| Cotton is one of the most important economic crops. It not only applys textile fibers, and the cotton seed is the source of edible oil; in recently years, with the economy development and textile technique improvement of China, the requirements of the output and fibers’ quality of cotton demand more and more, more and more plant breeders would go for efficient and reliable improved technology. As a whole, because the cotton research leg behind other crops, and especially the yield and fiber quality are complex quantitative traits, it is hard to make a breakthrough by conventional breeding. The combination of molecular markers and conventional breeding is the new approach for plant breeding, which would speed up the breeding process, improve the selection efficiency and decrease blindness.This paper used SSR markers to research two sets of materials:(1)51Upland cotton accessions from HuBei province were selected to analyze the genetic diversity and to evaluate the population structure, and combined with field traits to analyze LD and association mapping.(2) Based on an advanced backcross population (BC1F8) between G. hirsutum L.×G. barbadense L., the genotype was obtained and the agronomic traits QTL were mapped by BIL population.1. Molecular diversity evaluation and association analysis of Hubei Upland cottonIn order to evaluate the genetic diversity and evolution of51Upland cotton accessions from HuBei province,250SSR mapped markers were selected from26chromosomes covering the cotton genome. A total of117polymorphic primer pairs amplified213loci, polymorphism information content (PIC) values of the SSR primers ranged from0.04to0.83, with a mean of0.46.The highest PIC was BNL3257; average effective numbers of alleles (Ne) was1.366, general average value for the Shannon index (I) was0.326. According to the different source material crosses, HB materials could be divided into four subgroups. Namely, K=4, the5%molecular variation was exsiting among populations and95%within populations. At p<0.001, the general genetic differentiation index (PhiPT) was0.045.Genetic similarity coefficient among fifty one Upland cotton variety was0.598on average, ranging from0.378to0.817. We analyzed yield and fiber qualities by using the whole genome scanning association analysis with application Q+K+MLM model in two different environments. At p<0.05significant condition, there were24and23loci associated to the yield respectively in Huanggang and Jingzhou environments, the average rates that markers expain the variations were10.0%and7.0%; a total of31loci associated to5fiber quality indexes of significant correlation in Huanggang environment, the average rate of the model explaining characters variation was9.7%, ranging from1.6%to16.5%; a total of32loci associated to5fiber quality indexes of significant correlation in Jingzhou environment, the average rate about expaining the variations was10.9%, ranging from7.0%to18.5%.2. Genotype analysis and QTLs mapping for the interspecific BIL populationThe development of a new interspecific cotton backcross inbred line (BIL) population of54lines deriving from an interspecific cross between Emian22and3-79. Four hundreds and forty six SSRs were selected based on the interspecific linkage map constructed in our laboratory, the genotype of the population (BC1F8) was obtained with the SSR markers, significant markers were searched by oneway ANOVA (SPSS for Windows V17.0). It aimed to obtain more independent and accurate effect estimates and to solve the problem about QTLs positioning, and the mapping results were obtained and applyed on markers assisted selection and cloning.A total of446markers loci had been covered the cotton genome which length was4418.9cM, there were fifty gaps with those loci, the coverage rate in cotton genome was11.2%; the average recovery percentage of the population background was79.8%for every line, ranging from69.51%to89.25%; this recovery percentage was higher than the recovery percentage of classical genetics. The introgression segments for each strain covered10.8%of cotton genome on average, the ratio of the length of homozygous and heterozygous introgression segments was2.91.The genotypic data and traits data were used to search for significant marker by oneway ANOVA, the threshold was0.01(Prob>F). There were61markers detected which associated with yield traits, total30markers were detected for Hundred-seed weight, the percentage of variance explained (PVE) was from13%to29%, BNL1043, BNL2443, BNL3436, HAU1782, MGHES16, NAU3206and NAU3349existed significant in both environments and the additive effect was negatively correlated. The numbers of significant markers for5index of fiber quality were as follow:2markers with Fibre Strength,4markers with Micronaire value,7markers with fiber length,11markers with elongation,6with Uniformity. Among these markers, many markers showed simultaneity marker-trait associate with several traits. That:only one site named NAU1148on chromosome11was negatively associated with Fibre Strength, the PVE was21%, the additive effect was-1.29and-1.12respectively, NAU1148also positively correlated with elongation; NAU3468significant marker locus on chromosome13was detected for different traits, such as Hundred-seed weight, Boll number per plant, Output per plant and Lint, then NAU3468could reduce Boll number per plant, but have positive additive effect for other three traits; HAU2371on chromosome7could reduce Micronaire value and increase fiber Length and Uniformity. The development of population and the performance of phenotype character and cotton genetic improvement were discussed. |
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