a cross-pollinated, polymorphic plant in nature. It is generally a moderately salt-sensitive field crop (Iqbal et al. 2020). Maize Lines Giza 444 and Giza 504 were characterized by increased root dry weight: shoot dry weight ratio compared to the two Lines Giza 102 and Giza 241. The hybrids Giza 4 × Giza 241, Giza 4 × Giza 444, Giza 4 × Giza 504 and Giza 444 × Giza 241 showed high acclimatization to tolerate salinity conditions (sodium chloride: calcium chloride 1:3 ratio) (Fahmy et al. 1992). The Triple White Maize hybrids 321, 324 and 329 and Triple Yellow Maize hybrids Giza 352, 353, 360 and 368 have a satisfactory level of salt tolerance (Anonymous 2023). The foreign maize hybrid Arizona 8601 exhibited a great level of salt tolerance (Shannon and Noble 1990). In addition, Hichem et al. (2009) exposed two forage maize varieties (Aristo and Arper) at seedlings to 0, 34, 68 and 102 mM NaCl for 6 weeks under glasshouse conditions. A significant difference in salt response was detected between both maize varieties. A better performance

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was observed for a variety of Arper salt-challenged leaves compared to Aristo as a result of higher water content and polyphenol content. Whereas, Wang et al. (2020) assessed genotypic variation in salinity tolerance among 20 maize genotypes with contrasting root systems exposed to 0, 50 mM or 100 mM NaCl, for 10 days. Significant differences were detected among 12 shoot and root characters between the tested genotypes under NaCl treatments. The twenty genotypes were ordered as 8 salt-tolerant, 5 moderately tolerant and 7 salt-sensitive ones based on the mean shoot dry weight ratio. The more salt-tolerant genotypes like Jindan 52 had less reduction in growth, and lower shoot Na+ contents and higher shoot K+ /Na+ ratios under salt stress. Zahra et al. (2020) found that differences between the variety and stress were significant for carotenoids. The difference between priming was insignificant. The interaction between variety × stress × priming was insignificant. Varietal differences and the effect of stress as small for this attribute. The response of two maize genotypes selected as Sahwal-2002 (salt tolerant) and Sadaf (salt-sensitive) to salt stress was examined at controlled growth conditions. The salt-tolerant genotype Sadaf, experienced more oxidative damage than the Sahiwall-2002 genotype under salt stress.

5.2.5 Sorghum Sorghum [Sorghum bicolor (L.) Moench] is important as a candidate crop for both fodder and grain in salt-affected regions. It is grown in arid and semiarid regions of the world and is a moderately salt-tolerant crop (Gates et al. 2009). The species Sorghum bicolor and Sorghum halepense showed effective in the exclusion of sodium ion, and this mechanism was more evident in the first species, which is considered a genetic source of salinity resistance for the cultivars of the species S. bicolor (Yang et al. 1990). Evaluation of sorghum genotypes for salt tolerance was done by Abida et al. (2012), who found that the mean germination time of varieties were significantly differed and affected by the application of salinity levels. The sorghum hybrid Horus showed superiority in the yield of grain and green fodder by 18.4 and 5.5%, respectively, under saline conditions compared to the Mina hybrid, which are two hybrids that are used in the production of grain and green fodder (Elafendy et al. 2004). Parental sorghum Lines ICSA-37, ICSR-91022 and hybrids ICSA-37 × Dorado, ATX-631 × Dorado, ICSA-1 × ICSR-91022, ICSA-37 × ICSR-91022 and ICSA-8845 × ICSR-91022 were more salt tolerant compared to Strain ICSA-88015, ICSA-70, ICSA-1 and hybrids ICSA-1 × Dorado, ICSA-47 × Dorado, ICSA-70 × Dorado and ICSA-47 × ICSA-91022 (El-Menshawi et al. 2003). Furthermore, Hailu et al. (2020) concluded that soil salinity reduced yield and yield attributes of sorghum and showed an inversely relationship to increasing levels of salinity. Consequently, results at various growth stages and consistent results indicated that sorghum genotypes Meko and 76T1#23 had the highest values of yield and yield attributes, henceforth expressed as salt tolerant ones. Both Meko and 76T1#23 were

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more yielded rather than the national mean (23.69 qt ha−1 ) with regard to grain yield. Whereas, Teshale and Red swazi were the lowest ones.

5.2.6 Faba Bean Faba bean is one of the most important high-protein cool-season legumes, but it is sensitive to salinity stress (Asif and Paull 2021). However, Sharma (1995) showed that the faba bean is considered a medium-tolerant crop of salinity, with a critical salinity limit of 4.56 dS m−1 , and a 50% decrease in seed yield at 9.51 dS m−1 . Two genotypes of faba bean (Vicia faba), varied in drought tolerance based on the classification of the International Center for Agronomic Research in Dry Areas (ICARDA) were irrigated with waters of three salinity levels. The drought-sensitive varieties are more salt tolerant compared to the drought-tolerant genotypes. Under saline circumstances, the drought-sensitive genotypes display a much greater yield up to a salinity threshold, with an electrical conductivity (ECe ) between 5.5 and 6 dS m−1 for faba bean (Katerji et al. 2005). The Egyptian cultivars Nubaria 1, Giza 3, Cairo 241 and Lines FlIP 77/84, ILB 1814, ILB 1813, L 983/281/95 are characterized by a stable average performance of the seed yield, and it can be recommended to cultivate Nubaria 1 and the Strain FLIP 77/84, ILB 1814, ILB 1813 under salt-affected soils. While, Giza 3, Cairo 241 and L 983/281/95 can be grown under improved environmental conditions (Darwish et al. 2003). The response of five divergent faba bean genotypes, namely (NBL-Mar.3, NBL5, L3, Nubariya-1 and Misr-1) against salt stress was investigated by Afiah et al. (2016). They studied mean performance of number of seeds/pod, number of seeds/ plant and seed index under salinity levels. Genotype NBL-Mar.3 had the best number of seeds/plant under both control and highly salt stress (60 mM) treatment. While, Nubaria-1 provides the best seed index under salt stress. Seed yield/plant showed a wide range of differences among all genotypes under salt stress. Souana et al. (2020) registered quantitative differences between faba bean genotypes. The Aguadulce genotype exhibited healthy growth and physiological and molecular response under salt stress than the genotype Histal. The genotype Aguadulce performs better with 0.5 mM SA, while the Histal manifests superior behavior under 1 mM SA.

5.2.7 Chickpea Chickpea (Cicer arietinum L.) is deliberated a salt-sensitive species. However several genetic variations for salinity tolerance be present (Turner et al. 2013). The chickpea varieties, classified as drought-sensitive by ICARDA, are more salt tolerant compared to drought-tolerant varieties. Under a non-saline condition, seed yield of varieties is nearly the same. In saline locations, the drought-sensitive varieties gave a greatly higher yield up to a salinity threshold, matching with an ECe between 2.5 and

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3 dS m−1 (Katerji et al. 2005). Six chickpea genotypes were tested by Bruggeman et al. (2003) in sand-filled pots in the greenhouse. The chickpea seeds were watered with water of four salinity levels (0.5, 2, 4 and 6 dS m−1 ). The results revealed that the varieties responded differently to various salinity levels. Genotypes F.97-74, F.87-59 and ILC 3279 were found to be greater salt tolerance and gave more dry matter compared to genotype F.97-265. The two Indian chickpea Strains BGD-70 and BGD-1070 had good salinity tolerance, while the two Strains BGD-72 and BG-1073 were less in growth and root nodule formation under salinity conditions (Singh et al. 2003). The Indian chickpea Strain CSG 8893, H83-84, HK 81-69 and H 85-108 showed a good level of salt tolerance (Singh 2004). Meanwhile, Kaur et al. (2021) evaluated salinity tolerance in 10 chickpea genotypes including CSG-8962 (Karnal Chana-1), as salt tolerant check under control and salinity ECiw 6 dS m−1 and ECiw 9 dS m−1 . Chickpea genotypes ICCV 10, CSG 8962 and DCP 92-3 retained highest number of filled pods at ECiw 6 dS m−1 , while at higher salinity of ECiw 9 dS m−1 , genotypes CSG 8962, ICCV 10 and KWR108 gave the maximum filled pods. Genotypes S7 and ICCV-10 had grain yield reductions of 36.13% and 41.24%, respectively. However the salt tolerant check had a reduction of 46.94% at ECiw 6 dS m−1 . Yield indices showed that, genotypes S7, KWR108 and CSG 8962 indicated relatively higher tolerance than other genotypes. However BG 256 and ICC 4463 were the most salt-sensitive chickpea ones.

5.2.8 Lupine Lupines are fairly more tolerant to several abiotic stresses than other legumes and have a demonstrated possibility for the recovery of poor and polluted soils (Coba de la Peña and Pueyo 2012; Fernández-Pascual et al. 2007). Recognizing germplasm tolerance to a series of abiotic stresses might allow lupine cultivation to increase into a wide range of agro-climatic conditions. The local lupine cultivar Giza 1 and the French Dijon-2 showed high salinity tolerance compared to the rest of the cultivars and Strains, namely Mutation 7, Mutation 23 and Mutation 37/3 Giza 2 (El-Sayed and El-Ghobashy 2003). To assess the genetic difference between two lupine varieties viz. Giza 1 and Giza 2, Rady and Mahdi (2015) subjected both genotypes to exogenous proline treatment under a saline soil with 6.35–6.45 dS m−1 , on 20, 35 and 50-dayold seedlings. Results revealed that Giza 2 variety was found to produce greater growth and yield, thus reflecting more salt tolerance than Giza 1. Mahfouze et al. (2019) exposed seven genotypes of Lupinus albus L. to three different levels of salinity stress (2, 4 and 8 dS m−1 ). They indicated that two white lupine genotypes viz. CGN 10106 and CGN 10112 were tolerant to salt stress. Conversely, lupine accessions CGN 10102, CGN10104 and CGN10108 were moderately-tolerant. On the contrary, CGN 10109 and Balady were sensitive to salt stress.

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5.2.9 Cowpea It has even been found that the response to salt stress can differ depending on the time of exposure and the stage of plant growth, with more rapid exposure resulting in more stress (Maas and Poss 1989). One study has reported that the difference in germination rates within a particular species in cowpea ranged from 5.8 to 94.2% (Ravelombola et al. 2017). Within certain species, genetic differences exist in cowpea. Individual plants with salt-sensitive genotypes tend to display greater ion accumulation than salt-tolerant genotypes, leading to toxic effects (Murillo-Amador et al. 2006). Furthermore, Kang et al. (2023) found that ion accumulation was generally higher in salt-sensitive germplasms compared to salt-resistant ones. In particular, the sodium and chloride ion levels for the salt-resistant germplasms (Vu_191 and Vu_ 328) were 27.65 mg/g and 82.12 mg/g, respectively, compared to 51.86 mg/g and 139.35 mg/g, respectively, for the salt-sensitive germplasms (Vu_393 and Vu_396).

Soybean Soybean is an important cash crop and its production is significantly affected by salt stress. Soybean is ordered as a moderately salt-tolerant crop that shows a range of salt-tolerance-associated phenotypes (Phang et al. 2008). Although soybean is considered a medium tolerant crop, but the foreign Bragg soybean cultivar is characterized by its ability to tolerate salinity, while the Dowling cultivar was sensitive to salinity (Zenoff et al. 1994). Whereas, Lee et al. (2004) showed that soybean is identified as partially sensitive to salinity stress, which can result in up to 40% yield loss dependent on salinity level. The foreign soybean cultivar S-100 was also distinguished for its salt tolerance, while Tokyo cultivar was more sensitive. EL Sabagh et al. (2013) tried the influence of three salinity levels (0, 0.25 and 50 mM NaCL) on five soybean genotypes. The results revealed a large variability within the cultivars for salt tolerance at the early growth stages. The Egyptian cultivar Giza 111 and the Japanese cultivar TSU showed a greater of all seedling parameters as compared to the other cultivars under saline conditions. The Japanese cultivar TSU and the Egyptian cultivar Giza111 maintained lower Na+ and a higher potassium (K+ ) concentration and proline content at higher salinity levels than the other cultivars. The Japanese cultivar TSU and the Egyptian cultivar Giza 111 were less affected by salinity stress than the others. Thus, both cultivars Giza 111 are the most tolerant ones during germination stage. Saad-Allah (2015) conducted an experiment of six soybean varieties i.e. Crawford, G21, G22, G35, G82 and G83 under (8 and 16 dS m−1 ) levels of sea salt. Results indicated that the least salt-affected variety was G82 in terms of the highest protein content. Furthermore, three soybean cultivars (Crawford, G-111 and Clark) were tested under 200 and 400 mM NaCl stress by Abulfaraj and Jalal (2021). They detected that the final germination % was reduced in the three cultivars at all levels of salinity stress. Under 400 mM salt stress, the maximum reduction of final germination %

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(60%) was observed in cultivar Clark, while Crawford and G-111 exhibited 29 and 22% reduction, respectively. Whereas, the mean germination time was increased with increasing salinity level, and Crawford displayed the best behavior by lowering mean germination time values than other genotypes at both salinity stress and ordinary conditions.

Peanut Peanut (Arachis hypogaea L.) is categorized as a moderately salt-sensitive species and therefore, soil salinity can be a restrictive reason for peanut (Luo et al. 2021). Varieties and Strains of peanuts vary in their tolerance to salinity. The six genotypes Kopergaon 3, MH 2, Gangapuri, Tirupati 4, ICGV 86590 and GG 4 showed >70% germination in 80% salinity, whereas, cultivars VG 9521, Jawan, ICG (FDRS) 10 and DH 3–30 were more sensitive to salinity (Singh et al. 2007). The imported genotype Int 341 surpassed the other peanut genotypes in most of the yield, yield components as well as some quality characters. Giza 3 attained the maximum value of 100-pod weight and Int 276 produced the highest shelling percentage. Whereas, Giza 5 gave the highest value of seed oil content. Conversely, local cultivar 404 recorded the highest value of yield characteristics, while. Int 342 genotype recorded the lowest seed oil content. Int 341 gave the highest values in most characters studied under irrigation with saline water and was the most salt tolerance one than the other deliberated genotypes (Abd El-Aal et al. 2007). Singh et al. (2008) verified a lot of 127 genotypes for salinity tolerance and found genotypic variation in pod yield and related characters with 0–13 pods/plant and 0–136 g m−2 seed yield. Fifty-nine genotypes displayed pod and seed bearing of which 20 genotypes exhibited less than 10% mortality. Eleven genotypes NRCG 2588, 4659, 5513, 6131, 6450, 6820, 6919, 7206, TMV 2 NLM, TG 33 and JNDS-2004-15 with high standing ability and more than 50 gm−2 seed yield were recognized as salinity tolerant. Ten genotypes JNDS-2004-1, JNDS-2004-3, JNDS-2004-16, TG 28, TG 38C, TG 42, PBS 30031, PBS 30033, NRCG 6155 and ICGV 86031 with more than 35 gm−2 seed yield were classified as moderately tolerant at salt affected area up to 3 dS m−1 . Levels of salinity i.e., 0, 1000 and 3000 mgl−1 of NaCl were investigated on peanuts by Abbas et al. (2021). Results revealed that genotypes Ismailia1 and Samnut 22 of peanut are more salt-tolerant varieties than the others. Ismailia1 and Samnut 22 possess SNP in KAT1 gene due to increase salt tolerance levels. Therefore, they recommend that Ismailia1 and Samnut 22 could be involved in peanut salt tolerance breeding programs. According to the phylogenetic tree, Giza 6 is more close to Ismailia 1 compared to Samnut 22, whereas Ismailia 1 and Samnut 22 very close, while Ismailia 1 and Giza 6 are Egyptian peanut genotypes and Samnut 22 is Nigerian one. The screening results described that Ismailia 1 and Samnut 22 were tolerant to salinity, but Giza 6 was sensitive one.

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Sunflower Although the sunflower is classified as a moderately salt-tolerant crop, highly tolerant germplasm may be of value. Nevertheless, there are extensive genetic variances in tolerance among cultivars (Ashraf and Tufail 1995). PAC-36 cultivar was also more tolerant to salinity compared to APSH-1 MSFH-8 cultivars (Madhulety and Jyotsna 2003). Masor (2011) evaluated the salinity tolerance of 24 sunflower accessions at different stages of growth under differing environments. Results revealed that seed yield varied significantly Among 24 sunflower genotypes. Genotypes Syngenta 3732 NS, Triumph s668, and Advanta Aguara were the highest yielding whereas, lines HA 430 and PAR-1673-2 were among the lowest. Likewise, Azevedo Neto et al. (2020) select sunflower genotypes varied in their salt tolerance stress and evaluate some mechanisms of salt tolerance in two contrasting (salt-tolerant and salt-sensitive) genotypes. Sunflower genotypes AG963, AG967, AG972, BRS321, BRS324, H251, H360 and H863 displayed lower biomass production and were categorized as salt-sensitive. However, the genotypes BRS323, Catisol, EXP11-26, EXP44-49, EXP60050, EXP887, HLA860HO and Olisun 5 displayed higher biomass production and were deliberated as salt-tolerant. Significant differences were detected between the Na+ and K+ levels in the plant organs of the genotypes. In the leaves of the genotypes ordered as salt-sensitive, the highest Na+ and the lowest K+ levels were identified. However the leaves of tolerant genotypes showed the lowest Na+ and the highest K+ contents. However, in the stem and roots, no association was detected between the accumulation of these ions and the salt tolerance degree.

Sesame Sesame is classified as having moderate salt tolerance (Bahrami and Razmjoo 2012). The Indian sesame cultivars RT-127, RT-54 and RT-46 were distinguished as salinity tolerance compared to the sensitive cultivar RT-125 (Gehlot and Purohit 2003). Ramírez et al. (2005) evaluated 50 genotypes under saline solutions of 4 concentrations i.e. 0.5 (control), 3.0, 6.0 and 9.0 dS m−1 . They selected four salt-tolerant cultivars and one salt-sensitive cultivar in the germination experiment. Tolerant genotypes were single stem (G22), Ajimo Star S-13 (G41), White China (G42) and White Sindos (G12), whereas sensitive germplasm was Teras (G5). Germinated ‘normal’ plant values in the control (0.50 dS m−1 ) varied from 67% for genotype G24 to a maximum of 99% for G6. With increasing salinity to 6.0 dS m−1 , 8 genotypes reached above 90% germination level. With the application of the highest dose of calcium chloride, significant variances were found among genotypes. The most survival genotypes were G42, G41, G40, G35, G12, G22, 37 and 38, which attained 62 to 80% germination. Only G42 registered low Toxicity index values of 0.0 for 3.0 dS m−1 , −0.02 for 6.0 dS m−1 and 0.09 for 9.0 dS m−1 . The salt-sensitive cultivar during germination (G5) was also the most sensitive in growth. Seed yield and dry matter of G12 were significantly higher than the other genotypes representing more tolerant

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to salinity. G12 consistently accumulated more biomass up to a salinity level of 5.0 dS m−1 . Screening focuses on 23 sesame lines grown under a nature field and subjected to two levels of NaCl (70 and 105 mM) incorporated with algae at the Agricultural Production and Research Station, National Research Center, Egypt. Anter and ElSayed (2020) used six traits i.e. plant height, stem height to 1st capsule, fruiting zone length, number of capsules/m2 , seed yield/ha−1 to describe salinity tolerant in sesame. The results of combined analyses of variance indicated that interaction between lines and salinity levels was highly significant of deliberated characters. The correlation coefficients showed that select index comprises plant height, fruiting zone length, number of capsules/m2 and seed yield/ha−1 could be operative to classify the salinity tolerant lines. Two lines, C8.4 and C8.8 showed the best rank and low value of standard deviation than the others. Hereby, both lines, C8.4 and C8.8 exhibited promising marks for tolerance to saline stress, thus could be used as novel sources for salinity tolerance in sesame breeding programs. On the other hand, Mamo et al. (2021) evaluated hundreds of sesame accessions through exposing at different salinity levels and 10 of that exhibited higher germination percentages were promoted to seedling stage. At seedling stage screening, likewise the genotypes were subjected to various salinity levels and tested for agronomic characters and nine of them that performed well were again promoted under field stage screening. Field stage screening was conducted at saline filed condition of with soils 12.45% ESP and EC 14.05 dS m−1 as saline. Statistical analysis showed that there were significant differences in salinity tolerance between verified genotypes in terms of grain yield. Five sesame accessions i.e. EW-01, Acc-205-191, Acc-ew-018, Acc-ew-018 and Acc-205-184 gave greater yield compared to the grand mean of genotypes.

Canola Canola (Brassica napus L.) is generally grown for edible oils and other uses, for example, biodiesel fuel production. Although most types of canola are recognized as salt-resistant, but development and plant yield are decreased significantly by rising salinity levels (Shokri-Gharelo and Noparvar 2018). Evaluation studies of canola cultivars and strains in five experiments representing different agricultural environments (Fayoum, Giza and Inshas) in Egypt showed different degrees of stability and variation of protein patterns between canola strains and cultivars. The local cultivar Serw 6 and the foreign Licosmos displayed a high degree of stability under the salt-affected soil in Fayoum. While, the local cultivar Pactol and the foreign Evita responded to improved environments, and the imported cultivar Star showed moderate stability (Azzam et al. 2006). The selected highly promising canola strains in yield i.e. SL15A, SL21, SL18, SL 13, L6, L4, H8, H1 were more tolerant to salinity, while strains SL9B, L55, L54, L45, L8, H2 produced less yield under salt-affected lands in Fayoum (Ghallab and Sharraan 2002). Also, rapeseed germplasm of 82 entries was evaluated under both normal and salt-affected newly reclaimed soils (two adjacent fields) at the experimental farm of the faculty of

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agriculture at Fayoum, Sharaan and Ghallab (2002) showed that all yield component traits were affected by salinity but with varying degrees depending upon their tolerance to stress. The genetic variance to environmental variance (Vg /Ve ) and genetic coefficient of variation/phenotypic coefficient of variation (GCV/PCV) ratios and genetic advance estimates were higher under normal soil conditions than those of saline soil for most studied traits, indicating that environmental stress caused masking of the genetic effect. Zavareh et al. (2003) revealed that the foreign cultivars Eurol, Dp 94.8 were unique in high salinity resistance, while Bristol, Hyola 401, Fornax, Catles, 95,102.67, Symbol, Ceres and Orkan cultivars were more ones that are sensitive. Bybordi et al. (2010) demonstrated that oxidative stress plays a major role in salt-stressed canola cultivars and SLM046 has efficient antioxidative features with high accumulation of proline and glycine betaine which offer better protection against oxidative injury in leaves rather than the other four cultivars of canola i.e. Okapi, Fornax, Licord and Elite under salt-stressed condition. Fourteen canola genotypes were exposed to three salinity levels i.e. 0, 150, and 350 Mm by Kholghi et al. (2018). The impact of salinity effect was assessed on the basis of biomass yield reduction and physiological characteristics. A dendrogram classified 14 canola genotypes into four clusters showing diversity among them. The 2-dimensional principal component analysis (PCA) was also complete the output of classification from cluster analysis. Results showed that, among 14 canola genotypes, salinity stressed canola line Safi-7 was the best salt-tolerant based on biomass production and physiological features and gave the maximum amount of both fresh and dry weights. Whereas, genotype Zafar was the most salt-sensitive one. Furthermore, under Sinai region, Hozayn et al. (2021) tested three canola cultivars Pactol, Serw-4 and Serw-6 under three irrigation water treatments: (i) Brackish-water (BW), (ii) Magnetic-BW1; brackish water after magnetization through passing a three-inch static-magnetic unit, 3.75 mT, and (iii) Magnetic-BW2; brackish water after magnetization through passing a three-inch static magnetic unit, 0.75 mT. The results showed significant differences between the three canola varieties, where Serw6 came in the first order for morph-physiological and yield characters followed by Serw-4 and Pactol, correspondingly. Significant variances were detected owing to the interactions between the two factors, where irrigation with magnetically treated brackish water (M-BW1 or M-BW2) led to a positive effect on yield and yield components of the tested three cultivars compared to irrigation with brackish water.

Cotton Cotton is a dual-purpose crop, broadly used for fiber and oil purposes all over the world. Cotton is categorized as the moderately salt-tolerant group of plant species by a salinity threshold level 7.7 dS m−1 . Cotton growth and seed yield being strictly reduced at high levels of salinity and diverse salts affect cotton growth to a variable extent. Though, inter- and intraspecific variation for cotton salt tolerance is substantial to be exploited via selection breeding for enhancing salt tolerance (Ashraf et al. 2002). The two Egyptian cotton varieties Giza 83 and Giza 75 showed a high degree of

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tolerance, and the varieties Giza 70 and Dendera were moderate one, while Giza 45, Giza 77 and Giza 81 varieties displayed a high degree of sensitivity when cultivated in lands with a salinity of 8 dS m−1 , with irrigated water of salinity up to 7 dS m−1 (Afiah and Ghoenim 1999). Ten different genotypes of Gossypium hirsutum were tested in their response to five NaCl concentrations i.e. 0, 50, 75, 100 and 150 mM. Increasing levels of salinity caused a substantial reduction in fresh shoot weight as well as fresh root weight. According to relative salt tolerance, cultivars CIM 435, CIM 1100, CIM 443, B 630 and FH 682 were classified as the most tolerant to salinity and B 622 and FVH 57 were moderately tolerant, whereas B 496 and NIAB Krishma were sensitive one (Azhar and Ahmad (2000). The Syrian cotton cultivar Raqqa 5 of G. hirsutum was characterized by higher potassium, phosphorous and sodium content with salinity tolerance compared to cultivars Aleppo 133, Deir 22 and Aleppo 90 (Koubaili and Abd El-Aziz 2005). At Ras Sudr Agricultural Research Station of Desert Research Center, South Sinai, the local Egyptian cotton cultivars Giza 83 and Giza 85 were characterized by their tolerance to salinity, as they attained the lowest values of salinity index for seed and lint cotton yields per feddan compared to Giza 45 and Giza 86 and the Russian variety Karshenseki-2 (Moustafa 2006). In continuous, under salinity level (2000 ppm), Salem et al. (2006) indicated significant differences between 10 parental cotton genotypes in boll weight and seed cotton yield/plant. According to the mean of F1 ’s as compared with its respective parental genotypes, results in Table 5.2 revealed that, the F1 ’s exceeding the high performing parent for boll weight and seed cotton yield/plant in 1st cross only. The F1 ’s means were equal to the lower parent for boll weight in 4th one. The F2 ’s of the six studied crosses in each character ranged from 1.742 ± 0.185 (cross 5) to 2.121 ± 0.132 (cross 1) for boll weight and 11.171 ± 0.580 (cross 5) to 32.683 ± 0.832 (cross 1) for seed cotton yield/plant. The back cross population means are the mid-way between the F1 and the parental genotypes for boll weight and seed cotton yield/plant in most studied crosses. Chemical constituents mean performance in Table 5.3 revealed that the F1 ’s exceeding the high performing parent for potassium concentration in 3rd and 5th crosses; magnesium concentration in 4th cross; sodium concentration in 1st and 4th crosses and proline content in 2nd and 6th crosses. While, the F1 ’s means were less than the lower parent in sodium concentration in 2nd, 3rd, 5th and 6th crosses. The F2 of the six studied crosses in each character ranged from 68.788 ± 0.943 (cross 3) to 78.707 ± 1.399 (cross 5) for potassium concentration; 103.800 ± 0.772 (cross 3) to 112.300 ± 1.350 (cross 1) for magnesium concentration; 43.506 ± 1.088 (cross 6) to 50.117 ± 0.769 (cross 3) for sodium concentration and from 0.705 ± 0.149 (cross 5) to 1.228 ± 0.206 (cross 2) for proline content. Such a wide range indicates the presence of a fair amount of genetic variability. Thus, offer the breeder a great opportunity for effective selection to isolate specific patterns of cotton genotypes. The F2 values for potassium, magnesium, sodium concentrations and proline content tended to be decreased from F1 to F2 , indicating inbreeding depression and accumulation of decreasing alleles. The back cross population means are in the mid-way between the F1 and the parental genotypes for potassium, magnesium, sodium concentrations and proline content in most studied crosses. But, it deviated

206

5 Genetic Variability and Genetic Resources for Salinity Tolerance

from the mid-parent values and their respective F1 for the same characters in some crosses. Hence polygenic effect is more pronounced. A study was implemented using irrigated cotton genotypes with nutrient solution with an electrical conductivity of 10 dS m−1 and 15 dS m−1 since 10-day seedlings stage to 40 day by Farooq et al. (2019). Results indicated that the salt tolerant genotypes were KEHKSHAN, S-3, NIAB-824 and MNH-988, however C-26, FH-114 and FH-173 were classified as salt sensitive ones. Thus, selection for cotton will be difficult due to masking effects of environment, and suggest severe and careful selection of salt tolerant genotypes. Furthermore, Mahdy et al. (2021) did recent efforts under saline soil on cotton. They recorded significant differences among fifteen long-staple cotton genotypes regarding seed cotton yield/plant, lint yield/plant, seed index, number of bolls/plant, plant height and Pressley index. Cotton genotypes “G 90 × Aus”, G95, G 90, G 80, and G 83 exhibited the best performance in seed cotton yield/plant, lint yield/ plant, Lint%, number of bolls/plant and number of seeds /bolls either under normal circumstances or saline soil compared to the other genotypes.

Sugar Cane Sugarcane (Saccharum officinarum L.) is a glycophyte deliberated as moderately sensitive to salinity stress, but the degree of sensitivity differs from variety to variety. It is of major economic value in tropical and subtropical developing countries where salinity is a rising problem (Alam et al. 2018; Wahid et al. 1997). Another study classified sugarcane as one of the most sensitive and tolerant crops at the same time, depending on the genetic makeup of the genotype and the genomes of S. sinese, S. Barberi, S. spontaneum, S. officinalis, and S. robustum. On the basis of energy level and sodium accumulation in sugarcane genotypes, Dwivedi and Srivastava (2000) showed that salt-tolerant cultivars employed less energy per microgram of sodium than sensitive cultivars. The salt-tolerant sugarcane cultivars were characterized by the ability to accumulate a higher percentage of osmotic regulating chemicals, coinciding with the lowest yield loss (20–35%). While the sensitive cultivars took the opposite trend. Sugarcane cultivars GoJ 84, CH 24, Co 740, Coc 671, CoS 767, Up-5, CO449, Co997, Co 1148 and CoLk 8001 were moderately tolerant, while the cultivars CoLk 8102, CoLk 7901 and COj 64 showed sensitivity to salinity. The moderate and late-ripening sugarcane cultivars, CoS 90269, CoS 91269, CoS 93278 and CoS 88126, are characterized by their higher salinity tolerance compared to the early group cultivars CoS 95255, CoS 687, CoS 8436 and CoS 88230 (Srviastava et al. 2003). Cultivar CoM 9516 displayed a high degree of salt tolerance, followed by CoG 93079 and Co 86032, while, Co 85012 was the most sensitive to salinity (Panwar et al. 2003). The Indian cultivars Bo 91, CoS 767, Co 1148, Co 7717, Co 62399, Co 997, Co 453 had a high level of tolerance to salinity. The species of Saccharum spontaneum is an important genetic source of salt resistance (Singh 2001). Under six levels of salinity (0, 1.0, 2.0, 4.0, 6.0 and 8.0 dS m−1 ) prepared of irrigation water by adding NaCl, CaCl2.2H2O and MgSO4.7H2O to achieve an

±0.118

±0.202

BC2

BC1

F2

F1

P2

22.736

P1

16.359

±0.261

30.325

±1.410

±0.855

±1.412

23.670

±2.071

±0.832

19.845

27.944

32.683

17.806

±0.049

28.365

±0.040

±0.025

±0.114

36.636

25.453

±1.166

15.602

±0.391

15.724

±1.282

20.689

±0.135

23.038

±0.117

10.440

±0.119

30.743

3

28.246

1

Cross population

2

Seed cotton yield/plant (g)

Character

±1.157

15.257

±0.475

23.264

±0.733

18.995

±0.013

23.673

±0.037

40.493

±0.062

30.798

4

±0.528

11.310

±0.424

14.152

±0.588

11.171

±0.088

14.950

±0.056

14.300

±0.119

16.434

5

±1.724

36.575

±1.366

38.039

±0.557

12.659

±0.145

20.300

±0.018

37.062

±0.138

23.116

6 1.910

±0.131

2.598

±0.093

1.983

±0.132

2.121

±0.024

2.722

±0.004

1.813

±0.032

1 1.570

±0.064

2.268

±0.030

2.034

±0.209

1.932

±0.017

2.181

±0.003

2.986

±0.015

2

Boll weight (g) 2.270

±0.414

1.769

±0.059

1.465

±0.184

2.063

±0.018

1.450

±0.004

1.183

±0.008

3

2.032

±0.132

1.868

±0.053

2.006

±0.159

1.833

±0.014

2.040

±0.011

2.493

±0.004

4

1.693

±0.072

1.789

±0.132

1.683

±0.185

1.742

±0.003

1.502

±0.003

1.313

±0.004

5

2.644

±0.176

2.299

±0.100

2.317

±0.144

1.775

±0.003

1.853

±0.013

3.043

±0.003

6

Table 5.2 Mean ± S.E. of six populations for seed cotton yield/plant (g) and boll weight (g) at Ras Sudr agriculture research station (Salem et al. 2006)

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance … 207

±0.147

±0.217

F1

P2

±0.240

47.491

±0.175

49.791

±0.155

49.522

±0.177

47.180

±0.218

±0.164

48.400

±0.155

52.400

±0.092

±0.115

52.360

±0.149

46.326

±0.137

50.363

4

±0.181

50.260

3

50.520

48.150

2

1

P1

±1.551

69.644

±0.684

64.311

±1.574

72.100

±0.196

65.487

±0.148

77.410

±0.170

Cross population

±0.573

70.896

±1.003

70.563

±0.943

68.788

±0.238

71.366

±0.174

69.263

±0.192

Sodium concentration (gm/100 gm)

74.200

±0.712

76.555

±0.895

±2.246

±1.612

68.329

±1.399

±1.435

71.740

70.700

76.612

65.317

±0.190

68.866

±0.188

±0.228

±0.181

77.550

80.500

68.300

Character

BC2

BC1

F2

F1

P2

68.410

4

70.313

P1

3

68.520

1

Cross population

2

Potassium concentration (gm/100gm)

Character

±0.146

44.400

±0.261

47.271

±0.173

47.210

5

±1.197

77.947

±0.696

80.815

±1.399

78.707

±0.187

80.336

±0.150

76.450

±0.139

78.360

5

±0.161

45.274

±0.149

47.222

±0.171

48.311

6

±1.858

79.938

±1.769

73.205

±1.418

78.100

±0.179

75.270

±0.165

77.300

±0.124

70.320

6

±0.763

111.602

±1.708

106.505

±1.814

110.200

±0.208

110.363

±0.158

113.499

±0.171

105. 331

2

±0.416

104.804

±0.686

104.686

±0.772

103.800

±0.170

104.380

±0.192

106.280

±0.172

105.303

3

1.057

±0.008

0.989

±0.002

0.668

±0.005

1

0.648

±0.006

1.966

±0.003

0.973

±0.002

2

1.376

±0.005

1.332

±0.011

0.890

±0.002

3

Proline content (µ moles/gm f.w.)

±0.471

114.226

±1.332

107.863

±1.350

112.300

±0.188

113.291

±0.180

114.360

±0.133

107.450

1

1.375

±0.002

0.799

±0.001

1.141

±0.002

4

±0.668

112.761

±1.215

110.101

±1.746

109.501

±0.142

114.388

±0.140

113.282

±0.141

105.370

4

Magnesium concentration (gm/100gm)

1.674

±0.003

0.429

±0.002

1.217

±0.002

5

±1.633

107.000

±1.536

104.766

±0.952

104.217

±0.174

105.250

±0.168

112.320

±0.174

108.390

5

1.057

(continued)

±0.003

1.148

±0.003

0.975

±0.003

6

±1.705

108.847

±1.167

104.500

±1.373

108.811

±0.171

109.346

±0.192

114.360

±0.134

107.333

6

Table 5.3 Mean ± S.E. for the six populations for chemical composition potassium, magnesium, sodium concentration and proline content at Ras Sudr agriculture research station (Salem et al. 2006)

208 5 Genetic Variability and Genetic Resources for Salinity Tolerance

BC2

BC1

48.954

±0.831

46.455

±0.340

47.218

±1.191

47.721

±0.495

48.600

±0.452

46.711

±0.473

50.117

±0.518

50.368

±0.586

48.104

±0.767

±1.291

46.304

±0.831

48.771

±0.969

48.500

4

F2

3

Cross population

2

Potassium concentration (gm/100gm)

1

Character

Table 5.3 (continued)

±1.197

43.110

±0.975

44.813

±0.817

45.303

5

±1.237

45.244

±1.155

45.000

±1.088

43.506

6 1.057

±0.178

1.219

±0.218

1.104

±0.151

1 1.228

±0.141

1.372

±0.173

0.896

±0.206

2 1.125

±0.187

1.116

±0.189

1.080

±0.193

3 0.876

±0.200

1.157

±0.200

1.156

±0.102

4

Magnesium concentration (gm/100gm) 0.705

±0.180

1.288

±0.136

1.314

±0.149

5

1.013

±0.136

1.314

±0.179

1.185

±0.161

6

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance … 209

210

5 Genetic Variability and Genetic Resources for Salinity Tolerance

equivalent ratio among Na: Ca: Mg of 7: 2: 1. Ten sugar cane varieties (VAT 90212; RB 72454; RB 867515; Q 124; RB 961003; RB 957508; SP791011; RB 835089; RB 92579 and SP 943206) were evaluated. Simões et al. (2016) revealed that sugar cane varieties exhibited similar reactions for growth decrease as soil salinity increases, being considered moderately sensitive to salinity. The variable number of stalks showed that variety RB 835089 displayed the maximum value (8.4) followed by varieties RB 957508, SP 943206, RB72454, RB 867515 and SP 791011, with values of 6.6, 6.2, 5.8, 5.8 and 5.8, correspondingly. The potential reason for the variances among the varieties may be due to the respective degree of genetic potentiality to overcome the salinity stress. In Bangladesh, Alam et al. (2018) screened salinity-tolerant sugarcane varieties and revealed significant variances among the tested sugarcane varieties viz. Isd 37, Isd 38, Isd 39, Isd 40 and VMC-86–550 for yield, quality and economic parameters. The greatest number of tillers (144.50 × 103 ha−1 ) and millable cane (117.67 × 103 ha−1 ), and the highest values in brix (20.0%) and goor yield (9.23 t ha−1 ) were detected in variety Isd 39. But, the variety Isd 40 recorded the first position concerning cane yield (102.90 t ha−1 ) and benefit–cost ratio (2.14). Both sugarcane varieties, Isd 40 and Isd 39, exhibited more tolerance performance to salinity than the deliberated varieties. At the level of tissue culture of somaclones, salinity-tolerant clone of sugarcane collected less Na+ and more K+ compared to a sensitive corresponding clone. Therefore, displayed a higher K+ /Na+ ratio (Wahid and Ghazanfar 2006). Moreover, AboElwafa et al. (2021) determined the genetic difference between eleven somaclones of sugarcane through immature leaves of Egyptian commercial variety GT-54 9. Significant variances were recorded between the somaclones and also their donor. The highest values of genotypic coefficient of variation and phenotypic coefficient of variation were recorded in cane yield (18.11 and 18.53%) and in technological characters for sugar yield (17.65 and 17.76%) over two ratoon crops, correspondingly. The general mean over the two ratoon crops showed that somaclones number 7 and 8 exceeded the donor insignificant values of most agronomic characters viz. stalk height (14.35 and 9.48%), stalk weight (9.52 and 15.24%), stalk number/fed (21.00 and 31.25%) and cane yield (32.16 and 52.02%), respectively. Additionally, the somaclone number 4 exceeded the donor in significant values for all technological characters viz. sugar yield (23.52), brix (3.13), sucrose % (6.28), purity % (2.99), pol% (6.36) and sugar recovery % (7.72%).

Sugar Beet Sugar beet is a salt-tolerant global crop species that can tolerate up to 300 mM (Hossain et al. 2017). Under two soil salinity levels, representing low (3.54 dS m−1 ) and high (9.28 dS m−1 ), two sugar beet cultivars i.e. Romulus and Francesca were evaluated. Romulus cultivar had the highest relative water content, Fv/Fm, and performance index and more adapted to salinity stress compared to Francesca cultivar (El-Mageed et al. 2021).

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance …

211

Under different saline situations at the Sylhet region, Bangladesh, four sugar beet entries i.e. HI-0044, HI-0473, KWS-Allanya, and KWS-Serendara has been assessed under four NaCl levels viz., 0 mM NaCl (S0), 100 mM NaCl (S1), 200 mM NaCl (S2) and 300 mM NaCl (S3). The tested entries showed their steady state for SPAD value of chlorophyll content in response to salinity stress. The highest values of growth pattern and yield performance parameters were pronounced in the HI-0044 entry, followed by HI-0473, while KWS-Allanya and KWS-Serenada were the lowest performance under different salinity stress. Sugar beet entries showed the possibility of maintaining their growth and productivity under low to high salinity levels with decreasing trends, while genotype HI-0044 was the most tolerant to salinity stress (Hossain et al. 2021).

Alfalfa Alfalfa (Medicago sativa L.) is a perennial legume fodder crop which famous as a queen of fodders due to its valuable properties. Alfalfa provides green fodder throughout lean periods of fodder scarcity. Alfalfa is classified as moderately tolerant to salinity stress. Hence breeders largely focus to improving salt-tolerant varieties (Abdul Jabbar et al. 2021). The selected alfalfa strains Euver S1, CUF 101-T2, AZ-Germ Salt 2 and AZGerm Salt1 were characterized by their tolerance to salinity (Flowers and Yeo 1995). Evaluation studies under salinity conditions indicated that the local cultivar Ismailia 94 was recognized by its high salinity tolerance, followed by Ismailia 1 and Giza 1 (Oushy et al. 1999). Moreover, Sandhu et al. (2017) selected twelve alfalfa genotypes under salinity. They recorded significant differences in concentrations of Na and Cl in shoots and K/Na ratio among genotypes. Based on biomass for salinity tolerance, the most salt-tolerant genotypes SISA14-1 (G03) and AZ-90ST (G10), the top performers for biomass, exhibited the least effect on shoot number and shoot height. SISA14-1 (G03) accumulated low Na and Cl under salinity. Most genotypes displayed a net decrease in shoot Ca, Mg, P, Fe, and Cu. However Mn and Zn increased under salinity. In a comparative analysis for salt tolerance among seven alfalfa cultivars, Lei et al. (2018) showed that Zhongmu-1 is classified as relatively salt-tolerant, while Xingjiang Daye is salt-sensitive one. Genotype Zhongmu-1 displayed lower growth under low-salt conditions compared to Xingjiang Daye, but exhibited stronger tolerance to salt stress. Mbarki et al. (2020) focused on the salinity tolerance of Medicago ciliaris genotypes compared to M. intertexta and M. scutellata in respect to plant growth, physiology and biochemistry by exposing seeds to 0, 50, 100, 150, and 200 mM NaCl. Among seven alfalfa genotypes of M. ciliaris studied, Pop1, Pop 355 and Pop 667 were the most salt tolerant. Pop 355 and Pop 667 exhibited clear tolerance to salinity at both germination and seedling stages based on tolerance index TI and sensitivity index SI. The genotypes, 306, 773, and M. scutellata, were moderately tolerant to salt stress according to salt concentration.

212

5 Genetic Variability and Genetic Resources for Salinity Tolerance

The responses of two alfalfa cultivars (salt-tolerant ‘Halo’ and salt-sensitive ‘Vernal’) were deliberated by Bhattarai et al. (2021) during 12 weeks in five levels of salt stress in a sand-based hydroponic system in greenhouse. The pattern of chlorine accumulation for cultivar ‘Halo’ was: root > stem ≃ leaf at 8 dS m−1 , and root ≃ leaf > stem at 12 dS m−1 , possibly inhibiting toxic ion accumulation in leaf tissues. Otherwise, with respect to cultivar ‘Vernal’, it was leaf > stem ≃ root at 8 dS m−1 and leaf > root ≃ stem at 12 dS m−1 . The distribution of chlorine in cultivar ‘Halo’ was fairly uniform in the leaf surface and vascular bundles of the stem. The Amide content in the leaf and stem tissues was higher in cultivar ‘Halo’ than cultivar ‘Vernal’ at the tried salt levels. Herby, low ion accumulation in the shoot was a communal approach in salt-tolerant alfalfa up to 8 dS m−1 of salt stress, which was then switched by shoot tissue tolerance at 12 dS m−1 .

Quinoa Quinoa, which belongs to the Amaranthaceae family, is a dicotyledonous crop and is a pseudo cereal. Quinoa is deliberated a halophytic grain crop (Ruiz et al. 2016). It can tolerate salinity stress (Hariadi et al. 2011) and tolerate drought stress as well as soil and water salinity stresses (Wu et al. 2016). Quinoa has the potential to grow as an alternate crop in regions suffering from water scarcity, heat stress, salinity, and nutrient deficits that affect crop yield (Cocozza et al. 2013). The cultivation of salt-tolerant crops, for instance, quinoa has the potential to improve farm-level production and livelihoods in salt-prone environments (Kaya and Yazar 2016). In Egypt, Shams (2011) planted thirteen genotypes of quinoa in the sandy soil of North Sinai, and showed that the European varieties out-yielded the Peru varieties. Shabala et al. (2013) evaluated fourteen quinoa genotypes from different geographical origin, varied in salinity tolerance. All cultivars had significantly increased K+ content in the leaf sap. However the most tolerant cultivars exhibited lower xylem Na+ content. Most tolerant cultivars recorded lowest osmolality leaf sap. When varieties are grown under saline conditions, they reduce stomata density. The varieties clustered into two groups (includers and excluders) based on their strategy of handling Na+ in saline conditions. The varieties have clustered into two diverse groups according to their ability to accumulate Na+ in their shoot. The three genotypes #10, #16 and #15 were the most salt tolerant and had lowest amounts of Na+ in leaves in saline conditions. Therefore, they are classified as “excluders”. The rest eleven varieties accumulated significant quantities of Na+ in the shoot and were categorized as “includes.” Long (2016) studied the change in response of quinoa genotypes to diverse salinity stress conditions e.g. in controlled (net-house) and in different saline fields. Between quinoa genotypes, Moradas and Verde were tolerant to salt stress conditions with high potential for the number of leaves/main stem, number of branches/plant, dry matter accumulation and yield than the remaining. These varieties might be useful as genetic resources in breeding programs for salt-tolerant quinoa varieties.

5.2 Genetic Variability and Genetic Resources for Salinity Tolerance …

213

Al-Ghamdi and El-Zohri (2021) determined the response of four quinoa genotypes under irrigation with water at different salinity levels (800, 4000 and 8000 ppm). Based on salinity resistance indices, variety Chipaya was the most tolerant to salinity stress whereas variety Ollague was the most sensitive one. The results indicated that all characters were affected by high salinity level. Generally, most of the verified traits recorded clear variations between the four quinoa genotypes and salinity levels, and the tried varieties were classified into three groups according to their behavior under stress environments compared to the normal ones.

