INHIBITORY ACTIVITY OF YEASTS ISOLATED FROM FIG FRUITS AGAINST PENICILLIUM DIGITATUM

Abstract

We report the isolation of 129 yeast from the carposphere of fig fruits capable of inhibiting Penicillium digitatum development on artificially wounded citrus fruits. The wounds were challenged with a pathogen suspension (10 5 or 10 6 conidia ml -1 ) after yeast inoculation (10 cells ml -1 ). The best results (96-100% inhibition) were obtained with the following strains: 5A of Pichia guilliermondii; 43E, 44E and 69F of Candida famata. One isolate, 43E, showing particularly high activity, was further tested in order to better characterise its mode of action against the pathogen. Mechanisms of action were primarily competition for space and nutrients through colonisation of pathogen hyphae, as seen in SEM photographs; it was not possible to detect antibiotic or toxic substance production by the yeast. The isolate 43E of C. famata was found to be compatible with high thiabendazole (TBZ) concentrations (5 g l -1 ). A test was carried out to determine the inhibitory activity at lower cell concentrations than usual (10 7 , 10 6 and 10 5 ml -1 ) and in the presence of TBZ. The fungicide was employed at about one/seventh and one/fifteenth of the concentration in commercial use. The results show that the 43E strain of C. famata, when used together with 0.1 g l -1 TBZ at the concentration of 10 6 cells ml -1 , gives significantly better disease control than either TBZ or the yeast alone.