Genetic and phenotypic diversity within the Fusarium graminearum species complex in Norway

Authors: AAMOT, H - Bioforsk; Ward, Todd; ELAMEEN, A - Bioforsk; BRODAL, G - Bioforsk; VRALSTAD, T - Bioforsk; LARSEN, G - Bioforsk; KLEMSDAL, S - Bioforsk; HOFGAARD, I - Bioforsk

Submitted to: European Journal of Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/6/2015
Publication Date: 2/28/2015
Publication URL: http://handle.nal.usda.gov/10113/62198
Citation: Aamot, H.U., Ward, T.J., Brodal, G., Vralstad, T., Larsen, G., Klemsdal, S.S., Elameen, A., Uhlig, S., Hofgaard, I.S. 2015. Genetic and phenotypic diversity within the Fusarium graminearum species complex in Norway. European Journal of Plant Pathology. 142(3):501-519.

Interpretive Summary: Fungi within the Fusarium graminearum species complex (FGSC) are responsible for Fusarium head blight (FHB), an economically destructive disease of wheat, barley, and other cereals. In addition, these fungi contaminate grain with trichothecene mycotoxins that pose a significant threat to food safety and animal health. As part of a project to assess the diversity and distribution of FHB pathogens world-wide, we determined the prevalence of FGSC species and toxin types associated with FHB infected cereals in Norway. This study was also designed to determine if the recent increase in the prevalence of these fungi in Norway was associated with major changes in fungal species, populations, or toxin types. We demonstrate that F. graminearum, the most common FHB pathogen in the United States, is the only significant representative of the FGSC in Norway. Almost all Norwegian F. graminearum have the 3-ADON toxin type, which is uncommon throughout most of Europe. The 3-ADON toxin type was recently introduced into North America and has become prevalent in the Upper Midwest and Canada, where it is associated with greater toxin contamination potential. However, our analyses indicate that 3-ADON producing pathogens in Norway and North America are not closely related. Finally, we determined that increases in FGSC prevalence in Norway have not been associated with significant changes in species or toxin types, but we did detect significant changes in the prevalence of two distinct populations that differ in aggressiveness to spring wheat. As such, the results reported here contribute to promoting food safety and cereal production through improved understanding of pathogen diversity and improved methods for detection of novel FGSC pathogens or toxin types.

Technical Abstract: As has been observed in several European countries, the frequency of Fusarium head blight (FHB) caused by members of the Fusarium graminearum species complex (FGSC) has increased in Norwegian cereals in recent years, resulting in elevated levels of deoxynivalenol in cereal grains. The objective of this study was to determine if this increase was associated with changes in FGSC composition within Norway. FGSC isolates collected from wheat, oats, and barley in Norway during two periods, mainly 1993-1998 and 2004-2007, were characterized to determine species and trichothecene genotype composition and to assess levels of genetic variation and population structure. In vitro growth rates at different temperatures and aggressiveness in spring wheat were further characterized for a sub-selection of isolates. All Norwegian isolates were identified as F. graminearum. Three-acetyl-deoxynivalenol (3-ADON) was the dominant trichothecene type. However, isolates with the 15-ADON chemotype were detected in Norway for the first time and may represent a recent introduction of this trichothecene type. Bayesian-model based clustering and analyses of genetic differentiation indicated the persistence over the last twenty years of two sympatric and partially admixed populations of F. graminearum in Norway. Significant differences in average in vitro growth rates and aggressiveness were observed between these two populations. Our results demonstrate that the recent increase in prevalence of the FGSC in Norwegian cereals do not correspond to any dramatic changes in FGSC species or trichothecene chemotype composition. However, significant changes in population frequencies were observed among Norwegian F. graminearum.