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Crown rot (CR; Fusarium pseudograminearum) is a serious disease in winter cereals. Soil type, temperature, nutrients, water availability and stubble‐borne inoculum levels play major roles in determining disease severity. This paper reports the impact of two different watering regimes on the disease severity and gas exchange of F. pseudograminearum infected bread wheat for the first time. Fusarium pseudograminearum inoculated and noninoculated genotypes with different susceptibility to CR were watered to either field capacity or a reduced watering regime in three controlled environment experiments. Rate of photosynthesis, stomatal conductance, internal CO2 concentration and transpiration rate were measured using a portable photosynthesis system, together with disease severity of leaf sheaths at 28 days after planting. Significant differences in disease severity were reported between watering treatments with reduction in CR symptoms in the partially resistant genotypes in the reduced water treatment. Photosynthesis, stomatal conductance and transpiration rate were significantly decreased across most genotypes when inoculated with F. pseudograminearum. Differences in gas exchange between inoculum treatments were more evident in plants watered to field capacity. Water availability has been reported to be one of the crucial factors for initiating F. pseudograminearum infection and subsequent development of CR disease. This research demonstrates significant variation in genotype‐related responses to the complex interactions of F. pseudograminearum infection and water treatment, with a negative impact of both limited soil water availability and CR disease severity on plant gas exchange in bread wheat. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is one of the most devastating crop diseases worldwide, significantly reducing the yield and quality of small‐cereal crops such as wheat and barley when favourable weather conditions exist during anthesis. Additionally, FHB‐associated mycotoxins significantly impact global food and feed safety. Controlling FHB with fungicides applied near anthesis reduces visual FHB symptoms and associated mycotoxin production, thereby lowering disease‐related costs. However, when weather conditions are unfavourable for FHB occurrence, fungicide application can be costly and environmentally undesirable. Thus, fungicides should be used sparingly only when the pathogen is present and weather conditions are favourable. Modelling of FHB risk using weather data has grown rapidly in recent decades and plays an essential role in integrated crop disease management. In this review, several weather‐based FHB models are selected and described in detail. The models were developed globally for assessing the real‐time risk of FHB epidemics in various regions/countries. Most of these models are site‐specific and predict FHB visual observations such as the incidence and severity of FHB, Fusarium‐damaged kernels (FDK), and also deoxynivalenol (DON) levels. The review also highlights the limitations of these existing models, including their narrow applicability, low accuracy for high‐risk contamination situations, and omissions of certain factors. Also discussed are potential avenues for improvement and enhanced predictive capabilities including consideration of additional disease risk factors as well as a broader range of varieties. These predictive models can assist producers, regulatory agencies, and industry to mitigate potential food and feed security and safety concerns. [ABSTRACT FROM AUTHOR]

To enhance the framework of the mechanisms of action used by Trichoderma gamsii T6085 for the control of Fusarium head blight (FHB), this work investigated its ability to modulate the expression of defence‐related genes of wheat (Triticum aestivum 'Apogee') in response to endophytic colonization of plant tissues. Changes in relative expression of pal1, pr1, pgip2 and lox1 genes were assessed over time in wheat roots, in spikes colonized by T6085 alone and both T6085 and Fusarium graminearum, and in leaves from wheat seedlings root‐inoculated with T6085. Results indicate the ability of T6085 to induce local and systemic defence responses in wheat plants in the presence of one of the causal agents of FHB. There was a general significant up‐regulation of the plant defence‐related genes analysed, especially in the first days after the application of T6085. According to these results, modulation of plant defence genes could be included within the arsenal of mechanisms used by T6085 when applied to wheat, an additional feature of interest in the management of FHB. To evaluate the effect of the plant genotype on the ability of T6085 to endophytically colonize roots, root colonization was assessed on four cultivars of T. aestivum and two cultivars of T. durum. Data showed that roots of only two T. aestivum cultivars were endophytically colonized by T6085, similar to cv. Apogee used here as control, thus demonstrating an effect of the host genotype on the endophytic ability of T6085. [ABSTRACT FROM AUTHOR]

