Possible mechanisms of action of native yeasts against opportunistic spoilage fungi isolated from mature olive fruits

Abstract

Some genera of fungi can affect the quality of mature olive fruits. Aspergillus is one of the opportunistic genera that caused rot and showed potential to produce mycotoxins in olive fruits and derivate products. Yeasts metabolism have presented several advantages as biocontrol agents and different modes of action against fungal pathogens. Elucidation of the possible antifungal mechanisms of yeasts could be used for optimization, formulation, and application of a biocontrol agent. The objective of the work was to determine possible mechanisms of action of native yeasts against A. niger, an opportunistic fungal pathogen of mature olive fruits. Thirteen native yeasts from vitivinicultural (6) and olivicultural (7) environments were employed in the tests since they had shown antagonistic activity at in vitro and on mature olive fruits against two opportunistic fungi belonging to A. niger species (BoAn1 and BoAn2). Four mechanisms of action were evaluated in vitro: a- production of volatile metabolites (V), b- antifungal killer activity (K), c-siderophore production (S), d- hydrolytic enzymes secretion: chitinase (Q) and laminarinase (L). Eleven yeasts presented at least two of the modes of action assayed. The killer activity and volatile metabolites production were the main mechanisms involved in the biocontrol activity of the native yeasts against A. niger. Wickerhamomyces anomalus Bo128, isolated from healthy olive fruit surfaces, presented all the antifungal mechanisms assayed against.