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POSTERS: Population biology and genetics

Characterizing Pythium associated with Illinois soybean fields
Daniel Cerritos-Garcia - University of Illinois. Chase Kangas- University of Illinois, Santiago Mideros Mora- University of Illinois, Nathan Kleczewski- University of Illinois

Root rots can significantly impact yields of field crops. There have been no recent, detailed surveys of Pythium in Illinois field crops for at least a decade. The objectives of this project were to isolate and identify different Pythium associated with soybeans in Illinois and assess their aggressiveness level and sensitivity to select fungicides commonly used to control Pythium in field crops. Pythium spp. 2016 and 2018 through soil baiting and symptomatic plants. Isolates were identified by sequencing of the ITS region and morphology. Five species of Pythium were identified from 61 isolates recovered from 12 counties. These included P. ultimum (68.9%), P. dissotocum (8.2%), P. aphanirdermatum (6.6%) P. vexans (4.9%) and P. irregulare (1.6%). An additional 9.8% were only identified to genus. A petri plate assay was used to assess the aggressiveness of 61 isolates on soybean seed. All Pythium species reduced germination (76-100%) relative to non-treated controls. Phythium ultimum and P. aphanirdamatum caused significantly greater reduction in germination than all other species except P. irregulare. All species except P. vexans increased seed colonization relative to controls by 14-33%. Significant variation in aggressiveness existed within species. Poison plate assays were used to assess the sensitivity of 11 Pythium isolates to azoxystrobin and using a discriminative dose. Results indicated that 27% of isolates were insensitive to azoxystrobin. Additional studies to assess isolate sensitivity to other fungicides as well as aggressiveness to corn are ongoing.