Fitness and Resistance Mechanism of Fusarium graminearum from Fields to Demethylation Inhibitor (DMI) Fungicides in China

Tebuconazole and prothioconazole are triazole sterol demethylation inhibitor (DMI) fungicides widely used for controlling Fusarium head blight (FHB) in the world. In 2023, 3714 Fusarium graminearum isolates were collected from fields of 8 provinces in China, among which 116 (3.12%) isolates and 82 (2.21%) isolates showed low resistance to tebuconazole (Teb-R, resistance factor [RF] = 2.65–7.65) and prothioconazole (Pro-R, RF = 3.85–6.04), respectively. Importantly, 11 isolates (0.30%) showed dual resistance (Teb-/Pro-R). Teb-R, Pro-R, and Teb-/Pro-R isolates displayed fitness costs in vegetative growth, asexual and sexual reproduction, or pathogenicity. There was partial cross-resistance among the DMI fungicides. No mutations were found in CYP51s of Teb-R, Pro-R, and Teb-/Pro-R isolates. Under tebuconazole treatment, the expression of CYP51B in Teb-R isolates and CYP51A/B and ABC4 in Teb-/Pro-R isolates was significantly higher than in sensitive isolates. Under prothioconazole treatment, the expression of CYP51A in Pro-R isolates and CYP51A/B in Teb-/Pro-R isolates was significantly higher than that in sensitive isolates.