The yeast Wickerhamomyces anomalus acts as a predator of the olive anthracnose-causing fungi, Colletotrichum nymphaeae, C. godetiae, and C. gloeosporioides

Olive tree anthracnose is caused by infection with <i>Colletotrichum</i> fungi, which in Portugal are mostly <i>C. nymphaeae</i>, <i>C. godetiae</i>, and <i>C. gloeosporioides</i> s.s. Severe economic losses are caused by this disease that would benefit from a greener and more efficient alternative to the present agrochemical methods. Yeasts are serious candidates for pre-harvest/in field biocontrol of fungal infections. This work identified the yeast <i>Wickerhamomyces anomalus</i> as a strong antagonizer of the three fungi and studied <i>in vitro</i> this ability and its associated mechanisms. Antagonism was shown to not depend on the secretion of volatile compounds (VOCs), or siderophores or any other agar-diffusible compound, including hydrolytic enzymes. Rather, it occurred mostly in a cell-to-cell contact dependent manner. This was devised through detailed microscopic assessment of yeast-fungus cocultures. This showed that <i>W. anomalus</i> antagonism of the three <i>Colletotrichum</i> proceeded through (i) the adhesion of yeast cells to the phytopathogen hyphae, (ii) the secretion of a viscous extracellular matrix, and (iii) the emptying of the hyphae. Yeasts ultimately putatively feed on hyphal contents, which is supported by light microscopy observation of MB and PI co-culture-stained samples. Accordingly, numerous <i>W. anomalus</i> cells were observed packing inside <i>C. godetiae</i> emptied hyphae. This behaviour can be considered microbial predation and classified as necrotrophic mycoparasitism, more explicitly in the case of <i>C. godetiae</i>. The results support the prospect of future application of <i>W. anomalus</i> as a living biofungicide/BCA in the preharvest control of olive anthracnose.