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Fusarium head blight (FHB) is a destructive fungal disease in wheat worldwide. Efforts have been carried out to combat this disease, and the pore-forming toxin-like (PFT) gene at the quantitative trait locus (QTL) Fltbl was isolated and found to confer resistance to FHB in Sumai 3. In this study, we characterized PFT in 348 wheat accessions. Four haplotypes of PFT were identified. The wild haplotype of PFT had higher resistance than other haplotypes and explained 13.8% of phenotypic variation in FHB resistance by association analysis. PFT was highly expressed during early flowering and increased after Fusarium grartiinearum treatment in Sumai 3. Analysis of the 5' flanking sequence of PFT predicted that the cis elements of the PFT promoter were related to hormones and biological defense responses. However, PFT existed not only in the FHB-resistant accessions but also in some susceptible accessions. These results suggested that FHB resistance in a diverse range of wheat genotypes is partially conditioned by PFT. The profiling of FHB resistance and the PFT locus in this large collection of wheat germplasm may prove helpful for incorporating FHB resistance into wheat breeding programs, although more work is needed to reveal the exact role of the QTL Fhbl in conferring resistance to fungal spread. [ABSTRACT FROM AUTHOR]

Management of Fusarium graminearum-associated mycotoxins in wheat grain has been extensively evaluated, but little is known about management of mycotoxins in straw. Two research trials were conducted at four locations from 2011 to 2014. The objective of the first trial was to determine the efficacy of fungicides, and the objective of the second trial was to evaluate the use of integrated disease management strategies, for the control of Fusarium head blight (FHB) and reducing the concentration of the Fusarium mycotoxins deoxynivalenol, 3-acetyl-deoxynivalenol, and 15-acetyl-deoxynivalenol in straw. In the first trial, it was determined that demethylation inhibitor (DM1) fungicides did not offer significant (P ≤ 0.05) reductions of mycotoxin concentrations in the straw compared with a no-fungicide control treatment, but significant (P ≤ 0.05) reductions in mycotoxin concentration were observed in the control when compared with treatments with the application of quinone outside inhibitor (Qol)-containing fungicides. In the second trial, mycotoxin concentrations in the straw were significantly (P ≤ 0.05) reduced in the moderately resistant cultivar compared with the susceptible cultivar, but were not affected by the use of a fungicide. The practices typically used to manage Fusarium mycotoxins in wheat grain, especially the selection of resistant cultivars and not using a Qol fungicide, may be an effective means to reduce mycotoxin concentrations in the straw. [ABSTRACT FROM AUTHOR]

An in vitro spike culture method was optimized to evaluate Fusarium head blight (FHB) resistance in wheat (Triticum aestivum) and used to screen a population of ethyl methane sulfonate treated spike culturederived variants (SCDV). Of the 134 SCDV evaluated, the disease severity score of 47 of the variants was <30%. Single nucleotide polymorphisms (SNP) in the UDP-glucosyltransferase (UGT) genes, TaUGT-2B, TaUGT-3B, and TaUGT-EST, differed between AC Nanda (an FHB-susceptible wheat variety) and Sumai-3 (an FHB-resistant wheat cultivar). SNP at 450 and 1,558 bp from the translation initiation site in TaUGT-2B and TaUGT-3B, respectively were negatively correlated with FHB severity in the SCDV population, whereas the SNP in TaUGT-EST was not associated with FHB severity. Fusarium graminearum strain M7-07-1 induced early expression of TaUGT-2B and TaUGT-3B in FHB-resistant SCDV lines, which were associated with deoxynivalenol accumulation and reduced FHB disease progression. At 8 days after inoculation, deoxynivalenol concentration varied from 767 ppm in FHB-resistant variants to 2,576 ppm in FHB-susceptible variants. The FHB-resistant SCDV identified can be used as new sources of FHB resistance in wheat improvement programs. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is a destructive disease of wheat in humid and semihumid areas of the world. It has emerged in the Pacific Northwest (PNW) in recent years because of changing climate and crop rotation practices. Our objectives in the present study were to identify and characterize quantitative trait loci (QTL) associated with FHB resistance in spring wheat lines developed in the PNW and the International Maize and Wheat Improvement Center. In total, 170 spring wheat lines were evaluated in field and greenhouse trials in 2015 and 2016. Fourteen lines showing consistent resistance in multiple environments were identified. These lines are valuable resources in wheat variety improvement of FHB resistance because they have no Sumai 3 or Sumai 3-related background. The 170 lines were genotyped using a high-density Illumina 90K single-nucleotide polymorphisms (SNP) assay and 10 other non-SNP markers. A genome-wide association analysis was conducted with a mixed model (Q+K). Consistent, significant SNP associations with multiple traits were found on chromosomes IB, 2B, 4B, 5A, 5B, and 6A. The locus on chromosome 5B for reduced deoxynivalenol content may be novel. The identified QTL are being validated in additional mapping studies and the identified resistant lines are being used in variety development for FHB resistance and facilitated by marker-assisted selection. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) and maize stalk rot (MSR), caused by members of the Fusarium graminearum species complex (FGSC), are among the most destructive and economically important diseases in the world. Species identity and the trichothecene chemotype of 312 members of the FGSC from diseased wheat spikes and maize stalks in Henan was determined using phylogenetic analyses and a polymerase chain reaction trichothecene chemotype assay. F. graminearum sensu stricto accounted for more than 93% of the FGSC isolates associated with FHB (N = 168) and MSR (N = 130). The remaining isolates were F. asiaticum. Significant differences were found in the frequencies of the two species within the hosts (P < 0.01). However, the frequencies of the same species in FHB and MSR were similar (P > 0.05) for wheat and maize isolates, indicating that the composition of the FGSC with respect to wheat and maize in these fields varied little. The 15- acetyl-deoxynivalenol (15-ADON) trichothecene chemotype represented 92.7 and 98.5% of isolates from wheat (N = 167) and maize (TV = 130), respectively. However, the 3-acetyl-deoxynivalenol chemotype was found in 6.7% of wheat isolates, and the nivalenol chemotype in 1.5% of MSR isolates and in 0.6% of FHB isolates. Mycelial growth at different concentrations of carbendazim and difenoconazole did not differ between F. graminearum sensu stricto and F. asiaticum. These results suggest that the 15-ADON chemotype of F. graminearum sensu stricto is the predominant pathogen that causes wheat- and maize-related diseases in this region. [ABSTRACT FROM AUTHOR]

The semidwarfing alleles reduced height (Rht)-Dlb and Rht-Blb are widely deployed in wheat breeding. Both alleles have similar effects on plant height but differ in their effect on Fusarium head blight (FHB) severity. A double-haploid population and a backcross population, segregating for Rht- BlaJRht-Blb and Rht-Dla/Rht-Dlb, were evaluated for FHB severity, plant height, and anther retention in field trials in three consecutive years. The semidwarfing alleles reduced plant height and increased the proportion of retained anthers. Reduced plant height and a high proportion of retained anthers were associated with increased FHB severity. The Rht-Dlb allele had a significantly greater impact on anther retention and FHB severity than the Rht-Blb allele. Fusarium graminearum establishes infection sites predominantly inside the floral cavity and retained anthers potentially support colonization and initial hyphal growth, leading to a higher disease level in genotypes with a higher proportion of retained anthers. This is the first report demonstrating that differences in disease severity associated with Rht-Dlb and Rht-Blb can be partly explained by their different effect on the extent of anther retention. [ABSTRACT FROM AUTHOR]

