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Diversity and Multilocus Genetic Structure in Populations of Cryphonectria parasitica. Yir-Chung Liu, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Paolo Cortesi, Mark L. Double, William L. MacDonald, and Michael G. Milgroom. second author: Istituto di Patologia Vegetale, Universita degli Studi di Milano, Milan 20133, Italy; third and fourth authors: Division of Plant and Soil Sciences, West Virginia University, Morgantown 26506. Phytopathology 86:1344-1351. Accepted for publication 30 August 1996. Copyright 1996 The American Phytopathological Society. DOI: 10.1094/Phyto-86-1344.

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 vc type diversity but higher levels of fingerprint and 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 vc types than between vc types in Teano but not 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 vc type, which comprised 75% of the sample. Recombinant vc types between the two common vc types in Teano were found only rarely in the field, and DNA fingerprints did not always correlate to mtDNA haplotypes and vc types, indicating that recombination occurs infrequently in Teano. These results demonstrate that vc diversity does not necessarily correlate to diversity of other genetic markers but may be related to the reproductive biology of C. parasitica in nature.

Additional keywords: biological control, Endothia parasitica, hypovirulence, population structure.