Study of the efficacy of Aureobasidium strains belonging to three different species: A. pullulans, A. subglaciale, and A. melanogenum against Botrytis cinerea of tomato

The difference in antagonistic activity against the causal agent of grey mould (Botrytis cinerea) of tomato between Aureobasidium strains belonging to three different species, namely A. pullulans, A. melanogenum, and A. subglaciale, was evaluated by in vitro and in vivo assays. In the yeast-pathogen direct interaction experiment, all the strains significantly reduced B. cinerea growth, with A. melanogenum the least efficient species (17.8% of reduction) compared to A. pullulans and subglaciale (22% and 27.8%). The non-volatile metabolites produced by all three species reduced mycelial growth between 95 to 100%. These metabolites were characterized by FT-IR spectroscopy as polysaccharides, lytic enzymes, siderophores, and antibiotics. The inhibitory effect of Aurebasidium strains on pathogenic enzymes such as xylanase, polygalacturonase, and pectinase was measured showing A. pullulans strains as capable of strong inhibition of xylanase, an enzyme directly related to the virulence of necrotrophic pathogens such as B. cinerea. Our data demonstrate that the different species of Aureobasidium isolated from a range of non-conventional environments exerted variable efficacy against B. cinerea, with A. pullulans as the most active species followed by A. subglaciale, and A. melanogenum as ineffective and not suitable for biocontrol applications.