Antifungal potential of Bacillus amyloliquefaciens QY-1 against Alternaria alternata in peppers

Alternaria alternata, one of the most serious pathogenic fungi, causes a range of fungal diseases in pepper plants. In this study, we evaluated the inhibitory effect of QY-1 on Alternaria alternata in vitro, and investigated antagonistic mechanisms of the biocontrol strain QY-1 against A. alternata by transmission electron microscope and transcriptome analysis. We found that the Bacillus strain QY-1 demonstrated potent growth-inhibitory activity against A. alternata. The primary antifungal metabolites of QY-1 were produced from extracellular non-volatile compounds, which achieved an inhibition rate of 96.16% against A. alternata. Fungal cells treated with QY-1 exhibited morphological alterations including cell wall rupture and leakage of intracellular contents. Transcriptome analysis revealed the downregulation of numerous genes encoding the glycosyl hydrolase (GH) and cytochrome P450 (CYP450) families, suggesting that QY-1 may impede or delay the degradation of host plant cell walls by pathogenic fungi. Furthermore, QY-1 exerted its antifungal effects by suppressing fungal cell wall synthesis and compromising the structural integrity of fungal membranes. In vivo trials indicate that QY-1 CFS effectively mitigates A. alternata-mediated postharvest fruit black rot, with a critical concentration threshold of ≥60% (bacteria concentration was 1 × 109 cfu·mL−1) for optimal biocontrol activity.