Understanding the biocontrol mode of action of an epiphytic yeast of apple fruits against Penicillium expansum causal agent of postharvest blue mould

Postharvest biocontrol agents are considered a viable alternative to the use of synthetic chemicals as demonstrated by extensive research conducted worldwide. A yeast isolated from apple fruit proved to be effective in vitro and in vivo against Penicillium expansum, one of the most important postharvest pathogens of fruits and vegetables and a food safety issue as producer of the mycotoxin patulin. In the present investigation, the strain T1 of Meyerozyma caribbica proved to be able to control both fungal growth and patulin accumulation, and, in addition, to greatly affect disease incidence and severity on apples by a mixed mode of action, including both the competition for nutrients, the induction of resistance and the production of antifungal volatiles. Moreover, to evaluate the volatile organic compounds produced by M. caribbica in presence of P. expansum a HD-SPME GC-MS analyses was conducted. A total of 44 volatile compounds were detected in the DDS confrontations; thirteen of them not were accurately identified. These 44 compounds belonged to hydrocarbons (3 compounds), carboxylic acids (7), esters (7), aldehydes (5), alcohols (6), ketones (2), terpenes (4), terpenoids (3), furans (1), and others (6). Yeasts showed relevant differences in their volatile profiles, which presented different compounds associated to their growth. Although further large-scale trials are needed, the selected strain represents a potential interesting biocontrol agent to be applied after harvest.