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

Tebuconazole and prothioconazole are triazole sterol demethylation inhibitor (DMI) fungicides widely used for controlling head blight (FHB) in the world. In 2023, 3714 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 of Teb-R, Pro-R, and Teb-/Pro-R isolates. Under tebuconazole treatment, the expression of in Teb-R isolates and and in Teb-/Pro-R isolates was significantly higher than in sensitive isolates. Under prothioconazole treatment, the expression of in Pro-R isolates and in Teb-/Pro-R isolates was significantly higher than that in sensitive isolates.