Aketi Ramesh

Phytase, Phosphatase Activity and P-Nutrition of Soybean as Influenced by Inoculation of Bacillus

The efficiency of different Bacillus isolates on rhizosphere soil enzyme activities and P-nutrition of soybean was carried out under microcosm conditions. Significant increase in enzyme activities viz., fluorescein diacetate activity, phosphatase and phytase activity and consequent effects on P-nutrition were observed with the inoculation of Bacillus isolates over uninoculated control. Among the isolates, BD-3-1B, KHBD-6, BDKH-3, Bacillus amyloliquefacians, and Bacillus cereus were found to be promising. The phytic acid-P as a percentage of total P content in soybean seeds decreased with the inoculation of Bacillus isolates as compared to un-inoculated control. A decrease in phytic-P in soybean seeds not only results in better digestibility and increased feed efficiency. Pearson correlation studies revealed a significant positive association between acid, alkaline phosphatases, phytase activity on available P content in soil and P content in seeds with the inoculation of Bacillus isolates, indicating role of these enzymes in P mobilization and acquisition by soybean.

Isolation and Characterization of Plant Growth- Promoting Bacillus amyloliquefaciens Strain sks_bnj_1 and its Influence on Rhizosphere Soil Properties and Nutrition of Soybean (Glycine max L. Merrill)

The objective of this work was to isolate and characterize Bacillus bearing multiple plant growthpromoting traits from diseased roots of soybean and to further assess its inoculation effect on soil rhizosphere properties and nutrition in soybean. The isolate was putatively identified as Bacillus on the basis of cultural characteristics and FAMEs profile, and further sequencing of 16S rRNA gene revealed 98.7% similarity to Bacillus amyloliquefaciens and designated as strain sks_bnj_1 (AY 932823). The strain possessed multiple plant growth-promoting traits such as siderophore production, indole-3-acetic acid-like-compounds, ACC deaminase, phosphatases, phytases, HCN, cellulases, zinc solubilization and antagonisms to soil-borne pathogens. Microcosm study using soybean as an indicator crop revealed that inoculation of this strain sks_bnj_1 significantly increased rhizosphere soil properties (enzyme activities, IAA production, microbial respiration, microbial biomass-C), and nutrient content in straw (K, P, Zn, Fe, Cu, Mn) and seeds (K, P, Fe, Mn) of soybean over un-inoculated control. This study suggests that inoculation of B. amyloliquefaciens sks_bnj_1 improves most of the rhizosphere properties, plant growth, nutrient assimilation and yield of soybean and has potential to be promoted as a bioinoculant for soybean production following proper field evaluation.

Soil Biological Activity Contributing to Phosphorus Availability in Vertisols under Long-Term Organic and Conventional Agricultural Management

Mobilization of unavailable phosphorus (P) to plant available P is a prerequisite to sustain crop productivity. Although most of the agricultural soils have sufficient amounts of phosphorus, low availability of native soil P remains a key limiting factor to increasing crop productivity. Solubilization and mineralization of applied and native P to plant available form is mediated through a number of biological and biochemical processes that are strongly influenced by soil carbon/organic matter, besides other biotic and abiotic factors. Soils rich in organic matter are expected to have higher P availability potentially due to higher biological activity. In conventional agricultural systems mineral fertilizers are used to supply P for plant growth, whereas organic systems largely rely on inputs of organic origin. The soils under organic management are supposed to be biologically more active and thus possess a higher capability to mobilize native or applied P. In this study we compared biological activity in soil of a long-term farming systems comparison field trial in vertisols under a subtropical (semi-arid) environment. Soil samples were collected from plots under 7 years of organic and conventional management at five different time points in soybean (Glycine max) -wheat (Triticum aestivum) crop sequence including the crop growth stages of reproductive significance. Upon analysis of various soil biological properties such as dehydrogenase, β-glucosidase, acid and alkaline phosphatase activities, microbial respiration, substrate induced respiration, soil microbial biomass carbon, organically managed soils were found to be biologically more active particularly at R2 stage in soybean and panicle initiation stage in wheat. We also determined the synergies between these biological parameters by using the methodology of principle component analysis. At all sampling points, P availability in organic and conventional systems was comparable. Our findings clearly indicate that owing to higher biological activity, organic systems possess equal capabilities of supplying P for crop growth as are conventional systems with inputs of mineral P fertilizers.

