First Report on Antifungal Activity of Metschnikowia pulcherrima Against Ascosphaera apis, the Causative Agent of Chalkbrood Disease in Honeybee (Apis mellifera L.) Colonies

Chalkbrood is the manifestation of the fungal disease caused by Ascosphaera apis, which affects broods of developing honeybees, particularly in Apis mellifera colonies. Recently, Metschnikowia pulcherrima has been proposed as a biocontrol agent in winemaking and for the management of major postharvest and soil-borne plant pathogenic fungi. In this study, the antagonistic activity of three M. pulcherrima strains against fifteen A. apis strains, isolated from contaminated hives of A. mellifera, was evaluated, with a specific focus on the potential antifungal activity of volatile organic compounds (VOCs). The study revealed that M. pulcherrima was effective against A. apis and that the antifungal activity was related to various mechanisms including competition for nutrients, secretion of pulcherriminic acid, and biosynthesis of specific antifungal VOCs. We also found that each M. pulcherrima strain produced a unique combination of VOCs, and the antifungal activity was strain-dependent and varied depending on the specific yeast-mold combination. In addition, preliminary analyses showed that a temperature of 30 °C and a higher amount of glucose (40 g/L) in the growing medium promote the growth of A. apis. These results could be useful for designing new strategies for the biocontrol of chalkbrood disease in honeybee colonies.