Preface

Over the past few years, natural-based crop production substances, 'plant biostimulants', have been considered as environmentally friendly alternatives to agrichemicals. A plant biostimulant describes any microorganism and/or substance applied to seeds, plants, or soil microbiota to promote plant physiological pathways such as mineral nutrient uptake, crop quality, growth regulation, and tolerance to unfavorable environmental conditions. Nowadays, a large number of biostimulants are found as a complex chemical mixture originated from biological processes with plant-nutritive elements as bioinoculants enhancing nutrient availability to plants. In this sense, biostimulants may comprise fungal or bacterial inoculants, humic acids, amino acids, fulvic acids, seaweed extracts, etc. Biostimulants have biopesticide and biostimulant utilities affecting their regulatory classification.

Elucidations on direct or microbially mediated functions of biostimulants are presented in this book to illustrate fundamental principles, modes of action, and recent applications underlying this technology. The papers selected for this book comprise a cross-section of topics that reflect an overview on concepts of plant biostimulants from different points of view in order to describe effective strategies for using these substances and/or beneficial microorganisms within sustainable agroecosystems. This book, "Biostimulants in Plant Science", encompasses two main sections covering nine reviews focused on 'Elucidation of biostimulant functions on promoting plant growth', and 'The role of bacterial and fungal communities on enhancing nutrient bioavailability'. I hope that these chapters adequately reflect the objectives of this compilation.

### *Elucidation of Biostimulant Functions on Promoting Plant Growth*

The first chapter, "Biostimulants and Their Role in Improving Plant Growth under Abiotic Stresses", discusses the use of biostimulants in plant growth according to the raw material used in their compositions as well as their effects on plants subjected to abiotic stresses.

The second chapter, "Application of Bacteria as a Prominent Source of Biofertilizers", provides an overview of different bacterial biofertilizers and its associations with plants and nutrients transformations in soil. This chapter adopts a rational approach to use for the management of microbial fertilizers in sustainable agriculture and it has vast potential for the future.

The third chapter, "Applications and Constraints of Plant Beneficial Microorganisms in Agriculture", introduces biofertilizers as highly potent alternatives to inorganic fertilizers and also as an economically attractive route for augmenting nutrient supply. Beneficial microorganisms have the potential ability to fix atmospheric nitrogen, solubilize and mobilize plant nutrients from the insoluble form through a microbiological process.

The fourth chapter, "Biochar: A Vital Source for Sustainable Agriculture", reviews the contributions of biochar technology to environmental sustainability and food

**II**

**Chapter 7 101**

**Chapter 8 117**

**Chapter 9 135**

Arbuscular Mycorrhiza-Associated Rhizobacteria and Biocontrol of

*by Meenakshi Singh, Manjari Mishra, Devendra Kumar Srivastava* 

Ectomycorrhizal Fungi as Biofertilizers in Forestry *by José Alfonso Domínguez-Núñez and Ada S. Albanesi*

Microbes for Iron Chlorosis Remediation in Peach

Soilborne Phytopathogens

*and Pradeep Kumar Singh*

*by Saurabh Kumar Singh*

security. This strategy addresses the declining food security issues, depleting soil, and plant health challenges. Biochar enhances biological nitrogen fixation and productivity by facilitating changes in plants' physical conditions, rapid germination, and growth. It also enhances nutrient uptake, water holding capacity, and microbial activity or acts against biotic and abiotic stresses.

The fifth chapter, "Role of Soil Microbes on Crop Yield against Edaphic Factors of Soil", focuses on losing soil productivity where continuous usage of inorganic fertilizers coupled with depletion of organic matter results in deterioration of soil structure and its productivity. It also leads to a reduced input/output ratio unless soils are replenished with organic matter through green manure, compost, or microbial activity. Thus, the microbes can be utilized to overcome the harmful effect of chemical degradation of soil and waterlogging, which improves soil fertility.

### *The Role of Bacterial and Fungal Communities on Enhancing Nutrient Bioavailability*

The sixth chapter, "Role of Fungi in Agriculture", firstly gives a brief introduction on fungal filaments that enhance the nutrient availability by solubilizing insoluble nutrients like phosphorus, and increase the nutrient mobility due to faster intracellular nutrient mobility. Then, the arbuscular mycorrhizal fungi (AMF) are introduced for how to protect plants by up-regulating the activity of antioxidant enzymes and osmolytes, and by regulating the synthesis of phytohormones, which might possibly interconnect the various tolerance mechanisms for cumulative stress response.

