Mechanism of rhizosphere-derived Serratia plymuthica B2 and its volatile organic compounds against postharvest gray mold of tomato.

Gray mold caused by Botrytis cinerea seriously compromises the postharvest quality of tomato fruits, highlighting the need for safe and efficient biocontrol agents. In this study, strain B2 with broad-spectrum antagonistic activity was isolated from the rhizosphere soil of Aucklandia lappa and identified as Serratia plymuthica based on morphological, physiological, biochemical, 16S rRNA gene sequence, and whole-genome analyses. Serratia plymuthica B2 exhibited inhibitory activity against seven phytopathogenic fungi, with a dual-culture inhibition rate of 85.85 ± 0.23% against B. cinerea, and its volatile organic compounds (VOCs) achieved a mycelial growth inhibition rate of 99.70 ± 0.20% and significantly reduced the incidence of postharvest gray mold on tomato fruits. Scanning electron microscopy (SEM) and FDA/PI double-fluorescence staining revealed that B2 compromised the pathogen's cell membrane integrity and downregulated the expression of multiple pathogenicity-related genes. GC-MS identified 32 VOCs, among which dimethyl disulfide (DMDS) and dimethyl trisulfide (DMTS) showed potent antifungal activity, achieving 100% inhibition against B. cinerea at 32 μL/L and 8 μL/L, respectively. Further analysis indicated that B2-emitted VOCs significantly induced the expression of defense-related genes in the salicylic acid (SA) and jasmonic acid (JA) signaling pathways in tomato, thereby enhancing host resistance. Whole-genome sequencing predicted the presence of multiple biosynthetic gene clusters associated with antimicrobial secondary metabolites. Collectively, S. plymuthica B2 exerts effective biocontrol against postharvest tomato gray mold through multiple pathways, making it a promising candidate for developing green biocontrol agents.