Clonal diversity, gene flow and seed production in endangered populations of Betula humilis Schrk

Many plant species can reproduce by both sexual and vegetative means. Clonal diversity and degree of intermingling of clones in the vegetative reproductive mode can influence the mating and fertility of individuals. The aim of the study was to assess the clonal structure and its potential influence on gene flow and generative reproduction efficiency in six endangered Betula humilis populations from the southwestern margin of the species range. Analyses of seven microsatellite loci revealed 86 genets among 522 samples. In general, the phalanx strategy dominated in the populations considered, as 76% of ramets shared the same genotype with their closest neighbour. Nevertheless, substantial clonal and genetic diversities and high contribution of unrelated individuals in all B. humilis stands suggest that panmictic pollination prevails. On the other hand, positive and significant relationships between genetic and geographic distances in the two populations could be a consequence of biparental inbreeding resulting from the pollen and seed flow limitations. The seed germination capacity was very low (2.70%); however, the populations characterised by the lowest and highest values of clonal diversity parameters did not differ significantly in the number of germinated seeds, which indicates that clonality is not responsible for seed production failure.