Alkenylresorcinols in Peel of ‘Kensington Pride' Mango Have Antifungal Effects against Anthracnose Disease

Mango are a sought after tropical fruit that suffers from a short storage life. Anthracnose disease caused by the fungus Colletotrichum gloeosporioides is the most common postharvest disease responsible for quality deterioration in mango, and although commercial fungicides can control the disease, we are interested in compounds within the peel that can assist in natural postharvest disease control. Alk(en)ylresorcinols are secondary metabolites that are present in the peel and sap of mango fruit, and when mangoes are harvested, they are typically desapped, resulting in the loss of these metabolites. Here we report on the changes in concentration of two alk(en)ylresorcinols in mango peel during fruit development and ripening and results of preliminary tests on the effects of these compounds on C. gloeosporioides spore germination. ‘Kensington Pride’ mango fruit were sampled during growth in the orchard, at commercial harvest, and during ripening at 22 °C. Peels were taken, extracted in 95% ethanol, partitioned with dichloromethane, evaporated to dryness and resuspended in ethyl acetate before being separated and identified by HPLC. Ethyl acetate extracts were also run on thin layer silica gel chromatographs and identified spots were removed from the plates, extracted in ethanol and tested for their ability to inhibit germination of anthracnose spores and growth of mycelium. The results indicate that two identified alk(en)ylresorcinols (5-n-heptadecenylresorcinol and 5-n-pentadecylresorcinol) were present in higher concentrations during early fruit development compared with the mature-green fruit, but that the concentrations did not change from mature-green to eating ripe. Alk(en)ylresorcinol concentrations were 2-3 times higher in the peel of the sun-exposed side of the fruit than in the shaded side. Peel extracts eluted from thin layer chromatography plates inhibited germination of spores of C. gloeosporioides, and inhibited growth of cultures on agar plates. The results suggest that the alk(en)ylresorcinols have antifungal activity against C. gloeosporioides, the causal organism of anthracnose disease in ‘Kensington Pride’ mango. More extensive testing is needed, but with ‘Kensington Pride’ the desapping process at harvest removes much sap containing natural secondary compounds that can help protect the fruit against postharvest disease.