Fusarium asiaticum is a critical pathogen of Fusarium head blight (FHB) in the southern part of China. The fungicide phenamacril has been extensively used for controlling FHB in recent years, which reduced both FHB severity and mycotoxin production. Our previous report indicated that resistance of F. asiaticum to phenamacril was related to mutations in myosin5. A recent article revealed that the resistance level of phenamacril-resistant mutants was associated with the genotypes of myosinS in these mutants. In total, we obtained 239 resistant isolates by fungicide domestication, and 82 resistant mutants were randomly selected for further study. Of these mutants, 25.6,7.3, and 67.1% showed low resistance (LR), moderate resistance (MR), and high resistance (HR), respectively, to phenamacril determined by 50% effective concentration values. Point mutations A135T. V151M, P204S, 1434M, A577T, R580G/H, or 158IF led to LR. Point mutations S418R, I424R, and A577G were responsible for MR and point mutations K216R/E, S217P/L, or E420K/G/D conferred HR. Interestingly, all of the mutations concentrated in the myosin5 motor domain and mutations confening HR occurred at codon 217 and 420, which we called the core region. Homology modeling revealed that mutations far from the core region led to a lower resistance degree. Phenotype assays revealed that the most highly resistant mutants did not significantly change pathogenicity but decreased conidia production compared with the wild type, which may slow down the formation of the resistant pathogen population in the fields. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is a devastating disease that causes significant reductions in yield and quality in wheat, rye, and triticale. In triticale, knowledge of the genetic architecture of FHB resistance is missing but essential due to modern breeding requirements. In our study, four doubled-haploid triticale populations (N = 120 to 200) were evaluated for resistance to FHB caused by artificial inoculation with Fusarium cul- morum in four environments. DArT markers were used to genotype triticale populations. Seventeen quantitative trait loci (QTL) for FHB resis tance were detected across all populations; six of them were derived from rye genome and located on chromosomes 4R, 5R, and 7R, which are here reported for the first time. The total cross-validated ratio of the explained phenotypic variance for all detected QTL in each population was 41 to 68%. In all, 17 QTL for plant height and 18 QTL for heading stage were also detected across all populations; 3 and 5 of them, respectively, were overlapping with QTL for FHB. In conclusion, FHB resistance in triticale is caused by a multitude of QTL, and pyramiding them contributes to higher resistance. [ABSTRACT FROM AUTHOR]

Predicting major Fusarium head blight (FHB) epidemics allows for the judicious use of fungicides in suppressing disease development. Our objectives were to investigate the utility of boosted regression trees (BRTs) for predictive modeling of FHB epidemics in the United States, and to compare the predictive performances of the BRT models with those of logistic regression models we had developed previously. The data included 527 FHB observations from 15 states over 26 years. BRTs were fit to a training data set of 369 FHB observations, in which FHB epidemics were classified as either major (severity ≥ 10%) or non-major (severity < 10%), linked to a predictor matrix consisting of 350 weatherbased variables and categorical variables for wheat type (spring or winter), presence or absence of corn residue, and cultivar resistance. Predictive performance was estimated on a test (holdout) data set consisting of the remaining 158 observations. BRTs had a misclassification rate of 0.23 on the test data, which was 31% lower than the average misclassification rate over 15 logistic regression models we had presented earlier. The strongest predictors were generally one of mean daily relative humidity, mean daily temperature, and the number of hours in which the temperature was between 9 and 30°C and relative humidity ≥ 90% simultaneously. Moreover, the predicted risk of major epidemics increased substantially when mean daily relative humidity rose above 70%, which is a lower threshold than previously modeled for most plant pathosystems. BRTs led to novel insights into the weather-epidemic relationship. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) of wheat and barley has been extensively researched worldwide; in contrast, there is limited information on the effects of environmental conditions on Fusarium toxin accumulation in oat grains. More than 300 samples of oat grain from various regions of the United Kingdom from 2006 to 2008 were analyzed for mycotoxin contamination due to infection by Fusarium spp. HT2 and T2 toxins were the two most commonly detected, and their concentrations in individual samples were highly correlated. Hourly weather data were obtained from meteorological recording stations near most of the sampling sites. Statistical modeling was applied to both the original toxin (HT2 plus T2) data and the toxin data adjusted for oat cultivars and number of cereal crops in the previous four seasons. Accumulation of HT2 and T2 toxin was positively correlated with warm and wet conditions during early May and dry conditions thereafter. Using a collection of 51 environmental variables summarized over three lengths (10, 15, and 20 days) of time periods encompassing early May, late May, and early July, all-subsets regression showed that many models, consisting of three to six predictor variables, could be identified with similar explanatory strength for the effect of environmental conditions on toxin accumulation. Most important predictor variables were related to wet conditions during the early-May period, which was before anthesis. These results suggest that the predominant period for Fusarium langsethiae infection of oat is likely to be before rather than during anthesis, as for other head blight pathogens. These empirical models may be further improved by using quantified pathogen biomass within the grains and weather predictor variables summarized in relation to plant growth stages (instead of calendar times). [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is an important disease of wheat and barley worldwide. The disease is primarily caused by members of the Fusarium graminearum species complex, consisting of at least 14 phylogenetically distinct species. To determine the population structure of the FHB pathogens in a naturally infected disease nursery located at Jianyang, Fujian province, China, 160 isolates of the F. graminearum complex were recovered from symptomatic wheat spike samples collected in two consecutive years (2008 and 2009) and characterized using species- and chemotype-specific polymerase chain reaction as well as variable number tandem repeat (VNTR) markers. All isolates analyzed were identified as F. asiaticum except for one isolate, which was identified as F. avenaceum. Among the 159 F asiaticum isolates, 126 (79%) isolates were of the nivalenol (NIV) type while 29 (18%) isolates were of the 15-acetyl deoxynivalenol type and only 4 (3%) isolates were of the 3-acetyl deoxynivalenol type. The 10 VNTR markers revealed 124 distinct haplotypes and 76 polymorphic alleles across the whole population. The two subpopulations (FA-08 and FA-09) grouped based on the year of collection exhibited low genetic differentiation (Fst = 0.032) and high gene flow (Nm = 15.13). However, a significant genetic differentiation was found within the NIV-type isolates as revealed by the Structure software. The pairwise linkage disequilibrium tests did not support the hypothesis of random mating in the population because half (48.8%) of the locus pairs showed a linkage disequilibrium (P > 0.05). Our results suggest that FHB in this nursery was caused by a genetically homogenous and non-random mating population of F. asiaticum in 2008 and 2009, which consisted of all three trichothecene types with various levels of aggressiveness. [ABSTRACT FROM AUTHOR]

