| Sweetpotato (Iponoea batatas (Lam.)) is a kind of important food, feed, industrial raw material and new energy root crops. Nowadays it has been widely cultivated in over 100 countries all over the world. Its overall production ranks seventh in all the food production. Our country is the largest producer of sweetpotato in the world.The sweetpotato stem nematode disease has been passed from Japan to China since 1937. The production of our country's sweetpotato severely suffered from the stem nematodes disease. The general disease incidence is 20%-50% in the field infected with stem-nematode, while the sweetpotato could not be harvested to make values any more in seriously barren field. In recent years, the fundamental way to solve the sweetpotato stem nematode disease is to combine traditional breeding with molecular breeding techniques. While on the sweetpotato resistance breeding, there exists some limits in traditional breeding, genetic background of sweetpotato is very complex. It often show not affinal and other obstacles when hybrid breeding. This could make it difficult to obtain F1 seeds. There are also other shortcomings, such as cultivating time is too long. Molecular breeding is auxiliary means of traditional breeding. It consists of cloning of resistant genes (candidate genes) and selection of molecular markers, etc. Molecular markers which are based on polymorphism of DNA are not only the direct reflection of genetic polymorphism on DNA level, but a new kind of genetic markers. It can help sweetpotato resistance breeding and analyze genetic diversity of sweetpotato stem nematode disease resistance. In all, these marker techniques could improve the pace of sweetpotato disease resistance breeding.In this study, we examined the sweetpotato variety Xu781 which is highly resistant to stem nematode disease, the variety Xu18 which is highly susceptible to stem nematode disease and other varieties which are stored in our lab. Three molecular marker techniques (SRAP, SSR and RGA) were used to screen primers or to obtain genetic relationship between sweetpotato materials which could lay foundation for parents selection and future breeding study of sweetpotato. The obtained results were as followed.In SRAP-RGA experiment,1. Result of Polymorphism analysis on SRAP-RGA50 sweetpotato cultivars were amplified by 11 SRAP-RGA primer combinations which were polymorphic. The amplified products ranged mainly from 250 to 2000bp (Figure 1). A total of fifty-seven bands were observed, among which forty-nine were polymorphic (88.32%), ranging from 9 to 18 bands per primer combination, with an average of 12.5. Different primer combinations produced obviously different polymorphic rate.The highest polymorphic rate was 100%, produced by the EM4-S2-A07-F primer combination. The lowest polymorphic rate was 63.6% produced by the primer combination EM8-S1-FO3-F.2. Result of cluster analysisThere groups were completely separated at the level of a genetic similarity of 0.51. The first group included 30 cultivars including Nanshu88,702, Erhuang, Mei I,199029-1,559, Xu55-2, Qingnong2, Chuanshanzi, and Guangcai2, etc. The second group included 10 cultivars:Meiguohongshu,44104, Shuiguoganshu, Xuzi13-4, C-30, Jishu18, Ningzi1, Xu23, Xu781, Zhe78, etc. The third group included 10 cultivars: Xu22, Fushull,44057, and 59, Jinshan1225, and Xu18.3. Result of genetic diversity analysis on SRAP-RGABased on the SRAP-RGA data, the similarity coefficient was calculated with NTSYS pc version 2.0 statistical package. The accessions studied had similarly values ranging from 0.1818 to 0.9091, which indicated a high level of variation. Among all sweet potato cultivars, Yushu12 (31) and Wan702 (1),2004-28 (11) and Zhe6025 (13) formed a group with a similarity value of 0.1818. This showed their farther genetic distance. However, the genetic similarity coefficient between 199029-1(3) and Nanshu88 (5),559 (4) was 0.9091, which showed their closer genetic distance. In SSR experiment,Xu18 and Xu781 was used as parent material, they were amplified through PCR on SSR reaction system.21 polymorphic primers were selected from 82 primer combinations. They respectively were forth,14th,24th,28th,29th,30th,31st,33rd, 35th,36th,39th,40th,42nd,44th,45th,46th,48th,49th,50th,52nd,60th。... |
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