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.     

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.     

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.     

山东省小麦赤霉病菌种群组成及其致病力分化

由禾谷镰孢菌群Fusarium graminearum clade引起的赤霉病是小麦的重要病害。为明确山东省小麦赤霉病菌的种群组成及其致病力,于2011年和2012年从山东省15地市分离了95株小麦赤霉病菌,在形态和分子生物学鉴定种的基础上,采用鉴定B型毒素化学型的特异性引物进行毒素化学型分析。在95个菌株中,93株分离物为禾谷镰孢菌F.graminearum,2株为燕麦镰孢菌F.avenaceum。94株分离物为脱氧雪腐镰孢菌烯醇(deoxynivalenol,DON)化学型,1株为雪腐镰孢菌烯醇(nivalenol,NIV)化学型。在94株DON毒素化学型菌株中,90株为15-乙酰脱氧雪腐镰孢菌烯醇(15-acetyldeoxynivalenol,15-AcDON)化学型,4株为3-乙酰脱氧雪腐镰孢菌烯醇(3-acetyldeoxynivalenol,3-AcDON)化学型。在小麦扬花期,采用单花滴注接种法对29个菌株进行了致病力测定,供试菌株的致病力分化明显。表明在山东省冬小麦产区,产15-AcDON毒素的F.gra-minearum是小麦赤霉病菌的优势种群。     

Effect of lodging on the level of mycotoxins in wheat,barley, and rice infected with the <Emphasis Type="Italic">Fusarium graminearum</Emphasis> species complex

Lodging is one possible risk factor that leads to increased cereal mycotoxin contamination, but few reports have been published on the subject. We examined the effects of lodging on the level of deoxynivalenol (DON) and nivalenol (NIV) contamination in wheat, barley, and rice infected with the Fusarium graminearum species complex. Case-control and intervention studies were applied to test the hypothesis that lodging increases the level of mycotoxin contamination. A total of 66 grain samples were collected from each field in 12 Japanese prefectures from 2002 to 2006. Each sample set consisted of grains from lodged and nonlodged plants. The concentration of DON + NIV in lodged plants was significantly higher than in nonlodged plants. All samples of wheat and barley were contaminated with DON and NIV; however, most of the lodged rice samples were contaminated only with NIV. In intervention trials to investigate the effects of lodging duration, a small area of wheat inoculated with the pathogen was completely lodged by trampling. Even with 5 days of lodging, the levels of DON + NIV in wheat grain at harvest increased by 27–51% compared to nonlodged control plots. For rice, half of each plot area was completely lodged by trampling 20 days before harvest. The level of NIV in lodged rice grain was significantly higher than that in nonlodged rice at optimum and delayed harvests, because lodging significantly increased the level of Fusarium mycotoxins in the three crops. Thus, practices (e.g., rational use of fertilizers) to avoid lodging should reduce the risk of mycotoxin contamination. This is the first epidemiological study on the effect of lodging on mycotoxin production by the F. graminearum species complex in wheat, barley, and rice.     

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.     

Pathogenicity and In Planta Mycotoxin Accumulation Among Members of the Fusarium graminearum Species Complex on Wheat and Rice

ABSTRACT Fusarium head blight (FHB), or scab, is a destructive disease of small grains caused by members of the Fusarium graminearum species complex, comprised of at least nine distinct, cryptic species. Members of this complex are known to produce mycotoxins including the trichothecenes deoxynivalenol (DON) along with its acetylated derivatives and nivalenol (NIV). In this study, 31 strains, belonging to eight species of this complex and originating from diverse hosts or substrates, were tested for differences in aggressiveness and mycotoxin production. Large variation among strains, both in terms of their aggressiveness and the ability to produce trichothecenes on a susceptible cultivar of wheat was found; variation appears to be a strain-specific rather than species-specific characteristic. While pathogenicity was not influenced by the type of mycotoxin produced, a significant correlation was observed between the amount of the dominant trichothecene (DON and its acetylated forms or NIV) produced by each strain and its level of aggressiveness on wheat. Some isolates also were tested for their ability to infect rice cv. M201, commonly grown in the United States. While tested strains were capable of infecting rice under greenhouse conditions and causing significant amount of disease, no trichothecenes could be detected from the infected rice florets.     

