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Monitoring changes in population structure of an isolated research population of Phytophthora capsici.
A. R. DUNN (1), C. D. Smart (1). (1) Cornell University, Geneva, NY, U.S.A.

The vegetable pathogen <i>Phytophthora capsici</i> (causal agent of Phytophthora blight) is moved between fields in soil, water, or infected plants but not wind. Previous work has shown that field populations of <i>P. capsici</i> are very diverse, with limited gene flow between fields and resulting in relatively isolated inbreeding populations. It is not known how this may affect pathogen aggressiveness or ability to adapt to resistant host varieties or new fungicide chemistries. To begin to answer these questions, a research field with no prior history of Phytophthora blight was inoculated in Fall 2008 with two single-spored isolates of <i>P. capsici</i> collected from nearby farms. In 2009 and 2010 susceptible vegetables were planted in the field and 47 and 59 isolates, respectively, were collected and genotyped using six microsatellite loci. A total of 26 and 30 unique multilocus genotypes were identified in 2009 and 2010, respectively. Neither the fixation index (F<sub>IS</sub>) nor the pairwise F<sub>ST</sub> between years were significantly different from zero, suggesting that the population in this field is randomly mating and that populations from the two years are not significantly differentiated. Characterizing this research population immediately after infestation will allow future comparisons to be made after years or decades of isolation and inbreeding. Potential implications for understanding <i>P. capsici</i> population dynamics on vegetable farms and effects on disease management will be discussed.<p><p>Keywords: Oomycete, Vegetables

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