Fusarium graminearum populations from maize and wheat in Ontario, Canada

Ontario has suffered widespread epidemics of Fusarium Head Blight or Gibberella Ear Rot roughly every five years since the late 1970s. We undertook a study of the chemotype and genotype of Fusarium graminearum isolated from 1,800 samples of wheat and maize collected across the cereal growing areas over three years. 468 isolates obtained were genotyped and 60 were selected for chemotyping. The dominant genotype has remained the native 15-acetyldeoxynivalenol (15-ADON) population. Approximately 20% of the strains tested were of the native chemotype producing only 15-ADON and one strain producing solely 7α-hydroxy,15-deacetylcalonectrin (3ANX) was observed. The majority of the 15-ADON strains were also capable of producing 3ANX. There was consistent mismatch between chemotype and genotype. This reflects the considerable plasticity in the genes associated with trichothecene biosynthesis documented in several Fusarium species. Although there is a large gradient in climate from southern to eastern Ontario, we did not detect differences in the distribution of the chemotypes. Grain from which strains were isolated for chemotyping were analysed. Approximately half of the 53 samples had >2 mg/kg deoxynivalenol with a maximum of 400 mg/kg and median of 14 mg/kg. 7α-hydroxy,3,15-dideacetylcalonectrin (NX toxin) was detected in three of these samples at an average of 4.5 mg/kg. The stability of the F. graminearum genotype in Ontario can be explained by several factors. Since 1980, the area planted to maize has remained stable, however, the area given to wheat has about doubled. Minimum tillage was rare in 1980 but it is now the norm. Increased crop residue on the soil has greatly increased the biomass of ascocarps that overwinter. Overall, these data demonstrate the need to monitor the mycotoxins in Fusarium populations and for the need to consider the potential toxicity of NX in the feed supply.