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Assessment of pathotype variability in Phytophthora sojae populations across the North Central region of the United States

Linda Weber: The Ohio State University, Dept. of Plant Pathology

<div>Phytophthora root and stem rot of soybean, caused by the oomycete <em>Phytophthora sojae</em>, is a devastating disease that accounts for losses of approximately 32 million bushels of soybean across the North Central region of the United States annually. This pathogen is most effectively managed by <span><em>Rps</em></span>-gene mediated resistance and consequently, assessment of current <em>P. sojae</em> populations is of great importance. The aim of this study was to characterize the pathotype diversity of <em>P. sojae</em> populations across the North Central region of the US. Soil was collected from multiple locations in each state with a history of Phytophthora root and stem rot and baited with the moderately susceptible cultivar ‘Sloan’. Recovered isolates were pathotyped using 14 soybean differentials to assess their virulence against commonly deployed <em>Rps</em> genes. From over 2600 soil samples collected across 292 locations, recovery efforts have led to the collection of over 800 <em>P. sojae</em> isolates, with more than 350 <em>P. sojae</em> isolates recovered from Ohio and Kentucky soils alone. From Ohio soil samples, <em>P. sojae</em> was recovered from 128 of the 190 soil samples baited, for a recovery rate of 67%. The characterization of these <span> <em>P. sojae </em></span>populations provides greater awareness of the virulence that exists against <em>Rps</em> genes, and which can be effectively deployed to confer resistance against <em>P. sojae</em> populations in the North Central soybean producing region of the US.</div>