Growth of Penicillium verrucosum and production of ochratoxin A on nonsterilized wheat grain incubated at different temperatures and water content.

The results of two experiments with wheat grain inoculated with Penicillium verrucosum are reported. In Experiment I, wheat grain, containing 10, 20 and 30% water, was incubated for 2 weeks at 10, 15, 21 and 28 degrees C. In Experiment II, wheat grain, containing 14, 16, 18, 20 and 22% water, was incubated for 2 weeks at 10, 15, and 20 degrees C. At initial moisture content (IMC) of the wheat grain up to 16% neither P. verrucosum growth nor ochratoxin A (OTA) formation were observed. In the range of IMC from 18% to 22% both the fungal growth and OTA synthesis were distinct, and the parameters were higher at higher temperature in the range 10-21 degrees C. A temperature of 28 degrees C was probably too high for proper metabolism of the fungus, including OTA formation. OTA formation was distinctly related to P. verrucosum abundance in the temperature range 10-21 degrees C, expressed both as the counts of fungal colony forming units (CFU) on agar DYSG medium and diameters of the fungal colonies growing around the wheat kernels placed on the surface of DYSG medium. OTA formation and abundance of P. verrucosum were negatively correlated with the percentage of wheat kernels, placed on DYSG medium, with growing colonies of fungi different from P. verrucosum. CFU counts of P. verrucosum on the wheat grain were significantly related to the diameter of the fungal colonies growing around the wheat kernels placed on DYSG medium. The relationship is described by an exponential regression equation.