Wild grape-associated yeasts as a promising strategy of biocontrol against Vitis vinifera fungal pathogens

The increasing level of hazardous residues in the nature and food has led to the European Union to restrict the use of chemical fungicides, addressing the researchers to face this challenge. Exploiting new natural antagonistic microorganisms against fungal diseases could serve agricultural production reducing pre- and postharvest losses. The main aim of this work was to isolate epiphytic and endophytic yeasts from grape berries collected from Vitis vinifera ssp sylvestris populations in the Mediterranean Basin and from Vitis vinifera ssp vinifera cultivars in three different farming systems: organic, biodynamic and conventional. Strains able to prevent fungal pathogenic attacks of grape-berries were selected for in vitro and in vivo antagonism experiments against Botrytis cinerea, Aspergillus carbonarius and Penicillium expansum species. The more effective antagonist yeast strains were subsequently assayed for their capability to colonize and grow in grape wounds. Finally, the possible modes of action: nutrients and space competition, iron depletion, cell wall degrading enzymes, diffusible and volatile antimicrobial compounds, and biofilm formation, were investigated as well. Two hundred and forty-one yeasts strains belonging to 8 species were isolated, 20 of them showed antagonistic action against all molds. Yeast strains isolated from grape-berries from V. vinifera ssp sylvestris were more effective (up to 60%) against B. cinerea rather than other strains isolated from V. vinifera ssp vinifera. Six antagonistic yeasts, all isolated from wild vines, belonging to 4 species (Meyerozyma guilliermondii, Hanseniaspora uvarum, Hanseniaspora clermontiae and Pichia kluyveri) revealed one or more phenotypical characteristics associated to the analysed modes of action.