eChapters

Abstract

Agricultural production is often limited by low phosphorus (P) availability. In developing countries, which have limited access to P fertiliser, there is a need to develop plants that are more efficient at low soil P. Arbuscular mycorrhizal (AM) symbioses are widespread in the plant kingdom and contribute significantly to plant P nutrition and growth in natural ecosystems. Production and application of these beneficial fungi for agricultural purposes has grown over the last decades worldwide. However, the necessity of AM inoculum production via a host plant is still an obstacle to ample utilization of AM fungi in agricultural crops. The present article deals with the basic and applied aspects of AM research and its role in sustainable agriculture.

Abstract

Cyanobacteria comprise a group of photosynthetic prokaryotes, which exhibit versatility in their morphological, biochemical and molecular characteristics and represent an untapped source of novel metabolites and genes. Their structural-functional flexibility makes them successful in diverse and extreme environments including high temperatures or levels of UV light and salinity, and co-exist in symbiotic/parasitic/mutualistic associations with various members of Plant and Animal kingdom. The intracellular colonization of cyanobacteria in wheat and rice roots and their potential as plant growth promoting agents for several crops, besides rice, has led to the deployment of novel formulations of cyanobacteria and agriculturally useful bacteria as biofilms and disease suppressive options in field studies.

Abstract

The nutrition of tobacco plants relies upon the plant genotypic variation and soil characteristics which also influence the various microflora that inhabit the rhizosphere. The investigations were aimed to analyze the role of native and inoculated plant growth promoting bacteria on the uptake of major plant nutrients viz., nitrogen, phosphorus and potassium and also their supportive nature in reducing the infection caused by  Pythium aphanidermatum, the damping-off fungus of tobacco in nursery. Rhizosphere microorganisms include PGPR viz., Azotobacter, Azospirillum, Pseudomonas and Bacillus, AM fungi and Streptomyces. The addition of these microbes as bioinoculants in tobacco integrated nutrient and disease management resulted in better quality tobacco worth premium price.

Abstract
 
This work aimed to evaluate agromicrobes preponderance and activity in maize ecosystem of same soil types (diara land/fragile land) under different agricultural practices. We conducted a five year field survey of grower’s field to investigate the effect of tillage system, maize plant genotypes and soil organic carbon level on preponderance of diazotroph (Azotobacter), plant growth promoting rhizobacteria (Pseudomonas) and arbuscular mycorrhiza (AM) colonization of maize ecosystem. No tillage, traditional maize cultivar and soil organic carbon (>1%) appear to support the preponderance of targeted diazotrophs, plant growth promoting rhizobacteria (PGPR) in maize rhizosphere and AM colonization of maize root. Elevation in the preponderance of bacteria, Azospirillum population in maize root, AM colonization, microbial biomass, nitrogen mineralization, phosphate solubilising microbes, cellulose hydrolyzing microbes and acetylene reducing assay (ARA)  of maize root appeared due to organic fertilization of maize crop.

Abstract

Of the various rhizosphere associated bacteria, Azospirillum species are probably the most studied and appear to have significant potential for commercial application. During the last 35 years of studies of Azospirillum–plant interaction, over 20 proposals were suggested for the mechanism of action by which Azospirillum  enhances plant growth, yield and nutrient uptake. Besides, fixing the nitrogen with associative symbiosis, they impart a number of beneficial effects on plants such as phytohormone production, siderophore production, enzyme production, proliferation of root system, enhanced water and mineral uptake, mobilization of minerals, mitigation of environmental stressors of plants, and moderate biocontrol potential. The following plant responses to Azospirillum inoculation in agriculture crops were often reported: increase the germination percentage and height of the seedlings, increase the total number and length of adventitious roots and root hairs, increase the hydraulic conductivity of the root system, increase in the height of the shoot and dry matter production and yield of the crop plants. The effect of Azospirillum inoculation on the total yield increases of field grown plants generally ranged from 10 to 30 per cent. This article reviews the recent researches on role of Azospirillum in plant growth promotion.

