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Spatiotemporal population structure of Pseudoperonospora cubensis isolates in Michigan and Ontario, Canada
R. NAEGELE (1), L. M. Quesada-Ocampo (2), J. Kurjan (3), C. Saude (4), M. K. Hausbeck (3). (1) Michigan State Univ, East Lansing, MI, U.S.A.; (2) North Carolina State University, Raleigh, NC, U.S.A.; (3) Michigan State University, East Lansing, MI, U.S.A.; (4) Canadian Tobacco Research Foundation, Tillonsburg, ON, Canada

Cucurbit downy mildew (CDM), caused by the oomycete pathogen <i>Pseudoperonospora cubensis,</i> is a devastating disease that affects cucurbit species worldwide. Many cucurbits can be infected by this pathogen, but cucumbers are the most susceptible. Michigan is the number one producer of cucumbers for pickling in the U.S., and Ontario, Canada produces approximately 75% of the nation's greenhouse-grown cucumbers. This pathogen is dispersed by wind currents into Michigan or other northern regions from overwintering sites and introduced annually. Similar population structure among <i>P. cubensis</i> populations was identified within the northern U.S. and Canada, but not between the northern and southern U.S. in previous studies. To further evaluate the regional and temporal population structure of <i>P. cubensis</i> in Michigan and Ontario, Canada, sporangia from CDM lesions were collected from field-grown cucurbit foliage in 2011. Population structure and genetic diversity were assessed in 262 isolates using nine simple sequence repeat (SSR) markers.  Five genetic clusters were detected and change in population structure varied by site and sampling date within a growing season.

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