The Analysis Of Genetic Diversity And SSR Abundance In Cotton Germplasms

The genetic diversity of 96 cotton germplasms, which belong to four cultivated species: Gossypium hirsutum, G.barbadense, G.arboreum and G. herbaceum, were carried on phenotype character and SSR molecular markers. Based on the SSR types and the quantity of allele, we fistly established the SSR abundance statistical method and analyzed the SSR abundance difference in different types of cultivated cotton species and the elite germplasms of upland cottons. This has vital importance for establishing the precise variety fingerprints, identifying the purity of germplasms, appraisalling the heredity characteristic of germplasms as well as the breeding parent match and the superiority combination forecasting. The main conclusions were as follows:1,The main agronomic characters among different cotton germplasms of different species and different varieties of one species showed significant or very significant differences. The phenotypic diversity index of G.hirsutum was 1.54, which was higher than other types of cultivated cotton species. SSR diversity of 96 germplasms belong to 4 cultivar species was very rich, 618 alleles were detected in 84 SSR loci, and 94.01% of them were polymorphic alleles. SSR polymorphic loci ratio and the number of alleles of G. hirsuturn were higher than that of other cultivar species. In contrast to the domestic germplasms of upland cotton, the SSR genetic diversity of foreign upland cotton was lower, but the fiber quality and yield characters of them are better. The similar genetic diversity of agronomic characters and SSR markers implies that the cultivar species with abundance germplasms possessed high genetic diversity.2,Average 7.75 specific SSR belts were detected in each cultivar species .The specific alleles also exist in some elite germplasms of upland cotton. This can be initial identification the species and related elite germplasm, and evaluate the the elite traits of these distinguishing germplasms.3,Polymorphic loci with high PIC value (＞0.65) were screened, and the core SSR primer are further confirmed, which can be used for effectively constructing fingerprint and investigating genetic relations of different germplasms. The SSR loci distributed on different chromosomes have different evolutionary level, the SSR on A or D genome can easily identify the tetraploid cotton species, however, the SSR on A and D genome can effectively distinguish the diploid genome.4,The results of SSR abundance index were as follows: SSR abundance and motifs are significantly different among different germplasms, and SSR abundance in tetraploid cottons are higher than that of diploid cottons. The predominance SSR motifs of G.herbaceum, G.arboreum, G.barbadense and G.hirsuturn were (AT)n, (TC)n, (AC)n and (TTC)n respectively. This method can effectively analyze SSR loci diversity among the germplasms with close relationship, and maybe illuminate the relation between SSR abundance and agronomic and economic characters.5,The cluster analysis were accomplished based on agronomic traits and SSR markers. The cotton germplasms of cultivated species were separated into three groups, including diploid, sea island cotton and upland cotton group. In the group of upland cotton, the obsolescence varieties were separated into a single sub-group obviously. The two kinds of cluster dendrograms of agronomic traits and SSR markers of the germplasms with high genetic similarity in same species was different in some extent, and this rightly showed the differences of genome and trait expression of different types of germplasms.6,SSR similarity coefficiency analysis indicated that G.herbaceum may be the A genome donor for tetraploid Sea island cotton, while G.arboreum may be A genome donor for tetraploid upland cotton.7,The G.arboreum and G.raimondii ESTs were respectively assembled by bioinformatical methods, and the differences of Simple sequence repeat (SSR) types and abundance between these two species were analyzed. It manifested that the numbers of assembled tentative consensus sequences, SSR abundance and the most abundant SSR motifs are both very different between these two species. Therefore, the differential analysis of SSR types and abundance in the donor species for A and D genome of tetraploid provide us more useful information for SSR marker development and profound research of the origin and evolution of Gossypium species.