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Genetic variation at 32 polymorphic RAPD loci was analysed in the ascomycete canker pathogen fungus Gremmeniella abietina (Lagerb.) Morelet collected from one plantation of Pinus contorta (Dougl.) in northern Sweden. The genetic variability maintained in the G. abietina population was high. Many different multilocus genotypes were found on each tree and in each sampling site within the plantation. Clonal fraction of the population was small and identical genotypes were found either on the same tree/branch or on trees in the same sampling site. The finding of few widely distributed clones suggests that the effective dispersal of asexual spores is limited to a few metres and resulted in small clusters of clones in local sites. AMOVA analysis 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 differences. Allele frequencies at most of the loci varied significantly among the sampling sites and average Fst over the 32 loci was 0.27 indicating high population subdivision. The factors that could have contributed to the observed population structure were discussed.
Key words: Gremmeniella abietina, genotype/clone distribution, population subdivision, RAPD
by Alfred E. Szmidt