The genetic relationships among 96 peach and nectarine [Prunus persica (L.) Batsch.] genotypes and botanical varieties originating from different ecogeographical regions of China, Japan, North America, and South Korea were evaluated with 33 SSR markers screened from 108 published SSR markers developed for peach or sweet cherry (P. avium L.). The 33 SSRs detected polymorphisms among 96 genotypes and revealed a total of 283 alleles with an average of 8.6 alleles per locus. The polymorphism information content (PIC) value ranged from 0.40 (BPPCT041) to 0.98 (BPPCT009) with an average of 0.80. Unweighted pair group method average (UPGMA) cluster analysis based on Nei's genetic distances classified genotypes into six groups, corresponding to their ecogeographical origin. Group I consisted of northern Chinese and northwestern Chinese local cultivars, and was divided into two subgroups, white and yellow peaches. Group II contained mainly southern Chinese local, Japanese, and North American cultivars and can be divided into four subgroups: Japanese white, Chinese flat, North American yellow, and some Chinese local ornamental peach cultivars. Groups III, IV, and V were comprised of Chinese local ancient cultivars, and contained `Xinjiangdatianren' and `Renmiantao', Chinese dwarf cultivars, and `Fenshouxing', respectively. Group VI had only `Baishanbitao', a Chinese ornamental cultivar. Northern and northwestern Chinese local cultivars clustered together with a greater diversity than southern Chinese local cultivars, indicating that the northern and northwestern Chinese local cultivars are similar ecotypes, and southern Chinese local cultivars are a subset of the northern Chinese group. Moreover, the Japanese and North American genotypes had a close phylogenetic relationship with southern Chinese local cultivars. The taxonomic placement of P. ferganensis (Kost. et Kiab) Kov. et Kost. and the phylogenetic relationship of `Baishanbitao' with peaches are discussed.
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