Biocontrol Efficacy and Mechanisms of Bacillus velezensis AP6 Against Brown Rot in Yam by Fusarium solani

Yam is a valuable traditional Chinese medicinal and nutritional crop that has gained significant popularity in recent years. However, the production of yam is severely impacted by brown rot caused by Fusarium solani, which affects both yield and quality. In this study, we isolated a promising biocontrol strain, designated AP6, from the rhizospheric soil of healthy yam. Strain AP6 exhibited strong antagonistic activity against F. solani, with an inhibition rate of 60.2%, and demonstrated broad-spectrum antagonistic activity. Based on morphological, physiological, biochemical characteristics, and whole-genome sequencing, this strain was identified as Bacillus velezensis. Strain AP6 can produce siderophores, amylase, protease, cellulase, and form biofilms. It can also change the hyphal morphology of F. solani, inhibit spore germination, reduce the viability of pathogens, and alleviate the disease severity of yam. Additionally, strain AP6 was shown to induce the accumulation of reactive oxygen species in yam, thereby enhancing the yam’s defense responses. Field application trials demonstrated that a wettable powder formulation of strain AP6, when combined with commercial metalaxyl-M and fludioxonil, significantly reduced the incidence of brown rot in yam. These findings indicate that B.velezensis AP6 is a promising biocontrol agent, providing a practical and sustainable approach for integrated disease management in yam.