Abstract
Cranberry is a popular fruit due to its reported health benefits, including antibacterial and antioxidant properties. Fruit rot disease complex caused by several fungal pathogens and root rot disease caused primarily by Phytophthora cinnamomi are common causes of major losses in commercial fruit production and negatively affect fruit quality. It is important to investigate the pathogenesis of these diseases in common cranberry cultivars and their effects on production of flavonoids and other phenolics. The objective of this study was to determine the influence of fungal infections on the content of p-coumaric acid and quercetin derivatives, compounds that contribute to fruit quality and may also serve as markers of plant health. Plants were sampled in MA during the 2016 growing season, including 'Stevens', the most commonly grown cultivar worldwide, and three popular cultivars, 'Early Black', 'Mullica Queen' and 'Demoranville'. Identification and quantification methods were developed to analyze p-coumaric acid derivatives and quercetin derivatives in cranberry leaf flower and fruit tissues extracts using Waters ACQULTYTM UPLC-Q-TOF-MS system with a BEH C18 column. This UPLC-MS/MS method was proved to be a rapid method with high selectivity. In addition, it provided an ability to identify and quantify p-coumaric acid and quercetin derivatives simultaneously. Exposure to the two fungi produced different responses in certain cultivars. The total contents of p-coumaric acid and quercetin derivatives were significantly higher in Phytophthora infected 'Stevens' cultivar leaf flower and fruit compared to similarly healthy components, suggesting possible resistance of 'Stevens' to the impact of Phytophthora. Infection by fruit rot fungi reduced total p-coumaroyl and quercetin derivatives (Total 16 compounds) in 'Stevens' and 'Early Black' cultivars leaves, flowers and fruits, suggesting that this disease may negatively impact fruit quality. For cultivars 'Mullica Queen' and 'Demoranville' healthy and infected plants exhibited few differences in phenolic composition, suggesting that these cultivars may be less susceptible to fruit rot fungi than 'Stevens' and 'Early Black'. Of the cranberry leaf flower and fruit, the flower was most sensitive to Phytophthora infection. P-coumaroyl and quercetin derivatives may be considered specific markers of response to fungal stress and protect the plant by prolonging the non-destructive latent phase of some fungi in cranberry plants. The defense mechanisms of cranberry and their impact on phytochemical profiles need further study. The p-coumaric acid and quercetin derivatives contents in different cultivars including both cultivated and wild plants were compared using the same method in this study. Quercetin-3-galactoside and quercetin-3-arabinofuranoside were the most abundant quercetin derivatives in cranberry leaves, flowers and fruits. 1-p-coumaroylquinic acid and 6,7-dihydro-2,3'-p-coumaroyl iridoid glycoside (trans) were the most abundant p-coumaric acid derivatives in cranberry leaves, while the 2',3-p-coumaroyl iridoid glycoside (trans) and 6,7-dihydro-2',3'-p-coumaroyl iridoid glycoside (trans) were the most abundant p-coumaric acid derivatives in cranberry flowers and fruits. Principal component analysis of the mass spectra showed that some of the p-coumaric acid and quercetin derivatives contributed to the variations between the healthy and infected samples, cultivated and wild plants, and the leaf, flower and fruit samples..