Microsatellite analysis of genetic diversity in four populations of Populus tremuloides in Quebec

To determine overall genetic variability in aspen (Populus tremuloides Michx.) along the clay belt of northwestern Quebec, four populations were sampled at the transition zone between mixed-wood and conifer-dominated forests using a hierarchical strategy. Our objectives were (i) to estimate gene diversity among and within populations using microsatellite markers and (ii) to examine whether clonal structuring in aspen could be detected. For each population, three stands at least 1 km apart were sampled. Within each stand, five putative clones were sampled with a distance of 50 m between each clone. To examine potential genetic diversity within clones, for three of the putative clones sampled per stand, the three trees closest to this individual (potential ramets) were also sampled. All samples were analysed at four microsatellite loci. Measures of genetic variation all indicated that most of the variation occurred within rather than among the populations. R-st, based on a stepwise mutation model, was 0.0409, slightly higher than F-st, which was based on infinite allele model (0.0323). Within each stand, DNA fingerprint of five putative clones allowed the differentiation of genetically distinct individuals within these putative clones, and from 1.62 to 2.2 times more genetically distinct individuals were identified than by morphological identification. In the present study there was no correlation between the mean distance of the potential ramet to the central trunk (potential ramets were often within 2-3 m of the central trunk) and the possibility of the central trunk and ramet sharing the same genotype. The number of unique genotypes for the three putative clones sampled per stand varied from 11 genotypes per 15 samples to 14 per 15 samples. Consequently, it was not possible to identify clones by either distance from a given central trunk or morphological characteristics. Thus, after stand disturbance, suckers from different genotypes are likely to be closely mixed.