L. M. Quesada-Ocampo, Visiting Research Associate,
L. L. Granke, Visiting Research Associate,
J. Olsen, Undergraduate Research Assistant, and
H. C. Gutting, Undergraduate Research Assistant, Department of Plant Pathology, Michigan State University, East Lansing 48824;
F. Runge, Graduate Research Assistant, Institute of Botany 210, University of Hohenheim, D-70593 Stuttgart, Germany;
M. Thines, Professor, Department of Biological Sciences, Institute of Ecology, Evolution and Diversity, Johann Wolfgang Goethe University; Biodiversity and Climate Research Centre (BiK-F); and Senckenberg Gesellschaft für Naturforschung, D-60325 Frankfurt (Main), Germany;
A. Lebeda, Professor, Department of Botany, Palacky University in Olomouc, Slechtitelu 11, 783 71 Olomouc-Holice, Czech Republic; and
M. K. Hausbeck, Professor, Department of Plant Pathology, Michigan State University
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Accepted for publication 4 May 2012.
Pseudoperonospora cubensis is a destructive foliar pathogen of economically important cucurbitaceous crops in the United States and worldwide. In this study, we investigated the genetic structure of 465 P. cubensis isolates from three continents, 13 countries, 19 states of the United States, and five host species using five nuclear and two mitochondrial loci. Bayesian clustering resolved six genetic clusters and suggested some population structure by geographic origin and host, because some clusters occurred more or less frequently in particular categories. All of the genetic clusters were present in the sampling from North America and Europe. Differences in cluster occurrence were observed by country and state. Isolates from cucumber had different cluster composition and lower genetic diversity than isolates from other cucurbits. Because genetic structuring was detected, isolates that represent the genetic variation in P. cubensis should be used when developing diagnostic tools, fungicides, and resistant host varieties. Although this study provides an initial map of global population structure of P. cubensis, future genotyping of isolates could reveal population structure within specific geographic regions, across a wider range of hosts, or during different time points during the growing season.
© 2012 The American Phytopathological Society