Bacillus velezensis FX-6 suppresses the infection of Botrytis cinerea and increases the biomass of tomato plants

Botrytis cinerea causing tomato gray mold is a major cause of economic loss in tomato production. It is urgent and necessary to seek an effective and environmentally friendly control strategy to control tomato grey mold disease. In this study, Bacillus velezensis FX-6 isolated from the rhizosphere of plants displayed significant inhibitory ability against B. cinerea and could promote tomato plant growth. FX-6 could effectively inhibit the growth of Botrytis cinerea mycelium in vitro and in vivo, and the inhibitory rate in vitro could reach 78.63%. According to morphological observations and phylogenetic trees based on sequences of the 16S rDNA and gyrA (DNA gyrase subunit A) genes, the strain FX-6 was identified as Bacillus velezensis. In addition, B. velezensis FX-6 showed antagonistic activity against seven phytopathogens, this indicated that FX-6 had broad-spectrum biocontrol activity. We also found that FX-6 fermentation broth had the strongest antagonistic activity against B. cinerea when the culture time was 72 hours, and the inhibition rate was 76.27%. The growth promotion test revealed that strain FX-6 significantly promoted tomato seed germination and seedling growth. Further deeply study on growth-promoting mechanism indicated that the FX-6 produced IAA and siderophore, and had ACC deaminase activity. The trait of significant biological control activity and growth promoting effect on tomato imply that B. velezensis FX-6 has the potential to be used as a biocontrol agent for tomato gray mold management.