The role of iturin A from B. amyloliquefaciens BUZ-14 in the inhibition of the most common postharvest fruit rots

The aim of this work was to elucidate the role of the secondary metabolites produced by B. amyloliquefaciens BUZ-14 against B. cinerea, M. fructicola, M. laxa, P. digitatum, P. italicum and P. expansum both in vitro and in planta. The entire cell free supernatant (CFS) and the lipopeptide fraction (LPF) showed similar antifungal activities, completely inhibiting all the fungi at dilutions of 1:24 or even lower, whereas the non-butanolic fraction (NBF) barely inhibited the fungi. However, when the LPF and CFS were applied on fruit, only brown rot in peaches and blue rot in apples was totally inhibited. The main families of metabolites in the LPF were iturin A, fengycin and surfactin with maximum concentrations of 407, 853 and 658 μg mL−1, respectively. Subsequently, a TLC-bioautography revealed iturin A as the key metabolite in the inhibitions and allowed us to establish in vivo MICs of 16.9 and 33.9 μg mL−1 for Monilinia species and P. expansum, respectively. The application of 24 h-old BUZ-14 cultures suppressed brown rot in peaches and also blue rot in apples but failed to inhibit the other diseases. However, BUZ-14 was only able to grow and produce iturin A in peaches so we can deduce that the amount of iturin A brought with the cultures (36 ± 14 μg mL−1) could be enough to control both diseases. The strong antifungal activity of the iturin A present in the BUZ-14 CFS suggests that it could be successfully used for postharvest disease control. However, future research is necessary to maximize the iturin A production by B. amyloliquefaciens BUZ-14 in order to optimize a commercial application. •Lipopeptides of BUZ-14 are the main metabolites for controlling postharvest rots.•Iturin A is the key lipopeptide responsible for direct antibiosis.•Only 17 and 34 μg mL−1 are necessary to suppress brown and blue rots, respectively.•BUZ-14 is able to grow and produce significant iturin A in peaches.•First report quantifying the production of iturin A in fruit.