The goals of this study were to evaluate the role of salicylic acid (SA) in causing autotoxic stress in the faba bean root system and explore how the co‐culture of faba bean (Vicia faba) with wheat (Triticum aestivum) alleviates this stress. We designed a hydroponic pot experiment to study the effects of exogenous SA on the occurrence of Fusarium wilt, seedling growth, physiological resistance of faba bean and pathogenicity of Fusarium oxysporum f. sp. fabae (FOF). The results showed that SA significantly increased the incidence and disease index of faba bean Fusarium wilt, inhibited the growth of seedlings and reduced the physiological resistance of faba bean. An in vitro study of FOF found that SA increased the ability of the organism to produce fusaric acid, cellulase and pectinase, which increased the susceptibility of faba bean to Fusarium wilt. Interestingly, co‐cultivation with wheat significantly reduced the content of SA in exudates from the faba bean roots, which directly reduced the deleterious effects of SA. In addition, co‐cultivation could increase the activity of peroxidase and catalase, reduce the content of malondialdehyde, thus improving the ability of faba bean to defend itself. In conclusion, we found that SA, as an autotoxic substance, aggravates the occurrence of Fusarium wilt on faba bean and affects the growth of this crop. However, co‐cultivation of faba bean with wheat could alleviate this autotoxicity. This study has discovered a possible mechanism that could explain how co‐cultivation can alleviate the obstacles in cropping systems and control Fusarium wilt. [ABSTRACT FROM AUTHOR]

Wheat farmers rely on fungicides to protect fields against several foliar and flowering diseases, including Fusarium head blight (FHB). A range of active ingredients is used in isolation or in dual premixes that include a dimethylation inhibitor (DMI) or a quinone outside inhibitor (QoI) fungicide. Comprehensive information about fungicide resistance in F. graminearum is available for DMIs, while for QoIs the data are scarce. We characterized 225 strains obtained from two states in southern Brazil, Rio Grande do Sul (RS) and Paraná (PR), in relation to their response to two QoIs. The median EC50 (effective concentration leading to 50% inhibition of conidial germination) value for azoxystrobin (n = 25 isolates) was 2.20 μg/ml in the PR population and 4.04 μg/ml in the RS population. For pyraclostrobin (n = 50), the median EC50 was 0.28 μg/ml in the PR population and 0.24 μg/ml in the RS population. Evidence of cross‐resistance could not be detected. Screening using a discriminatory dose (DD) for azoxystrobin in a larger number of isolates from PR (n = 75) and RS (n = 100) states allowed the detection of 50% and 28% sensitive strains, respectively. Using the DD for pyraclostrobin, 33% and 18.8% were classified as less sensitive in the PR and RS isolates, respectively. In RS, the frequency of less‐sensitive isolates increased over time (2007–2011). No point mutation at any of the target spots (F129L, G137R, G143A) was detected. Our results represent an important step towards the establishment of a sensitivity profile for two of the most commonly used QoIs in commercial premixes targeting FHB control. [ABSTRACT FROM AUTHOR]

Isothiocyanates are biotoxic degradation products formed as a result of enzymatic hydrolysis of glucosinolates present in Brassica species. The application of biofumigant Brassica crops, as an alternative crop protection method for soilborne pathogens and pests is increasingly gaining interest. However, little is known of the potential of biofumigation to reduce the inoculum of Fusarium species affecting cereals. The aim of this study was to evaluate the antifungal activity of five isothiocyanates, namely allyl, benzyl, ethyl, 2‐phenylethyl and methyl isothiocyanates, against germination and growth of Fusarium graminearum under in vitro conditions. Aromatic isothiocyanates were more inhibitory than the aliphatic isothiocyanates against mycelial growth, whereas the reverse was observed for conidial germination. Among the tested isothiocyanates, allyl and methyl isothiocyanates were more efficient overall, showing lower ED50 values (35–150 mg/L) for conidial germination and mycelial radial growth. The findings suggest that Brassica plants containing allyl and methyl glucosinolates could have a suppressive effect, reducing the inoculum of F. graminearum in soil prior to cereal production. [ABSTRACT FROM AUTHOR]

