Role of Antifungal Gallotannins, Resorcinols and Chitinases in the Constitutive Defence of Immature Mango (Mangifera indica L.) against Colletotrichum gloeosporioides

Abstract

Conidia of Colletotrichum gloeosporioides germinate and form infection hyphae on inoculated, immature mango but remain quiescent until fruit ripening. Antifungal resorcinols have previously been implicated for quiescence of C. gloesoporioides and Alternaria alternata on mango. This study revealed the presence of a mixture of several gallotannins with glycosidic linkages, including 1,2,3,4,6-penta-O-galloyl-β-D-glucopyranose, with significant antifungal activity in the unripe mango fruit peel. Gallotannin antifungal activity was greater in a cultivar resistant (295.8 mm2 inhibition) to anthracnose than in a susceptible (148.4 mm2 inhibition) cultivar. In both, the activity decreased with ripening but the decrease was 10% less in the resistant cultivar. Three recorcinols, 5-pentadecylresorcinol, 5-(12-cis-heptadecenyl)resorcinol, AR 21 and another resorcinol derivative were present in the unripe fruit peel and all declined during ripening, more significantly the 5-(12-cis-heptadecenyl)resorcinol and AR 21. Mango latex, when drained out, separates into an oily and aqueous phase. The aqueous phase showed significant chitinase activity and the ability to digest conidia of C. gloeosporioides. The oily phase has previously been reported to contain resorcinols. Draining fruits of latex soon after harvest resulted in greater incidence and severity of anthracnose at ripe stage. Chitinase activity was less in the peel of fruits from which latex was drained. The evidence suggests that the resistance of unripe mango to C. gloeosporioides is because of an elaborate constitutive defence system comprising antifungal resorcinols, gallotannins and chitinases.