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ARS Home » Pacific West Area » Maricopa, Arizona » U.S. Arid Land Agricultural Research Center » Pest Management and Biocontrol Research » Research » Publications at this Location » Publication #380231
Research Project: Improved Environmental and Crop Safety by Modification of the Aspergillus flavus Population Structure

Location: Pest Management and Biocontrol Research

Title: Occurrence of quinone outside inhibitor resistance in Virginia populations of Parastagonospora nodorum infecting wheat

Author
item KAUR, NAVJOT - Virginia Tech
item MULLINS, CHASE - Virginia Tech
item KLECZEWSKI, NATHAN - University Of Illinois
item Mehl, Hillary

Submitted to: Plant Disease
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2020
Publication Date: 4/26/2021
Citation: Kaur, N., Mullins, C., Kleczewski, N.M., Mehl, H.L. 2021. Occurrence of quinone outside inhibitor resistance in Virginia populations of Parastagonospora nodorum infecting wheat. Plant Disease. 105:1837-1842. https://doi.org/10.1094/PDIS-11-19-2288-RE.
DOI: https://doi.org/10.1094/PDIS-11-19-2288-RE

Interpretive Summary: Stagonospora nodorum blotch (SNB) is an important foliar disease of wheat that has the potential to reduce grain yield up to 50% if the disease is not controlled. The primary method of SNB control is through application of foliar fungicides. However, reduced effectiveness of certain fungicides for control of SNB has been observed in the Mid-Atlantic U.S. Fungicide resistance in populations of the fungus that causes SNB has been documented in Europe, but prior to the current study, fungicide resistance had not been reported in the U.S. The objective of this study was to document and characterize fungicide resistance in populations of the SNB pathogen with a focus on the strobilurin class of fungicides. Leaves with signs and symptoms of SNB were collected from wheat fields throughout Virginia, and the fungal pathogen was isolated. Fungal isolates were evaluated for strobilurin fungicide resistance using a combination of culture-based methods and DNA sequencing. Approximately 10% of the isolates were resistant to stobilurin fungicides based on the inability of fungicides to inhibit fungal growth in culture and the presence of a mutation in the fungicide target site gene. A DNA-based assay to rapidly detect this mutation was developed and can be used in future efforts to monitor for strobilurin fungicide resistance. This is the first report of fungicide resistance within populations of the SNB pathogen in the U.S. Frequencies of fungicide resistance were relatively small, but continued use of strobilurin based fungicides by growers will likely increase levels of fungicide resistance over time. Thus, it is critical the growers utilize a variety of fungicide chemistries as well as an integrated approach to wheat disease management that is not entirely reliant on fungicides for disease control.

Technical Abstract: 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, 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 the cytochrome b gene was sequenced. One isolate was insensitive to both fungicides, and it had the G143A mutation in the cytochrome b gene. For azoxystrobin, 10 isolates without target site mutations had reduced sensitivity. Additional isolates (N=74) were sequenced, and seven had the G143A mutation; all seven isolates with the mutation had reduced sensitivity to pyraclostrobin and azoxystrobin compared to 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 U.S. Overall resistance frequency was low, but resistance management practices are needed to maintain the efficacy of fungicides for SNB control.