Glycosylated flavonoids: fruit's concealed antifungal arsenal.

Fruit defense against pathogens relies on induced and preformed mechanisms. In this manuscript, we evaluated performed resistance of red and green mango fruit against the fungal pathogen Colletotrichum gloeosporioides and identified the main active antifungal components. HPLC analysis of non-hydrolyzed mango peel extracts identified major anthocyanin peaks of glycosylated cyaniding and methylcyanidin, and flavonol peaks of glycosylated quercetin and kaempferol, which were more abundant on the 'red side' of red mango fruit. Organic extracts of red vs. green mango peel were more efficient in inhibiting C. gloeosporioides. Transcriptome analysis of the mango-C. gloeosporioides interaction showed increased expression of glucosidase genes related to both fungal pathogenicity and host defense. Glucosidase treatment of organic peel extract increased its antifungal activity. Additionally, quercetin and cyanidin had significantly higher antifungal activity than their glycosylated derivatives. Peel extract volatiles treated with glucosidase had antifungal activity. GCMS analysis identified 15 volatiles after glucosidase hydrolysis, 7 of them present only in red fruit. These results suggest that the fruit obtains a concealed arsenal of glycosylated flavonoids in its peel when they are hydrolyzed by β-glucosidase that is induced in both fungus and host during infection process, become more toxic to the fungal pathogen, inhibiting decay development.