Bacillus pumilus PTB180 and Bacillus subtilis PTB185: Production of lipopeptides, antifungal activity, and biocontrol ability against Botrytis cinerea

Abstract

Bacillus pumilus strain PTB180 and Bacillus subtilis strain PTB185 were recently reported for their strong in vitro antagonistic activity against several plant pathogens including Fusarium oxysporum, Rhizoctonia solani, Sclerotinia sclerotiorum, Phytophthora capsici, and Pythium ultimum. In this study, strains PTB180 and PTB185 were investigated for the production of lipopetides (LPs), antifungal activity, and biocontrol capabilities against Botrytis cinerea. Strain PTB185 was shown to secrete LPs of the surfactin, iturin, and fengycin families while strain PTB180 was shown to secrete exclusively surfactins. Dual-culture overlay assays indicated that both strains produced antifungal compound(s) that strongly inhibit(s) B. cinerea mycelial growth and conidial germination. The strains were shown to survive for at least 21 days with a survival rate varying from 43% to 61% in the tomato phyllosphere. Survival rate of both PTB180 and PTB185 was approximately 50% when they were applied as a mix (1:1) with almost no variation in the proportion of each strain over time. Preventive foliar applications of the strains alone or as a mix (1:1) reduced significantly (P ≤ 0.01) the incidence and severity of gray mold on tomato plants grown in greenhouse as compared to the control. Incidence and severity of gray mold of tomato plants treated with PTB180, PTB185, or mix of both strains (1:1) were not significantly different. Although PTB180 and PTB185 have a different LPs signature, they showed (1) comparable in vitro antagonistic activity against B. cinerea, (2) comparable survival in the phyllosphere of tomato plants, and (3) comparable biocontrol activity against B. cinerea on tomato plants.