Mode of action of an isolate of Candida famata in biological control of Penicillium digitatum in orange fruits

Biological control of Penicillium digitatum on orange fruits with an isolate of Candida famata (F35) obtained from fig leaves in Sardinia is reported. Inhibition values of from 90% to 100% in oranges were obtained in artificially wounded fruits, in terms of pathogen conidia concentration. Scanning electron microscope observations of the mode of action of the antagonist against the pathogen revealed rapid colonization of the fungal mycelium and the wounds, with lyric and phagocytic activity against the hyphae. With regard to the host-antagonist-pathogen interaction, it was observed that when the yeast was inoculated into the artificial wounds either alone or with the pathogen, it stimulated the fruit to produce phytoalexins (scoparone and scopoletin) in concentrations which varied significantly in relation to the time lag between inoculation with the antagonist and inoculation with the pathogen. The biosynthesis of scoparone in particular, four days after inoculation with the yeast only, was 124 mu g/g fresh weight of the fruit, 12 times higher than in the non-inoculated wound tissues, while it decreased to 47 mu g/g when F35 was inoculated at the same time as P. digitatum, and to 37 mu g/g when the pathogen only was inoculated.