Study On Genetic Structure Of Quercus Variabilis Natural Populations

Quercus variabilis is one of main constituents of deciduous broad-leaved forests in the temperate and subtropical areas in China. In this paper genetic diversity and population genetic structure of 5 natural populations were studied by means of the newly developed microsatellite (SSR) markers. Based on the study of population genetic structure, the strategies to conserve the germplasm resources of Q. variabilis were also discussed. The results as follows:With 16 polymorphic microsatellite loci screened from 54 to amplify and analysis the samples from the five populations, a relatively high level of genetic diversity was detected in Q. variabilis species. Average number of alleles (A) and effective number of alleles (Ne) were 8.4375 and 5.9512 at the species level, respectively. The mean expected heterozygosity (He) was 0.8059, the mean Nei diversity index (h) was 0.8041 and Shannon information index was 1.8308 on average.According to the genetic diversity of the five populations, the ranking among them was the mountain Huang population from Qimen county in Anhui province (AHQM) >the Panshiling population from Zhongxiang county in Hubei province (HBZX) >the mountain Zijin population from Nanjing city in Jiangsu province (JSNJ)>the mountain Kongqing population from Jurong county in Jiangsu province (JSJR) >the Mohegou population from Luding county in Sichuan province (SCLD). The result with other backgrounds of the five populations suggested that human activities had a direct effect on the genetic diversity of populations. Furthermore, higher diversity was found with the populations from the central range of the species in contrast to those from peripheral areas.Coefficient of genetic differentiation was 0.0455 on average and the majority of genetic variation occurred within populations. The mean of gene flow (Nm) was 5.2382, which showed relatively high level of gene flow among populations. Continued distribution, long life, predominantly outcrossing, wind pollination and high gene flow might be the main causes of low genetic differentiation of Q. variabilis populations. In addition, significant correlation was found between geographical distance and genetic distance.At the population level, the average of observed heterozygosity (Ho) was 0.4292, much lower than expected heterozygosity (He=0.7762). The fixationindex (F) was 0.4502 on the average and there were significant deviations from Hardy-Weinberg equilibrium in five populations. Subdivision, small population size and low density of population might lead to the deficiency of heterozygotes and excess of homozygotes. However, the existence of null alleles in the experiment could be another reason for it.Two-locus analysis revealed the existence of significant linkage disequilibria per population and the different number of pairs showing significant linkage disequilibria per population (9 to 14). The findings, D2ST> D2ISand D'2IS> D'2ST, implied that the stochastic causes such as genetic drift might be the main cause of linkage disequilibria.According to the facts that the majority of genetic variation occurred within populations and diversity was higher with the populations from the central range, the strategies to conserve the genetic diversity of Q. variabilis should be laid emphasis on conserving the different kinds of individuals in big populations, especially the populations from the central range. Moreover, efforts should be made to keep the Q. variabilis population from being further destroyed.