| In recent years, there has still been a wide gap between cotton molecular research and its demand for breeding, despite cotton molecular breeding has made great achievements. Intraspecific narrow genetic base has become a main problem for genetic improvement of Gossypium hirsutum especially, leading to the high genetic uniformity accompanying the genetic vulnerability to adverse natural conditions. To broaden cotton genetic base and increase genetic diversity to continuously improve cotton yield, fiber quality, resistance to biotic stress and tolerance to abiotic stress, wide utilization of wild species for distant hybridization may be of importance in cotton breeding. G. tomentosum, a tetraploid species, possesses many desirable traits, such as morphological resistance to insect pest (heavy leaf hair and nectarless leaf), drought tolerance and fiber quality. To effectively discover and utilize more favorable genes from G tomentosum introgress into G. hirsutum background, the linkage map based on SSR markers was constructed firstly and important unique traits from G. tomentosum were mapped.In this study, a population of93F2individuals was developed by single seed descended from the cross between G. hirsutum cv08N2162and G tomentosum. Rased on the F2population established a genetic mapping with SSR markers, the relationship between the cotton genome and the homologous chromosomes were studied at the molecular level by comparative mapping with the genetic map (Guo et al.,2008). Furthermore, the genes conferring leaf trichome and leaf nectary were tagged. The results were as the following:1. Construction of genetic linkage map was performed using interspecific cross population of cotton with SSR markersIn this study, a total of8488SSR markers were employed to screen polymorphisms between two parents, approximately15.9%(1347/8488) of all SSR markers showing polymorphic bands and yielding1800polymorphic loci in F2population. Among of the above1800polymorphic loci, there were1045and755polymorphic loci generated by5108gSSRs and3380eSSRs, respectively. And polymorphic percentages were15.8%(807/5108) and16.0%(540/3380).682loci are codominant,458loci dominant to G hirsutum and660loci to G. tomentosum.Genetic Mapping were performed in JoinMap3.0software, and1312loci including two phenotypic traits had been mapped onto26chromosomes of cotton genome at a LOD>4, including46linkage groups. The total length of the map is3752.3cM, and the average distance between adjacent markers is2.86cM. There were12short linkage groups established by26markers, not being located on chromosomes yet. Another464markers did not be mapped on any linkage groups.There were620and692markers anchored on A-subgenomes and D-subgenomes respectively. Average distance of adjacent markers was3.05cM in At genome covering1888.9cM;2.69cM in Dt genome covering1863.4cM. There were91markers on A5, whose polymorphic loci were the most among26chromosomes of cotton. Chromosome with the least markers was A7with30polymorphic loci. A6had the longest length and covered224.8cM, compared to the shortest genetic distance of90.1cM on A4.There were506(28.1%) markers showed segregation distortion, of which255(14.1%) markers located and24SDRs totally were detected. The distribution of distorted marker loci were very uneven between At and Dt subgenomes, less distorted marker loci were located into At (89) than D sub-genome (166),7SDRs appeared in the At and17SDRs appeared in the Dt. Five distorted markers located on12short linkage groups.2. Comparison with high-density molecular map between Upland cotton and Sea-island cotton (HB)By comparative analysis between the HT map and the high-density molecular HB map,442common markers were found, of which204markers located in At and238markers located in Dt. Comparisons among all common markers revealed that the distribution of loci largely were collinear in homologous chromosomes accompanied with some inversions. Two reciprocal translocations after polyploidization were further confirmed between A2and A3, and between A4and A5chromosomes on both genetic maps. The percentage of segregation distortion markers in HT was higher than in HB, segregation distortion markers were distributed on all chromosomes except A13and the most were distributed on D5with21loci, while segregation distortion markers were distributed in only a few chromosomes in HB and most of segregation distortion markers were distributed on A7and its homoeologous chromosome D7.3. Location of genes controlling leaf trichome and leaf nectaryUsing the HT genetic linkage map obtained, the gene controlling leaf trichome (T1) was mapped as a discrete marker and was located in the central region of A6,0.49cM from the nearest locus NAU2417-400. Nectarilessness (Ne1) was located in the central region of D12,0.39cM from the nearest locus NAU3897-160. |
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