Comparison Of Genetic Linkage Maps From F₂ And F_2:7 RIL Populations In Upland Cotton

Upland Cotton (Gossypium hirsutum L.) is the leading natural fiber crop in the world. With the improvement of textile technology, the better fiber quality will be required. As the yield and fiber quality of cotton belong to quatitaive traits, it is difficult to improve the yield and fiber quality by conventional breeding methods at the same time. The combination of conventional breeding and biotechnology can provide a new way for crop improvement. Transgenic and marker-assisted selection tecgnology implements the trait on molecular level and improves the economically important agronomic traits. Marker-assisted selection can reduce the blindness of selection in breeding, so the breeding efficiency can be improved.The previous studies show different cotton cultivars have different alles for the same trait, so the futural marker-assisted selection needs to locate QTLs for a large nomer breeding materials and pyramide more target QTL. At present, F2 and recombinant inbred line (RIL) populations are maianly used in upland cotton QTL mapping. F2 and RIL populations have their merit and demerit, eg:F2 population needs less time to establish, but it could not be used for long time or in multiple environments; RIL can be used in multiple environments, but it needs long time to construct. However, there are few map comparisons conducted between F2 and RIL population. In the present suty, F2 and RIL populations were developed from upland cotton cultivars, CRI 35 and Yumianl. F2 and RIL maps are constructed by SSR markers. The comparison of F2 and RIL maps may offer a theoretical basis for thire applications. The main results showed as following:Genotyping F2 and RIL populationA total of 180 F2 and recombinant inbred lines were genotyped with 312 primer pairs that showed polymorphism between two parents, and 318 polymorphic loci were detected. Six primer pairs obtained two loci.Segregation distortion loci ratioChi-square examination demonstrated that 139 of 318 loci deviated from the expected Mendelian segregation in F2 population (p<0.05), accounting for 43.7% of total loci. Seventy-eight (24.5%) loci shew severe distortion (p<0.001). A total of 125 loci deviated from the expected Mendelian segregation in RIL, accounting for 39.3%of total loci, whereas 35 (11.0%) loci deviated severely (p<0.001). F2 had more segregation distortion loci than RIL.Construction of F2 and RIL genentic linkage mapA total of 318 polymorphic loci were used to construct F2 and RIL linkage maps. The F2 linkage map included 287 SSR loci and 47 linkage groups, covered a whole length of 2425.8cM with an average interval of 8.6 cM between two markers, and accounted for 54.7% of the cotton genome. The RIL linkage map included 268 SSR loci and 46 linkage groups, covered 1759.6cM of total genomic length with an average distance of 6.6cM, and accounted for 39.6% of the cotton genome.Comparison of F2and RIL genentic linkage mapThe genome coverage, marker number and marker interval of F2 map were higher than that of RIL map, whereas the linakge gropu number of RIL map is higher than that of F2 map. A total 65.1% of marker distribution order was consistent in F2 and RIL maps. F2 map had more marker segregation marker than RIL map.