Integration of host resistance and prothioconazole + tebuconazole fungicide application at anthesis to manage Fusarium head blight (FHB) and deoxynivalenol (DON) in wheat was evaluated using data from over 40 trials in 12 U.S. states. Means of FHB index (index) and DON from up to six resistance class-fungicide management combina-tions per trial (susceptible treated [S_TR] and untreated [S_UT]; moderately susceptible treated [MS_TR] and untreated [MS_UT]; moderately resistant treated [MR_TR] and untreated [MR_UT]) were used in multivariate meta-analyses, and mean log response ratios across trials were estimated and transformed to estimate mean percent control ( C ) due to the management combinations relative to S_UT. All combinations led to a significant reduction in index and DON (P < 0.001). MR_TR was the most effective combination, with a C of 76% for index and 71% for DON, followed by MS_TR (71 and 58%, re-spectively), MRJJT (54 and 51%, respectively), S_TR (53 and 39%, respectively), and MS_UT (43 and 30%, respectively). Calculations based on the principle of treatment independence showed that the combination of fungicide application and resistance was additive in terms of percent control for index and DON. Management combina-tions were ranked based on percent control relative to S_UT within each trial, and nonparametric analyses were performed to determine management combination stability across environments (trials) using the Kendall coefficient of concordance (W). There was a significant concordance of management combinations for both index and DON (P < 0.001), indicating a nonrandom ranking across environments and relatively low variability in the within-environment ranking of manage-ment combinations. MR_TR had the highest mean rank (best control relative to S_UT) and was one of the most stable management com-binations across environments, with low rank stability variance (0.99 for index and 0.67 for DON). MS_UT had the lowest mean rank (poor-est control) but was also one of the most stable management combina-tions. Based on Piepho's nonparametric rank-based variance homo-geneity U test, there was an interaction of management combination and environment for index (P = 0.011) but not for DON (P = 0.147), indicating that the rank ordering for index depended somewhat on environment. In conclusion, although the magnitude of percent control will likely vary among environments, integrating a single tebuconazole + prothioconazole application at anthesis with cultivar resistance will be a more effective and stable management practice for both index and DON than either approach used alone. [ABSTRACT FROM AUTHOR]

U.S. populations of the Fusarium graminearum clade cause head blight on wheat and barley and usually contaminate grain with the trichothecene mycotoxin deoxynivalenol (DON). Recently, however, individual nivalenol (NIV)-type isolates from the United States were described that belonged to either the newly described species F. gerlachii or the genetically distinct Gulf Coast population of F. gmminearum sensu stricto (s.s.). Here, we describe the discovery of NIV-type F. graminearum s.s. populations that were found in high proportion (79%) among isolates from small-grain-growing regions of Louisiana. We genotyped 237 isolates from Louisiana with newly developed polymerase chain reaction (PCR) restriction fragment length polymorphism markers and multiplex PCR primers that distinguish among the three trichothecene types: the two DON types (15ADON and 3ADON) and NIV. These isolates were compared with 297 isolates from 11 other U.S. states, clustering, we discovered a southern Louisiana population of F. graminearum s.s. that was genetically distinct from the previously recognized pathogen population in the Midwest (MWl5ADON population). Population membership was correlated with trichothecene type. Most isolates from the southern Louisiana population were of the NIV type, while the majority of the isolates from the Midwest were of the 15ADON type. A smaller proportion of isolates from Louisiana belonged to the previously described Gulf Coast population that was mostly of the 3ADON type. The NIV type was also identified in collections from Arkansas (12%), North Carolina (40%), and Missouri (2%), with the collections from Arkansas and North Carolina being small and unrepresentative. F. asiaticum was detected from the two southern Louisiana parishes Acadia and Alexandria. All identified 41 F. asiaticum isolates were of the NIV type. Greenhouse tests indicated that U.S. NIV types accumulated four times less trichothecene toxin than DON types on inoculated wheat. This is the first report of NIV-type populations of F. graminearum s. s. and E asiaticum in the United States. [ABSTRACT FROM AUTHOR]

Head blight of wheat in the United States is caused primarily by the deoxynivalenol (DON)-producing chemotype of Fusarium graminearum. However, the discovery of the nivalenol (NIV) chemotype of F graminearum in Louisiana and Arkansas necessitates having resistance in wheat to both chemotypes. The objectives of this research were to quantify resistance of selected winter wheat lines to initial infection and pathogen spread within spikes, to determine whether wheat lines selected for resistance to the DON chemotype also have resistance to the NIV chemotype, and to improve the methods for quantifying resistance to initial infection. A susceptible check (Coker 9835) and 15 winter wheat lines, which are adapted to the southeastern United States and possess diverse sources of head blight resistance, were evaluated for head blight resistance in a series of greenhouse and growthchamber experiments. Significant levels of resistance to both initial infection and spread within a spike were found among the lines, and lines with resistance to isolates of the DON chemotype had even higher levels of resistance to isolates of the NIV chemotype. Quantifying resistance to initial infection was improved by standardizing the inoculum and environmental conditions. Additional information related to resistance to spread within a spike was obtained by calculating the area under the disease progress curve from 7 to 21 days after inoculation. [ABSTRACT FROM AUTHOR]

Knowledge of the movement of Gibberella zeae (Fusarium graminearum) from a local source of inoculum in infested cereal debris is critical to the management of Fusarium head blight (FHB) of wheat. Previous spatial dissemination and infection studies were unable to completely distinguish the contributions of released inocula from those of background inocula. Clones of G. zeae were released and recaptured in five wheat fields in New York and Virginia in 2007 and 2008. Amplified fragment length polymorphisms were used to track and unambiguously identify the released clones in heterogeneous populations of the fungus recovered from infected wheat spikes collected at 0, 3, 6, and ⩾24 m from small-area sources of infested corn residues. The percent recovery of the released clones decreased significantly at fairly short distances from the inoculum sources. Isolates of G. zeae recovered at 0, 3, 6, and ⩾24 m from the center of source areas shared 65, 19, 13, and 5% of the genotypes of the released clones, respectively. More importantly, the incidence of spike infection attributable to released clones averaged 15, 2, I, and <1% at 0, 3, 6, and ⩾24 m from source areas, respectively. Spike infection attributable to released clones decreased an average of 90% between 3 and 6 m from area sources of inoculum, and the spike infection potential of inocula dispersed at this range did not differ significantly from background sources. Our data suggest that FHB field experiments including a cereal debris variable should incorporate debris-free borders and interplots of at least 3 m and preferably 6 m to avoid significant interplot interference from spores originating from within-field debris. [ABSTRACT FROM AUTHOR]

Window-pane methodology was used to determine the length and starting time of temporal windows where environmental variables were associated with annual fluctuations of Fusarium head blight (FHB) intensity in wheat, initial analysis involved FHB intensity observations for Ohio (44 years), with additional analyses for Indiana (36 years), Kansas (28 years), and North Dakota (23 years). Selected window lengths of 10 to 280 days were evaluated, with starting times from approximate crop maturity back to the approximate time of planting. Associations were quantified with Spearman rank correlation coefficients. Significance for a given variable (for any window starting time in a collection of starting times) was declared using the Simes' multiplicity adjustment; at individual time windows, significant correlations were declared when the individual (unadjusted) P values were <0.l)05. In all states, moisture- or wetness-related variables (e.g.. daily average relative humidity [RH] and total daily precipitation) were found to be positively correlated with FHB intensity for multiple window lengths and starting times; however, the highest correlations were primarily for shorter-length windows (especially 15 and 31) days) at similar starting times during the fired 60 days of the growing season, particularly near the time of anthesis. This period encompasses spore production, dispersal, and fungal colonization of wheat spikes. There was no evidence of significant correlations between FHB and temperature only variables for any time window; however variables that combined aspects of moisture or wetness with temperature (e.g., duration of temperature between 15 and 30°C and RH ≥ 80%) were positively correlated with FHB intensity. Results confirm that the intensity of FHB in a region depends, at least in part, on environmental conditions during relatively short, critical time periods for epidemic development. [ABSTRACT FROM AUTHOR]

