Bacillus safensis NI2B displays strong antagonistic activities against rice blast pathogen Pyricularia oryzae through the production of volatile compounds

Abstract Seedling blasts in rice caused by the fungus Pyricularia oryzae are a major problem in nursery boxes. Microorganism-produced volatile compounds (VOCs) are emerging as promising candidates for the development of biofungicides as fumigants to control blast fungus. In this study, we identified an endophytic bacterial strain, NI2B, as Bacillus safensis that completely inhibited mycelial growth and conidial germination of P. oryzae through the production of VOCs. Using gas chromatography-mass spectrometry (GC–MS), we identified eight putative VOCs produced by the NI2B stain. Notably, three of these compounds- 1-octen-3-ol (1O3O), 2,3- dihydro-benzofuran (2,3BF), and 3-methyl-pentanoic acid (3MP)—were reported for the first time in bacteria. Among them, 3MP exhibited the most potent antifungal activity, completely hindering mycelial growth and conidial germination at concentrations of 31.25 and 5.26 μL/L, respectively. Further investigations employing FDA/PI staining and scanning electron microscopy (SEM) indicated that the antifungal effect of 3MP likely stems from alterations in the membrane permeability of P. oryzae . In seedling assays, both NI2B volatiles and 3MP (at 1.0 μL/L) effectively reduced blast disease severity, while other compounds exhibited phytotoxicity to rice seedlings at their minimum inhibitory concentrations. Collectively, these findings suggest that 3MP is a promising biofumigant for the management of rice blast disease in nursery boxes.