The seventh chapter, "Arbuscular Mycorrhiza-Associated Rhizobacteria and Biocontrol of Soilborne Phytopathogens", provides a general picture on understanding the mechanisms involved in arbuscular mycorrhizal fungi (AMF)/rhizobacteria interactions including the mechanisms of AMF-mediated biocontrol; interactions between AMF associated bacteria (AMB) and extraradical mycelium network of AMF; AM associated bacteria and biocontrol activities; and the unfavorable zone to pathogen development as the mycorrhizosphere.

The eighth chapter, "Ectomycorrhizal Fungi as Biofertilizers in Forestry", describes the value of ECM fungi from a global framework, not only to increase the production of edible fruit bodies but also for the regular practices of reforestation and restoration of ecosystems with implicit applications in biofertilization, bioremediation, and control of soil pathogens. Moreover, ecological functions, the direct implications of the ECM fungi as biofertilizers in forest management are briefly discussed: reforestation, plantation management, and ecosystem restoration.

The ninth chapter, "Microbes for Iron Chlorosis Remediation in Peach", addresses the current trend of detection methods and control measures of iron chlorosis in peaches, and gives attention to bioremediation techniques for the correction of lime-induced iron chlorosis. Traditional soil and foliar application methods including ferrous sulphate, Fe-EDTA, Fe-EDDHA chelates, etc. cannot be considered as reliable corrective measures of chlorosis. Besides, the importance of microbe-mediated correction strategies in iron fixation in calcareous soil and iron uptake by plants is discussed.

IntechOpen has taken a commendable step to publish a series of valuable books in the context of plant sciences. So, it is with great pleasure that this book has attracted attention from researchers who were selected based on their previous contributions in scientific journals. I sincerely hope that the materials of this book will help a wide range of readers to update their insights on the role of biostimulants in plant

**V**

science, and particularly in sustainable agriculture. Therefore, it can be useful especially when you are beginning your career or are just researching this topic. Last but not least, I would like to thank IntechOpen for inviting me to be the book editor. Special thanks also go to Ms. Rebekah Pribetic, Author Service Manager, for her

> **Dr. Ir. Seyed Mahyar Mirmajlessi**  Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University (UGent),

> > **Ramalingam Radhakrishnan**

Jamal Mohamed College (affiliated to Bharathidasan University),

Belgium

India

help and cooperation during the whole editing process.

science, and particularly in sustainable agriculture. Therefore, it can be useful especially when you are beginning your career or are just researching this topic. Last but not least, I would like to thank IntechOpen for inviting me to be the book editor. Special thanks also go to Ms. Rebekah Pribetic, Author Service Manager, for her help and cooperation during the whole editing process.

### **Dr. Ir. Seyed Mahyar Mirmajlessi**

Department of Plants and Crops, Faculty of Bioscience Engineering, Ghent University (UGent), Belgium

### **Ramalingam Radhakrishnan**

Jamal Mohamed College (affiliated to Bharathidasan University), India

**IV**

security. This strategy addresses the declining food security issues, depleting soil, and plant health challenges. Biochar enhances biological nitrogen fixation and productivity by facilitating changes in plants' physical conditions, rapid germination, and growth. It also enhances nutrient uptake, water holding capacity, and

The fifth chapter, "Role of Soil Microbes on Crop Yield against Edaphic Factors of Soil", focuses on losing soil productivity where continuous usage of inorganic fertilizers coupled with depletion of organic matter results in deterioration of soil structure and its productivity. It also leads to a reduced input/output ratio unless soils are replenished with organic matter through green manure, compost, or microbial activity. Thus, the microbes can be utilized to overcome the harmful effect of chemical degradation of soil and waterlogging, which improves soil fertility.

*The Role of Bacterial and Fungal Communities on Enhancing Nutrient Bioavailability*

The sixth chapter, "Role of Fungi in Agriculture", firstly gives a brief introduction on fungal filaments that enhance the nutrient availability by solubilizing insoluble nutrients like phosphorus, and increase the nutrient mobility due to faster intracellular nutrient mobility. Then, the arbuscular mycorrhizal fungi (AMF) are introduced for how to protect plants by up-regulating the activity of antioxidant enzymes and osmolytes, and by regulating the synthesis of phytohormones, which might possibly interconnect the various tolerance mechanisms for cumulative stress response.

