Interspecific hybridization contributes greatly to the origin of Asian pear cultivars - a Case study of pears from Gansu province of China

Interspecific hybridization or gene introgression has proven to be a major mode of Pyrus speciation. Several natural hybrid species have been identified and approved in Oriental pears: Pyrus × bretscheideri, P. × phaeocarpa, P. × hopeiensis, P. × serrulata. The cultivars of P. × sinkiangensis were morphologically and molecularly demonstrated to be hybridization origin involved in P. pyrifolia and P. communis. Cultivars of P. usssuriensis once were believed to be derived directly from wild P. ussuriensis. However, recent molecular evidences clarified that this cultivar group originated from the hybridization between wild P. ussuriensis and cultivated P. pyrifolia. Gansu Province, which is located in northwestern China is well known for its high level diversity of local pear cultivars. In this study, we collected 129 pear samples across Gansu Province and roughly divided the cultivars into different cultivar groups based on their morphological traits: Chinese white pears, Ussurian pears, Xinjiang pears and an unidentified type. The 129 local cultivars were resequenced together with 16 identified cultivars, which have been clearly assigned to specific pear cultivar groups or cultivated species to investigate their genetic relationship and genetic structure. The phylogenetic tree resulting from SNP makers showed that most cultivars were grouped according to their morphological classification, but some were not consistent with morphological classification, which inferred that interspecific hybridization was involved in the origin of local cultivars. P. communis, which probably were introduced along the Silk Road, contributed to the development of some local cultivars in Gansu Province. The genetic structure analysis clarified the genepool composition of local pear cultivars.