Analysis of fruit quality, composition of phenolic compounds and expression of genes related to pigment synthesis in ‘Zaosu’ pear and two sport varieties (strains)

Abstract:【Objective】Fruit quality, composition of phenolic compounds and expression level of the genes related to pigment synthesis of‘Zaosu’pear (Pyrus bretschneideri Rehd.) and the two sport vari- eties (strains) were evaluated to provide reference for extension of new varieties in production【. Meth- ods】Using the fruits of‘Zaosu’pear and two sport varieties (strains) as materials, the appearance, inter- nal quality, and composition of phenolic compounds expression level of the genes related to pigment synthesis of the fruits with different storage time were measured 【. Results】The values of brightness and color saturation of the fruits of‘Zaosu’were higher than those of‘Zaosu Red’and its bud sport. After 14 days storage, the values of brightness and color saturation of the fruits of all three varieties (strains) increased, the fruit skins brightened gradually. The content of anthocyanin in the fruits of bud  sport of‘Zaosu Red’was significantly higher than that of‘Zaosu Red’, while the content of anthocy- anin in the fruits of‘Zaosu’was very low. Compared with‘Zaosu’fruits, the single fruit weight and fruit shape index of the two red sport varieties (strains) decreased. The flesh firmness and rupture force of the fruits of three varieties (strains) were significantly different before and after storage, among them‘Zaosu’pear was the lowest and‘Zaosu Red’bud sport was the highest. The flesh firmness and rup- ture force of the fruits of the three varieties (strains) decreased after 14 days storage. In terms of internal quality, the contents of total soluble solids, titratable acid and vitamin C of‘Zaosu’fruits were the high- est, followed by‘Zaosu Red’bud sport and‘Zaosu’. After 14 days storage, the total soluble solids con- tents, titratable acid contents and vitamin C contents of the fruits of the three varieties (strains) de- creased, while the contents of total soluble solids and vitamin C of the fruits of‘Zaosu’were still the highest. While the ratios of solids and acids of the fruits of the two bud varieties (strains) were higher than that of‘Zaosu’before and after storage. 25 kinds of polyphenols were detected in the fruit peels of the two sport varieties (strains), including one simple polyphenol, two phenolic acids, five flavanols, twelve flavonols, three flavonoids and two anthocyanins. The content of arbutin was the highest and peonidin 3-O-galactosidethe was the lowest. respectively. 23 kinds of polyphenols were detected in the in the fruit peesl of‘Zaosu’pear, 2 kinds of anthocyanins (cyanidin galactoside and paeoniflorin galac- toside) were not detected. The content of arbutin was the highest and polyphenols B1 was the lowest, re- spectively. 8 kinds of phenols were detected in the fruit pulps of the three varieties, including one sim- ple polyphenol, two phenolic acids, three flavanols. The content of arbutin was the highest and procyani- din B1 was the lowest. On the day of harvest, the expression patterns of the PpPAL2, PpCHS1, PpCHS2, PpANS, PpUFGT2, PpbHLH and PpWD40 were the same in the fruits of the three varieties (strains), and the expression level of these genes in the fruits of‘Zaosu Red’bud sport was significant- ly higher than those of‘Zaosu’. The expression level of the PpCHI1 was the highest in the fruits of‘Zaosu Red’bud sport, followed by‘Zaosu’and‘Zaosu Red’. The expression level of the PpCHS4was the highest in the fruits of‘Zaosu Red’, significantly higher than those in the fruits of‘Zaosu Red’bud sport and‘Zaosu’. The PyMYB114 was expressed specifically in the fruits of‘Zaosu Red’bud sport on the harvest day and the level of expression decreased during storage. It was lower in the fruits of other two varieties (strains). The expression level of the PpPAL2, PpCHS1, PpCHS2, PpCHI1, PpANS, PpUFGT2, PyMYB114 in the fruits of the three varieties (strains) decreased after 14 days stor- age at 20 °C. The expression patterns of different genes for pigment synthesis in three varieties (strains) were different【. Conclusion】The fruits of the two red bud sport varieties (strains) of‘Zaosu’had a hard texture, and their contents of total soluble solids, titratable acid and vitamin C were all lower than those of‘Zaosu’. Most of the structural genes and regulatory genes were up-regulated in the two sport variet- ies (strains). The expression level of genes related to pigment synthesis might determine the types of coloration of the fruits of the bud sport varieties (strains) in pear.