Phosphorus Mobilization from Native Soil P-Pool upon Inoculation with Phytate-Mineralizing and Phosphate-Solubilizing Bacillus aryabhattai Isolates for Improved P-Acquisition and Growth of Soybean and Wheat Crops in Microcosm Conditions

Microbial transformation of both inorganic and organic forms of soil phosphorus to plant available P is an important trait contributing to plant P-nutrition and growth promotion. The present study was undertaken to evaluate phytate-mineralizing and phosphate-solubilizing Bacillus aryabhattai isolates on plant growth promotion, rhizosphere properties, P-mobilization from native P-pool of soil and acquisition by soybean and wheat crops in Vertisols of central India. Under microcosm conditions, a significant increase in plant growth parameters and plant P content of soybean (R5 stage) and wheat (panicle initiation stage) crops as a result of inoculation was recorded over un-inoculated control. Similarly, rhizosphere soil properties like activities of fluorescein diacetate, acid and alkaline phosphatase, phytase and microbial biomass-P were also increased with inoculation. These properties were found to be higher with inoculation of isolate MDSR14 followed by MDSR7. At maturity, inoculation with isolates MDSR7 and MDSR14 significantly increased shoot and seed weight, P content and decreased Phytic-P expressed as a percentage of total P content. There was a concomitant depletion in native organic P and acid extractable-P and increase in inorganic P in rhizosphere soil over un-inoculated control indicating mobilization of native unavailable organic P and inorganic insoluble P-pool of soil to available P. Moreover, inoculation also decreased the level of Phytic-P expressed as a percentage of total P content in seeds in soybean and wheat crops as compared to un-inoculated control. The decrease in Phytic-P results in better digestibility and increased feed efficiency and has implication in availability of minerals to human being and animals. The results suggest that B. aryabhattai isolates (MDSR14 and MDSR7) have potential to mobilize native soil P-pool and improve growth, yield and P-assimilation by soybean and wheat crops.

Nitric Oxide as a Signaling Molecule in Plant-Bacterial Interactions

Nitric oxide (NO), evolved during various biological processes occuring in soil, bacteria, and plants, is acting as signaling molecule to trigger different essential pathways involved in plant-microbe interactions. Reactive nitrogen species (RNS) is present at every developmental stage of plants and plays very important role in their life cycle. This valuable molecule also involved in signaling in response to biotic and abiotic stress in plants. Moreover, NO is very important or said to be a central molecule of nitrogen cycle. The NO is produced during different biological nitrogen transformation processes. Remarkably, the essential information of NO production and its efficient relations with plant and microbes are poorly characterized. This chapter covers the different processes of NO production in soil, bacteria, and plants and their role in different physiological processes. In particular, the role of NO is addressed as a signaling molecule in plant-microbe interactions including legume-rhizobium symbiosis.

Impact of Agricultural Management Practices on Mycorrhizal Functioning and Soil Microbiological Parameters Under Soybean-Based Cropping Systems

The use of modern agricultural techniques for enhanced production has been advocated, however, its impact on below ground microbial networks is overlooked and adversely affected. The abiotic stresses like temperature (heat, cold chilling/frost), water (drought, flooding/hypoxia), radiation (UV, ionizing radiation), chemicals (mineral deficiency/excess, pollutants heavy metals/pesticides, gaseous toxins), mechanical (wind, soil movement, submergence) are responsible for over 50% reduction in agricultural production. On the other hand, organic farming practices yield fruitful results. This has highlighted the emerging need of switching over to some eco-friendly agricultural practices which can enhance the growth of plant, improve soil quality, mitigate drought without having adverse impacts on environment. Rhizosphere which is the narrow zone surrounding the roots of plant (Hiltner 1904) contains microbial communities which have the potential to benefit plants. Arbuscular mycorrhizal fungi are obligate symbionts which form association with about 90% of the land plant species (Gadkar et al. 2001). However, agricultural practices like tillage, crop rotation, fallowing, organic farming, fertilizers, etc., influence the functioning of AMF in many ways. Soybean is rich in phytochemicals that are beneficial for human beings. The inoculation of soybean and some other crops including cereals, pulses, and other leguminous crops with AMF leads to an enhancement in abiotic stress tolerance, disease resistance, overall growth, soil carbon sequestration, nutrient uptake, etc. This chapter summarizes the overall impact of different agricultural practices on mycorrhiza and other soil microbial communities under soybean-based cropping system.

Microbial Diversity and Soil Health in Tropical Agroecosystems

Microbial diversity is one important factor which controls agroecosystem productivity and quality. Microbial diversity is critical to ecosystem functioning due to its specificity in processes for which microbes are responsible. The presence of diverse soil microbes, bacteria, fungi, and archaea plays a critical role in cycling of major elements (C, N, P) which helps to maintain good soil health. These microbes help in maintaining soil structure, reduce susceptibility to pests and diseases, and eliminate hazardous substances from soil. In this review we addressed two significant questions concerning soil health: (1) how microbial diversity and community structure most effectively describe soil health and can be used as indicators and (2) how can soil health assessed by such indicators be improved or maintained? A summary of available techniques to characterize microbial community structure and diversity is provided, and information pertaining to strategies that can improve microbial diversity in relation to soil health by adopting suitable agricultural practices to sustain soil and crop productivity is furnished. These techniques include those for structural profiling, functional profiling, and other tools being used to assess microbial community diversity and their management through agricultural practices for improving the quality of soil and enhancing the crop productivity. Healthy soil supports high microbial diversity, activity, fertility, nutrient cycling, and disease-suppressive abilities. There is a considerable interest in understanding the nutrient cycles that regulates C, N, and P (carbon, nitrogen, phosphorus) exchange between the soil and atmosphere and how this exchange responds into tropical agroecosystem functioning under diverse edapho-climatic conditions.