Atriplex Atriplex are cultivated as salt resistant fodder in grazing patterns. Mediterranean saltbush Atriplex halimus is an perennial fodder shrub, however giant saltbush Atriplex nummularia is woody perennial. The two species are cultured as salt resistant fodder in grazing patterns (Norman et al. 2004). Atriplex is a halophyte with significant benefit in saline soil reclamation and Phytoremediation (Benzarti et al. 2014). Substantial variations has been found in physiological, morphological and anatomical modifications as a result of salinity in Mediterranean saltbush Atriplex halimus and giant saltbush Atriplex nummularia. Two species, belong to Chenopodiaceae, are true xerophyte as revealed from anatomy structure and salt storage trichromes. The two species varied in their reaction to salt stress based on genetic makeup. Atriplex species leaves distinguishing by the existence of salt-accumulating cells on both upper and lower leaf epidermis, which are of importance in ecological acclimatization. A negative influence on anatomical characters was registered with increasing salinity on A. halimus leaves. But, low levels of salinity had enhancing effect on A. nummularia leaves (Al-Muwayhi 2020). Evaluate salinity response in the perennial C4 species Atriplex halimus, and in the three cultivars of the annual C3 Atriplex hortensis: green, red, and scarlet was investigated by Calone et al. (2021). They tested four genotypes for 35 days under water salinity ranged from 0 to 360 mM NaCl. The stomatal conductance and transpiration rate were more severely influenced by salinity in the C4 A. halimus than in the C3 species A. hortensis, due to lesser leaf water potential display stronger osmotic regulation, and higher relative water content related to more turgid leaves, in A. halimus compared to A. hortensis. Two species were tolerant to salinity. From an agronomic viewpoint, approaches of longer vs. quicker soil coverage, involved by A. halimus versus A. hortensis cv. scarlet, are feasible normal remedies for vegetating saline soils and improving soil organic carbon. Finally, this clearly indicates the importance of the aforementioned genetic materials as genetic resources in breeding programs for producing novel crop varieties that are more tolerant to salinity and meets the requirements of sustainable agriculture in light of the challenges of climate change.

214

5 Genetic Variability and Genetic Resources for Salinity Tolerance

5.3 Conclusion The development of salinity tolerance within plant materials is of great value in genetic improvement programs. Releasing crop varieties capable of producing appropriate yield under salinity conditions requires wide genetic variations in salinity tolerance. Previous studies support the existence of significant differences in salinity tolerance within species. According to the results and discussion of the reference studies, the following conclusions can be drawn: 1. Rapid climate change associated with abiotic stresses, particularly salinity stress directly poses a major challenge to present-day agriculture. 2. Crop-tolerant cultivars produce substantially greater yield compared with sensitive cultivars, especially under climate change conditions. Therefore, utilizing tolerant cultivars is essential to increase productivity, particularly in arid and semi-arid regions of the Mediterranean. 3. Considerable variations were found among crop genotypes for various morphphysiological, biochemical as well as yield traits. This helps in the possibility of producing novel cultivars that are more capable of tolerating salinity conditions, especially under climatic changes. 4. This genetic diversity represents a genetic base for salt tolerance in breeding programs to develop new varieties that are more stress tolerant.

5.4 Recommendations We recommend that researchers and scientists to focus on eco-friendly studies to mitigate the effects of salt on crops, examples include: 1. It is important to plan numerous studies to explore the potential of salt-tolerant genotypes as a genetic basis for tolerance in crop breeding programs. 2. It is important to evaluate promising genotypes based on their tolerance according to biomass yield reduction. 3. Emphasis should be placed on cultivating new varieties that are more tolerant to salinity in salt-affected lands to avoid yield reduction.

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Singh AL, Hariprassana K, Solanki R (2008) Screening and selection of groundnut genotypes for tolerance of soil salinity. Aust J Crop Sci 1(3):69–77 Singh DK, Singh KP, Pal M (2003) Antioxidant enzymes activity and salt tolerance in rice cultivars. Abstract 2nd international Cong of plant physiology, Jan 8–12, New Delhi, India, p 260 Singh P (2001) Essentials of plant breeding. Kalyan, Publishers, New Delhi, India Soni S, Kumar A, Sehrawat N, Kumar N, Kaur G, Arvind K, Mann A (2020) Variability of durum wheat genotypes in terms of physio-biochemical traits against salinity stress. Cereal Res Commun 46(6):1–10 Souana K, Taïbi K, Leila AA, Amirat M, Achir M, Boussaid M, Mulet JM (2020) Salt-tolerance in Vicia faba L. is mitigated by the capacity of salicylic acid to improve photosynthesis and antioxidant response. Sci Hortic 273:109641 Srviastava RP, Singh SP, Lal K, Singh SB (2003) Quantitative and qualitative losses in different maturity groups of the sugarcane crop under salt affected soil. Abstracts: 2nd international Cong of plant physiology, Jan 8–12, New Delhi, India, p 188 - c R, Kneževi´c D Stojšin MM, Petrovi´c S, Banjac B, Zeˇcevi´c V, Nikoli´c SR, Majstorovi´c H, Ðordevi´ (2022) Assessment of genotype stress tolerance as an effective way to sustain wheat production under salinity stress conditions. Sustainability 14(12):1–19 Turner NC, Colmer TD, Quealy J, Pushpavalli R, Krishnamurthy L, Kaur J, Singh G, Siddique KHM, Vadez V (2013) Salinity tolerance and ion accumulation in chickpea (Cicer arietinum L.) subjected to salt stress. Plant Soil 365(1–2):347–361 Wahid A, Ghazanfar A (2006) Possible involvement of some secondary metabolites in salt tolerance of sugarcane. J Plant Physiol 163:723–730 Wahid A, Rao RA, Rasul E (1997) Identification of salt tolerance traits in sugarcane lines. Field Crops Res 54:9–17 Wang H, Liang L, Liu S, An T, Fang Y, Xu B, Zhang S, Deng X, Palta JA, Siddique KHM, Chen Y (2020) Maize genotypes with deep root systems tolerate salt stress better than those with shallow root systems during early growth. J Agron 206(6):711–721 Warschefsky E, Penmetsa RV, Cook DR, Von Wettberg EJB (2014) Back to the wilds: tapping evolutionary adaptations for resilient crops through systematic hybridization with crop wild relatives. Am J Bot 101:1791–1800 Wu G, Peterson AJ, Morris CF, Murphy KM (2016) Quinoa seed quality response to sodium chloride and sodium sulfate salinity. Front Plant Sci 7(790):1–8 Yang YW, Newton RJ, Miller RF (1990) Salinity tolerance in sorghum. I whole plant response to dodium chloride in S.bicolor and S. halepense. Crop-Sci 30(4):775–781 Zahra N, Raza ZA, Mahmood S (2020) Effect of salinity stress on various growth and physiological attributes of two contrasting maize genotypes. Art-Agric, Agribusiness Biotechnol 63:1–11 Zavareh M, Mazaher D, Chaichi RM (2003) Effects of different levels of water salinity (seawater) on germination characteristics of rapeseed (Brassica napus L.) and brown mustard (B. Juncea Czem. And Coss) Genotypes. Abstract: 2nd international Cong of plant physiology, Jan 8–12, New Delhi, India, p 257 Zenoff AM, Hilal M, Galo M, Moreno H (1994) Changes in root lipid composition and inhibition of the extrusion of protons during salt stress in two genotypes of soybean resistant or susceptible to stress. Varietal differences. Plant Cell Physiol 35:729–735

Chapter 6

Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

6.1 Introduction The deficiency of arable land as a result of salinization represents an important challenge to provide an adequate supply of food in light of the growing population. Therefore, there is an urgent necessity to cultivate varieties of crops that are capable of tolerating high levels of salinity and produce acceptable yield levels under salinity conditions. Producing new recombinant lines falling outside parental range or exceeding F1 was important. Numerous genetic analyses models were conducted to estimate the nature of gene action and heritability of them Cavalli (1952); Falconer (1993); Hayman (1954, 1958); Jinks and Jones (1958); Kempthorne (1957); Kearsey and Pooni (1996); Mather and Jinks (1982); and Warner (1952). However, since salinity tolerance is a quantitative trait governed by multi genes, endeavors to adopt some methods that use both classical and novel strategies to improve salt tolerance are of interest. Understanding the genetic base of salinity tolerance in field crops is one of the essential issues that must be known before beginning the implementation of the breeding program. The effective breeding program relies on genetic variability, the nature of the gene action, heritability, genetic advance and response to selection controlling the inheritance of salinity tolerance. In this respect, eighteen TaSOS1 genes were detected as associated with salinity tolerance in bread wheat (Jiang et al. (2021), five genes in rice (Nayak et al. 2021), three genes in spring barley (Saade et al. 2020), six genes in sorghum (Wang et al. (2020), seven locus in faba bean (Asif and Paull 2021), six genes in canola (Gharelo et al. (2016) and Twenty-eight genes conferred salt tolerance in Atriplex canescens using qRT-PCR (Gang et al. 2017). According to Hu et al. (2012) and Souleymane et al. (2017) salt tolerance is a quantitative inherited character, which is governed by multiple genes, with additive and dominant effects, the former playing a major role. These genetic parameters could have important implications for the quantitative genetics and development of salt-tolerant cultivars in field crops (Omrani et al. 2022). © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_6

223

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6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

These genetic parameters are of great importance in choosing the appropriate breeding method. The purpose of the present chapter is to identify genetic peculiarities for salt tolerance in crops genotypes. Hence forward, the following is an explanation of the genetic behavior controlling the inheritance of salinity tolerance and related traits in field crops.

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants 6.2.1 Wheat Early studies on hereditary behavior indicated that, when the salinity-resistant genes of Agropyron elongatum were transferred to Chinese Spring bread wheat cultivar by hybridization, genetic analysis of the resulting offspring showed that the effects of salinity resistance of A. elongatum on Chinese Spring bread wheat cultivar are governed by interacting genes on different chromosomes (Dvorak et al. 1988). Potassium and sodium content of the leaf and potassium: sodium ratio is governed by genes located on the long arm of the chromosome 4D (Gorham and Jones 1990). The inheritance of the leaf juice content of potassium K+ , Na+ , chloride Cl− , yield and its components were subjected to known genes under the genetic control system. Estimates of the heritability coefficient in the narrow sense were 70 and 95% for the ionic content and 75 and 86% for grain weight/plant in the second and third generations, respectively, and that salinity-tolerant strains with high yields could be obtained by traditional breeding and progeny testing (Ahsan et al. 1996). Dominance gene action played a role in the inheritance of proline content in the leaves of the families in five crosses in the 3rd generation. And heritability in the broad sense ranged from 53.1 to 64.4% and in the narrow sense from 28.8 to 46.4% indicating the complexity of inheritance of the trait (Hassan 2002). Through genetic analysis of yields and its components by cross-breeding 10 cultivars of bread wheat differed in their tolerances to salinity and evaluation the parents, F1 and F2 generations under normal soil (ECe = 1.04 dS m−1 ) and saline soil field (ECe = 6.4 dS m−1 ). Dhayal et al. (2003) found that the additive-dominance genetic model is appropriate to explain the inheritance of earliness traits, plant height, number of spikes, spike grain weight, 1000-grain weight and plant grain yield. The effect of gene action varied from stress to normal conditions due to the influence of environmental conditions, the interaction between genotype × environment and masking genetic variations under stress conditions. The effects of the additive and dominance gene action were significant, but the estimates of dominance were important, indicating the prominence of over-dominance in the inheritance of these traits. The estimates of the heritability in the narrow sense were high for earliness traits, plant height and 1000-grain weight, and moderate for the number of spikes/plant and grain yield under normal and salinity conditions in the F1 and F2 generations.

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants

225

Al-Ashkar et al. (2019) detect salt tolerance variation in 15 wheat lines developed by doubled haploid (DHL) technique, which compared with the salt-tolerant check cultivar Sakha 93. Salinity stress was studied at three levels of salinity (0, 100, and 200 mM NaCl) for 25 days. The broad sense heritability were high valued (>60.0%) for root number, root length, root dry weight, shoot length, shoot dry weight, specific root length, relative water content, membrane stability index, and catalase, and varied from 62.71% for root length to 93.27% for shoot length. The ratio of PCV to GCV was approximately equal for most traits. However, the genotypic variance was smaller than the phenotypic one for all traits. Genetic gain ranged from 22.06% for relative water content to 48.00% for peroxidase activity. Under soil salinity of ECe 2.26 dS m−1 on test depth from 0 to 15 cm and 2.03 dS m−1 on test depth from 15 to 30 cm, Nassar et al. (2020) carried out an experiment at Toshka Agricultural Experiment Station of Desert Research Center, Aswan governorate, Egypt. The results revealed that the additive component exceeded the dominance portion for yield traits, which indicates to the efficiency of selection procedures in the early generations. Both additive and dominance components played a vital role in governing grain yield and its relevant traits in the F3 families for most deliberated traits in the five crosses. Whereas, narrow sense heritability estimates were relatively moderate to high for the five crosses, fluctuating from 50.33% for days to maturity in cross 3 to 98.60% for days to heading in the cross 2. The broad sense heritability in all crosses varied from 57.48% for days to maturity in the cross 3 to 98.64% for days to heading in the cross 3 representatives that the additive gene action may be accounted the most of part of the genetic variation in the F3 generation of most crosses. Days to heading, plant height, no. of spikes/plant, no. of spikelets/ spike and grain yield/plant displayed the maximum assessments of heritability and showed that additive component played a significant role in the inheritance of these traits. Meanwhile, the expected genetic advance values ranged from 1.01 for 100kernel weight in cross 2 to 20.95 for plant height in cross 5. Most of traits had moderate to high estimates of genetic advance. Thus, selection in segregating generations for days to heading, plant height and no. of grains/spike would be operative in realizing earlier genotypes in heading with higher grain yield than their corresponding parents. Moustafa et al. (2021) computed genetic parameters viz. broad-sense heritability (h2 b ) and response to selection (Rs) for three advanced generations; F6, F7 and F8 (Table 6.1). The results indicated that broad-sense heritability values were high for days to heading, 1000-grain weight and number of grains/spike. While, being moderate for grain yield and biological yield in the three generations under saline conditions. Jiang et al. (2021) identified the TaSOS1 gene in response to salt stress in two bread wheat genotypes i.e. Seri M82 as salt-sensitive and CIGM90.863 as salt-tolerant. They detected a higher expression of most of the eighteen TaSOS1 genes in the roots of salt-tolerant seedlings cultivar CIGM90.863 than the salt-sensitive cultivar Seri M82. Omrani et al. (2022) consider the quantitative genetic basis of agronomical traits i.e. days to heading, days to pollination, days to maturity, plant height, peduncle length, single grain weight, number of spikes per plant, number of grains per spike, grain yield per plant and physiological traits i.e. Na+ and K+ concentration, relative

226

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

Table 6.1 Genetic parameters for earliness and yield traits in the advanced bread wheat lines (Moustafa et al. 2021) Generation

Parameter

Days to heading

Number of grains/spike

1000-grain weight (g)

F6

h2 b

0.90

0.79

0.81

Rs

4.22

3.58

2.59

h2 b

0.92

0.81

0.84

0.69

Rs

0.71

0.35

0.30

26.99

h2 b

0.92

0.82

0.84

0.69

0.72

Rs

0.66

0.33

0.26

17.95

79.22

F7 F8

Grain yield (kg/ha) 0.67 667.7

Biological yield (kg/ha) 0.70 943.0 0.71 104.5

h2 b , heritability in broad sense and Rs, response to selection

water content, leaf chlorophyll and carotenoid concentrations related traits of salinity using seven generations (P1 , P2 , F1 , F2 , F3 , BC1 , and BC2 ) of wheat grown in the field under normal and saline conditions. The six-parameter genetic model was adequate to explain the inheritance of the traits. The epistatic gene effects were crucial, also additive and dominant gene actions were found to be controlled plant height, K/Na, and grain yield in salinity stress environments. Under saline conditions, the highest heritability was detected for total chlorophyll, carotenoid, SPAD chlorophyll and K/ Na ratio. The additive genetic component was more important than the dominance one for grain weight, K+ and K+ /Na+ under salinity conditions.

6.2.2 Barley After 10 days of incubation in 250 mM sodium chloride solution at germination stage in the parents and their F1 crosses, dominant gene action played the foremost role in the genetics of plumela length; the inheritance of plumela length is governed by over-dominant genes with a relatively high heritability in a broad and narrow sense (Mano and Takeda 1997a, b). Under two salinity levels, one of which is low (EC for soil = 7.84 and EC for irrigation water 8.23 dS m−1 ) and the other is high (EC for soil = 13.68 and EC for irrigation water = 12.65 dS m−1 ). Afiah et al. (2001) revealed that estimates of heritability coefficient decreased with increasing salinity stress from 80% under a low salinity level to 78% under a high salinity level in six-row barley lines and from 67% under a low salinity level to 61% under high salinity level for two-row barley lines. While, Singh (2004) got a low heritability estimate (28%) of the barley grain yield under saline conditions. The importance of additive and additive × additive gene action in controlling 1000-grain weight and proline content under salinity stress was noticed by ElMouhamady et al. (2012). Whereas, additive gene action was found to be controlled the inheritance of terhalose content in the crosses Giza 123 × Giza 124 and Giza

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants

227

2000 × Giza 124 under normal and salinity conditions. The cross combination Giza 2000 × Giza 124 showed significant positive heterosis over better parent for glycine betaine and grain yield/fed., emphasizing their importance as a good combiners for salinity tolerance in barley breeding programs. Moreover, Mansour and Moustafa (2016) under normal and salinity conditions, registered more contribution of the dominance gene action in the inheritance of plant height, spike length, number of spikes/plant, number of grains/spike, grain weight/ spike, 100-grain weight and grain yield/plant compared to the additive one. Narrow sense heritability estimates varied from one environment to another, it fluctuated from low (4.62%) for 100-grain weight to moderate (31.96%) for number of spikes/ plant. Saade et al. (2016) identified wild allele at the HvELF3 locus in barley causes earlier flowering and maturity under both control and saline environments and improves harvest index. The promoting effect of the wild allele on flowering under saline conditions is more pronounced than it is under control environment. In an advanced study, Saade et al. (2020) identified several loci associated with yield components associated with salinity tolerance, three regions containing known flowering genes (Vrn-H3, Vrn-H1 and HvNAM-1) were responsive to salinity stress, locus (7H) associated with a number of grains per ear, and a gene encoding a vacuolar H+ translocating pyrophosphatase HVP1, a new QTL on chromosome 3H was significant for a number of ears per plant, and a locus on chromosome 2H, previously recognized related to a yield component and acted with salinity stress. Furthermore, cell membrane stability index is a quantitative and moderately heritable trait that is highly genetically related to grain yield (Hemantaranjan 2014). PourAboughadareh et al. (2021) measured 10 traits including stomatal conductance, Root K+ content, cell membrane stability index, shoot K+ content, relative water content, stomatal conductance, and root Na+ content. The broad-sense heritability (h2 ) ranged from 0.56 for root K+ content to 0.92 in shoot Na+ content. High values of heritability were estimated for all traits, advising a strong possibility of selection gains for the measured traits. Among the selected traits, root Na+ content, shoot Na+ content, and root K+ content showed the highest genetic gains valued 19.60%, 10.60%, and 6.92%, respectively. However, only the cell membrane stability index exhibited an undesirable selection gain (−2.81%).

6.2.3 Rice By studying the genetic behavior of salinity resistance in rice through estimating root growth in 80 mM solution of NaCl in the F1 and F2 generation and backcrosses in two crosses, Jones and Stenhouse (1984) explained the importance of additive genetic variation in the inheritance of salinity resistance in one cross and the dominance in the second one, and transgressive segregations appeared in favor of the resistance. Estimates of the heritability in a broad sense ranged from 49 to 83%. The results

228

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

of the F2 generation indicated the presence of a few number of genes that control salinity resistance in the studied hybrids. Dominance gene action played a major role in the inheritance of potassium content, but the estimates of the heritability in narrow sense were greater than 50% (Sayed-Ahmed et al. 1999). While, the non-simple genetic model and the superiority of the complementary and duplicate types of interaction controlled the inheritance of the sodium: potassium ratio, yield and its contributions in eight crosses among six cultivars of varying tolerance to salinity (Thirumeni et al. 2000). The additive gene action was more important in inheriting of osmosis adjustment and chlorophyll content under salinity conditions, while the non-additive gene action played the main role in inheriting the ability to absorb sodium and potassium (Shehata 2004). On 120 F3 lines derived from F2 individual plants evaluated along with their parents in farmer’s field affected by the salt problem by Souleymane et al. (2017). They recorded significant additive gene action in controlling tiller number, panicle number and panicle weight. Partial dominance effect was noticed in plant height and duration. The additive maternal effect was registered for duration and plant height. Therefore, to improve the duration and plant height under salinity stress the offspring must have a salt-tolerant female parent. Whereas, Razzaque et al. (2019) detected 18 differentially expressed genes among tolerant and sensitive rice genotypes at 72 h of stress. Two of those 18 genes were upregulated in sensitive genotypes and 16 in tolerant genotypes. In sensitive genotypes, upregulated genes were interrelated with development, RNA binding, regulation of gene expression, epigenetics and further functions. Finally, Nayak et al. (2021) detected five candidate genes associated with salinity tolerance by composite interval mapping on four chromosomes 2B, 6B, 7B, and 9B. The additive genetic effects of individual QTL varied from −0.07 to 0.63. Genetic analysis showed that the dominance effect was more important than the additive one as (d/a) whichever was greater than 0.5 or lesser than −0.5.

6.2.4 Maize Maize plant is characterized by its polymorphism and enormous genetic variability due to the cross-pollinating nature of the crop. Initial studies indicated the presence of at least two major genes responsible for salinity tolerance of maize under conditions of saline-sodic soils (Nordquist et al. 1992). Genetic analysis of the F2 generation plants resulting from crosses of parents with different betaine content showed that the lack of betaine content in the 1506 inbred maize lines is due to a single recessive nuclear gene (Rhodes and Rich 1987). Evaluating 10,000 seedlings of the variety Akber at the salinity level of 80 mM NaCl, was performed by Rao and McNeilly (1999). Eighteen seedlings showed viability and their offspring were characterized by high salinity tolerance. The importance of both additive and non-additive gene action in the inheritance of salinity

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants

229

tolerance was revealed at the seedling stage of 10 days age. The values of heritability coefficient in broad and narrow senses were 70% and 40%, respectively. When screening the response of root growth of seedlings of 100 maize genotypes 10-day-old under the concentrations of zero, 60, 80, 150 mM of NaCl, the estimates of heritability in the broad sense were high for actual and relative root length, indicating the possibility of improving maize tolerance to salinity through breeding and selection programs (Khan et al. 2003). In another direction, Aslam et al. (2015) crossed six promising maize lines as parents in full diallel mating design. Resultantly, 30 F1 s were produced and tasted under saline environments. Mean squares owing to general combining ability, specific combining ability and reciprocal effects were highly significant for all the traits. Root length, shoot length, Na+ and K+ ion contents were controlled by the non-additive type of gene action while, leaf area was controlled by additive gene action. The cross Q67 × L7-2 showed the highest level of adaptability concerning SCA effects under saline conditions. Collado et al. (2019) evaluated six generation means (P1, P2, F1, F2, BC1 and BC2) during the osmotic phase of saline stress at 100 mM NaCl in maize seedlings. Three lines differed in their behavior in salt stress: SC2 (tolerant), AFE (sensitive) and LP3 (moderately tolerant) were crossed to produce different crosses (SC2 × AFE) and (SC2 × LP3). In none of the traits studied, there was evidence of adequacy to the three-parameter model, indicating important epistatic effects in genetic expression. The dominant gene effects were greater than the additive ones for all the characters i.e. leaf growth, root length, shoot dry mass, total dry mass, relative water content, leaf water loss and cell membrane stability. The dominance gene effect [h] was positive and significant in controlling the inheritance of leaf growth in both crosses, showing the presence of hybrid vigor. In the cross SC2 × LP3, the negative interaction of dominance x dominance [l] approves ambidirectional dominance, whereas for SC2 × LP3, a positive sign indicates directional dominance. The analysis of tolerance to salinity in the osmotic phase showed a complex polygenic inheritance for the traits. Narrow-sense heritability was high for root dry mass, and leaf water loss, moderate to high for leaf length, leaf growth and shoot dry mass, and low for total dry mass and root length.

6.2.5 Sorghum Genetic studies showed that resistance to salinity is inherited from the parental genotypes and is controlled by many non-allelic or over-dominant genes. When evaluating six hybrids of sorghum under salinity level of 100 and 150 mM of NaCl solution, a significant hybrid vigor was detected compared to the mid-parents as a result of the interaction of additive and non-additive genes, and hybrid vigor appeared compared to the best parent attributed to the influence of the over-dominance genes (Azhar et al. 1998). General combining ability effects were negative and significant for the salinity sensitivity index of grain yield for the parental genotypes, ICSA-37 and ICSR-91022,

230

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

referring to their tolerance and ability to produce hybrids more tolerant to salt stress. While, the effects of specific combining ability were negative and significant for the salinity sensitivity index in the hybrid ICSA-1 × ICSR-91022. This indicates the possibility of exploiting the phenomenon of hybrid vigor to produce hybrids more tolerant to salt in sorghum (El-Menshawi et al. 2003). Furthermore, Wang et al. (2020) detected six genes, namely qTB6, qSFW9, qJW9, qBrix2, qBrix10 and qSTIBrix9, were governed by salt tolerance. A positive QTL additive value showed that the allele was from sorghum genotype Shihong 137, but a negative QTL additive value revealed that allele was from L-Tian.

6.2.6 Faba Bean Estimating heritability in broad sense of some traits associated with salinity tolerance was computed in faba bean. Darwish et al. (2003) recorded high heritability (76%) for number of emerged seedlings 21-day-old and moderate (35%) under the high salinity level, while the estimate of the heritability coefficient was low (24%) for the number of plants able to survive until harvest at the moderate soil salinity level (from 2.5 to 3.45 mmhos/cm). At Nubaria, Egypt, under soil salinity stress, high heritability values for plant height, number of branches/plant, number of pods/plant, number of seeds/plant, 100seed weight and seed yield/plant were recorded by El-Sayed et al. (2020). Added that the expected genetic advance from selecting the top 5% of the characteristics was high except for plant height in the second season (18.5 cm) and No. of branches/plant in the first one (9.2). High heritability estimates accompanied by high genetic advance for yield traits showed an additive gene action in its inheritance. Likewise, Asif and Paull (2021) identified multiple trait loci for leaf ionic concentration (Na+ , K+ and Cl− ) under both normal and salinity treatments in a recombinant inbred line population of faba bean. of these, seven loci were detected under salt stress, comprising three for leaf K+ : Na+ and one each for Na+ accumulation, K+ accumulation, Cl− accumulation and Na+ : K+ .

6.2.7 Cowpea Previous studies on cowpea from the point of view properties and effect of NaClsalinity on its activation through seed germination and seedling establishment indicated that tolerance abiotic stress is restricted by the polygenic inheritance. A total of 234 Multi-Parent advanced generation inter-cross (MAGIC) lines with their 8 parents for salinity tolerance were tested in greenhouse environments by Ravelombola et al. (2022). They found that epistatic interaction analysis was detected for salt tolerance. A total of 6 annotated genes were found in controlling salinity tolerance. The broad sense heritability was 74.2% for the average number of dead plants per pot; 78.9%

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants

231

for leaf SPAD chlorophyll; 63.6% for relative tolerance index of SPAD chlorophyll; 61.3% for fresh leaf biomass; 64.1% for relative tolerance index of fresh leaf biomass; 61.5% for relative tolerance index of total above-ground fresh biomass as well as 67.2% for relative tolerance index of plant height of cowpea plants grown under salt treatment. Further, Kang et al. (2023) detected 245 annotated genes includeing various genes related to salinity stress in cowpea, for instance, late embryogenesis abundant protein 4–5 and potassium transporter 6.

6.2.8 Soybean Genetic studies showed that the ability to regulate chloride ion uptake in soybean is determined by an individual gene (Abel and Mackenzie, 1964). When crossing between soybean cultivars differed in chloride ion exclusion and estimation of salinity in the form of leaf necrosis and chloride content in leaves, Guan et al. (2014) showed that the segregation results showed the presence of a single dominant gene Ncl that controls the ability to exclude chloride ion. Whereas, Lee et al. (2004) performed genetic analysis of salinity tolerance in strains F2:5 of the hybrid between salt-tolerant S-100 × salt-sensitive Tokyo variety. They displayed variation in the heritability estimates for salinity tolerance from 48% under greenhouse conditions to 85% under field conditions. Moreover, Do et al. (2019) identified a region of new genes on Chromosome 8 that was associated with four traits i.e. leaf scorch score, chlorophyll content ratio, leaf sodium content and leaf chloride content and predicted as salt tolerance in soybean. They recorded low broad-sense heritability 29% for leaf sodium content, whereas higher heritability was detected for leaf scorch score, chlorophyll content ratio and leaf chloride content valued 82%, 94% and 63%, respectively. The results display that the four traits are valid and important for salt tolerance and could be utilized in the selection for salinity tolerance.

6.2.9 Cotton Genetic analysis of salinity tolerance in cotton was investigated by estimating the germination percentage of seeds exposed to 1% NaCl solution. Results showed the importance of additive and non-additive gene action in the inheritance of tolerance (Ying Xin and Xiang Ming 1998). Five NaCl concentrations i.e. 0, 50, 75, 100 and 150 mM were tried on ten cotton genotypes. The estimates of broad-sense heritability for fresh shoot weight and fresh root weight characters ranged from 0.75 to 0.98. Thus, the improvement in salt tolerance in Upland cotton is potential by using variability throughout classical breeding approaches (Azhar and Ahmad 2000). Moreover, Khan et al. (2001) carried out a solution culture experimentation to survey the influence of salinity on 35 cotton

232

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

hybrids at two different levels i.e. 0 and 250 mm NaCl. Broad sense heritabilities valued 0.96 0.93; 0.98 0.96; 0.98 0.73 and 0.96 0.88 for fresh shoot length, fresh root length, fresh shoot weight and fresh root weight under control and salinity at 250 mM NaCl levels, respectively. Estimation of broad sense heritability for salt tolerance would be very useful in the early segregating generations for further progress in the cotton-breeding program for salinity tolerance. Moreover, Ashraf (2002) indicated that salinity tolerance for growth, yield and fiber traits are genetically based and most being QTL controlled. The significant additive component of variation could be utilized for breeding to release cotton genotypes more tolerant to salinity. Under Ras Sudr Agriculture Research Station of Egypt, Salem et al. (2006) computed scaling tests, gene effects and heritability at 2000 ppm for seed cotton yield/plant and boll weight as well as chemical constituents using six populations in six cotton crosses. They found significant non-allelic interactions for boll weight and seed cotton yield/plant in all crosses as given in Table 6.2, indicating the presence of epistasis. The additive gene effect (d) was the major type controlling the inheritance of boll weight in 1st and 2nd crosses. Thus, superior genotypes could be recognized from its phenotypic expression. Contrariwise, the interaction type of gene action additive × additive was positive and significant for seed cotton yield/ plant in 6th cross and boll weight in 4th and 6th crosses; while in the 3rd only, it was negative and significant. The dominance (h) and its digenic interaction type, dominance × dominance (1) were significant and involved in the inheritance of boll weight and seed cotton yield/plant in 6th cross only. The considerable amount of non-fixable gene action type may suggest that, improving these characters could be achieved through hybrid breeding method. Moreover, the interaction type additive × dominance (j) was negative and significant for boll weight in 1st and 3rd crosses and seed cotton yield/plant in 3rd one, showing more frequent of decreasing alleles over increasing ones. Narrow sense heritability (Tn) was varied from low to moderate for boll weight and seed cotton yield/plant in most studied crosses with a few exceptions, indicating great effect of environmental changes on the gene expression. Based on a framework of the genetic behaviour of chemical constituents in cotton leaves was completed by Salem et al. (2006). Results in Table 6.3 indicated significant non-allelic interaction for potassium concentration in 1st, 2nd, 4th and 5th crosses; magnesium concentration in 1st, 5th and 6th crosses, sodium concentration in 1st, 4th, 5th and 6th crosses and proline content in 1st, 2nd and 5th crosses. These results revealed the existence of epistasis and the simple genetic model was failed to ascertain the genetic variation for these characters in the corresponding crosses. The insignificance of non-allelic interaction was observed in potassium concentration in 3rd and 5th crosses; magnesium concentration in 2nd, 3rd and 4th crosses; sodium concentration in 2nd and 3rd crosses and proline content in 3rd, 4th and 6th ones. Hence, the simple additive-dominance genetic model proved to be satisfactory in explaining the inheritance of the foregoing characters. The additive gene effect (d) was the major type controlling the inheritance of potassium concentration in 2nd, 5th and 6th crosses; magnesium concentration in 1st, 3rd and 4th crosses; sodium concentration in the 2nd and 3rd crosses and proline content in 2nd, 3rd, 4th and 6th crosses. Meanwhile, the additive (d) and additive × additive (i) interaction type

8.40

2.40

8.90*

B

C

−15.90*

10.90

3.97*

−8.90*

−10.50*

−3.20

11.90

16.71

11.16

h

i

j

l

T(b)

T(n)

*

2.50

−3.60

d

6.29

12.13

5.20

−3.50*

−6.80

−11.0**

0.04

7.10**

11.70

17.22

14.20

4.30**

0.36

−3.70

2.80

12.15

17.15

0.98

0.63

2.20

2.01*

0.98

3.90**

−5.30*

−14.9** 6.60**

−2.20

−0.90

5

−11.6**

−2.90*

4

5.40

11.30** C

B

A

d

j

6.30

12.15

T(n)

T(b)

−50.90** l

2.90

34.20** i

30.90** h

0.50

4.30** m

−17.50**

6

3

42.20

46.40

−0.64

−0.66**

0.66

1.50**

4

1.90**

−1.19

2.10**

2.14

0.91*

0.42*

39.35

43.13

−0.56

21.17

26.56

1.40

26.83

31.39

0.44

0.37

0.19 −1.78** 0.47** −0.73**

0.88

0.78

−1.94**

0.14

1.80**

−1.27*

−0.80*

0.23** −0.55** −0.06 −0.63**

2

−0.61** −0.23** −0.30

2.10**

−0.68

0.91**

−0.67*

1

and **, indicate significant and highly significant at 0.05 and 0.01 probability levels, respectively

15.41

20.69

17.90

9.60

11.27**

m

Appropriate genetic model

4.30

−7.50**

8.40*

−2.60*

0.44

−3.90

3

A

2

Cross

1

Cross

Scaling test

Character Boll weight (g)

Character Seed cotton yield/plant (g)

6 0.14

1.70**

0.96

19.96

14.76

20.09

1.97* 24.96

0.22 −0.91*

1.80**

1.10* −0.30

−0.02

0.03

0.12

1.80**

−2.30**

0.76** −0.29

0.17

−0.11

5

Table 6.2 Scaling tests, gene effects and heritability for seed cotton yield/plant and boll weight using six populations in six cotton crosses at Ras Sudr agriculture research station during summer season of 2002 (Salem et al. (2006)

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants 233

234

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

were important in the inheritance of potassium concentration in 4th and 6th crosses and proline content in 5th one. Hereby, phenotypic selection was more effective for improving these characters for such crosses. The dominance (h) and its digenic interaction type, dominance × dominance (1) were significant and involved in the inheritance of potassium concentration in 4th cross and magnesium concentration in 6th cross; Sodium concentration in 5th cross and proline content in the 1st one. Thus improving these characters could be achieved through hybrid breeding method. Both additive and dominance gene effects were important in the inheritance of potassium concentration in 1st and 4th crosses and magnesium concentration in 6th cross. Thus, potassium concentration and magnesium concentration as salinity tolerance criteria could be improved simultaneously through crossing and selection (pedigree method) to make the utmost of the type of gene effects. Narrow sense heritability “Tn” was high (>50%) for potassium concentration in 5th cross and magnesium in 2nd one. Thus, progress in salt tolerance could be achieved through selection for both characters. While, “Tn” ranged from low to moderate for the other characters in the corresponding crosses. Salt stress conditions was implemented through irrigated fifty cotton genotypes with nutrient solution with an electrical conductivity of 10 dS m−1 and 15 dS m−1 at 10th-day seedlings stage to 40th day. Farooq et al. (2019) recorded high broad sense heritability for salinity tolerance traits i.e. sodium, potassium, potassium: sodium ratio, chlorophyll contents, root length, shoot length, root fresh weight and shoot fresh weigh. But phenotypic variance is equal or less than genotypic ones. The genotypes that performed better under salinity conditions that took high broad sense heritability were designated as salt tolerant one.

6.2.10 Canola By genotyping the canola diallel (8 × 8) for the traits related with salinity tolerance, the parents and their F1 crosses were exposed to increased levels of NaCl in Hoagland’s solution in sandy cultures until reaching an electrical conductivity of 12.9 dS m−1 . Rezai and Saeidi (2005) results showed the importance of both additive and non-additive gene action in inheriting shoot dry weight, root length, shoot content of sodium, potassium, calcium, ratio of K+ /Na+ , Ca2+ , Na+ , tolerance index and salinity tolerance index. High estimates of the heritability in narrow sense (>50%) were recorded for the content of Ca, K+ , Na+ , Ca2+ , K + /Na + and salinity tolerance index. Whereas, Marwede et al. (2004) recorded low estimates of the heritability for antioxidants ranging from 23 to 44% for α tocopherol and from 33 to 50% for γ tocopherol in different cases. This was attributed to the significant interaction between genotype x environment. Whereas, under the conditions of newly reclaimed salt-affected lands, Sharaan and Ghallab (2002) recorded heritability coefficients 16.06, 43.12 and 84.73% and expected genetic advance from selection 11.71, 12.40 and 3.71% for seed yield/ fed, seed index and seed oil content, respectively. In continuous and from another

6.13

3.80

18.00**

B

C

−0.98

−3.60

−0.79 29.29**

2.20

−1.39

−10.53*

−9.90

0.25

1.80

18.15

12.69

h

i

j

l

T(b)

T(n)

−0.79

−2.61

0.80

−1.57

−9.41**

B

C

2

−4.54**

1

A

Scaling test

0.94

−0.20

−2.46

3

−2.10 12.07**

−2.09

−7.40

−3.58

−5.48*

−6.08**

6

−5.32** −2.02

5

21.66

26.66

−1.84

−3.21

T(n)

T(b)

l

j

41.48

45.09

9.59*

−2.95

−5.20

−2.82

−6.40**

112.30**

51.75

54.73

−11.55

−4.10**

113.99**

1.29

−0.65

−2.66

45.43

67.36

4.25*

−0.49

102.19**

−5.14

−1.06

−0.08

3

C

B

A

1

0.525

0.781*

0.162

2

−0.641

−0.195

−0.822*

−0.430

0.010

−0.548

3

Cross

4

64.74

80.09

h

−6.20** i

4.74

d

m

0.81

0.75

−5.14*

2

Cross

11.44

15.54

10.06

−6.70**

78.10**

C

B

A

1

Character Proline content (μ moles/gm. f.w)

32.23

46.42

20.29*

−27.91**

0.96**

74.81**

7.23**

0.81 14.24**

6

Character Sodium concentration (gm/100gm)

23.36

31.61

−20.52**

−5.54

−16.50**

d

−0.43

−5.9**

−4.80*

−5.30**

70.70**

76.60**

72.10**

11.75** −0.67

2.91

5

−5.17**

4

m

61.04**

−5.59

0.98

5.55**

Appropriate genetic model

1.23

2.78

4.38

3

A

2 0.45

0.374

0.140 −0.610

4

49.74

52.95

18.45

−3.96**

101.72**

−9.41

−2.26

4

Cross

1

Cross

Scaling test

Character Magnesium concentration (gm/100gm)

Character Potassium concentration (gm/100gm)

−3.57

4.44

5

−0.929

0.930*

0.525

7.91

13.68

1.61

0.44

6.40*

1.29

−2.40

104.20**

−14.41**

5

0.247

0.165

(continued)

−0.276

6

12.24

14.04

22.29**

−0.79

−8.60

−10.15*

−4.30*

108.80**

−5.09

−6.06*

−7.63**

6

Table 6.3 Scaling test, gene action and heritability for potassium concentration and magnesium concentration using six populations in six cotton crosses at Ras Sudr agriculture research station during summer season of 2002 (Salem et al. (2006)

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants 235

*

48.80

5.93

15.53

14.48

16.73 T(n)

T(b)

1.057**

16.36

26.84

−1.361*

−0.310

0.418

−1.779*

−0.115

and **, indicate significant and highly significant at 0.05 and 0.01 probability levels, respectively

20.63

19.02

11.85

T(n)

17.28

17.24

T(b)

69.87

l

3.11*

30.82

j

−0.75

1.73 12.90** −0.73

0.38 15.40*

−1.49

l

i

h

j

6.40*

3.91

−5.40

0.02 −4.00

−12.79

−14.32

i

d

m

3.00

5.12

h

43.50**

−8.23*

45.3** −0.20

2.40

48.50**

12.50

23.91

1.394*

−0.314

−0.376

−1.489

−0.476*

1.228**

34.13

46.29

−0.555

0.243**

1.241 2.297

0.117**

0.136

26.75

31.96

Character Magnesium concentration (gm/100gm)

1.70

d

45.93**

−1.07**

45.17**

−4.52**

46.50**

−1.00

m

Appropriate genetic model

Character Potassium concentration (gm/100gm)

Table 6.3 (continued)

14.41

26.66

−3.839*

−0.203

2.384*

−1.235

0.026

0.705**

27.03

33.84

2.694

0.041**

0.07

236 6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants

237

perspective, rapeseed germplasm of 82 entries was tested under both normal and salt-affected newly reclaimed soils in two adjacent fields at the experimental farm of the Faculty of Agriculture at Fayoum. Ghallab and Sharaan (2002) showed that the genetic variance to environmental variance (Vg /Ve ) and genetic coefficient of variation/ phenotypic coefficient of variation (GCV/PCV) ratios as well as heritability h2 and genetic advance GA estimates were higher under normal soil conditions than those of saline soil for most studied traits, indicating that environmental stress caused masking of the genetic effect. Furthermore, Saberi et al. (2023) evaluated line x tester analysis using five salinity-tolerant cultivars as lines and three salinity-sensitive cultivars as testers, under the normal experiment, irrigated with natural irrigation water (EC = 0.631 dS m–1 ), and under salinity stress (EC = 8.7 dS m–1 ). The GCA/SCA ratio was less than unity for the studied traits; this means that these traits are mainly controlled by non-additive gene action for plant height, pod length, number of seeds per pod, pods per plant, 1000-kernel weight, and grain yield per plant, days to 50% flowering and maturity and leaf relative water content. The values of broad heritability of traits varied among environments. The lowest value of narrow sense heritability for the trait 1000-kernel weight was 58.74%, while the highest value of narrow sense heritability was related to the grain yield (89.89%) under normal irrigation conditions. Heritability estimates decreased from normal to stress for number of days to flowering and seed yield valued 84.41 and 78.49; 89.89 and 87.43, respectively. Likewise, Kammoura et al. (2011) indicated that dominance (H1 & H2) genetic variances were highly significant in controlling seed yield/plant (Table 6.4). Therefore, the pedigree method could be exploited to improve seed yield. Whereas, additive genetic variance was the main component governing seed oil content. The covariance of additive and dominance gene effects in the parents as indicated by F value was positive and significant for seed yield/plant, revealing that the decreasing alleles were more frequent than increasing one in the parental population, but did not reach the significance level for seed oil content. The environmental value was significant for both characters, reinforcing the influence of environmental conditions on both characters. The proportion of genes with positive and negative effects among the parents (H2 /4H1 ) was less than its maximum value (0.25), indicating asymmetrical distribution of positive and negative alleles amongst the parental population. The proportion of dominance to recessive genes in the parents. The (KD/KD) was more than unity for seed yield/plant and seed oil content indicating an excess of dominant alleles than recessive ones in the parents. Narrow sense heritability was high (>50%) for the studied characters. Lee et al. (2008) stated that fifty-six genes that encode transcription factors in canola are altered under abiotic stresses. Furthermore, Gharelo et al. (2016) recognized six genes in salt-resistant canola cultivars, comprising malate dehydrogenase, heat shock protein 70, triose phosphate isomerase, fructose-bisphosphate aldolase, UDP-glucose dehydrogenase and methionine synthase under salt stress conditions.

238

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

Table 6.4 Components of genetic variance and their derived parameters for seed yield/plant and seed oil content (%) using 6 × 6 diallel crosses of canola in F1 generation (Kammoura et al. 2011)

Genetic parameters Seed yield/plant (g) Seed oil content (%) D

1.165**

5.555**

H1

0.846**

1.115

H2

0.756**

0.656

F

0.323**

0.042

h2

0.591

−0.208

E

0.015**

0.792**

0.852**

0.448

H1 /D

0.223**

0.147

H2 /4H1

1.824

4.943

KD/KR

69.5

75.74

Derived parameters

T(n) ** ,

indicate highly significant at 0.01 probability level

Sugar Cane The complexity and polygenic nature of salinity tolerance have seriously limited the efforts to develop the tolerant crop variety through conventional breeding practices (Jain 2000; Zhambrano et al. 2003). Ferreira et al. (2010) recorded high heritability values for sucrose, fiber content and production variables, showing a prevalence of the genetic component instead of the environmental constituent. Abo-Elwafa et al. (2021) recorded heritability in agronomic characters varied from 50.39 (stalk diameter) to 98.46% (cane yield) and in technological characters ranged from 73.02 (purity) to 98.78% (sugar yield) above both ratoon crops. Significant variances joined with GCV, PCV and heritability values described the variances between the somaclones. Whereas, Rao et al. (2015) identified 137 sugarcane salt-tolerant candidate cDNAs by cDNA-SSH, of which 20% represent novel sugarcane genes.

Sugar Beet Estimation of genetic variance components, combining ability and heritability has been estimated by Abbasi et al. (2019) using 24 physiological and root yield and quality-related characters by growing the crosses and their 14 parents under normal and salinity stress environments in the field. The dominance genetic variance was the prevailed type controlling root, sugar and white sugar yield than the additive one in both growing environments, with the prevailed type of the dominance variance under saline conditions. Narrow-sense heritability was higher in stress environments for physiological characters compared to those of normal ones and the reverse held true for the yield characters. Both general combining ability and specific combining ability were found to be important for the performance of individual cross combinations, and

6.2 Genetic Behavior of Salinity Tolerance in Crop Plants

239

no clear association between GCA and SCA was detected for sugar beet genotypes. Based on higher impact of dominance variance and the lower narrow sense heritability of sugar yield under saline environments rather than normal conditions, hereby hybrid breeding approach would be more preferred under saline environments than normal conditions. Furthermore, Geng et al. (2019) identified 1714 differentially expressed genes in the leaves of the salt-sensitive genotype, and 2912 in the salt-tolerant one. Several of the differentially expressed genes controlling stress and defense mechanisms, metabolic processes, signal transduction, transport processes, and cell wall synthesis have been identified. Furthermore, expression patterns of several genes varied between the two cultivars in reaction to salt stress.

