The use of SSRs for the identification of unknown Asian pear cultivars

Pear species belong to one of the longest-cultivated temperate species. A large number of cultivars is spread worldwide, that have different names in different countries. Probably the most famous is the cultivar ‘Williams’, which is known in the USA as ‘Bartlett’. However, not all synonyms are always known. Molecular methods, namely the SSR method, allow reliable identification of cultivars. In this study, an SSR marker set was applied to 31 Asian pear cultivars, 4 interspecific hybrids and 3 botanical species from the East China gene center. Six SSR primer pairs were used to determine the genetic relatedness. SSR primers were labeled with fluorescent dyes and the PCR products were evaluated using a genetic analyzer. Based on the obtained results, the cultivars were divided into two main clusters. Cluster I was divided into three subclusters, subcluster I contained P. pyrifolia and cultivars derived therefrom, subcluster II contained P. ussuriensis and several ussuriensis-type cultivars and Chinese white pear cultivars and subcluster III contained cultivars of the Chinese white pears. Cluster II was formed by only 4 cultivars probably being interspecific hybrids. Further, combinations of cultivars ‘Man San Gill’ and ‘Pung Su’; ‘Early’ and ‘Zaosu Li’; ‘Snow Flower’, ‘Shon Shu’ and ‘Dangshanshu Li’ had identical SSR profiles, which indicates, that they are probably identical cultivars or possibly different clones.