Comprehensive evaluation on the fruit quality of different age secondary branches in ‘Huizao’ jujube

Various modes are adopted in fruit tree cultivation, according to the growth and development of tree species and varieties, local climate, geography, water and soil resources, and human activities. There are also differences in shaping and pruning. The fruit quality and yield can depend mainly on the advantage ratio between nutrient sources and reservoirs in different parts of the tree crown. Taking 'Huizao' jujube as an example, there are different requirements in the renewal period of the fruiting branch group under cultivation modes. There are also great variations in the fruiting, yield, and fruit quality of secondary branches at different branch ages. In this study, an evaluation system was established for the pruning and fruit quality of 'Huizao' jujube. 21 quality indicators were also compared, such as biomass characteristic parameters, surface color difference values, and mineral element content of 1, 2, 3, and 4-year-old secondary branch fruits. The comprehensive quality model was proposed to rank the excellent degree, according to the comprehensive quality score. The results indicate that there was a significant difference in the variation coefficient (CV) of 21 fruit quality indexes. The CV values of the total P, Mn, Cu, and total acid content were all greater than 15.0%, among them the CV of total P content was the largest (19.2%); the CV of ascorbic acid content, Ca, Fe, and color difference value b* were between 10.0% and 15.0%, the CV of total flavonoids content and color difference value L* , Zn and color difference value a* were between 5.0% and 10.0%, the CV of other quality indexes were less than 5.0%. Three common factors with characteristic root values greater than 1 were extracted by factor analysis, where the cumulative variance contribution rate was 100.00%. The contribution rate of the first common factor was 44.81%, which was mainly determined by eight factors (the fruit surface color difference value L* , a* , b* , fruit longitudinal diameter, fruit transverse diameter, fruit shape index, single fruit weight and Mg content), indicating the fruit surface color, fruit size, and appearance quality indicators. The contribution rate of the second common factor was 32.21%, which was determined by the contents of protein, total flavonoids, soluble solids, total sugar, K, total acid and Cu, indicating the taste quality and level of some nutritional contents. The contribution rate of the third common factor was 22.99%, which was determined by the contents of total P, Zn, Ca, Mn, Fe and ascorbic acid, indicating the content of mineral elements and Vc in fruits. The comprehensive quality score of fruit on the secondary branch was ranked in the order of the three- > four- > two- > one -year-old secondary branch fruit. A suitable cultivation model was formed to balance the various advantages of the secondary branches with different ages. More than two-year-old branches should be left, whereas, the one-year-old secondary branches should be minimized as much as possible when pruning of 'Huizao' jujube.