Objective This study elucidated the antifungal rate and mechanism of lipopeptide extracts from Bacillus amyloliquefaciens against Alternaria alternata in tomatoes, aiming to provide scientific basis for green control of black spot disease in tomatoes.

Method A alternata, the dominant pathogen of tomato black spot, was taken as the research object. The antifungal mechanism of B. amyloliquefaciens lipopeptide extract on A. alternata was investigated through in-dish antifungal test, scanning electron microscope (SEM) observation test, in vitro fruit test and transcriptomic analysis.

Result In-dish antifungal test showed that the inhibition rate of B. amyloliquefaciens lipopeptide extract on the growth of A. alternata colony was 56.00% and the inhibition rate on mycelium biomass was 60.14% on the seventh day of culture. SEM showed that lipopeptide extracts treatment could lead to distortion and collapse of A. alternata mycelium and spores. In vitro fruit test showed that the diameter of tomato black spot disease lesion decreased by 89.97% after inoculation with lipopeptide extract. Compared with the control group, the incidence of black spot decreased from 17.94% to 6.25%, and the control effect of black spot disease was 65.16%. Transcriptome sequencing was performed on A. alternata mycelium treated with lipopeptide extract and untreated, and the differential genes of MAPK signaling pathway and glycolysis/gluconeogenesis signaling pathway were analyzed, respectively. And it was found that the gene encoding Ras homologous gene family A (Rho1) was significantly up-regulated. The genes encoding protein Ste50, glucose-6-phosphatase, hexokinase, pyruvate carboxylase and 6-phosphofructokinase were significantly down-regulated. These up-regulated and down-regulated genes may be the key genes related to the inhibition of A. alternata growth by lipopeptide extract.

Conclusion The lipopeptide extract can inhibit the growth of A. alternata by destroying spore and mycelium structure and regulating the expression of key genes.