Alfalfa Seven genes have been identified in alfalfa cultivars, which are responsible for the production of proteins associated with salinity resistance i.e. rbcS, psbD, psaB, atpB, rbcL, pCab4, and pCabl (Winicov and Button 1991). Heritability estimates for salinity resistance in the form of the percentage of germination reached 50% in alfalfa (About: Singh 2004). Several genes involved in salt tolerance were isolated and characterized in alfalfa, including TFs (Chen et al. 2012; Winicov and Bastola 1999). Also, four genes i.e. SOS1, SOS2, SOS3 and CDPK7 are well-known to play important roles in Na efflux from root to soil in alfalfa genotypes as salt-response by Sandhu et al. (2017), and several another genes associated with the biosynthesis of metabolites in the response to salt stress (Lai et al. 2014; Palma et al. 2013). Whereas, Lei et al. (2018) performed RNA-seq analysis and discovered 2237 and 1125 differentially expressed genes between ZM and XJ alfalfa varieties in the existence and absence of salt stress, among them many genes are associated with salt stress-related pathways. After salt treatment, in comparison with the controls, the number of genes in cultivar XJ (19373) was around four times than in cultivar ZM (4833). Under salt stress, ZM compared with XJ, preserved fairly more stable expression levels of genes linked to the ROS and Ca2+ pathways, phytohormone biosynthesis and Na+ /K+ transport.

Quinoa Disomic and allotetraploid inheritance are the prevalence for almost qualitative characters in quinoa (Galwey and Risi, 1984; Ward 2000). Salinity tolerance in quinoa is inherited as a polygenic character (Flowers and Colmer 2008). Saglam (2017) evaluated salt tolerance in 94 genotypes of the mapping population, the two parents and variety Pasto of quinoa. Under salt tolerance, grain weight and harvest index appeared six and four QTLs i.e. (LG 1B, 6B, 7A, 10A, 11B, 17B) and (LG 1B, 10A, 11B, 18B), with the most operative QTLs were LG-1B and LG10A as well as LG 1B and 11B for grain weight and harvest index, respectively. Heritability in broad sense

240

6 Genetic Analysis of Salinity Tolerance and Relevant Traits in Field Crops

was 73.65% and 65.38% for grain weight and harvest index, respectively. Six QTLs were detected (LG 1B, 2A, 7A, 11B, 14A and 18B) and the most related QTLs were LG 1B and 14A for 1000-seed weights, with heritability value 64.83%. Moreover, plant length, exhibited 7 QTLs for the salt treatment (LG 1B, 2A, 3B, 4A, 7A, 17B, 18B), the most operative QTLs were LG 1B and 4A, with heritability value 55.72%. Whereas, stomatal conductance attained 3 QTLs located in the linkage groups of LG 3B, 10B and 11B and the strongest effect was observed in LG 10b with low heritability in a broad sense (10.53%).

Atriplex Twenty-eight genes conferred salt tolerance in Atriplex canescens using qRT-PCR were identified by Gang et al. (2017). Most of the selected genes (28 genes) could be induced by salt treatment at an early time point (6 h, 12 h). Furthermore, Guo et al. (2019) recognized five genes play important roles in Na+ sequestration in salt bladders of A. canescens. They also identified 2, 2 and 9 genes responsible of accumulating proline, betaine and soluble sugar, respectively, showed a significant increase in leaves at 100 mM NaCl treatment of both 6 and 24 h. Also, 12 genes appeared to have upregulated expression in leaves however were downregulated in the roots at 100 mM NaCl for 6 h. To sum up, these results clearly indicate the importance of the aforementioned genetic information and genetic behavior in choosing the appropriate breeding program to produce novel, more salt-tolerant cultivars in the light of the threats of climate change.

6.3 Conclusion Previous studies showed the importance of identifying the genetic system, controlling salinity resistance as well as its associated traits in crop genotypes. This is useful in determining the appropriate breeding method and the outcomes of the breeding programs, and then we can focus on the following points: 1. To draw the appropriate breeding technique, the breeding programs aimed to estimate the type and magnitude of genetic components and genes involved in morpho-physiological, biochemical, yield components and quality traits during segregating generations. 2. Heritability refers to the additive sum of all genetic effects on a trait in a population. Hence, a heritability of (≥50%) suggests that genes contribute more to trait variance in the population than does a heritability of (≤30%). In the context of the previous presentation, types of gene action, heritability and genetic advance from selections are better tools to select suitable breeding system in order to improve salinity tolerance in crop plants.

References

241

3. Different types of gene action i.e. additive, dominance and epistasis have been found to be controlled the salinity tolerance traits.

6.4 Recommendations From the presented results in this chapter, we could recommend the following: 1. Heritability provides information on the transmissibility of genes controlling traits from one generation to another and could help plant breeders to predict the interaction between genes to improve salinity tolerance in the genetic makeup. Therefore, it is important to appreciate it. 2. Careful selection leads to improvement in next generation of selection between the promising genotypes. 3. Based on the types of gene action controlling the inheritance of traits related to salinity tolerance, the appropriate breeding method is followed to produce promising recombinations of the superior alleles at different loci.

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Moustafa ES, Ali M, Kamara MM, Awad MF, Hassanin AA, Mansour E (2021) Field screening of wheat advanced lines for salinity tolerance. Agronomy 11(2):281 Nassar SMA, Moustafa ESA, Farag HIA (2020) Selection for earliness, yield and its components in bread wheat. Egypt J Plant Breed 24(1):81–97 Nayak S, Bhandari H, Pantalone V, Saha MC, Ali S, Sams C (2021) Genomic regions associated with salinity tolerance in lowland switchgrass. Crop Sci 61:4022–4037 Nordquist PT, Hergert GW, Skates BA, Compton WA, Markwell JP (1992) Phenotypic expression of different maize hybrid genotypes grown on saline-sodic soil. J Plant Nutr (USA) 15(10):2137– 2144 Omrani S, Arzani A, Moghaddam ME, Mahlooji M (2022) Genetic analysis of salinity tolerance in wheat (Triticum aestivum L.). PLoS One 17(3):e0265520 Palma F, Tejera NA, Lluch C (2013) Nodule carbohydrate metabolism and polyols involvement in the response of medicago sativato salt stress. Environ Exp Bot 85:43–49 Pour-Aboughadareh A, Sanjani S, Nikkhah-Chamanabad H, Mehrvar MR, Asadi A, Amini A (2021) Identifcation of salt-tolerant barley genotypes using multiple-traits index and yield performance at the early growth and maturity stages. Bull Natl Res Cent 45(117):1–16 Rao VP, Sengar RS, Singh S, Sharma V (2015) Molecular and metabolic perspectives of sugarcane under salinity stress pressure. Prog Agric 15(1):77–84 Rao SA, McNeilly T (1999) Genetic basis of variation for salinity tolerance in maize (Zea mays L.) Euphytica 108:145–150 Ravelombola W, Shi A, Huynh B-L, Qin J, Xiong H, Manley A, Dong L, Olaoye D, Bhattarai G, Zia B, Alshaya H, Alataw I (2022) Genetic architecture of salt tolerance in a multi-parent advanced generation inter-cross (MAGIC) cowpea population. BMC Genomics 23(100):1–22 Razzaque S, Sabrina ME, Taslima H, Biswas S, Jewel GMNA, Rahman S, Weng X, Abdelbagi MI, Walia H, Thomas EJ, Zeba IS (2019) Gene expression analysis associated with salt stress in a reciprocally crossed rice population. Sci Rep 9:8249 Rezai AM, Saeidi G (2005) Genetic analysis of salt tolerance in early growth stages of rapeseed (Brassica napus L.) genotypes. Indian J Genet 65(4):269–273 Rhodes D, Rich PJ (1987) Genetics of glycine betaine deficiency in Zea mays. Plant Physiol 83(4 Suppl.):7 Saade S, Brien C, Pailles Y, Berger B, Shahid M, Russell J, Waugh R, Negrão S, Tester M (2020) Dissecting new genetic components of salinity tolerance in two-row spring barley at the vegetative and reproductive stages. PLoS ONE 15(7):e0236037 Saade S, Maurer A, Shahid M, Oakey H, Sandra MS, Sónia N, Pillen K, Tester M (2016) Yieldrelated salinity tolerance traits identified in a nested association mapping (NAM) population of wild barley. Sci Rep 6:Article number: 32586 Saberi AA, Ravari SZ, Mehrban A, Ganjali HR, Oghan HA (2023) Genetic analysis of important traits of rapeseed under normal and salinity stress conditions. Res Square 1–17 Saglam S (2017) Evaluation of salt tolerance in a mapping population of quinoa. Major thesis report, plant sciences—plant breeding and genetic resources, laboratory of plant breeding. Wageningen University & Research 6709 PB, Wageningen, The Netherlands Salem AH, Awaad HA, Hassan AIA, Moustafa ESA (2006) Genetic analysis of yield, yield components and some chemical constituents in six egyptian cotton crosses (Gossypium barbadense L.) under ras-sudr conditions. Zagazig J of Agric Res 33(1):1–26 Sandhu D, Cornacchione Monica V, Ferreira JFS, Suarez DL (2017) Variable salinity responses of 12 alfalfa genotypes and comparative expression analyses of salt-response genes. Sci Rep 7:1–18 Sayed-Ahmed M, Soliman SAA, Abd El-Maksoud AF (1999) A genetic approach to study some mineral contents in rice grains under salt and drought conditions. Zagazig J of Agric Res 26(6):1609–1623 Sharaan AN, Ghallab KH (2002) Selection in canola (Brassica napus L.) germplasm under conditions of newly reclaimed land. I. variability and genetic parameters in the base lines. Egypt J Plant Breed 6(2):1–13

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Chapter 7

Breeding Efforts and Biotechnology

7.1 Introduction Salinity is one of the prevalent problems in irrigated agriculture. Genetic improvement of salinity tolerance of the main crops is considered an essential goal in crop breeding programs. The process of discovering the salinity-resistant genotypes requires a screening process for the crop germplasm by exposing a large number of strains to salinity and selecting the best with the average performance. When determining the genotype or salt-tolerant genotype, the next step is to improve its crop characteristics by applying proper breeding methods. In general, any breeding program depends on the presence of a lot of genetic variability that allows the implementation of a breeding program on a good foundation. The breeding program also depends on determining the selection criteria related to salt tolerance based on the degree of correlation between salt tolerance and the relevant morphological, physiological, biochemical and production characteristics.. Selection for earliness, yield and its relevant in bread wheat was done for developing new varieties with ideal genetic makeup to raise the yield potential under abiotic stress as is the first goal for wheat breeders to increase production area and constrict the gap between the local production and consumption (Nassar et al. 2020). Furthermore, Stojšin et al. (2022) showed that releasing salt-tolerant wheat cultivars can provide a foundation for justifiable production in regions sensitive to salinity under climate change effects. They identified the genotype Harmonija as the most desirable to be grown under saline conditions. Survey and selected the most salinity tolerant rice line (SS1-14) based on physiological and metabolites criteria was higher in water and chlorophyll content at a lower rate of sodium ion accumulation (Ma et al. 2018) and Giza 171 and Sakha 95 in wheat (Anonymous 2022). Under Egyptian conditions, crop breeders released through selection and hybridization a lot of tolerant cultivars to salt stress viz. wheat, rice, barley, Egyptian clover, fodder sorghum, Sudan grass, cotton, alfalfa and others © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_7

247

248

7 Breeding Efforts and Biotechnology

(Anonymous 2023b). Breeders also mainly focus on developing salt-tolerant forage varieties, so alfalfa variety Naimat or (GR-722) was developed by the random selection of five lines through the mass selection breeding technique. The variety was appraised in diverse trials with check variety throughout 10 years. The variety was excellent in all fodder yield trials rather than check, high green fodder yielding, tolerant to salinity, and a wide range of adaptability (Abdul Jabbar et al. 2021). Classical breeding procedures can be substituted by gene manipulation. In certain situations, plant gene manipulation is comparable to the backcross breeding method in which desired genes are transferred. The backcrossing process transfers one simple trait of the donor parent to the recurrent parent, representing the basis for the implementation of classical breeding practices (Singer et al. 2021). Markerassisted forward and backcross breeding were exploited to improve the best crop genotypes against various abiotic and biotic stress tolerance (Ramayya et al. 2021). Marker-assisted selections can be used as an operative tool in direct applications in breeding programs aiming to improve salt tolerance in crop plants, for instance, in wheat (Irshad et al. 2022), rice (Sarah et al. 2021), faba bean (Asif and Paull 2021) and sunflower (Aghajari et al. 2018). Gene-transformation technique enables scientists to achieve gene transfer in an accurate and useful manner for manipulating the biosynthesis pathways of osmoticprotective substances to accumulate molecules that scavenge ROS, reduce lipid peroxidation, and maintain protein structure and function (Ashraf 2009). Recent studies illustrate the possible of metabolic genes in engineering the crops to engineer salinity stress tolerance (Ashraf 2009; Li et al. 2018; Ravelombola 2022). Salinity-tolerant clone of sugarcane mount up less Na+ and more K+ compared to a sensitive counterpart clone., Therefore displayed a higher K+ /Na+ ratio (Wahid and Ghazanfar 2006; Patade et al. 2008). Likewise, promising somaclones of sugarcane has been generated via tissue culture technique generated through immature leaves of Egyptian commercial variety GT-54 9 (Abo-Elwafa et al. 2021). Eight PIP family genes were obtained based on the sugarcane transcriptome database. Furthermore, the ScPIP2–1 gene in sugarcane was cloned and characterized played a significant role in salt stress resistance (Tang et al. 2021). So, this review offers a comprehensive overview of the current efforts carried out on classical and modern techniques regarding tolerating salinity stress.

7.2 Classical Breeding Approaches for Salinity Tolerance Classical breeding, for instance, selection, hybridization and mutations for salinity tolerant crops are likewise described as salinity mitigation techniques (Athar and Ashraf 2009; Plaut et al. 2013). In this respect, halophytes or salinity-tolerant crop genotypes might be bred with desired salinity-sensitive crop plants to develop salttolerant offspring. In general, according to Epstein (1983), there are three main requirements for the possibility of developing salt-tolerant varieties, which are:

7.2 Classical Breeding Approaches for Salinity Tolerance

249

1. Availability of appropriate genetic differences between varieties of plant species and their wild relatives. Comprehensive inventories of salt-tolerant wild plants and their preservation in gene banks are of great importance. 2. Availability of techniques to screen large numbers of salt-tolerant genotypes. 3. Availability of selection criteria for identifying salinity-tolerant germplasm among a large number of segregating populations.

7.2.1 Introduction and Gene Banks The exploitation of genetic resources and the roles of gene banks are important in preserving genetic materials. As workers in gene banks perform the inventory, characterization and identification of genetic materials, determining the origin and taking a DNA fingerprint. Under the Egyptian conditions, since 2004, the National Gene Bank in Giza, Egypt (Fig. 7.1) has been able to collect, conserve, identify and evaluate 12,000 samples of salinity and drought-tolerant field and horticultural crops to maximize the utilization of available genetic resources to meet the needs of plant breeders. Also, it was possible to bring many salt-tolerant crops and cultivate them under Egyptian conditions, including Canola, Quinoa, Cassava, Jojoba, guayule and Kochia. The Egyptian Deserts Bank “Genes” is one of the most important entities of the Desert Research Centre and is the major bank of rare wild agricultural genes in the Arab world (Fig. 7.2). Since its inception in 1977, it has collected and stored

Fig. 7.1 A section of the National Gene Bank and Genetic Resources in Giza, ARC, Egypt (Source Modified after, https://agricultureegypt.com/News/40575/%D8%A7%D9%84%D8%A8%D9% 86%D9%83_%D8%A7%D9%84%D9%82%D9%88%D9%85%D9%89_%D9%84%D9%84% D8%AC%D9%8A%D9%86%D8%A7%D8%AA)

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7 Breeding Efforts and Biotechnology

Fig. 7.2 The Egyptian Desert Gene Bank (Source https://drc.gov.eg/en/genebank/)

2,500 rare wild medicinal plants. The bank has stored and preserved them. They were preserved to be invested and re-planted. The bank has produced new genotypes are resistant to soil salinity and drought. Desert Research Centre has a corporation between the Egyptian Sahara Bank from one side and the England Gene Bank. According to this corporation, a similar sample is preserved in the England bank, and if an England researcher reaches a biological compound with any Egyptian seed, they are not allowed to use it commercially except after Egyptian approval. The Egyptian Sahara Bank was selected in 2003 as the center of expertise in the Middle East by the International Institute for Environmental Diversity in Rome (https://drc. gov.eg/en/genebank/). The gene bank is home to one of the world’s largest germplasm collections of heat, drought and salt-tolerant plant species. It stores over 16,000 entries of nearly 300 plant species from more than 150 countries and regions. Likewise, this includes about 270 seed samples of 70 wild and cultivated plant species from the UAE. Furthermore, the gene bank has about 5000 accessions of barley, one of the largest in the Middle East, and more than 1200 accessions of quinoa, the largest of its kind outside South America. ICBA also provides seed samples to different institutions worldwide for research, breeding and introduction. The center has distributed approximately 9000 seed samples to scientists, farmers, and other stakeholders in 60 countries (https:// www.biosaline.org/about-icba/facilities/genebank). Elouafi et al. (2020) indicated that traditional field crops face several challenges instigated by abiotic and biotic stresses i.e. salinity, drought, pests, diseases, etc.… Toward these restraints, alternative crops could be introduced to replace common crops in a particular geographic area to the benefit of the farming communities. These alternative crops include amaranth, atriplex, buffelgrass, canola, castor, colocynth, cowpea, guar, lablab, jujube, lupine, mustard, pigeon pea, purslane, quinoa, safflower, salicornia, sesbania, sunflower, triticale as shown in Table 7.1.

7.2 Classical Breeding Approaches for Salinity Tolerance Table 7.1 Seeds of diverse alternative crops in the International Center for Biosaline Agriculture (ICBA) gene bank*

251

Crop

Category/uses

Amaranth

Fodder

No. of accession 49

Atriplex

Fodder

40

Buffelgrass

Fodder

820

Canola

Oilseed, fodder

99

Castor

Oilseed

11

Colocynth

Oilseed

27

Cowpea

Grain, fodder, vegetable

48

Guar

Fodder, gum, vegetable

99

Jujube

Fruit

Lablab

Grain, fodder, vegetable

Lupine

Grain, fodder

217

Mustard

Oilseed, vegetable, fodder

100

Pigeon pea

Grain, fodder

137

Purslan

Vegetable

Quinoa

Grain, fodder

Safflower

Oilseed, fodder, ornamental

Salicornia

Oilseed, vegetable, fodder

Sesbania

Grain, fodder

Sunflower

Oilseed, ornamental

100

Triticale

Grain, fodder

370

6 44

3 1050 630 12 80

* After

Elouafi et al. (2020) and https://www.researchgate.net/ figure/Seeds-of-different-alternative-crops-in-the-ICBA-genebank_tbl1_344256405

7.2.2 Phenotypic Selection Plant populations grown under saline conditions represent a genetic pool that allows the process of natural or artificial selection in many crop species to isolate tolerant genotypes based on the additive genetic variance. The process of selecting plants with the desired traits, whether structural, physiological, or biochemical, responsible for salinity tolerance with stable yield and low salinity sensitivity index are considered the criteria in studying the behavior of genotypes and ordering them into tolerant or sensitivity to salinity (Bachiri et al. 2018; Bagues et al. 2018). Selection measurements such as salinity sensitivity index STI, mean productivity MP, geometric mean productivity GMP, harmonic mean HM and drought resistance index (DRI) could be considered the best tolerant indices in breeding programs. Mahdy et al. (2021) showed that the direct and indirect effects of seed cotton yield/ plant components differed greatly under both normal and salinity stress environments. The direct effects of the seed cotton yield/plant components under normal soil were valued 0.504, 0.401, 0.153 and 0.147 for a number of bolls / plant, lint

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7 Breeding Efforts and Biotechnology

yield/plant, seed index and number of seeds/boll, individually. Conversely, under saline soil, the direct effects were 0.802, 0.178, 0.128 and 0.050 for lint yield/plant, number of bolls/plant, number of seeds/boll and seed index, respectively. So, in both environments, selection should be mainly based on the number of bolls/plant and lint yield/plant. Selection for earliness, yield and its relevance in bread wheat was done for developing new varieties with ideal genetic makeup to increase the yield potential under abiotic stress, as is the first goal for cereal breeders to increase production area and constricted the gap between the local production and consumption. Early, Epstein et al. (1980) succeeded after one cycle of selection at a level of salinity equivalent to 50% of seawater salinity to isolate wheat lines that had better performance rather than the most tolerant Indian wheat cultivar (Kharchia). Then, an improvement in salinity tolerance could be achieved through conducting selection for a number of generations. Under Toshka Agricultural Experiment Station of Desert Research Center, Aswan governorate, Egypt, Nassar et al. (2020) evaluated ten divergent parents of bread wheat and their five crosses under soil ECe of 2.26 dS m−1 . Two cycles of pedigree selection scheme were followed. The first selection was done for the earliest lines in heading in F2 generation for sixty families and 300 plants from each cross were valued with their parents. The second selection cycle was practiced for higher grain number per spike and 100-grain weight in F3 plants. In F3 , data were verified on days to heading, days to maturity, plant height, spikes number per plant, spikelets per spike, 100-grain weight, grains number per spike and grain yield for each individual plant for P1 (Line-1), P2 (Line-2) and F3 families. Mean performance for the five F3 families and their parents revealed that selected plants of the cross (4) and cross (5) were the earliest in heading valued 72.29 and 69.40 days and days to maturity with 111.37 and 106.91 days and had the highest values for all traits that reached to 6.97 g for 100-grain weight and 124.99 cm for plant height in cross 5. The selected 33 plants from 4500 of F3 families were expressed to be superior segregants and could be promoted to the F4 generation to give promising lines for future bread wheat breeding programs under stress conditions in Toshka. Moreover, Stojšin et al. (2022) showed that the release of salt-tolerant wheat cultivars could provide a foundation for justifiable wheat production in regions sensitive to salinity under climate change effects. They established 27 wheat genotypes grown in both salinity stress and non-stress conditions. Agronomic characters i.e. plant height, spike weight, number of grains/spike, 1000-grain weight, grain yield/ plant and biochemical parameters viz. radical scavenging activity and total phenolic content were verified. The most sensitive parameter to salinity was grain yield/plant, with a 31.5% reduction. Salt tolerance indices viz. salinity tolerance index STI, mean productivity MP, and geometric mean productivity GMP preferred the selection of genotypes Renesansa, Harmonija, Orašanka, Bankut 1205, KG-58 and Jugoslavija. Yield Index and stability analysis indicated that, genotype Harmonija was the most desirable genotype to be grown under saline conditions. It has been possible by selection to produce some tolerant rice varieties suitable for cultivation in lands with high salinity levels (Anonymous 2023a). Ma et al. (2018) surveyed 92 rice genotypes and selected the most salinity-tolerant line (SS1-14) and

7.2 Classical Breeding Approaches for Salinity Tolerance

253

most sensitive one (SS2-18) based on physiological and metabolites criteria. The most tolerant genotype (SS1-14) was higher in water and chlorophyll content at a lower rate of sodium ion accumulation. Furthermore, substantial inter- and intraspecific differences for salt tolerance in cotton has been registered by Ashraf (2002). Therefore can be exploited by specific selection and breeding for improving salt tolerance. Reports regarding the crop response to salinity evidence that the crop preserves its degree of salt tolerance steadily through its entire developmental stages. Thus, effective selection for salt-tolerant genotypes is possible to be made at any growth stage of the crop. Screening has been practiced among 22 cotton genotypes for salt tolerance by Munawar et al. (2021) using a germination test in Petri plates under a growth chamber. Then, selected 11 genotypes for extra testing in a pot experiment in sand soil with 0, 15, and 20 dS m−1 NaCl treatments under glasshouse conditions. At 4-leaves stage, morpho-physiological characters were estimated for the genotypes. Whereas, biochemical characters were completed on selected seven highly tolerant and sensitive genotypes. NIAB-135, NIAB-512 and GH-HADI appeared to be more tolerant and had adaption capacity for salinity stress while IR-NIBGE-13 and BS-2018 were sensitive ones. After a series of experiments, they stated that NIAB-135, NIAB-512, and FH-152 could be exploited in cotton breeding programs to improve salinity tolerance and can increase cotton cultivation under saline regions. On the other side, In canola, selection for 15 lines was performed, and within these lines, the selection was practiced based on the best yield components showing high estimates of breeding parameters i.e. genetic parameters, heritability and expected genetic advance. In the second season, genetic analysis was again done and resulted in the marked increase in genetic parameters estimates. On which selection was re-practiced within lines among 15 lines grown in the third reason under salinity stress, 11 ones produced improved seed yield. Nine lines of them are considered as salt tolerance and suitable for growing in newly reclaimed salt-affected soil (Ghallab and Sharaan 2002). Breeders mainly focus on developing salt-tolerant varieties. The overall selection of alfalfa over five cycles also contributed to improving salinity tolerance in the resulting lines (Allen et al. 1985). Recently, Abdul Jabbar et al. (2021) developed alfalfa Naimat or (GR-722) variety by the plant breeders from the random selection of five lines through a mass selection breeding technique. The variety was appraised in diverse trials with check variety throughout 10 years. The variety was verified in diverse fodder yield trails accompanied by check variety Sargodha Lucerne. Alfalfa variety (Naimat) was excellent in all fodder yield trials rather than check and advanced lines of alfalfa. Moreover, the Naimat variety was highly green fodder-yielding, tolerant to salinity, and had a wide range of adaptability. Fifteen selected salicornia, genotypes were evaluated. The best performing salicoria populations for fresh biomass, seed yield, oil composition, protein and saponins contents were multiplication under saline groundwater. Six salicoria populations were also assessed for their growth performance under full-strength seawater. The promising results indicate that the cultivation of appropriately selected cultivars, along with appropriate agricultural practices can be economically viable and successful in marginal lands (Fig. 7.3) (ICBA 2015).

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7 Breeding Efforts and Biotechnology

Fig. 7.3 Salicornia halophyte that can be irrigated with seawater can be used for food, feed and fuel 2015 (Source ICBA, International Agriculture Center)

7.2.3 Recurrent Selection Any successful breeding program depends on the existence of genetic variability that can be utilized by the recurrent selection, where salt-resistant plants are selected from a genetically diverse population and self-pollinate, then all possible crosscombinations are made between these offspring. The seed is collected and the progeny are planted for at least another generation to procedure genetic recombination, and the selection cycles are repeated until an appropriate level of resistance is reached. This method improves the resistance of any crop to salinity. Repeated selection in sorghum breeding programs has led to the isolation of salt-tolerant genotypes (Azhar and Khan 1997). Under field experiments, screening for salt tolerance and evaluation for yield and yield component performance was undertaken at salt-affected area of the district. Hailu et al. (2020) practiced the selection of Meko and 76T1#23 sorghum genotypes as promising varieties to tolerate saline environments, particularly in the Raya Valley of Ethiopia.

7.2.4 Hybridization The choice of the parents involved in the cross-breeding programs with high yielding ability, tolerance to salinity, and good combining ability, is useful in giving the opportunity to increase the additive gene effect during the generations and the development of promising lines during the breeding program. Estimation of the heritability and combining ability is useful in understanding the nature of inheritance of characters related to salt tolerance. Also, DNA-markers assist in identifying genes controlling traits associated with tolerance and acceleration of the breeding program. Hybridization is useful in transferring foreign input genes to sensitive cultivars. There are many examples in this area in the cereals, pulses and oils crops. Crossing

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between parents followed by selection and backcrossing has achieved wide success in the arena of breeding to resist diseases and insects that are governed by individual genes. However, in the case of salinity, the matter is different. Salinity resistance is not a simple trait. The alternative trend is to try to introduce certain traits related to resistance to salinity, such as physiological traits, which are governed by a number and not by many genes, especially if this trait is available among the genotypes of the same crop. For the progress of a hybrid variety in the cross-pollinated crops some sequential methods comprising recurrent selection, production of inbred lines (gametic selection, hybridization), or screening of the promising inbred lines depending on general combining ability and eventually superior two inbred lines (best hybrid) according to specific combining ability estimate should be selected and utilized to produce a hybrid variety (Ramayya et al. 2021). Through the pedigree method in F2 generation of 19 crosses between parents varying in salinity tolerance of bread wheat, Afia and Darwish (2003) selected 26 lines of the F5 generation. The most superior of which in yield trails for salinity tolerance were Siwa Lines 1, Line18, Line 25 under Siwa Oasis environment. In backcross breeding programs for salt tolerance, known salt-tolerant genotypes with desired traits contributing in salt tolerance can be exploited as donor. Munns et al. (2000) selected a salinity-stress tolerant durum wheat line 149 having higher K+ / Na+ ratio. Furthermore, they used line 149 as a potential donor in breeding program. After introgression of this trait, they developed salinity stress tolerant durum and bread wheat lines named Nax1 and Nax219, respectively. The rice landrace Horkuch, as salt tolerance and can contribute to a high-yielding recipient for breeding objectives. They reciprocally crossed Horkuch with highyielding but salt-sensitive IR29 to detect the complement of genes responsible for conferring salt tolerance versus sensitivity at the seedling developmental stage. The results showed that the tolerant plants were characterized by the activity of acetyltransferase, glutamyl-tRNA synthase, and serine/threonine-protein kinase under salinity stress. Upregulated genes have been associated with evolution, RNA splicing, regulation of gene expression, epigenetics and other functions (Razzaque et al. 2019; Luo et al. 2021). To sum up, under Egyptian conditions, crop breeders release through selection and hybridization a lot of bread wheat cultivars tolerant to salt stress viz. Giza 168, Giza 171, Shandweel 1, Sids 1, Sakha 95, Misr 3 and Misr 4; six-row barley, i.e. Giza 123, Giza 133, Giza 134, Giza 137, Giza 138; Rice i.e. Giza 178, Giza 179, Giza 182, Sakha 104, Sakha 106 and Sakha super 300 and Egyptian Hybrid 1 and 2 tolerant or moderately tolerant to salinity; white maize hybrids differ in their tolerance to harsh environments i.e. single crosses 10, 128, 129, 130, 131 and 132, and three-way crosses 310, 314, 321, 324 and 329, as well as the yellow maize crosses, for instance, single crosses 162, 166, 167, 168, 173, 176, 178 and 180 and three-way crosses of 352, 353 and 368 (Anonymous 2021, 2022). Also, in forage crops, Egyptian clover, i.e. Serw 1; Rey grass i.e. Baldi; fodder sorghum i.e. Hybrid 102; Sudan grass i.e. Giza 2 as well as alfalfa i.e. Ramah 1, Ismailia 1 and Sewa which vary in their tolerance to salinity (Anonymous 2023b).

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7.2.5 Mutations Mutations are an important means of inducing valuable genetic variations in breeding programs to improve traits associated with salt tolerance that are controlled by individual genes or that change by a single mutation compared to quantitative traits. Manipulating natural or induced genetic variability is a verified approach in the development of strategic food crops. The use of mutagenesis to produce novel variants is mainly valuable in those crops with restricted genetic variability (Parry et al. 2009). It is worth mentioning that induced mutations have been generally used for genetic improvement of the annual oilseed crops, particularly in soybean, sesame, canola, sunflower and linseed (MacDonald et al. 1991; Ferrie et al. 2008; Velasco et al. 2008). Global efforts on mutation-based plant breeding have produced the official release to farmers of over 2700 novel crop cultivars in about 170 species (Lagoda 2008). Mahar et al. (2003) used Gamma radiation to induce early maturity in a salttolerant late-maturing bread wheat genotype KTDH 19. Selection in early generations was performed for earliness, and in M5 was implemented for high grain yield under 150 mol m−3 NaCl. The highest heritabilities were found for days to heading and yield under both saline and nonsaline conditions. Among 62 early-heading M5 genotypes, 10 genotypes had significantly lower leaf Na+ levels than the parents. Three of the ten had significantly higher grain yields. These promising genotypes were three weeks earlier in maturity, one had awns, unlike the parent, important for protection against bird damage. Meanwhile, Martínez-Atienza et al. (2007) obtained new rice mutants that are mutated at three loci, i.e. SOS1, SOS2 and SOS3. To enhance salinity resistance in rice, Zhang et al. (2019) exploit a genome editing technology by engineering a Cas9-OsRR22-gRNA expressing vector of the rice OsR22 gene. From 14 transgenic T0 plants, 10 mutant plants were recognized. Six mutation forms were discovered at the target site by sequencing, all of which were transferred efficaciously to the next generations. In T1 generation, mutant plants without transfer DNA (T-DNA) have been attained through segregation. Based on salinity tolerance and agronomic characters, 2 homozygous in T2 mutant lines were evaluated further. At seedling stage, the T2 homozygous mutants showed a significantly increased in salinity tolerance compared to the wild genotype. It was possible at Gemmeiza Research Station, Egypt, using gamma irradiation and sodium azide NaN3 , to produce five promising salinity-tolerant faba bean mutant strains, strain N.N.S-6 of Giza 2 variety and strains D-5, Long P-7, Long P-5 of Improved Giza 3 variety and the strain S.S-17 of Giza 716 variety. Moreover, it was possible to select three promising mutations with high-yielding ability under saline and normal soil conditions, the strain L.S-1 of the variety Giza 2, and the two strains L.F.E-6 and S.S-15 of Giza 714. Long P-7 strain was identified as the best promising strain under saline and normal conditions (Soliman et al. 2003). In oil crops, Hassan and Abo-El-Haleem (2013) treated homogeneous dry seeds of two canola cultivars i.e. Serw 4 and Serw 6 with 0, 5, 10 and 15 Kr of Gamma rays, and the resultant M2 generation was tested under saline field conditions (the soil and

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irrigation water salinity EC were 16.33 dS m−1 and 7.59 dS m−1 in 2009/2010 and 2010/2011, respectively. Results indicated higher variation in the treated population than the control for all studied traits, except for plant height in Serw 4 cultivar. The highest variation induced was observed due to the treatment of 15 Kr of gamma rays in most studied traits in Serw 4, while in Serw 6, 5 Kr does came in the first rank for most traits. They isolated 33 promising mutants in the M2 generation. These mutants included: from sixteen mutants for high yielding ability, the superiority in seed yield/ plant, the high yielding mutants ranged from 108.15 to 460.7% in mutants derived from Serw 4 and from 77.29 to 223.42% in mutants from Serw 6. Seventeen early promising mutants were selected from 15 Kr Serw 6. These mutants were earlier in flowering than the parent, ranging from 7 to 27 days. They decided that thirty-three promising mutants will be the backbone of the future breeding programs to improve the economic traits of canola under saline conditions. Zhu et al. (1998) identified salt overly sensitive (SOS) Arabidopsis mutants, characterized by hypersensitive to high external Na+ , Li+ , or K+ concentrations. Somaclonal variation combined with in vitro mutagenesis and selection has been performed to isolate agronomically beneficial sugarcane mutants (Jain 2000; Zhambrano et al. 2003). Radiation-induced mutagenesis followed by in vitro selection was performed in salt tolerance in Indian sugarcane cultivars (Patade et al. 2008; Abo-Elwafa et al. 2021).

7.3 Recent Approaches in Breeding for Salinity Tolerance Recent advances in molecular biology offer a recent opportunity for understanding the inheritance of stress-resistance genes. Tissue culture technique help in isolating and selecting salinity-tolerant lines to understand the mechanism of tolerance at the cellular level (Niknam et al. 2006) and the opportunity of developing salt-tolerant genotypes (Cheng et al. 2018). Molecular genetic maps were developed for main crop plants, including wheat, barley, rice, sorghum, maize and potato, which make it possible for scientists to tag desired traits using known DNA landmarks. Molecular genetic markers decrease the need for extensive field testing, time and space. To identify and characterize salt-tolerance genes, a combined approach is required to integrate genomics, molecular markers, proteomics, metabolism, transcription and transcription factors to engineer new salt-tolerant crop varieties. This is defined as integrated plant breeding, molecular approaches, biotechnology, and new breeding techniques to enhance salt tolerance mechanisms.

7.3.1 Molecular and DNA-Markers Biotechnological advances offer novel tools for breeding in stressful environment. Biotechnology techniques, together with molecular genetic markers provide a new

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strategy known as marker-assisted selection. These techniques are important in the programs of developing new varieties.

SDS-PAGE The use of SDS-PAGE (Sodium doecyle sulfate polyacrylamide gel electrophoresis) technique for the extracted soluble proteins is useful in deriving genetic and biochemical parameters that help in studying genetic background, ones. SDS-PAGE and SOD analyses are useful biochemical and molecular tools to distinguish different crop genotypes under saline conditions. Firstly, the advanced studies indicate that halophytic plants, whether salt-secreting or succulent, are distinguished by a high degree of enzymatic activity and the presence of certain distinct bands that are genetic evidence for salinity resistance, while they are absent in non-saline species. In wheat, El-Saber (2021) exploited patterns of proteins (SDS-PAGE) and superoxide dismutase (SOD) in discerning between salttolerant and salt-sensitive genotypes. SDS-PAGE indicated that, number of bands in 7 wheat genotypes ranged from 13 to 14 with molecular weights varied between 6 to 130 kDa, and the more intensive bands are existed at 25, 29, and 34 kDa. Furthermore, SOD patterns showed the existence of 5 bands; the main is obtainable at bands (No. 4 and 5) in the wheat genotypes. Therefore, L1 was the best wheat line then L3 and L7 as more tolerant to salinity stress, and this was connected with enhancing growth, yield and proline and reducing MDA content. Since improving salinity tolerance in rice by genetic means is an important goal, what has been achieved in light of modern agricultural advances is considered limited. Since changes in protein/gene expression are accompanied by a change in salt tolerance, and to confirm this concept, Djanaguiraman et al. (2003) employed SDS-PAGE technique to show the differences in salinity resistance among five rice strains, namely, White Ponni, TRY, ADT 39, ADT 38 and IR 20 at salinity stress of 200 mM NaCl and control. Results showed that there were variances between the strains in the protein segments at different stages of growth (seedling, tillering and panicle initiation) between stress treatment and the control. It was possible to discover new protein bands at the molecular weight of 16 and 15 kDa. An increase in the expression of proteins at a molecular weight of 70 kDa was observed in plants subjected to stress compared to the control. These proteins were called “Osmotin”. They are proteins responsible for osmotic regulation in salt-tolerant strains in which the activity of superoxide, peroxidase, catalase and dismutase enzymes was increased. Based on the clear-cut polymorphism that appeared in the band patterns between the tolerant and sensitive genotypes, strains TRY1, ADT 39, IR 20 were classified as tolerant, while strains ADT 38 and White Ponni were considered to be salt sensitive. This technique was useful in studies of salinity tolerance in parents and crosses of sorghum, where four protein bands with molecular weights 72.64, 59.59, 46.37 and 22.75 kDa were absent under salinity conditions in most of the crosses, which were considered negative signs, while one protein band with a weight appeared Molecular 37.19 kDa under saline conditions was considered a positive sign. The tolerant parents

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ICSA-37, ICSR-91022 and four tolerant hybrids showed almost the same protein bands distribution under both salinity and control treatment, as these genotypes were less suffering under salinity conditions and were able to store proteins closer to nature in their vitality. Where, El-Menshawi et al. (2003) recommended the importance of using these parents in sorghum breeding programs to salinity tolerance. In another study by Younis Rania et al. (2007), electrophoresis for soluble proteins showed that salt-tolerant sorghum genotypes were distinguished by nine protein bands that were absent in sensitive genotypes. The analysis of protein segments using SDS-PAGE technology for roots of chickpea variety H 96-99 under salinity levels of zero, 2.5, 5, and 10 dSm−1 in pot experiments showed the appearance of specific proteins and the absence of other proteins under salinity-stress conditions, while a reverse trend appeared in protein bands patterns after irrigation and regrowth, where Kukreja et al. (2003) observed that with increased salt stress, the level of Malondialdehyde (MDA) increased, which is a measure of lipid oxidation and H2O2 production that leads to loss of cell membrane integrity. The enzymes of the antioxidant defense systems were unable to overcome the superoxide buildup. In white lupine under three different levels of salinity stress (2, 4 and 8 dS m−1 ), the genetic variability using Sequence-related amplified polymorphism (SRAP) between the tested seven genotypes was determined. Mahfouze et al. (2019) used SDS-PAGE analysis of the total proteins extracted from the leaves of seawater-stressed plants and the control registered an increase or decrease in the protein content based on the genotype. Furthermore, salinity prompts the synthesis of novel proteins in tolerant and sensitive genotypes. Antioxidant defense activities seemed to be related to the different regulation of distinct peroxidase POX. POX isoenzymes showed an increase or decrease in the genotypes tolerant to seawater stress. They utilized SRAP technique to amplify coding regions of DNA of the verified seven white lupine genotypes with eleven primers targeting open-reading frames. Eleven polymorphic SRAP primer sets produced fifty-one alleles with average 0.710 polymorphism information content. The polymorphic bands percentage was 35.29%. The UPGMA dendrogram, which display genetic similarity between seven genotypes, was clustered into three groups varied from 0.80 to 0.94. The results indicate the opportunity of using diluted seawater to grow white lupine genotypes taking into concern the proper genotype and the available dilution factor.

DNA-Markers Molecular genetic advances and plant transformation have helped improve biosalt tolerance based on active signaling sequences, engineered biosynthetic pathways, expression of target genes or proteins, or alter the response of genes to natural stress to develop salt-tolerant crops (Hasegawa et al. 2000). The identification of molecular markers associated with salinity tolerance traits has provided plant breeders with a new tool for selecting cultivars with improved salinity tolerance.

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Currently, different approaches are being approved for alleviating salt stress’s opposing effects, such as screening of genotypes of diverse crop species. Indeed, molecular marker procedures are used to detect DNA marker associated with salt tolerance and crop stability as genetic variances are base for developing crop genotypes (Akber et al. 2009).

Randomly Amplified Polymorphic DNAs (RAPD) Random amplified polymorphic DNA (RAPD) markers were used by Bhutta and Amjad (2015) to estimate the genetic variability between three salt-resistant wheat genotypes, SARC-1, SARC-5 and S-24, exposed to saline situation. High-yielding and salt-sensitive genotype MH-97 was used as a check for comparison using the hydroponics technique at the seedling stage. They tested one hundred and fifty primers of which 52 primers showed variances between SARC-1 and SARC-5, 54 gave differences between SARC-1 and S-24, while 61 generated variances between SARC-5 and S-24. Polymorphism differences between MH-97 and SARC-1, MH97 and SARC-5 and MH-97 and S-24 valued 53%, 64% and 42%, respectively. Four primer pairs amplified specific fragments were located in all three salt-resistant varieties; however, none on the salt-sensitive variety MH-97. In barley, RAPDs were exploited to examine markers linked with salt tolerance. Pakniyat and Namayandeh (2007) investigated initial experiments that included growing 63 genotypes viz 5 tolerant and 5 sensitive genotypes of cultivated and wild barley under saline conditions and testing the sodium content in the shoot as well as the physiological characteristics. By using 30 different 10-mer of RAPD primers, results showed that one primer (P15) generated a 5100 bp band detected only in sensitive genotypes and additionally produced a 1300 bp product originating only in the tolerant genotypes. Primer P10 gave a band specific to tolerant bulk and P22 formed a band specific to the sensitive group. In rice, Randomly Amplified Polymorphic DNAs (RAPDs) were used to examine for markers linked with salt tolerance in crop plants. The RAPD technique was used to identify the somaclonal variations resulting from the salt-tolerant Pokkali rice variety, where significant differences were observed at the genetic level between the resulting strains. Elanchezian and Mandal (2003) isolated salt-tolerant strains from somaclonal variations. In faba bean, El-Sayed et al. (2020) showed unique bands referred to different saline conditions and variances between genotypes. Three RAPD primers were effective in producing reproducible and reliable amplicons concerning the twenty-five faba bean genotypes. In sugarcane, RAPD analysis yielded unique DNA fragments that appeared in the salt-tolerant strains had similar sequences of stress-tolerant genes compared to the salt-sensitive ones (Prammanee 2004).

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Reverse Transcription Polymerase Chain Reaction (RT-PCR) Additional validation by RT-PCR using reverse genetics methods confirms salttolerant strains as useful genetic resources for future salinity breeding programs. Irshad et al. (2022) followed the protocol of RNA extraction, cDNA formation, and qRT-PCR. Expression analysis of HKTs genes was done from the root and shoot samples of tolerant and susceptible wheat genotypes. The differential expression of HKT2; 1 and HKT2; 3 explained the tissue and genotype-specific epigenetic variations. In different wheat lines, there is a differential induced defense response to salt stress, demonstrating a functional association between salt stress tolerance and different expression pattern in wheat. In barley, the behavior of a set of 19 advanced genotypes for physiological and molecular mechanisms involved in salinity tolerance was assessed by Jadidi et al. (2022) at two control (0 mM NaCl) and salinity stress level (200 mM NaCl) under glasshouse in a hydroponic system. Results of RT-qPCR indicated that salinity stress increased the expression of HvSOS1, HvSOS3, HvHKT2, HvHKT3, HvNHX1 and HvNHX3 genes compared to the control condition. They revealed that the genotype G14 can be a candidate as a superior salt-tolerant barley genotype for supplementary trials prior to commercial introduction. In rice, RT-PCR technique also helped to identify nuclear proteins in salt-tolerant rice varieties (Mukherjee et al. 2003). Moreover, Adeel Zafar et al. (2021) exploited Quantitative real time-PCR (qRT-PCR) to define the comparative expression pattern of certain genes on StepOne RT-PCR in rice. OsActin1 was used as an endogenous reference gene for data regulation. Amanat et al. (2022) performed Quantitative RTPCR and revealed the expression of 1-5-phosphoribosyl -5-5-phosphoribosyl amino methylidene amino imidazole-4-carboxamide isomerase, DNA repair protein recA, and peptide transporter PTR2 related genes were upregulated in salt-tolerant rice lines, advising their possible role in salinity tolerance. In peanuts, Semi-quantitative RT-PCR was performed by Luo et al. (2021) to detect the expression levels of AhABI4 coding genes under salt stress. The expression levels of AhABI4s were significantly upregulated in the tap and lateral roots after 3 h treatment under salt-stress, while the high peak of expression level in leaf was present after 6 h treatment with salt-stress. AhABI4s exhibited higher expression levels in the germinating seeds and embryos than that in the vegetative organs. Thus. AhABI4s display similar expression patterns with other reported ABI4 coding genes in plants. In Atriplex canescens, Yu et al. (2017) identified salt stress-related genes. They constructed a cDNA library resulting from highly salt-treated in Atriplex genotypes according to a yeast expression pattern. A total of 53 transgenic yeast clones expressing improved salt tolerance were selected. Sequenced their plasmids and the gene features were annotated by a BLASTX search. Transformed yeast cells with the selected plasmids conferred salt tolerance to the resultant transformants. Patterns of expression of 28 in these stress-related genes were investigated in leaves of A. canescens by RT-qPCR. They screened genes for salinity stress tolerance in A. canescens.

