Abstract

Post-harvest rots are the main limiting factors in storing horticultural products. Currently, control of postharvest citrus diseases relies mainly on synthetic fungicides. Biologicalcontrol using naturally occurring substances has been recently explored for managing postharvest decay of citrus fruit. Essential oils of three medicinal plants (Ocimum basilicum, Mentha pulegium and Cassia angustifolia) were tested for their antifungal activity against the principal postharvest fungal pathogens of citrus fruit, that is Penicillium digitatum, Aspergillus flavus and Alternaria alternata at two storage temperatures (6 and 25°C). The three pathogenic fungi were collected from diseased Citrus sinensis Osbeck(cv. Valencia) from a citrus storage of Jahrom. Fruit epicarp of cv. Valencia was wounded by the tip of a sterilized pin and 15 ml of three concentrations of each essential oil suspension (200, 400 and 600 ppm) plus 0.5 ml Tween 20 were sprayed on the outer skin. The experimental samples were stored in plastic bags at 6 and 25°C for two months, with six replications per treatment. There were significant differences in infection percentages at the two temperatures. Applying different concentrations of essential oils, at both temperatures, reduced the percentage of fruits infected by fungi compared to controls. At 25°C, C. angustifolia and O. basilicum essential oils at 200 ppm, and 200 and 400 ppm of M. pulegium, caused minimum infection percentages by Al. alternata. Cassia angustifolia essential oil at 200 and 400 ppm had the same effect on infection percentages and gave the lowest infection percentages by As. flavus and P. digitatum. At 6°C the effects of all concentrations of tested essential oils on infection percentages by Al. alternata and As. flavus were the same and differed from controls. In the case of P. digitatum there were no differences for the different concentrations of C. angustifolia andM. pulegium essential oils. For O. basilicum essential oil, the highest and the lowest infection percentages by P. digitatum were for the 200 and 600 ppm concentrations, respectively. In summary, at 25°C, C. angustifolia essential oils cause the lowest infection percentages to all tested fungi. At 6°C the effects of all tested essential oils on infection percentages to all tested fungi were alike.

Key words: Ocimum basilicum, Mentha pulegium, Cassia angustifolia, Penicillium digitatum, Aspergillus flavus, Alternaria alternata, Valencia cultivar, storage.