Genetic variation in native and invasive populations of Erigeron annuus as assessed by RAPD markers

The winter annual Erigeron annuus is triploid and agamospermous. We used the RAPD method to investigate patterns of genetic variation within and between populations of this species in its native range in North America and in Europe where it has been introduced. On the basis of 39 markers, we found a total of 192 RAPD phenotypes: 134 among 219 plants in North America and 67 among 400 plants in Europe. There was a strong correlation (r^sup 2^ = 0.80) in the frequency of bands in the North American and European samples. Most RAPD phenotypes were recorded only once or twice, but a few were found very frequently. In a dendrogram constructed using the neighbor-joining method, frequent phenotypes and those found on both continents tended to cluster, indicating that they were closely related to each other. We conclude that sexual reproduction is an important process influencing the genetic structure of populations. Much of the allelic diversity present in North America has reached Europe, and subsequent sexual reproduction has produced a large range of phenotypes. Patterns in the relative abundance of RAPD phenotypes indicate that certain genetic lines have a much stricter agamospermy than others, and these lines were particularly successful in colonizing Europe. [PUBLICATION ABSTRACT]