Dual efficacy of Burkholderia pyrrocinia C3 volatiles against major postharvest fungal pathogens of citrus: Penicillium digitatum and Geotrichum citri-aurantii

Green mold ( Penicillium digitatum ) and sour rot ( Geotrichum citri-aurantii ) are the most devastating postharvest diseases of citrus fruit, creating an urgent need for eco-friendly biocontrol agents to complement synthetic fungicides. In this study, Burkholderia pyrrocinia C3 was identified through morphological observation, 16S rRNA gene sequencing, and phylogenomic analysis. Its volatile organic compounds (VOCs) inhibited spore germination and lesion expansion in both P. digitatum and G. citri-aurantii . Mechanistically, the VOCs induced accumulation of reactive oxygen species (ROS) and disrupted membrane integrity. Transcriptomic analysis showed that C3 VOCs primarily perturbed amino acid and energy metabolism, as well as oxidative stress pathways. These effects were mediated through altered expression of genes encoding ABC (ATP-binding cassette) and MFS (major facilitator superfamily) transporters, and oxidoreductases, thereby regulating drug resistance, ROS burst, and cell death in the pathogens. HS-GC-MS and plate inhibition assays revealed that C3 VOCs contain a broad spectrum of antifungal metabolites. Among them, dimethyl trisulfide (DT) and methyl phenylacetate (MP) displayed powerful inhibitory activity against P. digitatum. Several volatile compounds, including DT and 2-nonanol, exerted strong antifungal effects on G. citri-aurantii . Notably, both DT and MP could alleviate citrus postharvest decay. However, individual volatile monomers have notable application limitations, whereas the composite VOC mixture from strain C3 suppresses diseases efficiently without significantly impairing fruit quality. These results indicate that C3 VOCs represent a promising biofumigation strategy for citrus postharvest preservation, revealing that the mixed VOCs avoid the phytotoxicity associated with high-dose single compounds.