Natural occurrence of fusarium head blight,mycotoxins and mycotoxin‐producing isolates of Fusarium in commercial fields of wheat in Hubei

Combined analyses of the natural occurrence of fusarium head blight (FHB), mycotoxins and mycotoxin‐producing isolates of Fusarium spp. in fields of wheat revealed FHB epidemics in 12 of 14 regions in Hubei in 2009. Mycotoxin contamination ranged from 0·59 to 15·28 μg g^?1 in grains. Of the causal agents associated with symptoms of FHB, 84% were Fusarium asiaticum and 9·5% were Fusarium graminearum, while the remaining 6·5% were other Fusarium species. Genetic chemotyping demonstrated that F. asiaticum comprised deoxynivalenol (DON), 3‐acetyldeoxynivalenol (3‐AcDON), 15‐acetyldeoxynivalenol (15‐AcDON) and nivalenol (NIV) producers, whereas F. graminearum only included DON and 15‐AcDON producers. Compared with the chemotype patterns in 1999, there appeared to be a modest shift towards 3‐AcDON chemotypes in field populations during the following decade. However, isolates genetically chemotyped as 3‐AcDON were present in all regions, whereas the chemical 3‐AcDON was only detected in three of the 14 regions where 3‐AcDON accounted for 15–20% of the DON and acetylated forms. NIV mycotoxins were detected in seven regions, six of which also yielded NIV chemotypes. The number of genetic 3‐AcDON producers was positively correlated with amounts of total mycotoxins (DON, NIV and acetylated forms) or DON in wheat grains. Chemical analyses of wheat grains and rice cultures inoculated with different isolates from the fields confirmed their genetic chemotypes and revealed a preferential biosynthesis of 3‐AcDON and 4‐AcNIV in rice. These findings suggest the importance of chemotyping coupled with species identification for improved prediction of mycotoxin contamination in wheat.     

Nivalenol‐producing Fusarium cerealis associated with fusarium head blight in winter wheat in Manitoba,Canada

Fusarium head blight (FHB) in small grain cereals is primarily caused by the members of the Fusarium graminearum species complex. These produce mycotoxins in infected grains, primarily deoxynivalenol (DON); acetylated derivatives of DON, 3‐acetyl‐DON (3‐ADON) and 15‐acetyl‐DON (15‐ADON); and nivalenol (NIV). This study reports the isolation of Fusarium cerealis in infected winter wheat heads for the first time in Canada. A phylogenetic analysis based on the TRI101 gene and F. graminearum species‐specific primers revealed two species of Fusarium: F. graminearum sensu stricto (127 isolates) and F. cerealis (five isolates). Chemotype determination based on the TRI3 gene revealed that 65% of the isolates were 3‐ADON, 31% were 15‐ADON and 4% were NIV producers. All the F. cerealis isolates were of NIV chemotype. Fusarium cerealis isolates can often be misidentified as F. graminearum as the morphological characteristics are similar. Although the cultural and macroconidial characteristics of F. graminearum and F. cerealis isolates were similar, the aggressiveness of these isolates on susceptible wheat cultivar Roblin and moderately resistant cultivar Carberry differed significantly. The F. graminearum 3‐ADON isolates were most aggressive, followed by F. graminearum 15‐ADON and F. cerealis NIV isolates. The findings from this study confirm the continuous shift of chemotypes from 15‐ADON to 3‐ADON in North America. In Canada, the presence of NIV is limited to barley samples and the discovery of NIV‐producing F. cerealis species in Canadian wheat fields may pose a serious concern to the Canadian wheat industry in the future.     

Effect of nitrogen application at anthesis on Fusarium head blight and mycotoxin accumulation in breadmaking wheat in the western part of Japan

In the western part of Japan, two wheat cultivars, Nishinokaori and Minaminokaori, are currently cultivated for breadmaking. Breadmaking wheat requires a higher protein content compared to the Japanese noodle wheat (the major type of wheat in Japan). This high protein level in the grain is obtained by top-dressing with nitrogen (N) near anthesis. Because such N applications may increase levels of Fusarium head blight (FHB) and consequent mycotoxin [deoxynivalenol (DON) and nivalenol (NIV)] accumulation in the grain, the effect of N application (0, 4, and 8 g/m²) at anthesis on FHB and mycotoxin accumulation in Nishinokaori and Minaminokaori was tested in the greenhouse in 2004 and 2005 and in two fields in 2006. In the greenhouse, plants were spray inoculated at 3, 10, and 20 days after N treatment. In field experiments, colonized maize kernels, which generate ascospores during the testing season, served as inoculum. In all experiments for both cultivars, N application at anthesis significantly increased grain protein as expected, but had no significant effect on FHB and DON and NIV levels in grain. These results suggest that, at least in these cultivars, N can be applied close to anthesis without increasing the risk of FHB and mycotoxin (DON and NIV) accumulation.     

