A geometric and probabilistic framework for mechanistic antifungal screening from colony morphology

Fungicide discovery still relies heavily on scalar screening endpoints [e.g. inhibition zones, median effective concentration (EC₅₀) or minimum inhibitory concentration (MIC)] that summarize growth suppression but provide limited information about geometry-linked failure modes, constraining mechanistic prioritization during early screening. Because colony morphology encodes growth direction and polarity, we developed a geometric and probabilistic screening framework to separate potency from polarity-linked failure modes in cacao- and coffee-relevant pathogens.

From routine colony images, we computed a fixed-dose potency coordinate, λ, as the negative natural log of the area survival ratio, and a polarity coordinate, I, as the natural log fold-change in length-to-width ratio (treated/control). We then estimated polarity-disruption event probability (p̂) with exact 95% Clopper-Pearson confidence bounds at an operational threshold of τ = 1.10, with sensitivity analysis across τ = 1.10-1.20. In a single-dose primary screen across nine isolates and four phenolic-branched amide/acid candidates, amides consistently clustered in the (+λ, +I) quadrant, indicating an action direction characterized by concurrent growth suppression and polarity disruption relative to the acid analogues. The strongest combination was CGH5 treated with PhSOAM (λ = 0.67), which also showed high shape-disruption probability (p̂ = 0.75; 95% CI 0.43-0.95). Ellipse-based axis reconstruction linked I to axis-specific contraction ratios and showed strong agreement with direct length- and width-based ratios. Re-analysis of an independent UV-C exposure-time gradient (0-30 min) produced coherent dose-dependent λ(d) and I(d) trajectories and supported event-level inference at ~10 min.

The λ-I-p grammar converts colony images into an instrument-agnostic screening language describing how strongly an intervention acts at the tested condition (λ), whether it is associated with polarity-linked geometry change (I) and how often a defined failure mode occurs (p̂), thereby supporting mechanistic screening and prioritization of candidate fungicides. Published 2026. This article is a U.S. Government work and is in the public domain in the USA.