Combined application of antagonistic Wickerhamomyces anomalus BS91 strain and Cynara cardunculus L. leaf extracts for the control of postharvest decay of citrus fruit

Combined use of biocontrol agents and plant extracts can be considered a viable and promising strategy for protecting plant tissues with different synergistic mechanisms of action that improve the antimicrobial activity of the mixtures. Treatments of citrus fruits with Wickerhamomyces anomalus BS91 have been previously reported as effective measures to reduce the incidence of green mold caused by Penicillium digitatum. On the opposite, the knowledge of the antifungal activity of cultivated cardoon (Cynara cardunculus L. var. altilis DC.) leaf extract, vegetable widespread in some Mediterranean areas, is still very limited. In this study, experimental trials were conducted to evaluate the effectiveness in vitro of leaf aqueous, methanolic and ethanolic extracts of C. cardunculus against seven fungal pathogens responsible for considerable food losses in the postharvest stage. In addition, biocontrol yeast W. anomalus BS91 and the three C. cardunculus extracts were tested in vivo both as a single treatment and in mixture, against Penicillium digitatum on 'Tarocco' oranges and 'Femminello' lemons. The combination of W. anomalus BS91 and leaf ethanolic extract reduced with the highest efficacy the incidence and severity of green mold on orange and lemon fruits with respect to the control, and was more effective than treatment with antagonistic yeast or leaf extracts applied alone. Incidence and severity of citrus decay were more consistently reduced when mixtures were applied 24 h before the inoculation of the pathogen, thus suggesting the relevance of preventive treatments. The mixtures of antagonistic W. anomalus BS91 and ethanolic leaf extract were more effective in controlling green mold decay on oranges than on lemons. These results indicate that biocontrol agents and leaf extracts, used in appropriate combination, can provide a stronger protection than when used singularly. However, compatibility between microbial antagonist and antimicrobial extract should be preliminary verified.

Keywords: Biocontrol; Citrus; Cynara cardunculus; Green mold; Postharvest; Yeasts.