Fusarium head blight and mycotoxin contamination of wheat,a review

Summary An infection of bread wheat by fusarium head blight contaminates the crop with mycotoxins, particularly deoxynivalenol (DON) and nivalenol (NIV). The toxicity and natural occurrence of these mycotoxins in wheat are reviewed. Based on 8 years data of fusarium head blight epidemics of wheat in the Netherlands, DON contamination of the grain was estimated. Fusarium head blight ratings averaged an infection of 1.7% of all spikelets; estimates for DON contamination averaged 0.9 mg kg^–1. Taking a guideline level for DON in uncleaned bread wheat of 2 mg kg^–1, in 1979 and 1982 a wheat crop was produced with estimated DON concentrations above the limit of tolerance. Human and animal exposure to mycotoxins in the Netherlands appears to be small but chronic. The information presented in this paper illustrates the need for an annual evaluation of the crop for fusarium head blight incidence and mycotoxin content, and the necessity of fusarium head blight resistant wheat cultivars.Samenvatting Aaraantasting van tarwe doorFusarium culmorum enFusarium graminearum leidt tot vorming van mycotoxinen in het graan, waarvan deoxynivalenol (DON) en nivalenol (NIV) de belangrijkste toxinen zijn. In dit artikel wordt een overzicht gegeven van de toxicologische aspecten, en het voorkomen van deze toxinen in tarwe. Informatie over DON en NIV in tarwe in West-Europa is schaars. Gebaseerd op gegevens vanFusarium epidemieën in de jaren 1979–1986 wordt een schatting gegeven van de concentratie DON in Nederlandse tarwe. Rekening houdend met de herkomst en verwerking van tarwe, blijken zowel in dierlijk als menselijk voedsel lage concentraties DON chronisch voor te komen. Op basis van een maximaal toelaatbare dagelijkse dosis DON van 3 g kg^–1 lichaamsgewicht is de schatting van de dagelijkse opname van DON in het jaar volgend op de oogst van 1982 net op de grens. Zowel een jaarlijkse inventarisatie vanFusarium aantasting en DON besmetting van het graan, als de ontwikkeling vanFusarium-resistente rassen zijn noodzakelijk.     

Gramineous weeds near paddy fields are alternative hosts for the Fusarium graminearum species complex that causes fusarium head blight in rice

The objective of this study was to evaluate the potential role of gramineous weeds present near paddy fields as alternative hosts for the Fusarium graminearum species complex (FGSC) that causes fusarium head blight (FHB) in rice. A total of 142 weed samples were collected from 10 gramineous weed species near paddy fields from August to October 2018 in Jiangsu Province, China. Of the 145 isolates of seven Fusarium species isolated from the weed samples, F. asiaticum was the most abundant (86.9%), followed by F. fujikuroi (5.5%), F. proliferatum (2.8%), F. graminearum (2.1%), F. tricinctum (1.4%), F. acuminatum (0.7%), and F. sporotrichioides (0.7%). Genotype and mycotoxin analyses confirmed that 72.2% of F. asiaticum isolates were producers of deoxynivalenol (DON) with 3-acetyl deoxynivalenol (3ADON), and the remainder were nivalenol (NIV) producers. Pathogenicity assays showed that both 3ADON and NIV chemotypes of F. asiaticum could cause FHB in rice, but NIV chemotypes were significantly (p < .05) more aggressive than 3ADON chemotypes. Three Fusarium mycotoxins, DON, NIV, and zearalenone, occurred naturally at low concentrations in the weed samples. Taken together, this study provides insight into the mycotoxin production and aggressiveness of F. asiaticum isolates from gramineous weeds in China.     