Abstract

Microorganisms execute many key functions that regulate the processes related to the fertility status, nutrient transformation, nutrient conservation, and soil health management that are crucial for agronomic sustainability. Rice soils offer peculiar conditions for microorganisms that support diametrically opposite biochemical reactions under flooded conditions. It is pertinent to note that both reduction and oxidation reactions of several essential nutrients mediated by microbes occur simultaneously in the flooded soils at various depths, profiles and stages of rice crop growth in concurrence. This is peculiar and specific to rice soils as the cultivation process demands changes in water regimes, operative and management practices.

Abstract

Current trend of global agricultural systems entails preference towards sustainable crop production through organic agriculture (ecology based) as compared to conventional (synthetic input based). In order to claim as organic, it needs to be certified as per requirements organic standard. The soil fertility management organic standard requirements of major countries are outlined. This review article compares the agricultural management practices of organic and conventional systems so as to assess its impacts on microbial biodiversity, microbial activities on soil functioning and long term fertility based on long term field studies conducted in different parts of the globe.

Abstract

Any environmental variable, can adversely affect the optimal growth conditions of the plants. The stressed environment makes the plants to alter their physiology for survival rather than reproduction. Prolonged drought, intense raining, frequent floods, cold waves high and low temperatures are the predicted abiotic stresses in the future due to climate changes. Water stress is one of the important growth limiting factor which decreases plant growth during vegetative stage. Crops grown under rain-fed conditions are the most affected by seasonal variations in rainfall. Therefore failure of monsoon, high temperature and salinity usually result in water stress. In addition, it causes serious negative impacts on crop growth and yields. A greater stress tolerance capacity could also be largely attributed to the plants by the symbiotically associating microorganisms capable of modulating stress factors. The microorganisms having close association with plants are referred as plant associated bacteria (PAB), which can be grouped into rhizospheric (in vicinity of root) and rhizoplanic (on surface of root), endophytic (inside the plant tissue)  and phyllospheric (on the leaf surface ) bacteria. Among the PAB, pink pigmented facultative methylotrophic (PPFM) bacteria belonging to the  genus Methylobacterium are well known for their intimate ubiquitous occurrence in the plant.

Abstract

The medicinal plant, Nithyakalyani, Catharanthusroseus is valued for its alkaloid and the content varied, among root (0.14 to 1.43%), stem (0.48%), fruit (0.4%), seed (0.18%) and pericaup (1.14%). The biofertilizer consortium development includes Catharanthusroseus. Azosppirillumlipoferum CAZS-4, Azotobaterchroococcum CAZB-1, Bacillusmegaterium CPB-18 and Pseudomonasflourescens CPF-14. The relative chemotactic response (RCR) of the strains to anionic fraction is more than that of cationic and neutral fractions. The consortium treated plants possessed 1.120 mg g^-1 of ajmalicine on 180 DAS, and the antioxidant superoxide dismutase (SOD) (13.240 U mg of protein hr-1), peroxide (POX) (11.240 U mg of protein hr-1) and catalase (CAT) (9.000 U mg of protein hr^-1) values were higher on 150 DAS. The consortium increased the biomass production by 50-75 per cent with proportionate increase in the mineral nutrient content. Biofertilizer consortium is the most effective organic input for biomass production.

Abstract

Plant-associated microorganisms play a significant role in conferring resistance to abiotic stresses. These organisms include rhizoplane and endophytic bacteria and symbiotic fungi and operate through a variety of mechanisms like triggering osmotic response and induction of novel genes in plants. The development of stress tolerant crop varieties through genetic engineering and plant breeding is essential but a long and strained process, whereas microbial inoculation to alleviate stresses in plants could be a more cost effective environmental friendly option which could be available in a shorter time frame. Considering the current trends available, intensive future research is needed in this area, particularly on field evaluation and application of potential organisms.

