Characterization of species composition, chemotype, and in vivo and in vitro fungicide sensitivity of Fusarium isolates from wheat and corn in Michigan, USA

Authors: BREUNIG, MIKAELA - Michigan State University; BYRNE, ADAM - Fmc Corporation; JACOBS, JANETTE - Michigan State University; Ward, Todd; MCCOY, AUSTIN - Michigan State University; CHILVERS, MARTIN - Michigan State University

Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2025
Publication Date: 10/24/2025
Citation: Breunig, M.R., Byrne, A.M., Jacobs, J.L., Ward, T.J., Mccoy, A.G., Chilvers, M.I. 2025. Characterization of species composition, chemotype, and in vivo and in vitro fungicide sensitivity of Fusarium isolates from wheat and corn in Michigan, USA. Phytopathology. https://doi.org/10.1094/PHYTO-06-25-0214-R.
DOI: https://doi.org/10.1094/PHYTO-06-25-0214-R

Interpretive Summary: Fusarium Head Blight (FHB) of wheat and Fusarium Ear Rot (FER) of corn cause substantial crop losses worldwide and are a food safety concern because FHB/FER pathogens can contaminate grain with fungal toxins (mycotoxins) such as trichothecenes, fumonisins, and zearalenone. Because these diseases are caused by a diverse group of fungi, analyses of local and regional pathogen diversity are needed to develop effective disease control and toxin monitoring programs. In this study, we determined the species identity, mycotoxin potential, and fungicide sensitivity of 560 FHB/FER isolates from wheat, corn, and other crops in Michigan. In addition to identifying substantial species and mycotoxin diversity, we identified significant differences in sensitivity to common fungicides both within and between FHB/FER species in lab tests. Field plot tests indicated that no practical resistance to these fungicides currently exists within Fusarium graminearum, the most important FHB/FER species. However, the substantial differences observed in lab analyses suggest that additional monitoring of fungicide resistance in field populations is warranted.

Technical Abstract: Fusarium are a major concern due to mycotoxin contamination of wheat and corn grain. To characterize the population of Fusarium in Michigan, over 560 isolates were collected and species composition, chemotype and fungicide sensitivity were determined. In wheat, members of the Fusarium sambucinum species complex comprised 90% of isolates of which 82.5% were F. graminearum, multiple members of the Fusarium tricinctum species complex comprised 7%. In corn, members of the Fusarium sambucinum species complex comprised 40% with 37% identified as F. graminearum, while multiple species from Fusarium fujikuroi species complex comprised a total of 50%. Within this complex F. awaxy (4.6%) was present which is a first report in the United States. Across F. graminearum, chemotypes were found at the following proportions 92% 15-ADON, 6% 3-ADON, 1.6% NX and no NIV. In vitro mycelial growth sensitivity assays to triazole fungicides demonstrated Fusarium were most sensitive to metconazole, and less sensitive to prothioconazole and tebuconazole. Species-specific differences in sensitivity were identified, with Fusarium tricinctum species complex members significantly less sensitive than F. graminearum, and Fusarium fujikuroi species complex were significantly more sensitive. Within F. graminearum a small portion of isolates had EC50 values 10-fold greater than sensitive isolates. A subset of these F. graminearum isolates were chosen to investigate if reduced sensitivity in vitro would lead to practical resistance in vivo. Field plots were inoculated with spore suspensions however, no differences in the relative fungicide efficacy were found, signaling no practical resistance currently exists despite differences in vitro. While currently there may not be practical resistance, monitoring should continue as there is variation in in vitro sensitivities present within and among species of Fusarium.