An optical density assay to determine the sensitivity of Globisporangium and Pythium isolates to mefenoxam

Data related to following objectives: 1- To validate the OD assay by comparing the OD assay values with agar amended assay 2- To evaluate the sensitivity of isolates of these species from carrot fields in Ontario 3- to determine if sensitivity to mefenoxam varies among species and based on the history of applications of mefenoxam to the carrot production fields in the Holland Marsh from which the isolates originated. Isolates were classified as resistant (R) when inhibition of mycelial growth was <60% in cV8 broth amended with mefenoxam at 100 μg mL-1 and there was 0% inhibition at 10 μg mL-1 compared with growth of that isolate in non-amended cV8 broth; moderately resistant (MR) when inhibition was <60% at 10 μg mL-1 but >60% at 100 μg mL-1 and sensitive (S) when mycelial growth inhibition was >60% at 10 μg mL-1 and there was no growth at 100 μg mL-1.

Isolates with >60% growth inhibition at 0.1 μg mL-1 and >80% inhibition at 5.0 μg mL-1 were classified as highly sensitive (HS), those with >60% inhibition at 1.0 μg mL-1 and complete inhibition at 10 μg mL-1 as moderately sensitive (MS), those with >60% inhibition at 5.0 μg mL-1 and complete inhibition at 10 μg mL-1 as less sensitive (LS), and isolates with <60% growth inhibition at 5.0 μg mL-1 but >60% inhibition at 10 μg mL-1 as slightly sensitive (SS).