Analysis Of Genetic Diversity And Relationship Among Red Skinned Chinese Sand Pears Using SSR And AFLP Makers

Red skinned sand pear cultivars (Pyrus pyrifolia Nakai) native to Yunnan Province and southern part of Sichuan Province are expected to be of value for Chinese pear production in the future. Until now, little researches have been carried out on genetic diversity and genetic relationship among red skinned sand pear cultivars and types, which will not be beneficial for rational utilization of these cultivars. Therefore, the genetic relationship and genetic diversity of red skinned Chinese sand pear cultivars native to southwest of China were analyzed using SSR (Simple Sequence Repeat) and AFLP(Amplified Fragment Length Polymorphism) markers and main results were as follows:.A total of 29 cultivars were subjected to SSR analysis. Six pairs of SSR primers (BGA35, KU10, BGT23b, NH004a, NHOllb and NH015a) could generate a large number of alleles. The primer of NH004a, which produced the highest allele numbers and most effective alleles, and high heterozygosity and Shannon information index, showed the best identification power. Using six pairs of SSR primers, all accessions or types could be distinguished except for three pairs of cultivars, which might belong to the synonymy cases or bud mutants. Twenty nine pear accessions could be divided into four major groups obviously based on the UPGMA cluster analysis. Group 1 consisted of cultivars all native to Yunnan province, including two green and nine red skinned sand pears, inferring a near genetic relationship between the red and green skinned pears. In group 2 and 3, the red skinned pears from Huili county of Sichuan province and from Yunnan province mingled together. In group 4, not only were 'Xiangsuli' and 'Zaiyangli' from Huili county of Sichuan province, 'Miduxiangsuli' and 'Changshuihuobali' native to Yunnan province not closely clustered, but also were far from other groups. Huobali pear types distributed in Yunnan and Sichuan provinces might have different origin.On the basis of SSR analysis, a few cultivars were added and AFLP markerswere used to further assess genetic diversity and relationship of red skinned Chinese sand pear cultivars. The six primer combinations (ï¿¡coRI-AAG/MseI-CAT, Eco RI-ACT/Afrel-CTT, EcoBJ-AAC/Msel-CAG, EcoRl-AAC/Msel -CTA, EcoR I-AAC/Afrel-CAA, EcoRI-AAG/Msel -CTC) could generate 443 fragments from 38 pear accessions, of which 356 fragments were polymorphic. The percentage of polymorphism for six primer combinations was from 76% to 85% with a mean of 80%. Primer iscoRI-ACT/Msel-CTT showed highest fragment, polymorphic fragments, percentage of polymorphism, heterozygosity, Shannon information index and marker index. Six primer combinations could successfully distinguish 32 cultivars, of which one pair of cultivars might be homonym. The rest of three pair of cultivars could not be differentiated, which might belong to the synonymy cases or bud mutants. This finding was accordance with the results of SSR analysis. Dendrogram analysis clustered the accessions into five groups. Group 1 and 2 consisted of cultivars all native to Yunnan province, including six green and eight red skinned sand pears. Both group 3 and 4 included the red skinned pears from Huili county of Sichuan province and from Yunnan province. In group5, not only were 'Xiangsuli', 'Zaiyangli', 'Laoyali' and 'Changbahuobali' from Huili county of Sichuan province, 'Haidongli' native to Yunnan province not closely clustered, but also were far from other groups.On the whole, two types of DNA markers used in the present study were stabilized and efficient in cultivar identification, estimation of genetic diversity and genetic relationship. The results with two types of markers were consistent. Three pair of cultivars 'Yunhongli No.l' and 'Yanshanhongli', Yunhongli No.2' and 'Wenshanhongli', 'Wudinghuobali No.l'and 'Dalihuobali' could not be distinguished which might belong to the synonymy cases or bud mutants. The AFLP analysis also revealed that two 'Wudinghuobali' cultivars sampled from different instititutions and might be different cultivars and named as Wudinghuobali No.l' and 'Wudinghuobali No.2', respectively. The red skinned sand pears from Huili county of Sichuan province and native to Yunnan province mingled together, which supported the hypothesis of the cultivar movement from Yuannan to Sichuan. Huobali pear types distributed in Yunnan province scattered in different groups, revealing the possibility of differentorigin. The red skinned sand pears might be from the bud mutation or free pollinating seedlings of non-red skinned sand pears. The results above indicated a large genetic diversity and divergent origins of red skinned sand pear cultivars in China.