Abstract: Gray mold caused by Botrytis cinerea has been found to be the main fungal disease of tomato fruit. The dual culture method was used to screen for Bacillus strains with significant antagonistic activity to B. cinerea. Further testing of control efficiency was completed by spraying the antagonistic bacterium and its fermentation supernatant on tomato fruits. ESI-MS was utilized to detect main antifungal substances in the antagonistic bacterium’s fermentation supernatant crude extract. Further analysis using PCR allowed for the detection of genes related to antimicrobial substances synthesis. The species of the antagonist bacterium was identified through its colony and cell morphology，physiological and biochemical tests，and 16S rDNA and gyrB analysis. The control effect of the screened antagonist fqhm-13 and its fermentation supernatant on gray mold of tomato fruit was identified to be 69.0% and 78.1%，respectively. The main antimicrobial substances in the qhm-13 fermentation supernatant crude extract include lipopeptide antibiotics of C14–C16 surfactin A and C15–C17 iturin A. PCR detection showed.that the genome of fqhm-13 contained genes related to antibiotic synthesis，such as ituC，ituD，fenD and srfAB. Through species identification techniques，strain fqhm-13 was identified as Bacillus amyloliquefaciens. This study laid the foundation for the use of B. amyloliquefaciens and its metabolites to prevent and control gray mold on tomato fruit.

Key words: trifoliate, pH, cell wall, pectin, cellulose, boron content