Study On Genetic Diversity Of G.arboreum L. Germplasm Resources Conserved In China

The cultivated diploid, Gossypium arboretum .L(A genome) is an Old World cultivated cotton species, and plays a very important role in cotton gene bank of the world. It is an invaluable genetic resource for its early maturity, wide adaptability, tolerance to adverse circumstances, and other favorable traits. The present research was focused to analysis genetic diversity among 200 accessions of geographically different cultivars of G. arboreum in National Medium-term Gene Bank of Cotton in China. 19 morphological markers and 83 simple sequence repeat (SSR) markers were used to evaluate the genetic diversity of G. arboretum germplasm resources available in gene bank. The outcomes of this research could be useful in decreasing redundancy of effort and in constructing a core collection of cotton, important for gene discovery and efficient use of this genetic resource in cotton breeding. The main conclusions are as follows:1.The genetic diversity is extremely abundant based on 19 phenotypic traits in 200 accessions of G. arboreum L. There was significant or highly significant variation among 200 accessions based on each phenotype trait. Shannon-weaver index(H`)of the 19 phenotypic traits ranged from 0.34 to 2.15. The phenotypic diversity of the three main cotton-growing areas in China from higher to lower was Yangtze River, Yellow River and South China regions. The Euclidean distance among all 200 G. arboreum accessions ranged from 0.85 to 11.72(average 5.92). The 200 accessions were clustered into 16 phenotypic types when the value was 5.48, such as types of green broad leafe, red leaf, okra leaf, brown fiber, early maturity, late maturity, big boll, high lint percentage and so on. 8 accessions with specific phenotypic traits were selected.2.The genetic diversity was abundant based on SSR markers among 200 G..arboreum L. accessions.There were 368 alleles detected by 83 SSR primers, of which 329 polymorphic alleles and the mean number of polymorphic alleles per locus was 3.964. The PIC values was from 0.010 to 0.882 (average 0.578), and 33 loci (39.8% of the 83 SSRs) were selected with high level of information (PIC>0.7). The similarity coefficients among all 200 G. arboretum accessions ranged from 0.58 to 0.997(average 0.745), and the 200 accessions were clustered into 8 groups when the value was 0.73. The molecular genetic diversity of the three main cotton-growing areas in China from higher to lower was South China region, Yangtze River region and Yellow River region. This is clearly supporting the widely accepted history of the spreading ways of G. arboreum in China: it was introduced to South China from India and other countries. Subsequently it was introduced to Yangtze River region, Yellow River region and Liao River region in Northeast China, being cultivated and acclimatized under various ecological conditions since long time, a series of types and landraces developed.3.The clusters based on integration of phenotypic and molecular markers indicated that the accessions were clustered into 19 groups when the value was 1.48(Euclidean distance) and in an extremely biased distribution, of which 16 groups were made up of 16 accessions respectively, 2 groups were made up of 2 accessions respectively. There were more abundant genetic diversity among these 20 accessions than others, and 13 of them had special SSR markers.4.The comprehensive assessment revealed that there was rich genetic diversity among available G. arboreum germplasm resources in Chinese gene bank on both phenotypic level and molecular level. Even though, the two clustering results were not consistent and no apodictic relationships were observed between genetic distance and geographic distance. However, the molecular genetic distance, phenotypic distance and geographic distance were largely consistent among the varieties with extremely close or far genetic relationships. In other words, the varieties with very high SSR similarity coefficient had close geographic distance or similar phenotype, whereas, the varieties with very low SSR similarity coefficient had far geographic distance or more phenotypic variance.5.The results based on comparison and integration of morphological markers and molecular markers showed the the following inference: Changshujijiaomian and Haimenjijiaomian was the same variety with different names."Zhongyinzajiaozhong4"and"Zhongyinzajiaozhong5"were the same line without difference in theory. It was greatly possible that same variety with different names for these accessions: Xinpuxiaohua, Moyangxiaohua, Nayexiaohua, Shixiyayihao and"Duihua;"119S"and"India N.V50-70".