Abstract

The pressure due to increase in world population necessitates an increase in agricultural production and this warrants the vital importance of research in plant and soil productivity. Applications of chemical fertilizers and pesticides have resulted in soil pollution, desertification and salinisation which disrupted the agriculture production. A suitable microbial technology to improve the soil health and plant productivity has been invented. Increase in the use of bacterial fertilizers substantially reduced the use of chemical fertilizers. Similarly invention of specific antagonistic microbes which control pathogen and stimulate plant growth resulted in lesser use of agrochemicals. Selection, development and application of such microbial strains to the agronomic crops resulted improving the fertility of such affected soil. The studies on plant growth promoting rhizobacteria (PGPR) on the growth and nutrient uptake of various plants have been well studied. Presently, it has been found that the use of beneficial microbes can enhance the resistance ability to adverse stresses. Some mechanisms by which the beneficial microorganisms are able to stimulate plant growth and arrest plant pathogens include mobilization of nutrients, production of phytohormones, siderophores, organic acids, nitrogen fixation, lowering of ethylene levels in plants and antagonism. Here the recent developments that have been taken place on the interaction between plants and PGPR and their mechanism of action resulting in enhanced agriculture production and soil fertility are discussed.

Abstract

Endophytes are microorganisms  that live inside the living plant tissues for at least part of their life without causing any apparent disease symptoms in the host. In general  they  can be divided into two main types namely, obligate and facultative endophytes. Facultative endophytes are capable to survive in the soil, on the plant surface, inside the plants as well as on artificial nutrients and can be cultured away from their host. Endophytes which inhabit inside plant tissues throughout their lifespan are called as obligate endophytes. Natural products produced by endophytic microbes are found to be antimicrobial, antiviral, anticancer, antioxidants, antidiabetic and immunosuppressant. Therefore, endophytes form an untapped source of novel natural compounds for application in agriculture, medicine and industry.

Introduction

Microorganisms are a great source of genetic diversity, still far from completely known and explored. The intimate association of plants with complex microbial communities is of great importance for the growth and productivity of plants in agriculture. There exists a definite difference in microbial community present in the bulk soil and the neighboring micro environments like phyllosphere, endosphere, rhizosphere and endorhizae. Microorganisms that colonize the plants’ rhizosphere are either pathogenic or beneficial according to their effects on plants and the way they interact with roots. The rhizosphere supports a plethora of microbial populations capable of exerting beneficial, neutral or detrimental effects on plant growth and development. Microorganisms such as bacteria, actinomycetes, protozoa, algae, fungi, and viruses coexist in the rhizosphere; bacteria are the most abundant among them.

Abstract

With the growing awareness on the benefits of organically cultivated food, biofertilization and biocontrol by plant-associated bacteria are being used as alternatives to chemical fertilizers and conventional control methods. It therefore becomes essential to continue surveying different agroecological niches to identify plant growth promoting bacteria suitable for each microenvironment. Species belonging to the genus Enterobacter are versatile colonizers of numerous environmental niches. Several species and strains from this genus have also been routinely recovered from the rhizosphere of crops such as rice, canola, cucumber, banana, potato, corn, tomato and cotton. These isolates have been studied and shown to have beneficial effects on plant growth and protective action against phytopathogens.

Abstract

The greatest challenge facing us in the coming years is to produce adequate amounts of basic necessities of food, feed, fibre, fuel and raw materials for the rapidly shrinking per capita agricultural land. One alternative is to make a sustainable use of existing marginal lands. In many regions of the tropics and sub-tropics, the need to use marginal low-input soils with usually inadequate nutrient(s) supply permits only very low or unreliable yields to be achieved. It is frequently not possible  to supply required amounts of mineral fertilizers or chemical pesticides because of the low purchasing power of the marginal farmers. In particular, it is not possible to compensate for the deficient nutrient supply and this constitutes a yield limiting factor. The role of soil microorganisms in sustainable productivity has been well construed. In recent years, root inhabiting (rhizozosphere) bacteria (rhizobacteria) is gaining importance.

