During the last ten years, Norwegian cereal grain industry has experienced large challenges due toFusarium spp. andFusarium mycotoxin contamination of small-grained cereals. To prevent severely contaminated grain lots from entering the grain supply chain, it is important to establish surveys for the most prevalentFusarium spp. and mycotoxins. The objective of our study was to quantify and calculate the associations betweenFusarium spp. and mycotoxins prevalent in oats and spring wheat. In a 6-year period from 2004-2009, 178 grain samples of spring wheat and 289 samples of oats were collected from farmers’ fields in South East Norway. The grains were analysed for 18 differentFusarium-mycotoxins by liquid chromatography – mass spectrometry. Generally, the median mycotoxin levels were higher than reported in Norwegian studies covering previous years. The DNA content ofFusarium graminearum, Fusarium culmorum, Fusarium langsethiae,Fusarium poae andFusarium avenaceum were determined by quantitative PCR. We identifiedF. graminearum as the main deoxynivalenol (DON) producer in oats and spring wheat, andF. langsethiae as the main HT-2 and T-2-toxins producer in oats. No association was observed between quantity ofF. graminearum DNA and quantity ofF. langsethiae DNA nor for their respective mycotoxins, in oats. F. avenaceum was one of the most prevalentFusarium species in both oats and spring wheat. The following ranking ofFusarium species was made based on the DNA concentrations of theFusarium spp. analysed in this survey (from high to low):F. graminearum = F. langsethiae = F. avenaceum > F. poae > F. culmorum (oats);F. graminearum = F. avenaceum > F. culmorum > F. poae = F. langsethiae (spring wheat). Our results are in agreement with recently published data indicating a shift in the relative prevalence ofFusarium species towards moreF. graminearum versusF. culmorum in Norwegian oats and spring wheat.

The increased occurrence of Fusarium-mycotoxins in Norwegian cereals over the last decade, is thought to be caused by increased inoculum resulting from more cereal residues at the soil surface as a result of reduced tillage practices. In addition, weather conditions have increasingly promoted inoculum development and infection by Fusarium species. The objective of this work was to elucidate the influence of different tillage regimes (autumn plowing; autumn harrowing; spring plowing; spring harrowing) on the inoculum potential (IP) and dispersal of Fusarium spp. in spring oats. Tillage trials were conducted at two different locations in southeast Norway from 2010 to 2012. Oat residues from the previous year’s crop were collected within a week after sowing for evaluation. IP was calculated as the percentage of residues infested with Fusarium spp. multiplied by the proportion of the soil surface covered with residues. F. avenaceum and F. graminearum were the most common Fusarium species recovered from oat residues. The IP of Fusarium spp. was significantly lower in plowed plots compared to those that were harrowed. Plowing in either the autumn or spring resulted in a low IP. Harrowing in autumn was more effective in reducing IP than the spring harrowing, and IP levels for the spring harrowed treatments were generally higher than all other tillage treatments examined. Surprisingly low levels of F. langsethiae were detected in the residues, although this species is a common pathogen of oat in Norway. The percentage of the residues infested with F. avenaceum, F. graminearum, F. culmorum and F. langsethiae generally related to the quantity of DNA of the respective Fusarium species determined using qPCR. Fusarium dispersal, quantified by quantitative PCR analysis of spore trap samples collected at and after heading, generally corresponded to IP. Fusarium dispersal was also observed to increase after rainy periods. Our findings are in line with the general understanding that plowing is a means to reduce the IP of Fusarium spp. in cereal fields. The main inoculum source for F. langsethiae remains unclear. Our results will be useful in the development of forecasting tools to calculate the risk of Fusarium in cereals.

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.

High concentrations of the mycotoxins HT-2 and T-2 (HT2 + T2), primarily produced by Fusarium langsethiae, have occasionally been detected in Norwegian oat grains. In this study, we identified weather variables influencing accumulation of HT2 + T2 in Norwegian oat grains. Oat grain samples from farmers’ fields were collected together with weather data (2004–2013). Spearman rank correlation coefficients were calculated between the HT2 + T2 contamination in oats at harvest and a range of weather summarisations within estimated phenological windows of growth stages in oats (tillering, flowering etc.). Furthermore, we developed a mathematical model to predict the risk of HT2 + T2 in oat grains. Our data show that adequate predictions of the risk of HT2 + T2 in oat grains at harvest can be achieved, based upon weather data observed during the growing season. Humid and cool conditions, in addition to moderate temperatures during booting, were associated with increased HT2 + T2 accumulation in harvested oat grains, whereas warm and humid weather during stem elongation and inflorescence emergence, or cool weather and absence of rain during booting reduced the risk of HT2 + T2 accumulation. Warm and humid weather immediately after flowering increased the risk, while moderate to warm temperatures and absence of rain during dough development, reduced the risk of HT2 + T2 accumulation in oat grains. Our data indicated that HT2 + T2 contamination in oats is influenced by weather conditions both pre- and post-flowering. These findings are in contrast with a previous study examining the risk of deoxynivalenol contamination in oat reporting that toxin accumulation was mostly influenced by weather conditions from flowering onwards.

High concentrations of the mycotoxin deoxynivalenol (DON), produced by Fusarium graminearum have occurred frequently in Norwegian oats recently. Early prediction of DON levels is important for farmers, authorities and the Cereal Industry. In this study, the main weather factors influencing mycotoxin accumulation were identified and two models to predict the risk of DON in oat grains in Norway were developed: (1) as a warning system for farmers to decide if and when to treat with fungicide, and (2) for authorities and industry to use at harvest to identify potential food safety problems. Oat grain samples from farmers’ fields were collected together with weather data (2004–2013). A mathematical model was developed and used to estimate phenology windows of growth stages in oats (tillering, flowering etc.). Weather summarisations were then calculated within these windows, and the Spearman rank correlation factor calculated between DON-contamination in oats at harvest and the weather summarisations for each phenological window. DON contamination was most clearly associated with the weather conditions around flowering and close to harvest. Warm, rainy and humid weather during and around flowering increased the risk of DON accumulation in oats, as did dry periods during germination/seedling growth and tillering. Prior to harvest, warm and humid weather conditions followed by cool and dry conditions were associated with a decreased risk of DON accumulation. A prediction model, including only pre-flowering weather conditions, adequately forecasted risk of DON contamination in oat, and can aid in decisions about fungicide treatments.