Members of the Fusarium graminearum species complex are known to cause head blight of wheat. A natural nonpathogenic mutant, strain Fa0233007, was found in the strain collection of the Japanese F. graminearum species complex. In addition, this strain cannot form perithecia. Complete linkage of these deficiencies in the progenies obtained from crossing a wild‐type strain and the mutant strain suggested that a single genomic locus was responsible for deficiencies in both traits. The locus was mapped to chromosome 1 using sequence‐tagged markers. An NADPH oxidase gene (NoxA, FGSG00739) was identified in the mapped region, and a 2‐bp deletion that results in premature termination of the open reading frame was detected in the gene. Both pathogenicity and perithecium formation were recovered by FGSG00739 complementation in the mutant strain. [ABSTRACT FROM AUTHOR]

We conducted a five‐year survey (2011–2015) of barley and wheat fields in Paraná state, Brazil, obtaining 754 Fusarium isolates from spikes with fusarium head blight (FHB)‐symptoms. Multilocus genotyping and TEF‐1α gene sequence analyses confirmed the dominance of the F. graminearum species complex (FGSC, 75.7%), but F. poae (11.5%), as well as F. avenaceum and related members of the F. tricinctum species complex (FTSC, 8.1%) appeared as substantial contributors to FHB. Within the FGSC, F. graminearum of the 15‐ADON genotype was dominant (63%), followed by F. meridionale of the NIV genotype (23.1%), F. cortaderiae of the NIV (7%) or 3‐ADON (2.6%) genotypes, and F. austroamericanum (3.8%) of the 3‐ADON genotype. Substantial variation in pathogen composition was observed across years, with F. poae and F. meridionale frequencies significantly elevated in some years. Most F. poae strains produced DAS, diANIV, and butenolide, but not neosolaniol, T‐2, or HT‐2. All FTSC species produced moniliformin. Enniatin production was widespread among FTSC species, with the single F. acuminatum strain found to be the strongest producer of enniatins. Our findings confirm FGSC as a major contributor to FHB and expand considerably our knowledge of the presence, frequency, and conditions under which other pathogens may emerge, altering the spectrum of toxins that may accumulate in grain. [ABSTRACT FROM AUTHOR]

Canada is one of the largest wheat producers in the world, and wheat is grown over an area spanning most of the southern latitudes, with the prairie region (provinces of Saskatchewan, Alberta, and Manitoba) being the main producer. Several pathogens and pests attack wheat, but at present fusarium head blight (FHB), stripe rust, and leaf spots are the most damaging diseases to wheat production in Canada. Historically, smuts, stem rust, and leaf rust caused major crop losses in Canada and can still pose serious threat if management practices are relaxed. Cropping practices used by Canadian farmers to grow and harvest wheat over the last century have influenced disease development and pathogen biology, affecting the severity, incidence, and prevalence of crop diseases over time. Changes such as reduced tillage coincide with emergence of residue‐borne diseases, such as FHB and leaf spots, while the deployment of resistant cultivars and increased fungicide use has resulted in the reduction of common bunt, stem, and leaf rust. This review will discuss the influence of long‐term cropping practices, alone or in combination, on the biology, emergence, and prevalence of wheat diseases in Canada over the last century. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) of wheat is a destructive fungal disease worldwide and has become more severe over the last two decades. Development of FHB resistant wheat varieties is the most effective way to manage FHB. The middle and lower reaches of the Yangtze River are the traditional FHB epidemic areas in China. The landraces and germplasms with resistance to FHB originating from this region were used to identity FHB resistance quantitative trait loci (QTLs). Yangmai 158 and Ningmai 9 are the most popular varieties for commercial wheat production in this region and both have moderate FHB resistance. A high‐density genetic map was constructed using 282 recombinant inbred lines (RILs) from a cross between Ningmai 9 and Yangmai 158. Ten QTLs related to Type II FHB resistance were identified, and QFhb‐3B.1 and QFhb‐5A were stably detected across all environments. Based on position alignment, QFhb‐3B.1 from Ningmai 9 is likely to be Fhb1 and QFhb‐5A from Yangmai 158 is a novel QTL not previously described. A competitive allele‐specific PCR (KASP) marker closely linked to QFhb‐5A was developed and could be used for marker‐assisted selection. Distribution of QFhb‐5A was tested with numerous accessions from a widespread core collection. The results suggest that QFhb‐5A has undergone both natural and artificial selection. Some RILs with both Fhb1 and QFhb‐5A presented better FHB resistance than the parents and could be used in FHB resistance breeding. [ABSTRACT FROM AUTHOR]