Abstract

The phosphorus deficiency in soil is a major problem for agricultural production as phosphorus is one of the major constituents in energy metabolism and biosynthesis of nucleic acids and cell membranes. The phosphorous present in soil is an important macronutrient for the growth and development of the plants. The phosphorus occurs in two forms in soil, organic and inorganic. The phytates (salts of phytic acid) constitute the major form of organic phosphorus other than nucleic acids, phospholipids and other compounds in soil. Phytate-phosphorus is not readily available to plants due to its chelation with metal ions forming insoluble complexes or adsorbed to soil particles. Phosphate solubilizing and phytate hydrolyzing microorganisms, bacteria and fungi, are ubiquitous in cultivated, wetland, grassland and forest soils, which play an important role in supplying soluble phosphorus to plants. Microbes hydrolyze organic forms of phosphorus by secreting phytases and acidic/alkaline phosphatases. By genetic engineering, several attempts have been made to develop transgenic plants which are able to utilize phytates as sole source of phosphorus for their growth and development. This review focuses on the applicability of microbial phytases in promoting the growth and development of various crop plants.

Abstract

The structure and function of proteins involved in plant-microbe interactions is investigated through large-scale proteomics technology in a complex biological sample. Since the whole genome sequence are now available for several plant species and microbes, proteomics study has became easier, accurate and huge amount of data can be generated during plant-microbe interactions. Proteomics approaches are highly important and relevant in many studies and showed that only genomics approaches is not sufficient as much significant information are lost as the proteins and not the genes coding them are final product which is responsible for the observed phenotype.

Introduction

Biological nitrogen fixation (BNF), generally found in legumes, is a valuable nature’s gift through which atmospheric nitrogen is fixed by symbiotically associated rhizobia that make it available to plants. Among cereals, rice (Oryza sativa) is an important staple food crop that feeds a large proportion of the world population [1]. There is tremendous pressure on agriculturists worldwide to increase the yield to meet growing consumption to feed a world population increasing day by day. However, unlike symbiotic plant–microbe interactions commonly observed in legumes, in several cereal crop plants including Oryza sativa, endophytic associations have been observed [2-8].

Abstract

While, life on Earth is dependent on microbes for many essential services, microbes are intimate partners in virtually every life process of plants by way of mobilization/acquisition of nutrients, out-competition and antagonism of pathogens, plant stress alleviation, plant growth promotion, co-metabolism, degradation of toxins, etc. Exploitation of such interactions between microbes and plants and optimization of plant microbiome could allow farmers to apply less chemical fertilizer, and pesticides besides improving overall plant health which paves the way for sustainable development. What is less appreciated, and less well understood, is the mechanism of microbes exerting such benefits to the plants. A greater understanding of how plants and soil microbes live together, communicate, build innate plant immunity, triggers hormone synthesis and benefit each other can therefore provide new strategies to improve plant productivity, while helping to protect the environment and maintain global biodiversity.

1. Why Plant Nutrient Disorders?

Plant Nutrient Disorders result from nutrient imbalances in soils and plants. In-adequate use of one or more nutrients can result in nutrient imbalances. Presence or use of a nutrient in excess amount can hinder the absorption or uptake of another nutrient and thus,cause nutrient disorders. Lime induced iron chlorosis or use of excess Potassium can hinder the absorption of Ca²⁺/and, or Mg²⁺ by plants. Enhanced level of Mg can decrease the uptake of Zn. Excessive use of NPK fertilisers can result in micronutrient deficiencies.

Soils are being regularly depleted of their native reserves, due to intensive cropping and non-application of essential nutrients (primary, secondary and micronutrients). Lack or restricted use of quality organic manures, such as compost, green manures, crop residues etc. and cultivation of HYVs in most crops have accentuated the problem.