Biocontrol yeasts: mechanisms and applications

Abstract

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 yeast-based 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.

Fungal Microbiota of Sea Buckthorn Berries at Two Ripening Stages and Volatile Profiling of Potential Biocontrol Yeasts

“…Four yeast strains, belonging to different genera identified by metagenomics analysis of UB and RB microbiota with referred potential biocontrol properties [15,16,40] (Table S1, Figure 5), were selected for VOCs analysis. Morphologically different SB-18-2 and SB-18-25 yeast strains were recovered from UB berries while SB-18-34 and SB-18-31 yeast strains were isolated from RB berries.…”

“…6-Methyl 5-hepten-2-one (20), 6-methyl-5-hepten-2-ol (23), propionic acid (25) and 2-methylpropionic acid (26) were unique volatiles released by C. wieringae, while only ethyl 3-methylbutanoate (7) was specific for A. pullulans ( Figure 6B, Table 2). Ethyl butanoate (5), ethyl 2-methylbutanoate (6), 3-methylbutyl propionate (13), ethyl hexanoate (16), ethyl octanoate (21), and 2-phenylethyl propionate (31) were exclusively present in volatile blends of H. uvarum yeasts, and phenylmethanol (32) was unique for M. pulcherrima ( Figure 6B, Table 2).…”

“…Numerous microorganisms due to the production of volatile organic compounds (VOCs) have been found to promote plant growth and improve crop productivity [11]. Volatile production, secretion of antifungal compounds, and killer toxins allow for fruit-associated microorganisms to demonstrate increased antagonistic activity, an ability to modulate carposphere microbiota structure, and might mediate interactions with insects [12][13][14][15][16]. The role of bacterial and fungal microorganisms as producers of chemical indicators for the attraction of insects and their communication has also been revealed [17,18].…”

“…Insects from several orders are feeding on fruits, while yeasts use insects either as hosts or vectors [17]. The chemical composition of each blend of volatiles may vary depending on the producing yeast and the ecological niche where the cross-talking species are growing [14,16].The spreading of microorganisms on plants is determined by many factors, such as climatic conditions, application of agrochemicals, plant species, and ripening stage [19][20][21]. Changes in the planting regime alter microbial habitat and diversity, affect functional traits [22].…”

“…Insects from several orders are feeding on fruits, while yeasts use insects either as hosts or vectors [17]. The chemical composition of each blend of volatiles may vary depending on the producing yeast and the ecological niche where the cross-talking species are growing [14,16].…”