QTL Mapping Of Yield And Fiber Quality In Upland Cotton (Gossypium Hirsutum L.) Using F₂-derived Populations

Cotton is the most important natural textile fiber crop in the world and also an important plant oil and protein crop. Cotton genus comprises of four cultivated cotton species, including two diploid species Gossypium herbaceum L. and Gossypium arboreum L., and two tetraploid species Gossypium hirsutum L. and Gossypium barbadense L.. Upland cotton has the highest yield, and based on the importance of fiber, over 95% of the annual worldwide cotton crop is derived from G.. hirsutum L., upland cotton. However, as the vital raw materials of textile industry, the fiber quality of upland cotton is worse than that of sea-island cotton. With the rapid development of spinning technology, the request of cotton fiber quality become higher and higher. All these requests have attracted a lot of plant breeders to improve the yield and fiber quality of upland cotton.Traditional genetic strategies have been employed to enhance the yield and fiber properties of upland cotton for a long period. Recent progress in molecular markers provides plant breeders with a fast and precise way to modify quantitative traits in conventional selections. Using the markers close linked with yield and fiber quality QTLs to select traits will be effective in cotton improvement. In the present study, an F₂ population, which was derived from the cross of the two upland cotton cultivar CRI 35 and Yumianl, was used to construct a genetic linkange map with microsatellite markers, and QTLs affecting yield and fiber quality were detected based on the linkage map. The main results were as following:Yield and Fiber quality performances of mapping parents and F_2:3-5 populationThe lint percent of Yumian 1 was higher than that of CRI 35, whereas the boll number, boll weigh, seed cotton yield, lint cotton yield of CRI 35 were better than those of Yumian 1. With respect to the fiber quality of the two parents, the fiber length and fiber strength of Yumian 1 were better than those of CRI 35, and the fiber fineness, fiber uniformity and fiber elongation of the two parents were almost the same. For the F₂ and its derived population, the variations of all the yield and fiber qulity traits were large and continuous, and transgressive segregation was observed for most of these traits. This indicated that multigenic inheritance influenced all the yield and fiber quality traits.Primer polymorphism between the two mapping parentsIn the present study,8165 SSR primer pairs were used to screen the polymorphism between CRI 35 and Yumian 1,4707 of which were newly used, and 335 polymorphic primer pairs were obtained, accounting for 4.1% of the total numbers of primers.Screening the genotype of F₂ populationThe 335 polymorphic primer pairs described above were used to screen the 180 individuals of F₂ population(CRI 35×Yumian 1), and 340 loci were obtained. Among the total loci, co-dominant loci account for 82.95%, and dominant account for 17.05%. A total of 169 loci deviated from Mendelian segregation ratio(χ²ï¼ž3.85), accounting for 50.0% of the total loci.Construction of upland cotton genentic linkage mapA total of 340 SSR loci were included to perform linkage analysis, and a linkage map with 46 linkage groups and 303 loci was constructed. Among these linkage groups,45 linkages groups were located on 25 chromosomes except for one. The linkage map spanned 2543.6cM with an average interval about 8.39cM between adjacent markers, approximately accounting for 57.2% of the recombination length of cotton genome.QTL mapping of yield and fiber-related traitsMultiple QTL mapping was conducted to identify QTL for yield and fiber quality traits in four environments(Chongqing 2006-2008 and Hainan 2006) by using MapQTL5.0. The LOD threshold of significant QTL was calculated by permutation test with a genome-wide significance level of P= 0.05, and 48 QTLs were identified. Among the QTLs detected, twenty-five QTLs were for yield traits, and the others were for fiber quality. One QTL (qFS07-1) was detected in three environments, two (qFS20-1 and qFS21-1) was detected in two environments, and the other QTLs were detected in one environment. Twenty-two QTLs were distributed on A genome whereas 26 on D genome.