Induction of defense-related enzymes and enhanced disease resistance in rice against Sarocladium oryzae by Bacillus cereus RBS-57

Bacillus species have been identified as effective bioagents and plant growth boosters in rice. Currently, there is limited research on the effectiveness of Bacillus strains in managing the sheath rot disease of rice caused by Sarocladium oryzae, a significant threat to rice-cultivating areas in India. The aim of this study was to evaluate the efficacy of Bacillus spp. to control the sheath rot disease and promote growth in rice plants. We investigated the in vitro antagonistic activity and growth-promoting potential of eighty-four Bacillus spp. against S. oryzae. Ten efficient strains were carefully selected and analyzed at the molecular level based on their capacity for antagonism and growth promotion. A PCR study of the potential strains has revealed the presence of lipopeptide genes that produce bacilysin, bacillomycin, iturin, surfactin, subtilin, subtilosin and fengycin. Among the strains, RBS57 had the highest mycelial growth inhibition (74.44 %) of the pathogen as well as the highest number of antibiotic genes (6). The efficacy of talc and liquid formulations of Bacillus strains BS-5, RBS-57, and RBS-3 was further tested against sheath rot disease. Results indicated that a combined application of seed treatment + seedling dip + foliar spray of RBS-57 liquid formulation under pot culture conditions, showed a considerable reduction in the incidence of sheath rot disease, followed by BS-5 and RBS-3. Similarly, a significant increase in the plant growth attributes and yield was observed with RBS-57, when compared to the other treatments. Enzymatic activities such as PO, PPO, PAL, CAT and SOD were induced in the rice sheath by B. cereus (RBS-57) treatment. Real-time expression analysis was performed to validate the fold changes in defense enzymes and reactive oxygen species. The effectiveness of RBS-57 liquid formulation in reducing disease incidence was demonstrated when applied as a combination of seed treatment @ 10 ml/l + seedling dip @ 10 ml/l + foliar spray @ 10 ml/l. Moreover, higher defense enzyme activities, maximum plant growth promotion and higher yield were reported with RBS-57 treatment. This study has the potential to be exploited to manage sheath rot disease in an eco-friendly and sustainable manner.