Biocontrol efficiency and the functional mechanisms of Bacillus velezensis RT-30 against kiwifruit soft rot

Soft rot is a severe postharvest disease affecting kiwifruit production. The management of this disease primarily relies on the use of chemical fungicides. However, biological control using antagonistic microorganisms presents a promising alternative to fungicides. In the present study, whole-genome sequencing identified and characterized Bacillus velezensis RT-30, as a biocontrol strain. The antiSMASH (antibiotics & Secondary Metabolite Analysis Shell) analysis was employed to predict the possible secondary metabolites produced by strain RT-30. In vitro tests demonstrated that RT-30 inhibited the growth of both Botryosphaeria dothidea and Diaporthe phragmitis , while in vivo tests using Actinidia chinensis var. deliciosa ʻXuxiangʼ and ʻCuixiangʼ varieties also revealed a significant control effect. Molecular sequence analysis and Ultra-high pressure liquid chromatography-mass spectrometry (UPLC-MS) analysis of the fermentation filtrate of RT-30 indicated that the biocontrol strain primarily secreted three types of antimicrobial substances: macrolactin, bacillaene, and mycosubtilin. Furthermore, we explored the cultivation conditions of RT-30, recognizing the potential of this versatile bacterium for applications beyond antimicrobial production. This study provides a valuable biological tool for the management of kiwifruit soft rot and deepens our understanding of the biocontrol mechanism of B . velezensis .