The present application relates to a
bacillus velezensis strain B12, a
microbial agent comprising the same and an application thereof. The
bacillus velezensis strain B12 has a high and persistent antagonistic effect on
septoria (especially tomato
septoria), and can play a key role in the biological control of tomato late
blight. Further, through the study of its endogenous metabolites, it is found that the volatile
metabolite 4-hydroxy
coumarin can significantly improve the effect of antagonizing tomato
septoria and preventing tomato late
blight, and thus can be used for developing a more efficient compound
microbial agent. Whether the strain of the present application or the compound
microbial agent thereof has the characteristics of high efficiency, persistence, safety and
environmental protection when used for antagonizing septoria and preventing tomato late
blight caused by septoria, and thus has high industrial value and application prospect.