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. The 3-acetyl-deoxynivalenol (3-ADON) trichothecene type was dominant. 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 20 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.
Highlights
Fusarium head blight (FHB) is a disease of small grain cereals, which can cause major losses due to yield reduction and contamination of grain with trichothecenes and other mycotoxins
Corresponding least squares means for each factor group are listed in brackets (GLM model in Minitab) a The p-values for this factor are listed in brackets along with each dependent variable (GLM model in Minitab). n.s. indicate p-values above 0.05 b 11 isolates belonging to population 2 were included in the analysis of aggressiveness, ten of these were included in the growth rate analysis c 17 3-ADON isolates were included in the analysis of aggressiveness, 16 of these were included in the growth rate analysis
In Norway, the increased prevalence of the Fusarium graminearum species complex (FGSC) has coincided with increased adoption of reduced tillage practices and more frequent occurrence of weather conditions favorable for FHB development
Summary
Fusarium head blight (FHB) is a disease of small grain cereals, which can cause major losses due to yield reduction and contamination of grain with trichothecenes and other mycotoxins. The global incidence of FHB has increased over the past several decades (Goswami and Kistler 2004) and the International Maize and Wheat Improvement Centre has recognised FHB as a major factor limiting cereal production worldwide (Stack 2000) Because of their ability to inhibit protein synthesis and modify immune function in eukaryotes, trichothecenes pose a significant risk to food and feed safety (Rocha et al 2005). Similar changes in reduced tillage practices and precipitation during the growing season have been reported from Norway (Tørresen et al 2012) This may have contributed to the substantial increase in the overall Fusarium spp. infection levels in cereal seeds, as well as the increased levels of trichothecene contamination in cereal grains, observed in Norway in recent years (Bernhoft et al 2013). Members of the Fusarium graminearum species complex (FGSC) have become more prevalent in several European countries (Chandelier et al 2011; Jennings et al 2004; Stępień et al 2008; Waalwijk et al 2003) including the Nordic countries (Bernhoft et al 2010; Fredlund et al 2008; Nielsen et al 2011; Yli-Mattila 2010), partly replacing other Fusarium species
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