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-b-D-glucopyranose, with significant antifungal activity in the unripe mango fruit peel. Gallotannin antifungal activity was greater in a cultivar resistant (295.8 mm 2 inhibition) to anthracnose than in a susceptible (148.4 mm 2 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.

Retention of latex at harvest, enhanced mango (Mangifera indica L.) fruit resistance and reduced anthracnose and stem-end rot

“…Thin Layer chromatography bioassay studies conducted in the present study failed to detect any antifungal activity due to resorcinols but in a seeded plate assay the incorporation of even 1 % of the non-aqueous oily phase of latex in to the growth medium resulted in retardations of C. gloeosporioides growth (data not provided here). Retention of latex did not alter gallotannins levels in the tissue, since they are located in the peel tissue (Karunanayake et al 2011) and not in the latex. Since mango latex contains a larger proportion of antifungal resorcinols and chitinase activity, retention of latex during harvest could be expected to enhance the fungitoxicity, hence the mango fruit resistance.…”

“…The aqueous phase is a milky and viscous liquid containing mainly proteins and polysaccharides (Oka et al 2004) and chitinases activity (Adikaram et al 2010). The latter has the ability to digest conidia of certain plant pathogenic fungi (Karunanayake et al 2011(Karunanayake et al , 2014. The non-aqueous phase is a yellow-brown liquid with an oil consistency (Robinson et al 1993) and contains most of the fruit resorcinols (Hassan 2006;Bandyopadhyay et al 1985).…”

“…Since mango latex contains a larger proportion of antifungal resorcinols and chitinase activity, retention of latex during harvest could be expected to enhance the fungitoxicity, hence the mango fruit resistance. Karunanayake et al (2011) have shown that the resistance of unripe mangoes to C. gloeosporioides is due to a combined action of a more elaborate system of constitutive defences comprising antifungal gallotannins, resorcinols and chitinases. Hassan et al (2007) found a strong correlation between the level of 5-(12-heptadecenyl) resorcinol and 5-pentadecylresorcinol and the degree of fruit resistance to C. gloeosporioides.…”

“…Significantly higher levels of constitutive resorcinols are present in mango latex than in its peel (Bandyopadhyay et al 1985;Oka et al 2004;Hassan 2006). Mango latex, although less explored, appears to have a direct involvement in the resistance of immature mango fruit to fungal infection (Hassan et al 2009;Karunanayake et al 2011). The work reported in this paper investigated the contribution of mango latex in fruit defence against anthracnose and SER.…”

“…The resistance of unripe mangoes to Alternaria alternata ) and C. gloeosporioides (Hassan et al 2007) has been attributed to a combined action of an elaborate system of constitutive defences comprising antifungal resorcinols Cojocaru et al 1986), gallotannins and chitinase (Karunanayake et al 2011). Gallotannins are present in the peel tissue and the resorcinols are possibly in both the fruit peel and latex (Hassan et al 2009;Karunanayake et al 2011).…”