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Interaction of Fusarium graminearum and F. moniliforme in Maize Ears: Disease Progress, Fungal Biomass, and Mycotoxin Accumulation

First, second, third, fourth, and seventh authors: Eastern Cereal and Oilseed Research Centre, Central Experimental Farm, Agriculture and Agri-Food Canada, Ottawa, Ontario, Canada K1A 0C6; fifth author: Carleton University, Department of Chemistry, Ottawa, Ontario, Canada K1S 5H6; sixth author: Food Research Program, Southern Crop Protection and Food Research Centre, 43 McGilvray Street, Guelph, Ontario, Canada N1G 2W1; and eighth author: Ridgetown College, University of Guelph, Ridgetown, Ontario, Canada N0P 2C0

To investigate the interaction between two major ear-rotting pathogens, maize ears were inoculated with either Fusarium graminearum, F. moniliforme, or an equal mixture of the two. Silk and kernel tissues were periodically harvested throughout the growing season so that a time course of the experimental variables (disease severity, ergosterol content, fungal DNA content, and mycotoxin concentration) could be recorded. Over the 3 years tested (1992 to 1994), the highest levels of disease and ergosterol were found in the F. graminearum treatment, followed by the mixture treatment (F. graminearum plus F. moniliforme) and, finally, the F. moniliforme treatment. Kernel ergosterol content and disease rating were correlated for both pathogens, but the highest correlation coefficients were obtained in the F. graminearum treatment. The DNA analysis revealed that, in the mixed inoculum, F. moniliforme had a greater growth rate than did F. graminearum. In 1994, appreciable F. moniliforme from natural inoculum was found in the F. graminearum treatment. Fumonisin B₁ levels did not differ between the F. moniliforme treatment and the mixed inoculum treatment. The effect of temperature on the growth rate of the two species explained some of the field results, with temperatures in the silks being more favorable to F. moniliforme. Data on the growth rate on silks obtained by the incorporation of radiolabeled precursor to ergosterol demonstrated that F. graminearum was able to grow well at 26 to 28°C, whereas F. moniliforme grew well over a broader range, including at higher temperatures.