Fusarium crown rot of wheat has been spreading in the Huanghuai wheat‐growing area in China since 2010, leading to a potential yield loss. To investigate the pathogens associated with this disease in Jiangsu and Shandong provinces in recent years, 617 Fusarium isolates were isolated from nine sites in these two provinces between 2014 and 2016. Of these isolates, 372 were identified as Fusarium pseudograminearum, and the remaining isolates were identified as F. asiaticum and F. graminearum, suggesting that F. pseudograminearum is becoming a predominant causative pathogen of crown rot of wheat in eastern China. Trichothecene gene detection and chemical analyses of trichothecenes indicated that the F. pseudograminearum isolates belonged to the 3‐ADON or 15‐ADON chemotype, and one isolate had the NIV genotype but produced no detectable NIV. 3‐ADON isolates were predominant in Jiangsu, whereas 15‐ADON isolates were prevalent in Shandong. The mating type of the F. pseudograminearum isolates were identified. MAT‐1 and MAT‐2 existed, but in most collections, particularly those in Jiangsu, the ratios of the two mating types deviated significantly from an expected 1:1 ratio. The reason for the occurrence of F. pseudograminearum is hypothesized, and the chemotype and mating type distribution of this species in these two provinces are analysed. [ABSTRACT FROM AUTHOR]

Fusarium crown rot (FCR), caused predominantly by Fusarium pseudograminearum (Fp) in Australia, is an important fungal disease of wheat and barley. FCR causes significant yield losses and reduced grain quality worldwide. This study investigated the population dynamics of FCR‐causing F. pseudograminearum isolates from Western Australia (WA), a major wheat‐growing region. Wheat samples were collected from a total of seven different sites in 2008 and 2015. Two sites, Tammin and Karlgarin, with moderate to high FCR incidence, were intensively sampled in both years. The results revealed significant increase in Fp isolation frequency between 2008 and 2015. Over 86% of 1100 Fusarium isolates were Fp in 2015 compared with 59% of 639 isolates from 2008. Mating type idiomorphs, toxin chemotypes and population genetic structures were determined for a subset of 279 Fp isolates (132 isolates from 2008 and 165 from 2015). Mating type analysis revealed differences in MAT1‐1 and MAT1‐2 distributions between Tammin and Karlgarin for both years. Results also showed that 97.6% of Fp isolates analysed had the 3‐ADON trichothecene chemotype. Additionally, for the first time in Australia, the 15‐ADON chemotype was identified in 2.3% and 2.4% of Fp isolates from 2008 and 2015, respectively. The genetic structure of Fp population determined using 21 cleaved amplified polymorphic sequence (CAPS) markers revealed a high level of genetic variation within and between populations. In addition, 2015 isolates from Tammin and Karlgarin were significantly more aggressive (P < 0.0001) than 2008 isolates. This finding may have implications in managing this significant fungal disease. [ABSTRACT FROM AUTHOR]

Fusarium graminearum causes fusarium head blight ( FHB) of wheat and gibberella ear rot ( GER) of corn in Canada and also contaminates grains with trichothecene mycotoxins. Very little is known about trichothecene diversity and population structure of the fungus from corn in Ontario, central Canada. Trichothecene genotypes of F. graminearum isolated from corn ( n = 452) and wheat ( n = 110) from 2010 to 2012 were identified. All the isolates were deoxynivalenol ( DON) type. About 96% of corn isolates and 98% of wheat isolates were 15-acetyl deoxynivalenol (15 ADON) type. The fungal population structures from corn ( n = 313) and wheat ( n = 73) were compared using 10 variable number tandem repeat ( VNTR) markers. The fungal populations and subpopulations categorized based on host, cultivar groups, years and geography showed high gene ( H = 0.818-0.928) and genotypic ( GD = 0.999-1.00) diversity. Gene flow was also high between corn and wheat population pairs ( Nm = 8.212), and subpopulation pairs within corn ( Nm = 7.13-23.614) or wheat ( Nm = 19.483) populations. Phylogenetic analysis revealed that isolates from both hosts were F. graminearum clade 7. These findings provide baseline data on 3-acetyl deoxynivalenol (3 ADON) and 15 ADON profiles of F. graminearum isolates from corn in Canada and are useful in evaluating mycotoxin contamination risks in corn and wheat grains. Understanding the fungal genetic structure will assist evaluation and development of resistant cultivars/germplasm for FHB on wheat and GER on corn. [ABSTRACT FROM AUTHOR]