Quantification of the relationship between the environment and Fusarium head blight, Fusarium pathogen density, and mycotoxins in winter wheat in Europe

Measurements of local environmental conditions, intensity of Fusarium head blight (FHB) in wheat spikes, biomass of Fusarium graminearum, F. culmorum, and F. poae (pathogens causing FHB) and concentration of the mycotoxins deoxynivalenol (DON) and nivalenol (NIV) in harvested wheat grain were obtained in a total of 150 location-years, originating in three European countries (Hungary, Ireland, United Kingdom) from 2001 to 2004. Through window-pane methodology, the length and starting time of temporal windows where the environmental variables were significantly associated with the biological variables were identified. Window lengths of 5 to 30?days were evaluated, with starting times from 18?days before anthesis to harvest. Associations were quantified with nonparametric Spearman correlation coefficients. All biological variables were significantly associated with at least one evaluated environmental variable (P?≤?0.05). Moisture-related variables (e.g., average relative humidity, hours of relative humidity above 80%) had the highest positive correlations with the biological variables, but there also was a significant negative correlation between average temperature and several biological variables. When significant correlations were found, they were generally for all window lengths, but for a limited number of window start times (generally before anthesis for disease index and after anthesis for the toxins and late-season fungal biomasses). Semi-partial Spearman correlation coefficients were used to evaluate the relationship between the environmental variables and the concentration of DON and NIV after the effects of FHB intensity and fungal biomass on the mycotoxins were removed. Significant semi-partial correlations were found between relative humidity variables and DON, and between temperature and relative humidity variables and NIV for time windows that started after anthesis (and not for any earlier time windows). Results confirm that the environment influences disease, fungal biomass, and mycotoxin production, and help refine the time windows where the association is greatest. However, variability in the relationships was high, indicating that no single environmental variable is sufficient for prediction of disease or mycotoxin contamination.     

Species composition,toxigenic potential and pathogenicity of Fusarium graminearum species complex isolates from southern Brazilian rice

This study aimed to assess the extent and distribution of Fusarium graminearum species complex (FGSC) diversity in rice seeds produced in southern Brazil. Four species and two trichothecene genotypes were detected among 89 FGSC isolates, based on a multilocus genotyping assay: F. asiaticum (69·6%) with the nivalenol (NIV) genotype, F. graminearum (14·6%) with the 15‐acetyldeoxynivalenol (ADON) genotype, and F. cortaderiae (14·6%) and F. meridionale (1·1%), both with the NIV genotype. Seven selected F. asiaticum isolates from rice produced NIV in rice‐based substrate in vitro, at levels ranging from 4·7 to 84·1 μg g^?1. Similarly, two F. graminearum isolates from rice produced mainly 15‐ADON (c. 15–41 μg g^?1) and a smaller amount of 3‐ADON (c. 6–12 μg g^?1). One F. meridionale and two F. cortaderiae isolates did not produce detectable levels of trichothecenes. Two F. asiaticum isolates from rice and two from wheat (from a previous study), and one F. graminearum isolate from wheat, were pathogenic to both crops at various levels of aggressiveness based on measures of disease severity in wheat spikes and rice kernel infection in a greenhouse assay. Fusarium asiaticum and the reference F. graminearum isolate from wheat produced NIV, and deoxynivalenol and acetylates, respectively, in the kernels of inoculated wheat heads. No trichothecene was produced in kernels from inoculated rice panicles by any of the isolates. These findings constitute the first report of FGSC composition in rice outside Asia, and confirm the dominance of F. asiaticum in rice agroecosystems.     

Aggressiveness and mycotoxin production of eight isolates each of <Emphasis Type="Italic">Fusarium graminearum</Emphasis> and <Emphasis Type="Italic">Fusarium verticillioides</Emphasis> for ear rot on susceptible and resistant early maize inbred lines

