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 eva luate wheat cultivars for resistance to these Fusarium species. This i nformation is a prerequisite to the development of cultivars with effe ctive resistance to FHB in Manitoba. Eight Chinese and three Canadian wheat cultivars were evaluated against individual strains of seven Fus arium species singly in the field. Severity of FHB was measured as per centage of discolored peduncles and percentage of tombstone kernels. O n this basis, Fusarium culmorum and F. graminearum were highly pathoge nic, F. sporotrichioides had intermediate pathogenicity, and the other species were weakly pathogenic. For F. culmorum and F. graminearum, F HB severity correlated positively with kernel weight reduction and rec overy 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. poa e contained both type A and B trichothecenes, while that inoculated wi th F. culmorum and F. graminearum produced type B only. Wheat inoculat ed with F. sporotrichioides contained type A trichothecenes, while tha t inoculated with F. avenaceum contained no detectable trichothecenes. Concentration of DON correlated positively with percentage of tombsto ne kernels in F. culmorum and F. graminearum, and that of HT-2 toxin c orrelated positively with percentage tombstone kernels in F. sporotric hioides. Biggar, Katepwa and Sceptre wheats were susceptible to F. cul morum 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 adap ted cultivars and be monitored by use of artificial inoculation.