The fungal pathogen Fusarium graminearum is the causal agent of fusarium head blight in wheat and other small grain cereals. This fungus is known to produce high amounts of cell wall-degrading enzymes during infection of wheat spikes. In addition, wheat tissue is particularly rich in xylan, which can be hydrolysed by fungal xylanases. In order to establish the role of F. graminearum xylanase activity in pathogenicity, targeted gene disruption of the F. graminearum xyr1 gene, encoding the major regulator of xylanase gene expression, was performed. When grown on xylan as carbon source, the xylanase activity of the Δ xyr1 mutant was dramatically reduced and fungal growth was significantly reduced compared to the wildtype fungus. When grown on carboxymethylcellulose, the cellulolytic activity of the mutant was also reduced and the mutant did not grow on wheat cell walls. The disruption of the xyr1 gene greatly reduced the expression of xylanase-encoding genes both in vitro and during wheat spike infection, thus confirming the involvement of F. graminearum Xyr1 in the regulation of genes controlling xylan degradation. However, despite the deep impact caused by xyr1 gene disruption on the expression of xylanase genes and on total xylanase activity, the virulence of the Δ xyr1 mutant appeared unaffected on Triticum aestivum and T. durum spikes and on soybean seedlings. In conclusion, although a possible role for residual xylanase activity in the virulence of F. graminearum cannot be conclusively excluded, the results question the importance of xylanase activity during the infection process. [ABSTRACT FROM AUTHOR]

Fusarium head blight in wheat spikes is associated with production of mycotoxins by the fungi. Although flowering is recognized as the most favourable host stage for infection, a better understanding of infection timing on disease development and toxin accumulation is needed. This study monitored the development of eight characterized isolates of F. graminearum, F. culmorum and F. poae in a greenhouse experiment. The fungi were inoculated on winter wheat spikes before or at anther extrusion, or at 8, 18 and 28 days later. Disease levels were estimated by the AUDPC and thousand-kernel weight ( TKW). The fungal biomass (estimated by q PCR) and toxin concentration (deoxynivalenol and nivalenol, estimated by UPLC- UV- MS/ MS) were measured in each inoculated spike, providing a robust estimation of these variables and allowing correlations based on single-individual measurements to be established. The toxin content correlated well with fungal biomass in kernels, independently of inoculation date. The AUDPC was correlated with fungal DNA, but not for early and late infection dates. The highest disease and toxin levels were for inoculations around anthesis, but early or late infections led to detectable levels of fungus and toxin for the most aggressive isolates. Fungal development appeared higher in kernels than in the chaff for inoculations at anthesis, but the opposite was found for later inoculations. These results show that anthesis is the most susceptible stage for FHB, but also clearly shows that early and late infections can produce significant disease development and toxin accumulation with symptoms difficult to estimate visually. [ABSTRACT FROM AUTHOR]

The biocontrol effect of Clonostachys rosea (strains 016 and 1457) on Fusarium graminearum, F. avenaceum, F. verticillioides, F. langsethiae, F. poae, F. sporotrichioides, F. culmorum and Microdochium nivale was evaluated on naturally infected wheat stalks exposed to field conditions for 180 days. Experiments were conducted at two locations in Argentina, Marcos Juarez and Río Cuarto. Antagonists were applied as conidial suspensions at two inoculum levels. Pathogens were quantified by Taq Man real-time q PCR. During the first year at Marcos Juarez, biocontrol was observed in one antagonist treatment for F. graminearum after 90 days (73% reduction) but after 180 days, the pathogen decreased to undetectable levels. During the second year, biocontrol was observed in three antagonist treatments for F. graminearum and F. avenaceum (68·3% and 98·9% DNA reduction, respectively, after 90 days). Fusarium verticillioides was not controlled at Marcos Juarez. At Río Cuarto, biocontrol effects were observed in several treatments at different intervals, with a mean DNA reduction of 88·7% for F. graminearum and F. avenaceum, and 100% reduction for F. verticillioides in two treatments after 180 days. Populations of F. avenaceum and F. verticillioides were stable; meanwhile, F. graminearum population levels varied during the first 90 days, and low levels were observed after 180 days. The other pathogens were not detected. The study showed that wheat stalks were important reservoirs for F. avenaceum and F. verticillioides populations but less favourable for F. graminearum survival. Clonostachys rosea (strain 1457) showed potential to reduce the Fusarium spp. on wheat stalks. [ABSTRACT FROM AUTHOR]

