Genetic Diversity Of Salix Oritrepha Population In The Alpine Area Of Eastern Qilian Mountain

This paper applied polyacrylamide gel electrophoresis (PAGE) method to study the genetic diversity of 8 subpopulations of Salix oritrepha distributed at different altitude gradients in the Alpine Area of Eastern Qilian Mountain. Six enzymes encoded by fifteen loci were assessed. The enzyme systems determined include: Esterase (EST), Malate dehydrogenase (MDH), Isocitrate dehydrogenase (IDH), Alcohol dehydrogenase (ADH), Peroxidase (PER),Glutamate dehydrogenase (GDH). The software (ImageMaster ID) has been used to analyze electrophoresis zymogram by qualitative and quantitative. The indices we adopted to evaluate the genetic diversity involved percentage of polymorphic loci (P), mean number of alleles per locus (A), mean effective number of alleles per locus (Ae), mean expected heterozygosity per locus (He) and mean observed heterozygosity per locus (Ho), and so on. The results showed as follows:1. Salix oritrepha population maintained relatively high level of genetic diversity. The percentage of polymorphic loci (P), mean number of alleles per locus (A), mean effective number of alleles per locus (Ae), mean expected heterozygosity per locus (He), and mean observed heterozygosity per locus (H0) were 60.8%, 1.638,1.433,0.260 and 0.275, respectively.2. There were deviations in the different degree between the expected and observed values of genotype frequency in each subpopulation. The negative fixation index (F=-0.0535) indicated that there was excess heterozygote in Salix oritrepha population, but the total population conformed to the Hardy-Weinberg equilibrium.3. There was relatively low inter-subpopulation genetic differentiation. The total gene diversity (HT), intra-subpopulation gene diversity (HS), inter-subpopulation gene diversity (DST) and coefficient of gene differentiation (GsT) were 0.281, 0.260, 0.021 and 0.075, respectively. Genetic structure analysis revealed inter-subpopulation genetic variation at 7.5%, meaning 92.5% of the genetic variation in Salix oritrepha resided in intra-subpopulations. Inter-subpopulation gene flow (Nm) was 3.095, which explained the low inter-subpopulation genetic variation and could avoid the genetic differentiation arose from genetic drift.4. Genetic relationships among subpopulations were assessed by genetic identity (I) and standard genetic distance (D). The mean genetic identity and mean standard genetic distance were 0.9655 and 0. 0354, respectively. The results suggested that 8 subpopulations had closerrelationships. The highest genetic identity appeared between PI (3050m) and P2 (3100m), and the lowest between P1 (3050m) and PS (3250m). Genetic distances were correlated with spatial distances significantly (r=0.9347).5. The genetic variation indices in Salix oritrepha population, such as percentage of polymorphic loci (P), mean effective number of alleles per locus (Ae), mean expected heterozygosity per locus (He) and mean observed heterozygosity per locus (H0) showed insignificant correlation with the altitude gradient except mean number of alleles per locus (A) (r=0.9181).