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POSTERS: Fungicide and antibiotic resistance

Occurrence of quinone outside inhibitor (QoI) resistance in Virginia populations of Parastagonospora nodorum infecting wheat
Navjot Kaur - Virginia Tech Tidewater AREC. Nathan Kleczewski- University of Illinois, Chase Mullins- Virginia Tech Tidewater AREC, Hillary Mehl- Virginia Tech Tidewater AREC

Stagonospora nodorum blotch (SNB) of wheat, caused by Parastagonospora nodorum, is managed using cultural practices, resistant varieties, and foliar fungicides. Frequent fungicide use can select for fungicide resistance, making certain chemistries less effective; this may in part explain increasing severity of SNB in the mid-Atlantic U.S. Quinone outside inhibitor (QoI) resistance has been documented for a diversity of fungi, but it has not been reported for P. nodorum in the U.S. The objectives of this study were to 1) evaluate QoI sensitivity of P. nodorum from Virginia wheat fields, 2) screen P. nodorum for QoI target site mutations in the cytochrome b gene (cytb), and 3) develop a molecular assay to detect target site mutations associated with QoI resistance. Sensitivity of 16 isolates to pyraclostrobin and azoxystrobin was evaluated with radial growth assays, and cytb was sequenced. One isolate was insensitive to both fungicides, and it had the G143A mutation in cytb. For azoxystrobin, 9 isolates without target site mutations had reduced sensitivity. Additional isolates (N=74) were sequenced, and 7 had the G143A mutation. A pyrosequencing assay targeting G143A was developed as a rapid method to screen P. nodorum for the QoI resistance-conferring mutation. This is the first report of QoI resistant P. nodorum in the U.S. Overall resistance frequency was low, but resistance management practices are needed to maintain the efficacy of fungicides for SNB control.