Retrotransposon-based sequence-specific amplification polymorphism markers reveal that cultivated Pyrus ussuriensis originated from an interspecific hybridization

Pyrus ussuriensis Maxim. cultivars have long been considered to be directly derived from wild P. ussuriensis, which is distributed in northeastern China. However, recent studies have revealed that P us-, suriensis cultivars are similar to Pyrus pyrifolia, which is extensively cultivated in China. To clarify the origin of cultivated P ussuriensis, 12 primers of retrotransposon-based sequence-specific amplification polymorphism marker were used to analyze the genetic relationships among 92 Pyrus accessions, including cultivated P pyrifolia, cultivated and wild P ussuriensis, and a few Occidental species. We obtained 1,143 scorable fragments using 12 primer combinations, of which 871 were polymorphic (i.e., 76.20%). A dendrogram produced using Dice similarity coefficients and the unweighted pair group method with arithmetic mean indicated that wild and cultivated P. ussuriensis form a group parallel to the P. pyrifolia group, in which a few P. ussuriensis cultivars are scattered and further divided into independent subgroups. A Bayesian model-based analysis of population structures revealed that P ussuriensis cultivars consist of two major genepools, with one originating from wild P. ussuriensis and the other from cultivated P. pyrifolia. Our results suggest that cultivated P ussuriensis originated from an interspecific hybridization between P. ussuriensis and P pyrifolia. Our findings not only provide new insights into the origin of cultivated P. ussuriensis, but may contribute to the improvement of P ussuriensis cultivars.