In vitro fungicidal activity and in planta control efficacy of coumoxystrobin against Magnaporthe oryzae.

Rice blast, caused by Magnaporthe oryzae, is a destructive fungal disease in rice, causing serious losses in yield and quality. Coumoxystrobin is a novel methoxyacrylate strobilurin fungicide. In the current study, we determined the sensitivity of 100 M. oryzae strains to coumoxystrobin based on the mycelial growth inhibition method. The EC50 values ranged from 0.0089 to 0.0290 μg mL-1, with a mean EC50 value of 0.0163 ± 0.0036 μg mL-1, indicating that coumoxystrobin exhibits an excellent inhibitory activity in the mycelial growth of M. oryzae. In addition, the EC50 values had no significant difference among four populations from the different geographical regions. After treating with coumoxystrobin, cell membrane permeability increased, respiration decreased, and the hyphal tips were contorted, with offshoot of top increasing. Protective and curative activity tests showed that coumoxystrobin exhibited better protective and curative activities against M. oryzae in detached barley leaves in comparison to the currently used fungicides tricyclazole and azoxystrobin. Also, it was found that the protective activity was better than its curative activity. Furthermore, compared with the currently used fungicides, coumoxystrobin not only exhibited excellent control efficacy on rice blast, but also markedly reduced the dosages of chemical fungicides in the field trials. Overall, these findings provide important references for revealing the pharmacological effect of coumoxystrobin against M. oryzae and managing rice blast caused by M. oryzae.