Bacillus velezensis Yao Suppresses Fusarium Solani ‐Induced Pepper Root Rot via Fengycin and Induces Systemic Resistance

Pepper root rot, caused by Fusarium solani, is a destructive disease that leads to significant yield losses in pepper crops. In this study, strain Yao was isolated from pepper rhizospheric soil and identified as Bacillus velezensis based on morphological, physiological, biochemical, and molecular characteristics. Strain Yao exhibited strong antagonistic activity against F. solani in dual culture, causing fungal hyphae to be fractured, wrinkled, and shrivelled. In greenhouse pot experiments, strain Yao significantly decreased the incidence of pepper root rot, achieving a controlled efficacy of 73.79%, which was associated with increased activities of the defence-related enzymes (CAT and POD) and enhanced levels of osmotic adjustment substances (free proline, soluble protein, and soluble sugar). Additionally, strain Yao promoted pepper seedling growth by increasing plant height, stem thickness, and both fresh and dry weight, while also improving photosynthetic parameters (Pn, Tr, and Gs) and fluorescence parameters (qP, ETR). Lipopeptides produced by strain Yao, identified through high-performance liquid chromatography (HPLC) and MALDI-TOF MS, revealed fengycin as the main antagonistic metabolite inhibiting fungal hyphae growth. Transcriptome sequencing revealed that differentially expressed genes were primarily enriched in plant hormone signal transduction and the MAPK signaling pathway. Strain Yao induced resistance-related genes, eliciting pepper PTI and ETI defence systems, subsequently challenging F. solani. Overall, B. velezensis Yao shows great potential as a biological control agent (BCA) for managing pepper root rot and as a plant growth-promoting bacterium (PGPB).