| Cotton is the leading natural fiber crop for textile manufacture in the world, and is also an important source of oil and livestock feed protein Cotton occupies an irreplaced status in the economic system of the whole country. With the increasing living level, people need more cotton product with high quality. The conflict between growing demand for cotton fiber and limited field of cotton is more sever. Therefore, it's of great importance to develop the cotton production and modify the cotton varities, especially upland cotton, which provides more than 90%of the whole world's cotton production.Conventional breeding strategies have played an important role in improving upland cotton. Because cotton yield and fiber quality traits belong to quantitative traits, which are easily affected by the environment, and complex correlationship exists between yield and fiber quality traits, the breeding efficiency is low. The great advance of DNA marker has provided an effective and precise way to modify cotton cultivars. Based on the molecular linkage map, the QTLs affecting quantitative traits can be indentified and genetically evaluated. Using the markers closely-linked with QTLs to conduct marker assisted selection will be more effective in cotton breeding. In the preset study, a recombinant inbred line population (CRI 35×Yumian 1) F2:7 were used to construct a genetic map with SSR marker, and to detect QTLs for yield traits. The main results were as following:1. Yield trait performances of mapping parents and population (CRI 35 x Yumian 1) F2:7The phenotypic analysis of yield traits for parents and population (CRI 35 x Yumian 1) F2: showed that lint weight, seed cotton yield of CRI 35 were higher than those of Yumian 1. The lint percent of Yumian 1 was higher than that of CRI 35. The mean value and C.V. of population vary greatly under different environment. All yield traits of population segregated continuously, and suggested that yield traits were quantitative traits controlled by multiple genes.Variance analysis of yield traits for population F2:7 showed that cotton yield traits were affected not only by genotype but also by environment. 2. Polymorphism of SSR markersA total of 14529 SSR primer pairs (7965 pairs were newly used) were used to screen the polymorphisms between CRI 35 and Yumian 1, and 648 (4.5%) primer pairs showed polymorphism.3. Genotyping population F2:7The 648 polymorphic primer pairs were used to genotype the population F2:7 with 180 lines, and 648 loci were obtained. Among 648 loci,481 loci segregated as co-dominant marker (74.2%of total loci), and 167 as dominant marker (25.8%of total loci). Theχ2 test showed that 235 loci (accounting for 36.3%of total loci) significantly deviated from the expected segregation ratio 1:1 (P <0.05).4. Genetic map constructionA total of 648 loci were used to conduct on linkage analysis, and a linkage map with 605 loci and 68 groups was obtained. Sixty-five of 68 groups were assigned to 26 chromosomes and 3 groups were not assigned to any chromosome. The map spanned 2804.9cM with an average distance of 4.6 cM between adjacent markers, accounting for about 63.1%of the entire tetraploid cotton genome.5. QTL mapping of yield traitsBased on the lingkage map constructed,11 QTLs for yield traits were identified. These QTLs contained 2 QTLs for boll weight,5 QTLs for lint percent,2 QTLs for lint cotton and 2 QTLs for seed cotton. One QTL (qLP07-1) was detected in three years and two QTL (qLC07-1 and QTLqSC07-1) were detected in two years. |
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