| 1. A total of 6130 EST sequences were downloaded from the EST database of NCBI,371 EST-SSRs of which were screened using the software AutoSSR, and 79 SSR primer pairs were designed with Primer 3.0. A total of 1215 SSR primer pairs were derived from the genome sequencing of sweetpotato cv. Xushu 18,155 of which were sampled randomly. Screening for SSR primer pairs was performed on both parents and two progeny of two mapping populations, and 78 SSR primer pairs,38 and 40, respectively, produced good quality polymorphic markers. The first mapping population consists of 202 F1 individuals of a cross between Xushu 18, a cultivar susceptible to stem nematodes, with high yield and moderate starch content, and Xu 781, which is resistant to stem nematodes, has low yield and high starch content. The second mapping population consists of 240 F1 individuals derived from a cross between Luoxushu 8, a high starch content cultivar, and Zhengshu 20, a low starch content cultivar.2. The 78 SSR primer pairs were used for developing the polymorphic bands in two mapping populations. A total of 582 SSR markers were generated, which were 103,102,191 and 174 SSR markers in Xushu 18, Xu 781, Luoxushu 8 and Zhengshu 20, respectively. Using a two-way pseudo-testcross strategy and JoinMap 3.0 software, we developed genetic linkage maps of Xushu 18, Xu 781, Luoxushu 8 and Zhengshu 20 based on our previous study, and 55,46,126 and 140 SSR markers were added, respectively. The linkage map for Xushu 18 included 90 linkage groups with 1910 AFLP and 192 SSR markers and covered 10458 cM with an average marker distance of 5.7 cM; the map for Xu 781 contained 90 linkage groups with 1622 AFLP and 176 SSR markers and covered 9297 cM with an average marker distance of 4.6 cM; the map for Luoxushu 8 included 90 linkage groups with 964 SRAP and 126 SSR markers and covered 9181 cM with an average marker distance of 8.4 cM; the map for Zhengshu 20 contained 90 linkage groups with 826 SRAP and 140 SSR markers and covered 7798 cM with an average marker distance of 8.1 cM.Duplex and triplex markers were used to detect the homologous groups and 14 and 15 homologous groups were identified in Xushu 18 and Xu 781 maps, respectively, and 12 and 11 homologous groups were identified in Luoxushu 8 and Zhengshu 20 maps, respectively. Double-simplex markers were used to detect the homology of the corresponding linkage groups between both parent maps. In total,252 double-simplex markers revealed the corresponding relationships between 51 linkage groups of the Xushu 18 map and 45 of the Xu 781 map, and 156 double-simplex markers revealed the corresponding relationships between 48 linkage groups of the Luoxushu 8 map and 47 of the Zhengshu 20 map.3. Interval mapping (IM) and multiple quantitative trait locus (QTL) model (MQM) analysis were used to identify QTLs for storage root yield of sweetpotato in the population between Xushu 18 and Xu 781, a total of 9 major QTLs were located. Four QTLs were mapped on the Xushu 18 map, explaining 36.3% to 59.3% of the phenotypic variation, and three of them had a positive effect on the variation of yield. Five QTLs were detected on the Xu 781 map, explaining 37.0% to 51.2% of the variation, one of them had a positive effect on the variation.4. SSR fingerprinting of the 195 sweetpotato main varieties was constructed based on 7 primer pairs which generated 49 polymorphic bands. Each sweetpotato varieties could be clearly distinguished after genetic similarity analysis with NTsys software and cluster analysis with MEGA4 software. The genetic similarity ranged from 0.3265 to 0.9796, the maximum genetic variation existed within regions was in Fujian and the minimum genetic variation was in Anhui, the mean genetic distance was 0.3900 and 0.1643, respectively. The maximum genetic distance existed among regions was between Guangdong and Anhui, the minimum genetic distance was between Jiangxi and Anhui, the distance was 0.4002 and 0.2211, respectively. |
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