Fusarium graminearum and F. verticillioides are among the most important pathogens causing ear rot of maize in Central Europe. Our objectives were to (1) compare eight isolates of each species on two susceptible inbred lines for their variation in ear rot rating and mycotoxin production across 3 years, and (2) analyse two susceptible and three resistant inbred lines for potential isolate x line interactions across 2 years by silk-channel inoculation. Ear rot rating, zearalenone (ZEA) and deoxynivalenol (DON) concentrations were evaluated for all F. graminearum isolates. In addition, nivalenol (NIV) concentrations were analysed for two NIV producers. Fumonisin (FUM) concentrations were measured for all F. verticillioides isolates. Mean ear rot severity was highest for DON producers of F. graminearum (62.9% of the ear covered by mycelium), followed by NIV producers of the same species (24.2%) and lowest for F. verticillioides isolates (9.8%). For the latter species, ear rot severities differed highly among years (2006: 24%, 2007: 3%, 2008: 7%). Mycotoxin concentrations among isolates showed a broad range (DON: 100–284 mg kg⁻¹, NIV: 15–38 mg kg⁻¹, ZEA: 1.1–49.5 mg kg⁻¹, FUM: 14.5–57.5 mg kg⁻¹). Genotypic variances were significant for isolates and inbred lines in all traits and for both species. Isolate x line interactions were significant only for ear rot rating (P < 0.01) and DON concentration (P < 0.05) of the F. graminearum isolates, but no rank reversals occurred. Most isolates were capable of differentiating the susceptible from the resistant lines for ear rot severity. For resistance screening, a sufficiently aggressive isolate should be used to warrant maximal differentiation among inbred lines. With respect to F. verticillioides infections, high FUM concentrations were found in grains from ears with minimal disease symptoms.     

Trichothecene genotypes of Gibberella zeae from winter wheat fields in the eastern USA

Fusarium head blight (FHB), caused principally by Gibberella zeae (Fusarium graminearum), is a devastating disease of small grains such as wheat and barley worldwide. Grain infected with G. zeae may be contaminated with trichothecene mycotoxins such as deoxynivalenol (DON) and nivalenol (NIV). Strains of G. zeae that produce DON may also produce acetylated derivatives of DON: 3‐acetyl‐DON (3‐ADON) and 15‐acetyl‐DON (15‐ADON). Gradients (clines) of 3‐ADON genotypes in Canada have raised questions about the distribution of G. zeae trichothecene genotypes in wheat fields in the eastern USA. Tri3 and Tri12 genotypes were evaluated in 998 isolates of G. zeae collected from 39 winter wheat fields in New York (NY), Pennsylvania (PA), Maryland (MD), Virginia (VA), Kentucky (KY) and North Carolina (NC). Ninety‐two percent (919/998) of the isolates were 15‐ADON, 7% (69/998) were 3‐ADON, and 1% (10/998) was NIV. A phylogenetic analysis based on portions of three genes (PHO, RED and URA) from 23 isolates revealed two species of Fusarium (F. graminearum sensu stricto and one isolate of F. cerealis (synonym F. crookwellense)). An increasing trend of 3‐ADON genotypes was observed from NC (south) to NY (north). Punctuated episodes of atmospheric transport may favour a higher frequency of 3‐ADON genotypes in the northeastern USA, near Canada, compared with the mid‐Atlantic states. Discoveries of the NIV genotype in NY and NC indicate the need for more intensive sampling in the surrounding regions.     

Resistance against <Emphasis Type="Italic">Fusarium graminearum</Emphasis> and the relationship to β-glucan content in barley grains

Fusarium head blight (FHB) caused by Fusarium graminearum (FG) is a destructive disease impacting barley worldwide. The disease reduces the grain yield and contaminates grains with mycotoxins, such as the trichothecene deoxynivalenol (DON). Although the infection mainly affects the grain yield, little is known about its impact on grain structural and biochemical properties. Yet, such information is instrumental to characterize the facets of resistance in the grains. After artificial inoculation of six barley cultivars with FG in a 2 years field test, different levels of symptoms on spikes, of colonisation of grains and of DON content were observed. The infections caused a reduction in grain weight and an average decrease of 10% of the β-glucan content in grains, indicating alterations of grain filling, composition and structure. According to our results, we postulate the presence of two distinct resistance mechanisms in the grain, tolerance to grain filling despite infection as well as the inhibition of mycotoxin accumulation. Differently to wheat, in barley, type IV resistance (tolerance of the grain to infection) is directly linked with type III resistance (resistance against kernel infection). The resistance against toxin accumulation (named type V resistance in wheat) appeared to be independent to all other resistance types. Generally, the resistance was significantly influenced by the environment and by genotype x environment interactions explaining the generally weak stability of resistance in barley. Interestingly, a significant and inverse relationship between DON contamination and β-glucan content in grains suggests that high β-glucan content in grains contributes to type V resistance.     

