ABSTRACT
Soybean target spot, caused by the fungus Corynespora cassiicola, can be controlled with fungicide application. Succinate dehydrogenase inhibitors (SDHI) are the most recently registered group of site-specific fungicides. However, excessive use of these fungicides can contribute to the selection of less sensitive populations of the fungus. The current study aimed to assess the sensitivity of 54 C. cassiicola isolates to the SDHI fungicides bixafen and fluxapyroxad. The isolates were obtained from soybean (n=53) and cotton (n=1) leaves collected in five producing regions from 2014 to 2018. To determine the half-maximal effective concentration (EC50), the colorimetric microtiter plate assay was adopted. The EC50 values ranged from 0.02 μg mL-1 to 37.80 μg mL-1 for bixafen and from <0.0125 μg mL-1 to 44.40 μg mL-1 for fluxapyroxad, indicating the presence of C. cassiicola isolates with lower sensitivity to the tested fungicides. Isolates showing increased and reduced sensitivity were found in the same sampling site, which emphasizes the importance of adopting anti-resistance strategies to prevent the increase in less sensitive populations.
Keywords
chemical control; target spot; carboxamide; resistance