Antifungal activity and mechanism of volatile organic compounds produced by Bacillus siamensis NEAU-ZGX24 against Botrytis cinerea

Botrytis cinerea, a highly destructive phytopathogenic fungi, infects the plant and fruit of many economically important crops, causing severe economic losses. Here, we obtained and characterized the endophytic Bacillus siamensis NEAU-ZGX24 from Lonicera japonica Thunb, exhibiting strong antagonistic function toward B. cinerea. While this strain produces the cyclic lipopeptide antibiotic iturin A, its primary antifungal effect is mediated through volatile organic compounds (VOCs). The VOCs dramatically suppressed B. cinerea mycelial development, spore germination, and sporulation while also reducing the susceptibility of tomato to fungal invasion. Pot experiments demonstrated that NEAU-ZGX24 effectively suppressed gray mold development in tomato plants. Moreover, the VOCs exhibited broad spectrum antifungal reaction toward multiple phytopathogens, with inhibition rates ranging from 60.11 % to 100 %. Transmission electron microscope observation a significant reduction in mitochondria within B. cinerea hyphae following VOC treatment. Transcriptomic data of B. cinerea under VOC stress revealed significant downregulation of genes associated with key carbohydrate metabolic pathways, including starch and sucrose breakdown, pentose and glucuronate interconversions, pyruvate metabolism, as well as the tricarboxylic acid cycle. Headspace-gas chromatography-ion mobility spectrometry identified 14 NEAU-ZGX24-produced VOCs, among which pentanoic acid, 3-methylbutanoic acid, and ethyl heptanoate were identified as key antifungal compounds. These findings suggest that strain NEAU-ZGX24 has strong potential as a biocontrol agent to antagonize fungal pathogens in agriculture.