Genetic relationships of pear cultivars in Xinjiang, China, as measured byRAPD markers

Thirteen native pear species have been identified in China, of which P. arm eniacaefolia Yu and P. sinkiangensis Yu are specific to Xinjiang. P. armeni acaefolia grows wild and a few cultivars have been assigned to this species . Cultivars of P. sinkiangensis have been suspected to be of hybrid origin involving P. communis L. and P. bretschneideri Rehd. In this study, traditi onal pear cultivars in Xinjiang were evaluated using RAPD markers and compa red with representatives of Occidental pear species, cultivars of P. commun is and East Asian pear accessions. The combination of 72 pear accessions an d 20 selected primers produced 231 scorable polymorphic RAPD bands, of whic h some were specific to certain species. Five main groups of pear accession s could be distinguished from UPGMA analysis: 1) P. xerophila Yu, its relat ives and one cultivar of P. ussuriensis Max., 2) cultivars of P. sinkiangen sis, 3) cultivars of P. pyrifolia Nakai and P. bretschneideri, 4) wild Occi dental species, cultivars of P. communis and P. armeniacaefolia, and 5) hyb rids between P. communis and Chinese or Japanese pear cultivars. The result of PCA generally agrees with that based on UPGMA. Based on RAPD data, some cultivars traditionally classified as P. bretschneideri should be assigned to P. sinkiangensis. Some heirloom cultivars assigned to P. communis were found to be of hybrid origin involving the Chinese white pear (P. bretschne ideri) or sand pear (P. pyrifolia). Our results confirmed that P. sinkiange nsis is of hybrid origin and at least P. communis, P. armeniacaefolia and C hinese white pears or sand pears have been involved. A further study is nee ded to understand how pear species and cultivars in Xinjiang are related to those originated from countries in Central Asia.