Genetic Diversity and Population Structure of Seedling Populations of Pyrus pashia

Pyrus pashia, described as an intermediate species between oriental and occidental pear groups, is one of the most important wild pears. This study used microsatellite markers at 14 loci to assay genetic diversity and differentiation within P. pashia using three complementary methods. Four hundred and seventy seedlings were obtained from 38 half-sib families from four sites in the central Yunnan Province of China. These 14 loci displayed high polymorphism, and the descriptive statistics of diversity varied significantly among seedling populations. One hundred and seventy-three different alleles were detected, with an average of 12.4 alleles per locus. The overall expected and observed heterozygosity values were 0.749 and 0.643, respectively. Allelic richness at the different sites ranged from 1.00 to 20.36, and the Shannon's information index for each locus was from 0.35 to 2.37, with a mean value of 1.82. Genetic differentiation was detected at both family and site levels using Bayesian model and neighbor-joining clustering approaches and the results compared with that of principal coordinate analysis. Two clusters, each with a similar number of families, were detected in the data set. Analysis of molecular variation indicated that the major variation occurred within families and that the minimum partitions of genetic variation exist among families, representing 89.14 and 10.86 % of the total variety, respectively. Families derived from site 2 displayed the maximum allelic richness and had a greatly mixed genetic composition. We recommend that these, especially families 9, 11, and 12, should be the focus of future preservation and usage investigations.