Antifungal potential and mechanism of 2-methylbutyric acid, a volatile organic compound produced by Bacillus subtilis JY-7-2L, against Agroathelia rolfsii

Volatile organic compounds (VOCs) produced by Bacillus subtilis JY-7-2L showed strong antagonistic activity against Agroathelia rolfsii . This study investigated the antifungal activity and mechanism of 2-methylbutyric acid (2-MBA), one of the VOCs produced by B. subtilis JY-7-2L, through transcriptomic, metabolomic, and physiological analyses. 2-MBA significantly inhibited the growth of A. rolfsii both in vitro and in vivo , with significant inhibition observed at concentrations as low as 6.5 µL/L and 100% inhibition achieved at 65.0 µL/L. Under pot and field conditions, both 2-MBA and sodium 2-methylbutyrate significantly reduced southern blight disease index and promoted plant growth. Transcriptomic and metabolomic analyses indicated that 2-MBA induced significant differences in gene expression and metabolite production, mainly related to mitochondria, energy reservation, cell wall, and cell membrane of A. rolfsii . We detected that 2-MBA induced significant reactive oxygen species (ROS) accumulation, elevated hydrogen peroxide level, and decreased catalase activity in A. rolfsii . 2-MBA also impaired the integrity of cell wall and membrane of A. rolfsii . 2-MBA exhibited substantial potential as an effective fumigant to control southern blight of Aconitum carmichaelii caused by A. rolfsii . The potential mechanisms of 2-MBA to suppress the growth of A. rolfsii include ROS stress, cell wall disruption, and cell membrane impairment.