BETA-1,3-GLUCANASE ACTIVITY OF 2 SAPROPHYTIC YEASTS AND POSSIBLE MODEOF ACTION AS BIOCONTROL AGENTS AGAINST POSTHARVEST DISEASES

The yeasts Rhodotorula glutinis (isolate LS-11) and Cryptococcus laure ntii (isolate LS-28), showing different levels of antagonistic activit y against a range of postharvest pathogens, were examined for their po ssible mode(s) of action, in order to highlight the reasons for the hi gher 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 hyph ae was observed for the more active antagonist LS-28. The latter isola te was able to produce in vitro significantly higher levels of extrace llular beta-1,3-glucanase activity than LS-11 when grown in the presen ce of hyphal cell walls of the pathogens Penicillium expansum and Botr ytis cinerea as sole carbon sources. In our experimental conditions, a ntibiosis did not appear to be involved in the activity of either anta gonists. (C) 1997 Elsevier Science B.V.