PREFORMED ANTIFUNGAL COMPOUNDS OF LEMON FRUIT - CITRAL AND ITS RELATION TO DISEASE RESISTANCE

The young mature-green lemon fruit manifests a significantly lower lev el of postharvest decay as compared to the older yellow fruit. Inocula tion with Penicillium digitatum Sacc. demonstrated that the resistance of young fruit to decay is related to a factor localized in the oil g lands of the flavedo. The main antifungal compound of lemon flavedo wa s identified as the monoterpene aldehyde citral. The flavedo of green lemon contained 1.5-2 times higher levels of citral as compared to the yellow fruit. In parallel with citral decline, the flavedo extracts o f yellow lemons exhibited an increased level of the monoterpene ester neryl acetate, which exerted practically no inhibitory activity agains t P. digitatum and, in concentrations below 500 ppm, even stimulated d evelopment of the pathogen. During long-term storage of lemon fruit, c itral concentration decreased in parallel with the decline of antifung al activity in the peel and with an increase of decay incidence. It is suggested that the level of citral in the flavedo is related to the r esistance of lemon fruit to postharvest decay.