Native bioagents released phytohormones induce biochemical changes in rice against stem rot and false smut diseases

Abstract Rhizosphere essentially harbours native bioagents that are beneficial to plants growth and development, stress tolerance and competitive advantage over its rivals. The bioagents often exhibits multiple mechanisms including secretion of secondary metabolites, phytohormones and defense enzymes to offer such advantages to the host plants. Stem rot and false smut caused by Sclerotium hydrophilumand Ustilaginoidea virensrespectively, are two major constraints in India and other countries where rice is cultivated. There are reports on the critical role of microbial phytohormones viz., ABA and SA, IAA, GA, zeatin on growth and stress of plants. They play a role in the regulation of plant immune responses by eliciting induced systemic resistance (ISR) in host plants against invading pathogens. Accordingly, we studied the activity of native bioagents viz., Trichoderma asperellum strain TAIK 1, Bacillus cabrialesii strain BIK3, Pseudomonas putida strain PIK1 and Pseudomonas otitidis strain POPS1 on enhancement of plant growth, increase in defence enzymes and reduction in severity of stem rot and false smut diseases of rice. We followed the Liquid Chromatography Electrospray Ionization Tandem Mass Spectrometric (LC-ESI-MS/MS) method for the analysis of the phytohormones viz., IAA, GA, Zeatin, SA and ABA released by the bioagents. Bioagents treated plants showed 100% germination, enhanced plant growth parameters and reduction in percent disease index like 20.98% (stem rot), 23.14% (false smut) over the control plants (70.01% for stem rot and 75.24% for false smut). Our study indicated a direct relationship between the number and intensity of phytohormones released by the bioagents and the plant growth and disease suppression in rice.