The manner in which deoxynivalenol (DON) and nivalenol (NIV) accumulation progresses in wheat grain infected with Fusarium graminearum and the influence of the time of infection on the accumulation of toxins were investigated. Four cultivars were tested in a greenhouse environment, where the plains were spray inoculated at three different stages with a mixture of DON and NIV chemotypes of F. graminearum. The results indicate that high levels of DON and NIV can be produced beyond 20 days after anthesis (DAA), even by early infection. The results of field experiments performed on seven cultivars, where inoculation was conducted using colonized maize kernel inoculum, were consistent with the greenhouse results. In addition, in the greenhouse experiments, late infection, at least as late as 20 DAA, caused grain contamination with these toxins even without clear disease symptoms on the spike. These results indicate the importance of the late stage in grain development in DON and NIV contamination, suggesting that control strategies that cover the late as well as the early stage of grain development should be established to effectively reduce the risk of these toxins' contaminating wheat. [ABSTRACT FROM AUTHOR]

The level of the fungal toxin deoxynivalenol (DON) in milled flour and its partitioning between flour and bran of 15 spring wheat (Triticum aestivum) lines with different levels of Fusarium head blight (FHB; mainly caused by Fusarium graminearum) resistance was investigated in Hokkaido, Japan between 2004 and 2007. The DON levels in flour (DONf) and bran (DONb) showed positive linear relationships with DON levels in whole kernels (DONk) (R² = 0.94, n = 60, P ⩽0.01 and R² = 0.93, n = 60, P ⩽0.01, respectively). Results indicated that the DON partitioning ratio between flour and bran is primarily related to the level of DONk, and the DON level was approximately doubled in DONb and halved in DONf for any level of DONk. Only one pattern of DON partitioning supported the conventional strategy to select FHB-resistant lines. [ABSTRACT FROM AUTHOR]

One plant genotype displays a resistance phenotype at one development stage but a susceptible reaction to the same pathogen at another stage, which is referred to here as resistance inversion. In wheat, Fusarium head blight (FHB)-resistant cv. Sumai3 showed a Fusarium seedling blight (FSB)-susceptible reaction whereas FHB-susceptible cv. Annong8455 exhibited FSB resistance when challenged with a Fusarium asiaticum strain that produces deoxynivalenol (DON). The resistance to FHB and FSB in wheat was closely associated with expression of a plant cytochrome P450 gene in response to FHB pathogens and mycotoxins. Quantitative real-time polymerase chain reaction analyses showed that expression of nine defense-related genes in spikes and seedlings was induced by the fungal infection, in which a massive accumulation of a plant cytochrome P450 gene, CYP709CI, was clearly associated with the resistance reaction in both seedling and spike. The FHB-resistant Sumai3 accumulated 7-fold more P450 transcripts than did the FHB-susceptible Annong8455, while 84-fold more P450 transcripts were accumulated in the FSB-resistant Annong8455 than the FSB-susceptible Sumai3. A Fusarium strain with a disrupted Tri5 gene, which is not able to produce the first enzyme essential for trichothecene mycotoxin biosynthesis, also induced more P450 transcripts in FHB- and FSB-resistant cultivars. The fungal activation of the P450 gene was more profound in the FSB-resistant reaction than the FHB-resistant reaction relative to their susceptible counterparts. DON triggered a differential expression of the P450 gene with comparable patterns in spikes and seedlings in a resistancedependent manner. These results may provide a basis for dissecting mechanisms underlying FHB and FSB resistance reactions in wheat and revealing functions of the cytochrome P450 in plant detoxification and defense. [ABSTRACT FROM AUTHOR]

Seventy-seven studies reporting Fusarium head blight disease index (Y; mean percentage of diseased spikelets per spike) and wheat yield (W; MT/ha) were analyzed to determine the relationship between W and Y, and to assess the degree of variation for the relationship among studies. A linear random-coefficient model---comprising a population-average intercept and slope, a random residual term, and random effects of study on the intercept and slope (best linear unbiased predictors; BLUPs)--was successfully fitted to the data using maximum likelihood. From the predicted random effects, study-specific intercepts and slopes were obtained, and both population-average and subject-specific predictions of yield were determined. The estimated population-average intercept (expected yield when disease symptoms were not present) was 4.10 MT/ha, and the population-average slope was 0.038 MT/ha per unit increase of disease index. Wheat class had a significant effect on the intercept but not on the slope, with soft-red winter wheat having, on average, 0.85 MT/ha higher yield than spring wheat. Based on the estimates of the among-study variances, there was high variation in the effects of study on the intercept, but substantially lower variation in the effects of study on the slope. Thus, although one cannot predict with accuracy the actual wheat yield in a field or plot based on disease index using population-average results, one can predict with accuracy the decline in yield at a given level of disease index using the population-average slope. Through the modeling results, predicted relative yield (as a percentage of yield when disease is not present) can be determined, as well as predicted disease index at which a prespecified level of yield (or yield loss) is expected to occur. The predicted reduction in yield on a percentage scale was greater for spring than for soft-red winter wheat, on average, because of the lower estimated intercept in absolute units for spring wheat. [ABSTRACT FROM AUTHOR]

The relationship between inoculum dose and resulting disease levels and deoxynivalenol (DON) accumulation in the Fusarium head blight (FHB) of wheat pathosystem was' examined under controlled conditions. Greenhouse-grown spring wheat plants were inoculated at flowering with suspensions that varied in Gibberella zeae macroconidia concentration. The spikes were bagged for 72 h to promote infection and plants were then kept under ambient greenhouse conditions and disease allowed to develop. Spikes were rated at 15 days after inoculation for disease incidence and severity, removed from the greenhouse, and dried. DON concentration was determined in grain-only and whole-spike samples for each inoculation treatment. Regression analysis was used to evaluate the mathematical relationship between inoculum dose and the (i) disease metrics or (ii) DON concentration. Both disease incidence and severity were found to increase sharply in relation to inoculum concentration until an asymptote was reached. In both instances, a negative exponential function was found to best explain this relationship. By contrast, DON concentration in both grain-only and whole-spike tissues increased with additional inoculum. These relationships were best explained with linear functions for both sample types, although DON accumulation increased at a greater rate in whole-spike tissue. The functions were evaluated further using data collected from unrelated field studies and, although not particularly consistent, provided reasonably accurate predictions in growing seasons when the environment was only moderately favorable for FHB. [ABSTRACT FROM AUTHOR]

Chromosome 2A of wild emmer wheat (Triticum turgidum var. dicoccoides) genotype Israel A increases Fusarium head blight (FHB) severity when present in durum wheat (T. turgidum var. durum) cv. Langdon (LDN). The goal of this study was to identify regions of Israel A chromosome 2A associated with this difference in resistance. A recombinant inbred chromosome line population (RICL) from a cross between LDN and the LDN-Israel A chromosome 2A substitution line [LDN(DIC-2A)] was employed for analysis. Three greenhouse FHB evaluations were completed on the RICL to obtain phenotypic data on variation for FHB resistance, and a simple sequence repeat (SSR)-based molecular map of chromosome 2A was developed. Quantitative trait locus (QTL) mapping identified a region on the long arm of chromosome 2A that was associated with FHB resistance in each independent FHB evaluation. Depending on the evaluation, the single best SSR marker in this region accounted for between 21 and 26% of the variation for FHB resistance, with the Israel A marker alleles associated with increased FHB susceptibility. The single best markers from each evaluation reside within an interval of approximately 22 cM. This study identifies one or more new QTL on chromosome 2A in tetraploid wheat that can contribute to significant variation in FHB resistance. [ABSTRACT FROM AUTHOR]

