PATHOGENICITY AND MYCOTOXIN PRODUCTION OF FUSARIUM SPECIES CAUSING HEAD BLIGHT IN WHEAT CULTIVARS VARYING IN RESISTANCE

Fusarium head blight (FHB) of wheat has recently become more prevalent in Manitoba, Canada. The objectives of this study were to assess the pathogenicity of Fusarium species isolated from infected wheat spikes, determine their potential to produce trichothecene mycotoxins and evaluate wheat cultivars for resistance to these Fusarium species. This information is a prerequisite to the development of cultivars with effective resistance to FHB in Manitoba. Eight Chinese and three Canadian wheat cultivars were evaluated against individual strains of seven Fusarium species singly in the field. Severity of FHB was measured as percentage of discolored peduncles and percentage of tombstone kernels. On this basis, Fusarium culmorum and F. graminearum were highly pathogenic, F. sporotrichioides had intermediate pathogenicity, and the other species were weakly pathogenic. For F. culmorum and F. graminearum, FHB severity correlated positively with kernel weight reduction and recovery of Fusarium species from the seed and correlated negatively with seed germination. Fusarium species varied in their ability to produce trichothecenes in infected wheat spikes. Wheat inoculated with F. poae contained both type A and B trichothecenes, while that inoculated with F. culmorum and F. graminearum produced type B only. Wheat inoculated with F. sporotrichioides contained type A trichothecenes, while that inoculated with F. avenaceum contained no detectable trichothecenes. Concentration of DON correlated positively with percentage of tombstone kernels in F. culmorum and F. graminearum, and that of HT-2 toxin correlated positively with percentage tombstone kernels in F. sporotrichioides. Biggar, Katepwa and Sceptre wheats were susceptible to F. culmorum and F. graminearum. High levels of resistance, expressed as low FHB severity combined with low trichothecene production, were found in several Chinese cultivars. These traits could be incorporated in adapted cultivars and be monitored by use of artificial inoculation.