| Summary: | The scope of this study was the selection of bacterial strains from rice and maize and evaluation of their potential for plant growth promotion and biological control of rice diseases. 103 bacterial strains isolated from roots, rhizosphere and soil of rice and maize were assayed for production of siderophores, antibiotics, hydrolytic enzymes and HCN. From these, 33 strains were found to produce siderophores, eight were capable of producing diffusible antibiotics and four produced volatile antibiotics, while only one strain was found to produce HCN. Dual culture antagonistic assays were used to select strains capable of inhibiting growth of three major rice pathogens, Xanthomonas oryzae pv. oryzae (bacterial blight), Rhizoctonia solani (sheath blight) and Magnaporthe grisea (rice blast). When inoculated into soils, a number of strains suppressed the incidence of rice blast and sheath blight diseases in two different rice varieties. A strong correlation between siderophore production and in vitro antagonism was found, which extended to biocontrol assays for rice blast disease in the variety Super Basmati, but not Azucena, suggesting that bacterial strains use different mechanisms in suppressing the same pathogen in different rice varieties. As there was no direct contact between the pathogen and bacterial strains, the proposed mechanism for disease suppreSSIOn is induced systemic resistance (ISR). Gene expression analysis for sheath blight experiments confirmed the enhanced induction of chitinase IIb and the peroxidase P0X22.3 by selected bacterial strains. Selected bacterial strains from rice were also observed to enhance plant growth and yield, and this may be related to their ability to fix nitrogen (detected by acetylene reduction assay), solubilize phosphates and/or produce auxin. This study led to the isolation, selection and evaluation of potentially useful bacterial strains from rice and maize that were genetically diverse and persistently abundant in the rhizosphere and can be further utilized for integrated pest management of rice. Moreover, as these strains are . also capable of improving plant health and enhancing grain yield, they could be further utilized either individually or in consortia for integrated nutrient management of rice and maize.
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