In this study, the Arabidopsis thaliana NPR1 (non-expressor of PR genes) gene was integrated into an elite wheat cultivar, and the response of the transgenic wheat expressing NPR1 to inoculation with Fusarium asiaticum was analysed. With seedling inoculation, the transgenic lines showed significantly increased fusarium seedling blight (FSB) susceptibility, whereas floret inoculation resulted in enhanced fusarium head blight (FHB) resistance. Quantitative real-time PCR revealed that expression of two defence genes, PR3 and PR5, was associated with susceptible reactions to FSB and FHB, whereas the PR1 gene was activated in resistance responses. This inverse modulation by the constitutively expressed NPR1 gene suggests that NPR1 has a bifunctional role in regulating defence responses in plants. Therefore, it is unsuitable for improving overall resistance to FSB and FHB in wheat. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The spatial pattern of Fusarium-infected kernels and their mycotoxin contamination was studied in four wheat fields in Germany using geo-referenced sampling grids (12–15 × 20–30 m, 28–30 samples per field) at harvest. For each sample, frequency of Fusarium-infected kernels and spectrum of species were assessed microbiologically; mycotoxin contents were determined by HPLC-MS/MS analysis. Spatial variability of pathogens and mycotoxins was analysed using various parameters including Spatial Analysis by Distance IndicEs (sadie® ). Microdochium majus, the most frequent head blight pathogen in 1998, was less frequent in 1999 and could not be detected in kernels from two fields in 2004. Fusarium avenaceum, F. graminearum and F. poae were the most frequent Fusarium species, with 7–8 species per field. The frequency of Fusarium-infected kernels was 3–15% and the incidence of species showed considerable within-field variability. Spatial patterns varied among Fusarium species as well as from field to field. Although pathogens and mycotoxin were often distributed randomly in the field, F. avenaceum, F. graminearum, F. poae, F. sporotrichioides, F. tricinctum and the mycotoxin moniliformin had an aggregated pattern in at least one field. Patterns are discussed in relation to spread of Fusarium species depending on inoculum sources, spore type, kind of dispersal, availability of susceptible host tissue and micro-climate. Sampling of wheat fields for representative assessment of mycotoxins is complicated by random patterns of Fusarium-infected kernels, especially where the frequency of infection is small. [ABSTRACT FROM AUTHOR]

Using the mycelial reactions of 435 combinations of 14 Fusarium pseudograminearum and 15 F. graminearum isolates, it was demonstrated for the first time that mycelial reactions/barrage formation cannot be clearly used to distinguish F. graminearum and F. pseudograminearum. Mutually compatible isolates produced very different patterns of compatibility with other isolates. However, about 60% of pairings between F. graminearum and F. pseudograminearum isolates were compatible, indicating common ancestry. The Mantel tests used to determine any possible associations between mycelial compatibility reactions and AFLP genotypic diversity data revealed no association between the two systems in either species. In addition, no association was found between mycelial compatibility reactions and sexual reproduction in the two species. Implications of the higher frequency of mycelial compatibility reactions observed in F. pseudograminearum than in F. graminearum are discussed. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A significant negative relationship between tiller height and resistance to Fusarium ear blight (FEB), following inoculation, was observed in 17 cultivars of winter wheat in the 1995/96 growing season. Tall cultivars such as Kraka and Spark showed fewer symptoms of FEB (6 and 4%) than the shorter cultivars Brigadier and Virtue (35 and 51%). To determine if this relationship was caused by a genetic association or an effect of the microclimate, height and disease were measured in segregating populations derived from tall × short cultivars and humidity was measured in near-isogenic lines with and without the Rht1 and Rht2 dwarfing genes. Among random F3 populations there was a clear tendency for tall strawed lines to show less severe disease symptoms than shorter strawed lines following inoculation. The effect of the individual dwarfing genes Rht1 and Rht2 on the severity of FEB was also studied in an inoculation trial using a number of near-isogenic lines of Maris Huntsman and Maris Widgeon. Within isogenic lines of Maris Huntsman, there was a clear tendency for tall straw to be associated with fewer symptoms, but this was not apparent within lines of Maris Widgeon. Monitoring relative humidity at ear height in a short and tall isogenic line of Maris Huntsman revealed no significant differences between these genotypes from GS 65 to GS 85, suggesting that microclimate cannot explain differences in severity of FEB between these lines. It is suggested that there are independent genes affecting the severity of FEB that may allow plant breeders to select resistant cultivars of any height. [ABSTRACT FROM AUTHOR]

