Yeasts occur in all environments and have been described as potent antagonists of various plant pathogens. Due to their
antagonistic ability, undemanding cultivation requirements, and limited biosafety concerns, many of these unicellular fungi
have been considered for biocontrol applications. Here, we review the fundamental research on the mechanisms (e.g., competition,
enzyme secretion, toxin production, volatiles, mycoparasitism, induction of resistance) by which biocontrol yeasts exert
their activity as plant protection agents. In a second part, we focus on five yeast species (Candida oleophila, Aureobasidium
pullulans, Metschnikowia fructicola, Cryptococcus albidus, Saccharomyces cerevisiae) that are or have been registered for
the application as biocontrol products. These examples demonstrate the potential of yeasts for commercial biocontrol usage,
but this review also highlights the scarcity of fundamental studies on yeast biocontrol mechanisms and of registered yeastbased
biocontrol products. Yeast biocontrol mechanisms thus represent a largely unexplored field of research and plentiful
opportunities for the development of commercial, yeast-based applications for plant protection exist.