The seventh chapter, "Arbuscular Mycorrhiza-Associated Rhizobacteria and Biocontrol

The eighth chapter, "Ectomycorrhizal Fungi as Biofertilizers in Forestry", describes the value of ECM fungi from a global framework, not only to increase the production of edible fruit bodies but also for the regular practices of reforestation and restoration of ecosystems with implicit applications in biofertilization, bioremediation, and control of soil pathogens. Moreover, ecological functions, the direct implications of the ECM fungi as biofertilizers in forest management are briefly discussed: reforestation, plantation management, and ecosystem restoration.

The ninth chapter, "Microbes for Iron Chlorosis Remediation in Peach", addresses the current trend of detection methods and control measures of iron chlorosis in peaches, and gives attention to bioremediation techniques for the correction of lime-induced iron chlorosis. Traditional soil and foliar application methods including ferrous sulphate, Fe-EDTA, Fe-EDDHA chelates, etc. cannot be considered as reliable corrective measures of chlorosis. Besides, the importance of microbe-mediated correction strategies in iron fixation in calcareous soil and iron uptake by plants is discussed.

IntechOpen has taken a commendable step to publish a series of valuable books in the context of plant sciences. So, it is with great pleasure that this book has attracted attention from researchers who were selected based on their previous contributions in scientific journals. I sincerely hope that the materials of this book will help a wide range of readers to update their insights on the role of biostimulants in plant

of Soilborne Phytopathogens", provides a general picture on understanding the mechanisms involved in arbuscular mycorrhizal fungi (AMF)/rhizobacteria interactions including the mechanisms of AMF-mediated biocontrol; interactions between AMF associated bacteria (AMB) and extraradical mycelium network of AMF; AM associated bacteria and biocontrol activities; and the unfavorable zone to pathogen

development as the mycorrhizosphere.

microbial activity or acts against biotic and abiotic stresses.

**1**

Section 1

Elucidation of

Biostimulant Functions on

Promoting Plant Growth

Section 1

Elucidation of Biostimulant Functions on Promoting Plant Growth

**3**

**Chapter 1**

**Abstract**

**1. Introduction**

need for fertilizers [1].

Abiotic Stresses

*Ana Carolina Feitosa de Vasconcelos* 

their effects on plants subjected to abiotic stresses.

their constituents or on their modes of actions.

*and Lúcia Helena Garófalo Chaves*

Biostimulants and Their Role in

Improving Plant Growth under

Biostimulants are products that reduce the need for fertilizers and increase plant

growth, resistance to water and abiotic stresses. In small concentrations, these substances are efficient, favoring the good performance of the plant's vital processes, and allowing high yields and good quality products. In addition, biostimulants applied to plants enhance nutrition efficiency, abiotic stress tolerance and/or plant quality traits, regardless of its nutrient contents. Several researches have been developed in order to evaluate the biostimulants in improving plant development subjected to stresses, saline environment, and development of seedlings, among others. Furthermore, various raw materials have been used in biostimulant compositions, such as humic acids, hormones, algae extracts, and plant growth-promoting bacteria. In this sense, this chapter aims to approach the use of biostimulants in plant growth according to the raw material used in their compositions as well as

**Keywords:** drought, salinity, temperature, humic substances, seaweed extracts, hormones, arbuscular mycorrhizal fungi, plant growth-promoting rhizobacteria

Biostimulants are natural or synthetic substances that can be applied to seeds, plants, and soil. These substances cause changes in vital and structural processes in order to influence plant growth through improved tolerance to abiotic stresses and increase seed and/or grain yield and quality. In addition, biostimulants reduce the

Many definitions of biostimulants have been reported [2]. According to [3], biostimulants could be classified depending on the mode of action and the origin of the active ingredient; while Ref. [4] proposed biostimulants should be classified based on their action in the plants or, on the physiological plant responses rather than on their composition. In addition Ref. [1] has emphasized the importance of the final impact on plant productivity which suggests that any definition of biostimulants should focus on the agricultural functions of biostimulants, either on the nature of

Thus Ref. [2] proposed the following definition of a biostimulant as a formulated product of biological origin that improves plant productivity because of the novel or

### **Chapter 1**