Silicon amendment improves wheat defence against Fusarium graminearum and complements the control by fungicide of Fusarium head blight

A three-year field experiment with two wheat cultivars evaluated the effect of soil-applied silicon (Si), with and without fungicide spraying, on Fusarium head blight (FHB) control. Silicon treatment alone reduced FHB severity and the percentage of damaged wheat kernels, regardless of the cultivar. The best disease control was obtained for the cultivar with moderate disease resistance (MR), supplied with silicon and treated with fungicide during flowering. Silicon treatment alone promoted an increase in deoxynivalenol (DON) concentration in the disease-susceptible cultivar; however, in the MR cultivar, silicon amendment associated with fungicide treatment led to a reduction in DON concentration. Greenhouse experiments evaluated the effect of silicon combined with different timings of fungicide application on wheat defences against Fusarium graminearum. Plants supplied with silicon had a longer pathogen incubation period, lower FHB severity and lower DON concentration when compared to plants without silicon. In addition, silicon-supplied plants had higher soluble phenolic content and altered antioxidant enzyme activities (SOD, CAT, POX and PPO) that favoured early accumulation of hydrogen peroxide when compared to plants without silicon. Greater control of FHB and lower DON concentration in plants treated with silicon and fungicide before inoculation and up to 1 day after inoculation was associated with increased levels of defence-associated metabolites. Silicon contributed to the reduction of FHB and DON concentration in wheat, especially for the MR cultivar and, when combined with fungicide spraying, both MR and disease-susceptible cultivars had enhanced performances upon silicon amendment.     

Evaluation and characterization of resistance to fusarium head blight caused by Fusarium culmorum in UK winter wheat cultivars

Fusarium head blight (FHB) resistance of 50 cultivars from the National List of winter wheat cultivars approved for sale (or were undergoing trails for approval in 2003) in the UK was compared with 21 reference cultivars from continental Europe which had previously been characterized for resistance. Only three UK National List cultivars (Soissons, Spark and Vector) had stable resistance over trial sites that was significantly greater than that of the FHB susceptible cultivar Wizard. In addition, under moderate disease pressure, 21 of the National List cultivars had levels of the trichothecene mycotoxin deoxynivalenol (DON) above the proposed European Union limit of 1·25 ppm in grain. Surveys show that levels of FHB and DON in the UK crop are currently very low, however, should disease pressure increase for any reason, then an improvement in the overall levels of FHB resistance of UK winter wheat germplasm will be required. In order to infer the origin of resistance and to identify potentially novel resistance, allele sizes of microsatellite (simple sequence repeat, SSR) markers linked to quantitative trait loci (QTL) for FHB resistance were compared between the test cultivars and known, characterized resistance sources. The major FHB resistance QTL from the Chinese cv. Sumai-3 (3BS, 5A and 6B), the Romanian cv. Fundulea F201R (1B and 5A) and the French cv. Renan (5AL) were screened with 17 SSRs. No National List cultivar had haplotypes similar to any of these QTL. However, the highly resistant German reference cultivar Petrus had an identical haplotype to cv. Fundulea F201R on 1B indicating that this cultivar has an allelic FHB resistance QTL at that location.     

Assessment of infection in wheat by <Emphasis Type="Italic">Fusarium</Emphasis> protein equivalent levels

Determination of the Fusarium protein equivalent (FPE) levels in kernels for better characterisation of genotypes showing Fusarium head blight (FHB) resistance, and better detection of susceptibility to kernel infection among genotypes with slight symptom expression was carried out. Twelve wheat cultivars and eight hexaploid winter wheat lines derived from a cross of Triticum aestivum with related species T. macha, T. polonicum, and T. dicoccoides were evaluated for levels of spike and kernel infection, the content of the mycotoxin deoxynivalenol (DON) and FPE in kernels after artificial inoculation with the fungus Fusarium culmorum in the field in 2006–2007. The ELISA immunochemical method was employed for the quantitative analyses of DON and FPE. Three wheat lines had a significantly low infection of spikes and kernels compared to cvs Sumai 3 and Nobeoka Bozu, indicating the presence of specific resistance mechanisms to FHB. The significantly low AUDPC (area under the disease progress curve) and the high level of FPE and DON content in kernels indicated a lack of resistance in one wheat line (crossed with T. polonicum). The results showed highly significant correlations (P < 0.01) between FPE and DON content and between FPE and AUDPC. In addition, correlations between FPE and reductions in yield components were also highly significant. Quantification of Fusarium spp. in wheat kernels can be helpful for evaluating wheat genotypes for their levels of resistance to FHB.     

