clonal structure and reduced diversity of the invasive alien plant erigeron annuus in lithuania

the alien species erigeron annuus (l.) pers. is in an intensive spreading phase in lithuania. random amplified polymorphic dna (rapds) and inter-simple sequence repeats (issrs) assays were used to study the genetic structure of old and new invasive populations and to determine the most spread genotypes of this species in lithuania. pairwise genetic distances between populations established using rapd and issr markers significantly correlated (r=0.91, p<0.05). our study indicates that there are two genetically different types of e. annuus populations. the first type is represented by a widely spread main clone and related monomorphic populations. the second type is represented by polymorphic populations, some of them present at sites where e. annuus has not been previously observed. main clone predominates in nine populations and is from the region where this species was first described in natural ecosystems of lithuania. upgma cluster analysis revealed genetic relationships between the main clone and accessions from old cemeteries where e. annuus has been grown as an ornamental plant. we found high genetic differentiation among populations (g st=0.58 for rapds, g st=0.64 for issrs). taken together, our results will contribute to the monitoring of e. annuus spread in lithuania.