Sensitivity of Fusarium graminearum to metconazole and tebuconazole fungicides before and after widespread use in wheat in the United States

Authors: ANDERSON, NOLAN - University Of Kentucky; FREIJE, ANNA - University Of Kentucky; BERGSTROM, GARY - Cornell University; BRADLEY, CARL - University Of Kentucky; Cowger, Christina; FASKE, TRAVIS - Louisiana State University; KLECZEWSKI, NATHAN - University Of Delaware; PADGETT, GUY - Louisiana State University; PAUL, PIERCE - The Ohio State University; PRICE, TREY - Louisiana State University; WISE, KIERSTEN - University Of Kentucky

Submitted to: Plant Health Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2020
Publication Date: 3/15/2020
Citation: Anderson, N.R., Freije, A.N., Bergstrom, G.C., Bradley, C.A., Cowger, C., Faske, T., Kleczewski, N., Padgett, G.B., Paul, P., Price, T., Wise, K.A. 2020. Sensitivity of Fusarium graminearum to metconazole and tebuconazole fungicides before and after widespread use in wheat in the United States. Plant Health Progress. 21:85-90. https://doi.org/10.1094/PHP-11-19-0083-RS.
DOI: https://doi.org/10.1094/PHP-11-19-0083-RS

Interpretive Summary: Fusarium head blight (FHB), caused primarily by Fusarium graminearum, is a major disease of wheat in the United States. FHB is managed in part by applying fungicides called DMIs (demethylation inhibitors, or triazoles) during wheat flowering. We studied the sensitivity of U. S. populations of F. graminearum to the DMI fungicides metconazole and tebuconazole. Isolates of F. graminearum collected from wheat between 1981 and 2014 were tested for fungicide sensitivity using mycelial growth assays on Petri plates. We identified the fungicide concentration at which 50% of fungal growth was inhibited (EC50). A total of 45 isolates were tested for metconazole sensitivity, and 47 for sensitivity to tebuconazole. The mean EC50 for isolates collected prior to 2000 was 0.0240 µg/ml for metconazole and 0.1610 µg/ml for tebuconazole. For both fungicides, isolates collected between 2000 and 2014 were significantly less sensitive than isolates collected prior to 2000 (mean EC50 = 0.0405 for metconazole and 0.3311 µg/ml for tebuconazole). One isolate collected in Illinois in 2012 had lower sensitivity than other isolates collected between 2000 and 2014: it had EC50 values of 0.1734 µg/ml for metconazole and 1.7339 µg/ml for tebuconazole. This study is the first step toward developing a fungicide sensitivity monitoring program for F. graminearum in the United States.

Technical Abstract: Fusarium head blight (FHB), caused primarily by Fusarium graminearum, is a major disease of wheat in the United States. FHB is managed in part by applications of demethylation inhibitor (DMI) triazole fungicides during anthesis. The objective of this study was to examine the sensitivity of U. S. populations of F. graminearum to the DMI triazole fungicides metconazole and tebuconazole. Isolates of F. graminearum collected from wheat between 1981 and 2014 were tested for fungicide sensitivity using mycelial growth assays to determine the effective concentration at which 50% of fungal growth was inhibited (EC50). A total of 45 isolates were tested for metconazole sensitivity, and 47 for sensitivity to tebuconazole. The mean EC50 for isolates collected prior to 2000 was 0.0240 µg/ml for metconazole and 0.1610 µg/ml for tebuconazole. For both fungicides, isolates collected between 2000 and 2014 had significantly higher mean EC50 values (mean EC50 = 0.0405 and 0.3311 µg/ml for metconazole and tebuconazole, respectively) compared with isolates collected prior to 2000. Isolate, year and state of collection all affected the mean EC50 values of isolates collected between 2000 and 2014. A single isolate collected from Illinois in 2012 exhibited EC50 values of 0.1734 µg/ml for metconazole and 1.7339 µg/ml for tebuconazole, indicating reduced sensitivity compared to the mean EC50 of other isolates collected between 2000 and 2014. This study is the first step toward developing a fungicide sensitivity monitoring program for F. graminearum in the United States.