Construction Of High-density SSR Linkage Maps And Mapping Of QTLs For Dry Matter Content In Sweetpotato,Ipomoea Batatas (L.) Lam.

1.A total of 1215 g-SSR primer pairs were designed from the whole genome sequence of sweetpotato cv.Xushu 18.Meanwhile,1330 BES-SSR primer pairs were designed based on the BAC-end sequence of sweetpotato line Xu 781.Using Luoxushu 8(female parent,high starch content,low yield,resistance to Fusarium wilt disease)and Zhengshu 20(male parent,low starch content,high yield,susceptible to Fusarium wilt disease)and their ramdomly-sampled two F1 individuals,these SSR primer pairs were evaluated for the polymorphism and 273 and 298 polymorphic primer pairs were obtained in g-SSR and BES-SSR,respectively.2.From the 571 polymorphic SSR primer pairs,100 pairs were randomly sampled for evaluating their polymorphism through the use of 20 sweetpotato varieties.The results showed that all of the 100 SSR primer pairs amplified clear and stable polymorphic bands,and generated 3 to 34 bands per pair.Polymorphism information content ranged from 0.4118 to 0.9558 with an average of 0.8406.3.Seven SSR primer pairs,including 4 g-SSR and 3 EST-SSR,were used to construct the fingerprints of 96 sweetpotato varieties by capillary electrophoresis.A total of 47 polymorphic bands were generated.The genetic diversity analysis showed that the genetic similarity coefficient was 0.4894?0.9574,and the main variations were from varieties but not regions.4.The 571 polymorphic SSR primer pairs were used to amplify 240 individuals derived from a cross between Luoxushu 8 and Zhengshu 20,and 2428 and 2678 SSR markers were generated from Luoxushu 8 and Zhengshu 20,respectively.According to the pseudo-testcross strategy and JoinMap 4.0 software,high-density SSR molecular linkage maps were constructed in both parents.Both maps included 90 linkage groups.The linkage map for Luoxushu 8 was composed of 5057 SSR markers and covered 13299.9 cM with an average marker distance of 2.6 cM.The Zhengshu 20 linkage map contained 3009 SSR markers and covered 11122.9 cM with an average marker distance of 3.7 cM.5.MapQTL 5.0 software was used to map the QTLs for the dry matter content of sweetpotato.A total of 6 main-effect QTLs were identified,and 2 of them were mapped on the Luoxushu 8 maps,explaining 18.7%to 45.8%of phenotypic variations with negative effect,and 4 were mapped on the Zhengshu 20 maps,explaining 24.5%to 29.7%of the variations,in which 2 showed positive effect.