Current models for forecasting Fusarium head blight (FHB) and deoxynivalenol (DON) levels in wheat are based on weather near anthesis, and breeding for resistance to FHB pathogens often relies on irrigation before and shortly after anthesis to encourage disease development. The effects of post-anthesis environmental conditions on FHB are poorly understood. We performed a field experiment at Kinston, NC, to explore the effects of increasing duration of post-anthesis moisture on disease incidence, disease severity, Fusarium-damaged kernels (FDK), percent infected kernels, and DON. The experiment had a split-plot design, and one trial was conducted in each of two successive years. Main plots consisted of post-anthesis mist durations of 0, 10, 20, or 30 days. Subplots were of eight cultivars in the first year and seven in the second year, two being susceptible to FHB and the remainder each with varying degrees of apparent type I and type II resistance. Plots were inoculated by spraying Fusarium graminearum macroconidia at mid-anthesis. Averaging across years and cultivars, 10 or 20 days of post-anthesis mist had the same effect (P ≥ 0.198) and were associated with an approximately fourfold increase in mean disease incidence and eightfold increase in disease severity compared with 0 days of mist (P ≤ 0.0002). In both years, mean FDK percentages at 0 and 10 days post-anthesis mist were the same and significantly lower than FDK percentages under 20 or 30 days of post-anthesis mist. Mist duration had a significant effect on percent kernels infected with Fusarium spp. as detected by a selective medium assay of 2007 samples. Averaging across all cultivars, in both years, DON levels increased significantly for 10 days compared with 0 days of mist, and increased again with 20 days of mist (P ≤ 0.04). This is the first investigation to show that extended post-flowering moisture can have a significant enhancing effect on FHB, FDK, DON, and percent infected kernels of wheat. For all disease and toxin assays, cultivar rankings were significantly noncorrelated among mist durations in at least 1 year, suggesting that FHB screening programs might rank genotypes differently under extended post-anthesis moisture than without it. Our findings also imply that accurate forecasts of DON in small grains must take account of post-anthesis weather conditions. [ABSTRACT FROM AUTHOR]

A meta-analysis of the effect of tebuconazole (e.g., Folicur 3.6F) on Fusarium head blight and deoxynivalenol (DON) content of wheat grain was performed using data collected from uniform fungicide trials (UFTs) conducted at multiple locations across U.S. wheat-growing regions. Response ratios (mean disease and DON levels from tebuconazole-treated plots, divided by mean disease and DON levels from untreated check plots) were calculated for each of 139 studies for tebuconazole effect on Fusarium head blight index (IND; field or plot-level disease severity, i.e., mean proportion of diseased spikelets per spike) and 101 studies for tebuconazole effect on DON contamination of harvested grain. A random-effects meta-analysis was performed on the log-transformed ratios, and the estimated mean log ratios were transformed to estimate the mean (expected) percent control for IND (CIND) and DON (CDON). A mixed-effects meta-analysis was then done to determine the effects of wheat type (spring versus winter wheat) and disease and DON levels in the controls on the log ratios. Tebuconazole was more effective at limiting IND than DON, with CIND) and CDON values of 40.3 and 21.6%, respectively. The efficacy of tebuconazole as determined by the impact on both IND and DON was greater in spring wheat than in winter wheat (P < 0.01), with a 13.2% higher CIND) and a 12.4% higher CDON in spring wheat than in winter wheat. In general, CIND and CDON were both at their lowest values (and not significantly different from 0) when mean IND and DON in the controls, respectively, were low (≤2% for IND and <1 ppm for DON). CIND was 25% higher in studies with mean IND between 2 and 15% than in studies with mean IND ≤ 2%, whereas CDON was 28.8% higher in studies with mean DON between 1 and 10 ppm than in studies with mean DON < 1 ppm. The between-study variance was significantly greater than 0 (P < 0.01), indicating considerable (unexplained) variability in percent control. [ABSTRACT FROM AUTHOR]

A total of 126 field studies reporting deoxynivalenol (DON; ppm) content of harvested wheat grain and Fusarium head blight index (IND; field or plot-level disease severity) were analyzed to determine the overall mean regression slope and intercept for the relationship between DON and IND, and the influence of study-specific variables on the slope and intercept. A separate linear regression analysis was performed to determine the slope and intercept for each study followed by a meta-analysis of the regression coefficients from all studies. Between-study variances were significantly (P < 0.05) greater than 0, indicating substantial variation in the relationship between the variables. Regression slopes and intercepts were between -0.27 and 1.48 ppm per unit IND and -10.55 to 32.75 ppm, respectively. The overall mean regression slope and intercept, 0.22 ppm per unit IND and 2.94 ppm, respectively, were significantly different from zero (P < 0.001), and the width of the 95% confidence interval was 0,07 ppm per unit IND for slope and 1.44 ppm for intercept. Both slope and intercept were significantly affected by wheat type (P < 0.05); the overall mean intercept was significantly higher in studies conducted using winter wheat cultivars than in studies conducted using spring wheat cultivars, whereas the overall mean slope was significantly higher in studies conducted using spring wheat cultivars than in winter wheat cultivars. Study location had a significant effect on the intercept (P < 0.05), with studies from U.S. winter wheat-growing region having the highest overall mean intercept followed by studies from Canadian wheat-growing regions and U.S. spring wheat-growing regions. The study-wide magnitude of DON and IND had significant effects on one or both of the regression coefficients, resulting in considerable reduction in between-study variances. This indicates that, at least indirectly, environment affected the relationship between DON and IND. [ABSTRACT FROM AUTHOR]

Chinese Spring Sumai 3 chromosome 7A disomic substitution line (CS-SM3-7ADS) is highly resistant to Fusarium head blight (FHB), and an F7 population of recombinant inbred lines derived from the cross CS-SM3-7ADS x Annong 8455 was evaluated for resistance to FHB to investigate main effects, epistasis, and environmental interactions of quantitative trait loci (QTLs) for FHB resistance. A molecular linkage map consists of 501 simple sequence repeat and amplified fragment length polymorphism markers. A total of 10 QTLs were identified with significant main effects on the FHB resistance using MapQTL and QTLMapper software. Among them, CS-SM3-7ADS carries FHB-resistance alleles at five QTLs on chromosomes 2D, 3B, 4D, and 6A. One QTL on 3BS had the largest effect and explained 30.2% of the phenotypic variance. Susceptible QTLs were detected on chromosomes 1A, 1D, 4A, and 4B. A QTL for enhanced FHB resistance was not detected on chromosome 7A of CS-SM3-7ADS; therefore, the increased FHB resistance in CS-SM3-7ADS was not due to any major FHB-resistance QTL on 7A of Sumai 3, but more likely was due to removal of susceptible alleles of QTLs on 7A of Chinese Spring. QTLMapper detected nine pairs of additive-additive interactions at 17 loci that explained 26% phenotypic variance. QTL-environment interactions explained 49% of phenotypic variation, indicating that the environments significantly affected the expression of the QTLs, especially these epistasis QTLs. Adding FHB-enhancing QTLs or removal of susceptible QTLs both may significantly enhance the degree of wheat resistance to FHB in a wheat cultivar. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB), caused by Fusarium graminearum, is an important disease of wheat (Triticum aestivum). FHB reduces yield and quality, and the pathogen produces several toxins in the grain, the most important being deoxynivalenol (DON). In North America, the foliar fungicide tebuconazole is used to reduce FHB symptoms and DON accumulation. Because of the narrow window required for its application, uniform flowering of wheat is important. The objective of this study was to investigate the influence of variety, seeding rate, and seed treatment fungicides on the flowering period of winter wheat and their effect on FHB symptoms and DON accumulation. The seed of two winter wheat varieties (Pioneer 25W60 and Pioneer 25R57) was treated with Dividend XL (difeconazole+metalaxyl), Vitaflo 280 (thiram+ carbathiin). Raxil (tebuconazole), and Baytan 30 (triadimenol) and planted at 320, 480, and 640 seeds per m² for each treatment at Ridgetown, ON, Canada in 2000 and 2001. The plots were sprayed with tebuconazole at 50% anthesis and inoculated with F graminearum 3 days later. Increased seeding rate increased the number of emerged plants, tillers, spikes per m², and yield. All seed treatments, compared to nontreated controls, increased plant emergence and number of spikes per m², and all except tebuconazole increased tillering and yield. Increased seeding rate decreased the length of flowering period. As flowering period increased, FHB index and DON level decreased, suggesting that greater infection was linked to more uniform flowering. [ABSTRACT FROM AUTHOR]

