Genetic Map Construction,comparative Mapping Of Segregation Distortion Loci And Genetic Diversity Analysis Of Cotton

Cotton (Gossypium spp.) is an important cash crop. It is not only the important source of natural fiber for the world's textile industry, but also an important source of edible oil. Narrow genetic base has become a main problem for genetic improvement of Gossypium hirsutum L. Molecular genetic map provides a firm framework not only for gene loci tagging, marker-assisted selection to reduce linkage drag and map-based cloning of important genes, but also for investigation of genomic structure and evolution of cotton. In this study, utilizing interspecific crosses "TM-1×Hai / 7124" conscruction F₂ population for the mapping, using the same materials with the other four BC₁ and one F₂ groups and comparative mapping of population groups, while of the 57 cotton varieties from the phenotype and genotype cluster. The main resules are as follows:1. Using 677 marker locis including 170 TM-1 dominant marker loci, from 456 polymorphismic SSR primers, were mapped. The present map had 55 linkage groups distributing on all 26 chromosomes, covering 2799.57cM, with the average genetic distance of 5.78cM between two adjacent markers. At sub-genome level, 224 and 260 marker loci distributed on the At and Dt sub-genome and covering 1746.453 cM and 1323.117cM, respectively. On a single chromosome level, the marker number was from 4 (Chr.14) to 82 (Chr.16), the map distance was from 26.113 cM (Chr.14) to 215.876 cM (Chr.19).2. Segregation distortion (SD) is the deviation of genetic segregation ratios from their expected Mendelian fashion and is a common phenomenon found in most genetic mapping studies. In previously BC₁ genetic map, more distored markers and segregation distortion region in A7 and D7 be found. Through comparative mapping between different groups the results that in the map of F₂, the markers on SDR of A7-D7 were compared with the original BC₁, in the F₂ map, the segregation distortion locis on A7-D7 gathering area are 42, and in the original BC₁ there is 52 sites, and there is 15 sites are correspondence between F₂ and BC₁, deviation from the same direction, indicating A7, D7 section line on the segregation characteristics of SDR, and different groups detected stability; in the other three groups, 49 marker segregation, but segregation is different, by the markers of SD on SDR of A7-D7 in the comparative analysis between different groups that , the separation has relation with the choice of male gametes and the effect of the cytoplasm. At the same time, using composite interval mapping, a pollen fertility QTL was mapped in the segregation distortion region on D7, which further prove the segregation distortion loci and explain the possible mechanism of distiotion by male gamete selection. For cotton A7-D7 on the segregation of the genetic effects of loci analysis and comparative mapping is the first time at home and abroad.3. Based on phenotyptic and SSR data, genetic diversity and category analyses were performed for 57 cotton varieties/lines from China, USA and Australia. Results indicated that the genetic similarity coefficient among varieties ranged from 0.45 to 5.56, indicating a relatively large genetic variation. The tree diagram of UPGMA clustering on yield traits, at the average genetic distance level, indicated that 57 varieties were divided into three categories, of which the first category had the highest lint percentage and lint yield per plant, with an average of 38.22% and 29.35g respectively. The second category possessed the highest seed index and seed cotton per plant (up to 12.05g and 76.73g respectively), and the third category had high boll size up to 5.54g. The result of clustering based on fiber quality traits also had three categories, and the first category had higher fiber uniformity ratio and fiber micronaire reading, with an average of 48.04% and 4.36, respectively; the second category possessed higher fiber span length and fiber elongation with an average of 31.57 mm and 7.11% respectively. The third category had higher average fiber strength of 36.18 cN/tex. Clustering based on SSR markers, 57 germplasms could be clustered into three categories. Some differences were found among results of different clustering methods, which may be related to the different genetic diversity levels of different phenotypic traits and molecular genotypes used in this study. All clustering results indicated that there were relatively larger and smaller genetic diversity among varieties from one country and from different countries, respectively, with obvious mutual penetration between countries. Only a few varieties showed significant geographical differences.