Preface   Microorganisms are every where. Microorganisms can be found in the air we breathe, in the food we eat, and even within our own body. In fact, we come in contact with countless number of microorganisms everyday. Because microbes affect our everyday lives, microbiology provides many challenges and offers many rewards. Biotechnology is the product of interaction between the science of biology and technology. It is defined as “the controlled use of biological agents such as microorganisms or cellular components for beneficial use”. Biotechnology plays a very important role in agriculture as a result of its ability to modify microorganisms, plants, animals, and agriculture processes. The umbrella of microbial biotechnology in agriculture covers numerous scientific activities, ranging from production of biofertilizers to that of microbial pesticides; from biological nitrogen fixation to ligno-cellulose degradation; from production of biomass and bio-fuels to transgenic plants. Sustainability refers to productive performance of a system over time. It implies use of natural resource to meet the present needs without jeopardizing the future potential. A sustainable system must be sustainable both ecologically and economically. Most soils of the tropics are low in inherent fertility. Currently there is considerable resistance against the use of chemical pesticides and fertilizers; because of their hazardous influence on the environment, and on soil, plant, animal and human health. Hence the current day emphasis is on use of organic inputs including microbial inoculants which play an important role in sustainable agriculture, horticulture and forestry. Some books have been published on different groups of microorganisms used as biofertilizers, biocontrol agents and for composting of agricultural wastes, but there are a very few books bringing different aspects of microbial technology for enhancing plant growth and yield. Hence, the object of this book is to cover comprehensively different groups of microorganisms used for sustained productivity of plants important in agriculture, horticulture and forestry. The book is organized into 10 chapters. Chapter 1 gives an introduction to the subject highlighting historical developments in the field. Chapter 2 helps to understand the physico-chemical characteristics of soil and covers the different groups of soil microorganisms, nutrient cycles and soil-plant-microbe interactions. Chapter 3 deals with various types of nitrogen fixing organisms including the physiology of nitrogen fixation. Chapter 4 is devoted to microorganisms modulating phosphorus nutrition of plants like phosphate solubilizing microorganisms and mycorrhizal fungi. Chapter 5 deals with plant growth promoting rhizomicroorganisms. Chapters 6 and 7 provide up-to-date information on microorganisms used for the biocontrol of soil-borne plant pathogens and insect-pests respectively. Chapter 8 discusses the role of microorganisms for control of weeds. Chapter 9 covers the role of microorganisms in the conversion of organic wastes to compost. Chapter 10 provides an overview of microbial biotechnology used in the mass production of microbial inoculants including their quality control specifications.

Biotechnology plays a very important role in agriculture as a result of its ability to modify microorganisms, plants, animals, and agricultural processes. The umbrella of microbial technology in agriculture covers numerous scientific activities, ranging from production of biofertilizers to that of microbial pesticides; from biological nitrogen fixation to lignocellulose degradation; from production of biomass and biofuels to transgenic plants. Terrestrial ecosystem contains an important dynamic living matrix termed soil, which is critical for agricultural production and food security. Soil forms the medium for growth and maintenance of a variety of plant species. Soil is considered a store house of microbial activity, though the space occupied by living microorganisms is estimated to be less than 5% of total space.

The term soil refers to the outer, loose material of the earth’s surface, a layer distinctly different from the underlying parent rock. A number of features characterize this region of the earth’s crust. It is the natural medium, which supports plant growth. It provides the physical support needed for the root system and also supplies nutrients needed for plant growth. It is a perennial source of organic matter. It supports a vast population of microorganisms.

Nitrogen is the most important element on which depends growth and productivity of plants. It is also the most abundant molecule in the atmosphere (80%), yet it cannot be utilized by plants. The plant utilizable form of nitrogen is either, its most oxidized form, the nitrates or the most reduced state, the ammonia.  The indiscriminate use of nitrogenous fertilizers amounts to depletion of non-renewable fossil fuels used in fertilizer production. Sustainable agriculture depends largely on renewable resources and on-farm nitrogen contributions are achieved largely through biological nitrogen fixation (BNF), which helps in maintaining and/or improving soil fertility by using atmospheric nitrogen. Annually BNF is estimated to be around 175 million tonnes of which close to 79% is accounted for by terrestrial fixation.

