Genetic Diversity Evaluation And Establishment Of SSR Digital Fingerprint Of The Elite Germplasm Resources In Cotton

Genetic diversity evaluation of elite cotton germplasm resources is the foundation of cultivar improvement, and also it is beneficial for the cotton resource protection. The cases of tort were increasing along with the appearance of more and more new cultivars. Therefore, the establishment of unique fingerprint library means great significance for cotton cultivar intellectual property protection. The diversity and genetic distance among 330 accessions of elite cotton germplasm were analyzed by using 111 pairs of polymorphic simple sequence repeats (SSR) primers, and also the digital fingerprints of these accessions were established with 25 SSR primer pairs selected from them to distinguish them at DNA level and understand the genetic relationship among these accessions. Meanwhile, some agronomic characters of all the materials were also studied by Principal Component Analysis (PCA) for further breeding selection. The main results were as follows:1. The very significant differences for the main phenotype traits existed among the differently elite accessions. In these fiber quality traits, other traits had relatively lower variation except that fiber yellowness value showed the greatest variation. So fiber yellowness value could be selected as fiber quality related traits. Principal components analysis indicated that over 85 % of cumulative percentage resulted in the first three principal components which were fiber quality traits factor,plant height factor and bearing factor, respectively. It is important for cotton improvement select these accessions with excellent fiber quality, resistance to Verticillium wilt and early maturity.2. The dinucleotide and trinucleotide repeats with the main motif 'AG/TC were mostly observed by analysis of polymorphic SSR marker characteristics. The number of the polymorphism SSR loci located in D subgenome were more than those in the AD and A subgenome . The comparison of Genomic-SSR with EST-SSR indicated that the significant difference (0.050.05). From what mentioned above, it is inferred that the dinucleotide and trinucleotide repeats in D-subunit are apt to mutate among different accessions. 3. Four hundred and ninety-eight alleles were detected in 330 accessions of elite cotton germplasm by using 111 polymorphic SSR primers pairs. The percent of polymorphic loci was 87.15 % and the mean PIC value was 0.6452 with preferable polymorphism. The range for PIC of 25 core SSR primers pairs used to construct fingerprint maps was from 0.5121 to 0.8501 with the higher average of 0.7463.4. The bigger similarity coefficient among different accessions which was between 0.773 and 0.812 with the average value of 0.767, showed that less genetic variance was existed among most of all the materials. The standard error analysis of similarity coefficient matrix indicated that the standard error and the cluster was constant when the number of polymorphic SSR markers exceeded 80 loci. Therefore, it is suggested that 80 SSR markers were at least needed to correctly evaluate the genetic relationship among the accessions with less genetic difference.5. Based on UPGMA (un-weighted pair group method using arithmetic averages) cluster analysis, 330 elite cotton accessions were separated into two major groups: Group sealand cotton and Group upland cotton. In Group upland cotton, the obsolescence varieties were obviously separated into a sub-group. The materials with smaller genetic differences and similar agronomic characters were separately clustered into one group. In general, the narrow genetic basis was presented in upland cotton. And the origin of accessions were in good agreement with the pedigree of accessions by SSR analysis. So SSR marker could be looked upon as better marker to identify relationship among the accessions.6. 330 elite cotton germplasm could be distinguished by the fingerprint map, which was constructed with 25 SSR core primers pairs except the two accessions (309 and 310) which might have identical genetic background. And a simple method called denary numeric string was develeloped to describe fingerprints from different accessions.