| Cotton is one of the most important renewable natural textile fiber crops in the world, and it is also an essential oil resource. Our country is the biggest consumer of cotton. With the development of the textile industry and the improvement of the life quality, the demand for cotton is growing. Up to now, 52 species were identified in Gossypium genus, including 7 tetraploid and 45 diploid cotton species. Contemporary cotton production relies primarily on allotetraploid G. hirsutum L., which accounts for more than 95% of the world crop.The complex quantitative genetics of cotton yield and fiber quality leads to the slow progress of conventional breeding. The molecular marker-assisted selection(MAS)that use the molecular marker linked with quantitative trait genes/QTL to select quantitative trait make significantly more efficientIn this study, upland cotton high fiber strength cultivar Yumian 1 bred by Southwest University was crossed with upland cotton high fiber strength line CA3084 introduced from USA to establish a recombinant inbred line population. A genetic map was constructed with SSR marker and QTL for fiber strength was analyzed through one year fiber quality data. Additionally, new SSR markers designed from G. raimondii genome sequence were used to increase the marker density of chromosome 21.The present study lays the foundation for the genetic mechanism dissection of fiber strength and the molecular marker-assisted breeding in cotton. The main results are as following. 1. The polymorphic ration of SSR primersOut of 19,641 pairs of SSR primers which were used to screen the polymorphic primers between two parents, 389 polymorphic primer pairs were obtained and the polymorphism ratio was 2.2%. The polymorphic primers were used to genotype(Yumian 1 × CA3084) recombinant inbred line population, and 395 loci were obtained. 2. Genetic map constructionThe genetic linkage analysis was conducted on the 395 loci, and a genetic map including 356 loci and 73 linkage groups was constructed. The map covered 1594.6c M and the average distance between markers was4.48 c M.Among the 356 mapped loci, 143(40.2%) showed the segregation distortion. In all segregation distortion markers, 135(95%) distorted to Yumian 1 genotype and 8(5%) distorted to CA3084 genotype. 3. Mapping QTL for fiber strength traitsA total of 10 QTL for fiber strength were identified, which were anchored on nine chromosomes and explained phenotypic variation from 11.6% to 22.9%. Four QTL favorable alleles come from Yumian 1, and six QTL favorable alleles come from CA3084. 4. Increasing marker density and Mapping fiber strength QTL on chromosome21A total of 1022 pairs of SSR primers designed according to G. raimondii genome sequence were used to screen the polymorphic primers between two parents, and72 polymorphic primers were obtained. Seventy-two loci were added to the genetic map of chromosome 21. The genetic map of chromosome 21 included81 markers, and covered a total length of 110.4c M, with the average distance 1.36 c M between two markers. Fiber strength QTL was mapped between marker SWU16482 and CGR6578, and the genetic distance was 3.1c M whereas the QTL region covered 9.1 c M before the new markers were added. |
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