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Fusarium graminearum is the principal cause of fusarium head blight in North America, a disease that has caused severe losses in yield and quality of cereals. In North America, the vast majority of F. graminearum isolates produce 3-or 15-acetyl deoxynivalenol (ADON) in addition to DON. Until recently, 15-ADON isolates predominated, but a rapid shift from 15-ADON to 3-ADON producers in Canada and north central USA has been documented. In order to better understand the effect of this population shift on relative aggressiveness of isolates and mycotoxin accumulation, we tested a total of 58 isolates for 3-and 15-ADON production on two Canadian spring wheat cultivars, 'Roblin' (susceptible) and '5602 HR' (moderately resistant). In Experiment 1, three isolates from the Canadian provinces of Manitoba, Saskatchewan and Alberta, each of which produced either 15-ADON or 3-ADON, were tested using spray inoculation. In Experiment 2, 20 isolates which produced 15-ADON and 20 which produced 3-ADON from Manitoba, were tested using point inoculation. There were no significant differences in aggressiveness among isolates based either on geographic origin or mycotoxin type. Analysis of seeds from inoculated heads by gas chromatography/mass spectrometry indicated that the 3-ADON producing isolates had significantly higher DON levels than the 15-ADON isolates in 'Roblin' after both spray and point inoculation and in '5602HR' after point inoculation. DON levels following point inoculation by 15-ADON isolates were similar in the two cultivars. The 15-ADON isolates from Alberta produced less DON than 15-ADON isolates from Manitoba and Saskatchewan. Consistently, more ADON was produced by 15-ADON isolates than by 3-ADON isolates. The results of the study suggest that if the percentage of 3-ADON isolates in Canada increases, DON levels in cereals are likely to increase in epidemic years.

In 1985, abnormally high summer rainfall in southern Manitoba resulted in a high incidence of fusarium head blight symptoms in some samples of wheat delivered to primary elevators. Fifty-three wheat samples, containing between 0.2 and 5.4% (wt/wt) pink kernels and white "tombstone" kernels, were examined for Fusarium species and trichothecene mycotoxins. Fusarium species were found in 48 of the samples with F. graminearum in 30, F. sporotrichioides in 38, F. poae in 21, F. acuminatum in 21, F. avenaceum in 21, F. equiseti in 25, F. culmorum in 3, and F. oxysporum, F. sambucinum and F. subglutinans in 1 each. The mycotoxin deoxynivalenol was found in 39 samples at concentrations ≤ 1.40 ppm and in 1 sample at 3.65 ppm, diacetoxyscirpenol in 20 samples at ≤ 0.08 ppm, HT-2 toxin in 10 samples at < 0.05 ppm, and T-2 toxin in 11 samples at ≤ 0.20 ppm.Key words: Fusarium, trichothecenes, mycotoxins, wheat

Wheat contaminated with deoxynivalenol (DON), and distillers dried grain and solubles (DDGS) obtained after ethanol production from the contaminated wheat, were irradiated to doses ranging from 2.0 to 55.8 kGy using an electron accelerator. Samples of wet distillers grain, distillers solubles and stillage obtained during production of DDGS were also irradiated. All samples were analysed for Fusarium trichothecene mycotoxins by a method involving use of gas chromatography-mass spectrometry (GC-MS). The three production intermediates showed dose-dependent reductions in their DON contents ranging from 47.5 to 75.5% at the highest doses. Electron beam treatment produced a 17.6% reduction in the DON level of wheat at the highest dose used, but had no effect on DON in DDGS. These results indicate that electron beam treatment may provide a method for reducing DON levels in DDGS on an industrial scale.