ACTIVITY OF SECONDARY METABOLITES FROM PENICILLIUM EXPANSUM R82 STRAIN AGAINST POSTHARVEST FUNGAL PATHOGENS

In search for alternative means to conventional fungicides for postharvest disease control, a Penicillium expansum strain (R82) was assayed for its inhibitory activity against mycelial growth and conidial germination of some fungal pathogens. For this purpose a sterile fungal filtrate (SFF) was prepared from malt extract broth previously inoculated with R82 and incubated at 20°C for 10 days. The SFF was tested in vitro for inhibition of mycelium dry weight (DMW) or conidial germination of Botrytis cinerea, Colletotricum acutatum, Monilinia laxa and six P. expansum strains. All pathogens showed a significant decrease of DWM when grown in SFF of R82 with respect to the control. The highest growth inhibition was observed in P. expansum strains (-75.5%) followed by M. laxa (-63%), C. acutatum (-58%) and B. cinerea (-56%). The conidial germination of the six P. expansum strains was not inhibited by SFF and in some cases was stimulated. In all tested strains, microscopic observations of germinated conidia showed a consistent increase of the length of the germ tube compared to the control, however, the treated germ tubes appeared to be abnormal. Since the thin-layer chromatography tests revealed that the extracts from R82 SFF have no inhibitory activity against the target pathogens, a possible action of volatile organic compounds (VOCs) was supposed. The VOCs produced by R82 strain fully inhibited mycelial growth of B. cinerea, C. acutatum and M. laxa, while a growth reduction occurred in P. expansum strains. Conidial germination of B. cinerea, C. acutatum and M. laxa were completely inhibited, while in P. expansum ranged 18.1 to 32%, compared to the control. The potential of VOCs produced by P. expansum R82 strain as biofumigant is discussed.