Efficiency of bacterial isolates on suppressing brown spot in rice plants

Abstract

AbstractMany fungicides can control brown spot, caused by Bipolaris oryzae in rice (Oryza sativa L.), although searching for beneficial microorganisms for biocontrol will improve sustainable integrated pest management. The aim of this investigation was the selection of natural suppressors of the brown spot disease in rice. We performed biochemical (E1), molecular antagonism (E2) and severity suppression (E3) studies under laboratory and greenhouse conditions. The E1, E2 and E3 assays were performed with 21 isolates. The experimental design was completely randomized with three replicates. E1 characterized all 21 isolates for the production of extracellular enzymes, siderophores, biofilm, indole‐3‐acetic acid (IAA) and phosphate solubilization. E2 was conducted to test the in vitro antagonism between the 21 isolates and B. oryzae, and E3 was conducted under greenhouse conditions, where seeds of the rice cultivars BRS‐Primavera and Esmeralda were sown in plastic trays containing 3 kg of fertilized soil. After 45 days, rice leaves were sprayed and inoculated with a mixed suspension of bacterial cells (1 × 108 CFU) and B. oryzae. All of the 21 bacterial isolates produced lipase, N‐fixation, siderophore, IAA, biofilm and solubilized phosphorus. Bacillus cereus, Priestia megaterium, Stenotrophomonas nitritireducens, Serratia marcescens and Serratia nematodiphila reduced radial colony growth of B. oryzae and suppressed brown spot severity by up to 90%. This indicates the potential of these isolates for biocontrol of brown spot in rice as a component of rice disease management.