To determine the relationship between incidence (1; proportion of diseased spikes) and severity (S; mean proportion of diseased spikelets per spike) for Fusarium head blight of wheat and to determine if severity could be predicted reliably from incidence data, disease assessments were made visually at multiple sample sites in artificially and naturally inoculated research and production fields between 1999 and 2002. Ten distinct data sets were collected. Mean disease intensity ranged from 0.023 to 0.975 for incidence and from 0.0003 to 0.808 for severity. A model based on complementary log-log transformation of incidence and severity performed well for all data sets, based on calculated coefficients of determination and random residual plots. The I-S relationship was consistent among years and locations, with similar slopes for all data sets. For 7 of the 10 data sets and for the pooled data from all locations and years, the estimated slope from the fit of the model ranged from 1.03 to 1.26. Time of disease assessment affected the relationship between incidence and severity; however, the estimated slopes from each assessment time were also close to I. Based on the width of the 95% prediction interval, severity was estimated more precisely at lower incidence values than at higher values. The number of sampling units and the index of dispersion of disease incidence had only minor effects on the precision with which S was predicted from 1. The estimation of mean S from 1 would substantially reduce the time required to assess Fusarium head blight in field surveys and treatment comparisons, and the observed relationship between I and S could be used to identify genotypes with some types of disease resistance. [ABSTRACT FROM AUTHOR]

Fusarium head blight has been more severe when infection occurs during anthesis, indicating that floral organs may be important infection courts. Choline acetate and glycinebetaine have been extracted from wheat and reported to be growth stimulants of Fusarium graminearum. They are hypothesized to enhance infection and tissue colonization. Growth of E graminearum was examined on media amended with extracts from floral parts of nine wheat genotypes with various Fusarium head blight resistance levels. Results indicated no significant effect of anther, palea, or lemma extracts on radial growth when compared with unamended controls. Effects on spore germination and hyphal growth of F. graminearum by choline, betaine, and an equimolar mixture at concentrations ranging from 0.01 to 1,000 µM also were examined. Spore germination was not significantly (P ≤ 0.05) affected by choline, betaine, or a combination of the compounds compared with unamended controls. Radial hyphal growth also was not consistently affected (P ≤ 0.05) by choline or betaine when compared with controls. Equimolar mixtures of the two compounds showed significant slight reduction in growth rate at higher concentrations when compared with controls. The reduction in growth rate was due to higher concentrations of betaine. Results of this study indicate that endogenous compounds in floral parts may not be associated with wheat resistance to F. graminearum. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB, scab), caused by Fusarium graminearum or F. culmorum, results in yield and quality reductions and accumulation of mycotoxins. Two inoculation methods are commonly used. Spraying a spore suspension on the head (spray inoculation) will detect resistance to initial infection (type I) and to disease spread within the spike (type II). Injecting a spore suspension into individual florets (point inoculation) will detect type II resistance only. To analyze the association of spray and point inoculation, 20 elite winter wheat cultivars from Romania, Germany, and Switzerland were inoculated in factorial field experiments in seven environments (location x year combinations) in Germany and Romania. Response to FHB was assessed by the percentage of visually infected spikelets and head weight relative to the noninoculated control. Point and spray inoculations resulted in a mean disease severity varying from 52 to 63%. Significant (P = 0.01) genotypic variation was found within and across the environments. Genotype-environment interaction was important also. Estimates of entry-mean heritability were higher for spray than for point inoculation as assessed by percent infected spikelets (0.81 versus 0.77) and relative head weight (0.77 versus 0.52). Significant (P = 0.01) interaction was found between inoculation methods. Consequently, coefficients of phenotypic correlation between both methods were low to medium for percent infected spikelets (0.40, P > 0.1) and relative head weight (0.52, P = 0.05). We conclude that the application of both inoculation methods should provide additional information for selection and scientific studies. Spray inoculation, however, is less laborious for large-scale routine screening of breeding materials. [ABSTRACT FROM AUTHOR]

Attempts to control Fusarium head blight (FHB) with fungicides have been highly variable. Variability is caused by cultivar resistance, fungicide efficacy, fungicide coverage, timing, and pathogen aggressiveness. In this research, fungicides were tested on winter wheat cultivars with different levels of resistance to FHB using different isolates of Fusarium graminearum and F. culmorum to evaluate the role of host resistance and isolate aggressiveness on severity of FHB. Fungicides were applied to groups of wheat heads to provide full coverage. Incidence and severity of FHB was measured by the severity of head symptoms, percentage of Fusarium-damaged kernels (FDK), yield loss, and deoxynivalenol (DON) contamination. Development of FHB was affected by fungicides, cultivars, fungal isolates, and most of the two-way interactions of these variables. Among the fungicides tested, those containing tebuconazole tended to be more effective in reducing FHB. Reduction of disease in susceptible cultivars may not be adequate to produce marketable yields under conditions of high disease pressure. In most cases, if a fungicide reduced FHB visual symptoms, similar decreases were detected in yield loss, DON concentration, and FDK reaction. In 1998, an increase in DON contamination compared with the Fusarium check was observed with azoxystrobin and carbendazim on the more susceptible cultivar. This increase in DON with some fungicide requires additional research. Research to develop more resistant cultivars, better spraying technology, and more effective fungicides is also needed. [ABSTRACT FROM AUTHOR]

The article presents a study on the plant disease Fusarium boothii that cause head blight in wheat in the U.S.

Effective control of Fusarium-mycotoxin accumulation in grain affected by Fusarium head blight (FHB) (caused by Fusarium graminearum) begins with selecting moderately resistant wheat cultivars; however, little is known about how this resistance affects mycotoxin levels in the stem. A study was conducted from 2011 to 2014 in a mist-irrigated FHB nursery in Urbana, IL to determine whether the FHB resistance class of a cultivar (very susceptible, susceptible, moderately susceptible, and moderately resistant) affects the concentration of Fusarium mycotoxins in the stem. FHB incidence, FHB severity, and Fusarium-damaged kernel ratings were collected and used to calculate FHB index; incidence, severity, and kernel damage (ISK) index; and deoxynivalenol (DON), incidence, severity, and kernel damage (DISK) index. Grain was assayed for levels of DON, and the bottom 25 cm of plant stems was collected from each plot and assayed for DON, 3-acetyl-deoxynivalenol (3ADON), and 15-acetyl-deoxynivalenol (15ADON). Significant differences in DON concentration in the grain were detected among cultivars (P = 0.0001) and for the concentration of all DON (P = 0.003), 3ADON (P = 0.03), and 15ADON (P < 0.0001) in the stem. Significant differences among resistance classes were observed for FHB index value (P < 0.0001), ISK index (P = 0.006), and DISK index (P = 0.004). In all years of this study, the concentration of DON in the grain and the concentrations of all mycotoxins in the stem were consistently lower in the moderately resistant cultivars. All three indices were poor indicators of mycotoxin concentrations in the stem. Overall, the selection of a moderately resistant cultivar provides effective control of DON accumulation in the grain and mycotoxin accumulation in the stem. [ABSTRACT FROM AUTHOR]