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Inter-Simple Sequence Repeat ISSR-PCR Markers ISSR-PCR Markers were used for screening and recognizing genetic divergent genotypes for drought and salt tolerance experiments. These markers may aid breeders in any marker-assisted selection program for improving crop cultivars against salt stress. ISSR-PCR markers were exploited to measure genetic variation and population structure among wheat genotypes (Najaphy et al. 2011; Etminan et al. 2016). Seven bread wheat genotypes were distinguished by ISSR-PCR analysis for tolerance to saline stress (6195 ppm soil and 8934 ppm irrigated water) at Ras Sudr, South Sinai, Egypt. El-Saber (2021) detected 102 DNA bands through six ISSR primers, out of which 72 bands (51 non-unique bands and 21 unique bands) were polymorphic with 70.58% polymorphism. Primer ISSR2 produces the maximum polymorphism (92%), then ISSR-13 (86%) and ISSR-11 (78%). Herby, L1 was the best wheat genotype, followed by L3 and L7 for tolerance to saline stress. In barley under diverse soil salinity levels (4, 8 and 12 dS m−1 ), six Egyptian genotypes were evaluated by Mariey et al. (2022). They showed that ISSR (UBC 835) primer had amplified specific allele with molecular size 800 bp recognized in tolerant barley cultivars (Line 4 and Giza 137). Thus, this primer is highly informative as a positive marker for salinity tolerance. The heatmap cluster constructed by Euclidean distance and average linkage according to 12 traits, 7 salt tolerance measurements and 10 ISSR primers displaying that the six barley genotypes were grouped into two main clusters, each cluster comprising the most closed genotypes together according to salinity stress tolerance as high yield potential under salinity soil regions in Egypt. In faba bean, based on ISSR marker polymorphisms, Terzopoulosa and Bebeli (2008) developed a similarity matrix by NTSys computer package. The analysis was based on the number of markers which were different between any given pair of genotypes of faba bean. Similarity percentage between the deliberated genotypes revealed that, the maximum value of similarity (82.8%) was observed between NBLMar.3 and NBL-5 genotypes, whereas the minimum value (67.1%) was detected between NBL-Mar.3 and Misr-1 genotypes. Likewise, Afiah et al. (2016) exploited four primers (HB 11, 844A, 17898B and 17899B) for discriminating the highest seed index of five faba bean genotypes (NBL-Mar.3, NBL-5, L3, Nubariya-1 and Misr-1) by five positive markers at AF (16, 48, 71, 89 and 90) and two negative specific markers at AF (17 and 96). The sensitive genotype (Misr-1) for both biotic stresses tested distinguished by nine unique bands; five positive fragments at AF (2, 8, 34, 68 and 70) and four negative amplicons at AF (38, 79, 80 and 84). The highest water deficit newly bred tolerant genotype (NBL-5) was differentiated by either positive specific markers at AF (45 and 61) or three negative amplicons at AF (30, 32 and 33). The salt tolerant genotype (NBL-Mar.3) possess ten of the unique amplicons out of the 40 total number specific markers which containing either the existence or absence of a certain band. In cowpea, Mini et al. (2019) made molecular discrimination between salt-tolerant cowpea genotypes by Inter simple sequence repeat (ISSR) fingerprinting. Proteome analysis of cowpea leaves under salt stress revealed up-regulation of ATP synthase,

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vacuolar ATPase, pentatricopeptide repeat protein, flavanone 3-hydroxylase and outer envelope pore protein. Thus, ISSR and proteome analyses allow the identification of salt-tolerant cowpea cultivars. The nine primers generated 57 bands, of which 41 were polymorphic, with a total polymorphism of 72%. The ISSR marker UBC-809 displayed 100% polymorphism, and UBC-812 gave the highest number of bands. Genetic similarity, based on Jaccard’s coefficient, varied from 0.44 to 0.94. At the similarity level of 0.63, three main clusters were made. The first cluster contained the genotypes VBN1 and IVT-VCP-09-013, whereas DC15, KBC2 and VCP-09-001 were gathered in the second cluster; VBN2 located in the third cluster. The genotypes KBC2 and VCP-09-001 were a high similarity coefficient of 0.94. However VBN2 formed a unique cluster at the similarity coefficient of 0.44, representing that it is very different from the rest five genotypes. In cotton, Abdi et al. (2012) utilized inter-simple sequence repeat (ISSR) to study 28 cotton cultivars, under three salt treatments were imposed with salt solutions (0, 70 and 140 mM NaCl). They detected 65 polymorphic DNA fragments were produced at 14 inter-simple sequence repeat (ISSR) loci. Plants of 28 cultivars of cotton gathered into three clusters according to ISSR markers. Based on regression analysis of markers in relation to traits, 23, 33 and 30 markers connected with the estimated traits in three salt treatments, respectively. In pearl millet, based on yield, yield components, chemical and molecular analyses using the Inter-Simple Sequence Repeat (ISSR) marker, Sayed et al. (2022a; b) tested five genotypes of pearl millet (Pennisetum glaucum L.) under salinity soil of 9.42 EC (dS m−1 ) at Sahl El-Hussinia, Agricultural Research Station, El-Sharkia Governorate, Egypt. A total of 56 ISSR bands were detected, 27 and 29 of monomorphic and polymorphic bands, respectively. Three out of eight primers displayed some molecular markers for tolerance to salinity. Similarity associations between pearl millet genotypes according to ISSR were varied between 0.884 and 0.635. The dendrogram divided the five pearl millet genotypes into two main groups and sub-main groups. A principal component study (PCA) has collected the genotypes into three diverse groups that valued 68.7% of the total variance. The first and second principal components (PC1 and PC2) elucidated 40.4% and 28.3%, respectively. Heat map assignment analysis classified genotypes into two major clusters. Hence, genotypes PE00463 and PE00200 could be expressed as new promising and more tolerant to salt stress. In conclusion, the previous specific markers could be effectively used as marker assisted selection for the best genotypes utilizing in crop breeding programs.

Quantitative Trait Loci (QTLs) The quantitative trait loci (QTLs) technique has been useful in identifying the genetic loci responsible for salt tolerance. Quantitative trait parameters (QTLs) were used to develop 100 plants in F2 generation. It helped in identifying a genetic locus in durum wheat on AL2 chromosome, which accounted 38% of the phenotypic variance of salt tolerance (Lindsay et al. 2002). Identification of the QTLs of salt tolerance genes in wheat was Q. chl2D AND and Q. chl5A on chromosome 5 for chlorophyll content;

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Q. mat5A on chromosome 2 for days to maturity; Q. Na2A and Q. Na 2B1 on chromosome 2 for Na+ concentration (Genc et al. 2010). Meanwhile, Devi et al. (2019) utilized quantitative trait loci (QTL/s) of salt tolerance using recombinant wheat inbred lines produced from a cross between Kharchia65 (KH 65) and HD 2009 cultivars. Parents and recombinant inbred lines were assessed under controlled and sodic stress environments for 11 morpho-physiological and yield characters through two repeated crop cycles. They identified 11 QTLs on 6 chromosomal regions (1B, 2D, 5D, 6A, 6B and 7D) of 7 different characters clarifying that the proportion of the phenotypic variance ranged from 2.5 to 12.8% under control condition. Three of the QTLs (QCph.iiwbr-2D.1, QCle.iiwbr-6A and QCle.iiwbr-6B) were consistent at all the environments and explained 5.1–12.8% of the phenotypic variance at control condition. Twenty-five QTLs were discovered on 7 chromosomal regions (1A, 1B, 2D, 4D, 5D, 6A and 7D) for 10 diverse characters clarifying that the proportion of the phenotypic variance ranged from 2.6 to 15.1% at salt stress. Six of the QTLs i.e. QSNa? iiwbr-1B, QSK?.iiwbr-2D, QStn.iiwbr-4D, QSph.iiwbr-2D.1, QSph.iiwbr6A and QSdth.iiwbr-2D were steadily reproducible in all the situations and the clarified proportion of the phenotypic variance varied from 2.6 to 15.1%. SSR markers, namely gwm 261, wmc112 and cfd 84 were strongly connected with QTLs for K+ content; days to heading and days to anthesis; and tiller number and umber of ear heads, respectively. Some QTLs caused salt tolerance has existed on 2D chromosome. The QTLs related with salt-tolerant characters were inherited from genotype KH 65 demonstrating the existence of numerous genes related to salt tolerance in the previous genotype. In barley, the technique of quantitative trait parameters (QTLs) has been applied to identify the genetic loci responsible for salt tolerance seedlings of barley dihaploid Steptoe/Morex lines on chromosomes 4 (4H), 6 (6H), and 7 (5H) as well as in the strains of hybrid Harrington/TR 306 on chromosomes 7 (5H), 5 (1H) and the most active locus was 7 (5H). The genetic analysis of chromosome 7 (5H) showed a genetic correlation between salinity tolerance at germination and the response to ABA abscisic acid (Mano and Takeda 1997). Identification of the QTLs of salt tolerance genes have been distinguished in barley qRWC1n for relative water content on chromosome 2; qSPAD5n for SPAD on chromosome 5; qDMA1.1n for days to maturity on chromosome 1 (Barati et al. 2017)). A set of 103 recombinant inbred line (RIL) populations, developed between Badia and Kavir cross, was evaluated for barley’s physiological and morphological traits under normal, salinity and drought at phytotron conditions. The markers were mapped to seven barley chromosomes and enclosed 999.29 centimorgans (cM) of the barley genome. Also, composite interval mapping indicated 8, 9, and 26 QTLs under normal, drought, and salinity stress situations respectively. Results show the importance of chromosomes 1, 4, 5 and 7 carrying genes governing stomata length, leaf number, leaf weight and genetic score. Three main steady pleiotropic QTLs were qSCS-1, qRLS-1 and qLNN-1 associated with a genetic score, root length, and root number in both normal and salinity, and two main steady pleiotropic QTLs qSNN-3 and qLWS-3 linked with the stomata number and leaf weight seemed to be promising for marker-assisted selection. Two majoreffect QTLs i.e., SCot8-B-CAAT5-D and HVM54-Bmag0571 on chromosomes 1

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and 2 were described for their positive allele effect for drought conditions. The new identified alleles i.e., qLWS-4a, qSLS-4, qLNS-7b, qSCS-7, and qLNS-7a are useful in pyramiding elite alleles for improving salinity tolerance in barley (Makhtoum et al. 2022). In rice at the young seedling stage, Bimpong et al. (2013) using 384-plex SNP markers for mapping salt-tolerant QTL. Moreover, De Leon et al. (2016) used 9303 SNP markers produced by genotyping-by-sequencing (GBS) were mapped to 2817 rice recombination points for salinity-tolerant QTL identification. A recombinant inbred rice line (RIL) population derived from a super hybrid Liang–You–Pei–Jiu (LYP9) parents 93-11 and PA64s were verified under 50 and 100 mM NaCl stress by Jahan et al. (2020). They used a high-density genetic map to detect QTLs for rice salinity tolerance at seedling stage. A total of 38 QTLs were identified across two stress levels. Six clusters were known with 21 stable QTLs. A new major QTL for SL, qSL7 was known on chromosome 7. LOC_Os07g43530 was described as a transcription factor for potassium ion transporter gene among 40 marked genes recognized in the target region and play a vital role in rice tolerance to salt stress. The lines resulting from CSSL-qSL7 will offer genetic resources for the development of rice salinity tolerance. Furthermore, Sarah et al. (2021) screened 25 rice genotypes belonged to Oryza sativa L. for tolerance to salinity stress at seedling stage and to recognize the markers, which may be effectively utilized for discriminating rice genotypes for salt tolerance. Five haplotypes were recognized using FL478 as a reference. Fifteen RBL lines displayed similarity with FL478 haplotype and all of them were determined as tolerant to salt stress. Some of the salttolerant genotypes may be possible donors for introgression genes/QTLs of salinity tolerant in rice breeding programs. The two markers RM493 and RM10711 were capable of distinguishing among salt sensitive and tolerant rice genotypes. Therefore, these QTL markers can be operative as the marker-assisted selection of salt tolerance in rice. Moreover, in faba bean, Asif and Paull (2021) phenotyped a recombinant inbred line (RIL) population derived from the bi-parental cross of ‘Icarus’ × ‘Ascot’ under control and saline treatments. Quantitative trait locus (QTL) analysis of this population detected multiple QTL for leaf ionic concentration (Na+ , K+ and Cl− ) under both treatments. Of these, seven QTL were identified under salt treatment, comprising three for leaf K+ :Na+ (qK:Na-S-1, qK:Na-S-2 and qK:Na-S-3) and one each for Na+ accumulation (qNa-S), K+ accumulation (qK-S), Cl− accumulation (qCl-S) and Na+ :K+ (qNa:K-S). A vital region was identified on linkage group I.A/III/V, which enclosed three co-located QTL (qNa-S, qCl-S and qK:Na-S-3) of leaf Na+ , Cl− and K+ :Na+ accumulation. Potential candidate genes between the QTL intervals were recognized using genome of Medicago truncatula. The results achieved help in the breeding of new salt-tolerant faba bean varieties. Furthermore, in sunflower, Aghajari et al. (2018) identify lines tolerant to salinity stress by QTLs. The QTL analysis identified a totally 5 QTLs significantly linked with salt tolerance indices. The results show co-localization of the recognized QTLs for mean productivity MP, geometric mean productivity GMP and harmonic mean HM in linkage group 14 with QTL celebrated for grain yield under salt stress environments.

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Single Nucleotide Polymorphism Markers (SNP) Direct applications in breeding programs aim to improve salt tolerance in crop plants through marker-assisted selection. In this respect, Kim et al. (2020) subjected twentysix Tunisian durum wheat germplasm to a salinity stress level of 500 mM NaCl. Also, two cultivars, namely ‘Om Rabia’ (salinity-tolerant) and ‘Mahmoudi’ salinity sensitive), were exposed to RNA sequencing (RNA-Seq) study, and single-nucleotide polymorphisms (SNPs) were identified from the RNA-Seq results of the two cultivars. The effects of all SNP variants on genes were determined, and 157 primer pairs of candidate SNP were engineered by high-impact transcripts. Following confirmation using PCR technique of results of ‘Om Rabia’ and ‘Mahmoudi’, 17 SNP markers were developed to measure the rest of 26 wheat lines. Three developed SNP markers i.e. KUCMB_TRIDC7AG078450.6_12, KUCMB_TRIDC2BG061830.1_05, and KUCMB_TRIDC2BG061830.1_08 revealed PCR bands only in salinity-tolerant lines and absent in moderately tolerant or sensitive ones. Association study (GWAS) has been used to recognize the genomic regions/genes controlling salt tolerance in spring wheat at seed germination and seedling establishment. Hasseb et al. (2022) found that a set of 137 SNPs showed a significant correlation with the evaluated characters. Across the whole genome, 33 regions displayed high linkage disequilibrium. The high linkage disequilibrium regions protected 15 SNPs with pleiotropic effect. Nine genes attributable to diverse functional groups were linked to the pleiotropic SNPs. Chromosome 2B contains the gene TraesCS2B02G135900 which acts as a potassium transporter. One SNP marker was found to be related to salt tolerance, was validated in this investigation. Thus, genetic network data joined with GWAS, selective sweeps, and the functional gene survey provided a quantitative genetic outline for recognizing differentially retained loci related to salinity tolerance in wheat. A genetic framework of salinity tolerance at the reproductive stage was studied by genome-wide SNP markers and major adaptability genes in synthetic-derived wheat, and trait-associated loci were utilized to predict phenotypes. Shan et al. (2022) evaluated a lot of 294 wheat germplasm comprising synthetic-derived wheat lines (SYNDERs) and modern bread wheat advanced lines under control and high salinity environments in two sites. The GWAS analysis indicated a quantitative genetic framework of more than 200 loci with minor effect of salinity tolerance at the reproductive stage. The significant trait-associated SNPs were exploited to expect phenotypes utilizing a GBLUP model, and the prediction accuracy (r2 ) varied from 0.57 and 0.74. The r2 estimates for flag leaf weight, days to flowering, biomass and number of spikes/ plant were all exceeded 0.70, confirming the phenotypic effects of the detected loci. The germplasm sets were compared to recognize selection sweeps related to salt tolerance loci in SYN-DERs. Six loci associated with salinity tolerance appeared to be differentially selected in the SYN-DERs. A linkage disequilibrium block on chr5A, including Vrn-A1 gene and its homologs on chr5D, were strongly linked with multiple yield-related characters and days to flowering under salinity stress conditions. The diversity panel was screened more than 68 allele-specific PCR (KASP)

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markers of functional genes in wheat, and the pleiotropic effects of superior alleles of Rht-1, TaGASR-A1 and TaCwi-A1 were discovered under salinity stress. In barley, genetic associations uncover candidate SNP markers and genes associated with salt tolerance have been detected using SNP markers in barley (Thabet et al. 2021). Furthermore, Sayed et al. (2022a, b) identify SNP markers connected with germination and seedling development at 150 mM NaCl as a salinity stress. They performed a genome-wide association (GWAS) by a panel of 208 intermedium-spike barley (H. vulgare convar. intermedium (Körn.) Mansf.) genotypes and their genotype data (i.e., 10,323 SNPs) exploiting the genome reference sequence of “Morex”. Phenotypic results revealed that the 150 mM NaCl salinity treatment significantly decreased germination parameters and seedling-associated traits compared to the control treatment. Also, six accessions (HOR 11747, HOR 11718, HOR 11640, HOR 11256, HOR 11275 and HOR 11291) were celebrated as the most salinity tolerant of the intermedium-spike barley collection. GWAS analysis showed that a total of 38 highly significantly connected SNP markers at control and salinity traits were recognized. From these, two SNP markers on chromosome (chr) 1H, two on chr 3H, and one on chr 4H were significantly allied with seedling fresh and seedling dry weight at salinity stress treatment. Whereas, two SNP markers on chr 7H were significantly linked with fresh and dry weight seedling at control condition. Whereas, under salinity stress, one SNP marker on chr 1H, 5H and 7H was identified for more than one phenotypic trait. In rice, the development of new salt-tolerant germplasm using speed propagation is of interest. So, Rana et al. (2019) precisely introgressed the hst1 gene, transferring salinity tolerance from “Kaijin” into high-yielding “Yukinko-mai” rice by single nucleotide polymorphism (SNP) marker-assisted selection. They exploited a biotron speed-breeding procedure to produce a BC3 F3 population of “YNU31-2-4”, in six generations through 17 months. Whole-genome sequencing revealed that the BC3 F2 genome showed 93.5% similarity to Yukinko-mai and fixed only 2.7% of donor-parent alleles. “YNU31-2-4” seedlings exposed to 125 mM NaCl salt stress had a significantly higher survival rate and improved shoot and root biomasses than the Yukinko-mai. At the tissue level, electron probe microanalyzer assessment designated that seedlings of “YNU31-2-4” avoided Na+ accumulation in shoots under salt stress. At the reproductive stage, “YNU31-2-4” plants showed improved performance and significantly higher net CO2 assimilation and lower yield decline compared to “Yukinko-mai” under salt stress. “YNU31-2-4” is a possible candidate for a novel rice cultivar as it is highly tolerant to salt stress, and could preserve yields under global climate change. In cowpea, a total of 234 Multi-Parent Advanced Generation Inter-Cross (MAGIC) lines along with their 8 founders were utilized by Ravelombola et al. (2022) to improve salt-tolerant cowpea cultivars under greenhouse conditions. Phenotyping was validated using salt-tolerant and salt-sensitive controls. Genome-wide association study (GWAS) was performed using a total of 32,047 filtered SNPs. Results indicated that great variation in characters evaluated for salt tolerance was recognized between the MAGIC lines, a total of 7, 2, 18, 18, 3, 2, 5, 1 and 23 were connected with the number of dead plants, salt injury score, leaf SPAD chlorophyll in salt condition,

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relative tolerance index of leaf SPAD chlorophyll, fresh leaf biomass in salt condition, relative tolerance index of fresh leaf biomass, relative tolerance index of fresh stem biomass, relative tolerance index of the total above-ground fresh biomass and relative tolerance index of plant height, respectively, with overlapping SNP markers between characters. Candidate genes encoding for proteins controlling ion transport, for example, Na+ /Ca2+ K+ independent exchanger and H+ /oligopeptide symporter were known, and epistatic interactions were distinguished. In peanut, Abbas et al. (2021a, b) used polymerase chain reaction to amplify KAT1 gene. Sequence analysis established presences of KAT1 gene in peanut and revealed that Giza 6 and Ismailia1 shared in one SNP (A) in codon 195, whereas Ismailia1 and Samnut 22 shared in SNPs (T) at codon 258, 259, 263 and 406. Sequence Alignments of KAT1 gene between Egyptian and Nigerian peanut genotypes produced in salinity conditions generated 554 base pair with six stop codons and no gaps. The results of sequencing revealed presence of SNPs among the three diverse samples, wherever Giza 6 exhibited one SNP, 4 and 5 SNPs for Samnut 22 and Ismailia 1 rather than KAT1 gene of Arapidopsis thaliana, respectively. In soybean, the quantitative characteristics QTLs for strains F2:5 of the hybrid between the salt-tolerant soybean variety S-100 and the sensitive variety Tokoy was assessed by Lee et al. (2004). The two techniques of SSR and RFLP assisted to discover a major locus of salinity tolerance close to Sat 091 SSR marker on the linkage group (LG) N descended from the tolerant cultivar S-100 represented 41, 60 and 79% of the genetic variance for salinity tolerance in field, greenhouse and combined analyses, respectively.

7.3.2 Gene Transfer Technology to Improve Salt Tolerance Plant breeding programs for salinity resistance necessitate the cooperation between geneticists, biochemistry, physiologists and soil and water scientists with plant breeders in evolving salinity-resistant genotypes. The progress achieved in tissue culture and genetic engineering is of unlimited importance in assisting to succeed this goal. In several situations, plant gene manipulation is comparable to the backcross breeding technique in which desired genes are transmitted (Singer et al. 2021). Contrariwise, the backcross process can supplement one simple trait to a recurrent cultivar, which acts as a backbone to carry out classical breeding practices. Genetic engineering is one of the recent trends in the advanced scientific research system as a fast and accurate technique for the production of plants and lines that tolerate abiotic stresses. Since, the phenomenon of enduring severe environmental conditions appears to be complex, governed by the simultaneous expression of several genes, the use of isoenzyme analyzes and DNA markers is useful in identifying and diagnosing genotypes, identifying genes and assisting in the selection process for progeny carrying desired genes in segregated generations. Genetic engineering depends on gene cloning and plant transformation by selective genes into

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elite breeding lines. Sairam and Tyagi (2004) revealed that the success of genetic engineering experiments depends on the availability of the following three inputs: 1. The gene of interest. 2. An effective technique for transferring the preferred gene from one species to another. 3. Promoter sequences to regulate expression of that gene. Amongst these, the first is deliberated a rate-limiting factor. Stress-responsive genes could be analyzed following targeted or non-targeted approach. The targeted approach depends on the availability of related biochemical information (i.e., defined enzyme, protein, a biochemical reaction or a physiological phenomenon).The nontargeted approach to obtain a preferred gene is indirect. This strategy, for example, includes differential hybridization and shotgun cloning. From the perspective that, plant genetic engineering approaches for salinity stress tolerance are relies upon modulation of enzymes governed the synthesis of functional metabolites (Li et al. 2018). It also, depend on antioxidant enzymes, enzymes for cell membrane lipid biosynthesis and transporters (Ji et al. 2016; Zhang et al. 2017). In the genotype screening technique, superior distinguishing gene can be recognized and separated via exploring natural allelic variation. And the isolated superior gene can be transferred into the targeted superior yield performing cultivars to improve salt tolerance. The gene-based allele specific multiple markers genotyping might be a potential methodology in increasing salt-tolerant varieties. Several works on transforming plants to improve salt tolerance focus on genes that control ion transport, through regulation of sodium uptake and fractionation under salinity stress, and several candidate genes that control this mechanism for the generation of salt-tolerant plants have been identified (Kumawat and Xu 2021; Kumawat et al. 2021). Identification of the osmotin gene, which plays a vital role in the tolerance of tobacco to abiotic stress, and transferred through Agrobacterium as a transmission medium to canola plants let to produce genetically modified plants of Brassica juncea cultivar Pusa Jaikisan. A high expression of the osmotic control gene happened and its transmission was established by PCR procedure Southern analysis in improving salinity and drought tolerance (Tayal et al. 2003). It was also possible to transfer the mtl-1D gene that controls the production of Mannitol-1-phosphate dehydrogenase enzyme from E. coli bacteria to tobacco plants to produce transgenic plants more tolerant to salinity (Tarcyunski et al. 1993). As well as the production of genetically modified lines of chickpea, lentil, peanut and sorghum with the genes tsp1, P2 CSF 1294, coda, mtl-21D, are highly salt-tolerant (Sharmila and Saradhi 2003). In wheat, transgenic genotypes harboring the choline dehydrogenase (betA) gene from Escherichia coli were more tolerant to salinity stress due to an increase of glycine betain content in transgenic plants (He et al. 2010). Transformed genotypes of A. thaliana expressing dehydrin (DHN-5) of wheat increased salt tolerance by enhancing the level of proline synthesis enzyme (P5CS), stimulating antioxidant enzymes and reducing the levels of H2 O2 (Saibi et al. 2015). A codominant-linked marker, cslinkNax2, was exploited effectively by a backcrossing method in durum wheat for the TmHKT1; 5 gene MAS by Munns et al. (2012). They used it to introduce

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salinity tolerance into the elite genotype from donor without passing hostile genes from donor parents after validating the main QTLs in the target genotype for tolerance to salinity. Marker-assisted backcrossing is also an operative traditional breeding procedure used to transmission alleles at target loci (donor-recipient) (Hasan et al. 2022). To recognize key genes and distinguish salt tolerance genes, a collective method is necessary to merge genomics, molecular markers, proteomics, produce new salt tolerant genotypes. Incorporated crop breeding, molecular techniques, biotechnological, and novel breeding approaches to improving salt tolerance mechanisms are essential. Ramayya et al. (2021) utilized Marker-assisted forward and backcross breeding for development of elite Indian rice variety Naveen for multiple biotic and abiotic stress tolerance. Rice plants transformed with Escherichia coli’s trehalose biosynthetic gene(s) (otsA and otsB) as a fusion gene displays less photo-oxidative injury and a more favorable mineral balance under salt, low-temperature and drought stress conditions (Garg et al. 2002). But, the gene transfer for trehalose can also produce changes in rice plant growth for instance delayed flowering, dwarfism, abnormal root development and lancet-shaped leaves (Avonce et al. 2004). On the other hand, ectopic expression of ADC gene from Datura stramonium in rice improved tolerance of transgenic plants to stress by increasing putrescine levels during the stress (Capell et al. 2004). Ectopic expression of P5CSF129A gene of Vigna aconitifolia showed higher proline accumulation and better root growth in transgenic plants of rice under salinity stress (Kumar et al. 2010). Under salt stress, trehalose and proline contents were enhanced and the expression of several stressrelated genes was up-regulated for example OsTPS1 gene in transgenic rice plants and enhanced tolerance of transgenic plants to salt stress (Li et al. 2011). Moreover, Liu et al. (2014) showed that ABA-dependent regulatory pathways enhanced rice tolerance to high salt situations and extreme by introgression the OsbZIP71 gene into transgenic plants. Pi et al. (2018) evaluated the salt tolerance levels of transformed soybean roots overexpressing the 35S promoter-driven coding sequence and RNAi constructs of GmMYB173 and GmCHS5. Also, phospho-mimic (GmMYB173S59D ) and phosphoablative (GmMYB173S59A ) versions of GmMYB173 controlling flavonoid increase. They stated that overexpression of GmMYB173S59D and GmCHS5 conferred salt stress tolerance and increase of cyaniding-3-arabinoside chloride, a dihydroxy B-ring-substituted flavonoid. Application of 5-Aminolevulinic acid (5-ALA) caused improve salt tolerance, Sun et al. (2015) stated that transgenic canola by the 5-ALA-encoding gene, the YHem1 produced higher yield under 200 mmol L−1 NaCl with the ability to produce further 5-ALA, than wild-type canola. Transformed canola produce more product, more chlorophyll content, a larger antioxidant enzyme, high proline content, high sugar content, as well as more free amino acids compared to wild-type canola. Transformed canola plants for high expression of DREBs appearance a distinct improve in salinity tolerance via expression of genes for instance HSF3, COR14, RD20, HSP70, and

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PEROX, indicating better tolerance. Genetically modified plants, can survive in a saline circumstance, compared to wild species (Shafeinie et al. 2014). In another direction, transforming cotton (Gossypium hirsutum) with the choline monooxygenase (AhCMO) gene of Atriplex hortensis enhanced the content of glycine betain in transgenic plants, which gave a better protection of the cell membrane under salinity stress (Zhang et al. 2009). Transcript expression profiling of stress-responsive sugarcane genes in response to short-term salt was investigated by Patade et al. (2012). They obtained transgenic sugarcane plants via engineering higher contents of proline began with the overexpression of genes controlling enzymes pyrroline-5-carboxylate synthetase (P5CS)), which stimulate the two steps between the substrate, glutamic acid and the product proline. Furthermore, Tang et al. (2021) obtained eight PIP family genes, termed ScPIP1–1, ScPIP1–2, ScPIP1–3, ScPIP1–4, ScPIP2–1, ScPIP2–2, ScPIP2–4 and ScPIP2–5, based on the sugarcane transcriptome database. Then, ScPIP2–1 in sugarcane was cloned and characterized. Confocal microscopy observation indicated that ScPIP2–1 was located in the plasma membrane and cytoplasm. Real time quantitative PCR (RT-qPCR) analysis showed that ScPIP2–1 was mainly expressed in the leaf, root and bud, and its expression levels in both below- and aboveground tissues of ROC22 were up-regulated by abscisic acid (ABA), polyethylene glycol (PEG) 6000 and sodium chloride (NaCl) stresses. The chlorophyll content and ion leakage measurement suggested that ScPIP2–1 significantly impacted salt stress resistance in Nicotiana benthamiana through the transient expression test. Overexpression of ScPIP2–1 in Arabidopsis thaliana proved that this gene enhanced the salt tolerance in transgenic plants at the phenotypic level i.e. healthier state, more stable relative water content and longer root length, physiologic i.e. more stable ion leakage, lower malondialdehyde content, higher proline content and superoxide dismutase activity and molecular levels i.e. higher expression levels of AtKIN2, AtP5CS1, AtP5CS2, AtDREB2, AtRD29A, AtNHX1, AtSOS1 and AtHKT1 genes and a lower expression level of the AtTRX5 gene). In alfalfa, Sandhu et al. (2017) selected twelve genotypes under salinity and cloned to decrease genetic variability within each genotype. The most salt-tolerant regenerated clones were G03, followed by G10 and G08 were among the best yielders under saline conditions. The behavior of those genotypes were stable with their mother plants where, all three mother plants displayed great biomass and low Na+ and Cl− shoot contents. The overexpression of P5CS gene from A. thaliana increases proline accumulation and enhanced salt tolerance in transgenic potato (Solanum tuberosum) plants (Hmida-Sayari et al. 2005). Transfer of the yeast TPS1 into tomato caused in higher chlorophyll, starch content and enhanced tolerance against drought, salt and oxidative stresses (Cortina and Culiáñez-Macià 2005). The arginine decarboxylaseADC gene can be employed in conferring tolerance to various stresses (Capell et al. 2004). Hence, the introduction of the (ADC) gene from Avena sativa into Lotus tenuis conferred salinity stress tolerance by additional proline production, which helps stabilize the cell membrane (Espasandin et al. 2018).

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7.3.3 Tissue Culture Technology Tissue culture is one of the best procedures to study the response of crop genotypes to stress situations. In view of the difficulties that plant breeders face in the genetic improvement programs at the whole plant level, the taking of traditional breeding methods for a relatively long time, and the problems facing the breeder in sterility of the F1 plants from divergent parents, incompatibility, deterioration of embryos and genetic barriers that limit the utilization of wild germplasm. Tissue culture technology enables the production a lots of regenerated plants or products within a short period of time from the explants in an artificial nutrient medium (Dogan 2018; Oseni et al. 2018). Therefore, the fashion has raises to use tissue culture technology to take advantage of the genetic variations found in wild species and to overcome barriers in divergent crosses, to develop and produce genotypes resistant to salinity. In general, the use of tissue culture technology achieves the following advantages (About: Rains et al. 1986). 1. Evaluation of a large number of genotypes and selection in vitro using a relatively small space. 2. Shortening the time between generations. 3. Accurate control in the homogeneity and symmetry of environmental and nutrition conditions. 4. The plants produced from cell cultures are similar in growth and development and then the complications due to the difference in plant morphology are reduced. 5. Obtaining large variances between genotypes during cultivation. 6. Selected traits can be evaluated at the cellular level with respect to somaclonal variances from the resulting regenerated plants and their offspring. 7. Isolated protoplasts, cell cultures and callus can be used to study the physiological and biochemical processes that regulate tolerance to salinity stress. Plant cell culture procedures have long been exploited to interpret the secondary metabolite biosynthesis as they are an attractive alternative source for producing high-value secondary metabolites (Daud and Keng 2006). Meanwhile, Verpoorte et al. (2002) utilizing in vitro culture techniques to induce the rapid growth of callus and cell suspension cultures, and extract secondary metabolites. The production of secondary metabolites is influenced by nutritive factors, hormone regimes and environmental circumstances (Kolewe et al. 2008). In vitro culture procedure assists as a beneficial tool to study the salt stress response of suspension cells for salinity under controlled conditions. Therefore, avoiding difficulties rising from physiological and structural variability at the entire plant. Cell and tissue cultures help explore the salinity reactions of crop genotypes at physiological and biochemical levels (Yang et al. 2010). However, McCoy (1987) added that the process of producing regenerative salt-tolerant plants from acclimatized cells appears difficult due to the high level of somaclonal variability. In this respect, the plant breeder is more concerned with the breeding materials that when evaluated in the field show better average performance under salinity stress conditions. In general,

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tissue culture is considered a way to increase variations and produce plants and strains are resistant to salinity, as it has recently been possible to select and produce strains of crops of wheat, rice, flax, canola and alfalfa that are resistant to salinity. The production of pure lines by conventional breeding practices is a timeconsuming process (7–12 generations) and could delay new varieties production. One area of biotechnology, anther culture technique, derived from tissue culture techniques, offers great promise for plant breeding. Anther culture (androgenesis) is to obtain haploid embryo using immature pollens (microspores) in anthers cultivated on nutrition media. This procedure usually needs short time to be conducted (only one generation) and could accelerate the production of new varieties with improved traits (Barakat et al. 2012). Another culture is a technique utilized to produce haploid embryos using immature pollen microspores from anthers cultivated on nourishment media. This technique generally needs only a short time (one generation) and can speed up the release new promising genotypes (El-Hennawy et al. 2011). The technique of cultivating immature embryos in wheat was used to produce highly tolerant strains to salinity with a high yield. The immature embryos of Sakha 8 (saline tolerant) and strains 25 and 28 (salt sensitive) were cultured on MS media under three levels of seawater salinity (Zero, 6000 and 9000 ppm). They were able to produce plants grown in pots under a greenhouse under controlled conditions of temperature and lighting and produce R1, R2 and R3 generation plants under the same conditions (Sabry et al. 2006). The researchers completed the study by cultivating grains of 71 plants of the R4, the three parents, Sakha 8, and the two strains 25, 28 with four other commercial varieties i.e. Sids 1, Gemmeiza 10, Sakha 93 and Sakha 94 in a field experiment in two cement basins filled with soil. The first basin was designated for salinity treatment (Irrigation with sea water with dilution to a concentration of 10,000 ppm), and the second basin was designated for treating irrigation water with tap water (without salinity) in three replications. It was possible to select eight strains in the R4 generation. Four of them were characterized by salinity resistance and high yield with an increase of > 45% over the original parents. The effect of genotype is the key restrictive element of in vitro androgenesis. Several wheat genotypes are incapable to complete morphogenesis in anther culture (Yermishina et al. 2004). Through the selection method, information about the combining ability of parental genotypes used for hybrid breeding is vital. This information is necessary for the appropriate selection of appropriate parents, to recognize promising crosses. In this respect, Gemmeiza 7, Gemmeiza 9, Giza-164, and Giza-168 and Line-115 were selected on the basis of anther culture response (ElHennawy et al. 2011; Al-Ashkar et al. 2014), while the check cultivar Sakha 93 was unresponsive of anther culture (El-Domiaty et al. 2009 and Amin et al. 2010). Barakat et al. (2012) improved a simple anther culture protocol for a variety of Saudi wheat genotypes. Seven wheat genotypes were tested in anther culture on five different medium protocols for their ability to initiate callus and green plants. Results revealed that in vitro characters were highly significantly affected by the genotypes, medium protocol, and their interactions between G x E on callus induction, callus weight and shoot formation resulting from anther explants. The explants

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% that developed calli reached from 0.41% (Lang) to 15.39% (Irena) with an average 4.45%. The genotype Irena formed the highest shoot formation (69.65%). Genotype Yecora Rojo (13.73%) was significantly inferior to all the tested genotypes for shoot formation. The response of anther culture of four F1 wheat crosses and their parental genotypes was evaluated by Al-Ashkar (2013) on four different media for their ability to initiate callus and green plantlets. Regarding NaCl concentrations, medium without NaCl provided better response to multiple shoots rather than the other media. Two crosses Line-A*Misr-1 and Line-A*Gemmiza-11 exhibited the highest response in multiple shoots had parent that displayed very good response. The parental Line-A and the cross Line-A*Msir-1 gave the maximum values of salt tolerant index, whereas check parental Line-A recorded salt sensitivity index (0.13) as compared to its derived crosses. Salt tolerance index revealed that, parental Line-A and the cross LineA*Msir-1 produced the highest mean estimates, but the cross Line-A*Gemmiza-7 was the lowest one. Doubled-haploid technique is vital to speed up the release of a recenr genotypes tolerant to salinity stress. Production of doubled haploid plants through anther culture together with gene stacking for multiple agro-morphological and nutritional value traits is an attractive approach to fix these traits. More than 280 varieties have been produced with the use of doubled haploid technique in several crops (Kaushal et al. 2015). And in another study, Al-Ashkar et al. (2019) detect salt tolerance variation in 15 wheat lines developed by doubled haploid (DHL) technique that compared to the salt-tolerant check variety Sakha 93 at three levels of salinity (0, 100 and 200 mM NaCl) for 25 days. Three traits i.e. shoot length, shoot dry weight and catalase activity appeared to be more important in enhancing salt tolerant. The salinity tolerance indices categorized one novel line DHL21 and the check cultivar Sakha 93 as greatly salt-tolerant; DHL25, DHL26, DHL2, DHL11 and DHL5 as tolerant as well as DHL23 and DHL12 as moderate. Discriminant function analysis and MANOVA suggested differences among the five groups of tolerance and Sakha 93 selected as donor to improve salinity tolerance during seedling stage. The tolerated lines; DHL21, DHL25, DHL26, DHL2, DHL11 and DHL5 could be also recommended as novel genetic resources for improving wheat to salinity tolerance in breeding programs. Doubled-haploid salt tolerant lines in rice were produced through anther culture. Anther culture technique was employed in the production of rice genotypes tolerant to salinity up to a level of 10 dS m−1 , namely Hexi 30//SK 101, SK 101/GZ 5844//IR 65600-91 (Draz 2004). Under normal (0 mM NaCl) and saline (25 mM NaCl ~ 5.6– 5.8 dS m−1 ) 42 genotypes; consisted of 36 doubled-haploid lines, four commercial varieties, and two check varieties were evaluated by Anshori et al. (2022). Salinity selection index model including yield and productive tiller was utilized for selecting rice genotypes tolerant to salinity stress under soil artificial screening. Salinity selection index was developed through a combination of factor analysis, stress tolerance index and path coefficient analyses have recognized 15 doubled haploid rice lines which were expressed as good tolerant lines under salinity stress.

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Also, it is helpful in producing 144 dihaploid winter raps strains of hybrids between the two cultivars of Samourai x Mansholt’s Hamburge, some of them were distinguished by their high productivity and endurance of stress conditions (Gull 2002). Biochemical studies through tissue culture have explored several aspects of crop plants cell metabolism, of the adaptive mechanisms to osmotic and ionic stresses caused by high salt. In-vitro cultures displayed genetic variances between the produced somaclones, which could be utilized to develop new promising somaclones and overawed the classical crop breeding. The resulting somacolnal variations in tissue cultures are an important tool in selection programs for salinity tolerance. It is observed that the NaCl-treated calli compared to the control calli, implicating that sugarcane can be expressed as a Na+ -excluding plant species. The retained K+ content was significantly higher under the control than in the NaCl-treated calli. Growth retardation and reduced cell viability were correlated with a marked increase in Na+ and a corresponding reduction in K+ concentrations, indicating the typical glycophytic nature of sugarcane (Patade et al. 2008). Salinity-tolerant sugarcane clone accumulated less Na+ and more K+ rather than a sensitive counterpart clone, therefore displayed a higher K+ /Na+ ratio (Wahid and Ghazanfar 2006). Whereas, Prammanee (2004) produce regenerated plants from sugarcane tolerate to salinity level of 1.0–2.0% (w/v) in a NaCl environment compared to the original variety F36-819. Moreover, Abo-Elwafa et al. (2021) obtained genetic difference between eleven somaclones of sugarcane generated through immature leaves of Egyptian commercial variety GT-54 9. General mean over the two ratoon crops showed that somaclones number 7 and 8 exceeded the donor in stalk height (14.35 and 9.48%), stalk weight (9.52 and 15.24%), stalk number/fed (21.00 and 31.25%) and cane yield (32.16 and 52.02%), correspondingly. The In-vitro cultures displayed genetic differences between the produced somaclones, which could be exploited to improve new genetic recombinations and overawed the classical cane breeding. In Parkia biglobosa cell suspension culture, Abbas et al. (2021) application of NaCl concentration levels of (0, 100, 200, 300, 400, 500, 600 and 700 mM) to identify the effects of NaCl stress on several physiological and biochemical parameters through 18 days. Results revealed that the highest percentage of viability and viable cells/ml was detected at 500 mM at 12th day with significant variances than the other treatments. NaCl treated cell suspension culture amplified Na+ accumulation and reduced accumulation of K+ , Ca2+ , P3+ and N3+ , whereas Na/K ratio increased gradually as a function of external NaCl. Proline content of treated cell suspension at 200 mM reached the maximum rate at 18th day with significant difference than the other treatments then steadily reduced up to 700 mM registered the lowest proline content. The difference in protein patterns band induced in all different cultures, particularly in callus cells and 600 mM NaCl verified the most variations than other cultures. Generally, with tissue culture technology, numerous valuable plants were propagated such as wheat (Lutts et al. 2004; Benderrad et al. 2012), rice (Miki et al. 2001; Taratima et al. 2022), Chickpea (Kaashyap et al. 2018), Soybean (Mangena 2021), potato (Hossain et al. 2007; Queirós et al. 2007; Hassanein and Salem 2017),

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sugarcane (Nikam et al. 2014; Granja, et al. 2018), tobacco and Medicago truncatula (Elmaghrabi et al. 2019) and Moringa oleifera (Salem et al. 2017; Bharati et al. 2022).

7.3.4 Epigenetic and Methylation of DNA Crop plants developed a number of approaches, including regulation of genes through epigenetic changes, to manage with environmental pressures. Thus, understanding epigenetic regulation and the function of High-affinity potassium transporters HKTs would enable development salt-tolerant genotypes. The DNA methylation is dynamically regulated by the methylation and demethylation of cytosine in reaction to environmental pressures. High-affinity potassium transporters (HKTs) may contribute to the homeostasis of sodium and potassium ions in plants under salt pressure. The alteration in the expression of HKTs has been reported to confer tolerance to salt stress in plants. A rapid increase in histone H3 Ser-10 phosphorylation was detected in the leaves of tobacco and Arabidopsis subjected to high salinity. Whereas, the level of change in this modification was much slower than in cultured cells (Sokol et al. 2007). The methylation of DNA and changes of histones in response to salinity showed, de novo methylation and demethylation processes happen at CpCpGpG sites (Labra et al. 2004). DNA methylation, histone alterations, as well as chromatin reconstruction are the main constituents of epigenetic regulation (Attwood et al. 2002). Ethyleneresponsive element binding factor (EBF) is the most important gene that undergoes DNA methylation of salinity stress in crop plants (Guangyuan et al. 2007). Genetic differences in cytosine methylation and their effects on HKT genes expression was assessed by Kumar et al. (2017) in different wheat genotypes under salt stress. A genotype- and tissue-specific increase in cytosine methylation was stimulated by NaCl stress that downregulated the expression of TaHKT2; 1 and TaHKT2; 3 in the shoot and root tissues of Kharchia-65. Thus, contributing in improving salttolerance ability. While, TaHKT1; 4 was expressed in wheat roots and was downregulated under salt stress in salt-tolerant genotypes, it was not regulated by changing in cytosine methylation. Through a protocol of RNAextraction and formation (cDNA) and qRT-PCR, Irshad et al. (2022) performed expression analysis of HKTs genes from samples of root and shoot of tolerant and sensitive wheat strains. The differential expression of HKT2; 1 and HKT2; 3 explained the tissue and genotype specific epigenetic variations. DNA methylation plays a vital role in gene expression by the RNA-directed DNA methylation (RdDM) of genes and induction of histone modulations. Yan et al. (2010) indicated that cytosine methylation is involved in numerous vital biological processes such as transposon movement, genome imprinting and regulation of gene expression in rice. And these epigenetic modifications can be inherited in the epigenetic memory form (Boyko and Kovalchuk 2010). Moreover, Uddin et al. (2013) on three maize hybrids with contrasting salt tolerances showed an accumulation of highly methylated pectin in the salt-tolerant maize genotype, which favoured their cells’ elongation.

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In canola, Jian et al. (2016) stated that more than 340 miRNAs contribute in the post transcription mechanism of regulation of the salt-responsive genes. Sixty NAC TFs were described in Brassica napus (Wang et al. 2015). Moreover, Two B. napus NAC TFs (BnNAC2 and BnNAC5) factors act in negative regulation of salinity and osmotic tension tolerance were recognized by Zhong et al. (2012). Whereas, Wang et al. (2016) stated that MET18 represents a component of the active DNA demethylation pathway. MET18 has been shown to play an epigenetic role in regulating gene expression in Arabidopsis.

7.3.5 Proteomic Approaches Since 1996, Marc Wilkins introduced the phrase ‘proteome’ for the first time, a term. Proteomic technology utilized in protein isolation and protein recognition based on mass spectrometry. In sensitive varieties to salinity stress, the plant proteome is differentially expressed. Proteome has a direct role in the detection of genes and proteins controlling plant salinity stress response and tolerance mechanisms (Wang et al. 2014). Also, in the detection of cell surface markers/biomarkers, and the manufacture of drugs (Abdallah et al. 2012). Proteomics has become beneficial in the field of plant genomics in latest years, and may be utilized to recognize proteins extracted from tissues or cells in response to growth and particular environmental environments and to recognize the levels of expression of the proteins found (Aslam et al. 2017). The insertion of genes encoding proteins, for the synthesis of osmolytes, receptors, ion channels, and salt-responsive signaling factors or enzymes into salt-sensitive genotypes, to confer them salinity-tolerance (Tuteja 2007). Many research related to the comparative analysis of proteomes between crop genotypes subjected to salinity stress and control condition have been directed in several crops for instance, wheat (Ma et al. 2018), rice (Nyong’a et al. 2019), barley (da Silva et al. 2019), Brassica napus (Bandehagh et al. 2011), soybean (Yin et al. 2015), Arabidopsis thaliana, Bruguiera gymnorhiza (Tada and Kashimura 2009) and Andrographis paniculata (Hossain 2016).

