Diversity and multilocus genetic structure in populations of Cryphonectria parasitica

Genetic diversity and multilocus genetic structures of four populations of the chestnut blight fungus, Cryphonectria parasitica, were analyzed. Two populations in Michigan had very low vegetative compatibility (vc) type diversity and also low diversity of DNA fingerprints and mitochondrial DNA (mtDNA) haplotypes. A population in Teano, in southern Italy, had low ve type diversity but higher levels of fingerprint anti mtDNA haplotype diversity. In contrast, a population in Finzel, Maryland, had high diversity for all markers. Mating type was in a 1:1 ratio in one Michigan population and in Finzel but significantly deviated from 1:1 in the other populations. DNA fingerprints were more similar within ve types than between ve types in Teano but nor in Finzel; lack of diversity for all markers precluded similar analyses for the Michigan populations. Based on tests for gametic disequilibrium and genotypic diversity, the multilocus structure in Finzel was consistent with a hypothesis of random mating. In contrast, the random mating hypothesis was rejected in Teano for the full sample but not within the dominant ve type, which comprised 75% of the sample. Recombinant va types between the two common ve types in Teano were found only rarely in the field, and DNA fingerprints did not always correlate to mtDNA haplotypes and ve types, indicating that recombination occurs infrequently in Teano. These results demonstrate that ve diversity does not necessarily correlate to diversity of other genetic markers but may be related to the reproductive biology of C. parasitica in nature.