Genetic analysis of fruit traits and selection of superior lines in F1 generation of jujube JMS2 × Jiaocheng 5

Abstract:【Objective】The aim of this experiment is to investigate the segregation characteristics and genetic variation of fruit traits in the F1 generation, so as to provide a theoretical basis for cross breeding and variety selection in jujube.【Methods】The 26 descriptive and numerical traits such as fruit shape, fruit color, shape of fruit shoulder, shape of fruit top, size of fruit dot, density of fruit dot, stigma state, smoothness of fruit skin, thickness of fruit skin, texture of fruit flesh, color of fruit flesh, juice of fruit flesh, coarseness of fruit flesh, single fruit weight, fruit longitudinal diameter, fruit transverse diameter,fruit shape index, edible rate, soluble sugar, organic acid, soluble solids, vitamin C, single core weight, kernel longitudinal diameter, kernel transverse diameter and kernel shape index were described and measured using 140 plants of F1 generation of Jujube JMS2 × Jiaocheng 5 and the parents, and the fruit ripening period was investigated. The data obtained from the investigated traits were compiled and analyzed by EXCLE 2019 and SPSS 26.0, and genetic diversity parameters such as mean, standard deviation, skewness, kurtosis, coefficient of variation, genetic transmission power, ultra- high parental rate, low parental rate, pro-median and mid-parental dominance, and correlation analysis were performed to analyze the genetic variation of the investigated traits, and the fruit quality was comprehensively evaluated using the equal- weighted and weighted gray correlation method.【Results】The F1 generation showed a separation in fruit ripening, with 36.26% of the F1 offerspring ripening mostly in late September. In the F1 generation, the 13 descriptive traits including fruit shape, fruit color, shape of fruit shoulder, shape of fruit top, fruit point size, size of fruit dot, density of fruit dot, stigma state, smoothness of fruit skin, thickness of fruit skin, texture of fruit flesh, color of fruit flesh, juice of fruit flesh, coarseness of fruit flesh all showed different trait separation, among which six variant types of fruit shape appeared, and the top three fruit shapes of the offspring were obovoid, oblong and ovoid in that order. The fruit shape tended to be obovoid in the paternal genetic effect, with 35.85% of the offspring, while the fruit shape tended to be ovoid in the maternal genetic effect, with 17.92% of the offspring. Four types of variation in texture of fruit flesh were observed, and the percentage of flesh compact was 46.23%, and their traits tended to be in the paternal genetic effect. Two traits, shape of fruit shoulder and stigma status, were tested by chi-square test (p=0.737＞0.05, p=0.502＞0.05), and the separation ratios were 3∶1 and 1∶2∶1 in that order, which were in accordance with Mendelian genetic separation law. The 13 numerical fruit traits, including fruit size, kernel size, edibility and intrinsic quality content of the F1 generation group, showed continuous variation and conformed to normal or skew- normal distribution, with the characteristics of quantitative traits controlled by multiple genes. The coefficients of variation for fruit size and edibility ranged from 0.85% to 32.27%, with the largest coefficient of variation for single fruit weight and the smallest coefficient of variation for edibility; the coefficients of variation for kernel size traits ranged from 14.52% to 31.53% , with the largest coefficient of variation for single kernel weight and the smallest coefficient of variation for longitudinal kernel diameter; The coefficients of variation for intrinsic fruit quality traits ranged from 11.29% to 24.44%, with the largest coefficient of variation for organic acid content and the smallest coefficient of variation for soluble solids. The mean values of soluble solids content and single kernel weight, were higher than those of the middle parents, and the heterosis rates were positive, 5.56% and 28.81%, respectively, showing high genetic tendency and strong heterosis advantage; 11 traits including single fruit weight, longitudinal fruit diameter, transverse fruit diameter, fruit shape index, edibility, soluble sugar, organic acid, vitamin C, longitudinal kernel diameter, transverse kernel diameter, and kernel shape index, showed low genetic tendency. There were highly significant positive correlations between fruit size and kernel size traits; highly significant positive correlations between edibility and fruit size and other traits, and highly significant negative correlations with kernel size; significant positive correlations between soluble sugars and organic acids contents, and highly significant positive correlations with soluble solids content.【Conclusion】In this study, fruit ripening was mainly affected by paternal genetic and eight descriptive traits, namely fruit shape, fruit color, shape of fruit shoulder, shape of fruit top, density of fruit dot, stigma state, smoothness of fruit skin and coarseness of fruit flesh were found to be affected by maternal genetic factor in the F1 generation. Both traits, fruit shoulder shape and stigma status, may be quality traits one or a fewpairs ofgenes. All 13 numerical traits including fruit size, kernel size, edibility and intrinsic quality content, were quantitative traits controlled by multiple genes. In summary, the traits with a great influence on fruit quality were selected, and five offspring with excellent overall quality performance were initially screened using the equal-weighted and weighted gray correlation method.