| Petrosimonia sibirica, which belonged to Petrosimonia Bunge in Chenopodiceae, was a kind of ephemeretum and only distributed in Xinjiang of China. This thesis is mainly studying the genetic structure and variation of P. sibirica with RAPD and the correlation with the surrounding environmental factors. And the survey provide the accurate and scientific information for understanding the genetic background systematic evolutionary of the desert plants and planning the effective conservation strategy.With 2+CTAB method, we can successfully extract total DNA from the leaf tissues of P. sibirica. By a series of tests, we obtained an economic and effective RAPD reaction system for adapting to P. sibirica RAPD markers. The optimized system included 0.1U Taq DNA polymerase, 1.5μl buffer (1+), 2μl Mg2+(2.5mM), 0.6μl dNTP (0.3μM), 8μl primer (12μM), 8ng temlpate DNA, 5.6μ1 ddH2O.The genetic diversity of P. sibirica, which is represented by 98 individuals collected from all 5 subpopulations, investigated with RAPD markers. 77 loci were selected by fourteen 10-mer primers, of which 76 were polymorphic. The percentage of polymorphic loci (PPB) of five subpopulations was 70.13%, 77.99%, 62.34%, 67.53%, and 61.04% respectively. The higher PPB (77.99%) was in subp.2 and lower (61.04%) in subp.5. The PPB's order was subp.2> subp.l> subp.4> subp.3> subp.5. The result revealed higher genetic diversity level in P. sibirica.By Shannon phenotypic diversity index from RAPD data, it was found that 69.33% of molecular variation existed within subpopulations while 30.67% of which among subpopulations. The result with Nei's index also identified it. And the genetic differentiation coefficient was 0.3052, which showed the genetic differentiation had occurred among subpopulations of P.sibirica in the oasis-desert zone. The genetic average distance among five subpopulations of P.sibirica was 0.1664; the largest was 0.2445 between subp.2 and subp.4, and the smallest was 0.1258 between subp.l and subp.2. It also showed the genetic variation existed among the subpopulations.Moreover, the gene flow of P. sibirica population (Nm=1.138) was lower than that of cosmopolite species (Nm= 1.881), and much lower than that of Caragana spp. populations over Maowusu sandy grassland (Nm =5.9529). It suggested that relativelylimited gene flow might be one of important factors influencing on the genetic structure of the species.In addition, through the correlation analysis, we observed the correlation between the genetic distance of P. sibirica and latitude, longitude and altitude was not significant. It showed the geographical difference was not one of the potential factors, which affected the genetic differentiation of P. sibirica.The cluster analysis could classify 98 individuals into 5 centers by Ward's method. It also showed there were some differentiations among subpopulations. The individuals within subp.4 were clustered firstly into one group as well as subp.5 In fact, because of the similarity of the environment, subp.4 and subp.5 had the same genetic characteristics. And then subp. 1, subp.2 was clustered. Lastly, the individuals of subp.3 were clustered, which indicated the greater genetic differentiation among those individuals.The relationship between molecular variation and habitat of P. sibirica was shown by PCA analysis with RAPD data. At the first principle axis(X-axis), 98 individuals concentrated on four region: subp.1 was mainly distributed at -2-1 range, subp.2 at -1-0, subp.3 and subp.4 at 0-1, subp.5 at 1-3. It revealed the distribution of the individuals related to the soil water and nutrition. And similarly, P. sibirica individuals scatter at the second principle axis (Y-axis), which representing the altitude and latitude. All individuals were focused on two zones at the third principle axis (Z-axis), which showed the distribution of soluble salt in soil.At the same time, the soluble salt in soil of the oasis desert transitional zone might play a role in maintaining the genetic diversity of P. sibiri...
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