Mist chamber experiments were conducted to quantify and model the effects of post-anthesis moisture on Fusarium head blight (FHB) index (IND) and deoxynivalenol (DON). Four mist treatments, one daily and three intermittent, were applied during an 8-day window immediately after anthesis, plus an untreated check. All intermittent mist treatments received moisture on 4 of the 8 days, but the distribution of the supplemental moisture during the treatment window varied among the treatments. Separate sets of spikes in each treatment were either spray or point inoculated with a spore suspension of Fusarium graminearum. Based on results from linear mixed-model analyses, mist treatment had a significant effect on arcsine-square root-transformed IND (arcIND) and log-transformed DON (logDON) in spray-inoculated spikes but only a marginal effect on DON in point-inoculated spikes. The daily mist treatments (Mist1) consistently had the highest mean IND and DON but several of the 4-day intermittent mist treatments were not significantly different, particularly for point inoculations. Only Mist1 and one of the intermittent mist treatments (Mist2; 2 days of mist at the beginning and end of the treatment window) had significantly higher infection efficiency (estimated diseased spikelets per spore) than the check; however, none of the treatments increased the rate of disease spread within the spike (based on visual symptoms) relative to the check. For all treatments, there was a significant, positive linear relationship between IND and logDON, with estimated mean regression slopes (rates of logDON increase per unit increase in IND) of 0.04 and 0.02 logDON %-' IND for the point- and spray-inoculated experiments, respectively. Mist treatment did not have a significant effect on the slope but had a significant effect on the intercept. The height of the regression line (logDON after adjusting for IND) was consistently higher for Mist2 than for Mist1 for both point- and spray-inoculated spikes. Estimated mean back-transformed DON at a fixed level of IND was 4.9 and 2.9 ppm higher for Mist2 than Mist1 in the spray- and point-inoculation experiments, respectively. Generalized linear mixed models were used to estimate the risk of IND and DON exceeding critical thresholds, showing similar results among treatments in terms of estimated probabilities. The estimated probabilities of IND > 10% at 20 days after inoculation and DON ≥ 2, 5, and 10 ppm were not significantly different between Mist1 and Mist2. These results suggest that post-anthesis moisture patterns may play a role in DON exceeding critical thresholds even when FHB level are relatively low. [ABSTRACT FROM AUTHOR]

Our objective was to identify weather-based variables in pre- and post-anthesis time windows for predicting major Fusarium head blight (FHB) epidemics (defined as FHB severity ≥ 10%) in the United States. A binary indicator of major epidemics for 527 unique observations (31% of which were major epidemics) was linked to 380 predictor variables summarizing temperature, relative humidity, and rainfall in 5-, 7-, 10-, 14-, or 15-day-long windows either pre- or post-anthesis. Logistic regression models were built with a training data set (70% of the 527 observations) using the leaps-and-bounds algorithm, coupled with bootstrap variable and model selection methods. Misclassification rates were estimated on the training and remaining (test) data. The predictive performance of models with indicator variables for cultivar resistance, wheat type (spring or winter), and coin residue presence was improved by adding up to four weather-based predictors. Because weather variables were intercorrelated, no single model or subset of predictor variables was best based on accuracy, model fit, and complexity. Weather-based predictors in the 15 final empirical models selected were all derivatives of relative humidity or temperature, except for one rainfall-based predictor, suggesting that relative humidity was better at characterizing moisture effects on FHB than other variables. The average test misclassification rate of the final models was 19% lower than that of models currently used in a national FHB prediction system. [ABSTRACT FROM AUTHOR]

We used a real time polymerase chain reaction-based assay and visual disease assessment to evaluate the efficacies of Js399-19, tebuconazole, a mixture of tebuconazole and thiram, azoxystrobin, carbendazim, and thiram on the development of Fusarium head blight (FHB) and deoxynivalenol (DON) contamination and on the yield of winter wheat (cv. Nannong no. 9918) after artificial inoculation under field conditions with Fusarium graminearum. The incidence of infected spikelets (IIS), amount of F. graminearum DNA (Tri5 DNA), total DON (containing DON, 3-acetyl-deoxynivalenol, and 15-acetyl-deoxynivalenol) concentration, and 1,000-grain weight (TGW) were quantified in 2006 and 2007. A strong positive correlation was found between IIS or Log10Tri5 DNA and total DON concentration in the harvested grain. The Js399-19, tebuconazole, and the mixture of tebuconazole and thiram significantly reduced IIS of FHB, amount of Tri5 DNA, and total DON within the grain and increased TGW. Although azoxystrobin, carbendazim, and thiram can increase TGW, they had no effect on the occurrence of F. graminearum compared with those of the untreated controls. Surprisingly, azoxystrobin and carbendazim significantly increased the total DON content in the harvested grain because they might have stimulated the amount of total DON production per Tri5 DNA. The fungicides Js399-19, tebuconazole, and the mixture of tebuconazole and thiram were the most effective in controlling FHB and reducing DON contamination of the wheat. [ABSTRACT FROM AUTHOR]

