Linkage Mapping And Germplasm Enhancement For Superior Fiber Quality Using Interspecific Hybrid Of G. Hirsutum×G. Darwinii

Cotton is an important cash crop and the largest source of textile fiber and the fifth edible oil throughout the world. But because of the genetic basis of the cultivated species is too narrow, resulting in cotton breeding stagnant in respects of yield, quality or stress resistance. So it is very necessary to find the good traits of wild cotton, G darwinii belongs to tetraploid wild cotton, which has many favorable traits like fine fibre, drought resistance and verticillium wilt resistance. However, few studies on G. darwinii cotton study are reported. Here, a genetic linkage map was constructed using interspecific population of G hirsutum (TM-1)×G. darwinii with SSR molecular markers and several qualitative genes were mapped in G darwinii.In this study,181 of F2 population were produced by F1 selfing, which was from a cross between TM-1 and G darwinii, to construct a genetic linkage map. The map constructed was used to map the genes for petal color (Y1), petal red spot (R2), yellow pollen (P1), okra leaf (L1), and map QTLs for the initial blooming time.1. Construction of genetic linkage map by interspecific population of cotton with SSR markersTotal of 8,488 SSR markers were employed to screen polymorphisms, and 388 markers revealed polymorphism between two parents, yielding 400 polymorphic loci in F2 population. Among of the above 400 loci, there were 91 loci dominant, with 31 loci (7.75%) to TM-1 and 60 loci (15.00%) to G darwinii and 309 loci codominant. There were 185 (46.25% eSSR loci) and 215(53.75%) gSSR loci mapped on the map.Genetic linkage map was performed by software JoinMap 3.0,330 loci including four morphological traits had been mapped onto 26 chromosomes of cotton at a LOD≥4, including 46 linkage groups. The total length of the map is 2379.09 cM, and the average distance between adjacent markers is 7.20 cM. Meanwhile,12 markers constituted two linkage groups, which were 91.4 cM, and located in none of chromosomes.The remaining 53 loci can not be mapped onto any linkage group.There are 149 loci on A-subgenomes, covering 1164.32 cM, with the average genetic distance 7.81 cM and186 loci on D-subgenomes, covering 1214.77 cM, with the average genetic distance 6.53 cM. There were 20 markers on Chr D3, whose polymorphic loci were the most in 26 chromosomes of cotton. Chromosome with the least markers was Chr A8 with 2 polymorphic loci. Chr D1 had the longest length and coverd 225.7cM.There are 85 loci (21.2) which showed segregation distortion, of which 64 loci (19.1%) located on the map were detected.29 segregation loci were on A-subgenomes, and 14 loci (48.3%) of them tend to TM-1; 35 segregation loci were on D-subgenomes, and 15 loci (42.8%) of them tend to TM-1. The separation of loci ratio on A-subgenomes and D-subgenomes was 1:1.2. Segregation loci of D-subgenomes were more than D-subgenomes’.2. Location of important geneIn this study, the map between upland cotton TM-1 and Gdarwinii was used to locate cotton morphological markers, petal color (Y1) was located on the A13,4.1 cM from the nearest marker dPL0083-175; petal red spot (R2) was targeted to the A7, with the nearest marker NAU2887-450; yellow pollen (P1) was located on the A5,3.1 cM from the nearest marker NAU4106-390; okra leaf (L1) gene was located on the D1,2.0 cM from the nearest marker TMG11-240.By using WinQTLCart2.5 composite the interval map and the the first flowers blooming time of F2,4 QTLs were detected, which were located on the D1, A5,D1 1. There were one part dominant effect QTL, and one dominant effect QTL and two super-dominant effect QTLs, which explained the range from 0.48% to 11.7% of the phenotypic variance (PV). One QTL was located on the D11, which showed positive additive effect and the negative part dominant effect, and explained 11.7% of the phenotypic variance (PV), which seems to be a major QTL for further research.3. Development of germpalsmThree lines with stronger fiber and three with longer fiber were selected from a population of BC3F2. The average fiber length and fiber strength were 31.9mm and 37.47cN/tex, respectively, beign better than TM-1, but it needs to further confrimed.