Biocontrol activity of novel and known bioproducts based on Bacillus strains and basic products against Botrytis cinerea in tomato fruit

The use of bioproducts based on native microorganisms improves pre- and postharvest disease control by enhancing adaptability during storage and colonizing ability of fruit surface. This study aims to evaluate the effectiveness of three tomato-isolated Bacillus strains (B. cereus 6C, B. thuringiensis 18D and B. velezensis 23A) and of three commercial bioproducts based on B. amyloliquefaciens subsp. plantarum D747, chitosan hydrochloride and Equisetum arvense, alone and in mixture, in controlling B. cinerea on tomato fruit, investigating the possible mechanisms of action involved in the biocontrol activity of bacterial strains. All the tested strains reduced disease incidence and severity by more than 60 % when applied 3 days before pathogen inoculation, in both wound- and dip-treatments, showing performance similar or better than commercial bioproducts. B. velezensis 23A showed the best performance and persistence through time, even when applied 10 days before pathogen challenging. Monitoring of Bacillus population dynamics during tomato storage revealed good survival of the antagonists. Bacillus strains were able to secrete toxic metabolites and enzymes responsible for cell wall degradation. Conversely, the expression of tomato genes involved in salicylic acid (SA) and jasmonic acid (JA) signaling, as well as in pathogenesis related proteins (PRs) biosynthesis, was not induced by B. velezensis 23A. Taken together, the results highlighted that the ability of bacterial strains to colonize the host surface for long periods and to secrete toxic metabolites and enzymes is probably the main factor on which the level of disease control depends. Moreover, this study provides the basis for future developing carposphere-competent bio-inoculants to be used in preharvest for an ecofriendly management of postharvest grey mold.