Regulation of microbial dynamics and nutrient status in the rice micro ecosystem due to application of bioagents for management of bacterial blight of rice

Abstract

The present study was made to evaluate an ecofriendly management newlinestrategy using different microbe based bioformulations, viz., Bioveer (Talc based newlineformulation of T. viride), Biotime (Talc based formulation of M. anisopliae, newlineP. fluorescens and T. harzianum), Biogreen (Talc based formulation of T. viride, newlineP. fluorescens, B. thuringiensis, B. bassiana and M. anisopliae), Biosona (Talc based newlineformulation of B. bassiana) and Biofor-Pf (Vermicompost based formulation of newlineT. harzianum and P. fluorescens) for management of bacterial blight (BB) of rice newlinecaused by Xanthomonas oryzae pv. oryzae (Xoo). Regulation of microbial dynamics and newlinenutrient status in rice micro-ecosytem due to application of these bioformulations was newlinealso assessed. About 30 isolates of Xoo were collected, of which Xoo2 was selected for newlinefurther experimentations, due to its aggressiveness in causing BB in rice. In vitro newlineefficacy results revealed that Bioveer was significantly highest in inhibiting the growth newlineof Xoo (54.14%). Field evaluation of bioformulations against BB showed lowest disease newlineincidence (29.20%) and disease severity (29.43%) when Biogreen was applied as seed newlinetreatment, seedling root dip treatment and foliar application at 2% along with newlineenhancement in rice grain yield (31.06 q/ha) and plant growth parameters. The total newlinephenol content (23.16%) was significantly highest in rice leaves treated with Biogreen newlineat 2%. Moreover, Biogreen at 2% was most effective in increasing the nutrient newlineavailability and uptake in rice plants and enhancing the microbial biomass carbon and newlinesoil enzyme activity. Population dynamics study of both endophytic and rhizospheric newlinemicrobes revealed that maximum colonization frequency of both bacterial and fungal newlinedynamics was associated in rice plots treated with talc based bioformulation Biogreen newlineat 2%. The study also revealed higher count of bacterial diversity as compared to fungal newlinediversity. Two endophytic (EPK 5 and EPK 10) and rhizospheric (RPK 2 and RPK 8) newlinemicrobes showed maximum inhibition against Xoo in vitro, which were found newlinecompatible among each other. Based on morphological, cultural, biochemical and newlinemolecular gene sequencing studies, the isolate EPK 5 was identified as Pseudomonas newlinefluorescens, RPK 2 as Bacillus amyloliquefaciens, EPK 10 as Trichoderma asperellum newlineand isolate RPK 8 as Talaromyces flavus. Compatible combination of these microbes newlinecould inhibit the growth of Xoo in vitro. Five best compatible combinations were tested newlinefor in planta along with a Biogreen at 2% for suppression of BB. Studies revealed that newlinecombination of EPK 5 (P. fluorescens) + EPK 10 (T. asperellum) + RPK 2 newline(B. amyloliquifaciens) + RPK 8 (T. flavus) showed lowest BB incidence (17.75%) with newlinehighest grain yield (46.74 g/plant) and growth attributing characters. newline