Genetic diversity patterns in Phragmites australis at the population, regional and continental scales

Genetic diversity, population structure and interrelationships were investigated in eight populations of the common reed, Phragmites australis, in the Po Plain, Italy, by means of amplified fragments length polymorphisms (AFLPs) and random amplified polymorphic DNAs (RAPDs). Patterns of genetic diversity were analysed in relation to size, age and degree of human impact in the wetlands and compared with that of a distant population in Romania. Genetic distances between Po Plain clones and geographically distant clones were measured to determine the geographical extent of the gene pool. Nearly all populations studied are polyclonal and little correlation was found between genetic diversity and size, age and degree of human impact on the wetlands. One large (86 ha) monoclonal stand occurred in an old wetland with rather stable environmental conditions over a long time period, whereas polyclonal stands were younger and characterized by disturbance. On the interpopulation level it was not possible to differentiate between Po Plain populations and the Romanian population, indicating that a very extensive gene pool exists in Europe, to which both Po Plain and Romanian populations belong. There is however a certain degree of genetic structure among the populations that is not correlated with geographic distance, but is most likely related to P. australis colonization dynamics. A significant "stepwise" increase in average genetic distances was observed between clones >500 and >1500 km distant suggesting some kind of genetic pattern on a very large scale. Based on these results, P. australis populations in Europe could be considered members of a single meta-population. © 2007 Elsevier B.V. All rights reserved.