Special areas for in situ protection of Populus tremula autochthonous populations - gene reserve units – are mainly chosen based on phenotypic characteristics of trees, species biology and abundance, but detailed information on the genetic composition of stands is lacking. The aim of the study was to assess the genetic diversity in common aspen stands in Latvia to provide information on the optimum area and designation of gene conservation units. A total of 20 pure common aspen stands from 8 populations were analysed using 6 SSR markers at the age 6 to 8 years after first pre-commercial thinning. The average number of ramets per clone was only 1.4 and most of the analysed individuals (80±4.9 %) had a unique genotype. The maximum distance between identified ramets of most clones was 10 to 20 m. However, the maximum distance between identified ramets of some clones exceeded 80 m, reaching as much as 169.4 m. Analysis of molecular variance (AMOVA) shows that 7% of the total genetic variation was between populations and 93% within populations (P < 0.001). A comparison of genetic diversity parameters was made between the two regions designated as genetic resource units and the other analysed regions. The mean number of alleles was lower in the genetic resource stands (8.333 vs 11.333). The effective number of alleles (Ne) and heterozygosity was also slightly lower in the genetic resource units (Ne – 3.513 vs 3.967; Ho – 0.597 vs 0.655; He – 0.705 vs 0.731). To account for the sample size difference, a rarefaction approach implemented in the software Fstat was used to compare allelic richness and observed heterozygosity, and no significant differences were found between the two groups. Cluster analysis of genetic distances demonstrated some congruence with the geographical distances between regions: regions in the western part of Latvia formed a separate group from those located in the eastern part of the country.
Keywords: genotypic diversity, heterozygosity, gene reserve units, population, genetic distance.