Limiting the production of virulence factors as a mechanism of action for the control of Penicillium expansum by the Antarctic antagonistic yeast Debaryomyces hansenii F9D

Fungal decay, predominantly caused by Penicillium expansum, is the main cause of apple postharvest losses. To overcome this problem, synthetic fungicides are applied to fruit before storage. Public concern about this practice has raised interest in developing alternative biocontrol strategies for postharvest diseases. Debaryomyces hansenii F9D, a psychrotrophic Antarctic yeast, has been previously selected as a promising biocontrol agent due to its ability to reduce blue mold incidence in apples and pears. Previous in vitro studies indicated that the biocontrol mechanism of this yeast does not involve the production of antifungal metabolites or other inhibitory or competitive interactions with the pathogen. In this work, we conducted further studies in order to understand the interaction between Penicillium expansum and D. hansenii F9D within apple wounds. The growth of both microorganisms in apple wounds during cold storage was followed over time by q-PCR and viable cell counts. Scanning electron microscopy observations of co-inoculated and control wounds (inoculated only with the yeast or with the pathogen) were conducted to evaluate if the pathogen conidia could germinate in presence of the yeast and to determine the colonization patterns of P. expansum and the biocontrol yeast. Our results indicate that Debaryomyces hansenii F9D is able to prevent cold stored apples' wounds rot by inhibiting the virulence factors produced by the pathogen without impeding its growth. These findings provide circumstantial evidence for a new biocontrol mechanism associated with the prevention of fungal decay in apples by biocontrol yeasts during cold storage of fruit.