Postharvest yeast treatments control strawberry rots and shift the fruit microbiome

Strawberries are highly perishable fruit and managing postharvest decay remains a major challenge. Biological control agents have gained increasing attention as sustainable alternatives to synthetic fungicides. However, their effects on the fruit-associated microbial communities as well as on quality parameters have not been widely investigated. This study explored the use of antagonistic yeasts as a sustainable strategy to control postharvest decay on strawberries, focusing on the selection of effective strains and on evaluating the impact of their use on fruit quality and microbiome. Epiphytic and endophytic yeasts were screened for their biocontrol activity on naturally infected fruit. The most effective strains, identified as Aureobasidium pullulans and Metschnikowia pulcherrima, were further tested for their efficacy. The applied yeasts significantly reduced gray mold incidence and severity compared to the untreated control after 10 days of cold storage and two days of shelf-life, showing results comparable to those of a commercial M. fructicola-based biofungicide. None of the treatments, however, had any significant effect on key fruit quality parameters, such as firmness, total soluble solids and titratable acidity. Metabarcoding analysis revealed that yeast application significantly affected the fruit microbiome, reshaping both fungal and bacterial communities. The antagonistic strains generally successfully colonized the fruit surface and reduced Botrytis abundance. Furthermore, they promoted the development of beneficial fungal and bacterial taxa, particularly Achromobacter. These findings suggest that mechanism of action of yeast biocontrol agents extends beyond direct pathogen inhibition, fostering interactions with resident microbial communities and contributing to the establishment of a beneficial fruit microbiome to prevent disease development.