7.4 Transcriptional Regulation and Gene Expression in Relation to Salinity Stress Tolerance The advanced research fashions indicate the appearance of induced variations in the types of messenger-RNA and proteins in response to osmotic and salinity stress conditions. This causes a change in the biochemical and physiological processes and the plant phenotype. These changes also occur in response to external treatment with abscisic acid as a mediator of osmotic stress. Several reports indicate

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the induction of specific genes and/or proteins associated to tolerance of salinity and other environmental stresses. In this context, transcriptional factors like WRKY (Banerjee and Roychoudhury 2015), LEA, NAM, ATAF and CUC (Singh and Laxmi 2015) and DREB (Wang et al. 2019) are involved in signaling pathway and tolerance response against different abiotic stresses. These transcriptional factors are involved in the biosynthesis of numerous osmoprotectants, expression and regulation of different genes encoding various proteins, phytohormones and secondary metabolites (Banerjee and Roychoudhury 2015; de Zelicourt et al.2016; Wang et al.2019).

7.4.1 Genes up or Down Regulated by Salinity Gene expression studies permitted us to categorize genotypes according to their ability to regulate various salt tolerance mechanisms. Pyramiding diverse components of the salt tolerance mechanism may cause more salt-tolerant crop genotypes (Sandhu et al. 2017). It has been confirmed that there are many genes that respond to salinity stress and perform the function of ion homeostasis, including what is responsible for elimination of the sodium ion Na+ across the plasma membrane, the partitioning and distribution of sodium in the vacuoles, or the absorption of potassium, which works on osmotic balance. Evidence indicates that salinity and drought response genes operate under a complex system and can be divided into early responsive genes and delayed responsive genes. Examples of early response genes are the rd 29A gene in Arabidopsis, the Em gene in wheat and the Ms PRP2 gene in alfalfa, Hijazi and the gene family AtMyb, RD22Bp, CBF/DREB, ABF/AB 15/AREB in sugarcane (Dwivedi 2004). Significant advances in the molecular biology of stress have been made in recent decades to identify the Cis-regulatory elements in late response genes and the cloning of early response genes encoding proteins under saline conditions. It has been possible to induce the production of many proteins under salt stress in many crops such as barley, wheat, tobacco, beans and others. In barley, it was found that salt stress reduces the total mRNA content in roots by about 20–30% and induces about 21 new species of RNA, while inhibiting of DNA (Ramagopal 1987). Differences were recorded between salt-tolerant and sensitive cultivars in inducing protein synthesis in roots, stems and callus tissues under saline conditions (Ramagopal 1988). These changes occur in gene expression at the transcription level or after the translation and translocation process. The regulatory action and activity of a specific group of proteins and/or genes increased under salinity and drought stress. Whereas, the osmotic stress associated with the lack of water and salinity was accompanied by a decrease in cell turgor and an increase in the stimulation of secretion of abscisic acid, which followed the induction of gene action by an increase or decrease of specialized polypeptides (Plant et al. 1991). Germin-like proteins GLPs are ubiquitous plant proteins, it is of vital importance in plant responses to various abiotic stresses. Germin gene expression changes in

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wheat and barley during plant development under salinity stress and treatment with abscisic acid or indole acetic acid (Hurkman and Tanaka 1996). The Germin gene is also expressed during the normal germination process of cereal crop embryos, and it was identified in the form of oxalate oxidase production (Lane et al. 1993). Germin-like protein genes display modular expression in salt stress in the best rice cultivars (Anum et al. 2021). Some Osmotin-like proteins, including SRgp 24, glycoprotien-24-KD, were found in ice plant and it was noted that SRgp 24 protein has the same sequence similar to osmotin, but its down action is reduced in the tissues of leaves and stems under saline conditions (Yen et al. 1994).). It has been found in halophytes, such as artiplex, a protein related to osmotin that is less active in salinity, temperature, disease and insect infestations (Casas et al. 1992). At the level of tissue cultures, it was observed that the tolerance of cells may be lost during the process of breeding, and that there are many genes that increase or decrease their activity under sodium chloride stress. And that a single mutation at the promoter site in the selected strain of alfalfa can affect the expression of many genes. Winicov (1994) detected a correlation between salinity tolerance in the selected strain and the increase in the expression of ribulose-1.5-bisphosphate carboxylase/oxygenase enzymes activity due to the nuclear (rbcS) and cytoplasmic (rbcL) genes, and heritability coefficient values indicated that it is a semi-dominant trait in regenerated plants. It was potential to isolate 16 salinity-induced (ESI) genes in the specific hybrids between bread wheat T. aestivum 2n = 6 x = 42, AABBDD Chinses Spring variety and Lophopyrum elongatum variety Löve 2n = 2 x = 14, EE. Octaploid amphiploid plants showed higher tolerance to salinity compared to wheat, and it was exploited in the development of salt-tolerant strains (Zhong and Dvorak 1995). The genes ESI 4, ESI 14, ESI 15, ESI 28 and ESI 32 were found on chromosome E 5. Chromosome 3 E and 5E contribute to most of the tolerance to salinity shock, while gradual salt tolerance was attributed to chromosomes 3E, 4E, 5E with contributing effects from chromosomes 1E and 7E. The ESI 13 gene, which is located on the long arm of chromosome 4 with similar genes on chromosomes 4 LB and 4 LD, is also induced under stress treatments with potassium chloride, abscisic acid and mannitol shock in wheat (Gulick et al. 1994) and the expression of the ESI 35 gene is also induced by an increase in UP-regulated which is located on the chromosome 6 L with similar genes on the same chromosome in wheat genomes A, B and D under osmotic stress conditions. Identification at least three chromosomes responsible to salt tolerance in the cross between wheat and barley (Forster et al. 1990). Similar genes were found in wheat to those in Lophpopyram elongatum whose action is increased regulated with salinity stress (Dubcovsky et al. 1994). In sorghum, an induced gene was identified in some genotypes when exposed to salinity (Lerner et al. 1994). Recently, HAL1 gene controlling salt tolerance in yeast at high expression, as well as the gene (mtlD) Manitol-1-phosphate dehydrogenase transgene in bacteria, increase mannitol levels in roots and salt tolerance in higher plants. These genes can be utilized in the process of genetic modification to produce higher salt tolerant crop

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varieties. This indicates that salt tolerance is linked to the regulation of the action of genes responsible of salt tolerance, if present. A large number of transcription factors and salt-responsive genes that are either up regulated or down regulated in response to salt stress have been identified and characterized using transcription and genomics approaches (Gisbert et al. 2000; Abebe et al. 2003; Maheswari et al. 2010; Patel et al. 2017). Transcription factors are the most important regulators controlling gene expression, among which the bZIP, WRKY, AP2, NAC and C2H2 zinc families and DREB families comprise a great number of stress-responsive members. These transcription factor genes are able to control the expression of a wide range of target genes by binding to the cis-influencing element in the promoters of these genes. Johnson et al. (2002) showed that the expression of bZIP genes was up regulated in the salt-sensitive wheat cultivar, when subjected to long-term salinity, but declined in the salt-resistant species. Overexpression of the NAC transcription factor in both rice and wheat grants salt tolerance, thus predicting their role in alleviating stress (Nakashima et al. 2007). Indeed, barley over-expressing the HKT subfamily 2 gene, HvHKT2;1, had greater xylem and leaf Na+ content in plants grown in saline and was linked with increased salt tolerance (Mian et al. 2011). These genes mainly carry out ion transport or homeostasis functions such as the SOS genes, AtNHX1 and H+ -ATPase, aging-related genes i.e. SAG, and molecular chaperones i.e. HSP genes. Some ROS genes that scavenge and regulate osmosis are also regulated by salinity in some plant species. In this respect, continuous exposure of rice plants to salinity for approximately 24 h led to an up-regulation of glutathioneS-transferase and ascorbate peroxidase, which play an vigorous role in the scavenging of reactive oxygen species (Kawasaki et al. 2001). Menwhile, Baisakh et al. (2006) found that when exposed plant species of halophytes Spartina alterniflora to salt stress show upregulation of ten genes associated with osmotic regulation. Roshandel and Flowers (2009) recognized PRP, SAG, HSPC025 genes in rice expressed under NaCl concentration (50 mM) and expression of OsHsp17.0, OsHsp23.7 genes under 200 mM NaCl concentration (Zou et al. 2012). Sandhu et al. (2017) showed that salt-tolerant genotypes exhibited upregulation of the SOS1, SOS2, SOS3, HKT1, AKT1, NHX1, P5CS1, HSP90.7, HSP81.2, HSP71.1, HSPC025, OTS1, SGF29 and SAL1 genes. Gene expression studies helped in classifying genotypes according to their ability to regulate different salt tolerance mechanisms and producing salt tolerant genotypes. Results of several studies point to that ∼8% of all genes 98 responsible for crop adaptation to poor soil are transcriptionally converted by salt stress in Arabidopsis, and approximately 70% of the affected genes differ from those altered by water stress (Bohnert et al. 2001) as well as in rice (Rabbani et al. 2003). Also, a set of 444 genes being regulated by salinity stress and the transcription pattern of a number of genes differed markedly between the primary, crown and seminal root in response to salinity stress (Zhang et al. 2015) and a total of 7 SiGolS and 15 SiRS genes were recognized in the sesame genome under multiple abiotic stresses (You et al. 2018). A unique maize homeodomain-leucine zipper (HD-Zip) I gene, Zmhdz10, positively adjusts salt tolerance in rice and Arabidopsis (Zhao et al. 2014).

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The expression of maize MYB transcription factor ZmMYB3R improve salt stress tolerance in transgenic plants (Wu et al. 2019). Whereas, WRKY114 Maize gene negatively regulates salt-stress tolerance in transgenic rice (Bo et al. 2020).

7.5 Transformation and Tolerance to Salinity The effects of salinity on crop plants include osmotic stress, disruption of membrane ion transport, direct toxicity of high cytoplasmic concentrations of sodium and chloride to cellular processes and induced oxidative stress. Ion transport is a dangerous feature that controls salinity tolerance in crop plants. This includes cation and anion transport through the plasma membranes of cell roots, transport across vacuolar membranes, transport of ions over long distances across xylem and phloem, and salt secretion and increase by specialized cells. One of the most harmful effects of salt stress is the disruption of the plant’s ionic balance mechanisms. The similar radii of Na+ and K+ make it problematic for passage proteins to discriminate between both ions. So, in situations of high sodium, there is a significant uptake of Na+ through transporters or K+ channels (Blumwald et al. 2000). The activity of Na+ /H+ antiporters might be limited by their number or by the H+ difference across the membranes. Increasing the capability of a proton pump would enhance the salt tolerance of the plant. The vacuolar H+ -PPiase, AVP1, which might be essential to energize the vacuole membrane under salt stress, was over-expressed in Arabidopsis and improved its salt tolerance (Gaxiola et al. 2001). Transgenic genotypes were capable of growing under 250 mm NaCl, while the wild type died. The improved performance of transgenic genotypes may be due to its high accumulation of Na+ and K+ (Laurie et al. 2002). Halophyte plants living in high salt concentrations provide a unique source of tolerance traits and genes for transmembrane proteins involved in ion transport and their regulators, such as genes that function under salinity and can be transferred to important agricultural crops to increase their tolerance. The HAK5 plant vector plays an important role in potassium uptake at low soil potassium concentrations. HKT cation transporters play a significant role in the transfer of Na+ and K+ into the xylem and in the uptake of ions by roots. Over-expression of a Na+ -and K+ -permeable HKT transporter increases salt tolerance in barley (Mian et al. 2011). Shi et al. (2002) stated that salt overly sensitive SOS1 encodes a plasma membrane Na+ /H+ antiporter, while, SOS2 encodes a serine/threonine protein kinase which motivates SOS1 in Arabidopsis (Liu et al. 2000). Meanwhile, Surekha et al. (2005) showed that Arabidopsis mutants proved the presence of the SOS signaling pathway that senses salt stress, whichever by the Ca2+ sensing activity of SOS3 or direct sensing of Na+ by SOS1 and adjusts Na+ efflux and other ion transport and salt tolerance mechanisms. Transport via membranes is commonly intermediated by ion channels and transporters that confirm selective passage of specific ions. For the salt-sensitive plant

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ideal, Arabidopsis thaliana, over a thousand genes are expected to encode membrane proteins, over one hundred of these determine the cation channels and transporters (Mäser et al. 2001). High Na+ concentration in the external solution cause a decrease in both K+ and 2+ Ca concentrations in plant tissues (Hu and Schmidhalter 2005) due to the antagonism of Na+ and K+ at uptake site in the roots, the effect of Na+ on K+ transport into the xylem (Lynch and Lauchli 1984) or the inhibition of uptake processes (Suhayda et al. 1990). Sodium chloride is the main form of salt in the soil as the Na+ ion entering the cytoplasm is transported into the vacuole via the Na+ /H+ antiporter. There are two types of H+ pumps exist in the vacuolar membrane: vacuolar-type H+ -ATPase (V-ATPase) and vacuolar pyrophosphatase (V-PPase) (Dietz et al. 2001, Wang et al. 2001). Furthermore, Schroeder et al. (2013) detected transporters occurred on the plasma membrane, belong to the histidine kinase transporter family, similarly play an dynamic role in salt tolerance through regulating transportation of Na+ and K Class 1 HKT transporters secure the plant against adverse effects of salinity thru preventing excess accumulation Na+ in leaves as observed in rice. Under saline circumstances, seedlings of Atriplex canescens accumulated more Na+ in both plant tissues and salt bladders, and reserved fairly constant K+ in leaf tissues and bladders by increasing the selective transport capability for K+ over Na+ from stem to leaf and from leaf to bladder (Pan et al. 2016).

7.6 Role of Cellular Signal Transduction in Salinity Tolerance Exposure of crop plants to salinity stress, induces plant cells to send many intercellular signals, inducing the expression of several genes and activating the pathways of the synthesis of many biochemical responsible for resistance to abiotic stresses. The salinity signals of plant cells play a vital role under osmotic stress conditions, eliciting several metabolic responses. Biotechnology and molecular biology have benefited in understanding the genomic structure, gene function and responses associated with salinity. It has been possible to isolate many stress-related genes from different plant species. It was observed that several osmotic active substances were accumulated in plants under stress conditions, including sucrose, sorbitol, mannitol, glycerol, arabinol, benitol, nitrogenase compounds such as proline, betaine, glutamate, aspartate, glycine, choline, and organic acids such as oxalate and malate. The plasma membrane acts as a natural barrier to the passage of aqueous solutes and as a substance for proteins associated with solute uptake and transport. In general, the recognition and discrimination of the salinity signal in the plasma membrane entails the occurrence of many changes in the biochemistry and physiology of the cell (Fig. 7.4). Kissoudis et al. (2014) enhancing crop resistance to stress through physiological and molecular crosstalk.

7.6 Role of Cellular Signal Transduction in Salinity Tolerance Fig. 7.4 Systemic crop resilience induced under the influence of salinity stress (Modified after Kissoudis et al. 2014)

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Abnormal stomata functions

Leaf Na+ accumulation

SAR Signaling interference

Systemic signals

Na+ H2O H2O Na+

Na+ H2 O

Osmotic salinity stress

Uptake/homeostasis

The start of salinity stress in crop plants triggers pathways, who comprise a receptor, which understands the stress, changes in protein activity, alterations in gene transcription through signaling intermediates, and phosphoprotein cascades (Hasegawa et al. 2000; Zhu 2002). The small ubiquitin—like modifier (SUMO) was identified as a critical component to the alteration of salt—signaling molecules (Conti et al. 2008). Attempts have been completed to adapt the Glyoxalase pathway to produce transgenic, salt-tolerant tobacco plants. This pathway is governed by two enzymes, Glyoxalase I and II, which interact cooperatively in the presence of reduced glutathione as a co-factor for the conversion of the cytotoxic Methylgyloxal-a ctyotoxic compound to lactic acid. Where, Gly enzyme showed overexpression in rapeseed, leading to improve salinity tolerance in transgenic tobacco plants. This trait showed genetic stability, and the first generation T1 of transgenic plants were characterized by the ability to complete their life cycle under salinity conditions. Moreover, a high expression of Gly II enzyme when transferred from rice to tobacco, either alone or in cooperation with Gly I, led to a complete adaptation of the Glyoxalase pathway to produce double trangenics plants that were more resistant to salinity compared to those resulting from a single genetic modification just. The genetic transformation

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analysis of the first generation with two genetic modifications indicated the genetic and functional stability of the salinity tolerance. Also the excess Na+ ions were retained in aged leaves without any effect on seed quality (Pareek et al. 2003). Hydrogen peroxide also acts as a signal molecule inducing biosynthesis pathways for antioxidants from various enzymes and substances. These protect the biochemical system and cellular functions in wheat plants under environmental stress conditions (Angrish et al. 2003). The level of free sterols and triglycerides increased in soybean cultivars in response to the salinity signal, while the fatty acid composition remained unchanged in the tolerant and sensitive cultivars. Salinity affects the activity of the proton enzyme H+ -ATPase associated with the plasma membrane and the tonoplast. Induction of proton-emission activity occurs as a result of changes in membrane fluidity as a signal explaining the mechanism of drought and salinity tolerance. H+ -ATPase interacts with the plasma membrane and acts as a pump and transporter of extracellular salts, and contributes to inducing H+ proton emission, Ca2+ influx, and translocation in the endoplasmic membranes, cell organelles, mitochondria and chloroplast membranes (Bautista et al. 2002; Quintana et al. 2006). Ca2+ channels and cytosolic calcium levels act as second salt signal transduction. Research reports indicate the presence of many types of calcium channels in higher plant cells, which increase the induction of biological processes, protein kinase expression and other regulatory proteins. The recorded changes in calcium levels indicate its role in the root response to salinity stress. Rengel (1992) showed that the calcium signal is transmitted to the leaves, if the signal is not preceded by a limited water supply. Glycoprotein is a receptor molecule to recognize and perceive the sodium chloride salt signal. And it was known that the type of proteins G-proteins play a role in stimulating and encouraging cells and making connections between the bases of DNA. Raghuram and Sopory (1995) explained the importance of Gproteins, protein kinases and phosphoinositides in signal transmission, regulating nitrate reductase gene expression, regulating expression and functions of a number of other enzymes, modulating protein synthesis, providing metabolic energy and stimulating plant response to environmental stresses. In maize, the process of transferring and redistributing the metabolites to the meristem apical and the elements necessary for the elongation and expanding the leaves during the initial stages of stress, occurs in response to the signal that stimulates the development of the plant (Lazot and Lacuhli 1991). In sugar cane, abscisic acid acts under severe salinity stress as an effective signal for sodium exclusion and uptake calcium and potassium (Dwivedi and Qadar 2004). Ashraf (2002) showed that the pattern of uptake and accumulation of toxic ions (Na+ and/or Cl− ) in cotton tissues of plants exposed to saline circumstances seems to be due to the mechanism of partial ion exclusion of Na+ and/or Cl− . Maintenance of high tissue K/Na and Ca/Na ratios is advised to be a significant selection trait for salt tolerance in cotton. Whereas, judging the proper mechanism of ion transport through cell membranes in the literature, it was obvious that the PM-ATPase responds to an increasing supply of Na+ in the growth environment. However, the activity of the transport proteins on the plasma membrane alone was inadequate to regulate

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intracellular Na+ levels. The incapability of Vacuolar-ATPase to respond to Na+ gave an indicator of the deficiency of effective driving force for the compartmentalization of Na+ in cotton. Furthermore, the role of antioxidants in the salt tolerance of cotton suggested that high levels of antioxidants and an active ascorbate–glutathione cycle are related to salt tolerance in cotton. Gao et al. (2018) showed that calcium-dependent protein kinases are vital in regulating responses to salt stress in cotton. Based on RNA-seq analysis, Lei et al. (2018) discovered 2237 and 1125 differentially expressed genes (DEGs) between alfalfa cultivars ZM and XJ in the presence and absence of salt stress. Under salt management, the number of DEGs in cultivar XJ (19373) was four times of that in cultivar ZM (4833). Also specific differential gene expression patterns were also detected. Under salt stress, ZM compared to XJ, maintained fairly more stable expression levels of genes associated with the ROS and Ca2+ pathways, phytohormone biosynthesis, and Na+ /K+ transport. Numerous salt resistance-associated genes revealed higher levels of expression in ZM than in XJ, containing a transcription factor. The expression of numerous photosynthesis and growth hormone-related genes reduced more intensely in cultivar XJ than in cultivar ZM. Through comparison, the levels of expression of photosynthetic genes were lower in cultivar ZM under low-salt situations.

7.6.1 Cell-Specific Signaling Cell-specific Signaling has been detected in Arabidopsis thaliana roots by Kiegle et al., (2000). They examined the changes in cytosolic Ca2+ in response to a sudden and large Na+ stress and detected distinctive oscillations in cytosolic Ca2+ in endodermal and pericycle cells. Salt environment leads to cellular desiccation, which causes osmotic stress and removal of water from the cytoplasm which causes a reduction in the cytosolic and vacuolar volumes. Salt stress often leads to ionic and osmotic stress in plants, either accumulating or decreasing specific secondary metabolites in crop plants (Mahajan and Tuteja 2005). Phosphoethanolamine N-methyltransferase transcripts have been revealed to be intensely upregulated by salinity stress in sugar beet cell cultures (Yang et al. 2013), in roots, stems, and leaves of maize (Wu et al. 2007), and in shoots of barley (Walia et al. 2006) and roots (Ueda et al. 2002). Overexpression of a maize Phosphoethanolamine N-methyltransferase improved the salt tolerance of transgenic Arabidopsis (Wu et al. 2007). Overexpression of certain genes that contribute to altered salt tolerance in canola has been reported, including drought-responsive element-binding transcription factors (DREBs). These genes include malate dehydrogenase, triose phosphate isomerase, fructose-bisphosphate aldolase, UDP-glucose dehydrogenase, methionine synthase and heat shock protein 70 are under salt stress conditions (Gharelo et al. 2016). In rice, Zhang et al. (2011) found three GPDHs (OsGAPC1-3) are responsive against salinity tolerance. OsGAPC3 was overexpression of the most highly saltinduced transcript, conferred tolerance to salinity compared with the wild type.

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Enhancing salt tolerance of rice via overexpressing GPDH was achieved by regulation of hydrogen peroxide levels. However, the plants, i.e. glycophytes and halophytes respond differently under diverse salt stress conditions. Many studies have shown an induce photosynthesisrelated proteins under salt stress conditions in A. thaliana (Pang et al. 2010), T. aestivum (Peng et al. 2009), Triticum durum (Caruso et al. 2008), rice (Oryza sativa) (Kim et al. 2005), Glycine Max L. (Sobhanian et al. 2010), Tabacum (Razavizadeh et al. 2009) and D. salina (Katz et al. 2007). Contrarily, salt-tolerant crops such as T. halophile (Katz et al. 2007), S. salsa (Li et al. 2011), and S. aegyptiaca (Askari et al. 2006) downregulate the expressions of salt-tolerant photosynthetic proteins in high salt stress conditions. Occasionally, proteins associated with carbohydrate and energy metabolism are also induced under saline situations in glycophytes, whereas the reverse is detected in halophyte plant S. salsa (Li et al. 2011). Several transcription factors are regulated by different kinases and they have been found to play an significant role in plant adaptation to salinity stress. Genes upregulated in response to salinity stress has been recognized also in rice by Schmidt et al. (2013). Responsive ERF1 (SERF1) is a rice transcription factor gene that showed root-specific stimulation under salt stress and H2 O2 treatment. They showed that plants lacking the SERF1 gene are more sensitive to salt stress than the wild type, whereas constitutive overexpression of SERF1 gene improves salt tolerance. Furthermore, Ravelombola et al. (2022) recognized that candidate genes in cowpea encode for various proteins played vital roles in salinity tolerance for instance mitochondrial folate transporter/carrier, auxilin/cyclin g-associated kinase-related, clathrin coat assembly protein, phytoene dehydrogenase, retinaldehyde binding protein-related, succinate dehydrogenase flavoprotein subunit, protein Da1-related, cysteine-rich secretory protein family, vacuolar protein sorting-associated protein VPS13, alpha/ beta hydrolase fold, and xyloglucan: xyloglucosyl transferase.

7.7 Problems in Breeding for Salinity Resistance There are a number of difficulties faced by plant breeders when breeding for salinity resistance, which can be listed in the following topics: 1. The difficulty of achieving a suitable, controlled and reliable saline environment in the accurate selection programs for salinity resistance. 2. The lack of an accurate, simple and appropriate scale to be relied upon as a selection criterion in the breeding programs for salinity resistance. 3. Resistance to salinity is governed by a complex genetic system and there are many genes that should be transferred from germplasm strains and wild relatives, which appear to be a difficult task for plant breeders.

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4. Knowing the physiological, biochemical and genetic basis of salt resistance requires more understanding, which requires further analysis and cooperation between plant breeders and specialists in related science fields.

7.8 Conclusion Under Egyptian conditions, crop breeders released through selection, and hybridization a lot of tolerant cultivars to salt stress viz. wheat, rice, barley, forage crops, Egyptian clover, fodder sorghum, Sudan grass, alfalfa and others. Also, functional genomics have opened up novel opportunities for crop improvement. So, identifying genes associated with physiological, biochemical and agronomic traits under salinity stress in crop genotypes is very important. Because of its effectiveness, ease and specificity, genome editing is valuable for crop development initiatives. Molecular genetics viz. gene markers and gene transfer beside tissue culture, all of them represent novel tools in dealing with the problem of salinity.

7.9 Recommendations Our article may be used as an efficient strategy to reveal genetic variation in response to salt stress. This approach allows choose for desired traits, enabling more efficient applications of selection, hybrid breeding and mutation procedures to realize stresstolerant populations. Identification of molecular genetic markers associated with salt tolerance in crop plants is important to employ techniques as markers assisted selection in breeding programs. The most of them are RAPD-PCR, Inter-Simple Sequence Repeat (ISSR), SSR and QTL Markers to study genetic diversity among crop genotypes in respect to salinity stress tolerance. Epigenetic modification-heritable responses is a new research area that warrants further studies to understand modifications that occur in epigenetic memory in response to environmental stress. The study of crop plant development, including gene regulation through epigenetic changes, is one of the recent methods to manage with salinity stress. Genetic engineering and tissue culture techniques are among the recent tendencies in the advanced scientific research system as fast and accurate methods for producing plants and lines that tolerate abiotic environment pressures.

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Yang L, Zhang Y, Zhu N, Koh J, Ma C, Pan Y, Yu B, Chen S, Li H (2013) Proteomic analysis of salt tolerance in sugar beet monosomic addition line M14. J Proteome Res 12:4931–4950 Yen HE, Edwards GE, Grimes HD (1994) Characterization of a salt-responsive 24-kilodalton glycoprotein in Mesembryanthemum crystallinum. Plant Physiol 105:1179–1187 Yermishina NM, Kremenevskaja EM, Gukasian ON (2004) Assessment of the combining ability of triticale and secalotriticum with respect to In vitro androgenesis characteristics. Russ J Genet 40:282–287 Yin Y, Yang R, Han Y, Gu Z (2015) Comparative proteomic and physiological analyses reveal the protective effect of exogenous calcium on the germinating soybean response to salt stress. J Proteomics 113:110–126 You J, Wang Y, Zhang Y, Dossa K, Li D, Zhou R, Wang L, Zhang X (2018) Genome-wide identification and expression analyses of genes involved in raffinose accumulation in sesame. Sci Rep 8(4331) Younis Rania AA, Ahmed MF, EL-Menshawi Mervat M (2007) Molecular genetic markers associated with salt tolerance in grain sorghum. Arab J Biotech 10(2):249–258 Yu G, Li J, Sun X, Liu Y, Wang X, Zhang H, Pan H (2017) Exploration for the salinity tolerancerelated genes from xero-halophyte Atriplex canescens exploiting yeast functional screening system. Int J Mol Sci 18(11):2444 Zhambrano AY, Demey JR, Fuch M, Gonzalez V, Rea R, de Souza O, Gutierrez Z (2003) Slection of sugarcane clones resistant to SCMV. Plant Sci 165:221–225 Zhang A, Liu Y, Wang F, Li T, Chen Z, Kong D, Bi J, Zhang F, Luo X, Wang J (2019) Enhanced rice salinity tolerance via CRISPR/Cas9-targeted mutagenesis of the OsRR22 gene. Mol Breed 39(3):1–10 Zhang H, Dong H, Li W et al (2009) Increased glycine betaine synthesis and salinity tolerance in AhCMO transgenic cotton lines. Mol Breed 23(2):289–298 Zhang M, Kong X, Xu X, Li C, Tian H, Ding Z (2015) Comparative transcriptome profiling of the maize primary, crown and seminal root in response to salinity stress. PLoS ONE 10(3):e0121222 Zhang N, Zhang L, Zhao L, Ren Y, Cui D, Chen J, Wang Y, Yu P, Chen F (2017) ITRAQ and virus-induced gene silencing revealed three proteins involved in cold response in bread wheat. Sci Rep 7:7524 Zhang Z, Zhang S, Zhang Y, Wang X, Li D, Li Q, Yue M, Li Q, Zhang Y-E, Xu Y, Xue Y, Chong K, Bao S (2011) Arabidopsis floral initiator SKB1 confers high salt tolerance by regulating transcription and pre-mRNA splicing through altering histone H4R3 and small nuclear ribonucleoprotein LSM4 methylation. Plant Cell 23(1):396–411 Zhao Y, Ma Q, Jin X, Peng X, Liu J, Deng L, Yan H, Sheng L, Jiang H, Cheng B (2014) A novel maize homeodomain-leucine zipper (HD-Zip) I gene, Zmhdz10, positively regulates drought and salt tolerance in both rice and arabidopsis. Plant Cell Physiol 55(6):1142–1156 Zhong GY, Dvorak J (1995) Chromosomal control of the tolerance of gradually and suddenly imposed salt stress in the Lophopyrum elongatum and wehat, Triticum aestivum genomes. Theor Appl Genet 90:229–236 Zhong H, Guo QQ, Chen L, Ren F, Wang QQ, Zheng Y, Li XB (2012) Two Brassica napus genes encoding NAC transcription factors are involved in response to high-salinity stress. Plant Cell Rep 31(11):1991–2003 Zhu J-K (2002) Salt and drought signal transduction in plants. Annu Rev Plant Biol 53:247–273 Zhu J-K, Liu J, Xiong L (1998) Genetic analysis of salt tolerance in arabidopsis: evidence for a critical role of potassium nutrition. Plant Cell 10(7):1181–1191 Zou J, Liu C, Liu A, Zou D, Chen X (2012) Overexpression of OsHsp17.0 and OsHsp23.7 enhances drought and salt tolerance in rice. J Plant Physiol 69(6):628–635

Part V

Management Options, Mitigation and Genotype Assessment Techniques

Chapter 8

Mitigation Options Towards Sustainability Via Agricultural Practices

8.1 Introduction Soils that have an excessive amount of soluble salts or exchangeable sodium in the root zone are known as salt affected soils. Due to limited rainfall and high evapotranspiration, with poor soil and water management practices, salt stress has become a severe hazard for crop production in arid and semi-arid areas of the world (Flowers and Yeo 1995; Munns 2002). So, soil salinization is predicted to increase at a rate of 10% annually (Shrivastava and Kumar 2015), hereafter an assessed 50% of arable land is expected to be salinity affected by 2050 (Jamil et al. 2011). Sodium (Na+ ) is an abundance element in the earth. Ocean itself comprises 71% of the earth surface, so it is not surprising that most plants come into contact with Na+ in their growth stage. Agricultural practices viz. fertilizer application, poor irrigation systems, and increasing sea levels have cause poor water quality and saline soil conditions (Basu et al. 2009). The area of land affected by salinity is ~ 1125 million ha, which is approximately 6% of total global area including 20% of cultivated land and 33% of the irrigated land (Hossain 2019). Egypt is expressed one of the countries that suffer from severe salinity problems. Approximately 35% of the cultivated lands in Egypt are salinized (Kotb et al. 2000). Intensive efforts are being for enhancing land production to meet any local consumption particularly out of the Nile Valley of Egypt, i.e. Siwa Oasis, where salinity is considered of the major problem. Moreover, agricultural practices must be improved to increase land productivity (Hassan et al. 2021). In this respect, influence of deficit furrow irrigation with diverse salinity levels and planting methods i.e. in-furrow and on-ridge as approaches for managing with water and salinity stress on wheat yield and quality was studied by Mosaffa and Sepaskhah (2019). They showed that in-furrow cultivation resulted in 4% significant increase in grain yield compared to on-ridge planting with 5% higher irrigation water productivity. In in-furrow cultivation, grain yield at salinity level of 7.5 dS m−1 was © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_8

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adequate with irrigation regime of 0.65FI; whereas, for on-ridge cultivation suitable salinity is 5.0 dS m−1 . The selection of salinity-tolerant crop varieties released from breeding techniques is an operative strategy to tolerate salinity stress (Anonymous 2023a, b). Nitrogen source significantly affected salinity-stressed plants of wheat and maize in response to salt stress (Lewis et al. 2006). Also, the application of Salinity-Tolerant PhosphateSolubilizing-Bacteria (ST-PSB) can be as a significantly effective and economical way to increase the P availability, and recover the P-deficit in saline-land and mitigating the negative impacts of salinity on crop plants and might enhance salinity tolerance (Dey et al. 2021). Potassium has been recognized to adjust ion synergistically homeostasis in sugar beet under saline situation by promoting the transport of assimilates and preserving osmotic charge (Li et al. 2022). In recent years, biological materials have been used to reduce the effects of salinity in crop plants. Organic amendments are among the recent research areas to mitigate salinity stress in crop plants without the effect of pollution on the living environment (Hoque et al. 2022). Example include biochar actions for the mitigation of plant abiotic stress (Imran et al. 2022), also biofertilizer in adaptation to salinity in different plants (Attia and Abd El Salam 2016; Khalilzadeh et al. 2017). In this framework, the saline lands suffer from an increase in the concentration of salt in the soil solution. The aim of controlling the salinity of the soil is to maintain an economic production of field crops. The exploitation of salt-affected soils depends on understanding how plants respond to salinity, the relative resistance and sensitivity of different crops at different stages of growth, and the extent of the impact of the land and environmental conditions on increasing salt stress and plant growth. Consequently, this chapter was proposed to shed light on the agricultural procedures that have an important role in the possibility of overcoming the problem of salinity and mitigating its effects, which were discussed as shown.

8.2 How to Deal with Salinity Problem: Role of Agricultural Practices in Improving Crop Tolerance to Salinity 8.2.1 Application of Leaching Irrigations Process Pre-planting The extent of plant yield loss when irrigated with saline water relies on soil type and drainage. The key to successful salt water irrigation with saline water is to leach or move salts downwards away from the root zone. In well-drained sandy soils, irrigation water can easily flush salts out of the root zone but this is less successful on poorly drained, heavy soils. The amount of water leaching to maintain acceptable growth depends on, the amount of additional water required to leach salt from the root zone is called the leaching fraction. Frequency and timing play an important role as

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the salt concentration in the root zone changes continually after irrigation. It should be noted that with the drying of the soil and the intensity of heat and lighting, the concentration of salt in the soil solution increases, and this decreases the moisture available to the plant. Therefore, it is important to carry out the leaching process (Gupta and Abrol 2016; Bashir et al. 2023). This is done to reduce the soil solution’s osmotic potential and get rid of the accumulated salts along the root system before they negatively affect the yield. It is preferable to carry out the leaching process before the soil salinity rises to more than 2 dS m−1 for sensitive crops and 4 dS m−1 for moderate-sensitive crops, and 8 dS m−1 for salinity-resistant crops. Many crop plants are somewhat insensitive to salinity during the later stages of growth, but are more sensitive to salinity at germination. Thus, the soil must be given a heavy primary irrigation to wash the salts from the surface. Also, since salts tend to accumulate at the highest point, so the crop should be grown away from the top of the ridge. They are usually grown on both sides of the ridge (Fig. 8.1), with avoiding the risk of waterlogging, so many sensitive crops can be grown. Saline lands can be reclaimed by leaching salts from the soil with water of good qualities to dissolve the salts and remove them from the root zone, with attention to the drainage system and the cultivation of salinity-tolerant crop types and varieties. Also, it is preferable to irrigate before planting the crop with shortening the irrigation intervals and the frequency of the irrigation process. But if the problem of soil salinity is a permanent problem resulting from the high level of groundwater, attention should be given to the drainage system (Keren 2000). The Egyptian government is currently continuing its activity in the reclamation of salt-affected lands, from the implementation of three major programs to the productivity of the land and addressing the effects resulting from the problem of salinity and alkalinity of the soil.

Fig. 8.1 A schematic diagram of salinity levels in plant growth areas, where plants are grown on both sides of the ridge to avoid the high level of salt at the top of the ridges, which discourages seed germination (Modified after, https://www.fao.org/3/s8684e/s8684e04.htm)

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The first program: Through the application of the tender disbursement network at the level of the Republic. The second program: Implementation of the salt-affected land reclamation program. The third program: Land improvement. The salt-affected land reclamation program in Egypt includes the following: 1. Reclamation of pristine lands affected by salts with high ground water and salinity levels, for example, lake bed lands in the northern delta. 2. Reclamation of saline lands with weak or pristine water level, for instance, oases and desert lands. 3. Reclamation of wetlands in the North Delta. 4. Use chemical enhancers for instance: 4.1 High calcium salts, for example, gypsum and calcium chloride. 4.2 Acidic substances, for instance, sulfuric acid, ferric sulfate, eu-sulfate, lime, sulfur, pyrite. 4.3 Calcium salts with a solubility product. 5. Use of electricity. 6. Improving the lands that suffer from secondary salinity resulting from irrigation with water with a low level of validity. 7. Cultivation of crop varieties that improve the Soddy lands, for instance, rice, sugar beet and pasture plants. 8. Maintenance and preservation of land from the secondary problems such as, salinity waterlogging and conservation of drainage networks.

8.2.2 Application of Gypsum Saline sodic soil can be cultivated by the use of Ca2+ -containing compounds which replace Na+ at soil exchangeable sites, followed by leaching with good quality water supply (Gupta and Abrol 1990). It is commonly used to supply Ca2+ . However, sulphuric acid is recommended for soil containing high carbonate content (Horney et al. 2005), which raises soil Ca2+ levels by dissolving CaCO3 in soils (Zia et al. 2007; Vance et al. 2008). Application of gypsum in soil with low concentrations of carbonate has been extensively important. Gharaibeh et al. (2011) suggested reclamation of highly calcareous saline sodic soil by using Atriplex halimus and by-product gypsum. Gypsum (CaSO4•2H2O) and bio-organic amendments have been recognized to enhance saline soils’ physical, biological and chemical properties. It regulates the exchange of sodium (Na+ ) for calcium (Ca2+ ) on the clay surfaces, thereby increasing the Ca2+ /Na+ ratio in the soil solution. Ca2+ also promotes a higher K+ / Na+ ratio. Concurrently, gypsum provides crops by sulfur for improved growth and yield via the increased production of phytohormones, amino acids, glutathione and osmoprotectants, that are important elicitors in plants responses to salinity stress.

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Furthermore, gypsum application, in combined with biochar and compost tea (containing organic matter and beneficial microbes), has also been revealed to ameliorate the effect of soil salinity on wheat production by reducing the SAR, EC and ESP (Bayoumy et al. 2019). because of the important properties of gypsium, different studies demonstrated the potential of gypsium and S-containing compounds to improve the growth and yield of many crops for instance; increased grain yield and reduced soil and irrigation water salinity in wheat (Aboelsoud et al. 2020), barley (Chen et al. 2015), maize (Riffat and Ahmad 2020) and canola (ur Rehman et al. 2013); decreased soil pH and EC, increased soil available K, increased growth, herbage production and forage quality in Berseem clover (Abd El-Naby et al. 2018) as well as decreased soil pH, SAR, EC and bulk density and increased root and shoot biomass production in Fodder beet (Ahmed et al. 2015).

8.2.3 Choosing Crop Species and the Cultivar Crops species differ in their tolerance to salinity, and the varieties of one species of crop also differ in the degree of tolerance. Crops varied in viability and yield satisfactory when cultivated under salt-affected soils. Some crops show high sensitivity in their early growth stages, while they are less sensitive to salinity in their later stages of growth. Therefore, it is useful in screening programs to conduct the test process at the most sensitive stages of crop growth in order to differentiate between sensitive and salt-tolerant genotypes. Also, crops differed in the level of relative tolerance to salinity, which leads to a 50% reduction in germination or yield, according to their genetic makeup. Barley ranks first in tolerance with the highest field emergence rate and the highest relative yield. While, wheat was moderate tolerant, and beans came in the last order, as they were the least tolerant and most sensitive to salinity. When the degree of electrical conductivity reaches 4 dS m−1 , the soil becomes saline and the degree of conductivity continues to increase to reach high levels. Some field crops can tolerate degrees of salinity reached to 16 dS m−1 . Crop genotypes differ greatly in their ability to tolerate salt accumulation in soils, but if levels are high enough (more than 16 dS m−1 ), only tolerant crops will survive. Table 8.1 serves as a universal guide of salt-tolerance ratings for crops, recognize that agricultural managements, quality of irrigation water, environment and crop variety also influence tolerance. Crops vary in tolerance of high concentrations of salt and high concentrations of sodium (Batarseh 2017). Commonly, soybeans are quite sensitive, corn and grain sorghum are intermediate, but wheat and alfalfa are more tolerant. Moreover, crested and tall wheatgrass and some sorghum-Sudan hybrids are very tolerant and capable of growing on soils with exchangeable sodium percentages above 50%. The selection of nutrient-efficient, salt-tolerant plant varieties that can use ammonium as the predominant N source is an emerging strategy (Iqbal et al. 2015). There are more than 1500 plant species that can be grown in salty areas, and high-salinity water can be used for irrigation. Also, it has been possible to survey numerous saline

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Table 8.1 Salt tolerance ratings for various field, forage, and horticultural crops (Jamalkhan et al. 2010) Sensitive (0–4 dS m−1 )

Moderately tolerant (4–6 dS m−1 )

Tolerant (6–8 dS m−1 )

Highly tolerant (8–12 dS m−1 )

Field beans (dry)

Corn

Wheat

Barley

Red, ladino, alsike Grain sorghum

Oats

Rye

Clovers

Soybean

Triticale

Bermudagrass

Strawberry

Bromegrass

Sunflower

Crested wheatgrass

Onion

Sudangrass

Alfalfa

Asparagus

Pea

Sorghum-Sudan

Tall Fescue

Carrot

Sweet clovers

Lettuce Pepper

environment plants that are tolerant or highly tolerant to salinity in many Arab regions that suffer from salinity stress. These plants are characterized by the ability to grow in high salinity environments as a result of the presence of some modifications in the morphological, botanical, physiological and biochemical processes, enabling them to tolerate severe environmental conditions. These crops include barley, sugar beet, cotton, canola, safflower, jojoba, Atriplex and several pasture grasses. Some crop cultivars derived from breeding methods characterized by specific salinity tolerance released under Egyptian conditions are listed in Table 8.2.

8.2.4 Applied of Proper Agricultural Practices Following the agricultural procedures that suit the conditions of saline soils improve the ability of crop plants to tolerate these conditions which can be discussed as follows.

