Broad-spectrum biocontrol of postharvest rot in cold-stored table grapes by psychrotrophic yeasts and grapevine-derived extracts.

Under postharvest conditions, table grapes are exposed to multiple fungal pathogens that coexist and interact on the fruit surface. Therefore, effective biocontrol agents should exert antagonistic activity across multiple pathogens (broad-spectrum biocontrol) while operating within a complex host-microbiota-pathogen system. In this context, four psychrotrophic yeast strains, Metschnikowia pulcherrima RCM2 and ULA146, and Aureobasidium pullulans FUL14 and FUL18, were evaluated for their broad-spectrum biocontrol performance in Red Globe table grapes. Grapevine-derived extracts, rich in phenolic compounds, were included as complementary components capable of enhancing antagonistic activity. Yeasts were tested alone and in combination with extracts from canes (5% and 25%) and bunch stems (5%) on cold-stored table grapes. Treatments were evaluated under three scenarios: single-pathogen inoculation with Botrytis cinerea or Penicillium polonicum, pathogen co-inoculation with B. cinerea, P. polonicum and Alternaria alternata, and non-inoculated storage conditions. A quantitative integrative framework was applied to support the selection of broad-spectrum biocontrol treatments. Overall, the yeast strains showed biocontrol activity against all three pathogens. Yeast-extract combinations significantly reduced P. polonicum infection (p < 0.05). RCM2 exhibited the most consistent performance under pathogen co-inoculation and non-inoculated storage conditions, reaching levels comparable to sulfur dioxide (SO2) treatment. These results support the potential of psychrotrophic yeasts and grapevine by-products as eco-friendly tools for broad-spectrum postharvest disease control in table grapes. They also highlight the importance of integrative approaches that account for pathogen co-occurrence and host complexity when selecting biocontrol agents for successful technological development.