| China is one of the largest cotton cultivating countries, but it is not the original country of cotton. Our cotton production and breeding are developed from the introduced species. Stoneville2B and DPL15which had been cultivated in the large areas of china are the most successful introduced species to improve the cotton yield and fiber quality in our history. It is on the basis of these kinds of resources, China has cultivated a large number of breeders of fine varieties. Therefore, the research on these basic varieties such as Stoneville2B and DPL15will help us to understand the basis of cultivated varieties of cotton and provide useful information for future research.The germplasm resources of cotton have abundant genetic diversity which is the basis of breeding excellent varieties. The research of genetic diversity about upland cotton and its offspring lines can reveal the genetic base of cotton in China on breeding origin, and help us to know the background and diversity of germplasm nowadays being used. And the research also can help breeders to mine important traits and use these good germplasm in high efficiency, and have great meaning of creating new germplasm. The goal of genetic research is to know the relationship between phonotype and genotype.Stoneville2B, Foster6, DPL15and CRI7are four core parents in cotton breeding in China. We constructed a four-way cross segregated population and its F23inbreed lines with these varieties. A linkage map was developed for the four-way cross with SSR markers and JoinMap V3.0software. The map with201SSR loci and58linkage groups was constructed, and covered a whole length of1691.0cM with an average interval of8.4cM between two markers, accounting for33.8%of the total recombination length of the cotton genome.54out of58linkage groups were located on25chromosomes, and4linkage groups were not located on any chromosomes. The data of yield and fiber qualities of the220F2plants and F2:3family lines were used to detect QTLs by interval mapping, and83QTLs were identified, including8significant QTLs. The results presented here help us to know the genetic base of cotton in China on breeding origin, and provide useful messages for cotton breeding, and for further research.At the same time, the genetic diversity of upland cotton (G hirsutum L.) with different ecological growing areas and parental origins in China was evaluated by207SSR markers covered the whole genome of cotton and12phenotypic traits, based on81representative variety accessions cultivated in China, seven of which were introduced from America. A total of541gene alleles were detected from207SSR primers, and the average genotype diversity index (He) was0.3174. The Neighbor-Joining cluster diagram of the81accessions based on SSR results was only partly consistent with the pedigree diagrams, which was accorded with the practice that some varieties were developed from hybridization of different pedigrees. The genotype diversity of domestic varieties was narrow while phenotypic traits represented better than introduced. The difference between the varieties from Yangtze River and Yellow River Basin was un-obvious. When evaluating the varieties according to different pedigrees, the genetic distance between DPL and Stoneville which were widely used by Chinese breeders was low, at the same time, the phenotypic traits of King and Foster were excellent.In our research, in order to use association mapping to test association sites and alleles of several traits, we need to know the LD in cotton genome. With the help of software TASSEL, we see low level of LD in cotton genome, cross-pollination and frequent hybridization and selection in breeding is the main reason. We detected numerous associations between marker sites and agronomic or quality traits. After that, we tried to find out alleles with good variation of different markers, and the typical variety with these alleles. It will provide useful messages for cotton breeding, and for further research. |
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