Soil Preparation and Sowing Methods When preparing the salt-affected land for planting, it is preferable to use the digging plow instead of the tipper plow, to avoid raising salts from under the soil surface that has previously been washed inside the sector. Leveling the land surface by laser helps to regularize and homogenize the distribution of irrigation water and thus permeate and wash the land. Where the land surface heterogeneity leads to the accumulation of salts in the high areas and the accumulation of water in the low areas, causing waterlogging conditions. Hence, the processes of seed germination and plant growth are weak in high regions due to lack of water and high salt concentration in it. Similar effects may occur in low areas

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Table 8.2 Some crop genotypes derived from breeding programs with certain tolerance levels to salinity stress Crop

Genotype

Tolerance level Source

Wheat

Giza 168, Giza 171, Shandweel 1, Sids 1, Sakha 93, Sakha 95, Misr 3, Misr 4 and Sakha 8 (from Egypt)

Tolerant

Al-Ashkar et al. (2019) and Anonymous (2023a, b)

S-24, LU-26S and Pasban-90 (from Pakistan)

Tolerant

Hussain et al. (2021)

MH-97, Kohistan-97, Inqilab-91 and Iqbal-2000 (from Pakistan)

Sensitive

Giza 123, Giza 133, Giza 134, Giza 137 and Giza 138 (from Egypt)

Tolerant

Anonymous (2022)

Jau-83, Pk-30109, Pk-30118, 57/2D and Akermanns Bavaria (from Pakistan)

Tolerant

Mustafa et al. (2019)

Barley

Rice

Maize

Faba bean

Cotton

Giza 178, Giza 179, Giza 182, Sakha 104, Tolerant Sakha 106, Sakha super 300, Egyptian Hybrid 1, Hybrid 2 and GZ 6296 (from Egypt)

Anonymous (2022) and EL-Emary et al. (2013)

IR85427, IR86126, IRRI 152 and CT18237 (from IRRI)

Sensitive

Kakar et al. (2019)

Pokalli, FED 473, IR86174, PALMAR and IRRI 154 (from IRRI)

Tolerant

White maize single crosses 10, 128, 130, Sensitive to 131 and 132 Moderate Three-way white maize crosses 321, 324 sensitive and 329 Yellow maize single crosses 166, 167, 168, 173, 176, 177, 178 and 180 Three-way yellow maize crosses 352, 353, 360 and 368 (from Egypt)

Anonymous (2022) and Anonymous (2023a, b)

Sahwal-2002 (From Pakistan)

Tolerant

Zahra et al. (2020)

Nubaria 1 (from ARC, Giza, Egypt) Strains FLIP 77/84, ILB 1814 and ILB 1813 (from ICARDA, Aleppo)

Tolerant

Darwish et al. (2003)

Giza 3 (ARC, Giza, Egypt), Cairo 241 (Agron. Dept., Fac. Agric, Cairo University, Egypt) and L 983/281/95 (ARC, Giza, Egypt)

Less tolerant

Giza 70, Giza 75, Dendera, Giza G 80, Giza 83, Giza 85, Giza 90, Giza 95 (from Egypt)

Tolerant

Anonymous (2023a, b)

Raqqa 5 (from Syria)

Tolerant

Koubaili and AbdEl-Aziz (2005)

Aleppo 133, Deir 22 and Aleppo 90 (from Less tolerant Syria)

(continued)

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Table 8.2 (continued) Crop

Genotype

Tolerance level Source

Flax

Giza 12, Sakha 5 and Sakha 6 (from Egypt)

Moderate tolerant

Anonymous (2023a, b)

Sakha1and Sakha 2

Tolerant

Sakha101 and Sakha 102 (from Egypt)

Moderate tolerant

Atwa and Elgazzar (2013)

Giza 11 (from Egypt)

Tolerant

Abido and Zsombik (2019)

Lines 193 (K-5843) and 194 (K-6970) from Russia and 215 (inbred from cv. At125) from Sweden

Tolerant

Kaya et al. (2012)

Baldi (from Egypt)

Tolerant

Anonymous (2023a, b)

Expo

Tolerant

https://www.dai rynz.co.nz/feedpa sture/pasture

Rey grass

Paragon (from TMI Turf Merchants, Inc.), Tolerant Divine (from Scotts Co.) and Williamsburg (from LESCO, Inc)

Marcum et al. (2013)

Fodder sorghum

Hybrid 102, Sakha 20 and Sids 105 (from Tolerant Egypt)

Anonymous (2022)

Grain sorghum

Sohag 1, Sohag 3 and Sohag 4 (from Egypt)

Tolerant

Anonymous (2023a, b)

Sudan grass

Giza 1, Giza 2 (from Egypt)

Tolerant

Anonymous (2023a, b)

Alfalfa

Ramah 1, Ismailia 1 and Sewa 1, New Valley (from Egypt)

Tolerant

Anonymous (2022)

SISA14-1 (G03) and AZ-90ST (from USA)

Tolerant

Sandhu et al. (2017)

Canola

Quinoa

Cassava

Serw 4, Serw 6, Sakha 1 (from Egypt) and Tolerant Pactol (from France)

Anonymous (2023a, b)

Safi-7 (from Iran)

High tolerant

Zafar (from Iran)

Sensitive

Kholghi et al. (2018)

Giza 1 and Misr 1 (from Egypt)

Tolerant

Anonymous (2023a, b)

Pandela rosada, Huallata, Utusaya (from Bolivia, Southern altiplano)

Tolerant

Shabala et al. (2013)

3706, 5206, KVL 37 and KVL 52 (from Denmark)

Sensitive

Misr 1

Tolerant

Anonymous (2023a, b)

IBA120008 and I920326

Tolerant

Abiola et al. (2021)

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due to waterlogging conditions. The importance of leveling the surface of the soil under the conditions of surface irrigation increases and is less important when using sprinkler or drip irrigation, as it needs a limited settlement in place of the distribution of water around the sprinkler or points. The surface layer rich in nutrients must be preserved when leveling. When planting crops, it is preferable to do this on ridges direction from east to west, with the seeds placed on the marine feather, which is least exposed to intense sunlight, so the concentration of salts on them decreases, and the seeds are not placed in the middle ridge to avoid the concentration of salts. It is also desirable to reduce service operations after planting and not repeat the hoeing process, to avoid raising the salts and collecting them around the crop’s root system. Egypt produces about half of the 20 million tons of consumed wheat and imports the other half. So that Egypt became the world’s largest importer of wheat. Hassan et al. (2021) showed that intensive efforts are being made to enhance wheat production to meet any local consumption, particularly out of the Nile Valley, i.e. Siwa Oasis, Egypt, where salinity is considered the major problem. However, Siwan farmers are not acquainted with wheat crop from the beginning sustain policy of wheat flour as well as with agricultural practices. Two on farm trials were carried out in Agricultural Experimental Station of Desert Research Center at Khemisa, Siwa Oasis with soil EC 4.1 dS m−1 . They investigated the effect of sowing methods (broadcast and row) and seeding rates (30, 45, 60 and 75 kg/fed.) on two bread wheat cultivars of Triticum aesivum L. (Misr 2 and Sakha 94). Results indicated that the row sowing method produced 37.2% and 12.5% more grain yield than the traditional broadcast method in the 1st and 2nd seasons, respectively. Misr 2 wheat cultivar produced the highest biological and grain yields as well as harvest index. The highest values of number of spikes/m2 , grain yield and harvest index were noticed with 45 and/or 60 kg/fed seeding rates in two seasons. Hereby, sowing Misr 2 wheat cultivar at 60 kg/fed. with row sowing method is suitable for wheat production under saline conditions at Siwa Oasis. Influence of deficit furrow irrigation with diverse salinity levels and planting methods i.e. in-furrow and on-ridge as approaches for managing with water and salinity stress on wheat yield and quality was tested by Mosaffa and Sepaskhah (2019). Irrigation treatments were full irrigation (FI), 0.65FI, and 0.35FI, and salinity levels of irrigation water were 0.6 (healthy water), 5.0, 7.5, and 10.0 dS m−1 . Results showed that irrigation regimes of 0.65FI (381 mm) and 0.35FI (217 mm) reduced grain yield by 20 and 26%, in the 1st season and by 17% and 30% in the 2nd season, respectively. Results also showed that in FI with irrigation application efficiency of 80% (leaching fraction of 20%), the salinity level of 3.36 dS m−1 did not decrease grain yield. Moreover, salinity level of 7.5 dS m−1 for irrigation regimes of 0.65FI and 0.35FI, did not display significant difference in grain yield compared to those attained at salinity level 0.6 dS m−1 . In-furrow cultivation resulted in 4% significant increase in grain yield rather than on-ridge planting with 5% higher irrigation water productivity. Under in-furrow cultivation, grain yield at salinity level of 7.5 dS m−1 was adequate with an irrigation regime of 0.65FI; while, for on-ridge cultivation suitable salinity is 5.0 dS m−1 . Therefore, under non-limited irrigation, full irrigation with salinity

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level of 5.0 dS m−1 and in-furrow cultivation is the proper irrigation management for wheat. But, with restricted water supply, 0.65FI with salinity of 7.5 dS m−1 and in-furrow cultivation would be adequate in wheat irrigation management. In this connection, under saline soil of Sahl El-Tina, North Sinai Governorate, Egypt, Amer et al. (2018) studying the effect of some agricultural practices (raised bed system, nitrogen fertilizer rates and seed soaking in concentrations of cobalt solution) whether alone or combined with both to enhance fertility of saline soil and its productivity of Nubaria 1 faba bean cultivar. Results showed that, the reducing in soil salinity values (EC) was more pronounced in the method of raised bed shoulder than furrow ridge with increasing of irrigations number. The growth and yield components traits increased with the highest ratio when using the raised bed compared to furrow row system. EL Azab and Mahmoud (2017) indicated the significant positive effect of raised bed system on plant growth and yield components of faba bean compared to the furrow row system particularly with saline soil. Sugar beet crop is adapted to saline, sodic and calcareous soils, therefore, it can be grown under new reclaiming lands in Egypt, at Nubaria Region, with soil EC = 4.8 dS m−1 . Nassar et al. (2022) study the effect of three sowing methods and planting density on yield and quality of sugar beet cultivar monogerm Salama. Treatments were organized in a split-plot design in three replicates, the three methods of sowing viz. mechanical planting by a planter in rows, hand sowing on ridges at the two sides of the ridge and hand sowing on ridges at one side of the ridge randomly distributed to the main plots, whereas, the three-planting density (60,000, 64,000, and 68,000 plant/fed) were randomly allocated within the subplots. Results displayed that planting methods for instance mechanical method in rows (flat) or on the two sides of ridges besides the plant density (60,000 or 64,000 plants/fed) and their interaction improved sugar beet productivity parameters and increased root and sugar yield and sugar quality under Nubaria region conditions.

Plant Population Density Increasing plant density is one of the agricultural procedures used to deal with the lack of crop productivity under salinity conditions to compensate the reduction in yield resulting from plant lost during growth. Zeng and Shannon (2000) found that increasing the density in rice from 400, 600 to 720 grains m−2 under salinity levels of 1, 3.9 and 6.5 dS m−1 in the greenhouse led to a significant increase in plant stability and panicle density. The results indicated that the decrease in the yield under the average salinity level was not compensated by the increase in the plant density than the normal rate. The recommendations for wheat and barley crops indicate the importance of relying on the main stem spike as a crucial component of the yield under the conditions of salt-affected soils. Where it is preferable to increase the seed rate to overcome the problem of unproductive tillers and the production of parasitic tillers that affect the productivity of the crop variety. In this connection, Shalaldeh and Thalji (2007) investigated the effects of plant population (300, 350 and 400 plants/m2 ) on the

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performance of five wheat genotypes (Jumaizeh, Bin-bashair, Cham-3, Cham-6 and Snb1s1) under salinity conditions at Central Jordan Valley. They noticed that wheat genotypes did not differ significantly in grain and straw yields. Plant population of 400 plant m−2 gave the highest biological, grain and straw yields. For the interaction effects, Jumaizeh at 400 plants/m2 significantly increased biological, grain and straw yields. A plant population at 400 plant m2 is recommended for the highest yield of wheat when planted under saline conditions. Zhang et al. (2011) design an experiment with a split plot system where the main plots were allocated to soil salinity levels i.e. weak (electrical conductivity of soil saturated paste extract, ECe = 5.5 dS m−1 ), moderate (ECe = 10.1 dS m−1 ) and sever (ECe = 15.0 dS m−1 ). Whereas, plant density (3.0, 4.5 and 7.5 plants m−2 ) was allotted to the subplots. Soil salinity had a negative impact on seed cotton yield. However this effect was offset by increasing plant density under sever-salinity conditions. Seed cotton yield under weak salinity changed slightly with varying plant density, however medium plant density yielded better than low or high plant density under moderate salinity. Salinity, plant density and their interaction significantly affected plant biomass, leaf area index and harvest index.

Plant Nutrition Providing crop plants with their requirements of fertilizer elements in an appropriate and easy-to-use form is one of the useful means in improving the growth and tolerance of plants to salinity. Therefore, following appropriate fertilization programs for saline soil conditions seems important.

Organic Matter The great importance of organic matter is due to its containing of nutrients, in addition to its role in improving the natural, chemical and biological properties of agricultural soil and making open pores for the movement of water and improving the condition of plants under salinity conditions. Reda et al. (2003) showed that the presence of organic matter with proline increases the ability of wheat plants to tolerate soil salinity and that the increase in soil salinity from 2.62, 5.93, 9.28 to 15.18 dS m−1 was accompanied by an increase in the plant’s content of proline. The increase was higher in the organically fertilized plants than the non-fertilized ones. The treatment with proline spray at a rate of 20 mg/L reduced the effect of salinity on plant growth and the accumulation of sodium ions in plant tissues. El-Sayed et al. (2006) recorded significant increases in grain, straw and protein yields in both maize and wheat with increasing compost rates from 10, 20 to 30 metric tons/feddan, under calcareous soil conditions. Organic amendments, such as vermicompost (VC), vermiwash (VW), biochar (BC), bio-fertilizer (BF) and plant growth promoting rhizobacteria (PGPR) are gaining attention reduce salt stress and improves crops growth, development and

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yield of crop plants. Organic amendment enhances salinity tolerance and improves the growth and yield of plants by modifying ionic homeostasis, photosynthetic apparatus, antioxidant machineries and reducing oxidative damages (Hoque et al. 2022). Several studies showed that bio-fertilizers and biochar enhance plant growth under salinity stress by improving antioxidant enzyme activities and reducing oxidative damage in different plants (Khalilzadeh et al. 2017; Imran et al. 2022). For example, Alamer et al. (2022) revealed that vermi-compost improves morphological traits, chlorophyll content, antioxidant enzyme activities, and enhances salinity tolerance of maize plants. Jabeen and Ahmad (2017) add vermi-compost to sunflower under EC: 0.5, 4.8 and 8.6 dS m−1 . They recorded an increase in plant growth, yield, nitrate and protein content; decreased sodium (Na+ ), chloride (Cl− ), ammonium; increased N-assimilation in sunflower plants. Liu et al. (2019) showed that Vermicompost and humic fertilizer improve shoot biomass, and grain yield of wheat cultivar Yelken. Also, they increased soil macro-aggregates, soil physical, chemical and biological properties, and ameliorated salt-induced stress in Coastal salinity Soil. Furthermore, under stress level NaCl 4.12 dS m−1 , Djajadi et al. (2022) found that treating sugarcane commercial variety of ‘Bululawang by vermicompost with ( 0, 10, 20 t/ha) and nitrogen fertilizer by 50, 75 and 100 kg N/ha, increased N, K uptake and the growth of sugarcane and mitigated salinity effects.Application of Spirulina platensisinoculated humified leguminous compost is a promising sustainable approach in amending rhizospheric soil properties, nutrient availability, maximizing forage yield and quality of Atriples nummularia under a saline calcareous arid region. Alghamdi et al. (2023) applying bio-organic amendments, particularly Spirulina platensisinoculated humified leguminous compost, ameliorated soil defects through the improvement of hydro-physico-chemical properties by lowering soil reaction (pH), ECe, CaCO3 content, and exchangeable Na+ and Ca2+ , increasing cation exchange capacity, organic matter, and water retention at field capacity, thus maintaining higher nutritional status. These findings were positively reflected in morpho-physiological attributes, forage yield, and nutritive value e.g., increased soluble protein and nutrients. Also improved B-group vitamins e.g., thiamin, riboflavin, niacin, pyridoxine, folic acid, and cyanocobalamin of multi-stressed A. nummularia forage. Furthermore, this treatment significantly enhanced non-enzymatic and enzymatic antioxidants, detoxifying reactive oxygen species i.e., superoxide and hydrogen peroxide, nitrite and nitrate contents, and decreasing malondialdehyde and electrolyte leakage, associating with greater stress tolerance in A. nummularia.

Nitrogen Nitrogen is one of the determinant elements of growth under saline or non-saline conditions. Application of nitrogen always leads to an improvement in plant growth and an increase in crop production. Enhancement the growth of barley, beans, corn, alfalfa, wheat, rice, peas and beans. In the same experiments, plants did not respond to nitrogen application when salinity was high. However, few studies showed an increase in yield under high salinity levels, when nitrogen was added at higher than

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optimum rates for non-saline soils. However, the increase in nitrogen fertilization increases the resistance of plants to salinity, in maize crop, which were fertilized with 375 kg of nitrogen/ha. The positive effect of nitrogen on increasing salinity tolerance may be due to the role of the nitrate ion NO3 − in reducing the absorption and accumulation of chloride Cl− (Bernstein et al. 1974), in addition to the effect of nitrogen in increasing the content of proline, total soluble proteins and amino acids. The form of nitrogen added to the soil in which plants grow under salinity stress plays an important role, as it was found that nitrogen added in the form of ammonium NH4 + is more sensitive to salinity than the form of nitrate NO3 − with maize and wheat plants. It was also found that adding Ca2+ to the growth environment improves the growth rate in the presence of nitrate NO3 − . Therefore, it is considered the best source of nitrogen that can be added to saline lands is nitrate salts or a mixture of nitrates or ammonium so that the percentage of nitrate is greater than the percentage of ammonium. The effect of nurturing maize and wheat with ammonium and nitrate on salinity stress was evaluated. In both maize and wheat, the ammonium-grown plants were greatly sensitive to salinity toxicity than nitrate-grown plants, particularly when exposed to 60–80 mM salinity. Shoot growth was significantly more retarded than root growth in salinity-stressed plants of both wheat and maize with either nitrogen source. In nitrate-fed wheat, increasing calcium concentration from 2 to 12 mM in the presence of 60 mM salinity gave an 11% increase in growth. This effect was attributed to improved nitrate absorption owing to calcium protection of the nitrate transporter and was not obvious in wheat grown with ammonium (Lewis et al. 2006). Besides the forms of nitrogen fertilizer, bacterial inoculation with rhizobium improves the productivity of leguminous crops under salinity soil conditions. AbdelHameed et al. (2003) studied the influence of salinity levels i.e. 4.2 and 4.7 dS m−1 and three forms of nitrogen fertilizer i.e. ammonium nitrate, ammonium sulfate and urea with rhizobium treatments on faba bean. They found that inoculation with rhizobium enhanced the amount of yield and protein content of seeds when adding ammonium nitrate fertilizer, as it was the best at salinity level of 4.2 dS m−1 , whereas the form of ammonium sulfate was best at the level of salinity of 4.7 dS m−1 . Under saline soil of Sahl El-Tina, North Sinai, Egypt, Amer et al. (2018) study the effect of nitrogen fertilizer rates and seed soaking in concentrations of cobalt solution on Nubaria 1 faba bean cultivar. Results showed that, seed and straw yield kg/fed. were significantly increased with a gradual increase in N-levels up to 100% combined with 12 mg L−1 of cobalt on all the deliberated growth parameters. Compared with furrow row system, macronutrient contents in faba bean plants were significantly increased with raised bed system, and reached to 34.3, 36.7 and 37.9% for N, P and K. In the case of the normal lands in India, the usual agricultural managements for the cultivation and production of sugar cane in the Sodic lands are followed, except for the added of an additional 10% nitrogen with light frequent irrigation and the addition of 25 kg zinc sulfate to overcome the problem of zinc deficiency (Dwivedi 2004). At El-Hag Ali region at west Siwa, Siwa Oasis, with soil EC dS m−1 6.22, Matrouh Governorate, Egypt, during 2011/2012 and 2012/2013 growing seasons investigate

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the effect of mineral, organic, and bio-fertilizer on yield and yield components of bread wheat to improve wheat productivity and minimizing pollution. Attia and Abd El Salam (2016) tried three levels of organic fertilizer (10, 15, 20 m3 /fed of organic manure), two regimes of biofertilizer (without bio-fertilizer and bio-fertilized with Microbein as Pseudomonas sp., Azotobacter sp., Azospiirillum sp., and B. megaterium), and two levels of mineral fertilizer (100% and 50% of recommended NPK fertilization levels) on Sakha-93 wheat cultivar. Results revealed that grain yield and its relevant traits viz. plant height, number of tillers/m2 , number of spikes/ m2 , number of spikelets/spike, number of grains/spike, 1000-grain weight, straw and grain yields were increased significantly by adding bio-fertilizer compared to control in both seasons. The effect of organic fertilizer on yield and its components showed that all characters were significantly affected by addition organic fertilizer. The highest values of number of spikes/m2 , number of tillers/m2 , 1000-grain weight, straw, biological and grain yields/fed. were attained with 20 m3 /fed of organic manure compared to 10 and 15 m3 /fed. The increment in yield and its components could be due to the rise in vegetative growth of wheat plants and enhancing root growth and dry matter accumulation. The studied characters were significantly affected by inoculation of wheat grains with Microbein and significantly increased with the application of microbein bio-fertilizer rather than the control. Interaction between mineral, organic and bio-fertilizer was significant for all characters under study in both seasons. The highest grain yield was gained by using rate 100% NPK mineral fertilizer, 20 m3 /fed organic manure with adding bio-fertilizer. Furthermore, Ahanger et al (2019) indicated that salinity (100 mM NaCl) stress has harmful effects on the chlorophyll, carotenoid synthesis and the photosynthetic efficiency of wheat. But, nitrogen supplementation increased photosynthetic rate, stomatal conductance and internal CO2 concentration with effects being very clear in seedlings treated with higher dose of nitrogen. The antioxidant defense system was up-regulated under saline and non-saline growth situations due to nitrogen addition. This leads to protection of the key cellular process such as photosynthesis, membrane structure and function, and mineral assimilation. Increased osmolyte and secondary metabolite assimilates, and redox components in nitrogen fertilized plants regulated the ROS metabolism and salinity tolerance by enhancing the antioxidant mechanisms.

Phosphorus Nutritional-imbalance is also identified as one of the negative impacts of salinity on crop growth and productivity. Among the essential crop nutrients, phosphorus (P) is a nutrient whose uptake, transport and distribution in plant is adversely affected by salinity-stress. Bouras et al. (2021) revealed that supplementary phosphorous application could be one of the best practices to reduce the adversative impacts of high salinity on growth, development and yield of forage corn. Furthermore, the application of additional P fertilizer is usually recommended to cope P deficit in salt affected-soils. Applying salinity-tolerant phosphate–solubilizing-bacteria (ST-PSB) can be a significantly effective and economical way to increase the P availability,

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and recover the P-deficit in saline-land. Adding ST-PSB to saline soils can alleviate salinity’s negative effects on crop plants and might improve salinity tolerance (Dey et al. 2021). The importance of nutrition with phosphorous under saline conditions appears to be more complex than in the case of nitrogen. This depends on the plant species, the stage of growth, and the type and level of salts in the growth environment. Champagnol (1979) found that adding phosphorous to saline soils or environments increases growth and yield for 34 crops out of 37 studied crops, which means that this effect is the dominant on phosphorous behavior in saline environments. The yield of cereals, straw and protein improved in maize and wheat with phosphate fertilization at a rate of 45 kg P2 O5 /feddan in calcareous lands (El-Sayed et al. 2006). Plant resistance to salinity increases by adding phosphorous to environments with high salinity levels. While, salinity resistance decreases at moderate salinities in the presence of phosphorous. Whereas, the analysis conducted on barley, wheat, maize, sorghum, tomato and carrot crops showed that the increase in phosphorus had no effect with low salinity. So, salinity increases the need of a large number of crops for phosphorous to be added to the growth environment. Meanwhile, Bouras et al. (2021) showed that irrigation water salinity had a negative influence on growth and yield parameters of forage corn. The dry matter yield decreased by an average of 19.3 and 25.1% rather than the control at saline irrigation with an EC 4 and 6 dS m−1 , respectively. Whereas, phosphorous applications lead to a significant increase in root weight, root length, stem length, leaf stomatal conductance, grain yield and dry matter yield under salinity conditions. For instance, supplementary phosphorus with a rate of 126 and 150 kg P2 O5 ha−1 enhanced dry matter yield by 4 and 9% under (ECw = 2 dS m−1 ) low salinity level, by 4 and 15% under medium (4 dS m−1 ) salinity, and by 6 and 8% under a high (6 dS m−1 ) salinity level, respectively. And in another direction, as per the foregoing report, salinity-tolerant phosphate–solubilizing-bacteria (ST-PSB) facilitates the development of saline-alkalisoil-based agriculture via preserving P availability and salt alleviation. Especially, salinity-tolerant phosphate–solubilizing-bacteria increases the N, P and K uptake and improves the salt tolerance efficiency in diverse crop plants, for instance, wheat (Upadhyay et al. 2012; Upadhyay and Singh 2015), maize (Adnan et al. 2020) and quinoa (Mahdi et al. 2022).

Potassium Potassium K is a key nutrient for crop growth and productivity (Hasanuzzaman et al. 2018). It is an essential element for photosynthesis, osmotic regulation, water relations and the transport of current assimilates (Wang et al. 2013 and Wang and Wu 2017). Potassium affects the osmotic adjustment of the plant, by promoting the transport of assimilates and preserving osmotic charge (Marschner 2012). So, potassium played an important role in water-plant relationship under salinity stress and assisted the plants to absorb more water to reach turgidity and membrane stability (Abbasi et al. 2016).

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A number of kinds of K+ and Na+ transport patterns, for example, inward-rectifier shaker K+ channel, high-affinity K+ transporter 5, shaker-like K+ outward rectifying channel, high-affinity K+ transporter 1; 5, tonoplast Na+ /H+ antiporter 1, and plasma membrane Na+ /H+ antiporter 1 has been documented to regulate ion synergistically (K+ and Na+ ) homeostasis in sugar beet under saline situation (Li et al. 2022). Potassium is similar to phosphorous in terms of its relatively low concentration in the ground solution. Potassium is also absorbed and fixed on the surfaces and between the crystal units of the earth’s mineral colloids. The plasma membranes of the root cells are characterized by their high ability to attract potassium more than sodium and to make harmonization between the high concentration of sodium and the plant’s requirement for potassium and to maintain a sufficient level of calcium in the roots, which leads to supplying the roots with a sufficient level of oxygen. If salinity is a problem, it is recommended to avoid chloride fertilizers. And replace muriate of potash (potassium chloride) with sulphate of potash and use nitrogen, phosphorus and potassium (NPK) fertilizers which contain sulphate of potash. Kafkafi (1984) found that salinity-resistant crops such as sugar beet have a higher ability to attract potassium compared to salt-sensitive crops such as faba bean. Many crops appear to be highly selective to potassium compared to sodium. There is evidence that sodium partially replaces potassium in many crop plants without affecting growth and yield. Marschner (1995) divided crop plants into four groups in terms of the replacement and exchange of sodium for potassium. The first group: a large part of sodium replaces potassium, such as sugar beet and turnip plants. The second group: replacement of potassium is moderate, and it is represented by the group of plants with moderate resistance to salinity, such as tomatoes. The third group: potassium is replaced with a little sodium, which is considered ineffective in growth, as in the case of rice plants. The fourth group: no replacement of potassium by sodium, and this group represents corn, beans and lettuce. In this regard, Sherif et al. (1998) found that adding potassium sulfate at a rate of 150 kg/ha in pot experiments led to an improvement in the growth and dry matter yield of wheat cultivars, under levels of sodium chloride salinity ranging from zero, 5, and 10 dS m−1 . El-Sayed et al. (2006) recorded significant increases in grain, straw and protein yield in wheat and maize by increasing potassium fertilization up to 24 kg P2 O/feddan, under calcareous conditions. Sugar beet can tolerate the salinity of irrigation water up to 2000 ppm without a significant effect on growth, yield or quality characteristics (sugar %, sucrose % and juice purity). Potassium fertilization improved sugar beet yield and quality, whether irrigated with water of salinity with 4000 ppm or with fresh water (Abd El-Mawly and Zanouny 2004). Moreover, addition of potassium under salinity increased root length, shoot fresh weight, and root fresh weight of maize (Mehmood et al. 2020). Salt tolerance in crop plants is improved by increasing potassium uptake, leading to an increase in plant cells’ potassium/sodium ratio (Ali et al. 2019). Addition of potassium under salinity improved root length, shoot fresh weight, and root fresh weight of Maize (Mehmood et al. 2020). Furthermore, adding potassium to soybean

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under salinity induced salt tolerance as the production of malondialdehyde content and electrolyte leakage decreased, but growth parameters, chlorophyll contents, antioxidant enzymes, gas exchange features, and sugar contents were enhanced (Parveen et al. 2020). Mean integrated peak area of potassium was higher in alfalfa leaves of ‘Halo’ at 12 dS m−1 than in ‘Vernal’, showing its capability to preserve higher potassium ions under salinity stress. Potassium and sodium, as monovalent cations, are generally considered as being competitive elements for root uptake and transport in the plant (Schachtman and Liu 1999). Retention of potassium under conditions of salt stress was considered crucial to the salt tolerance in glycophytes (Chen et al. 2007). Also a salt-tolerant barley genotypes had a higher capacity to retain potassium compared to sensitive ones (Shen et al. 2016). Adequate potassium rate, mitigated the injury ionic effects of saline soils besides improving the genetic makeup of sugar beet cultivars, expressed in sugar yield and quality. El-Mageed et al. (2021) under two soil salinity levels (3.54 and 9.28 dS m−1 ), representative low and high salinity, respectively, two sugar beet cultivars (Romulus and Francesca) were subjected to three potassium levels (0, 48, 96 and 144 kg K ha−1 ). They illustrated that K at a rate of 144 kg ha−1 improved cell membrane stability, relative water content and performance index by 1.17, 1.01, and 2.73 times, correspondingly, at high salinity soil, in comparison with low salinity × no K addition. At high salinity, adding of 48 and 144 kg K ha−1 registered the greatest values of total phenolic content and total antioxidant activity, respectively. Under high salinity soil, K applying (144 kg ha−1 ) caused the maximum enhancements in gross and white sugar content with a reduction of 42.0% in sodium content and a rise of 35.9% in root yield ha−1 . Romulus genotype fertilized with 144 kg K ha−1 produces the highest relative water content, F v /F m , and performance index. Francesca genotype with 144 kg K ha−1 was the effective combination for elevation total soluble sugars, total phenolic content, total flavonoid content, as well as total antioxidant activity. While, Romulus genotype fertilized with 144 kg K ha−1 was the best practice for improving wholly agronomic sugar beet characters.

Irrigation Management System Plants are generally more sensitive to salinity damage during germination and the seedling stage than when established. So, the best quality water should be used at this stage. Drip irrigation allows the use of water with higher salt content than other supply methods, as evaporation losses are minimal. Drip irrigation can also reduce the effects of salinity by keeping continuously moist soil around plant roots and providing steady leaching of salt to the edge of the wetted zone. Spray-irrigated crops are likely to suffer additional injury from salt uptake into leaves and burn from spray contact with leaves. If saline water is used for sprinkler irrigation, irrigation should be done when temperatures are cooler. Where irrigation in the heat of the day leads to the concentration of salts due to high evaporation. Watering during high winds also leads to a concentrates of salts. Therefore, do not

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use sprinklers which produce fine droplets and misting and avoid knocker sprinklers if possible, mainly slow revolution sprinklers which allow drying periods, which lead to a build-up of salt on the leaves. Selection of suitable irrigation systems viz. drip-surface and subsurface, sprinkler, bubbler, furrow, etc. for irrigated agriculture is one way to improve water use efficiency and manage root zone salinity. Zaman et al. (2018) showed that the development of irrigation systems is important in managing to salinity, as it is the place the seeds for good germination and maintaining a salinity level below the crop threshold salinity level. Drip irrigation is often desired compared to sprinkler irrigation for crop plants with a high sensitivity to leaf necrosis. In surface drip irrigation, salts are concentrated along the perimeters of the expanding wetting soil zone, with the lowest salt concentrations happening in the immediate vicinity of the water basis, the greatest are on the soil surface, and in center of any two drippers, that is the limits of the volume of wetted soil. Meanwhile, in the subsurface drip irrigation, the salts accumulate continuously on the soil surface through an upward capillary motion from the buried irrigation lines during growing season, so the concept of leaching requirement does not work specially serve to leach salts from surface above the buried drip lines. Whereas, in furrow irrigation method maximum salts accumulate in the soil ridges between the furrows. The accumulation of salt in furrow irrigation using diverse bed shapes viz. flat top bed and sloping beds appears in various figures which guide the growers to place seeds in safe region to achieve a high germination rate. Chauhan et al. (2008) revealed that supplemental irrigation of wheat in fields with irrigation water salinity of 8–12 dS m−1 reduced grain yield by 10%. In an arid climate, Jiang et al. (2012) showed that the maximum wheat grain yield was attained with 300 mm of water and salinity level of 3.2 dS m−1 , and through using salinity level of 6.1 dS m−1 yield reduction valued 8–10%.

8.3 Environmental Factors Environmental factors and pollution affect the degree of salinity tolerance in crop plants. The salinity tolerance of crops increases in cool, humid weather compared to hot and dry weather. Temperature and humidity play an important role in avoiding salinity damage by the mechanism of salt exclusion. Rice plants suffer greatly from salinity damage at 30.7 °C and 63.5% relative humidity compared to 27.2 °C and 73.4% relative humidity (Ota and Yasue 1959). The heat effect is attributed to an increase in the rate of transpiration over the rate of absorption. The regression of genotypes on the environment under salinity conditions in Ras Sidr Valley was shown for the seed cotton yield, lint cotton and most of its components as an indication of the differential response of the cultivars to the salinity conditions, environment elements and seasons (Moustafa 2006). Climate change also affects soil moisture content, water holding capability and soil particle size. Increased soil surface temperature increases evaporation rate and

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constrains water movement in soil profile (Onwuka and Mang 2018). So, reduced production of cultivated crops is directly associated with -scale climatic changes (Malla 2008). Although an increase in the level of carbon dioxide enhances the growth of C3 plants, higher temperatures reduce the amount of important agricultural yields due to a higher rate of evaporation. These two factors fundamentally impact soil salinization and agricultural production, affecting water and food security (Ullah et al. 2021).

8.4 Improvement of Salinity Tolerance by Exogenous Treatments with Metabolites Management of sustainable crop production under salt-affected soils will be a great challenge in the future. While the crop variety has its own strategies to manage with the injurious effects of salinity stress, occasionally, these adaptation strategies of genotypes are not satisfactory. In this perspective, external mitigation options practiced by humans to sustain the plants against stresses or bypass the stress situation by adopting certain novel strategies are important to minimize agricultural losses. Over the past periods, the enhancing effects of exogenous metabolites on the improvement of salt tolerance has been established in crop plants. It has been reported that salinity stress tolerance could be improved by exogenous treatments, using natural and synthetic combinations for seeds or plants to protect them against salinity stress. Various types of naturally occurring metabolites have been used, such as non-protein amino acids, antioxidant enzymes, hormones, sugar, vitamins, and polyamines, which lead to osmotic regulation, scavenging reactive oxygen species and detoxification. The application of exogenous protectants was recognized to ameliorate salinity stress effects via better growth performance of the crop genotypes. Ashraf et al. (2002) reported that one approach to induce tolerance to oxidative stress would be achieved by increasing the cellularity of enzyme substrates for example ascorbic acid. It seems important to highlight the potential ameliorative effects of proline in mitigating the harmful effects of salinity stress in growing plants. The protective role of Melatonin against salt stress has been well established in bread wheat, Ke et al. (2018) suggested treatment with Melatonin to mitigate salt stress in wheat seedlings by modulating polyamine metabolism. They showed that exogenous treatment improves seedlings’ tolerance against salinity stress as mediated by the increases in shoot dry weight, chlorophyll content, leaf photosynthesis rate and indole-3-acetic acid content, and reduction levels of H2 O2 . It also increased endogenous melatonin content in bread wheat seedlings by enhancing expression levels of the TaSNAT gene which encodes for a regulatory enzyme controlling biosynthesis of melatonin. Plant extracts enhanced physiological and biochemical processes in crop plants. Seed priming with sorghum extracts enhanced wheat genotypes to salt tress (Bajwa

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et al. 2018), and exogenous methyl jasmonate adjusts cytokinin content by modulating cytokinin oxidase activity in wheat seedlings under salinity stress (Avalbaev et al. 2016). Systemic resistance in plants is induced by exposure of roots or plant tissues to environmental stimuli. It depends on the production of plant hormone chains (salicylic acid) and the accumulation of PR-proteins associated with resistance to environmental stresses (About: Vallad and Goodman 2004). Salicylic acid (SA) is a phenolic plant hormone that acts as a signaling molecule that plays a vital role in plant tolerance to salinity conditions. It plays a vital role in plant growth, ion uptake and transport, and preventing oxidative damage in the plant by detoxifying superoxide radicals, caused by salinity and induced salt stress tolerance in plants as illustrated in Fig. 8.2 (Rajeshwari and Bhuvaneshwari 2017). Arif et al. (2020) showed that exogenous application of Salicylic acid facilitates seed germination, growth, and flowering, up-regulates photosynthesis and increases the activity of enzymatic and non-enzymatic antioxidants. Salicylic acid is a potent tool for sustainably mitigating environmental stresses in many plants by modulating the physiological and metabolic processes of plants. Based on recent reports, Salicylic acid biosynthesis and its regulation are discussed. Involvement of various proteins, and ROS interaction during Salicylic acid signaling, regulating diverse physiological and biochemical processes in healthy and stressed plants and assesses Salicylic acid effects in plants exposed to various abiotic stress. In rice, exogenous treatment by Salicylic acid, Cold plasma treatment, and exogenous priming enhance salinity tolerance in rice seedlings (Sheteiwy et al. 2019). In faba bean, the application of Salicylic acid would offer a useful basis for wide cultivation of faba bean in marginal and wastelands under-cultivated and might propose an effective ecological and economical alternative solution to treat with salt-affected soils primarily in arid areas. Souana et al. (2020) evaluate the role of salicylic acid (SA) application in mitigating the adverse effects of salinity on faba bean at the physiological and molecular bases. They exposed two faba bean genotypes to several NaCl and salicylic acid concentrations. The results verified that salinity induced several limitations in plants growth and physiological attributes. In response, salt stressed faba bean plants showed improve in water status and enhanced antioxidant enzymatic activities. Remarkably, salicylic acid application significantly improved salt-tolerance of both genotypes, which allowed the maintenance of cell membrane and photosynthetic process, restoring ion homeostasis and the diminution of oxidative damages. Faba bean genotype Aguadulce performs better with 0.5 mM SA, whereas Histal exhibits greater performance with 1 mM SA. Therefore, salicylic acid can be considered as a potential growth regulator to improve the salt response of faba bean. Furthermore, the potential role of Salicylic acid (SA) and Plant Growth-Promoting Bacteria (PGPB) (Stenotrophomonas sp.) was assessed by Nigam et al. (2022) on soybean and spinach cultivars at two variable salt levels 50 and 100 ppm salt. Results revealed exogenous apply of protectants improved plant growth and yield, enriched relative water content, accumulated osmolytes, and improved enzymatic and nonenzymatic antioxidants with two levels of salinity. Furthermore, applied protectants

8.4 Improvement of Salinity Tolerance by Exogenous Treatments …

Exogenous Salicylic acid

- Induction of antioxidants - Production of osmolytes - Improve plant-water relations

- Restore ion homeostasis, - Regulating growth and development

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Salt stress

- Induction of reactive oxygen species (ROS) signaling - Disruption of cell functions

- Regulate photosynthetic process - Improved cell membrane stability

- Protection plants against salinity

Salt stress tolerance

Fig. 8.2 Mechanism of salt stress resistance induced in plants by exogenous salicylic acid (Modified after, Rajeshwari and Bhuvaneshwari 2017)

prompted new protein bands. They concluded that the exogenously treated with PGPB and SA manage salinity-induced yield loss through increased growth, osmotic adjustment, protein accumulation, and ascorbate peroxidase APX activity. The PGPB appeared to be more effective protectant than SA for reducing the salinity-induced yield loss due to strong low molecular weight protein profiling, greater strength of ionic homeostasis and greater APX activity. The results of several studies showed that the negative impacts of salinity on legumes such as soybeans, mung beans and peanuts can be mitigated by applying salt-tolerant rhizobial strains (Dobbelaere et al. 2001; Bashan et al. 2004; Yasin et al. 2018; Kumar et al. 2019). Salt-tolerant species of Pseudomonas are described to increase the viability and vigor of faba bean (Metwali et al. 2015), chickpea (Jatan et al. 2019) and groundnut (Saravanakumar and Samiyappan 2007). Furthermore, in comparison to the control, El-Esawi et al. (2018) showed that the application of ST-PGPR B. firmus SW5 on soybean cultivated under salt stress was a beneficial effect on nutrient uptake, chlorophyll content, osmolyte levels, gas exchange, total phenolics, flavonoid contents as well as antioxidant enzyme activities. Furthermore, exogenous application by proline and trehalose improved salt stress tolerance (Nounjan et al. 2012). In maize, de Freitas et al. (2018) exogenous proline application lead to improve salt tolerance as its related to low oxidative damage and

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favorable ionic homeostasis. Moreover, de Freitas et al. (2019) detected physiological and biochemical changes and regulation of proline metabolism enhancing salt acclimation in sorghum plants by exogenous proline. Rady et al. (2015) assessed exogenous effects of proline treatments on salinity stress on 20, 35 and 50-day old seedlings of two lupine varieties viz. Giza 1 and Giza 2 planted on a saline soil with 6.35–6.45 dS m−1 . Genotypes were sprayed with 0 (tap water as a control), 3, 6 or 9 mM proline. Proline treatments significantly increased growth characters, physiological attributes, yields and anatomical traits of the tow lupine varieties rather than the control. Among proline levels, 6mM proline gave the highest levels of plant growth, leaf photosynthetic pigments, total soluble sugars, endogenous proline and yields and represented the best anatomical characteristics of the two lupine varieties. On the contrary, the level of 6mM proline caused the lowest contents of alkaloids under salinity stress. In this context, 5-aminolevulinic acid improves salt tolerance mediated by regulation of tetrapyrrole and proline metabolism in Brassica napus L. seedlings under NaCl stress (Xiong et al. 2018). Glycine betaine improves growth and proline accumulation and retards senescence in rice varieties under salinity stress (Demiral and Türkan 2006). Moreover, the effect of exogenously mushroom polysaccharides (β-glucan) on growth of two rice Oryza sativa L. cultivars i.e. (MRQ74 and MR269) was tested by Alhasnawi (2016). Rice seedlings grown in vitro in 200 Mm sodium chloride (NaCl). They discover an inhibition effect of sodium chloride treatment on growth features, comprising shoot and root height, and fresh and dry weight of salt-stressed rice seedlings, the degree of which depends on the rice variety. However, treatment with exogenously applied polysaccharides (β-glucan) ameliorated the stress generated by NaCl and improved the parameters mentioned above. Selenium plays a vital role in many enzymatic and non-enzymatic processes, for example, antioxidants for glutathione and GSH-related enzymes and phytochelatins, helping to overcome salt-induced massive production of ROS, and reduce generation of lipid peroxidation under saline environments (Astaneh et al. 2019). Sobahan et al. (2012) found that low amounts of selenite (Na2 SeO4 ) protect crops from ROSstimulated oxidants in rice cultivars. Zong Xj et al. (2009) observed that Selenium improves the antioxidant enzymes activity in maize to cope with environmental stresses. Spermidine or spermine were exogenously applied on three varieties of Indica rice differing in their level of salt tolerance. The salt injuries were reduced by spermidine and spermine particularly in Gobindobhog genotype (Roychoudhury et al. 2011). Exogenous application of penconazole alleviates salt-induced damage in safflower plants (Shaki et al. 2018). Whereas, in Arabidopsis thaliana, exogenous allantoin improves tolerance to NaCl stress and adjusts the expression of oxidative stress response genes (Irani et al. 2018). Algae plays a role in salt tolerance. In this respect, the effect of treating crop plants by algae to mitigate the effect of salt stress was investigated by Anter and El-Sayed (2020). They screened twenty-three sesame genotypes under a nature field

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and subjected to two levels of NaCl (70 and 105 mM) incorporated with algae, at the Agricultural Production and Research Station, National Research Center, Egypt. Six yield traits to describe salinity tolerant have been measured. Results indicated that interaction between genotypes x salinity levels was highly significant of considered traits. Genotypes performance for plant height, stem height to 1st capsule, fruiting zone length, number of capsules/m2 , seed yield/ ha−1 traits were negatively affected by salinity levels with algae compared to normal situations. However, in irrigation with saline water without algae, the genotypes cannot grow, demonstrating that algae have a negative effect on salinity and are essential to lessen the harmful impact of salinity. The two lines, C8.4 and C8.8 revealed promising marks in adaptation studies to salinity stress, and both lines could be utilized as novel sources of salinity tolerance in sesame.

8.5 Conclusion More than 1500 plant species can be grown in salty areas, and high salinity water can be used for irrigation. These crops include barley, rice, sugar beet, cotton, canola, safflower, jojoba, and many pasture grasses. However, improving the growth environment in saline lands seems of great importance to the possibility of expanding the cultivation of salt-affected lands. So, saline lands can be reclaimed by levelling the land surface by laser that helps to regularize and homogenize the distribution of irrigation water and thus permeate and wash the land. So, leaching salts from the soil with water of good quality to dissolve the salts and remove them from the root zone, with attention to the drainage system is very important. Also, application of gypsum and bio-organic amendments have been recognized to enhance the physical, biological and chemical properties of saline soils. At the same time, gypsum provides crop plants with elemental sulfur to improve growth and productivity. Moreover, the cultivation of salinity-tolerant crop species and varieties released from breeding techniques is an operative strategy to tolerate salinity stress, beside the application of appropriate agricultural practices suitable for saline soil conditions.

8.6 Recommendations According to aforementioned literature, numerous strategies should be implemented to minimalize the salinity impressions and improve soil productivity as follow: 1. Application of the leaching process pre-planting. 2. Implementation of soil leveling by laser. 3. Choosing proper agricultural practices i.e. sowing methods, cultivation of suitable crop species, tolerant variety and exploiting the best nutrient tactics. 4. Application of natural plant extracts to osmotic regulation.

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5. Application of environmentally friendly additives, for instance, Plant Growth– Promoting Bacteria to improve salt tolerance.

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Upadhyay SK, Singh DP (2015) Effect of salt-tolerant plant growth promoting rhizobacteria on wheat plants and soil health in a saline environment. Plant Biol 17:288–293 Upadhyay SK, Singh JS, Saxena AK, Singh DP (2012) Impact of PGPR inoculation on growth and antioxidant status of wheat under saline conditions. Plant Biol 14:605–611 Vallad GE, Goodman RM (2004) Systemic acquired resistance and induced systemic resistance in conventional agricutlutre. Crop Sci 44:1920–1934 Vance GF, King LA, Ganjegunte GK (2008) Soil and plant responses from land application of saline–sodic waters: implications of management. J Environ Qual 37:139 Wang Y, Wu WH (2017) Regulation of potassium transport and signaling in plants. Curr Opin Plant Biol 39:123–128 Wang M, Zheng Q, Shen Q, Guo S (2013) The critical role of potassium in plant stress response. Int J Mol Sci 14:7370–7390 Xiong JL, Wang HC, Tan XY, Zhang CL, Naeem MS (2018) 5-aminolevulinic acid improves salt tolerance mediated by regulation of tetrapyrrole and proline metabolism in (Brassica napus L.) seedlings under NaCl stress. Plant Physiol Biochem 124:88–99 Yasin NA, Khan WU, Ahmad SR, Ali A, Ahmad A, Akram W (2018) Imperative roles of halotolerant plant growth-promoting rhizobacteria and kinetin in improving salt tolerance and growth of black gram (Phaseolus mungo). Environ Sci Pollut Res 25:4491–4505 Zahra N, Raza ZA, Mahmood S (2020) Effect of salinity stress on various growth and physiological attributes of two contrasting maize genotypes. Art Agric Agribusiness Biotechnol 63:1–11 Zaman M, Shahid SA, Heng L (2018) Irrigation systems and zones of salinity development. In: Guideline for salinity assessment, mitigation and adaptation using nuclear and related techniques. Springer Zeng L, Shannon MC (2000) Effects of salinity on grain yield and yield components of rice at different seeding densities. J Agron 92:418–423 Zhang HJ, Hezhong Dong, Li WJ, Zhang DM (2011) Effects of soil salinity and plant density on yield and leaf senescence of field-grown cotton. Journal of Agronomy and Crop Science 198(1):27–37 Zia MH, Saifullah SM, Ghafoor A, Murtaza G (2007) Effectiveness of sulphuric acid and gypsum for the reclamation of a calcareous saline-sodic soil under four crop rotations. J Agron Crop Sci 193:262–269 Zong X, Li DP, Gu L, Li D, Liu L, Hu X (2009) Abscisic acid and hydrogen peroxide induce a novel maize group C MAP kinase gene, ZmMPK7, which is responsible for the removal of reactive oxygen species. Planta 229(3):485

Chapter 9

Techniques and Measurements of Assessing Genotypes for Salinity Tolerance

9.1 Introduction Salinity is one of the major problems in marginal areas that limit crop plants’ productivity because most crop plants are affected by salinity caused by high concentrations of salts in the soil. Also, the interaction between salinity tolerance and environmental factors reduces the effectiveness of the selection process for salinity tolerance. These variables related to salt damage are improbable to control under field screening techniques (Khan et al. 2022; Lee et al. 2008; Pathan et al., 2007). The breeding program’s success depends on the proper evaluation of the salinity tolerance of the various genotypes. Negrao et al. (2017) studied how to measure the effect of salinity on different traits of crop plants. Therefore, it becomes clear the importance of identifying and separating random environmental effects from genetic effects to allow the development of salt-tolerant varieties. Screening of crop plants for salinity tolerance has been conducted for a long time and different methodologies have been utilized. Screening under controlled conditions given better results because of reduced environmental effects. Talei et al. (2013) indicated that the successful application of screening methods for improving salt-tolerant crops has been restricted by several factors, for instance, the shortage of a standard and operative technique for assessing salt tolerance. Zhu (2016) showed that it should be noted the importance of screening a large number of genotypes to study salt tolerance and using certain traits as major selective criteria for salt tolerance in evaluation programs. Bai et al. (2018) improved the effectiveness of screening procedures using three methodologies: (1) increasing the number of cultivars, (2) finding a suitable salt treatment system that offers optimum discriminating power in examinations of salt tolerance including the suitable concentration and volume of salt solution, and (3) choosing proper criteria for salt tolerance. Several studies have explored different salt intensity methods as optimal techniques for screening salt tolerance (Matthew and Stacy 2010; Peterson and Murphy 2015) and demonstrating differences between tolerant and sensitive cultivars. For © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_9

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example, in wheat (Ehtaiwesh Amal (2019), rice (EL-Emary et al. 2013), maize (Meihan et al. 2022), barley (Makhtoum et al. 2022), oats (Bai et al. 2018), faba bean (Afzal et al. 2022), soybean (Ledesma et al. 2016), in cotton (Munawar et al. 2021) and Atriplex spp. (Calone et al. 2021). In this regard, and given the variation in salinity conditions under field conditions, it is important to subject different plants or genotypes to controlled salinity levels. The evaluation under controlled saline environments should be conducted. So, this chapter lists and discusses various evaluation methods and salinity measurements.

