Glycosylated flavonoids: fruit's concealed antifungal arsenal.

Fruit defense against pathogens relies on induced and preformed mechanisms. The present contribution evaluated performed resistance of red and green mango fruit against the fungal pathogen Colletotrichum gloeosporioides and identified the main active antifungal components. High-performance liquid chromatography analysis of nonhydrolyzed mango peel extracts identified major anthocyanin peaks of glycosylated cyanidin 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, seven 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 ß-glucosidase that is induced in both fungus and host during infection process, become more toxic to the fungal pathogen, inhibiting decay development.

Improved Cold Tolerance of Mango Fruit with Enhanced Anthocyanin and Flavonoid Contents.

Red fruits were suggested to be tolerant to cold. To understand cold-storage tolerance of red mango fruit that were subjected to sunlight at the orchard, mango cv. Shelly from inside (green fruit) or outside (red fruit) the tree canopy was stored for 3 weeks at 5, 8 or 12 °C and examined for flavonoids, antioxidant, volatiles and tolerance to biotic and abiotic stress. Red fruit from the outer canopy showed significant increases in total anthocyanin and flavonoids, and antioxidant activity. Ripening parameters for red and green mango fruit were similar at harvest and during storage. However, red fruit with high anthocyanin and flavonoid contents were more tolerant to biotic and abiotic stresses. After 3 weeks of suboptimal cold storage, green fruit showed significantly more lipid peroxidation and developed significantly more chilling-injury symptoms-black spots and pitting-than red fruit. Volatiles of red and green peels revealed significant modulations in response to cold-storage. Moreover, red fruit were more tolerant to biotic stress and had reduced general decay incidence. However, during long storage at 10 °C for 4, 5 or 6 weeks, red fruit showed a non-significant reduction in decay and chilling injuries. These results suggest new approaches to avoiding chilling injury during cold storage.

Induced defense response in red mango fruit against Colletotrichum gloeosporioides.

Mango fruit exposed to sunlight develops red skin and are more resistant to biotic and abiotic stresses. Here we show that harvested red mango fruit that was exposed to sunlight at the orchard is more resistant than green fruit to Colletotrichum gloeosporioides. LCMS analysis showed high amounts of antifungal compounds, as glycosylated flavonols, glycosylated anthocyanins, and mangiferin in red vs. green mango skin, correlated with higher antioxidant and lower ROS. However, also the green side of red mango fruit that has low levels of flavonoids was resistant, indicated induced resistance. Transcriptomes of red and green fruit inoculated on their red and green sides with C. gloeosporioides were analyzed. Overall, in red fruit skin, 2,187 genes were upregulated in response to C. gloeosporioides. On the green side of red mango, upregulation of 22 transcription factors and 33 signaling-related transcripts indicated induced resistance. The RNA-Seq analysis suggests that resistance of the whole red fruit involved upregulation of ethylene, brassinosteroid, and phenylpropanoid pathways. To conclude, red fruit resistance to fungal pathogen was related to both flavonoid toxicity and primed resistance of fruit that was exposed to light at the orchard.