Streptomyces sp. FX13 inhibits fungicide-resistant Botrytis cinerea in vitro and in vivo by producing oligomycin A.

Botrytis cinerea is one of the most destructive fungal pathogens which can cause gray mold diseases of numerous plant species, while the frequent applications of fungicides also result in the fungicide-resistances of B. cinerea. In this study, a new Streptomyces strain FX13 was obtained to show biocontrol potentials against fungicide-resistant B. cinerea B3-4. Its in vitro and in vivo antifungal mechanisms were further investigated. The results showed that the culture extract of strain FX13 could significantly inhibit the mycelia growth of B. cinerea B3-4 with the EC value of 5.40 mg L, which was greatly lower than those of pyrisoxazole, boscalid and azoxystrobin. Further bioassay-guided isolation of the extract had yielded the antifungal component SA1, which was elucidated as a 26-membered polyene macrolide of oligomycin A. SA1 could inhibit the mycelia growth, spore germination, germ tube elongation and sporogenesis of B. cinerea B3-4 in vitro, and also showed significant curative and protective effects against gray mold on grapes in vivo. Moreover, SA1 could result in the loss of membrane integrity and the leakage of cytoplasmic contents, which might be related to the accumulation of reactive oxygen species (ROS) and membrane lipid peroxidation. Besides, intracellular adenosine triphosphatase (ATPase) activity and adenosine triphosphate (ATP) content of B. cinerea B3-4 decreased after SA1-treatment. Overall, the oligomycin A-producing strain FX13 could inhibit fungicide-resistant B. cinerea B3-4 in vitro and in vivo, also highlighting its biocontrol potential against gray mold.