Phosphorus is one of the essential nutrients for plant growth. It is an integral part of the cellular activities of the living organisms. It has a defined role in plant metabolism such as cell division, development, photosynthesis, break down of sugar, nutrient transport within the plant, transfer of genetic characteristics from one generation to another and regulation of metabolic pathways. Phosphorus is a frequently limiting macronutrient next only to nitrogen for plant growth and makes up about 0.2% of plant dry weight. The plants obtain their P requirement from the soil pool. It occurs in soil as inorganic phosphates, produced by weathering of parent rock or as organic phosphate derived from decayed plant, animal, or microorganisms.

The rhizosphere is the narrow zone of soil surrounding the root that is under the immediate influence of the root system. This zone is rich in nutrients when compared with the bulk soil, due to the accumulation of a variety of organic compounds released from roots by exudation, secretion and deposition. Organic compounds released by plant roots include amino acids, fatty acids, nucleotides, organic acids, phenolics, plant growth regulators, putrescine, sterols, sugars and vitamins. Because these organic compounds can be used as carbon and energy source by microorganisms, microbial growth and activity is particularly intense in the rhizosphere.

Emphasis of present day agriculture is to produce more with lesser land, water and man power. Apart from natural calamities like drought, flood etc., biotic stresses like pests, diseases and weeds also influence the crop productivity greatly. Sixty to eighty per cent of the total crop losses are attributed to the devastations caused by pests and diseases. Farmer’s income in recent years is decreasing gradually due to increased cost of inputs particularly in plant protection. The excessive dependence on chemical pesticides leads to the development of resistance in insect pests and pathogens, out breaks of secondary pests and pathogens / biotypes and occurrence of residues in food chain. To avoid this situation the concept of Integrated Pest Management (IPM)/ Integrated Disease Management (IDM) approach should be considered on top priority.

The adoption of modern agricultural technologies has culminated into serious problems of pesticide resistance in major pests, resurgence in minor pests, elimination of populations of natural parasites, predators and pollinators, environmental pollution, pesticide residues in food chain and health hazards. World Health Organization (WHO) estimates one million pesticides poisoning cases and 20,000 deaths every year globally. This is due to high pesticide residues in food chain including cereals, pulses, vegetables, fruits, milk and milk products (including mother’s milk), fishes, poultry, meat products and water. Twenty five per cent of Indian food products contain pesticide residues above tolerance level compared to only 1.2% globally.

Herbicides are the chemical substances used to kill weeds, i.e., unwanted plants that compete with crop plants for soil nutrients. Chemical herbicides are the most effective immediate solution to most weed problems. Use of chemicals, however, can be harmful to wildlife, to the environment and to humans. Chemicals are also expensive, and weeds develop resistance to the chemicals. For these reasons, there is now a move toward alternative methods of controlling the weeds. One of the most promising is biological weed control, which involves using one living organism to control the activities of another organism.

Sustainable agriculture or organic farming wherein biological inputs are maximum and chemical inputs are minimal, is drawing the attention of farmers across the world including India. For replacing chemical fertilizers, which supply plant nutrients by organic manure, the basic requirement is the availability of raw material i.e. the organic matter or biomass that can be decomposed to organic manure. The question that is often asked is what are the different sources of available biomass and how much of it is available? Different sources of biomass can be categorized as

Microbial inoculants in agriculture, horticulture and forestry can be defined as preparations containing strains of microorganisms which can augment the microbiological process such as nitrogen fixation, phosphate mobilization, excretion of growth promoting substances, decomposition of organic wastes, biocontrol of insect pests and diseases etc. Thus they become an important component of sustainable agriculture. Microbial inoculants are based on renewable sources available in soil and nature and are low cost input and eco-friendly. These inoculants carrying the microorganisms when applied to soil/plant promote plant growth and productivity.

Media Composition 1. Ashby’s mannitol medium