Interaction of Fusarium graminearum and F-moniliforme in maize ears: Disease progress, fungal biomass, and mycotoxin accumulation

To investigate the interaction between two major ear-rotting pathogens, mai ze ears were inoculated with either Fusarium graminearum, F. moniliforme, o r an equal mixture of the two. Silk and kernel tissues were periodically ha rvested throughout the growing season so that a time course of the experime ntal variables (disease severity, ergosterol content, fungal DNA content, a nd mycotoxin concentration) could be recorded. Over the 3 years tested (199 2 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 er gosterol content and disease rating were correlated for both pathogens, but the highest correlation coefficients were obtained in the F. graminearum t reatment. The DNA analysis revealed that, in the mixed inoculum, F. monilif orme had a greater growth rate than did F. graminearum. In 1994, appreciabl e F. moniliforme from natural inoculum was found in the F. graminearum trea tment. Fumonisin B-1 levels did not differ between the F. moniliforme treat ment and the mixed inoculum treatment. The effect of temperature on the gro wth rate of the two species explained some of the field results, with tempe ratures in the silks being more favorable to F. moniliforme. Data on the gr owth 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 degrees C, whereas F. moniliforme grew well over a broader range, inc luding at higher temperatures.