Diversity of the Fusarium graminearum species complex on French cereals

Fusarium graminearum is an important pathogen causing Fusarium head blight (FHB) on wheat and barley and Fusarium ear rot (FER) on maize, and harvested grains often are contaminated with trichothecenes such as deoxynivalenol (DON) and nivalenol (NIV) that are a major health and food safety concern due to their toxicity to humans and farm animals. In this study, species identity and trichothecene toxin potential of 294 members of the Fusarium graminearum species complex (FGSC) collected from wheat, barley and maize in France in 2011 was determined using a microsphere-based multilocus genotyping assay. F. graminearum was predominant on all three hosts, but three isolates of F. cortaderiae and two isolates representing F. graminearum × F. boothii hybrids were also identified from maize. The 15-ADON trichothecene chemotype predominated on all three hosts, representing 94.7 %, 87.8 % and 85.4 % of the strains on barley (N?=?19), wheat (N?=?90), and maize (N?=?185), respectively. However, the NIV chemotype was found in 12.2 % of the wheat isolates and in 14.6 % of the maize isolates. Only a single FGSC isolate from this study, originating from barley, was found to have the 3-ADON chemotype. Regional differences could be observed in the distribution of the 15-ADON and NIV chemotypes, with the NIV producing-isolates being present at higher frequency (21.2 %) in the South of France compared to the rest of the country (4.4 %). Such information is critical because of the increased concern associated with NIV contamination of cereals. In addition, these results are needed to develop management strategies for FHB and FER in France and to improve understanding of the distribution and significance of FGSC diversity in Europe and worldwide.     

Infection conditions of <Emphasis Type="Italic">Fusarium graminearum</Emphasis> in barley are variety specific and different from those in wheat

Fusarium head blight is one of the most noxious cereal diseases. Worldwide, F. graminearum (FG) and the mycotoxin deoxynivalenol (DON) is the most dominant species/mycotoxin in barley and wheat. Barley is often produced as on farm feed and thus routine mycotoxin analyses similar to those of cereals for human consumption are not performed. Hence, an early prediction of mycotoxin levels is important for farmers to minimise the risk of contaminated feed but also of contaminated cereals entering the cereal supply chain. Therefore, climate chamber experiments with artificial FG infection of barley investigating the influence of different temperatures (10 °C, 15 °C, 20 °C) and durations (4 h, 8 h, 12 h) at 99% relative humidity were conducted to accumulate data to develop a forecasting system. An up to three times higher DON contamination in the 15 °C treatments for the feed barley variety Ascona was detected compared with the 10 °C and 20 °C treatments. For the malting barley variety Concerto, the prolonged humidity durations had a stronger effect under all tested temperatures and resulted in up to two times higher DON contaminations. In addition, field experiments where spore deposition during anthesis as well as disease incidence, fungal amount and mycotoxins were observed, showed that the overwintered straw treatment resulted, depending on the year, in a three times higher FG incidence and DON content compared with the control and freshly inoculated straw treatment.     

Within-field variability of Fusarium head blight pathogens and their associated mycotoxins

Within-field variability in the Fusarium head blight (FHB) and its associated mycotoxins was studied in four European countries. At each of 14 sites, each FHB pathogen and associated mycotoxins were quantified in 16 quadrat samples at harvest. Overall, the incidence of quadrat samples with detectable and quantifiable pathogen DNA was significantly lower in the grain than in the corresponding chaff. Deoxynivalenol (DON) was the most frequently detected toxin in the samples and its accumulation was most strongly associated with the presence of Fusarium graminearum. Nivalenol (NIV) accumulation was significantly associated only with the presence of F. culmorum. Zearalenone (ZON) accumulation was strongly associated with the presence of all three pathogens (F. graminearum, F. culmorum and F. poae). The levels of both DON and ZON concentrations were positively related to the amount of F. graminearum DNA in the grain or in the chaff. The presence/absence of FHB pathogens within a single quadrat appeared to be independent of each other. The presence of a particular FHB pathogen and the amount of its DNA, as well as the associated mycotoxin(s), varied greatly among samples at each site. This study demonstrated the large extent of within-field variability of FHB and its associated mycotoxins, and the importance of representative sampling in FHB studies.     

