Analysis On Genetic Diversity Of Tetraploid Species Of Gossypium

There are five tetraploid cotton species including 2 cultivated species, G.hirsutum and G.barbadense, and 3 wild species, G. darwinii watt, G. mustelinum Miers ex Watt and G. tomentosum. From the perspective of germplasm resources, G.hisutum L.races also belong to the tetraploid wild species. They are primitive types of the Gossypium hirsutum without cultivation and domestication, which not only has unique hereditary property of disease or insect resistance, drought or salt tolerance, high sthength and quality fiber but also easier to transfer good gene into cultivated species than wild resouces. So there was good value for utitilization to improve fiber quality and resistance. In order to verify the results of relationship among cotton species reported in previous studies and discover the diversity level of races and its genetic relationship, the genetic diversity of 18 allotetraploid cotton species and 42 upland cotton races were assessed based on agronomic and SSR analysis. Its significance lies in providing theoretical basis for effective utilization of races in future and offering more germplasm for breeders, thereby promoting the collection, conservation and effective utilization of cotton germplasm resources.The main results are as follows:1. Morphological observation of races revealed:The stylus height of the most Punctatum and Latifolium were low, but the plant height of the Latifolium was the lowest. Most of the Morrlli and Marie-galante were late-maturing, but there were petal base spots in most of the Marie-galante. Chicken foot-shaped and Super chicken foot-shaped were the clearest characteristic of Palmeri.2. Statistical analysis based on 17 morphological and phenological characters of races revealed:There were obvious differences in various materials, and different traits of different materials have expressed some degree of diversity, especially the coefficient of variations (CV) of Stem solfandthick, Leaf shape, Petal base spot size and Boll number were larger than 50.00%, but the CV of plant height was the smallest, only 21.10%. 3. The results of diversity indices indicated that the average diversity indice of 13 qualitative trait was 0.992, which among 4 quantitative trait was 1.972. So the whole diversity was relatively high, but the diversity indexes of different traits varied in larger interval. The diversity indices of each race were distinctly lower than general, the diversity indice of qualitative trait was the smallest in Morrlli, only 0.435.4. The cluster results based on morphological data showed that the genetic distance of all races was among 0.602-2.127 with an average of 1.387.28 cotton germplasms among 42 cotton germplasms mentioned above that were classified into 4 branches exactly:Punctatum(â… ),Marie-galante(â…¡), Morrlli(â…¢),and Latifolium(â…£). However, other 3 races could not be clusted branches respectively because of small amount of materials, which were clustered in other races.5.95 pairs of primers used in 60 different germplasm accessions, and a total of 658 DNA fragments were scored, of which 580 polymorphic bands were obtained, accounting for 88.15% of the total bands; The range of allele (NA) per SSR locus were 2 to 14 with the average of 6.93; Similarly, with 90 primers among 95 primers produced polymorphisms in all materials, we could detecte 530 DNA fragments in 42 upland cotton races, of which 438 polymorphic bands(82.64%) were obtained; The range of allele (NA) per SSR locus were 2 to 12 with the average of 5.89.6. The variation limit of polymorphism information content(PIC), Shannon-weaver diversity index(H') and Effective number of alleles(Ne) varied widely, indicating a wide genetic variation among 60 tetraploid cotton species and 42 upland cotton races by SSR markers, but diversity among the five tetraploid cotton species were more abundant than races.7. The genetic similarity (GS) coefficient in 60 germplasms ranged from 0.157 to 1.000, the minimum of which in 42 races reduced to 0.306 and with the average of 0.493. Count the numbers of the coefficient in 10 interval distribution, the percentage was 92.56% in the range of 0-0.700, which displayed that genetic similarity were very low in upland cotton races, in other words, the genetic diversity of upland races were so abundant.8. UPGMA cluster analysis based on SSR showed that the genetic relationship is the nearest between upland cotton and G. hirsutum race.Latifolium, Gossypium barbadense and G. darwinii watt is very close, G.mustelinum Miers ex Watt and G.tomentosum L.Nuttall ex Seeman is a bit close, It's the farthest between upland cotton and others.