Valsa canker of the Korla fragrant pear severely reduces yield and fruit quality. Biological control, owing to its environmental friendliness and safety for humans and animals, has become a major focus of recent research on plant disease management. Bacillus species are well known for their antagonistic activity against plant pathogens, and a biocontrol strain previously isolated in our laboratory (Bacillus atrophaeus YL84) exhibited strong inhibitory activity against Valsa pyri. The present study aimed to further evaluate the inhibitory effects of volatile organic compounds (VOCs) produced by YL84 on V. pyri and to elucidate the underlying antagonistic mechanisms. A paired double-Petri-dish assay was employed to evaluate VOC effects on hyphal growth, conidial germination, sporulation, hyphal penetrability, and activities of cell wall-degrading enzymes (CWDEs). Extracellular leakage was quantified to assess cell membrane integrity, while intracellular reactive oxygen species (ROS) levels were assessed by fluorescent probe staining and image analysis. SPME–GC–MS was used to characterize the VOC profile. Results showed that YL84 VOCs significantly inhibited V. pyri hyphal growth, with an inhibition rate of 54.94%. VOC treatment reduced sporulation, abolished hyphal penetrability, and significantly decreased the activities of three CWDEs. The peak extracellular conductivity in the treatment group was 6.15-fold that of the control. ROS levels accumulated significantly over time, with fluorescence intensity increasing by 24.66% and 68.01% on days 3 and 7, respectively, relative to day 1. YL84 VOCs also significantly suppressed toxin biosynthesis, including a 28.97% reduction in protocatechuic acid; assays on detached plant material demonstrated that reduced toxin levels correlated with diminished lesion expansion. Additionally, six potential bioactive compounds, including branched-chain aldehydes and dimethyl disulfide, were identified. In summary, VOCs from YL84 exhibit notable antagonistic activity against V. pyri, providing a theoretical basis for further elucidation of their biocontrol mechanisms and potential application.
Tang et al. (Tue,) studied this question.