Effect of Dose Rate of Azoxystrobin and Metconazole on the Development of Fusarium Head Blight and the Accumulation of Deoxynivalenol (DON) in Wheat Grain

Glasshouse studies were undertaken to determine if fungicides used for the control of Fusarium head blight (FHB) result in elevated concentrations of the trichothecene mycotoxin, deoxynivalenol (DON) in harvested wheat grain. Metconazole and azoxystrobin, at double, full, half or quarter the manufacturer's recommended dose rate, were applied to ears of wheat (cv. Cadenza), artificially inoculated with conidia of either Fusarium culmorum or F. graminearum. Metconazole demonstrated high activity against both pathogens, reducing significantly the severity of FHB and the DON concentrations at each of the four dose rates tested when compared to untreated controls. Applications of azoxystrobin significantly reduced FHB and DON compared to unsprayed controls. However, their effectiveness was significantly less than that of metconazole and no dose rate response was observed. Quantification of the amount of trichothecene-producing Fusarium present in harvested grain was determined using a competitive PCR assay based on primers derived from the trichodiene synthase gene (Tri5). Simple linear regression analyses revealed strong relationships between the amount of trichothecene-producing Fusarium present in grain and the DON concentrations (r ²=0.72–0.97). It is concluded that fungicides, applied for the control of FHB, affect DON concentrations indirectly by influencing the amount of trichothecene-producing Fusarium species present in wheat grain. There was no evidence that fungicide applications directly increase the concentration of DON in grain.     

Development of PCR assays to Tri7 and Tri13 trichothecene biosynthetic genes, and characterisation of chemotypes of Fusarium graminearum, Fusarium culmorum and Fusarium cerealis

Fusarium graminearum, Fusarium culmorum and Fusarium cerealis are major causal agents of Fusarium Head Blight (scab) which is a disease of global significance in all cereal growing areas. These fungi produce trichothecene mycotoxins, principally nivalenol (NIV) and deoxynivalenol (DON). Genes Tri13 and Tri7 from the trichothecene biosynthetic gene cluster convert DON to NIV (Tri13) and NIV to 4-acetyl-NIV (Tri7). We have developed positive–negative PCR assays based on these two genes, which accurately indicate a DON or NIV chemotype in F. graminearum, F. culmorum and F. cerealis. These assays are useful in assessing the risk of trichothecene contamination, and can be informative in epidemiological studies. All NIV chemotype isolates studied have functional copies of both Tri13 and Tri7, and all DON-producing isolates have both genes disrupted or deleted. We have identified several mutations in these genes, which are conserved across F. graminearum lineage, RAPD and SCAR groupings and between the three species. There appears to be evidence of inter-species hybridisation within the trichothecene biosynthetic gene cluster.     

Resistance in winter wheat lines to deoxynivalenol applied into florets at flowering stage and tolerance to phytotoxic effects on yield

In Europe and North America, deoxynivalenol (DON) is the most prevalent mycotoxin associated with wheat head blight caused by Fusarium graminearum and Fusarium culmorum. Because DON is toxic to plants and enhances the ability of the pathogen to spread within a spike, wheat lines with resistance to DON should be more resistant to head blight. Resistance to DON has been associated with resistance gene Fhb1 that confers resistance to spread within a spike. The objectives of this study were to determine if wheat lines resistant to head blight were also resistant to DON, if genes other than Fhb1 confer resistance to DON, and to identify lines able to fill grain in the presence of DON. Susceptible controls and diverse North American and European winter wheat lines with resistance to head blight were screened for molecular markers linked to known head blight resistance genes, and evaluated in a greenhouse for resistance to DON and relative yield after application of DON to spikes at flowering. Fhb1 appeared to have the unique ability to confer resistance to DON, as measured by the number of DON‐bleached primary florets. However, this resistance did not protect plants from the phytotoxic effects of DON on kernel formation as measured by the relative yield of treated spikes. Furthermore, measuring the relative yield loss following DON application may be useful for identifying lines with tolerance to head blight.     

