Genetic diversity analysis of quantitative traits of fruit stone and kernel in apricot

Abstract: 【Objective】The kernel-using apricot is a unique apricot resource in China, which includes Siberian apricot (Armeniaca sibirica L.), common apricot (A. vulgaris L.) and A. cathayana D. L. Fu et al. Although apricot germplasm resources in China are very rich, the available materials in the breeding of kernel- using apricot are very few. The evaluation of stone and kernel related quantitative traits of apricot is the basis for the effective breakthrough of genetic improvement and breeding in kernel-using apricots.【Methods】Based on the phenotypic data of 195 apricot germplasm resources in the two consecutive years, the variation coefficient analysis, principal component analysis, correlation analysis and cluster analysis were carried out on the 17 traits of stone and kernel using Origin 9.0 software.【Results】The coefficients of variation of the 17 quantitative traits ranged from 9.61% to 36.88%, and the coefficient of variation of the stone breaking force (SBF) was largest, and the coefficient of variation of the stone lignin content (SLC) was smallest. The result of the Shapiro-Wilk test showed that those data were normally distributed except for SBF and SLC traits. The evaluation data in two consecutive years was stable and well repeatable. The coefficient of variation of the stone dry weight (SDW), kernel dry weight (KDW), stone hardness (SH) and kernel weight ratio (KR) were all over 20%, indicating that 195 accessions of germplasm resources had abundant genetic diversity. The distribution of the SHranged from 305.31 to 1 573.37 N, with an average of 902.32 N. The distribution of the KR ranged from 12.83% to 51.20%, with an average of 27.88%, indicating that there was a great potential for genetic improvement in the SH and KR traits. There was a significant correlation between the size and weight of the stone and kernel. In particular, the correlation coefficient between the stone length (SL) and the kernel length (KL) was as high as 0.899 indicating that the kernel size was closely related to the size of the stone. The positive correlation between the KR and kernel thickness (KT) trait (r= 0.395) or kernel weight (KW) trait (r= 0.377) was extremely significant, and the negative correlation between the KR and the SH trait (r= -0.551) or SBF trait (r= -0.346) or stone shell thickness (SST) (r= -0.570) was very significant. This result indicated that the KR could be increased by enlarging the KT or decreasing the SH. The principal component analysis showed that the 17 traits could be integrated into four main factors, and the accumulative contribution rate was over 81% in two years. The first principal component, accounted for 32.37%, was composed of the SL, stone width (SW), SDW, KL, KW, and KDW, and represented the size of stone or kernel. The second principal component, accounted for 26.43% , was composed of the stone thickness (ST), SL/SW, SL/ST, KT, KL/KT, and KL/KT traits, and represented the shape of stone or kernel. The third (14.87%) and fourth (7.86%) principal component represented the SH and SLC traits, respectively. The 195 accessions were grouped into 5 major clusters by cluster analysis when the genetic distances were 15. Cluster I only included one accession of Siberian apricot (Lve), and cluster Ⅱ comprised of one common apricot accession (Luren) collected from Liaoning province. The most varieties of the A. cathayana apricot, usually with thin stone shell, slightly juice and astringent flesh and large sweet kernel, were clustered into the cluster Ⅲ. The cluster Ⅳ was composed of 27 varieties, most of them had the traits of thin stone shell and high kernel ratio. The cluster Ⅴ was further divided into 6 subgroups when the genetic distance was 10. In the Va subgroup, four accessions were included, with oval shape stone and the great hardness in stone. The Vb subgroup was composed of four accessions with the hard stone. The accessions in the Vc subgroup were consisted of 29 accessions with full kernels and high kernel ratio, such as Dashanxin, Kelala, Boxing, and Liaomei, and so on. The Vd subgroup were consisted of 12 accessions with oblate stone and long transverse diameter. the Ve subgroup comprised of seven accessions, for example Caotancaoxing, Zhanggongyuan, Mituo luo, and Hongyu, etc. These accessions had large stone, poorly developed kernels and low kernel yield. The remaining 90 accessions were constituted the Vf subgroup, accounting for 46.15% of the total accessions. The stone or kernel traits of these accessions were intermediate types. Except for the group Ⅲ, the other groups are different types of germplasm of common apricots and Siberian apricots.【Conclusion】The quantitative traits of apricot stone or kernel had abundant genetic diversity, and the improvement of the SL or KL trait would be beneficial to the increase of kernel yield in the breeding of kernelusing apricot. The 6 excellent and 21 specific germplasms, especially the common apricot germplasm such as Tianren Huangkouwai, Dapiantou, Kuerdaisheke and Saimati, could be used as important breeding parents to increase the genetic diversity of kernel-using apricot.