Role of spring wheat seed infested withFusarium graminearumin spread and development of fusarium head blight and effects on agronomic performance

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Abstract
The importance of Fusarium-infested seed as a cause of fusarium head blight (FHB) was assessed for two spring wheat cultivars, 'AC Domain' (1998, 1999) and 'Glenlea' (1998-2000), at four prairie locations. Initial infection levels of 'AC Domain' and 'Glenlea' were 74 and 65%, respectively. Six treatments using mixtures of Fusarium-free and Fusarium-infested seed, in the ratios 100:0, 90:10, 75:25, 50:50, 25:75, and 0:100 of free to infested, were evaluated. Seedling emergence and number of tillers per metre of row significantly decreased with rising proportions of infested seed. In 2 of the 3 years of the study, yield was significantly reduced (up to 20%) in the 100%-infested seed treatment, which was attributed to lower stand establishment and lower plot density. Test weight was significantly reduced only in 1999 and thousand-kernel weight only in 2000. Seedling blight was not observed during the study. Fusarium graminearum was isolated from infected spikes only in the Manitoba trials at Brandon and Glenlea, while Fusarium culmorum was the only species isolated from the Vauxhall material, Alberta. Fusarium head blight did not develop at Swift Current, Saskatchewan. Severity of FHB was not significantly different across treatments. Fusarium equiseti, the predominant Fusarium sp. found in this study, was isolated from 8.1% of leaf sections averaged over 1998 to 2000, while F. graminearum was isolated at low levels, 0.1%. There was no pattern in the distribution of the Fusarium spp. across treatments. Since treatment effects were not associated with development of FHB, it can be concluded that Fusarium-infested seed was not a major cause of FHB in the year it was planted. Concerns of root infection of rotation crops, and of dispersal of the pathogen via infested seed are discussed.