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.     

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.     

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.     

镰刀菌毒素脱氧雪腐镰刀菌烯醇脱毒菌及脱毒酶研究进展

 脱氧雪腐镰刀菌烯醇(Deoxynivalenol,DON)是由镰刀菌在侵染小麦等禾谷类作物过程中产生的一种有毒次级代谢产物,是目前小麦及其制品中污染最为普遍的一种真菌毒素。DON能够对真核细胞产生多种毒性作用,严重危害人畜健康。DON又是一种毒力因子,促进镰刀菌扩展蔓延,加重赤霉病发病程度。利用脱毒菌、脱毒酶对DON毒素进行生物脱毒是最好的脱毒方式之一,其可将DON转化成低毒或无毒代谢产物,减少毒素对人畜健康的危害。脱毒基因还可作为新型抗源用于小麦赤霉病抗性改良,加速抗性品种的选育,从源头防止DON毒素的污染。本文概述了DON毒素生物脱毒的类型、代谢产物的毒性、脱毒基因的鉴定以及脱毒材料的应用等方面的研究进展,以期为DON毒素的生物防控和小麦赤霉病抗性改良提供参考。     

Host genetic effect on deoxynivalenol accumulation in fusarium head blight of barley

ABSTRACT One of the major concerns with Fusarium head blight (FHB) of barley is the potential health risks to livestock and humans through the accumulation of the mycotoxin deoxynivalenol (DON) in infected grain. To define the role of the host in DON accumulation during the early stages of disease development, we conducted a series of greenhouse experiments. We inoculated single spikelets of greenhouse-grown plants with Fusarium graminearum, moved the plants to a dew chamber, and harvested the inoculated spikelets after 72 h for DON analysis. We conducted a quantitative trait locus (QTL) analysis using a genetic mapping population, constructed with the parents Stander and Frederickson, that segregated for DON accumulation after single-spikelet inoculation in two experiments. A single QTL on chromosome 3 explained 18 and 35% of the phenotypic variation in the two experiments. To validate this QTL for DON accumulation, we used a DNA marker to select near-isogenic lines from a family from the mapping population that was segregating at this QTL. Disease symptom development was similar between the nearisogenic lines; however, the mean DON concentration of the lines homozygous for the allele from the high DON parent was 2.5-fold more than the lines homozygous for the alternate allele. A time course experiment showed that this effect on toxin accumulation was observed at 10 days post inoculation. The near-isogenic lines developed in this study should prove useful for further exploration of the role of DON in FHB.     

镰刀菌毒素脱氧雪腐镰刀菌烯醇脱毒菌及脱毒酶研究进展

 脱氧雪腐镰刀菌烯醇(Deoxynivalenol,DON)是由镰刀菌在侵染小麦等禾谷类作物过程中产生的一种有毒次级代谢产物,是目前小麦及其制品中污染最为普遍的一种真菌毒素。DON能够对真核细胞产生多种毒性作用,严重危害人畜健康。DON又是一种毒力因子,促进镰刀菌扩展蔓延,加重赤霉病发病程度。利用脱毒菌、脱毒酶对DON毒素进行生物脱毒是最好的脱毒方式之一,其可将DON转化成低毒或无毒代谢产物,减少毒素对人畜健康的危害。脱毒基因还可作为新型抗源用于小麦赤霉病抗性改良,加速抗性品种的选育,从源头防止DON毒素的污染。本文概述了DON毒素生物脱毒的类型、代谢产物的毒性、脱毒基因的鉴定以及脱毒材料的应用等方面的研究进展,以期为DON毒素的生物防控和小麦赤霉病抗性改良提供参考。     

Interactions Between <Emphasis Type="Italic">Barley yellow dwarf virus</Emphasis> and <Emphasis Type="Italic">Fusarium</Emphasis> spp. Affecting Development of Fusarium Head Blight of Wheat