This review of Fusarium ear blight (scab) of small grain cereals has shown that up to 17 causal organisms have been associated with the disease, which occurs in most cereal-growing areas of the world. The most common species were Fusarium graminearum (Gibberella zeae), F. cuitnorum, F. avenaceum (G. avenacea) , F. poae and Microdochium nivale (Monographella nivalis). The disease was recorded most frequently under hot, wet climatic conditions where significant yield losses and mycotoxin accumulation in grain were reported. Possible sources of inoculum were reported as crop debris, alternative hosts and Fusariurn seedling blight and foot rot of cereals. The mode of dispersal of inoculum to ears remains unclear, but contaminated arthropod vectors, systemic fungal growth through plants, and wind and rain-splash dispersal of spores have been proposed. Infection of wheat ears was shown to occur mainly during anthesis, and it has been demonstrated that fungal growth stimulants may be present in anthers. Despite the importance of the disease, particularly during epidemic years, control methods are limited. Much effort has gone into breeding resistant wheat varieties and into improving our understanding of the possible mechanisms and genetic basis of resistance, with only moderate success. There are also surprisingly few reports of successful fungicidal or biological control of the disease in the field. [ABSTRACT FROM AUTHOR]

Genetic variation in Fusarium species on wheat was investigated using restriction fragment length polymorphism (RFLP) analysis. Single-spore lines (76) of Fusarium were recovered from 24 ears of wheat in a field plot exhibiting severe symptoms of Fusarium ear blight and identified using classical taxonomic criteria. Four Fusarium species were present, of which F. avenaceum and F. culmorum were predominant with F. lateritium and F. poae present in two ears and one ear, respectively. RFLP analysis using rDNA (pTA71) or total genomic DNA from an F. culmorum isolate clearly distinguished the four species. Genetic fingerprints of the isolates generated using DNA of bacteriophage M13 (which contains a mini-satellite repeat sequence) revealed considerable variation within three of the four species (except F. poae). Generally, only a single clone was recovered from each ear and in all but one case only a single species was obtained from each spikelet. However, in several instances it appeared that more than one clone of a species was present within a single spikelet. [ABSTRACT FROM AUTHOR]

Dryland root rot of wheat and barley in South Australia is a syndrome from which the associated fungi Fusarium equiseti, F. acuminatum, F. oxysporum and Bipolaris sorokiniana were isolated consistently. Fusarium infections were concentrated on the subcrown internodes, crown roots and culm bases, and occurred with equal frequency on wheat and barley. Bipolaris infections were more numerous on barley than on wheat, and were concentrated on culm bases and subcrown internodes. Recoveries of each of the four fungi showed a pattern of infection that was neither randomly nor evenly distributed. Each fungus had preferences for certain sites which resulted in a stratified distribution over the roots and crown. When two barley cultivars were compared, the patterns of infection were different; the subcrown internode was attacked more severely, and there was a substantial increase in the amount of infection by all four fungi on one of the cultivars. Pathogenicity tests on barley and oats showed that all four species of fungi were capable of causing damage to roots, but there were differences between isolates of each fungus and differences in their ability to damage barley and oats. [ABSTRACT FROM AUTHOR]