QTL Mapping For Fiber Quality Using F₂ Population In Upland Cotton (Gossypium Hirsutum L.)

Cotton is the leading natural fiber crop, and fiber is the main resource of the textile manufacture. The world cotton production was supplied by two tetraploid species, G. hirsutum L. and G. barbadense L., and G. hirsutum L. accounted for 90% of the total production. However, as the basic raw materials of textile industry, upland cotton generally has lower quality fibers than sea-island cotton, i.e., short or coarse fibers of relatively low strength. With the advances in spinning technology and the needs of the people, the better fiber quality will be required. These requirements of fiber quality have attracted a lot of efforts of governments and scientists to improve cotton fiber quality, especially that of upland cotton.Conventional genetic strategies have been employed to enhance the fiber properties of upland cotton for over half a century. Recent advances in DNA markers offer plant breeders a rapid and precise alternative approach to conventional selection schemes to improve quantitative traits. Using the markers which were close linked with fiber quality QTLs to conduct marker assited selection will be helpful to improve fiber quality of cotton in China. An F₂ population developed from upland cotton cultivar Zhong 35 and Yumian1was used to construct a genetic linkange map with SSR markers which have stable polymorphism, and the linkage map was used to detect and map QTLs affecting fiber quality. The mainly results were as.following:Fiber quality performances of mapping parents, F₂, F_2:3 and F_2:4 populationIn the three environments (2006 chongqing, 2006 hainan and 2007chongqing), the fiber strength of Yumian 1 were 34.10 cN/tex, 31.60 cN/tex and 38.60 cN/tex , while which of Zhong35 were 29.30 cN/tex, 28.50 cN/tex and 33.50 cN/tex respectively. The fiber strength of Yumian 1 was better than that of Zhong 35 obviously, and the other fiber quality traits of the two parents were close to each other.For the F₂, F_2:3and F_2:4 population, all fiber-related traits were mostly ranged between the two parents, except the fiber strength, which were beyond the lower parent zhong35. The fiber quality traits segregated continuously, and the result suggested that the fiber-related traits were controlled by multiple genes.The correlation analysis indicates that except the correlations between uniformity and micro, strength, the others were all prominent. The correlation coefficients between fiber length and strength was higher than others.The variance analysis indicated that fiber-releted traits were affected by both the genotype and environment.Primer pair polymorphism between mapping parentsA total of 216 polymorphic primer pairs were obtained from 5518 cotton SSR primer pairs between the two mapping parents, acconting for 4% of the tatal primer pairs. The polymophic ratios were different in different primer types. DPL has the highest polymorphic ratio(8.50%), next is BNL(8.49%), and HAU has the least polymophic ratio(0.84%).Genotyping F2 populationThe 216 polymorphic primer pairs were used to genotype the 180 individual plants from (Zhong 35×Yumian 1) F₂ population, and 221 loci were obtained. 189 loci segregated as co-dominant markers (86.9% of the total loci) and 29 as dominant markers (13.1% of the total loci).Chi-square examination demonstrated that 71 out of 221 loci exhibited severe deviation from Mendelian segregation (X²>10), accounting for 32.0% of the total loci.Construction of upland cotton genentic linkage mapA total of 221 SSR loci were employed to perform linkage analysis, and a linkage map with 189 loci and 40 linkage groups was construced. Out of these linkage groups, 35 were assigned on 24 chromosomes, while the other 5 were not assigned on any chromosomes. The linkage groups included 2 to 17 molecular markers, with a length of 3.6cM to 151.2cM. The linkage map covered 1588.2 cM with a average distance about 8.4cM between two markers, accounting for approximately 35.71% of the total recombination length of the cotton genome.QTL Mapping of fiber qualityBased on the linkage map and the fiber quality detected, 37 QTLs controlling fiber quality traits were identified by using MapQTL5.0. Six QTLs affect fiber length, explaining phenotypic variance 5.4% to 11.0%. Three QTLs affect fiber uniformity, explaining phenotypic variance5.8% to 11.0%. Ten QTLs affect fiber micro, explaining phenotypic variance 5.1% to 10.7 %. Six QTLs affect fiber enlongation, explaining phenotypic variance 5.9% to 14.6%. Twelve QTLs affect fiber strength, explaining phenotypic variance 5.0% to 19.4%. The favorable alleles of Twenty-seven fiber quality QTLs originated from Yumian 1.