The use of yeasts, including Wickerhamomyces anomalus, as biocontrol agents of fungi responsible for postharvest diseases of fruits and vegetables has been investigated for the past two decades. Among a variety of mechanisms, the production of glucanases coded by the "killer genes" WaEXG1 and WaEXG2 have been reported to play a role in the ability of yeast to inhibit other fungi. The objective of the present study was to determine the expression of these genes by RT-qPCR, utilizing gene-specific primers, when W. anomalus was grown on grape berries and oranges that were either non-inoculated or inoculated with Botrytis cinerea or Penicillium digitatum, or in minimal media supplemented with cell walls of various plant pathogens and different amounts of glucose. Results indicated that WaEXG2 was more responsive than WaEXG1 to the nutritional environment (including the addition of glucose to cell wall-amended media) in vitro and appeared to play a greater role in the cellular metabolism of W. anomalus. WaEXG2 expression also appeared to be more responsive to the presence of cell walls of P. digitatum and B. cinerea than other fungal species, whereas the same level of induction was not seen in vivo when the yeast was grown in wounded/pathogen-inoculated fruits.
Keywords: Lytic enzymes; Nutritional environment; Postharvest fungal pathogens; Tritrophic interactions.