Phenotypic and genetic variation of hybrid progenies of Xiangshui lemon × Baihua lemon

Abstract: 【Objective】SSR and SCoT markers and phenotypic traits were analyzed to study the population genetic diversity of the hybrid offsprings of Xiangshui lemon × Baihua lemon. The genetic develop- ment of main traits such as leaves, flowers and fruits of lemon was preliminarily understood to provide reference for subsequent genetic linkage map construction, QTL mapping and germplasm innovation.【Methods】152 individuals of Xiangshui lemon, Baihua lemon and their F1 hybrids were used as test ma-terials. The leaf length, leaf width, leaf shape index, leaflet color, flower color, longitudinal diameter,transverse diameter, fruit shape index, single fruit weight, pericarp thickness, soluble solids, total acid,solid-acid ratio, vitamin C and juice rate were observed and described of the stable flowering and fruit-ing hybrid individuals. The variance coefficient analysis, normality test and correlation analysis were conducted using software SPSS 18.0. The genetic transfer ability, heterosis rate, super high parent rate and low parent rate were calculated, and the frequency distribution histogram was ploted. Based on the SSR and SCoT markers, the genetic diversity parameters were calculated and UPGMA cluster analysis  was performed by POPGENE software and MEGA software.【Results】The genetic variation of the phe-notypic traits was abundant, and the coefficients of variation was 9.76%-45.37%. The coefficient of variation of single fruit weight was the largest, and that of soluble solids was the smallest. The genetic transfer ability (Ta) ranged from 34.27% to 152.27%. The total acid had the highest genetic transfer abil-ity and the soluble solid substance and acid ratio had the lowest genetic transfer ability. The heterosis rate (H) ranged from −65.73% to 52.27%. The leaf length, leaf shape index, fruit shape index, pericarp thickness and total acidity showed positive heterosis, while the leaf width, longitudinal diameter, trans-verse diameter, single fruit weight, soluble solids, soluble solid substance and acid ratio, vitamin C and juice rate showed negative heterosis. The following traits showed normal or partial normal distribution in the hybrid offsprings: The leaf length, leaf width, leaf shape index, longitudinal diameter, transverse diameter, fruit shape index, single fruit weight, pericarp thickness, soluble solid substance, total acid,soluble solid substance and acid ratio, vitamin C and juice rate, which was consistent with the genetic characteristics of quantitative traits. The inheritance of fruit shape index, total acid and pericarp thick- ness showed a variation tendency to the high-parent. The inheritance of longitudinal diameter, trans-verse diameter, single fruit weight, solid-acid ratio and juice rate showed a variation tendency to the low-parent. The leaf width, leaf shape index and soluble solid substance showed a genetic variation ten- dency the mean of the parents. The leaf length and vitamin C were widely separated. The leaflet color separation ratio in the hybrid population was approximately 3∶1. The purple-red leaflet presented as dominant to the green ones. The inheritance of flower color was greatly affected by the purple-red color of the female parent, and showed significant differences in the degree of the color. The white flowers were not observed in hybrid progeny. Among the leaf, flower and fruit traits, there were 23 pairs of traits with extremely significant correlation and 12 pairs of traits with significant correlation. 57 alleles were amplified by the 20 SSR markers, and the polymorphism was 100%. A total of 49 alleles were de-tected by 11 SCoT markers, and among them 35 were polymorphic, accounting for 71.43%. The aver-age gene diversity index (H) based on the SSR and SCoT markers, were 0.460 9 and 0.158 3, respective-ly. Shannon's information index (I) of the SSR and SCoT markers were 0.722 8 and 0.272 1. The SSR marker analysis showed that the mean values of genetic differentiation coefficients (Fst) and gene flow(Nm) were 0.312 7 and 0.549 4, respectively. The results showed that there was obvious gene recombi-nation in the hybrid population and there was abundant genetic diversity at the molecular level. The av-erage Nei’s genetic distance of the SSR and SCoT markers were 0.247 7 and 0.176 2. The cluster analy-sis results were similar but not exactly the same. In the clustering results of the SCoT markers, the popu-lation could be divided into six categories at the genetic distance of 0.11. The SSR marker clustering showed that when the genetic distance was 0.13, the population could be divided into six categories.When the genetic distance was 0.1, the clustering results of the two markers showed that only a few hy-brid progenies were clustered with their parents, and there were abundant variations among the hybrid individuals. The Mantel test showed that there was no significant correlation (r=0.302 1, p=1.000) be-tween the genetic distance of SSR and SCoT markers in the hybrid population.【Conclusion】The pheno-typic traits of Xiangshui lemon × Baihua lemon hybrids were widely separated, and there was a certain correlation. Some traits had a certain number of super-parent hybrid plants. The genetic diversity was rich, there was a certain genetic recombination in the hybrid population.