GENETIC-VARIABILITY IN THE CANKER-PATHOGEN FUNGUS, GREMMENIELLA-ABIETINA .2. FINE-SCALE INVESTIGATION OF THE POPULATION GENETIC-STRUCTURE

Genetic variation at 32 polymorphic random amplified polymorphic DNA l oci was analysed in the ascomycete canker pathogen fungus Gremmeniella abietina (Lagerb.) Morelet collected from one plantation of Pinus con torta Dougl, ex Loud. in northern Sweden. The genetic variability main tained in the G. abietina population was high. Many different multiloc us genotypes were found on each tree and in each sampling site within the plantation. The clonal fraction of the population was small, and i dentical genotypes were found either on the same tree or branch or on trees in the same sampling site. The finding of very few widely distri buted clones suggests that the effective dispersal of asexual spores i s limited to a few metres and resulted in small clusters of clones in local sites. Analysis of molecular variance revealed that 45.3% of the total variation was attributable to differences among isolates within trees, 22.5% to trees within sites and 32.3% to sampling sites differ ences. Allele frequencies at most of the loci varied significantly amo ng the sampling sites and average total genetic diversity over the 32 loci was 0.27 indicating high population subdivision. The factors that could have contributed to the observed population structure were disc ussed.