Exploring the Biocontrol Potential of Rhizospheric Bacteria against Bipolaris oryzae L. Infecting Rice

Rice brown spot, caused by Bipolaris oryzae, is one of the most significant diseases affecting rice cultivation and was a major contributor to the Bengal famine. The disease continues to threaten rice production, especially in Tamil Nadu. Excessive reliance on chemical fungicides for its control has led to environmental and health issues, necessitating eco-friendly alternatives such as biological control.

Infected rice leaf samples were collected from five major rice-growing districts of Tamil Nadu. The pathogen was isolated and morphologically identified as Bipolaris oryzae, characterized by fusiform, slightly curved conidia with septations. Bacillus isolates were obtained and screened for antifungal activity using dual culture assays. The isolates showing significant inhibition of B. oryzae were further analyzed. Molecular confirmation of the pathogen and bacterial isolates was performed using PCR (Polymerase Chain Reaction) analysis.

Several bacterial antagonists exhibited notable effects against B. oryzae, with isolates BC34 (Alcaligenes faecalis-PV992712), BC 5 (Alcaligenes faecalis-PV991184) and MS8 (Serratia marcescens-PV992713) showing the highest levels of mycelial inhibition. PCR analysis confirmed the identity of both the pathogen as B. oryzae and the effective bacterial strains as Bacillus spp. The results demonstrate that these bacterial antagonists act through multiple mechanisms, including direct antagonism, enzymatic activity and the production of volatile organic compounds (VOCs), highlighting their potential as sustainable biocontrol agents in rice cultivation.