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POSTERS: Population biology and genetics

Diversity and fungicide sensitivity of Phytophthora pathogens of soybean in Illinois
Daniel Cerritos-Garcia - University of Illinois. Santiago Mideros Mora- University of Illinois, Nathan Kleczewski- University of Illinois, Shun-Yuan Huang- University of Illinois

Several species of Phytophthora cause damping-off and root rot on soybeans. However, response to resistance genes and fungicide seed treatments can vary between species and isolates. The objectives of this study were to determine pathotype diversity of Phytophthora in Illinois and determine their sensitivity to fungicide active ingredients found in soybean seed treatments. Pythium spp., P. sojae, and P. sansomeana were isolated between 2016 and 2018 through soil baiting and from symptomatic plants. Isolates were identified by sequencing of the ITS region and morphology. Twenty-one isolates of P. sojae and six of P. sansomeana were recovered from 12 counties. The pathotype of each Phytophthora isolate was determined by inoculating 14 differentials with known Rps genes. Twenty and sixty percent of the isolates were able to cause disease on plants with the Rps1c or Rps1k, respectively. The sensitivity of Phytophthora spp. to the fungicides metalaxyl, mefenoxam, azoxystrobin, and ethaboxam were determined using poison plate assays and calculating EC??. All Phytophthora spp. isolates were sensitive to metalaxyl, mefenoxam, azoxystrobin, and ethaboxam at concentrations lower than 1 µg a.i. ml ? ?. The characterization of the population of oomycete pathogens causing disease on soybeans will enable better use of resistance and fungicide seed treatments.