Interactions between Barley yellow dwarf virus (BYDV) and Fusarium species causing Fusarium head blight (FHB) in winter wheat cvs Agent (susceptible to FHB) and Petrus (moderately resistant to FHB) were studied over three years (2001–2003) in outdoor pot experiments. FHB developed more rapidly in cv. Agent than in cv. Petrus. The spread of FHB was greater in BYDV-infected plants than in BYDV-free plants. Thousand grain weight (TGW) was reduced more in Fusarium-infected heads of cv. Agent than in cv. Petrus. A highly significant negative correlation was found between disease index and TGW in cv. Agent (r = −0.916), while in cv. Petrus the correlation was less significant (r = −0.765). Virus infection reduced TGW in cv. Petrus more than in cv. Agent. In plants with both infections, TGW reductions in cv. Petrus corresponded to those of BYDV infection, and in cv. Agent TGW was more diminished than in BYDV infection. Effects of different treatments determined over three years on ergosterol contents in grain were generally similar to effects on disease indices. Grain weight per ear and ear weight of the different treatments of both cultivars largely corresponded with the TGW results. Deoxynivalenol (DON) content in grain of cv. Agent infected with Fusarium spp. was 11–25 times higher compared to the corresponding treatments in cv. Petrus. The DON content in grain of plants of the two cultivars infected with both pathogens was higher than that of plants infected only with Fusarium over the three years.     

Fusarium graminearum and Fusarium pseudograminearum caused the 2010 head blight epidemics in Australia

Wheat crops in southeast Queensland (Qld) and northern New South Wales (NSW) were infected with fusarium head blight (FHB)‐like symptoms during the 2010–11 wheat growing season. Wheat crops in this region were surveyed at soft dough or early maturity stage to determine the distribution, severity, aetiology and toxigenicity of FHB. FHB was widespread on bread wheat and durum, and Fusarium graminearum and/or F. pseudograminearum were diagnosed from 42 of the 44 sites using species‐specific PCR primers directly on spikelets or from monoconidial cultures obtained from spikelets. Stem base browning due to crown rot (CR) was also evident in some samples from both states. The overall FHB and CR severity was higher for NSW than Qld. Deoxynivalenol (DON) concentration of immature grains was more than 1 mg kg^?1 in samples from 11 Qld and 14 NSW sites, but only 13 of 498 mature grain samples sourced from the affected areas had more than 1 mg kg^?1 DON. DON concentration in straw also exceeded 1 mg kg^?1 in eight Qld and all but one NSW sites but this was not linked to DON concentration of immature grains. The proportion of spikelets with positive diagnosis for F. graminearum and/or F. pseudograminearum and weather‐related factors influenced DON levels in immature grains. The average monthly rainfall for August–November during crop anthesis and maturation exceeded the long‐term monthly average by 10–150%. Weather played a critical role in FHB epidemics for Qld sites but this was not apparent for the NSW sites, as weather was generally favourable at all sites.     

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.     

Ultrastructural and immunocytochemical investigation of pathogen development and host responses in resistant and susceptible wheat spikes infected by Fusarium culmorum

Pathogen development and host responses in wheat spikes of resistant and susceptible cultivars infected by Fusarium culmorum causing Fusarium head blight (FHB), were investigated by means of electron microscopy as well as immunogold labelling techniques. The studies revealed similarities in the infection process and the initial spreading of the pathogen in wheat spikes between resistant and susceptible cultivars. However, the pathogen’s development was obviously more slow in the resistant cultivars as in comparison to a susceptible one. The structural defence reactions such as the formation of thick layered appositions and large papillae were essentially more pronounced in the infected host tissues of the resistant cultivars, than in the susceptible one. β -1,3-glucan was detected in the appositions and papillae. Furthermore, immunogold labelling of lignin demonstrated that there were no differences in the lignin contents of the wheat spikes between susceptible and resistant cultivars regarding the uninoculated healthy tissue, but densities of lignin in host cell walls of the infected wheat spikes differed distinctly between resistant and susceptible cultivars. The lignin content in the cell walls of the infected tissues of the susceptible wheat cultivar increased slightly, while the lignin accumulated intensely in the host cell walls of the infected wheat spikes of the resistant cultivars. These findings indicate that lignin accumulation in the infected wheat spikes may play an important role in resistance to the spreading of the pathogen in the host tissues. Immunogold labelling of the Fusarium toxin DON in the infected lemma showed the same labelling patterns in the host tissues of resistant and susceptible cultivars. However, there were distinct differences in the toxin concentration between the tissues of the susceptible and resistant cultivars. At the early stage of infection, the labelling densities for DON in resistant cultivars were significantly lower than those in the susceptible one. The present study indicates that the FHB resistant cultivars are able to develop active defence reactions during infection and spreading of the pathogen in the host tissues. The lower accumulation of the toxin DON in the tissues of the infected spikes of resistant cultivars which results from the host’s defence mechanisms may allow more intensive defence responses to the pathogen by the host.