Occurrence of quinone outside inhibitor (QoI) resistance in Virginia populations of Parastagonospora nodorum infecting wheat

Navjot Kaur, Chase Mullins, Nathan Michael Kleczewski, Hillary Laureen Mehl

Research output: Contribution to journalArticlepeer-review


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 the increasing severity of SNB in the mid-Atlantic United States. Quinone outside inhibitor (QoI) resistance has been documented for a diversity of fungi, but it has not been reported for P. nodorum in the United States. The objectives of this study were (i) to evaluate QoI sensitivity of P. nodorum from Virginia wheat fields, (ii) to screen P. nodorum for QoI target site mutations in the cytochrome b gene, and (iii) to 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 the cytochrome b gene was sequenced. One isolate was insensitive to both fungicides and had the G143A mutation in the cytochrome b gene. For azoxystrobin, 10 isolates without target site mutations had reduced sensitivity. Additional isolates (n = 58) were sequenced. A total of seven isolates had the G143A mutation and also had reduced sensitivity to pyraclostrobin and azoxystrobin compared with a sensitive control isolate without the mutation. A pyrosequencing assay targeting G143A was developed as a rapid method to screen P. nodorum for the QoI resistance-conferring mutation. To our knowledge, this is the first report of QoI-resistant P. nodorum in the United States. Overall resistance frequency was low, but resistance management practices are needed to maintain the efficacy of fungicides for SNB control.

Original languageEnglish (US)
JournalPlant disease
Issue number6
Early online dateOct 1 2020
StatePublished - Jun 2021


  • Azoxystrobin
  • Cereals and grains
  • Chemical
  • Disease management
  • Field crops
  • Fungi
  • Parastagonospora nodorum
  • Pathogen detection
  • Pyraclostrobin
  • Pyrosequencing
  • Quinone outside inhibitors
  • Stagonospora nodorum blotch

ASJC Scopus subject areas

  • Agronomy and Crop Science
  • Plant Science


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