9.2 Evaluation Methods of Crop Genotypes 9.2.1 Lysimeter Micro Plots Small experimental plots of specific sizes are designed to bring about uniformity in the salinity level. Lysometers are used in screaming and evaluation programs for salinity tolerance. This technique has been used in CSSRI Institute in India and several research stations in evaluating the germplasm of crops for salinity tolerance (Singh 2001). In wheat, Khan et al. (2009) experimented lysimeters (cemented tanks), filled with river sand. The growing media was irrigated by 1/4th strength Hoagland solution, salinized by commercial NaCl salt to reach a salinity level of 1.5 dS m−1 (control) and 12.0 dS m−1 . Six wheat genotypes viz., Lu-26s, Sarsabz, KTDH-22, V-7012, Khirman and Bakhtawar were seeded in a randomized method with three replications. They recorded growth parameters at maturity. Plant samples of flag leaves were analyzed for soluble salts i.e. Na, K and K/Na ratio. Lysometer ponds were used at the Research and Training Institute in rice, SakhaKafr El-Sheikh, Egypt. Shehata (2004) evaluated five rice genotypes for salinity tolerance using the Line x tester analysis, using two cultivars: Giza 177 (non-tolerant to salinity and drought) and Giza 178 (saline tolerant) and three testers are IET (drought tolerant), IR 47686-6-2-2-1 (moderate tolerance to salinity and drought) and IRAT III (tolerant to salinity) and 6 resulting crosses, under salinity and normal conditions to identify the gene action controlling salinity tolerance and yield features. They recorded variations in the behavior of genotypes under different levels of salinity. Furthermore, in maize, Meihan et al. (2022) used irrigation with saline water through three seasons (2017–2019) of field experimental of mulched maize water use in two cropped weighing lysimeters by measurements comprised crop characters i.e. plant height, leaf area index, days to development stages, the salinity of soil and water, and daily actual crop evapotranspiration (ETc). In the 2017 and 2018 seasons, deficit surface irrigation was scheduled, whereas in 2019 drip irrigation was used to meet crop water needs to improve irrigation management and control impacts of salinity. The model uses the FAO-56 dual crop factor method and the joint effect of water stress and salinity of both soil and irrigation water. The standardized basal crop

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coefficients (Kcb) for initial, mid and end of maize stages were 0.15, 1.15 and 0.25, respectively. As a result of the effects of both water and salt stress, ETc act was greatly below the potential value ETc, ranging from 64 to 83%. The irrigation scheduling practice was measured using water use and productivity parameters, which have revealed the advantage in the use of drip irrigation with short intervals between irrigations and adopting irrigation management that may save water and control salinity. Lysimeter experiment was utilized for evaluating two genotypes of chickpea (Cicer arietinum L.) and faba bean (Vicia faba), varied in drought tolerance based on the classification of the International Center for Agronomic Research in Dry Areas (ICARDA), were irrigated with water of three different salinity levels in a lysimeter experiment to analyze the salt tolerance. The drought-sensitive genotypes are more salt-tolerant compared to the drought-tolerant ones. At saline situations, the droughtsensitive genotypes display a much greater yield up to a salinity threshold, with an electrical conductivity (ECe ) from 2.5 to 3 dS m−1 for chickpea and between 5.5 to 6 dS m−1 for faba bean. The drought-sensitive genotypes are capable of increasing water-use efficiency after being irrigated with saline water. This capability could be attributed to the greater biomass production due to the later senescence, which permits a better use of the irrigation water (Katerji et al. 2005).

9.2.2 Laboratory Conditions The germination stage is the first stage of selection and there are many methods for estimating germination under saline stress conditions, including filter papers, antibiotic-agar, pots filled with soil, pots filled with sand and gravel, nutrient solution cultures and growth chamber.

Filter Paper Blotter/Filter paper that is pure white and perfect for seed germination tests. It is considered one of the simple methods for estimating germination under stress conditions. Seeds of genotypes are grown in Blotter/Filter papers moistened with an appropriate salt solution (usually sodium chloride and calcium chloride), and placed in containers or boxes. In this way, the discrepancy in the micro-environment inside or between vessels is taken as a result of evaporation, condensation and concentration of salts, which leads to variation in the exposure of the seeds to salt stress, in addition to fungal infections of the seeds with the length of the exposure period. In a randomized complete block design with five replications, Ehtaiwesh Amal (2019) conducted a series of control environment experiments to evaluate the response of two spring wheat and two winter wheat cultivars to various salinity levels. She placed 20 seeds of each genotype on pre-moistened filter paper in Petri dishes and located in an incubator at 20 °C under 4 levels of salinity 0, 50, 100,

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and 150 mM NaCl. The results indicated that winter and spring wheat genotypes significantly varied for germination %, rate of germination, mean daily germination, shoot and root lengths and seedling fresh and dry weight. The results showed that increasing salinity level significantly decreased shoot and root length. The root growth could be operative criteria for screening wheat genotypes to salt tolerance at seedling stage.

Antibiotic—Agar Plate Carlson et al. (1983) suggested replacing moistened filter papers with a agar-salinized antibiotic agar plate containing an appropriate fungicide to prevent infection of the seeds with mold fungi. The seeds are positioned on the media containing the required concentration of the saline solution, and this approach is more appropriate than filter papers. When evaluating alfalfa strains and selecting for salinity tolerance using standard Moist-paper and comparing them with the agar method, the agar selection led to an increase of 3.75 times in germination than the filter paper method. This technique was used in the rapid evaluation and estimation of the physiological basis and enzymatic activity associated with salt tolerance in a large number of chickpea germplasm. Singh et al. (2003) conducted superficial sterilization of chickpea seeds, then the seedlings aged 8 days were exposed to different levels of a saline solution consisting of sodium chloride: calcium chloride: sodium sulfate in a ratio of 7:2:1 and the electrical conductivity of salinity levels was controlled by a Conductivity meter and tested levels were zero, 4 and 8 dS m−1 . In this connection, Grare (2010) evaluated salt tolerance mechanisms as tools and orientations for traits of salt tolerance in Miscanthus sinensis. The competent cells were plated in a flow ambient on LB-ampicillin agar plates and developed for 17 h at 37 °C. Blue/white-capable cloning vectors like pGEM-T have multiple cloning sites within the α-fragment coding sequence. The transformation was performed with an insert-containing plasmid to produce colonies. Results provided evidence of salt tolerance variability in Miscanthus sinensis and revealed the existence of different tolerance mechanisms.

Petri Plates Germination parameters could be used as indicators and help crop breeder evaluate strains and varieties of field crops for salinity tolerance in the early germination stage of growth. EL-Emary et al. (2013) planted four hundred rice seed of nine rice genotypes in 8 petri dish with three levels of salinity concentration, 4000 ppm, 6000 ppm and 8000 ppm of NaCL, as well as the tap water. They found that, rice variety Giza 179 verified highly desirable estimates for yield characters and might be expressed as a promising genotype under saline soil conditions. Munawar et al. (2021) screened twenty-two cotton genotypes for comparative salt tolerance using germination test in Petri plates of growth chamber. They selected eleven genotypes

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for further evaluated in pot experiment (sand) using 0, 15, and 20 dS m−1 NaCl treatments under glass house conditions. Various morphological and physiological traits were estimated for all genotypes while biochemical analysis was assessed on selected seven highly tolerant and sensitive genotypes. Results indicated that NIAB135, NIAB-512, and FH-152 genotypes had adaption capability for salinity stress compared to the sensitive genotypes, namely, IR-NIBGE-13 and 6071/16. At three stages of growth and conditions through exposing to salt stress condition, Hailu et al. (2020) screened a collection of sorghum germplasm. At germination stage, 46 genotypes were screened through placed 20 seeds/Petri plates of each sorghum genotype using saline solution with ECe value of 0 and 20 dS m−1 of NaCl level in completely randomized design (CRD) with factorial arrangement in three replications. According to total germination % and germination stress index, 10 highperforming genotypes were selected in the first stage of germination and progressive to second germination stage of evaluation, and imposed on four treatments (0, 10, 15 and 20 dS m−1 ). Total germination percentage, Mean germination time and Germination stress tolerance index were calculated. The experimental work was completed in the next stage: Seedling stage screening; was carried out in pots under small lath house condition. Bulk surface soil i.e. non-saline and non-alkaline was collected and packaged into pot. Ten sorghum seeds of each selected genotype were planted per pot. Then prepared saline solutions were added to each pot containing respective sorghum while maintaining the soil moisture at field capacity. Once saline treatments were (0, 10, 15 and 20 dS m−1 ) in complete randomized design with factorial arrangement in three replications. Non-saline water was used for subsequent irrigations and applied at 7 day intervals to a field capacity. Emerged seedlings were calculated at 7, 10 and 14 days after planting. After making the last count, 5 seedlings were kept/pot. After 45 days of the experiment, weights of fresh and dry shoot and root were measured. The study was completed under field conditions as follows: Field experiments; were conducted at salt affected area of Raya Alamata district, in northern Ethiopia, for screening salt tolerance and evaluation performance of genotypes for yield and yield components. A plot size was 4.50 m × 4.50 m with Latin square design was used. Selected sorghum varieties were sown over two successive seasons. Results revealed that, sorghum traits were affected by salt stress at germination, seedling stages. Likewise, soil salinity decreased yield and yield components of sorghum under field conditions. Genotypes Meko and 76T1#23 were more yielded and promising ones.

9.2.3 Phytotron Conditions Under normal, salinity and drought circumstances, a set of 103 recombinant inbred line populations, developed between Badia and Kavir crosses, was tested under phytotron conditions in a completely randomized design. Makhtoum et al. (2022) aimed to identify genomic regions of morphological and physiological traits for

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barley genotypes. Composite interval mapping displayed 8, 9 and 26 quantitative trait loci (QTLs) under normal, drought and salinity stress situations, respectively. Results show the importance of chromosomes 1, 4, 5, and 7 in salinity stress. Specific regions were involved in genes governing stomata length, leaf number, leaf weight and genetic score. The new identified alleles i.e. qLWS-4a, qSLS-4, qLNS-7b, qSCS7, and qLNS-7a are useful in pyramiding elite alleles for molecular breeding and marker assisted selection for enhancing salinity tolerance in barley.

9.2.4 Growth Chamber Conditions Growth chambers (Fig. 9.1) are useful in breeding programs to assess salinity tolerance. This system allows providing the appropriate growing conditions of temperature, relative humidity and lighting. The growth chambers were useful in differentiating between barley and wheat cultivars. An increased accumulation of betaine was detected in barley varieties Jeoniju, Gondar 1, Haru-nanijou, and wheat cultivar Gogatsu in response to salt stress by Arakawa et al. (1992) and Ishitani et al. (1993). The experiment was performed in controlled conditions under growth chamber at the Faculty of Agriculture and Veterinary Medicine, An-Najah National University, Tulkarm (Khadouri), Palestine. Seeds of three local wheat landraces i.e. Norsi, Black Heteyeh and White Heteyeh were sown in November in plastic pots (2L) filled with clay soil and sand mixture (1:1, v/v) in complete randomized block design with three replications. The experiment included 50 and 100 mM NaCl salinity levels and tab water as control. Shtaya et al. (2019) found that Salinity stress decreased relative water content, while chlorophyll content, fresh weight and dry weight were not affected. Results showed that “Norsi” landrace was classified as the most tolerant genotype, as it exhibited the lowest reduction % in relative water content under 50 and 100 mM NaCl. It also assisted to evaluate ten genotypes of chickpea with different genotypes in soil supplemented with zero, 50, 75, and 100 mM sodium chloride, to study the effect of salinity on growth characteristics, root nodule formation and nitrogen fixation (Singh et al. 2003).

9.2.5 Greenhouses Crop genotypes are assessed in potting experiments under greenhouse conditions. Initially, soil washing is followed, and salinity levels are tested. Plants under these conditions are exposed to variation and change in salinity status between the pots over time, as a result of the difference in the rate of evaporation resulting from the difference in the size of the plant, despite the similarity of the salt content of the pots in the beginning. The pot experiments helped in evaluating a group of bread wheat germplasm, which included three American, three Mexican and four Egyptian cultivars in 20 × 19 cm pots filled with 8 kg of calcareous soil from Wadi Sidr mixed

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Fig. 9.1 Plant growth chamber to assess salinity tolerance (Source Modified after, https://bionic sscientific.com/test-chambers/plant-growth-chamber.html)

with clay soil at a ratio (1:1) and salinity levels were used. Irrigation water (tap water, 4000 and 8000 ppm), where Sallam and Afiah (1998) discriminated between the cultivars by studying the chemical components, salinity sensitivity index, yield and its components. Moreover, Saqib et al. (2004) conducted a pot experiment to evaluate the effect of soil salinity on root growth and leaf ionic content in two wheat varieties i.e. Aqaab and MH-97. The target salinity level (15 dS m−1 ) was prepared by mixing required amount of NaCl in the soil before filling the pots. Results revealed that salinity decreased the content of K+ and K+ : Na+ ratio, but increased the leaf contents of Na+ and Cl− . The behavior of a genotype under stressed environment is associated with maintenance of higher root length density, leaf K+ content and K+ : Na+ ratio and lower leaf Na+ and Cl− contents. The use of greenhouse (Fig. 9.2) is useful in the process of evaluating crop genotypes of salinity tolerance. This system allows controlling the level of salinity and other major environmental factors. Where, plants are grown in containers or boxes in a saline environment. The salt concentration is adjusted to the efficiency of the selection process. This concentration varies according to the sensitivity of the plant species under evaluation, which fluctuates with most plants of non-saline crops from

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Fig. 9.2 Designed and implemented greenhouse in the faculty of agriculture of Zagazig University of evaluating crop genotypes to stress tolerance (Fath et al. 2021)

50 mM in rice to 300 mM sodium chloride in barley. Parents and their crosses are evaluated under a range of graded salinity levels and the desired concentration is determined in the selection process. Various methods can be used to study germination and seedling characteristics in lines and cultivars of field crops under these conditions as follows:

Pots Filled with Sand and Gravel in Greenhouse In this system, the pots filled with sand and gravel and irrigated with tried salt water levels. This method is considered useful to a large extent, provided that the irrigation process is controlled and regular, and the irrigation and drainage processes can be adjusted automatically. Pots filled with sand were used under greenhouse conditions to evaluate two Kenyan sorghum cultivars Seredo and Serena under concentrations of NaCl in a complete nutrient solution with zero salinity levels (control), 50, 100, 150 and 250 mM NaCl. Netondo et al. (2004) observed a significant decrease in the relative growth rates of stems, stem dry weight, leaf and blade areas with the highest salinity concentration. Leaf water potential, osmotic stress, leaf pressure stress and relative water content were significantly affected by the increase in salinity in the two cultivars, but the percentage of decrease was higher in some cases in Serena cultivar compared to Seredo one. Carbon isotopes discrimination and growth performance were measured in a greenhouse to select suitable salt-tolerant wheat genotypes. Nine developed double haploids (DH) wheat lines were verified under gravel culture, together with salt

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tolerant (LU-26s) and high yielding (Sarsabz) checks. Wheat genotypes were irrigated by non-saline (control) and saline (12 dS m−1 ) water and raised to maturity. Where, Shirazi et al. (2015) observed a significant decrease due to salinity in all the growth and yield contributing trails i.e. plant height, plant biomass, spikes/plant, spike length, number of spikelet’s/spike, number of grains/spike, grain weight/spike and grain yield/15 plants). Based on the performance of different parameters, wheat lines V3-DH, V9-DH, V10-DH, V13-DH, and LU-26s had good response at 12 dS m−1 .

Pots Filled with Different Soil Texture in Greenhouse Evaluating wheat’s plant growth, biochemical and yield traits against saline conditions was conducted under pot trial in greenhouse by Khan et al. (2022). The soil was ground and passed through a 2 mm sieve, with EC 2.1 dS m–1 . Pot was filled by 12 kg of soil and arranged in a complete randomized design with three replicates. Salinity levels, i.e., 6, 12, and 18 dS m–1 , were developed by carefully mixing the deliberated amount of NaCl in the sieved soil, combined with numerous plant growth promoting rhizobacteria. Results showed that, at the highest level of salinity, the multi-strain consortium of PGPR gave a significant positive effect on both shoot and root lengths, shoot and root fresh weights, and reducing electrolyte leakage and improving chlorophyll content, relative water content and K/Na ratio. Whereas, a pot experiment containing coarse sand was conducted and watered and flushed daily with 50 mM NaCl in one-half-strength modified Hoagland solution for assessing transpiration rates in durum wheat. The ability of plants to reject Na+ was determined by measuring the Na+ concentration at the fourth fully expanded leaf blade at harvest. (James et al. 2006). Samples were harvested, fresh and dry weights were recorded, then digested in 10 mL of 1% HNO3 at 95 °C for 4 h in a 54-well HotBlock (Environmental Express, Mount Pleasant, SC, USA). Na+ concentration in the digested samples was estimated using a flame photometer (model 420, Sherwood, Cambridge, UK). To examine osmotic tolerance, the decrease in plant growth after the addition of NaCl relative to the control was measured through the imaging system. Plants that preserved similar growth rates under salinity conditions compared to the control were considered osmotic tolerant. To measure Na+ tissue tolerance, false color images taken on the 19th day after salt applied were used to estimate the healthy leaf area and the senescing leaf area. These assessments were collective with the leaf Na+ contents to relate the amount of leaf damage/death with leaf Na+ contents. Results indicated that plants showed low leaf damage and high leaf Na+ contents were considered as high tissue tolerance, however plants with high leaf damage and high or low Na+ contents were considered sensitive. Rice genotypes through doubled-haploid approach were screened in a pot experiment of greenhouse condition based on factor analysis. Anshori et al. (2022) used a split-plot design with salinity stress treatments as the main plot, viz., normal (0 mM NaCl) and saline (25 mM NaCl ~ 5.6–5.8 dS m−1 ) and 42 genotypes in the subplot. The results indicated that a salinity selection index model through a combination of factor analysis, stress tolerance index (STI), and path analyses have identified

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15 doubled haploid rice lines as good tolerant under salinity stress in soil artificial screening. At ICARDA, under the greenhouse, experiments comprised 120 plastic pots (6 chickpea genotypes × 5 replications × 4 treatments) with a top diameter of 19.5 cm and a depth of 18 cm, filled with sand were conducted by Bruggeman et al. (2003). Ten seeds were sown per pot. They prepared water with three salinity levels 2, 4 and 6 dS m−1 , by adding a mixture of NaCl and CaCl in a 3:1 ratio to the water using a randomized block design. Six genotypes (FLIP 96-59, FLIP 96-74, ICCV2, FLIP 87-85, ILC 3279, FLIP 97-265) were sterilized by 0.1% mercuric acid for 5 min and washed in sterile water afore germination. The salinity had slight effect on germination. Lines F 0.97-74, F 0.87-59 and ILC 3279 were found to be higher salt tolerance than F 0.97-265 one. Pot experiments in Greenhouse experiments are conducted by Afiah et al. (2016) to examine the response of five divergent faba bean genotypes namely (NBL-Mar.3, NBL-5, L3, Nubariya-1 and Misr-1) against salt stress. The five faba bean genotypes were verified in 50 cm. diameter plastic pots, filled with clay soil in winter growing seasons (2011–2012). Five plants were grown in each pot and three pots for each treatment. The two experiments were conducted with a split plot design for both water and salinity stresses. In the first experiment, the soil was irrigated when moisture reached 70, 50 and 30% of field capacity (FC) by tap water, and FC of soil was determined. Irrigation every one week; soil moisture content depleted from 100 to 70% of field capacity. Irrigation every two weeks; soil moisture content depleted from 100 to 50% of field capacity. Irrigation every three weeks; soil moisture content depleted from 100 to 30% of field capacity. The second experiment comprised three concentrations of salt [tap water (control), 30 mM (1755 ppm) and 60 mM (3510 ppm)] of sodium chloride were used for irrigation water salinity two weeks after planting sowing. They found a fluctuation response in genotypes for eleven tolerance indices. NBL-Mar.3 was a best tolerant genotype under salinity experiment conditions while, Nubariya-1 and Misr-1 were the most sensitive ones. Furthermore, NBL-5 was the highest drought tolerant genotype, while Misr-1 was the most sensitive one. In this concern, at Etay Elbaroud Research Station, Agriculture Research Center, MALR, Egypt, Abdelraouf et al. (2016) investigate the effect of salinity levels (0, 25, 50 and 100 mM of NaCl) on growth and genetic diversity of broad bean cultivars (Etay 1, Giza 3, Giza 843, Nubaria 1, and Lozodo) using a randomized complete block design in split arrangement. Cultivars were seeded in pots containing 1 kg pre-washed quartz sand. Pots were irrigated three times weekly by adding 100 mL of solution consisting of base nutrient solution and the salt level to every pot. Four weeks after sowing, entire plants were collected. The results showed that increasing salt concentration reduced fresh and dry weights of shoots and roots, shoot length, and leaf area of the tried cultivars. But, the ratio of shoot/root on fresh and dry weight basis and moisture content of shoots and roots increased with the increase in salt concentration. The content of chlorophyll and band carotenoids tends to decrease with increasing salt concentration. Analyses of genetic diversity categorizing the broad bean cultivars into three main clusters; Cluster A contains Giza 3 and Giza

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843, cluster B comprises Lozodo and Itay 1, and cluster C includes Nubaria 1. The various salt concentrations produced the synthesis and enhanced the intensity of the original protein bands and led to the appearance of supplementary novel bands of broad bean total protein. The cultivars were clustered into tolerant such as Lozodo and Itay 1, moderately tolerant likewise Giza 3 and Giza 843 as well as sensitive Nubaria 1. Moreover, a pot experiment (30 cm height × 20 cm width) was conducted under greenhouse in a split-plot arrangement with a randomized complete block design to test the efficacy of the multivariable morpho-agro-physiological characters of salt tolerance for twelve faba bean genotypes (Vicia faba L.) at the College of Food and Agriculture Sciences, Riyadh, Saudi Arabia. The average temperature was ±20 during the day and ±16 °C during the night and photoperiodic under greenhouse system was a 16 h light and 8 h dark cycle with relative humidity of about 60–70%. The pots were filled with pure sand watered twice a week with tap water with 1/10th of strength Hoagland nutrient solution. Three seeds were sown in each pot, and after the seedling was established, two seedlings were maintained under controlled and pressure conditions and then the average was calculated. Where, Afzal et al. (2022) evaluated the genotypes under three salinity levels (control, 100, and 200 mM NaCl). The seeds of each genotype were allowed to grow for 15 days to establish the seedlings before subjecting and seedlings were gradually exposed to salt stress from 100 mM for two weeks to evade osmotic shock. After reaching full stress levels, different morpho-physiological characters i.e. stomatal conductance, leaf temperature, and SPAD readings at the vegetative stage were estimated. Also, ionic concentration (Na+ , K+ ) and total chlorophyll content were determined. The results indicated that Hassawi-2, ILB-4347, Sakha-1, Misr-3 and Flip12501FB were the most tolerant genotypes. However, FLIP12504FB represents a sensitive genotype based on its final grain yield. Indices results revealed significant index correlations with grain yield. Furthermore, pot experiment under greenhouse conditions was conducted to evaluate 28 cotton cultivars, including 8 Iranian cotton varieties, imposed under three salt solutions (0, 70 and 140 mM NaCl). Abdi et al. (2012) assessed 8 agronomic characters comprising root length, root fresh weight, root dry weight, chlorophyll and fluorescence index, K+ and Na+ contents in shoot, also K+ /Na+ ratio were estimated. Results showed significant difference between cotton genotypes for salinity tolerance. Four genotypes i.e. Atriplex halimus, A. hortensis red, A. hortensis scarlet, and A. hortensis green were evaluated under salinity stress in pot experiment. In all genotypes, excluding those grown at 0 mM NaCl, salt treatments were applied 20 days after transplanting, on the 20 July, at age of six to eight leaves. Salt stress was induced by additional increases of 90 mM in the irrigation water every 3 days, until the final concentrations of 90, 180, and 360 mM NaCl were reached on the 27 July. Calone et al. (2021) recorded substantial variation between genotypes in response to salinity stress levels.

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Tanks in Greenhouse Recently, a new and simple screening technique, the plastic “cone-tainer” method, was suggested. This technique is less laborious and time consuming than heretofore testified ways. Bai et al. (2018) used plastic “cone-tainer” to assess salt tolerance among a collection of oat genotypes. They conducted a set of four experiments to develop techniques for screening oat to salt and alkali tolerance. Results revealed that: (1) In experiment 1, 68.5 mmol L-1 salt and 22.5 mmol L-1 alkali were recognized as suitable concentrations for identifying oat tolerance to salinity and alkalinity in germination stage. (2) The previous concentrations were exploited in experiment 2 to evaluate 248 oat germplasm and 21 were recognized as tolerant to salinity and alkalinity in germination stage. (3) In experiment 3, one salt treatment, 40 L of Na2 SO4 :NaCl (1:1), 150 mmol L-1, was optimized for examining salinity tolerance of oat through growth and development stages. For alkalinity tolerance, the optimum treatment was 40 L of Na2 CO3 :NaHCO3 (1:1) at 75 mmol L-1. (4) Results revealed insignificant association was showed between tolerance at the germination and mature stages or between tolerance to salt and alkali. Three lines were found to be tolerant to salt and alkali in germination and adult stages. In experiment (5), 25 out of 262 oat genotypes were classified as tolerant to both salinity and alkalinity. Generally, entries (ND131936), 199ND130775 classified as the most tolerant genotype, while 260ND132528 was a sensitive genotype. (6) GGE biplot analysis was operative in understanding the multivariate data, and the plastic cone-container system was a cost-effective scheme for screening adult plant tolerance to salt and alkali. In a greenhouse conditions at the University of Missouri, Columbia, MO, with artificial lights and a 13 h photoperiod from September to December 2016, Do et al. (2019) evaluated five soybean genotypes for salinity tolerance. Seedlings of each line were grown per cone-tainer using tanks in a randomized block design with three replications, and treated at growth stage by salt water via exposing seedlings in conetainers to a 120 mM NaCl solution in a tank. Once tests for salt-sensitivity checks showed severe leaf scorch, 2 weeks after the treatment, leaf scorch score (LSS) has been visually recorded for each plant using a 1–5 scale, where 1 = no apparent chlorosis; 2 = slight (25% of the leaves showed chlorosis); 3 = moderate (50% of the leaves showed chlorosis and some necrosis); 4 = severe chlorosis (75% of the leaves showed chlorosis and severe necrosis); and 5 = dead (leaves showed severe necrosis and were withered), mean of LSS of each genotype was then estimated (Lee et al. (2008). The results show that the four characters i.e. leaf scorch score, chlorophyll content ratio, leaf sodium content and leaf chloride content are effective of salt tolerance and might be exploited in selection for salinity tolerance.

Hydroponic Culture Tanks in Greenhouse Evaluation in nutrient-saline-aerial environments is considered one of the best systems for controlling salt stress. The base of this system is a balanced supply

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of nutrients, proper ventilation, and control of saline solution concentration and pH of the medium. In this system, tanks are filled with saline solution under greenhouse conditions, and the tank is covered with polystyrene net and the net is covered with a layer of cheese cloth. Seeds are placed and covered with another layer of cheese cloth. It has been possible to implement the hydroponics system in the greenhouse at the University of California, which allows the evaluation of germination and growth of seedlings. The system includes a 450 tank size 1 × 4 m, and the tank can accommodate 300 experimental pieces 7 × 10 cm containing 40–35 wheat seeds/tank, which are placed on the cheesecloth and cover with another layer of it and raise the level of the solution to a degree sufficient to wet the cheesecloth while spraying the seed with a solution farming environment. The use of a fungicide is taken into account to protect the seed from seed rot diseases and the death of seedlings. The emerged seedlings are counted on the basis of the characteristics of root and shoot development in the solution (Kingsbury and Epstein 1984). It is taken into account when exposing plants to salinity in hydroponics, to avoid the occurrence of salt shock, which the process is carried out gradually at intervals of several days until reaching the final concentration without adding salt at the beginning of the dark period, as the plants are more sensitive to shock. When transferring plants from a saline system to a normal growing environment, shock by decreasing salt concentration gradient should also be avoided before plants are transferred to the growing environment. Screening 96 accessions rice genotypes was performed under hydroponics sterile plastic containers with Styrofoam sheets by Yadav et al. (2021). Styrofoam with 10 × 16 matrix of hole was utilized. The bottom of the hole was covered by stitching nylon net to avoid the seeds falling into the nutrient solution. Plastic trays were filled with 15 L of Yoshida’s modified nutrient solution (Yoshida 1997) and Styrofoam sheet was permitted to float on the solution. The experimental setup comprised plastic trays with a nutrient solution in completely randomized design by two replications. Significant phenotypic variation was observed among the genotypes for yield and its components traits. Eleven high salt tolerance genotypes at seedling stage were recognized. Plastic recipients and floating hydroponic system in a greenhouse were exploited for two experiments in a completely randomized design of factorial (Azevedo Neto et al. 2020). The conditions were correspondingly mean air temperature, relative air humidity, and photosynthetic active radiation (at noon) of 34 °C, 65%, and 1200 μmol m−2 s−1 . The first experiment including; 26 (entries) × 2 (salt levels— 0 and 100 mM NaCl) in factorial with four replicates, and the second included a 2 (genotypes) × 2 (salt levels—0 and 100 mM NaCl). To select of sunflower genotypes that different in salt tolerance, seeds of 26 sunflower genotypes were verified. Seeds of genotypes seeds were surface-sterilized with 2% sodium hypochlorite five minutes and washed three times by distilled water for three minutes each. Sterilized seeds were sown in 200-mL plastic recipients comprising washed sand and watered by half-strength Hoagland’s nutrient solution. Seven days after germination, seedlings were transferred in plastic containers with 12 L of Hoagland’s nutrient solution in a floating hydroponic system. The nutrient solutions were changed weekly and daily

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volume was supplemented with distilled water. The pH was monitored daily and adjusted at 6.0 and 6.5 by 1.0 M hydrochloric acid or 1.0 M sodium hydroxide. After eight days, treatments of salt were applied to the seedlings i.e., Control—nutrient solution without NaCl or salt stress and nutrient solution with 100 mM NaCl. NaCl was gradually added (25 mM day−1 ) to avoid osmotic shock. Plants were harvested ten days after the end of salt additions. They select sunflower genotypes tolerant to salt stress based on dry mass yield and physiological and biochemical indicators. Salinity tolerance of halogeton (Halogeton glomeratus), gardner’s saltbush (Atriplex gardneri), forage kochia (Bassia prostrata) potentially has been done compared to tall wheatgrass (Thinopyrum ponticum) and alfalfa (Medicago sativa). Plants were assessed under hydroponic tanks, at 0, 150, 200, 300, 400, 600, and 800 mmol/L NaCl. Results showed that alfalfa and tall wheatgrass shoot mass decreased by 32% of the control at 150 mmol/L. Forage kochia persisted at 600 mmol/ L, however mass was decreased under all levels of salinity. Halogeton and Gardner’s saltbush increased or kept shoot mass up to 400 mmol/L. A linear passive Na+ accumulation was observed with increasing salinity levels in Forage kochia. Thus, Gardner’s saltbush was saline tolerant as halogeton, but, forage kochia was less tolerant (Sagers et al. 2017).

9.2.6 Pots in Glasshouse Glasshouses (Fig. 9.3) are used to evaluate germplasm of crops for salinity tolerance. In this connection, Rajendran et al. (2009) determined wheat’s three main components of salinity tolerance. So, seeds of 12 cultivated einkorn wheat were germinated at room temperature for 4 d on moist filter paper in Petri dishes wrapped in polythene bags to keep high humidity. When the plumule was about 2 cm long, seedlings were transplanted into a supported hydroponics environment. Then, individual plant genotypes were placed into separate PVC tubes (280 mm long × 45 mm diameter) filled with cylindrical black polycarbonate pellets and placed into a 25 L bath over a reservoir tank. Modified Hoagland’s solution (Genc et al. 2007) has been pumped from the reservoir into the 25 L bath in a 20 min fill, 20 min drain cycle. Plant genotypes were grown in two separate trials under a glasshouse in the South Australian winter and spring, with max/min temperatures of 28 °C during the day and 15 °C during the night. A selection of lines were grown in both experiments to monitor the effects on plant growth. For salinity stress and destructive measurements of plant growth, ten replicates of each genotype were distributed randomly in salt and control trolleys. At the time of fourth leaf emergence, about 12 d after germination, NaCl was added to the hydroponics in 25 mm increases over 1.5 d to a final concentration of 75 mm. To maintain the levels of free Ca2+ constant with control conditions (Tester and Davenport 2003), an supplementary 1.71 mm CaCl2 was added. After 19 d of Na+ stress, they measured the fourth leaf blade and remaining shoot, total shoot fresh weight, total shoot dry weight, total leaf blade area. They develop assays for high throughput the three components of salinity tolerance i.e. quantification of

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Fig. 9.3 A typical glasshouses used for evaluating crop germplasm to salinity tolerance (Source Modified after, https://www.altercom.org/page/page-145/)

Na+ exclusion, Na+ tissue tolerance and osmotic tolerance in 12 wheat accessions, chiefly using commercially available image capture and analysis equipment. Results showed that different genotypes utilized different combinations of the three tolerance mechanisms in the direction of increase their total salinity tolerance. Also, positive association was recorded between a plant’s total salinity tolerance and the sum of its efficiency in Na+ exclusion, osmotic tolerance and tissue tolerance. Glasshouse experiments were conducted by Ouertani et al. (2021) on two diverse barley; salt-stress tolerant genotype, Barrage Malleg (tolerant) and Saouef (sensitive), in a completely randomized design with three replications. Ten seeds were seeded in 5 kg polyvinyl chloride (PVC) pots in each genotype and filled with pre-ovensterilized. Pots were irrigated for 15 days by distilled water (0 mM NaCl) until the emergence of the second barley leaf i.e. 10 days old. Then the pots were irrigated with Hoagland solution, 100 mL per day/pot. A week later when the third leaf has been fully expanded, 200 mM NaCl was added gradually by applied 50 mM NaCl dialy to avoid salt-stress shock damage. Whereas, control treatments were irrigated with standard growth solution. Results showed better behavior of Barrage Malleg over Saouef for leaf dry weight, root dry weight, root length and salt-tolerant under salinity stress. Hichem et al. (2009) studied two forage maize varieties (Aristo and Arper) germinated in Petri dishes comprising two sheets of Watman no. 1 filter paper moisturized with half strength Hoagland’s nutrient solution. After germination, once the cotyledons fully appeared, the seedlings were transferred into plastic pots (45, 66 and 23 cm) filled with peat/perlite mixture (2:1, v/v) and subjected to 0, 34, 68 and 102 mM NaCl

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for 6 weeks under glasshouse conditions. A significant difference in salt response was detected between both varieties. The better performance of Arper salt-challenged leaves compared to Aristo, could be associated with their higher water content and polyphenol content principally anthocyanins that exhibited to participate efficiently in controlling of oxidative damages caused by the H2 O2 generation. In a pot under a glasshouse in Perth, Western Australia, Turner et al. (2013) screening 55 genotypes of chickpea (Cicer arietinum L.) exposed to 0, 40 or 60 mM NaCl added to the soil to identify the differences in salt tolerance. Results revealed that when genotypes were grown in soil with 40 mM NaCl, a 27-fold range in seed yield was recorded between the 55 chickpea genotypes.

9.2.7 Pots in Lath House Lath house (Fig. 9.4) is used for evaluating crop germplasm to environmental stress tolerance. In this concern, Tadesse et al. (2016) evaluated 13 genotypes and two checks (one tolerant and one sensitive) of rice. Experiments were performed by sowing rice seeds in plastic pots of 22 cm top diameter, 15 cm bottom diameter, and 23 cm depth. Pots filled with 5 kg soil at a 3:1 ratio of soil and sand, correspondingly. Each pot contains 10 seeds and kept in the lath house under sunlight. Rice genotypes were subjected to 4 salinity levels (0, 4, 8 and 12 dS m–1 ) in factorial combination in a completely randomized design with three replications. Results showed that salinity levels affected traits in germination and vegetative growth. Interaction between genotype x salinity was highly significant on all traits. Rice genotypes IR 71991and IR 71901 appeared to be tolerant compared to the remaining genotypes.

Fig. 9.4 Lath house used for evaluating crop germplasm to environmental stress tolerance (Source Environment sector, Faculty of Agric, Zagazig Univ, Egypt)

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9.2.8 Pots in Net-House The change in response of quinoa genotypes to various salinity stress conditions i.e. in controlled (net-house) and in the different saline fields was deliberated by Long (2016).They carried out a pot experiment under a net-house at Vietnam National University of Agriculture, Hanoi, to assessment growth and yield of six quinoa genotypes at four NaCl levels (0, 10, 20 and 30 dS m−1 ). Likewise, in Nam Dinh and Hai Phong provinces, two coastal provinces most affected by seawater intrusion in the North of Vietnam. Results revealed that salinity stresses decreased growth and yield characters of quinoa genotypes and fluctuating due to diverse saline situations. Salinity stresses cause a reduction in plant height, number of leaves/main stem, number of branches/plant, head panicle length, number of branches/panicle, dry matter accumulation, 1000-seed weight and grain yield of quinoa genotypes. While, most of quinoa genotypes gave adequate yield even under high salt situations in the field.

9.2.9 Vinyl House Under a vinyl house of Banghabandhu, Sheikh Mujibur Rahman, three soybean genotypes i.e. Galarsum, BD 2331 and BARI Soybean-6 were tested by Khan et al. (2015) through January to March, 2012. Leaf water status, leaf temperature, xylem exudation and proline accumulation were measured under salt and water stress environment. Treatments comprised control, water shortage, 50 mM NaCl irrigation, 50 mM NaCl irrigation with water shortage, 75 mM NaCl irrigation, and 75 mM NaCl irrigation with water shortage environments. The relative water content, xylem exudation, leaf water potential of soybean plants were severely declined under 75 mM NaCl salt combined with water shortage situation. But, the changeability were lesser in Galarsum genotype which registered 74.28% relative water content, 7 mg hr-1 xylem exudation rate and −1.03 MPa leaf water potential.

9.3 Evaluation at Tissue Culture Level (In-Vitro) Understanding the various biochemical and physiological bases and cellular activity in plants at the microenvironment level is important in salinity tolerance studies. Tissue cultures are useful in achieving this purpose. The results obtained from tissue culture vary, depending on the genotype and conditions of the growing environment. For example, 100 of plants bred from callus alfalfa in NaCl environment were stunted and susceptible to disease, and riceregenerated plants did not flower (Yano et al. 1982). However, on the other hand, with the development of tissue culture techniques, it was possible to obtain stable

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variations of resistance to salinity in wheat, oats, rice, canola tobacco, and sugarcane (Nabors, 1983; Patade et al. 2008; Tang et al. 2021).

9.3.1 Growth and Seeding Survival Ability In this direction, the seeds germinate under normal (non-saline) conditions and then expose the seedlings to saline conditions at the required growth stage. The salting process is carried out in growth chambers or hydroponics in a step-wise manner at intervals of several days. It also follows a step-by-step gradient method when transferring plants from salinity experiments. The salinity level must not change at the beginning of the dark period due to the sensitivity of the seedlings at this time and to avoid salt shock. The composition of the saline solution used in the evaluation should be similar to the quality of the salts in the target soil. The most common salts in saline lands are sodium chloride, sodium sulfate, potassium chloride, magnesium chloride and calcium chloride. However, in most methods of selection, sodium chloride solution is used, which is usually added with calcium chloride solution in a ratio of 1: 2.

9.3.2 In-Vitro Selection The selection system for salinity resistance using plant tissue culture techniques is one of the easy and fast systems. Cells are cultured either separately or in callus form on a liquid or solid nutrient environment depending on the plant part used. The nutrient environment contains the basic elements and components that plant cells need for their continued division and growth, while providing the nutrient environment with graded levels of sodium chloride salt, which is the most common in salinity assessment experiments. The concentration of sodium chloride is determined in the nutrient environment at which the activity of the cultured cells stops, which is known as the lethal concentration, which is the concentration sufficient to kill more than 95% of the cells, as the resistant and viable cells are re-selected to produce plants and then more resistant regenerated plants. Where it was possible to isolate cell lines resistant to salinity in many field crops. Stepwise selection is one of the most effective methods for distinguishing, detecting and producing regenerative plants, which explains that step-by-step tissue acclimation by increasing NaCl concentrations is one of the best selection methods for salinity tolerance. It should be noted that there are some studies conducted in which sea water was used, as it is considered a representative of different salts. Many researches have been conducted to evaluate salinity tolerance and produce plants using tissue culture in different crops. It was also possible to identify gene loci on chromosomes that control resistance and their associations, which facilitated the process of genetic

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improvement of salinity tolerance. The most important results that were reached are the following. Cultivation of callus can give reliable tolerant genotypes in response to saline osmotic stress conditions. Trivedi et al. (1991) tested the response to salt stress at the callus level for six wheat cultivars varying in salinity tolerance: Sakha 8, Plainsman, salinity-resistant; Chinese Spring, modrate-resistant, and salt-sensitive Cappelle Desprez, Regina, Caribo. These cultivars were grown in an environment containing. The results indicated that at a concentration of 0.1 mol of sodium chloride, the resistant cultivars Sakha 8 and Plainsman maintained their growth rate, while the growth of callus of the moderate resistance cultivar Chinese Spring and the sensitive cultivars Regina, Caribo, Capplle Desprez was inhibited. Nitrogen and phosphorous levels were low in the callus of the saline-resistant cultivars Sakha 8 and Plainsman, while the content was high in the callus of the sensitive cultivars Regina, Caribo, Cappelle Desprez. Potassium content of the resistant cultivar Sakha 8 increased with the increase of salt stress, while it remained the same without decreasing in the rest of the other cultivars. This indicates that growth measurements, nitrogen, phosphorous and potassium content are considered as adaptation factors for saline stress conditions. Protoplast cultivation is used in the study of different environmental stresses, as the vitality of the protoplast depends on the vigor of the genotype. Moreover, Abdrabo and Reda (1994) study the response of protoplasts separated from young leaves of wheat cultivars Giza 155, Giza 157, Sakha 8 and Sakha 92 under different salinity levels (zero, 2000, 4000, 6000, 8000, 10,000 ppm of NaCl). The results indicated that Sakha 92 was superior to the rest of the cultivars in protoplast vitality with increased salinity concentration, as it was the most tolerant at high levels of salinity. While, Giza 155 was the least tolerant to salinity, especially at high concentrations. The difference in protoplast vitality among the four genotypes under saline stress conditions may be due to the variation in gene expression under salinity conditions. Furthermore, a rapid in vitro screening for salinity tolerance of bread wheat was studied by Diaz-de-Leon et al. (1995). They cultured 14 of embryos cultivars and examining them for salinity tolerance on MS media in addition to 30 gm of sucrose/ L with 50, 100 and 150 mmol of sodium chloride. The seedlings were evaluated after 8 days of treatment for characteristics of seedling height, root length and number of roots. The cultivars were divided according to their tolerance to salinity into the following sections: 1. Tolerant: the percentage of inhibition ranged between zero—35% compared to the control. 2. Moderately tolerant: The percentage of inhibition ranged from 36 and 68% compared to the control. 3. Sensitive: its inhibition rate ranged between 69 and 100% compared to the control.

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By measuring seedling height and root traits, they found that the two cultivars Kharchia and Shorawaki were more tolerant to salinity until the concentration of 150 mmol NaCl, but NaCl did not significantly affect the number of roots. Since alfalfa is one of the forage crops that is relatively tolerant to salinity and water deficiency, and that the enzyme activity of acid phosphatase and phytase is associated with salinity tolerance of varieties. Ehsanpour and Amini (2003) grown the callus of the two alfalfa cultivars Yazdi and Hamedani on MS media containing zero, 2, 4, 6, 8 and 10% Manitol, and add zero, 0.2, 0.4, 0.6, 0.8 and 1% sodium chloride. Results revealed that acid phosphatase activity increased with the increase in salt stress in the two cultivars. The enzyme activity increased significantly in Yazdi cultivar compared to the Hamedani cultivar. Callusing potential of sunflower cultivars versus osmotic potential and tissue ionic strength under salt stress has been performed by Madhulety and Jyotsna (2003). They use the technique of cultivating explants of roots, epicotyl and hypocotyl of seedlings of four 7-day-old cultivars under salinity levels (zero, 80, 160, 240 and 320 mM of NaCl solution) in assessing salinity tolerance by estimating the content of ions (Na+ / K+ , Cl− , K+ , Na+ ). The results showed that the cultivar PAC-35 had a high ability to produce the highest rate of rapid and early growth at the callus level, which is an indicator of the cultivar’s ability to tolerate salinity. Furthermore, to screen salinity tolerance at in vitro level, Abass et al. (2021) investigate the effects of NaCl stress on several physio-biochemical traits of Parkia biglobosa cell suspension culture. They used (0, 100, 200, 300, 400, 500, 600 and 700 mM NaCl concentration levels) through 18 days. Results showed that the maximum percent of viability and concentration of viable cells/ml was detected at 500 mM at 12th day with significant differences than the other treatments.

