Understanding the mechanism of biological control of postharvest phytopathogenic moulds promoted by food isolated yeasts

In this study, a reduction of postharvest decay of table grapes, strawberries and citrus, caused by Botrytis cinerea, Penicillium digitatum, and P. italicum moulds was demonstrated by using in in vivo experiments four food-isolated yeasts strains, Wickerhamomyces anomalus BS91, Metschnikowia pulcherrima MPR3, Aureobasidium pullulans PI1, and Saccharomyces cerevisiae BCA61. Mechanisms of fungal inhibition were elucidated in in vitro experiments. All yeast strains demonstrated antagonistic activity against B. cinerea, P. digitatum, and P. italicum based on competition for nutrients at different level, depending on species and pathogen. The competition for iron, the ability to form biofilm and to colonize fruit wounds were hypothesized as the main mechanisms of action for M. pulcherrima. The biocontrol abilities of S. cerevisiae and W. anomalus strains proved to be correlated with killer phenotype. The production of glucanase, pectinase, and protease, and the ability to colonize the wounds were the most important mechanisms for biocontrol activity in A. pullulans and W. anomalus, which also showed high ability to form biofilm. The production of VOCs with in vitro and in vivo inhibitory effect was observed for all the tested species. It is concluded that the understanding of the multiple and different modes of action of the tested yeast species represents a key step to explain the excellent control of postharvest grey mould and blue and green moulds of grapes, strawberries and mandarin fruits.