Endophytic Bacillus amyloliquefaciens Mdgb15 is a potential biocontrol agent against tree peony gray mold caused by Botrytis cinerea

Botrytis cinerea is the causal agent of gray mold disease affecting Paeoniaceae plants. The present study focuses on the potential of Bacillus amyloliquefaciens Mdgb15 as a promising biological control agent toward B. cinerea . The strain Mdgb15 showed the highest inhibition rate (55.56%) among all the strains tested against B. cinerea growth and was effective in controlling tree peony gray mold in detached leaves. A conventional PCR with three specific primer pairs detected lipopetides substance synthesis genes of Mdgb15. The results revealed that Mdgb15 had srfAA , fenA and ituD genes, which resulted in the production of surfactin, fengycin and iturin. An accurate qRT-PCR protocol with specifically designed primers was developed to characterize the expression of lipopeptide synthesis gene of Mdgb15. The qRT-PCR analysis revealed that the expression of the ituD and fenA genes in Mdgb15 was significantly up-regulated during the coculture with B. cinerea . Subsequently, the lipopeptides were extracted by acid precipitation of culture filtrate of Mdgb15 and were separated by Sephadex Gel chromatography. Three separated fractions exhibited strong antifungal activity against B. cinerea , and were identified as bacillomycin D by MALDI-TOF-MS analysis. This study has demonstrated that B. amyloliquefaciens Mdgb15 is a future potential new biocontrol agent for controlling tree peony gray mold disease. It suggests that the antifungal mechanisms of Mdgb15 may be at least partially associated with its ability to secret bacillomycin D.