9.4 Evaluation Under Field Conditions (In-Vivo) The soil salinity level may vary under the conditions of the same field from a low level to a high level of 50 dS m−1 . This difference may be horizontal, which can be just observed by looking at the field, or it may be vertical within the land sector. It is difficult to know except by chemical analyses by taking samples at different depths of the soil surface. Environmental conditions such as temperature and humidity also affect the rate of evapotranspiration and the movement of ions, making evaluating the genotypes for salt tolerance difficult. Plant roots can avoid salty areas and get water and nutrients from less salty areas. The plant’s appearance and growth under these conditions is evidence of escape, not resistance, depending on the spread of the root system in the non-saline areas of the soil profile. Testing the breeding materials at different levels of soil salinity and irrigation water is one of the methods that seem appropriate for the evaluation process. It is useful to present a control treatment in yield trails. This allows the selection process to be practiced in the breeding materials during the segregating generations.

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It should be noted the necessity of conducting the screening process for genetic material under conditions of moderate evapotranspiration potential, with the select the appropriate site and time so that the breeding material is tested according to its real environment. Since the problem of salinity is due to the presence of one species or combination of salts such as sodium chloride, calcium chloride, magnesium chloride, potassium chloride and sodium sulfate, it is necessary to determine the kind of salts prevailing in the target environment and the appropriate salt solution concentration for the selection process. In general, breeding materials can be evaluated under field conditions through the following methods.

9.4.1 Nonsaline Filed with Saline Irrigation In this case, the breeding material is evaluated and screened in ordinary non-saline fields with well-drained clay-sand soils. Irrigation water with controlled salinity levels is used, for example, 3000, 6000, and 9000 ppm. It was taken into account frequent irrigations to remove the accumulated salts and stabilize the homogeneity of the soil before planting. This trend can be used to evaluate parents and select lines under several salinity levels or to evaluate segregating generations under a single salinity level. Where it was possible to practice the selection process in wheatgrass by irrigation with salinity water of 6000 and gradation up to 12,000 ppm, and it was possible to exclude about 50% of the sensitive populations and keep the more tolerant materials (Dewey 1962). Field screening of 127 groundnut (Arachis hypogaea L.) genotypes has been done for salinity tolerance by Singh et al. (2008). The experimental soil initially exhibited 1.6 dS m−1 EC, which increased to 4 dS m−1 by first irrigation with saline water (EC 11.7 dS m−1 ) after sowing. Therefore, the second irrigation was done after five days with water of EC 1.4 dS m−1 to ensure maximum germination. The subsequent irrigations were done at interval of 10–15 days by saline water of EC about 6– 7 dS m−1 . Salinity accumulation and pH were measured in the experimental plot at regular intervals during the growing season. The soil EC at various crop stages ranged between 4.0 and 8.0 dS m−1 . The salinity level ranged between 3 and 4 dS m−1 , during kharif season, the plant mortality varied from 0 to 88% (average 30%) and genotypes number produced seed, was optimal for screening. Results revealed a large variation among genotypes in pod yield and related characters with 0–13 pods plant and 0– 136 g m-2 seed yield and only 59 genotypes exhibited pod and seed bearing of which 20 genotypes recorded less than 10% mortality. They arranged groundnut genotypes for their plant stand and seed yield in descending order and mortality in ascending order. The genotypes were clustered under diverse degree of salinity tolerance. They identified 11 entries NRCG 2588, 4659, 5513, 6131, 6450, 6820, 6919, 7206, TMV 2 NLM, TG 33, JNDS-2004-15 as salinity tolerant as they attained high plant stand and more than 50 gm−2 seed yield. 10 genotypes JNDS-2004-1, JNDS-2004-3, JNDS2004-16, TG 28, TG 38C, TG 42, PBS 30031, PBS 30033, NRCG 6155, ICGV

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86031 which more than 35 gm−2 seed yield were recognized as moderately tolerant to be grown in regions with salinity up to 3 dS m−1 .

9.4.2 Saline Field with Saline Irrigation Salinity tolerance of crop lines and cultivars can be assessed by cultivation in sites of known salinity level. Field experiments could be designed in replicates, after collecting soil samples prior to planting at the experimental site at depths of 20 and 40 cm. The degree of electrical conductivity (EC) on the saturated soil paste extracts is determined and calculated as an average in mmose/cm at 25 °C for the sample. Experimental research work is being carried out with irrigation water with controlled and known concentrations of salinity. In this regard, Sallam and Afiah (1998) designed a field experiment with replicates and estimation the saturated soil paste extracts (9 dS m−1 ) and irrigation with water of low salinity (3260 ppm) and high salinity (7680 ppm) to evaluate ten wheat genotypes based on the indicators of salinity sensitivity index, yield, its components and some physiological properties such as chlorophyll content and some chemical components i.e. proline, free amino acids, soluble protein, DNA, RNA, sodium, potassium, calcium and magnesium content. The salinity sensitivity index arranged the genotypes according to their tolerance to salinity as follows: Line 1, Yacora Rojo, Line 3, Giza 160 and Mexipak 69, referring to the distinction of Line 3 and Yacora Rojo as the best genotypes for salinity tolerance. In continuous, Farag et al. (2020) tried two experiments to evaluate 19 durum wheat lines under saline soil conditions with ECe dS m−1 8.54 at depth 0–15 and 8.84 at depth 15-30 cm over two seasons at Ras Sudr, South Sinai, Egypt. The first experiment irrigated by salinity 6300 ppm and the second irrigated by salinity 3900 ppm, respectively. The principle component and cluster analyses indicated highly significant positive association between wheat grain yield under the two environments. Hereby, genotypes with high performance in non-stress condition give in comparatively great yield under salinity stress. Also, correlation was also found between grain yield/plant under non-stress and stress with stress tolerance index, mean productivity, geometric mean productivity and harmonic mean, however significantly negative relationship with abiotic tolerance index and stress sensitivity percentage index indices. Both genotypes, ACSADs 1566 and 1567 were designated as promising ones under salinity. In an arid Mediterranean climate, Mansour et al. (2021) implemented field experiments to evaluate 21 different barley genotypes to naturally occurring salinity for agronomic reactions. Three saline fields (7.72 dS m−1 ) were irrigated with well water of three increasing salinity levels viz. low (5.25 dS m−1 ), moderate (8.35 dS m−1 ) and high (11.12 dS m−1 ). Dendrogram of phenotypic distances based on yield index classified 21 genotypes into six groups; (A) is highly salt tolerant (genotype No. 14), (B) is salt-tolerant (genotypes No. 4 and No. 17), (C) is moderate salt tolerant (genotypes No. 1, No. 10 and No. 16), (D) is moderate salt-sensitive (genotypes No.

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Fig. 9.5 Dendrogram of phenotypic distances among 21 barley genotypes based on yield index. The genotypes were classified into six groups; A is highly salt-tolerant (1 genotype), B is salttolerant (2 genotypes), C is intermediate salt-tolerant (3 genotypes), D is intermediate salt-sensitive (8 genotypes), E is salt-sensitive (5 genotypes) and F is highly salt-sensitive (2 genotypes) (Mansour et al. 2021)

5, No. 7, No. 9, No. 11, No. 12, No. 15, No. 18 and No. 19), (E) is salt-sensitive (genotypes No. 2, No. 3, No. 8, No. 13, and No. 20) and (F) is highly salt-sensitive (genotypes No. 6 and No. 21) as given in Fig. 9.5. In this continuous, Moustafa (2006) estimated stability of ten varieties of Egyptian cotton under the prevailing soil salinity conditions in Ras-Sidr, South Sinai, Egypt which amounted to 7.5 dS m−1 (average of the two seasons) and irrigation with graded concentrations of salinity irrigation water 2000, 4000, 6000 and 8000 ppm by mixing well water + tap water in large tanks. When the required salinity concentration is reached, which is measured by an EC-meter, the irrigation process is performed. Thus the rest of the salinity levels of the irrigation water are adjusted. They registered variation between cotton varieties based on crop measurements, its components, salinity sensitivity index, and chemical components i.e. proline, potassium, sodium and magnesium. Furthermore, under saline soil, fifteen long-staple cotton belong to Gossypium barbadense L. were evaluated for salinity tolerance by Mahdy et al. (2021). They showed that salinity indices i.e. salinity tolerance index STI, mean productivity MP, Geometric Mean Productivity GMP, Harmonic Mean HM and salinity resistance index SI could differentiate between both tolerant and sensitive genotypes. Hereby, could be considered the best tolerant indices. The direct and indirect effects of seed cotton yield/plant components varied greatly under both environments.

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9.4.3 Evaluation in Screening Microplots Small experimental plots with different levels of controlled salinity or sodic are used to evaluate the average performance of cultivars and their response to salinity. This method allows maintaining certain levels of salinity that simulate the conditions of the field without varying the degree of soil variation. In sugar cane, small trial plots were used, ranging from a 1 line to 2–3 lines, or 2 × 2 square meters in size. Moreover, under saline microplots, an experiment with 26 parental lines of hybrids was conducted to identify salt tolerant recombinations. Salinity treatments (Control, 6 dS m−1 , 10 dS m−1 ) were applied from tillering to maturity. Results showed that salinity increased Na+ , decreased K+ and K+ /Na+ ratio in flag leaves. Number of panicles/plant and grain yield declined by the salinity of 6 and 10 dS m−1 . Rice genotypes IR60997-16-2-3-2-2R, IR29723, BR827-35, BCW-56, KMR-3, IR80155B and CSR23 were more tolerant to salinity compared to other genotypes (Islam et al. 2011).

9.5 Measurements and Scoring Systems of Salinity Tolerance The availability of genotypes with good yielding ability and viability with a combination of important traits associated with salinity tolerance is of great importance in selection programs. It is of great importance to study physiological, metabolism processes and enzymes controlling biosynthesis pathways, and to identify the genes responsible for them in their relationship and salt tolerance. Several studies have shown the importance of selection for a single measure of selection from a group of traits (Ashraf 1994). Whereas, focusing on simple, easy-tomeasure traits that encourage salinity tolerance during germination, seedling growth, flowering, or any stage at which the plant appears to be sensitive to salinity is more effective in isolating salinity-tolerant promising lines (Cruz et al. 1990). There are a number of points that must be taken into consideration in this regard, including: 1. Not all of the traits are related to salinity tolerance in all crop species. 2. The physiological mechanics differ in many cases from one variety to another within the same species. 3. Estimating these indicators requires a great effort, especially when estimating on a large number of genotypes under salinity and control conditions to assess the relative importance. 4. Also, a good indicator of stress should be standardized throughout the plant’s life cycle. Scientists have suggested that biomass production as a standard measure indicates stress, and therefore selection based on the plant performance indicates selection for salinity tolerance.

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There are many selection criteria used to estimate resistance to salinity, which can be listed as follows.

9.5.1 Cell Viability Immersing sections of plant tissues measure the ability of cells to survive for 24 h in a solution with a known concentration of saline. Then transferring the sections to a strong hypertonic glucose solution, where the percentage of cells that have plasmolysis gives an indication of the viability. This criterion is considered a good evidence of resistance to salinity compared to standards that depend on dry weight or yield, especially when different levels of salinity are tested.

9.5.2 Germination Seed germination test in saline media is used as an individual criterion for salinity resistance, especially in more sensitive species to salinity at germination stage than in the subsequent growth stages. The effect of salt stress is largely related to the stage of seed imbibition. Notably, there are no indications of the correlation between resistance at the germination stage and resistance at the late stages of growth. Therefore, this measure may not be significant in species whose later stages of growth are more sensitive to salt stress than the germination stage.

9.5.3 Dry Matter Accumulation Seedlings dry weight/plants is a good indicator of resistance to salinity, as it expresses the integration of the different effects of the response to salinity, but the following points are taken into account: 1. The estimation of dry matter leads to the loss of the plant before seed production, and therefore it cannot be applied in the segregating generations. 2. Genetic differences in growth has the ability to affect the reliability of the scale. 3. Using the criterion under specific stress conditions and non-stress for all genotypes under evaluation is preferable, which doubles the effort and expense.

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9.5.4 Leaf Ion Content Since the resistance to salinity depends on the exclusion of salt, the leaf content of ion element provides an indication of the resistance to salinity. However, this estimate is usually undesirable for many plant breeders.

9.5.5 Leaf Necrosis Usually the accumulation of certain ions such as chloride Cl− , sodium Na+ or potassium K+ cause color changes and leaf necrosis. This scale is used as a criterion for resistance to salinity based on ion exclusion.

9.5.6 Root Growth Good root growth expresses the relative resistance of the genotype to mineral toxicity and salinity damage. Currently, many methods are available to measure root system indicators, which help plant breeders in linking the of root indicators with salt tolerance.

9.5.7 Osmoregulation Osmoregulation is measured in the form of the accumulation of organic solutes, such as proline, glycine betaine, and carbohydrates in response to salt stress. Osmoregulation is determined by the ability of cells to maintain a turgor pressure under stress conditions. This criterion is estimated in the form of leaf wilting, dryness and premature maturity. This criterion is preferable, especially when osmotic pressure is important in resisting salinity.

9.5.8 Yield Economic yield is an important criterion for selection and indication of resistance to salinity. The individual plant yield is estimated during the segregating generations. While, the estimation of the yield per unit area is more acceptable in the case of the selected genotypes under different salinity levels.

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359

Visual Evaluation of Salt Stress Symptoms Leaf Color or Death (Senescence) Salt stress induces leaf death and senescence. This can be estimated simply visually on a scale of 1–9, where: 1: indicates that the variety is highly tolerant. 9: Indicates that the variety is highly sensitive. On the basis of either of the two directions, the first is the area of total dead leaves, and the second: the number of dead leaves.

IRRI-Modified Standard Evaluation Score and measurements of morpho-physiological traits based on visual symptoms of salt toxicity on rice seedlings was done according to (Gregorio et al. 1997) using a scale of 1–9 based (SES, Table 9.1) to rating the visual symptoms of salt toxicity. This scoring distinguishes the sensitive from the tolerant and the moderately tolerant genotypes. Scoring could start 10 days after salinization and final scoring 16 days after salinization. At 10 d after salinization, Pokkali scores: 1; IR74: 5; and IR29: 7. During this time, sensitive genotypes could be distinguished from the test entries. Conversely, tolerant genotypes could not be readily recognized from the moderate ones. At 16 d after salinization Pokkali scores: 3; IR74: 7; and IR29; 9 (Gregorio et al. 1997). Table 9.1 IRRI-modified standard valuation score (SES) of visual salt injury on rice at seedling stage (Gregorio et al. 1997) Score

Observation

Tolerance

1

Normal growth, no leaf symptoms

Highly tolerant

3

Nearly normal growth, but leaf tips or few leaves whitish and rolled

Tolerant

5

Growth severely retarded, most leaves rolled, only a few are elongating

Moderately tolerant

7

Complete cessation of growth, most leaves dry: some plants dying

Sensitive

9

Almost all plants dead or dying

Highly sensitive

Notes 1. Using the criterion under specific stress conditions and non-stress for all genotypes under evaluation is preferable 2. This measurement must be taken before the leaves begin to enter the natural senescence 3. This indicator is considered more effective in isolating resistant plants from plant populations

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Salinity Scale Classes The salinity scale classes was estimated simply visually on a scale of 1–5 in the experiments by Dasgan et al. (2002) to classify tomato genotypes for the severity of salt sensitivity as follows (Table 9.2).

Leaf Scorch Score Determination Leaf scorch ratings were carried out when plants of the sensitive check soybean cultivar ‘Hutcheson’ (Buss et al. 1988) showed severe salt injury or generally reached a leaf scorch of 4 according to Pantalone et al. (1997). Leaf scorch was scored from 1 to 5 follows (Table 9.3) as follows: The average leaf scorch score for each genotype was calculated by following formula: ∑ (LSSi)(No. of plants) Average leaf scorch score = Total no. of plants per replication where LSSi the level of leaf scorch score. Table 9.2 Salinity scale classes Score

Observation

Tolerance

1

Normal green plants with or without slight inward curly leaves

Highly tolerant

2

Green plants with complete inward curly leaves

Tolerant

3

Addition to complete curly leaves, dry leaves from moderate to severe damages

Moderately tolerant

4

Most leaves (50/ 80%) with drying damages

Sensitive

5

All leaves of the plant with drying damages

Highly sensitive

Table 9.3 Leaf scorch score Score

Observation

Tolerance

1

No apparent chlorosis

Highly tolerant

2

Slight (25% of the leaves showed chlorosis)

Tolerant

3

Moderate (50% of the leaves showed chlorosis and some necrosis)

Moderately tolerant

4

Severe chlorosis (75% of the leaves showed chlorosis and severe necrosis)

Sensitive

5

Dead (leaves showed severe necrosis and were withered)

Highly sensitive

9.5 Measurements and Scoring Systems of Salinity Tolerance

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Days to initial symptoms of leaf scorch was registered from initial salt treatment until an average leaf scorch reached a rating of 3 on plants of the sensitive check soybean cultivar Hutcheson.

9.5.9 Tolerance Indices Tolerance indices were used to determine the tolerance of crop genotypes and listed in Table 9.4. Table 9.4 Salinity tolerance indices, formula and reference No

Index name

Formula

References

The high values of these indices indicated to salinity stress tolerance 1

Mean productivity (MP)

(Yn + Ys)/2

Rosielle and Hamblin (1981)

2

Harmonic mean (HM)

{2*(Yn*Ys)}/(Yn + Ys)

Jafari et al. (2009)

3

Geometric mean productivity (GMP)

(Yn*Ys)1/2

Fernández (1992)

4

Stress tolerance index (STI)

(Yn × Ys)/(Ýn)2

Fernández (1992)

5

Yield index (YI)

Ys/Ý s

Gavuzzi et al. (1997)

6

Yield stability index (YSI)

Ys/Yp

Bouslama and Schapaugh (1984)

7

Sensitivity salinity index (SDI)

(Yni − Ysi)/Yni

Farshadfar and Javadinia (2011)

8

Abiotic tolerance index (ATI)

9

Relative efficiency index (REI)

√ (Yni − Ysi)/(Yn/(Ys) * ( Yni Moosavi et al. (2008) * Ysi) Ys/Y¯s × Yn/ Ýn

Fischer and Wood (1979)

The low values of these indices indicated to salinity stress tolerance Yn − Ys

10

Tolerance index (TOL)

Rosielle and Hamblin (1981)

11

Stress sensitivity percentage Tol*100/(2*Ý n) index (SSPI)

Moosavi et al. (2008)

12

Stress sensitivity Index (SSI) [1−(Ys/Yn)]/[1−(Ýs/Ýn)]

Fischer and Maurer (1978)

– Yn and Ys indicate to average grain yield of each genotype under normal and stress conditions – Ýn and Ýs indicate to average grain yield overall genotypes under normal and stress conditions

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Applied Experimental Studies Farag et al. (2020) computed several salt tolerance indices in newly durum wheat lines under salinity stress in many applied studies. The six lines ACSAD 1453, ACSAD 1487, ACSAD 1553, ACSAD 1566, ACSAD 1567 and ACSAD 1575 displayed the highest estimates and similar ranks for mean productivity, harmonic mean, geometric mean productivity, stress tolerance index, Yield Index and abiotic tolerance index as well as for tolerance index, excluding the line ACSAD 1553. Thus, these parameters could be considered as the best in selection breeding programs. Consequently, previous lines were deliberated the most tolerant and high-yielding under salinity stress and non- stress environments. Temporarily both lines ACSAD 1483 and ACSAD 1573 exhibited the highest estimates for Yield Stability Index (YSI) and lowest estimates of Sensitivity drought or salinity index (SDI), tolerance index (TOL), Stress Sensitivity Percentage Index (SSPI) and Stress Sensitivity Index (SSI) as well as grain yield under stress and non-stress circumstance. Based on the salt sensitivity index, barley genotypes G1, G2, G4, G6, G9, and G16 belong to Hordeum disticum were superior in their tolerance to salinity compared to barley genotypes G3, G5, G7, G8, G10, G11, G14, and G15 belong to Hordeum vulgare. Lines G2, G4, G5, G7, and G8 are more salt tolerant compared to Lines G1, G3, G9, G10 (Afiah et al. 2001). Genotypic differences in salinity tolerance among 30 genotypes and 14 cultivars of sorghum were assessed by Shakeri and Emam (2017). They used a new indicator, Storage Factor Index (SFI), to measure the Na+ partitioning between shoot and root. Stress tolerance index was found useful as a selection measure. Moreover, the tolerant genotypes had higher K+ /Na+ ratio in shoot and root with greater SFI, demonstrating that most of Na+ was stored in their roots. The activity of peroxidase and superoxide dismutase were higher under salinity conditions in the sensitive and tolerant genotypes, Catalase activity was found to be promoted in tolerant genotypes. Proline accumulation did not appear to be related to salinity tolerance in sorghum. Hence, salinity tolerance in sorghum genotypes was associated with Na+ exclusion from the shoot and with the enrichment of Catalase activity. Five faba bean entries with great YSI is predicted to have high yield under sever stressed and low yield under low-stress conditions. Afiah et al. (2016) found a variation response in the eleven tolerance parameters it orders first under the severe stress level. Thus, the lowest estimates of SSI and TOL parameters and the highest estimates of STI and YSI for entries NBL-5. Also, NBL-Mar.3 as a best tolerant under salinity conditions. However, Nubariya-1 and Misr-1 were the most sensitive one. Ravelombola et al. (2022) evaluated salt tolerance of 234 Multi-Parent advanced generation inter-cross (MAGIC) lines of cowpea with their 8 parents. They observed a large variation in traits related to salt stress tolerance i.e. number of dead plants, salt injury score, leaf chlorophyll content under salt stress, relative tolerance index of leaf chlorophyll content, fresh leaf biomass under salt stress, relative tolerance index of fresh leaf biomass, relative tolerance index of fresh stem biomass, relative tolerance index of the total above-ground fresh biomass, and relative tolerance index of plant height, correspondingly, with overlapping SNP markers between traits.

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363

Application of leaf scorch score, Lee et al. (2008) exposed 14 soybeans genotypes (Hutcheson was the salt-sensitive check and S-100 and Forrest were the salt-tolerant checks) to 0 and 100 mM salt (NaCl) rates under plastic cone-tainers method. Leaf scorch ratings show that the checks S-100 and Forrest are classified as salt tolerant and Hutcheson is salt sensitive. The 11 other genotypes were determined to be sensitive or tolerant based on the leaf scorch score in comparison with the tolerant and sensitive checks. Only 3 of 11 genotypes, S01-9370, Hartwig, and PI506820, were salt tolerant. Aghajari et al. (2018) assessed yield of sunflower genotypes under normal and salinity conditions and salinity indicators i.e. geometric mean productivity GMP, mean productivity MP and harmonic mean HM. Results showed that entries C86, C61, C142, C134a, C62, C70a, LR1, C153, C108, C6, C106, C98b and C148 are categorized as salt tolerant ones. High relationship between sunflower yield under normal and salinity conditions with mean productivity, geometric mean productivity and harmonic mean. Consequently, these indices are considered as the most applicable measures to recognize sunflower entries tolerant to salinity stress. Sandhu et al. (2017) selected twelve alfalfa genotypes under salinity. They found that the genotypes’ Salt tolerance (ST) index fluctuated from 0.39 to 1. The supreme salt-tolerant genotypes SISA14-1 (G03) and AZ-90ST (G10), the top behavior in biomass, exhibited the smallest influence on shoot number and height. Genotype SISA14-1 (G03) accumulated little Na and Cl under salinity.

Carbon Isotope Discrimination in Salinity Tolerance Studies Carbon isotope discrimination (CID) technique is used as a convenient, rapid and inexpensive physiological indicator in screening crop genotypes programs to tolerate environmental stresses. Distinguishing relationships between foliar carbon isotopes, element content in soil, roots and leaves of crops can be used as an indicator of environmental stress tolerance (Tsialtas and Maslaris 2006). The CID could be utilized as physiological marker to select tolerant crop genotypes under stress conditions (Bachiri et al. 2018). Several studies have shown the possibility of using the discriminating carbon isotope (Δ) as a valid measure to indicate the gas exchange response in the photosynthesis process to environmental variables such as salinity, drought, heat, light and others. Low values of (Δ) under salinity stress were recorded in barley (Bagues et al. 2018; Isla et al. 1998), cotton, beans (Brugnoli and Lauteri 1991; Saranga et al. 1999) and wheat (Kafi 2009; Kafi et al. 2007; Rivelli et al. 2002; Zoubeir et al. 2022). Carbon isotope discrimination studies were carried out in green house to select appropriate salt tolerant wheat genotypes based of growth performance and carbon isotopes discrimination technique. Nine developed double haploids (DH) wheat genotypes were verified with salt tolerant (LU-26s) and high yielding (Sarsabz) checks. Irrigation was applied by non-saline (control) and saline (12 dS m−1 ) water and raised up to maturity. Results of carbon isotopes discrimination (CID) indicated a reducing trend under salinity. Mean CID estimates were 20.86 and 17.49‰ under non saline and saline environments, respectively, showing an overall 19% decrease

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9 Techniques and Measurements of Assessing Genotypes for Salinity …

under salinity. The wheat genotypes taking greater grain yield also had high CID. The relationship between wheat grain yield and carbon isotopes discrimination (Δ) was positive. Wheat genotypes V10-DH and V13-DH with lower reduction in CID i.e. 1.2 and 11.0%, respectively, also exhibited high grain yield under salinity (Shirazi et al. 2015). Carbon isotope discrimination CID technique is considered a good criterion for screening salt-tolerant germplasm in barley. Barley grown in soil with high salt concentration have displayed a reduction in carbon isotope discrimination Δ (Isla et al. 1998). Soil salinity produced significant differences in carbon isotope discrimination Δ in barley genotypes, showing that salt stress can lead to less discrimination against the heavier carbon isotope. Mustafa et al. (2019) estimated CID to verify salt tolerance of 35 barley (Hordeum vulgare L.) entries at four salinity levels i.e. 0, 100, 200, and 300 mM NaCl in Hoagland nutrient solution during germination and vegetative growth stages. The CID was decreased linearly with increasing salinity in root zone. But, salt-tolerant genotypes sustained their turgor by osmotic regulation and by lowest increase in diffusive resistance and revealed minimum reduction in CID (Δ) with gradual increasing salinity in root zone. Most of the barley genotypes produced high dry matter and grain yield exhibited high Δ values. In general, a higher ratio (Ci/Ca) of intercellular (Ci) to atmospheric (Ca) of CO2 leads to higher carbon isotope discrimination Δ, mainly because of smaller stomatal conductance (Taiz et al. 2015). In rice genotypes, carbon isotope discrimination technique has benefited in screening salinity tolerance rice in seedling stage under the conditions of nutrient solution cultures. The salt-tolerant Pokkali rice cultivar was distinguished by higher (Δ1 ) values (3.2%) than the salinity-sensitive strain IR 29. This was attributed to the accumulation of salts in the cell vacuoles and cytoplasm of chloroplasts, which led to a significant decrease in the photosynthesis process in the sensitive strain. The tolerant variety produced an amount of dry matter was twice that of the sensitive one, and the medium tolerant isogenic lines produced average values of (Δ1 ) and dry matter production. Where, Shaheen and Hood-Nowotny (2005) recorded a negative and highly significant correlation (r = 0.95) between the values of (Δ1 ) and the salinity tolerance scale. Distinguishing relationships between foliar carbon isotopes, element content in soil, roots and leaves of crops can be used as an indicator of environmental stress tolerance (Bagues et al. 2018). Dadkhah (2013) evaluate four sugar beet cultivars comprising Madison (British origin) and three Iranian ones i.e. 7233-P12, 7233-P21 and 7233-P129 for salt tolerance using carbon isotope discrimination (Δ). Cultivars were grown in sand culture medium under greenhouse conditions. Sugar beet cultivars were irrigated with saline water (tap water as control, 50, 150, 250 and 350 mM of NaCl and CaCl2 in 5: 1 molar ratio) from 4-leaf stage for 16 weeks. Results showed significant decrease in CID with increasing salinity. Differences of Δ between shoot and root were significant in all cultivars and at different levels of salinity. Madison cultivar exhibited lower Δ in shoot and root compared to the remaining three cultivars at different levels of salinity except the control. However, cultivar 7233-P29 exhibited significantly higher Δ estimates at saline environment

9.7 Recommendations

365

of 150 mM and above. The regression of Δ and Ci/Ca was positive. Relatively higher 13C (lower Δ) was detected in root as compared with shoots.

9.6 Conclusion Determination of salt tolerance among breeding germplasm is required to develop recent crop cultivars with improved performance under saline conditions. Different techniques have been conducted under the laboratory and greenhouse to screen germplasm for salt resistance. Breeding materials can also be evaluated under field conditions through using nonsaline filed with saline irrigation or saline field with saline irrigation. Moreover, there is a lot of tolerance indices for measuring salinity tolerance in screening programs, for example Yield stability index (YSI), Yield index (YI), Salinity sensitivity index (SSI), Salinity tolerance index (STI), Tolerance index (TOL), Mean productivity index (MPI), Relative efficiency index (REI), Stress tolerance index (STI), Leaf scorch score (LSC), Carbon Isotope Discrimination (CID) and other indices can be used to differentiate between the tolerant varieties and the sensitive ones.

9.7 Recommendations Based on previous literature studies, the following points can be recommended: 1. A distinction must be made between genetic and environmental differences and the use of the evaluation method and appropriate statistical design in the evaluation process. 2. The composition of the saline solution used in the evaluation should be similar to the quality of the salts in the target soil. 3. Success in the salinization process in tissue culture requires a step-by-step gradient when transferring plants from one environment to another in salinity experiments. 4. Not all traits are correlated with salinity tolerance in all crop species. Hence, it must be based on correlation, regression, factor and principal components analysis. 5. The physiological mechanics differ in many cases from one variety to another within the same species. 6. A good indicator of stress should be standardized throughout the life cycle of the plant. Scientists have suggested that biomass production as a standard measure is indicative to selection of salinity tolerant genotypes.

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7. It should be noted the necessity of conducting the screening process for genetic material under conditions of moderate evapotranspiration potential, with the select the appropriate site and season so that the breeding material is tested according to its real environment.

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Part VI

General Conclusions and Recommendations

Chapter 10

Update, General Conclusions and Recommendations of “Salinity Resilience and Sustainable Crop Production Under Climate Change”

10.1 Introduction The Paris Climate Agreement (COP21) is one of the efforts to alleviate climate change in which an agreement has been signed to bring global temperature increase well below 2 °C (3.6 °F) and to pursue efforts to limit to 1.5 °C. However this needs accurate implementation. The economic development of countries depends on the agriculture sector. The agricultural sector is considered one of the most sensitive sectors to climate change and the effects of salinity, especially in developing countries. Agriculture is the main sector that contributes to hunger and poverty reduction, especially with the low percentage of people living on less than $1.25 a day. Therefore, it is required to build a resilient system according to the changing climate to eliminate hunger and poverty and reduce the effects of extreme weather events and the effects of salinity to ensure the sustainability of yields and achieve food security (Ahmed and Stockle 2017). Salinity stress affects physiological and biochemical characteristics and plant growth of sensitive crop varieties causes oxidative stress through increased production of reactive oxygen species (Nigam et al. 2022). All continents on the globe are facing the problem of soil salinity (Fig. 10.1). The Food and Agriculture Organization (FAO), the United Nations Educational, Scientific and Cultural Organization-United Nations Environment Program (UNESCOUNEP), and the International Soil Science Society (ISSS) are the leading global agencies that have paid attention to collecting data on soil quality worldwide. The world soil map documented that the salt-affected land area is 953 million hectares (Mha). Hence, the soils of more than 100 countries with an area estimated at about one billion hectares suffer from salinity. Salinity stress is the main abiotic factor affecting physiological and biochemical properties and plant growth of sensitive crop varieties, causes phytotoxic and eventually decreasing plant growth and crop production. These salinity effects hinder the crop plant’s biological processes, for instance, respiration, photosynthesis, stomatal © The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 H. A. Awaad, Salinity Resilience and Sustainable Crop Production Under Climate Change, Earth and Environmental Sciences Library, https://doi.org/10.1007/978-3-031-48542-8_10

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Fig. 10.1 Global distribution of saline and sodic soil. Source FAO and ITPS (2015)

functioning, transpiration, hormone regulation and functioning, seed germination, and water relation in plants, and reduced significantly yield (Jamil et al. 2011; Nigam et al. 2022; Wang and Huang 2019). However, the physiology, and biochemistry of tolerant crop varieties subjected to salinity exhibit numerous reactions that depend on the genetic makeup and growth stages. Crop varieties undergoes numerous physiological modifications and adapted mechanisms to manage with salinity stress (Chourasia et al. 2022; Fang et al. 2021; Kaya et al. 2020; Shah et al. 2021). Several crop genotypes adaptation strategies can be employed in conventional breeding and crop improvement activities, i.e., avoidance, tolerance and resistance. Gene-transformation technique enables scientists to achieve gene transfer in an accurate and useful manner for manipulating the biosynthesis pathways of osmotic-protective substances to reduce lipid peroxidation, and maintain protein structure and function (Ashraf 2009). Recent studies demonstrate the possibility of engineering metabolic genes to release salinity stress-tolerant crop genotypes (Li et al. 2018; Ravelombola et al. 2022). Numerous mitigating strategies such as leaching irrigations (Gupta and Abrol 2016), choosing proper agricultural practices (Hassan et al. 2021; Hoque et al. 2022; Saade et al. 2020), cultivation tolerant variety (Batarseh 2017; Iqbal et al. 2015) and exploiting the best nutrient procedures (Bouras et al. 2021; Djajadi et al. 2020; Liu et al. 2019) are very important to mitigate the effects of salinity. Environmentally friendly additives like organic amendments are also among the recent research areas to mitigate salinity stress in crop plants without the effect of pollution on the living environment (Dey et al. 2021; Hoque et al. 2022; Imran et al. 2022). The results of several studies showed that the negative effects of salinity on legumes such as soybeans, mung beans and peanuts can be mitigated by applying

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salt-tolerant rhizobial strains (Bashan et al. 2004; Dobbelaere et al. 2001; Kumar et al. 2019; Meena et al. 2017; Yasin et al. 2018). Furthermore, several studies have also shown the importance of various types of naturally occurring metabolites in osmotic regulation and detoxification of reactive oxygen species such as amino acids, antioxidant enzymes, hormones, Melatonin, plant extracts, proline and trehalose, Selenium, Salicylic acid and Plant Growth– Promoting bacteria (Arif et al. 2020; Avalbaev et al. 2016; Bajwa et al. 2018; Ke et al. 2018). For that reason, an in-depth study of salinity and its impact on sustainable crop production under climate change, protective mechanisms and relevant traits associated with salinity resilience are extremely important. The next theme will present a transitory between the important results of the recently published research on the relationship of diversity and genetic analysis to breeding and biotechnology approaches in resilience to salinity stress on wheat, barley, rice, maize, sorghum, faba bean, chickpea, lupine, peanut, soybean, sunflower, sesame, cotton, canola, sugar cane, sugar beet, alfalfa, quinoa and Atriplex. Also, management options, mitigation and genotype assessment techniques. Finally, the main conclusions and recommendations of the book chapters are for researchers and decision-makers.

10.2 Update Thus, global agricultural production’s sustainability is threatened by abiotic stresses (Yadav et al. 2020). Abiotic stresses are one of the major factors affecting crop growth and productivity of crops worldwide. Crop genotypes are continuously confronting the severe environmental conditions, for instance soil salinity, alkalinity/sodicity, drought, cold, heat, flooding and heavy metal contamination (Awaad et al. 2023; Joshi et al. 2021, 2022; Ling et al. 2015). Salinity reduces the productive capability of crops by up to 40%, which is estimated at about $27 billion annually (Kaur et al. 2021; Munns and Gilliham 2015). Salinity tolerance can be defined by maintaining plant growth in an environment containing NaCl or a mixture of salts. Crop genotypes differed significantly in their tolerance to salinity stress and showed different levels of resilience (Mansour et al. 2021; Soni et al. 2022; Souana et al. 2020; Zahra et al. 2020). Primary metabolites originate through the primary metabolic processes of growth. Examples of these metabolites are carbohydrates, amino acids, proteins, lipids, Nucleic acid DNA and RNA, Abscisic acid, alcohols, lactic acids and vitamins (Ahanger et al. 2018; Hussain et al. 2021; Laus et al. 2022; Mansour et al. 2020; McLay et al. 2022). Furthermore, there are more than 100,000 secondary metabolites in crop plants that participate in defense reactions to salinity i.e. alkaloids, phenolics, sterols, steroids, essential oils and lignin’s (Benjamin, et al. 2019; Hasanuzzaman et al. 2020; Wink 2015; Zagorchev et al. 2013). Among the unique observations found, the tonoplast proteins NHX1 and NHX2 were discovered to function in K+

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and pH homeostasis, other than in salt tolerance (Barragan et al. 2012; van Zelm et al. 2020). It is interesting to mention that halophytes can be used in Phytoremediation measures to adjust salinity levels of surrounding soils (Brito et al. 2021), aiming to permit glycophytes to survive in formerly uninhabitable areas through an environmentally safe and cost-effective process (Mann et al. 2020). Molecular markers and genetic engineering offer opportunities to improve salt tolerance in crops by activating different signaling pathways involved in stress perception, signal transduction, osmotic regulation and production of antioxidant enzymes (Ishaku et al. 2020). Research results indicate the potential for improvement in salt tolerance of the major crops through breeding programs and biotechnology, in addition to improving the plant environment through appropriate agricultural practices (Hassan et al. 2021; Hoque et al. 2022; Saade et al. 2020) Hence, in this book, the salinity-crop yield relationship and the impact of climate change will be focused on a lot of crop plants under salinity stress.

10.3 General Conclusions 10.3.1 Introduction The book chapters cope with areas of research and results that represent various challenges facing the production of numerous important crops, including wheat, barley, rice, maize, sorghum, faba bean, chickpea, lupine, peanut, soybean, sunflower, sesame, cotton, canola, sugar cane, sugar beet, alfalfa, quinoa and Atriplex. The book focuses how to cope with salinity stress through the protective mechanisms, selection criteria, and nature of inheritance of salinity tolerance using breeding efforts, biotechnology beside agricultural practices to mitigate the impact of climate change on agricultural crops in Egypt and the world. The main themes comprised in the current book are (a) the Impact of Salinity on Sustainable Crop Production, (b) the relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress (c) Management options, mitigation and genotype assessment techniques. The general conclusions from each theme will be presented in the next subsections.

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10.3.2 Impact of Salinity on Sustainable Crop Production Strategies Since soil salinity is major abiotic restriction disturbing crop productivity. Where, salinity threatens the sustainability of global agricultural production. General, globally approximately 20–50% of irrigated land is affected by salt stress. Salinity stress affects many aspects of plant physiology, making it difficult to fully study them. Instead, studying plant traits that are hypothesized to be involved in plant tolerance to salinity is very useful. At this respect, we discuss how to quantify the impact of salinity on growth, development, morpho-physiological, biochemical, yield and quality traits of crop plants. Research reports have confirmed a decrease in growth as a result of the effect of salinity on the metabolic pathways of the plant cell. Therefore, developing organized programs to release new varieties of field crops that are characterized by tolerance to salinity with high-yielding ability while implementing appropriate agricultural operations is considered very important in this regard.

10.3.3 Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? Understanding the mechanisms and future perspectives of adaptation of crop species to salinity-induced changes in the plant environment is of great importance in developing strategies to mitigate its effects on crop production. Understanding salt tolerance mechanisms is crucial to maintaining the productive potential of crop varieties. These mechanisms include ion homeostasis and partitioning, ion transport and absorption, biosynthesis of osmoprotectants and compatible solutes. The morphological, anatomical, physiological and biochemical traits are involved in resistance, avoidance or tolerance to salinity in crop plants. Primary metabolites originate through the primary metabolic process of growth, photosynthesis and respiration of the cell. These metabolites include carbohydrates, amino acids, proteins, lipids, Nucleic acid DNA and RNA, Abscisic acid, alcohols, lactic acids and vitamins (Ahanger et al. 2018; Laus et al. 2022; Soni et al. 2020). Furthermore, secondary metabolites for instance alkaloids, phenols, sterols, steroids, essential oils and lignin are involved in salt stress tolerance, where crop plants containing more than 100,000 secondary metabolites (Hasanuzzaman et al. 2020; Stojšin et al. 2022; Wink 2015; Zagorchev et al. 2013). We have therefore compiled evidence on the responses of different traits of crop genotypes to salt stress.

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10.3.4 Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress One foremost approach to produce salt-tolerant crop cultivars through breeding is to maximize the genetic diversity between parental genotypes. This diversity is usually assessed by measurements of morpo-physiological and biochemical indicators. Furthermore, it is surprising that salt tolerance among genotypes can be changed by environmental factors for example temperature, light or humidity beside salinity. Identifying genetic variations of different salt-tolerance genotypes based on genetic makeup proposes numerous advantages in producing salt-tolerant cultivars. Improving crop varieties to salinity tolerance requires wide range of genetic variances in salinity tolerance. Previous reports support the presence of substantial differences in salinity tolerance within crop genotypes. These reports have yielded the following conclusions: (1) Rapid climate change associated with abiotic stresses, especially salinity stress, poses a main task to current-day agriculture, (2) Cropresilience genotypes produce significantly greater yields compared to sensitive, especially under climate change, (3) Great variation has been revealed in crop plants for different morpho-physiological, biochemical and yield traits and (4) The genetic diversity represents a genetic basis for salt tolerance in breeding programs to develop more tolerant promising genotypes to stress. So, understanding the genetic system of salt tolerance helps to determine the appropriate breeding program. Through traditional breeding methods i.e. selection, hybridization, and recent techniques, enable crop breeders to release a lot of varieties tolerant to salt stress in cereal, legume, oil, sugar and forage crops. Furthermore, genome editing, molecular genetics viz. gene markers and gene transfer besides tissue culture, all of them represent novel tools in dealing with the problem of salinity.

10.3.5 Management Options, Mitigation, and Genotype Assessment Techniques More than 1500 plant species can be grown in salty areas. These crops include barley, rice, sugar beet, cotton, canola, safflower, jojoba, and several pasture grasses. However, improving the growth environment in saline lands seems important to the possibility of expanding the cultivation of salt-affected lands. So, saline lands can be reclaimed by general agricultural management’s viz laser leveling, leaching salts from the soil with good water quality, drainage system, choosing salinitytolerant crop species and varieties besides applying appropriate agricultural practices for instance gypsum, balanced fertilization, biofertilization, and using modern technology such as magnetized water. Finally, screening salt tolerance among breeding germplasm is required to develop recent crop cultivars with improved performance under saline conditions. Different

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techniques have been conducted in the laboratory, greenhouse and under field conditions to screen germplasm for salt resistance. Also, a several indices can be derived from yield measurements i.e., Yield stability index (YSI), Yield index (YI), Salinity sensitivity index (SSI), Salinity tolerance index (STI), Tolerance index (TOL), Mean productivity index (MPI), Relative efficiency index (REI), Leaf scorch score (LSC), Carbon isotope discrimination (CID) and other indices. Previous indices can be exploited to differentiate between the tolerant and the sensitive genotypes in crop breeding programs.

10.4 General Recommendations 10.4.1 Introduction Salinity is considered one of the most important abiotic stresses that limit the growth and productivity of crop plants in many regions around the world, especially with the increased use of poor-quality water for irrigation and the high level of soil salinity in light of climate change. Soil salinity is expected to affect 3,230,000 km2 in more than 100 countries around the world, and these numbers are steadily increasing (FAO 2015; Shahid et al. 2018.( Therefore, it is important to study the different traits that regulate the adaptation of a crop genotype to salinity stress, and comprehensively understand how plants respond to salinity stress at different levels, and to follow an integrated approach to combine breeding methods and molecular tools to produce salt-tolerant crop varieties for cultivation in salt-affected areas. The author recommends the need for more research to provide more ideas to deal with the problem of salinity in light of climate change in the context of the rapid scientific progress witnessed by the world.

10.4.2 Impact of Salinity on Sustainable Crop Production Strategies In light of the literature and based it is recommended to focus on the following points: 1. Implementing integrated adaptation strategies and understanding the nature of the relationships between different defense mechanisms to mitigate the effects of salinity stress on physiology, biochemistry, germination, nodulation, vegetative growth, yield and quality. 2. Application of advanced statistical programs to determine the contribution of the principal components, factor and hierarchical clusters in salinity tolerance

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10.4.3 Protective Mechanisms and Salinity Resilience-Relevant Traits. How Do Plants Resilient Salinity Conditions? Based on the comprehensive view of the mechanisms of resistance, it is recommended to focus on the following mechanisms: 1. Ability of genotype to exclude ions, regulating ion absorption by the roots and the transition to the shoot system and leaves. 2. Selectivity of xylem in releasing and elimination of salts. 3. Compartmentalization of ions at the cellular level and at the entire plant. 4. Accumulation of compatible solutes, osmotic-protective substances and their role in salt tolerance. 5. The importance of silicon in defense mechanism against saline stress and improved growth and ion balance. 6. If the plant breeder wants to raise the level of salinity tolerance in the recent cultivars, he must focus on the following characteristics; early maturity, morphological, physiological and biochemical characteristics that have a strong correlation with salt tolerance, and transfer these traits through breeding programs to the novel cultivars for the possibility of expanding the cultivation of salt-affected soils.

10.4.4 Relationship of Diversity and Genetic Analysis to Breeding and Biotechnology Approaches in Resilience to Salinity Stress Researchers and scientists who are interested in eco-friendly studies recommend the following to mitigate the effects of salt on crops: 1. Exploring the potential of salt-tolerant genotypes as a genetic basis for tolerance in crop breeding programs. 2. Evaluating promising genotypes based on their tolerance according to economic yield. 3. Providing information on types of gene action controlling the inheritance of traits related to salinity tolerance and heritability. 4. Careful selection leads to improvement in the next generation of selection between the promising genotypes. 5. Our article reveals genetic variation in response to salt stress. This approach allows choose for desired traits, enabling more efficient applications of selection, hybrid breeding and mutation procedures to produce stress-tolerant populations. 6. Identification of molecular genetic markers associated with salt tolerance in crop plants by employing markers-assisted selection in breeding programs.

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7. Epigenetic modification-heritable responses is a new research area that warrants further studies to understand modifications that occur in epigenetic memory in response to environmental stress. The study of crop plant development, including gene regulation through epigenetic changes, is one of the recent methods to manage salinity stress. 8. Genetic engineering and tissue culture techniques are among the recent tendencies in the advanced scientific research system as fast and accurate methods for the production of plants and lines that tolerate abiotic environment pressures.

10.4.5 Management Options, Mitigation and Genotype Assessment Techniques According to the literature, several strategies should be implemented to minimalize the salinity effects through choosing tolerant genotype and proper agricultural practices for instance, laser soil leveling, leaching process, and environmentally friendly additives to the improve salt tolerance and others. Furthermore, implementation of the evaluation method and appropriate statistical design in the evaluation process. Besides, the composition of the salt solution used in the evaluation must be similar to the quality of salts present in the target soil and irrigation water. It is necessary to standardization of a good criterion of stress throughout the plant’s life cycle, as biomass production as a standard indicator refers to the selection of tolerant genotypes to salinity. It is also necessary to carry out a screening process for genetic material under moderate conditions of evaporation and transpiration, while choosing the appropriate location and season so that the breeding material is examined according to its real environment.

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