Analysis of Genetic Diversity in Pear Genotypes Using Apple EST-SSRs

A total of eight apple Simple Sequence Repeat markers derived from expressed sequence tags (EST-SSRs) were used to assess the genetic diversity among 48 genotypes of pear (Pyrus).  Primer pairs of all eight EST-SSRs gave amplification products when tested on all pear cultivars, and sizes of amplification bands were similar to those observed from apple.  A total of 140 gene loci were identified, of which 129 (92.14%) were polymorphic, and different pear cultivars could be readily distinguished.  Based on polymorphisms revealed by these markers, an Unweighted Pair Group Method with Arithmetic mean (UPGMA) cluster analysis was performed using soft NTY-SIS-pc2.01.  Pear genotypes were classified into two major clades and grouped based on Asiatic and European origin of these genotypes with a stringency coefficient of 0.62.  It is interesting to note that the following three species, P. bretschneideri Rehd., P. ussuriensis Maxim, and P. pyrifolia Nakai., originating from China, could not form an independent group .