Different mechanisms of action of isolated epiphytic yeasts against Penicillium digitatum and Penicillium italicum on citrus fruit

The different modes of action of three isolated epiphytic yeast species (Metschnikowia citriensis FL01(T) and FL02, Candida oleophila FL14 and Pseudozyma antarctica FL17) against Penicillium digitatum and Penicillium italicum were investigated, and they showed better biocontrol efficacy than the P. membranaefaciens strain. These yeast species could be divided into two general classes according to their mechanisms against pathogens: species that caused growth inhibition of pathogens, which were mostly well-adapted to the wound environment, including M. citriensis FL01(T) and FL02 and C. oleophila FL14; species that caused severe cell damage and lysis, similar to P. antarctica FL17. An important mechanism involved in the biocontrol activity of P. antarctica FL17, which showed high lytic enzymes activity responsible for fungal cell wall degradation, was direct parasitism. The biofilm formation, the adhesion to mycelia, and the iron depletion were hypothesized as the key action mechanisms of M. citriensis FL01(T) and FL02. The induction of host resistance and quick growth to colonize wounds played essential roles in the biocontrol activity of C. oleophila FL14. This study indicates that excellent biocontrol yeasts involve multiple modes of action, but yeasts with different morphological characteristics vary greatly in their key mechanisms of action.