Study on Pear (Pyrus spp.) Germplasm Resources Collected at the Protection District of 'Dangshansuli' by ISSR Markers

Twenty-six accessions were assessed for genetic diversity and phylogenetic relationships among Pyrus species by Inter-Simple Sequence Repeat (ISSR) markers. Among 45 ISSR primers used, only 16 ones were suitable for pear genomic DNA analysis and the range of polymorphic band rate was 55.6%-100% by primers. The 16 primers generated 173 markers, and the fragments size ranged from 200 bp to 2400 bp. According to Nei (1987) molecular evolutionary genetics, the summary of generic variation statistics for all loci in different species or groups showed that observed number of alleles was 1.20-1.44, effective number of alleles was 1.14-1.25, Nei's gene diversity was 0.08-0.15, Shannon's information index was 0.12-0.23, number of polymorphic loci was 35-76, and rate of polymorphic loci was 20.23-43.93%. P. bretschneideri and Dangshan local variety group had the highest genetic identity and the closest genetic distance, followed by inter-species hybrid group and 'Dangshansuli' and its mutant group. Occidental pear (P. communis) and Oriental pear (P. bretschneideri, P. pyrifolia, P. sinkiangensis, and P. ussuriensis) had lower genetic identity and farther genetic distance. Occidental pear and Oriental pear showed less relationship on the dendrogram of pear species and groups based on Nei's Unbiased Measures genetic distance and the method of unweighted pair group method with arithmetic average (UPGMA) clustering modified from Neighbor Procedure of Phylip Version 3.5. Hierarchical cluster analysis showed there was positive difference between the clusters when all assayed accessions were divided into eight ones at the threshold value of 0.507-0.560. It was postulated that 'Dangshansuli' pear would originate by inter-species hybridization. The standpoints that P. bretschneideri, P. pyrifolia, and P. ussuriensis had closer relationship, and that Occidental pear (P. communis) and Oriental pear (P. bretschneideri, P. pyrifolia, P. ussuriensis, and P. betilaefolia) had the farthest genetic distance have been supported by analysis of ISSR markers in this experiment.