Genetic Diversity And Relationship For The Semi-cultivar Races And Cultivated Germplasms Of G. Hirsutum L. Using SSR Markers

Cotton (Gossypium L.) is the leading fiber crop in the world. The genus has approximately 51 species, including 46 diploids (from A to G, and K) and five allotetraploids (AD), in which four of them are cultivated, including two diploid species:G. herbaceum L. (A1A1) and G. arboretum L. (A2A2), and two tetraploid:G. hirsutum L. (AD1AD 1) and G. barbadense L. (AD2AD2), the rests are wild species. The narrow genetic base of the G hirsutum L. had became a major constraint in cotton breeding. It is necessary to enrich the gene pool with utilizing cultivated varieties and wild germplasms. The semi-cultivated races of G. hirsutum L. possess many favorable traits that the tetraploid cultivars lack, such as excellent quality, resistance to a lot of diseases and so on. Besides, it has the same chromosome number with cultivar. Therefore, the research on genetic diversity and variation of information among semi-cultivar races of G. hirsutum L. and cultivars of G. hirsutum L. would facilitate efficient use for developing superior cotton cultivars. The genetic diversity and relationship of the semi-cultivated races of G. hirsutum L. were analyzed with SSR markers, using TM-1 (the standard line of G. hirsutum L.) as check and 3-79 (the standard line of G. barbadense L.) as reference check in this experiment. Meanwhile, the relationship and evolution of semi-cultivated races of upland cotton and their cultivated germpalsms were analyzed by 82 SSR primer pairs, and the main results were as follows.1. Diversity of SSR markers among the semi-cultivated races of G hirsutum L. To evaluate the genetic diversity and relationship of 7 semi-cultivated races of G. hirsutum L.,64 accessions were analyzed with SSR markers, using TM-1 (the standard line of G. hirsutum) as check and 3-79 (the standard line of G. barbadense) as reference check. A total of 502 gene alleles with 78% polymorphism were detected from 112 SSR primers. The number of DNA bands per primer ranged from 2 to 10 with an average of 4.5. The average coefficient of genetic similarity among the tested germplasms was 0.690, ranging from 0.533-0.995, which indicated that the genetic diversity among the semi-cultivated racesof G. hirsutum L. were rich. The average coefficient of each race was 0.653-0.796, with the highest of Marie-Galante and the lowest of punctatum, which indicated that the genetic diversity among Marie-Galante is much higher than the other races. Generally, the genetic diversity among the seven races of G. hirsutum L. was in order as:Marie-Galante> yucatanense> latifolium> palmerii >Morrilli>richmondii>punctatum. The UPGMA cluster analysis showed that the races of G. hirsutum L. could be clustered into four groups when genetic similarity coefficient was given as 0.690, and palmerii and latifolium were more closed with the cultivated upland cotton than others.2. The genetic relationship between semi-cultivated races and the cultivated germplasms:To evaluate the genetic relationship and evolution of semi-cultivars cotton and cultivated tetraploid cotton,64 accessions of 7 semi-cultivated races and 30 upland cotton germplasms from ten production countries were analyzed by 82 pairs of SSR primers. A total of 412 gene alleles with 76% polymorphism were detected. The number of alleles per primer ranged from two to ten with an average of 5.0. Genetic- similarity showed that the upland cotton cultivated germplasms was the nearest relationship to latifolium, and that from United States was the closest ones.3. Genetic diversity and relationship between seven semi-cultivated races and upland cotton germplasms:The average coefficient of the cultivars and seven semi-cultivated races of G. hirsutum L. were 0.681-0.758, with biggest one of that between cultivated germplasms and latifolium. The average coefficients of seven semi-cultivated races and upland cotton cultivated germplasms were in order as: latifolium> richmondii> palmerii> punctatum> Morrilli> yucatanense> Marie-Galante. The average coefficient of seven semi-cultivated races and TM-1 were 0.689-0.772, and latifolium was the closest one to TM-1. The average coefficient of seven semi-cultivated races of G. hirsutum L. with their cultivated germplasms come from different countries were 0.673-0.765, and latifolium was the nearest one to the upland cotton germplasms from United States.