Effect of infection timing on fusarium head blight and mycotoxin accumulation in open- and closed-flowering barley

ABSTRACT Barley has two flowering types, chasmogamous (open-flowering) and cleistogamous (closed-flowering). We examined the effect of the timing of Fusarium graminearum infection on Fusarium head blight (FHB) and mycotoxin accumulation in barley cultivars with different flowering types using greenhouse experiments. In the first experiment, 13 cultivars were spray inoculated at two different developmental stages, and the severity of FHB was evaluated. The effect of the timing of infection differed among cultivars. Cleistogamous cultivars were resistant at anthesis but susceptible at 10 days after anthesis, whereas chasmogamous cultivars were already susceptible at anthesis. In the second experiment, five cultivars were inoculated at three different developmental stages and the concentrations of deoxynivalenol (DON) and nivalenol (NIV) in mature grain were analyzed. Cleistogamous cultivars accumulated more mycotoxins (DON and NIV) when inoculated 10 or 20 days after anthesis than when inoculated at anthesis, whereas chasmogamous cultivars accumulated more mycotoxins when inoculated at anthesis. Thus, the most critical time for F. graminearum infection and mycotoxin accumulation in barley differs with cultivar, and likely is associated with the flowering type. Late infection, even without accompanied FHB symptoms, was also significant in terms of the risk of mycotoxin contamination.     

Enhanced mycotoxin production of a lipase-deficient <Emphasis Type="Italic">Fusarium graminearum</Emphasis> mutant correlates to toxin-related gene expression

Fusarium graminearum causes important diseases of small-grain cereals and maize and produces several mycotoxins. Among them, deoxynivalenol (DON) and zearalenone (ZEA) can accumulate in feedstuffs and foods to health-threatening levels. Although DON is important for fungal virulence in wheat, disease severity in the field does not correlate with mycotoxin concentrations. We compared gene expression and mycotoxin production of lipase-deficient mutants (Δfgl1), strongly reduced in virulence, and the respective wild-type isolate. Δfgl1 mutants exhibited up-regulated DON production during wheat head infection. On isolated wheat kernels, DON was only produced in low quantities, but higher in wild-type than in Δfgl1 mutants. In contrast, neither wild-type nor Δfgl1 mutants produced ZEA during wheat head infection. However, ZEA was clearly detectable on wheat kernels. Here, Δfgl1 mutants revealed a dramatically enhanced ZEA production. We could correlate the altered amounts of DON and ZEA directly with the expression of the toxin-related genes Tri5 for DON and PKS4 and PKS13 for ZEA. Based on Tri5 expression and the infection pattern of the wild-type and Δfgl1 mutants, we suggest that the transition zone of rachilla and rachis is important in the induction of DON synthesis. Gene expression studies indicate an involvement of the lipase FGL1 in regulation of 8 PKS genes and ZEA production.     

Development of three fusarium crown rot causal agents and systemic translocation of deoxynivalenol following stem base infection of soft wheat

Fusarium pseudograminearum, F. culmorum and F. graminearum are the most important fusarium crown rot (FCR) causal agents. They have the common ability to biosynthesize deoxynivalenol (DON). To elucidate the behaviour of each of the three species, a comparative study was carried out to investigate symptom progression, fungal systemic growth and translocation of DON following stem base inoculation of soft wheat. FCR symptoms were mainly localized in the inoculated area, which extended up to the second node for all inoculated species. Only the most aggressive strains caused symptoms up to the third node. Real‐time quantitative PCR showed that fungal colonization reached the third node for all the tested species, but a low percentage of plants showed colonization above the third node following inoculation with the most aggressive strains. Fungal growth was detected in symptomless tissues but none of the three species was able to colonize as far as the head tissues. However, even if the pathogens were not detected in the heads, DON was detected in head tissues of the plants inoculated with the most aggressive strains. These results demonstrate that F. pseudograminearum, F. culmorum and F. graminearum, under the same experimental conditions, follow a similar pattern of symptom progression, fungal colonization and DON translocation after stem base infection. Differences in the extent of symptoms, fungal colonization and mycotoxin distribution were mainly attributable to strain aggressiveness. These findings provide comparative information on the events following infection of the stem base of wheat by three of the most important FCR casual agents.     

DON content in oat grains in Norway related to weather conditions at different growth stages

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.