| Pear,one of the most important temperate fruit crops,with the largest growing area worldwide.With the long time self-incompatibiliy and natural selection,many cultivars show highly complex genetic components,undoubtedly increased the difficult of genetic identification.however,a set of core collection SSR markers developed from pear genome would be important for pear germplasm evaluating,saving and breeding.1.Pear is high genetic diversity and controversial classification of some genotypes or species.Our study evaluates the polymorphism of 385 pear resources belonging to five cultivated species or interspecies of Pyrus,based on a set of 134 core simple sequence repeat(SSR)markers.A total of 690 variant alleles were detected,from 2 to 12 per locus,with an average of 5.45,as well as 30 rare alleles.The clustering relationship divided the pear genotypes into three groups,with the primary division between occidental and oriental pears,revealing separate evolution processes,followed by division of Pyrus ussuriensis,Pyrus pyrifolia,and Pyrus bretschneideri.Population structure analysis with K values of 2 to 8 reflected a clear genetic composition within different genotypes,supporting Pyrus sinkiangensis as a hybrid of oriental and occidental pears and P.pyrifolia and P.bretschneideri sharing a common ancestor.However,the division of genetic components also revealed separate evolution at the different geographic and environmental conditions of South China and North China.The varieties BPingguoli^ and BChaoxianyangli,^ which currently have controversial classification,were classified into P.bretschneideri and Pyrus communis,respectively.A core collection of 88 accessions was chosen,covering all of the rare alleles and 95.54%of all alleles.2.Sand pear is a most important species in cultivation pear species.Along with the long time natural selection based on the generally self-incompatibility,a complicated genetic diversity was occurred.The assessment of genetic diversity and population structure of a whole sand pear germplasm would be useful for making efficient usage of these germplasm as well as applying them in genetic breeding and resource conservation.From this study,a total of 470 sand pears were analysed based on a set of 17 SSR markers,we investigated the molecular diversity and the results indicated a high level of genetic variation as quantified by the average values of the observed heterozygosity,the expected heterozygosity and the Wright’s fixation index with 0.776,0.77 and 0.0237,respectively.The analysis of the genetic structure and Principal Component Analysis in the sand pear collection revealed several levels of stratification.The division of four groups we detected within cultivated sand pear representing different eco-geographic groups,meanwhile,the cultivars originated from Yunnan,Sichuan and Guizhou had a higher allelic diversity than those originated from other areas with respect to the rare alleles’ richness.The pairwise FST results suggest a moderate genetic exchange and differentiation among sand pear germplasm.A core collection of 82 out of 470 cultivars were selected,accounting for about 17.4%of whole accessions and capturing 91%of all alleles and the whole rare alleles.These results provided a molecular aspect for understanding genetic diversity and gene differentiation of sand pear germplasm.3.A set of core SSR markers and SRAP markers developed from pear genome were used to identify 7 groups of somatic mutation and 2 groups of variant lines.The results revealed that all somatic mutations could be identified with their comparison varieties,which indicated the high efficiency of the markers we selected.Cultivar ’Dabali’ and the somatic mutation was divided by one SRAP marker,and cultivar NO.8 and its mutation,cultivar NO.4 and its mutation were divided by SSR markers.Meanwile,we has verified the cultivar ’Early Red Comice’ was the same with ’Solanum integrifolium Poir’,and also the mutation of ’Comice’... |
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