Activity and cell toxicology of fluazinam on Fusarium graminearum.

Fusarium graminearum is an important plant pathogen and the causal agent of Fusarium head blight (FHB). At present, the principal method of controlling FHB is through fungicides. Fluazinam is an agent with strong broad-spectrum antifungal activity and has been used to control many diseases. However, there are no reported uses of fluazinam for controlling FHB. This study reports the activity and cell toxicology mechanisms of fluazinam on the filamentous fungus F. graminearum and its effect on fungal growth and development. The activity of fluazinam was tested for 95 wild-type field strains of F. graminearum. The EC values (the 50% effective concentration) of fluazinam for inhibition of mycelial growth and spore germination ranged from 0.037 μg/ml to 0.179 μg/ml and from 0.039 μg/ml to 0.506 μg/ml, respectively. The fluazinam sensitivity of these strains varied in 4.9 and 13.0 folds, implying that the target of the fungicide remained unchanged. After treatment with 0.3 μg/ml (≈EC) fluazinam, the production of conidia was reduced, and the cell wall and cell membrane had shrunked; the cell nucleus and septum morphology, cell membrane permeability, and sexual development were not affected. When treated with 0.1 μg/ml (≈EC) or 0.3 μg/ml fluazinam, the mycelial respiration and deoxynivalenol (DON) synthesis of F. graminearum were decreased. Confocal images showed that the formation of toxisomes was disturbed after fluazinam treatment, suggesting that fluazinam reduces DON synthesis by inhibiting toxisome formation. Infection of wheat coleoptiles revealed that fluazinam had a strong protective activity against F. graminearum. At 250 μg/ml fluazinam the control efficacy of protective treatments reached 100% and controlled strains resistant to carbendazim. These results contribute to the understanding of the mode of action of fluazinam and its application.