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POSTERS: Genetics of Resistance I

P-271 - The utility of a molecular assay in determining Phytophthora sojae pathotypes

Monday, August 4, 2025
3:45 PM - 4:30 PM HST
Location: Exhibit Hall 3
Abstract Text: The accepted method used to identify pathogenic variants (pathotypes) of Phytophthora sojae, a soilborne pathogen of soybeans (Glycine max), is resource-intensive, time-consuming, and challenging to conduct accurately. Identifying P. sojae pathotypes is crucial to determine which soybean varieties will potentially be most resistant to Phytophthora root rot in a field. The accepted pathotyping method involves injecting soybeans that carry resistance (Rps) genes with P. sojae isolates, then evaluating the soybean’s response. We used a rapid PCR-based pathotyping assay developed by Dussault-Benoit et al. (2020) to detect avirulence genes in P. sojae isolates previously pathotyped by the accepted method described above. We found little pathotype agreement between the two methods (about 15%). The reason for the discrepancy is uncertain, but it could be because the P. sojae isolates were in culture too long, the accepted method yielded false positives or negatives, or the PCR method did not detect the appropriate avirulence genes in P. sojae. To pathotype a few new isolates of P. sojae from Minnesota, we are comparing the PCR method, the accepted pathotyping method, and a soil inoculum method that might better mimic natural field infection. Our goal is to highlight discrepancies in pathotype identification that arise from different methods and initiate discussions within the P. sojae community about developing a standardized, rapid, and accurate pathotyping approach.