Comparative aggressiveness of isolates ofFusariumspp. causing head blight on wheat in Canada

Fusarium head blight (FHB) is an important disease of wheat in Canada. To supplement the development of FHB-resistant cultivars, the aggressiveness of Fusarium isolates representing eight species was investigated. Six wheat lines and cultivars were artificially inoculated with 12 isolates of F. graminearum and 6 isolates each of F. acuminatum, F. avenaceum, F. crookwellense, F. culmorum, F. equiseti, F. poae, and F. sporotrichioides at 50% anthesis. Symptoms of FHB were rated as disease severity on a 0 to 9 scale, 4, 7, 14, 21, and 28 days after inoculation, and as percentage of infected spikelets (IS) after 21 days. All species caused visible infections to the wheat lines and cultivars, but only F. graminearum, F. crookwellense, and F. culmorum resulted in severe disease development (>35% IS) and were considered highly pathogenic while the remaining species, which had <15% IS, were moderately and weakly pathogenic. There were significant differences (P < 0.05) in aggressiveness among isolates within species and in susceptibility among wheat lines and cultivars, suggesting that screening for resistance to FHB requires a mixture of several isolates. A new technique for a rapid and mass production of conidial spores of Fusarium spp. was described. This is also the first report showing that F. crookwellense is highly pathogenic to wheat.