Genetic structure of Melampsora epitea populations in Swedish Salix viminalis plantations

Amplified fragment length polymorphism (AFLP) was used to study the genetic structure of populations of the willow leaf rust, Melampsora epitea, in Sw edish willow plantations. In total, 197 isolates collected from Salix vimin alis clones in three locations in Sweden were analysed. AFLP profiles based on 83 markers were used to compute genetic distances between pairs of indi viduals. High levels of gene and genotypic diversity were detected in all p opulations, with 96% of the AFLP loci being polymorphic and with normalized Shannon's diversity indices ranging from 0.977 to 1.0. Analysis of molecul ar variance (AMOVA) showed small significant differences among locations, a lthough most of the molecular variability was found within locations (97.5% ). Five isolates from one willow clone in one location differed markedly fr om the common pattern. When these five exceptional isolates were excluded, no significant differences among willow clones were found with AMOVA. Sexua l reproduction and spore migration appear to be important factors for the p opulation genetic structure of this pathogen.