Significant variation in sensitivity to a DMI fungicide in field populations of Fusarium graminearum

Fusarium head blight caused by Fusarium graminearum (Fg) is a destructive disease on cereals around the world. Intensive application of fungicides on cereals has selected for resistance in many cereal pathogens. Two hundred and twenty‐four isolates of Fg from 13 different German field populations, 22 isolates from the UK and six reference isolates from Italy and the USA were tested for sensitivity to propiconazole. Propiconazole sensitivity showed a high heritability (H² = 0·97), with mean EC₅₀values ranging from 5·4 to 62·2 mg L⁻¹. Nearly 80% of the variance for propiconazole sensitivity was distributed within field populations, suggesting significant potential for selection of resistant isolates at the field scale. Sequence analysis revealed that the CYP51A and CYP51C genes carried several non‐synonymous substitutions but the CYP51B protein was not polymorphic. The non‐synonymous substitutions were distributed randomly among populations and were not correlated with fungicide sensitivity. Although not conclusive, the findings suggest that genes outside of the CYP51 family may make the most important contribution to DMI resistance in F. graminearum.