beta-1,3-glucanase activity of two saprophytic yeasts and possible mode of action as biocontrol agents against postharvest diseases

The yeasts Rhodotorula glutinis (isolate LS-11) and Cryptococcus laurentii (isolate LS-28), showing different levels of antagonistic activity against a range of postharvest pathogens, were examined for their possible mode(s) of action, in order to highlight the reasons for the higher activity of isolate LS-28. Competition for nutrients appeared to play a role in the activity of both yeasts, especially in the case of isolate LS-11. Direct interaction with pathogen hyphae was shown only by cells of this same isolate, whereas no interaction with fungal hyphae was observed for the more active antagonist LS-28. The latter isolate was able to produce in vitro significantly higher levels of extracellular beta-1,3-glucanase activity than LS-11 when grown in the presence of hyphal cell walls of the pathogens Penicillium expansum and Botrytis cinerea as sole carbon sources. In our experimental conditions, antibiosis did not appear to be involved in the activity of either antagonists.