Assessing the susceptibility of shelled corn to invasion by storage fungi

Shelled corn samples taken from different storage environments were rewetted and evaluated for susceptibility to fungal invasion (SFI) using ergosterol measurements and a test kit that measured CO2 evolution from 100 g samples placed in 0.473 liter air-tight containers. The kit uses a gel that changes color as ambient percent CO2 changes. Sample attributes measured included kernel damage, percent germination, electrolyte leakage from soaked kernels, and percent kernel infection. Using linear regression attribute measurements were compared to the difference in ergosterol (EGD) before and after rewetting and incubation for three days (21% mc, 24°C). Differences in CO2 kit measurements were consistent with expectations regarding SFI and CO2 kit measurements were well correlated with EGD (0.44 \u3c r2 \u3c 0.57). These results indicate the test kit effectively measures SFI. Except for percent kernel infection and percent fines (6.35 mm sieve), coefficients of determination (r2) for regressions of EGD with the sample attributes were statistically significant and varied from 0.47 for percent germination to 0.12 for percent fines (4.76 mm sieve). Correlations between the attributes and CO2 kit measurements were statistically significant (0.13 \u3c r2 \u3c 0.49) with the exception of percent fines (6.35 mm sieve) and percent kernel infection. A fungal susceptibility damage index (FSDI) was defined that was significantly correlated with EGD (r2 = 0.28). The performance of a digital color reader (DCR) for determining gel color was also investigated. The DCR was better able to distinguish differences among samples and the plot of DCR color number versus time was smoother than the plot for color numbers determined visually (VR). The r2 for EGD versus DCR color number was slightly higher (0.75) than the r2 for EGD versus VR (0.73). The DCR was used to assess the effect of incubation temperature (24°C versus 30°C) and moisture content (16% versus 21%) on CO2 kit readings for five samples representing a wide range of SFI. The 75th hour color number rankings for both moistures were similar at 24°C, but were more evident at 21%. Incubation at 30°C changed the rankings slightly. Kernel plating revealed differences in fungal growth that explained these changes