First, third, and fifth authors: Department of Plant Pathology and Microbiology, Texas A&M University, College Station 77845-2132; second author: TerraGen Diversity Inc., Suite 300, 2386 East Mall, University of British Columbia, Vancouver, BC V6T 1Z3 Canada; and
fourth author: Institute for Plant Sciences, Phytopathology Group, Federal Institute of Technology, Zurich, Switzerland
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Accepted for publication 19 November 1996.
Restriction fragment length polymorphisms (RFLPs) were used to characterize the genetic structures of three field populations of Phaeosphaeria nodorum from Texas, Oregon, and Switzerland. Data from seven nuclear RFLP loci were used to estimate gene diversity and genetic distances and to make indirect measures of gene flow between populations. Three of the seven RFLP loci differed significantly in allele frequencies across populations. On average, 96% of the total gene diversity was found within populations. There was little evidence for population subdivision, suggesting that gene flow was not restricted among populations. Based on an average population differentiation of 0.04, we estimated that the exchange of 11 migrants among populations per generation would be needed to account for the present level of population subdivision. Genotype diversity based on DNA fingerprints was at a maximum for the Swiss population, whereas populations in Texas and Oregon had lower genotype diversities. Many multilocus haplotypes were found in each population. Ninety-five percent of RFLP allele pairs were in gametic equilibrium. The data were consistent with random mating within each population.
© 1997 The American Phytopathological Society