Biocontrol Effects and Potential Defence Mechanism of Bacillus velezensis JS6-1 Against Fusarium solani-Induced Postharvest Rots in Muskmelon.

The purpose of this study was to examine the biocontrol effects and potential defence mechanism of Bacillus velezensis JS6-1 in controlling rot in muskmelons caused by Fusarium solani. The results indicated that Bacillus velezensis JS6-1 could directly inhibit the growth of Fusarium solani mycelium and demonstrated high stability of antibacterial activity under varying temperatures, pH levels, and UV exposure times. The volatile organic compounds (VOCs) produced by Bacillus velezensis JS6-1 and the lipopeptide and protein extracts derived from the fermentation broth of Bacillus velezensis JS6-1 both exhibited broad antagonistic activity. Genes associated with the synthesis of the antimicrobial substances iturin, fengycin, and surfactin were identified in the lipopeptide extract obtained from JS6-1. Subsequently, the protein extract from the fermentation broth of Bacillus velezensis JS6-1 was identified, revealing 12 proteins associated with antibacterial activity. Consequently, we applied the Bacillus velezensis JS6-1 for the control of muskmelon decay caused by Fusarium solani. Under greenhouse conditions, the Bacillus velezensis JS6-1 fermentation broth was able to inhibit the decay of muskmelon caused by Fusarium solani. Additionally, the strain enhanced the activity of superoxide dismutase (SOD), peroxidase (POD), and phenylalanine ammonia lyase (PAL) in the fruit, thereby strengthening the fruit's defensive capabilities. In summary, this strain has the potential as a biological control agent for managing postharvest rot.