Long-term impact of pulses and organic amendments inclusion in cropping system on soil physical and chemical properties.

Mono-cropping of maize-wheat, mechanical disintegration of soils, and continuous chemical fertilization have deteriorated soil health in the Indo-Gangetic Plains. We studied the long-term impact of pulse-based cropping systems with integrated nutrient management on soil physical and chemical properties and yield sustainability. We evaluated four different cropping systems: (1) maize-wheat (M-W), (2) maize-wheat-mungbean (M-W-Mb), (3) maize-wheat-maize-chickpea (M-W-M-C), (4) pigeonpea-wheat (P-W) each with three degrees of soil fertilization techniques: (1) unfertilized control (CT), (2) inorganic fertilization (RDF), and (3) integrated nutrient management (INM). The field experiment was undertaken in a split-plot design with three replications each year with a fixed layout. P-W and M-W-Mb systems enhanced soil properties such as volume expansion by 9-25% and porosity by 7-9% (p < 0.05) more than M-W, respectively. P-W and M-W-Mb increased soil organic carbon by 25-42% and 12-50% over M-W (RDF). P-W system enhanced water holding capacity and gravimetric moisture content by 10 and 11% (p < 0.05) than M-W. Pulse-based systems (P-W and M-W-Mb) had higher available nitrogen (8-11%), phosphorus (42-73%), and potassium (8-12%) over M-W (p < 0.05). M-W-Mb increased 26% maize yield and 21% wheat yield over M-W (p < 0.05) at the thirteenth crop cycle. P-W system had a higher sustainable yield index (p < 0.05) of wheat over the M-W. Thus, pulse inclusion in the cropping system in combination with INM can enhance physical and chemical properties vis-à-vis sustainable yield index over the cereal-cereal system.

Rhizobia: a potential biocontrol agent for soilborne fungal pathogens.

Rhizobia are a group of organisms that are well known for their ability to colonize root surfaces and form symbiotic associations with legume plants. They not only play a major role in biological nitrogen fixation but also improve plant growth and reduce disease incidence in various crops. Rhizobia are known to control the growth of many soilborne plant pathogenic fungi belonging to different genera like Fusarium, Rhizoctonia, Sclerotium, and Macrophomina. Antagonistic activity of rhizobia is mainly attributed to production of antibiotics, hydrocyanic acid (HCN), mycolytic enzymes, and siderophore under iron limiting conditions. Rhizobia are also reported to induce systemic resistance and enhance expression of plant defense-related genes, which effectively immunize the plants against pathogens. Seed bacterization with appropriate rhizobial strain leads to elicitation and accumulation of phenolic compounds, isoflavonoid phytoalexins, and activation of enzymes like L-phenylalanine ammonia lyase (PAL), chalcone synthase (CHS), peroxidase (POX), polyphenol oxidase (PPO), and others involved in phenylpropanoid and isoflavonoid pathways. Development of Rhizobium inoculants with dual attributes of nitrogen fixation and antagonism against phytopathogens can contribute to increased plant growth and productivity. This compilation aims to bring together the available information on the biocontrol facet of rhizobia and identify research gaps and effective strategies for future research in this area.

Development of Mesorhizobium ciceri-Based Biofilms and Analyses of Their Antifungal and Plant Growth Promoting Activity in Chickpea Challenged by Fusarium Wilt.

Biofilmed biofertilizers have emerged as a new improved inoculant technology to provide efficient nutrient and pest management and sustain soil fertility. In this investigation, development of a Trichoderma viride-Mesorhizobium ciceri biofilmed inoculant was undertaken, which we hypothesized, would possess more effective biological nitrogen fixing ability and plant growth promoting properties. As a novel attempt, we selected Mesorhizobium ciceri spp. with good antifungal attributes with the assumption that such inoculants could also serve as biocontrol agents. These biofilms exhibited significant enhancement in several plant growth promoting attributes, including 13-21 % increase in seed germination, production of ammonia, IAA and more than onefold to twofold enhancement in phosphate solubilisation, when compared to their individual partners. Enhancement of 10-11 % in antifungal activity against Fusarium oxysporum f. sp. ciceri was also recorded, over the respective M. ciceri counterparts. The effect of biofilms and the M. ciceri cultures individual on growth parameters of chickpea under pathogen challenged soil illustrated that the biofilms performed at par with the M. ciceri strains for most plant biometrical and disease related attributes. Elicitation of defense related enzymes like l-phenylalanine ammonia lyase, peroxidase and polyphenol oxidase was higher in M. ciceri/biofilm treated plants as compared to uninoculated plants under pathogen challenged soil. Further work on the signalling mechanisms among the partners and their tripartite interactions with host plant is envisaged in future studies.