I am testing fungicides on plant pathogenic fungi, by using microplate spectrophotometer assay with OD measurements and use AUC (area under the growth curve) to compare test wells with positive growth control, but I can't find any clear guidelines, on with what % of inhibition should the antifungal compound be regarded as highly, moderate, or non - inhibitory. Some studies, that compare OD at certain time points determine the concentrations of compounds that cause 50 % growth inhibition, and ChatGPT says, that fungal growth up to 20 % compared to control indicates good inhibition by the fungicide. But looking at the results I have so far I am not sure that would be applicable. For example compounds, that show around 80 % inhibition (AUC compared to control) increase the fungi lag growth phase up to 24h longer than the control, but with in week after the start of experiment wery good mycelim growth is visible in these wells, should that be considered as a high inhibitory activity?
Take a look at the protocols at the Fungicide Resistance Action Committee (FRAC).
Note that an EC50 (effective concentration for 50% reduction in growth or spore germination, depending on the antifungal being tested) is a fairly standard measure of activity. Comparing the concentrations that give a 50% reduction in growth gives an indication of activity. For example, an EC50 of less than 1 microgram per ml is in the range for many commercial antifungals. An EC50 of more than 100 microgram per ml or higher than one can get into suspension is generally not effective.
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