Study On The Genetic Variation Of Tamarix Chinensis Lour. Populations

Tamarix chinensis Lour. possesses high alkali and water tolerance and is widely used as one of pioneer trees in coastal areas reforestation. In this study,9 natural T. chinensis Lour. populations and 1 artificial T. chinensis lour. population were sampled to study the genetic variation of this species. Systematic investigations were carried out including growth characteristics, the genetic structure derived from nuclear SSR and cpSSR so as to provide inference to T. chinensis lour. protection and management. The main results are as follows:T. chinensis Lour. cutting had high surviving rates and so it may become the paramount reproduction materials in later breeding. There existed significant variation in the biomass, the mortality rates, the number of branches, and the ground diameter of cutting seedlings among different provenances and among clones as well, with variation among clones being higher than that among provenances. The great growth performance difference between the 1a cutting seedlings and 3a cutting seedlings suggested that it should take a relatively long time to fully recognize the growth performance of different clones and to breed novel superior clones.8490 unigenes were obtained from 22724 Tamarix spp. ESTs using Phrap software.206 SSRs were distributed in 202 unigenes, which accounts for 2.14% of the total number of unigenes.164 primers were designed by PRIMER5.0 and we randomly chose 75 of them to be synthesized. By screening these primers on T. chinensis lour. individuals we found 40 primers amplified DNA fragments and 14 primers were polymorphic.14 polymorphic EST-SSR and 2 gSSR primers were used to reveal the genetic diversity of the 10 sampled populations. The results showed that the genetic diversity was high at the species level, with the average number of alleles (A) being 4.3750, the effective number of alleles (Ne) 2.758, the mean expected heterozygosity (He) 0.5917, the mean Nei's diversity index (Nei) 0.5906, and Shonnon's information index (I) 1.0689. T. chinensis lour. had the relatively high genetic diversity among shrub species. The differences of genetic diversity were small among the 10 populations, with the highest genetic diversity index 0.5759 and the lowest genetic diversity index 0.5493. The genetic diversity order of the 10 sampled populations was: ZCX2 population>SHK population>LST population> ZCX1 population> SLJ population >NDM population.>SKL population>SCY population>ZYY population>ZHY population. The coefficient of genetic differentiation (Gst) was 0.0503, which means the majority of genetic variation occurred within populations. The gene flow (Nm) revealed was 4.7635, which indicated considerable gene exchange among the sampled populations. At the population level, the average of observed heterozygosity (Ho) was 0.5257, a bit lower than the expected heterozygosity (He=0.5916). The average of population fixation index was 0.0765, suggesting a low level of the excess of homozygotes. At the species level 12 of the 16 loci exhibited significant deviations from Hardy-Weinberg equilibrium, yet at population level, at least 10 loci were at Hardy-Weinberg equilibrium for each population. Bottleneck effect analysis indicated recent bottleneck event in each population. The detection of dump genes partly account for the relatively large number of loci at disequilibrium in some populations. Mantel test showed a low positive correlation coefficient (r=0.2865) between the genetic distance and geographic distance at non-significant level (p>0.05), while the cluster analysis of the 10 sampled populations showed an obvious geographic pattern, which means the genetic distance between populations from the same geographic region is less than that from different geographic regions.In this study,76cpSSR primers were used to reveal the genetic diversity of these 10 populations yet only 3 primers were polymorphic, producing 6 haplotypes in total. The 6 haplotypes identified had clear geographic distribution pattern. The southern populations and the northern populations possessed different haplotypes, which may imply the two kinds of populations originated from two different refugia. The population from the upper reaches of the Huanghe River, namely Damao population from Neimeng Province had more haplotypes than the populations from the lower reaches of the Huanghe River. We speculated the dispersal route of the northern populations may be along the direction of flowing water of the Huanghe River. The haplotype H1 found in the southern populations possibly originated from the Huanghe River areas, while the dispersal route of other haplotypes remained unknown.