Optical Density Assay to Determine the Sensitivity of <i>Globisporangium</i> and <i>Pythium</i> Isolates to Mefenoxam
Bibliographic record
Abstract
Several species of Globisporangium and Pythium cause cavity spot of carrot. Disease management in conventional production relies primarily on application of the fungicide mefenoxam. Growers’ reports in Ontario, Canada, of severe cavity spot, even when using mefenoxam applications, suggest that mefenoxam resistance may be prevalent in pathogen populations in this region. The objectives of the study were to develop a rapid and accurate optical density (OD) assay to assess mefenoxam sensitivity of 188 isolates of Globisporangium and Pythium species collected from 13 carrot fields in Ontario from 2020 to 2023. The isolates belonged to seven species: G. intermedium, G. irregulare, G. rostratifingens, G. sylvaticum, G. ultimum, G. violae, and P. sulcatum. The OD was measured at 600 nm in broth amended with different concentrations of mefenoxam, with OD readings at nine positions per well in a 96-well plate. The OD assay was validated by comparing half maximal effective concentration values with a standard fungicide-amended agar medium assay using 20 representative isolates. There was a significant linear relationship ( R 2 = 0.97, P < 0.0001) between the two assays. Of the 188 isolates tested, 24% exhibited <60% inhibition of mycelial growth at 5 μg ml −1 mefenoxam, 50% were inhibited by >60% at 5 μg ml −1 , 19% were inhibited by >60% at 1 μg ml −1 , and 7% were inhibited by >60% even at 0.1 μg ml −1 . The OD assay proved to be efficient, rapid, and accurate for monitoring the mefenoxam sensitivity of these oomycetes. [Formula: see text] Copyright © 2025 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 0.001 |
| Meta-epidemiology (narrow) | 0.002 | 0.001 |
| Meta-epidemiology (broad) | 0.001 | 0.001 |
| Bibliometrics | 0.002 | 0.002 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.003 | 0.002 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".