Application Of SSR Molecular Markers To Different Salt-tolerant Traits Of Alfalfa

With SSR molecular marker technology, the genetic variability of 320 individuals of 8 alfalfa populations both in home and abroad was analyzed in this thesis. The materials consisted of 5 salt-tolerant alfalfa varieties, named Zhongmu NO.1, Alfanafa, AZ-90NDC-ST, AZ-Germ Salt-â…¡, SALADO; and 3 salt-sensitive alfalfa varieties, named AZ-88NDC, Atlantic and Weinan. The results were as follows:1. The 9 SSR loci with ideal bands were selected from 20 pairs of SSR primers. 65 alleles were found in them. The allele frequencies were calculated with 0/1 method and tetraploid method.2. With the allele frequencies, we calculated the genetic heterozygosity, polymorphism information content (PIC), and effective allele number. A high level of variability within populations was found in this study. It was shown by the 0/1 method that the PIC of all loci except AFca15 were more than 0.5. Among these 8 loci, there were 4 loci with 0.6.7. The highest PIC was 0.7989 in AFca11. By the 0/1 method, the range of average genetic heterozygosity of each population was from 0.6197 to 0.6963, and that of average effective alleles number of each population was from 3.1 to 3.9. By the tetraploid method, the range of average genetic heterozygosity of each population was from 0.6036 to 0.7308, and that of average theoretical effective allele number of each population was from 3.9 to 6.8.3. With the DISPAN software, genetic distance (DA/DS) and genetic resemble coefficient among populations were calculated and the NJ dendrogram was constructed to evaluate the genetic variability and genetic relationship among populations. A high level of variability among populations was found in this study. A very near relation between the two salt-tolerant populations of Atlantic and Weinan was observed in our study, whose genetic resemble coefficient was 0.9077 by the 0/1 method, and 0.9592 by the tetraploid method. The Zhongmu NO.1 had a far relation with the others. The 5 populations of Salado, AZ-90, AZ-salt, Alfanafa, and AZ-88 could be regarded as the third cluster.4. It was the first time to develop and apply the tetraploid method to analyze the genetic diversity in tretraploid alfalfa with SSR molecular markers. The calculating method of the allele frequencies and the genetic heterozygosity of tretraploid species was developed and applied. The fact that the difference of genetic heterozygosity between the 0/1 method and the tetraploid method was nonsignificant (p>0.05) gave the evidence that the tetraploid method was also a suitable method to analyze SSR polymorphism in alfalfa.