Comparison Between Prothioconazole and Prothioconazole-Desthio in Poison-Plate Mycelial Growth Assays of Fusarium graminearum

Abstract

The active ingredient prothioconazole is a demethylase inhibitor (DMI) widely used in numerous commercial fungicide formulations for crop protection. However, prothioconazole converts in planta to prothioconazole-desthio, which was found to be the primary active form inhibiting CYP51 activity in fungi. Here, experiments were performed on Fusarium graminearum to compare the use of technical-grade prothioconazole-desthio, technical-grade prothioconazole, and formulated product Proline in poison-plate mycelial growth assays to investigate the relevancy of using prothioconazole for sensitivity testing. Prothioconazole-desthio was significantly more efficacious at mycelial growth inhibition than prothioconazole but mycelial growth and effective concentration to reduce growth by 50% (EC50) values between the two correlated significantly. Although care should be taken in interpreting EC50 values of prothioconazole, the compound is still suitable for monitoring sensitivity rather than purchasing the more expensive prothioconazole-desthio.