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Fungal Susceptibility at Four Temperature-Moisture Combinations and Carbon Dioxide Kit Color Reader Evaluation

The susceptibility of shelled corn to invasion by storage fungi was assessed using a carbon dioxide (CO₂) test kit. Shelled corn samples were rewetted to either 16 or 21% wb moisture content (MC) and incubated ≤80 hr at either 24 or 30°C in sealed glass jars. CO₂ concentration in the jars was quantified using the color number (0–5) of an indicator gel, which was determined either by visual comparison to a color card (VR) or using a Digital Color Reader (DCR). Plots of DCR color numbers versus time were smoother than those for VR color numbers. The DCR was better able to distinguish differences among samples, especially when color numbers were <2.0. The highest coefficients of determination (r²) for linear regressions of color number versus ergosterol difference were 0.75 for the DCR readings and 0.73 for the VR readings. Rankings of fungal susceptibility were similar at all four temperature-MC combinations and many r² values for linear regressions comparing readings at other conditions with those at 21% MC and 24°C were statistically significant (α ≤ 0.05). Incubation conditions and time of prior storage had a noticeable yet relatively minor effect on which fungi infected the kernels.