Preface

Microbes can be found in any kind of habitats from normal to extreme conditions. Microbes are playing a major role in ecosystem functioning, and some of the microbial functions in the ecosystem are decomposition, biogeochemical cycling, biocontrol agents, bioremediation, and bioaugmentation. Microbial biosynthetic abilities have been highly influenced in the search for solutions to problems faced by mankind in maintaining a quality environment. Microbes have enabled constructive and cost-effective responses, which would have been impossible through physical or chemical methods. Nowadays, microbial technologies have been applied to a wide area of environmental problems, with considerable solutions. Interaction among microbial populations in natural environments and their potential roles in the food web, biogeochemical cycles, and evolution of life makes microbial ecology as an essential study area.

Microbes are the most abundant organisms in the biosphere and regulate many critical elemental and biogeochemical phenomena. They are the key players in the carbon cycle and related biological reactions, and microbial ecology is a vital research area for understanding the contribution of the biosphere in global wanning and the response of the natural environment to climate variations. This book provides basic to advanced infonnation in environmental microbiology by exploring fascinating insights into microbial diversity.

In this context, this book briefly discusses the diversity of microbes and their potential application in nutrient cycling, environmental stress, plant growth, biocontrol, melanin production, bioremediation of xenobiotics, wastewater treatment, radiation resistance, and vermicomposting of organic wastes with updated infonnation and usefiil illustrations. The potential of applying mycorrhiza and endophytic bacteria as bioenhancers, biofertilizers, and bioprotectors hi commercial agricultural and horticultural systems and its impact on nutrient cycling, hormone signaling, environmental stress, plant growth, siderophore production, and biocontrol are discussed in Chapters 1 to 3. Chapter 4 discusses the interaction of fungi with plants and its effect on agriculture with special reference to Penicillium as phytopathogen and phytoaugmentor. A comprehensive discussion has been attempted on the ill effects of wastes, effluents, and dyes on the environment and human health and their degradation using microbes and biofilms in Chapters 5 through 8. Bioremediation of metal contamination using soil microbes, treatment of wastewater by indigenous and effective microbes, and resistance against radiation through thennophiles are discussed in detail in Chapters 9 to 11. Finally, biodegradation of organic wastes using microbe and earthworm mediated vennicomposting is briefly discussed in the last chapter of this book.

This book contains chapter contributions from well-established experts in their respective fields and is currently reviewed by many academic professionals. The editors wish to specially thank the authors and coauthors for then valuable contributions and extraordinary effort in revising and finalizing respective chapters towards the successful publication of this book. We would like to express our gratitude to Sandy Jones Sickels, Vice President, and Ashish Kumar, Publisher and President, Apple Academic Press, Inc., USA, for bringing out this book with excellent quality and for timely production.

—Jeyabalan Sangeetha, PhD Devarajan Thangadurai, PhD Saher Islam, MPhil

: Mycorrhiza: A Potential Bio-Enhancer in the Agriculture Production System

BAKULRANJAN JANA

ICAR-RCER, Research Center on Makhana, Darbhanga, Bihar-846005, India

INTRODUCTION

The agriculture industry is confronted today with the pressure of bourgeoning population, depleting, and degrading natural resources of soil and water, climate change, and shortage manpower and the non-availability of optimal technology. Due to rapid urbanization, we are losing the fertile soil for agriculture, and on the other hand, infertile and degraded soils have been taken for cultivation with a view to area expansion. In such a scenario, research on abiotic stresses is gaining momentums in India. This has been termed as a gray revolution, which may play a vital role for future agriculture in tropical and subtropical areas. In abiotic stress conditions, mycorrhizae are economically important symbionts to plant in arable conditions (Table 1.1). Mycorrhizae are simply a symbiotic association between numerous fungi and roots of higher plants/vascular host plants (Kirk et al., 2001). The term mycorrhizae mean fungus root, and it was derived from the Greek words ‘mykos' means fungus, and Thiza' means root' (Frank, 1885). This type of plant and fungus association was first observed in certain forest plant species, now is widespread and to affect most of the agricultural plant species, including many agronomic or field crops (Brady, 1995). From an economic point of view, the mycorrhizal associations have great importance because it significantly increases the availability of water and nutrients to the plants. It has been found that several essential nutrients especially from arable degraded soil to plant, resulted in better crop stand and thereby minimizing the irrigation facility and increasing productivity of several horticultural and agronomic crops in the agriculture production system. In a broad sense, fungal plant symbiotic association makes available the fungi with current photosynthates, i.e., sugar and other organic metabolites in the form of plant root exudates to use as food for VAM fungi. On the other hand, the fungi help in enhanced availability of water and other essential micronutrients, including phosphorous, which are essential for plant growth and development. The most common type of mycorrhizal association in the plant is VAM fungi, which are recently known as arbuscular mycorrhizal (AM) fungi, and its distribution in the plant kingdom is substantial covering 2/3 of land plants (Hodge,

2000).

Although several kinds of myconhizae present in the entire plant kingdom, with regard to practical importance in agriculture, there are mainly two types of mycorrhiza, like Ectomycorrhiza and Endomycor- rhiza, which are actively engaged with host plants in a natural ecosystem. The former group includes hundreds of different fungal associations, primarily with tree species of horticulture and forestry systems, such as pine-oak, fir, and hemlock. These fungi are actively involved in colony formation with fungal mantle forming common mycelia network (CMN) on the root surface and stimulated by the root exudates of the plant. The fungal hyphae do not penetrate the cell wall. They only penetrate the feeder root and develop around the cells of the cortex. On the other hand, the economically most important group of fungi are endomycorrhizae, which penetrate the root cells and forms two types of hyphal masses within the root cells, which are known as vesicles and arbuscules (Figure 1.1). The cell walls of the root cortex of the host plant are accessed by fungal hyphae of the vesicular-arbuscular myconhizae (VAM), which are presently known as AM fungi (AMF). Inside the root cells, highly branched small structures are fonned sporadically, which are known as arbuscules fonned by fungi and act as a medium that transfers the mineral nutrients from fungi to the host plant species. Vesicles are another structure, which is served as a storage organ for plant nutrients and other organic metabolites. A vast range of agronomical crops like wheat, maize, bajra, cotton, potatoes, sugarcane, cassava, and diy land rice have the AMF association with their root systems. Many horticultural crops, including apple, grapes, citrus, cocoa, coffee, and rubber, also have AMF associations. Many

economically important trees like maple, yellow poplar, and redwood have been found to exist with AMF associations for mutual benefits.

FIGURE 1.1 Myconhizae association with host plant at the cellular level.