Germplasm Evaluation And QTL Mapping For Flesh Polyphenols In Malus

Polyphenol content is an important indicator of fruit nutritional quality. But high polyphenol content lead to the fruit taste astringent and flesh browning. It has important significance for breeding nutrition and processing new apple varieties, that are research polyphenol of Malus germplasm resources and the mechanism of apple polyphenol accumulation. With the development of molecular markers, polyphenol and browning molecular marker are used in early assisted selection apple. The technology will greatly improve the efficiency of breeding.As analyzed the diversity of fruit polyphenols of germplasm. In 2012 and 2013,16 polyphenol traits (gallic acid, p-hydroxybenzoic acid, catechin, procyanidin B1, chlorogenic acid, caffeic acid, epicatechin, procyanidin B2, p-coumaric acid, m-coumaric acid, trans-cinnamic acid, (2R,3R)-dihydroquercetin, phloridzin, rutin, myricetin, quercetin) were evaluated in 142 accessions (20 species and 10 hybrid). The average content of these 16 polyphenolics were 0.90、36.45、195.14、115.29、 674.85、1041.31、3.22、6.83、0.51、76.09、6.71、1739.81、3.59、1.27、12.06 and2.26μg/g(D.W.). Great differences were found among these specis and inter specis about total phenolic concentrations. The main polyphenols of fruit are chlorogenic acid and proanthocyanidin (catechin, epicatechin, proanthocyanidin B1 and proanthocyanidin B2), and the main polyphenols accounted for more than 88% of the total phenol content. The intraspecific and interspecific variation coefficient of chlorogenic acid and total phenolic content were 0.9342,0.7636 and 0.2386,0.2386. It were showed that interspecific diversity the greater than intraspecific diversity. Using Malus domestica varieties to hybridize is effective breeding practice. In 142 accessions, the highest chlorogenic acid content was found in M. ioensis and M. sieversii 9, the content are 113.68 and 85.03 μg/100g (D.W.), respectively. The howest chlorogenic acid content was found in’Yoshiaki’and’Redgold’, the content are 0.32 and 0.92 μg/100g(D.W.), respectively. The highest proanthocyanidins content was found in ’Wufengshan Crab’and M. ioensis, the content are 170.98 and 91.84 μg/100g(D.W.), respectively. The howest proanthocyanidins content was found in’Redgold’and M.sylvestris, the content are 0.19 and0.99 μg/100g(D.W.), respectively. Excellent germplasm of low browning are’Meile", Jonathan’and NY543".In order to research the development of fruit polyphenols,13 germplasms with differences of main polyphenols consentrate selected from germplasm evaluation.Days after bloom 30,60,90,120 and 150 days, chlorogenic acid, catechin, epicatechin, proanthocyanidin B1 and proanthocyanidin B2 content were mearsured, and the lanthocyanidin reductase and anthocyanin reductase activity, Md-LAR1, Md-ANR and Md-HCT17.2 genes were also analyzted. With fruit expansion, the chlorogenic acid, catechin, epicatechin, proanthocyanidin B1 and proanthocyanidin B2 unit mass concentration continues decreased, and lanthocyanidin reductase and anthocyanin reductase unit mass activity also continues decreased. But polyphenolics content and enzyme activity of per a fruit were increased or didn’t changed. High rise significantly expressed of Md - LAR1, Md - ANR and Md - HCT17.2 genes in the fruits of high polyphenols content germplasm than low polyphenols content germplasm. The results show that dilution effect of fruit polyphenol accumulating is obvious during fruit expansion.Chlorogenic acid and proanthocyanidins content and fruit browning have positive significant correlation in 142 Malus assessions, and the correlation coefficient are 0.3018 and 0.4596. The correlation coefficient of Chlorogenic acid and proanthocyanidins content and fruit browning are 0.3615 and 0.3457, and they have positive significant correlation in 13 assession during fruit development. In ’Jonathan’×’Golden Delicious’ of F1 progenies 544 seeding tree, chlorogenic acid and proanthocyanidins content and fruit browning have positive significant correlation, and the correlation coefficient are 0.2488 and 0.1704. It were show that chlorogenic acid and proanthocyanidins were key incentives of fresh browning. In breeding practice, new line of high chlorogenic acid content and low proanthocyanidins should be selected, and it will has strong antioxidant capacity and not astringency.Using of Mapqtl software and the traits polyphenolic of F1 progenies (198 seeding) in 2014, the QTLs of fruit polyphenol and browning were indentified, and 22 QTLs were taken which were browning, catechin, chlorogenic acid, p-coumaric acid, phloridzin and procyanidins B2. These QTLs arranged in the 5,15,16 linkage group of ’Jonathan’, and in 11,14 and 17 linkage groups of’Golden delicious’. The main effect QTL of chlorogenic acid and catechin in seventeenth linkage group can explain the phenotypic variation of 37.1% and 45.3%. In major QTL peak of chlorogenic acid, according to functional annotation MdHCT (MDP0000307780 and MDP0000371737) genes, which are related biosynthesis of chlorogenic acid, were obtained.The gene expression of MDP0000371737 in accordance with change of chlorogenic acid content, and its coding region exists with mutations in 11. So presumably MDP0000371737 is a key candidate gene of fruit chlorogenic acid synthesis.