Efficacy and mode of action of the biocontrol yeast Meyerozyma caribbica BBJ against blue mold and patulin production by Penicillium expansum

Penicillium expansum is one of the main postharvest pathogens of several fruits including apples, resulting in decay and causing severe economic losses. Furthermore, it might represent a safety issue as the main producer of the mycotoxin patulin. In this study, we investigated the efficacy and related mode of action of the strain BBJ of the yeast Meyerozyma caribbica in controlling blue mold by P. expansum and consequent patulin contamination. The yeast M. caribbica BBJ was selected within a screening of the epiphytic population of apple fruit. It was found to significantly control the incidence of blue mold in apples, apricots, and sweet cherries, reducing in vitro P. expansum growth and patulin presence, showing toxin-degrading abilities. In addition, the results of this study showed that M. caribbica strain BBJ induced resistance in the host tissues, causing an up-regulation of apple defense-related genes, particularly coding chitinase enzyme. These experiments also indicated that yeast BBJ's biocontrol ability against P. expansum relied on competition for nutrients and production of volatile compounds. When tested on a semi-commercial scale, M. caribbica BBJ proved to be effective against apple rots, particularly as a preharvest treatment. In summary, although further large-scale trials are needed, M. caribbica BBJ has the potential to be used as antagonistic yeast against postharvest blue mold of apples and other fruits susceptible to P. expansum infection.