Antifungal activity of volatile organic compounds produced by Bacillus subtilis GB519 against blast pathogen Magnaporthe oryzae in rice

The use of microbial-derived volatile organic compounds (VOCs) for the biocontrol of plant diseases has attracted increasing attention. This study, using a two-compartment petri dish assay, investigated the antifungal activity of VOCs produced by <i>Bacillus subtilis</i> GB519 against <i>Magnaporthe oryzae</i>, the causal pathogen of rice blast disease. The results revealed that the VOCs emitted by strain GB519 significantly inhibited the mycelial growth and biomass accumulation of <i>M. oryzae</i> by up to 30.7% and 20.9%, respectively. Exposure to GB519 VOCs disrupted hyphal morphology, increased cell membrane permeability, and induced substantial leakage of intracellular contents, evidenced by significant increases in extracellular pyruvate (59.9%), alkaline phosphatase activity (33.7%), nucleic acids (249.4%), and electrical conductivity (31.8%). Furthermore, VOCs markedly reduced the activity and gene expression of superoxide dismutase (SOD) and catalase (CAT), leading to ROS and subsequent severe hyphal damage. The VOCs also downregulated the expression level of melanin biosynthesis gene <i>BUF1</i> in <i>M. oryzae</i>, which correlated with suppressed lesion development on rice leaves. Additionally, GB519 VOCs exhibited broad-spectrum antagonism against multiple soil-borne pathogens. SPME-GC-MS analysis of the volatilome identified 12 major VOCs produced by strain GB519. Collectively, these results indicate that GB519 VOCs trigger oxidative stress and mitochondrial dysfunction in <i>M. oryzae</i>, thereby exerting potent antifungal effects. These findings provide new insights into the application of microbial VOCs and their bioactive constituents in the sustainable management of blast disease in rice.