Genetic Difference And Differentiation Route Of Pear Accessions From Western China To European Based On SSR And CpDNA Markers

Pear（Pyrus.L）belongs to Rosaceae is cultivated in China from a cold zone to a tropical zone and from the western plateau to the eastern coast.China is the main origin of oriental pears,with abundant germplasm resources.During the spread of pears,three centers of diversity of pears were formed,including the Chinese Center,the Central Asia Center and the Near East Center.SSR markers are a valuable tool to classify and evaluate the genetic diversity,relationship and examine genetic evolutionary route due to a high degree of polymorphism and co-dominance inheritance in Pyrus.Microsatellites have been confirmed as the desirable genetic markers and have many excellent characteristics of multi-allelic changeability due to their abundantly,great degree of polymorphism,reproducibility co-dominant inheritance and transferability within Pyrus or the whole family of Rosaceae.SSR markers and chloroplast molecular markers are derived from the nuclear genome and chloroplast genome,respectively,which complement each other and represent more comprehensive genomic information.To evaluate the genetic diversity of western China and European pear accessions,identify the phylogenetic relationship between western China pear accessions and European pear accessions,reveal the differentiation route,a total of 131 pear accessions containing 66 accessions of P.communis,33accessions of P.Sinkiangenesis,4 accessions of P.ussuriansis,15 accessions of P.bretschneideri,2accessions of P.phaeocarpa Rehd and 2 accessions of P.armeniceafolia,4 accessions of P.xerophila,one P.pyrifolia Kai-4,Kai-9 from Kyrgyzstan and Pu-0234,Pu-0268 from Tajikistan were used in this study using seventeen pairs of SSR primers and five chloroplast DNA genome.Total SSR markers indicated high level of polymorphism with a total of 377 putative alleles obtained from two geographical germplasm counted 131 accessions.Chinese pear accessions displayed extra diversification than European pears using diversity measurements by SSR markers.The（Ho and He of western China accessions were 0.65 and 0.84 while Ho and He of eastern accessions was differ identified 0.57 and 0.73）.The clustering method was created to identify the relatedness among accessions belonging to different geographical locations.However,there was no kinship assessed by clustering method and identified significantly differed from each other.PCoA analysis method also showed the great distinction between two geographical groups,without Xingyeli fitted to P.armeniacaefolia and Muli-3 concerned to P.xerophila was perfectly close with European pears.However,Structure analysis method also denote geographical separation of the European pears and Chinese pears,but some oriental pears have proximity with western pears detected in Structure method followed by Qili amuti and Xiacuili and little similarity have with Changba,Bajiaoli,Kuike amuti,and Youjiaotian.These pear species including P.sinkiangensis.Xingyeli and Muli-3 also indicated proximity with European pears in this method.These results related to these accessions were reliable with PCoA analysis.All accessions that distributing into two populations was the best-using Cluster and PCoA analysis and the genetic relationship of pear germplasms of China are close.Total 5 chloroplast DNA（cpDNA）have been applied in this research to estimate the genetic diversity between two geographical pear accessions namely European and China.The frequency of haplotypes trnL-trnF-1,trnL-trn F-2,trnS-psbC,rbcL and accD-psa I have been counted three,seven,four,three and ten haplotypes,respectively.The plentiful H_d=0.7348 was covered in the hypervariable region accD-psaI.The extreme V_h and S_h were both noticed in accD-psa I（V_h=0.00236 and S_h=0.049）while the lowest were both in rbcL（V_h=0.00044,S_h=0.021）.The smallest Tajima’s D value was in accD-psa I with（-0.14472）and uppermost in rbcL with（2.82532）.Polymorphic segregating（S）was highest 10,haplotype diversity(H_d)was 0.8333,an average number of differences K were 14.000,highest nucleotide diversity（P_i）was 0.00302.All highest value were identified richer in oriental pears than European pears without a number of polymorphic segregating.15 haplotype was obviously discovered within 9 species and identified by a hypervariable and intergenic spacer.H-1 to H-6 were diagnosed in western accessions and H-2 to H-15 haplotypes were detected in Eastern accessions.H-7 to H-15 have been unobserved in Unknown and P.communis,while H-1 was unidentified among Chinese accessions.According to geographical distribution of accessions haplotypes,H-1,H-5,and H-6 were discovered in abroad pears,H-2 was identified in P.sinkiangensis and P.bretschneideri,Kréd Sobieshi and Menie accession that belonged to Po population,H-3 were usually diagnosed in abroad pears,however,few haplotypes identified in oriental accessions fitted to P.sinkiangensis.This reflecting that occidental pears and P.sinkiangensis accessions showed a close proximity.Gene immigration was recognized in H-2 and H-4 mirrored from Xinjiang to Poland and Xinjiang to Bulgaria while another gene migrant occurred from Kyrgyzstan to Xinjiang in H-3,Xinjiang might be the key route of occidental and oriental pears,and gene traveling happened in this direction.