Gibberella zeae, causal agent of Fusarium head blight (FHB) of wheat and barley and Gibberella ear rot (GER) of corn, may be transported over long distances in the atmosphere. Epidemics of FHB and GER may be initiated by regional atmospheric sources of inoculum of G. zeae; how- ever, little is known about the origin of inoculum for these epidemics. We tested the hypothesis that atmospheric populations of G. zeae are genetically diverse by determining the genetic structure of New York atmospheric populations (NYAPs) of G. zeae, and comparing them with populations of G. zeae collected from seven different states in the northern United States. Viable, airborne spores of G. zeae were collected in rotational (lacking any apparent within-field inoculum sources of G. zeae) wheat and corn fields in Aurora, NY in May through August over 3 years (2002 to 2004). We evaluated 23 amplified fragment length polymorphism (AFLP) loci in 780 isolates of G. zeae. Normalized genotypic diversity was high (ranging from 0.91 to 1.0) in NYAPs of G. zeae, and nearly all of the isolates in each of the populations represented unique AFLP haplotypes. Pairwise calculations of Nei's unbiased genetic identity were uniformly high (>0.99) for all of the possible NYAP comparisons. Although the NYAPs were genotypically diverse, they were genetically similar and potentially part of a large, interbreeding population of G. zeac in North America. Estimates of the fixation index (GST) and the effective migration rate (Nm) for the NYAPs indicated significant genetic exchange among populations. Relatively low levels of linkage disequilibrium in the NYAPs suggest that outcrossing is common and that the populations are not a result of a recent bottleneck or invasion. When NYAPs were compared with those collected across the United States, the observed genetic identities between the populations ranged from 0.92 to 0.99. However, there was a significant negative correlation (R = -0.59, P < 0.001) between genetic identity and geographic distance, suggesting that some genetic isolation may occur on a continental scale. The contribution of long-distance transport of G. zeae to regional epidemics of FHB and GER remains unclear, but the diverse atmospheric populations of G. zeae suggest that inoculum may originate from multiple locations over large geographic distances. Practically, the long-distance transport of G. zeae suggests that management of inoculum sources on a local scale, unless performed over extensive production areas, will not be completely effective for the management of FHB and GER. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is a fungal disease that affects small cereal grains, such as wheat and barley, and is becoming more prevalent throughout much of the world's temperate climates. The disease poses a health risk to humans and livestock because of the associated production of the mycotoxin deoxynivalenol (DON or vomitoxin) by the causal organism, Fusarium graminearum. A study was undertaken to examine the efficiency of high-speed, optical sorting of intact wheat (Triticum aestivum) kernels for reduction of DON concentration. Soft red winter (n = 32) and soft white (n = 3) wheat samples, known to have elevated levels of FHB, were obtained from commercial mills throughout the eastern United States. An additional seven samples of wheat from the discard piles of in-mill cleaners were also studied. Fusarium-damaged wheat, cleaned of nonkernels and foreign material (∼4.5 kg/sample, DON range = 0.6 to 20 mg/kg), was fed into a commercial high-speed bichromatic sorter operating at a throughput of 0.33 kg/(channel-min) and a kernel rejection rate of 10%. A wavelength filter pair combination of 675 and 1,480 nm was selected for sorting, based on prior research. Visual measurements of the proportion of Fusarium-damaged kernels were collected on incoming and sorted seed (separate analyses of accepted and rejected portions), as were measurements of DON concentration. Results indicated that the fraction of DON contaminant level in the sorted wheat to that in the unsorted wheat ranged from 18 to 112%, with an average of 51%. Nine of the 35 regular samples and all seven of the discard pile samples underwent a second sort, with five from this second set undergoing a third sort. Multiple sorting was effective in producing wheat whose DON concentration was between 16 and 69% of its original, unsorted value. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) is currently the primary disease of concern in barley in Canada and sources of FHB resistance need to be identified. A diverse collection of 77 two-rowed and 81 six-rowed barley lines was screened for resistance to FHB in inoculated, irrigated nurseries from 1995 to 1998. Barley spikes were spray inoculated with conidia of Fusarium graminearum and visual symptoms of FHB were scored to determine an FHB index. Deoxynivalenol (DON) content was determined from harvested seed samples during 1997 and 1998. Although there was variation in the average FHB index and DON content among the different years of testing, the rankings of the lines generally were correlated among the years of testing and the two measures of FHB. Based on the FHB index from 1995 and 1996, a subset of 18 lines with low FHB and 12 lines with high FHB were compared with 20 FHB resistance sources and 7 Canadian lines or cultivars during 1997 and 1998 in both inoculated and noninoculated nurseries. Lines Nepolegajuscij, Krasnojarskij, Nordic, Murakaki-mochi, Golozernyj 1, Maris Mink, Symko, Ussurijskij 8, Suvenir, and Canadian cultivars AC Sterling and Morrison were similar to the best resistance sources (Zhedarl, Seijo II, and Chevron) and had consistently low DON content. [ABSTRACT FROM AUTHOR]

Fusarium graminearum is a toxigenic fungal pathogen that causes Fusarium head blight (FHB) and crown rot on cereal crops worldwide. This fungus also causes damping-off and crown and root rots at the early stage of crop development in soybean cultivated in North and South America. Several F. graminearum genes were investigated for their contribution to FHB in cereals but no inherent study is reported for the dicotyledonous soybean host. In this study we determined the disease severity on soybean seedlings of five single gene disrupted mutants of F. graminearum, previously characterized in wheat spike infection. Three of these mutants are impaired on a specific function as the production of deoxynivalenol (DON, Δtri5), lipase (ΔFgl1), and xylanase (Δxyl03624), while the remaining two are MAP kinase mutants (ΔFgOS-2, Δgpmk1), which are altered in signaling pathways. The mutants that were reduced in virulence (Δtri5, ΔFgl1, and ΔFgOS-2) or are avirulent (Δgpmk1) on wheat were correspondently less virulent or avirulent in soybean seedlings, as shown by the extension of lesions and seedling lengths. The Δxyl03624 mutant was as virulent as the wild type mirroring the behavior observed in wheat. However, a different ranking of symptom severity occurred in the two hosts: the ΔFgOS-2 mutant, that infects wheat spikelets similarly to Δtri5 and ΔFgl1 mutants, provided much reduced symptoms in soybean. Differently from the other mutants, we observed that the ΔFgOS-2 mutant was several fold more sensitive to the glyceollin phytoalexin suggesting that its reduced virulence may be due to its hypersensitivity to this phytoalexin. In conclusion, lipase and DON seem important for full disease symptom development in soybean seedlings, OS-2 and Gpmk1 MAP kinases are essential for virulence, and OS-2 is involved in conferring resistance to the soybean phytoalexin. [ABSTRACT FROM AUTHOR]

Certain Fusarium species cause Fusarium head blight (FHB) in wheat and other small grains. Differences in characteristics of the pathogen species/isolates used in breeding programs may affect reaction of host genotypes, leading to erroneous results. To clarify differences among Fusarium isolates from different geographical zones, the phylogenetic, chemotypic, and pathogenic abilities of 58 isolates collected from three wheat-producing countries (Canada, Mexico, and Iran) were investi-gated. Phylogenetic relationships among the isolates were character-ized using the TrilOl gene sequence. All Canadian and Iranian isolates clustered in one group and were identified as F. graminearum lineage 7 (=F. graminearum sensu stricto) within the F. graminearum (Fg) clade. The isolates from Mexico were identified as either F graminearum lineage 3 (=Fusarium boothii) within the Fg clade or Fusarium crookwellense. A polymerase chain reaction assay based on the Tri12 gene identified three trichothecene chemotypes of 15-ADON, 3-ADON, and NIV, with 15-ADON being the most common. All F. boothii isolates from Mexico were of the 15-ADON chemotype, while all F. crookwellense isolates were determined to be NIV producers. While we did not find the NIV chemotype among the Canadian iso-lates, 25.6% of the Iranian isolates were determined to be NIV pro-ducers. High level of variation in aggressiveness was also observed among and within the species tested: F. graminearum sensu stricto isolates were the most aggressive, followed by those of F. boothii, and lastly by F. crookwellense. The differences observed among the isolates may explain why wheat lines/cultivars demonstrate different reactions to FHB in different geographical zones. [ABSTRACT FROM AUTHOR]

Fungicide application to control Fusarium head blight (FHB) and accompanying mycotoxin contamination in wheat is generally performed at anthesis because wheat is most susceptible to FHB around this stage. In this study, we evaluated the effect of the timing of fungicide application on FHB and mycotoxin (deoxynivalenol and nivalenol) accumulation in wheat based on our previous finding that the late period of grain development (beyond 20 days after anthesis [DAA]) is important to determine the final toxin contamination level in wheat. Thiophanate-methyl fungicide was tested under artificial inoculation conditions in which moisture and inoculum spores were provided throughout the testing period. Eight treatments differing in application timing (anthesis, 10, 20, and 30 DAA) and in the number of applications (0 to 2) were tested for 2 years. The results indicated that fungicide application timing differentially affects FHB (disease) and mycotoxin concentration. Fungicide application at 20 DAA reduced mycotoxin concentration in matured grain without reducing FHB severity, whereas application at anthesis was crucial for reducing FHB. These results and our previous findings suggest that around 20 DAA (late milk stage) is a potentially critical timing for mycotoxin control in wheat. [ABSTRACT FROM AUTHOR]

Fusarium head blight (FHB) of wheat and other cereals, caused mainly by Fusarium graminearum, is one of the most economically important diseases worldwide, especially in the United States and China. The benzimidazole fungicides, particularly carbendazim (MBC), have been consistently used during the period of wheat heading and flowering in areas with warm and moist weather to control FHB in China for over 30 years. The effectiveness of MBC, however, has been threatened by the emergence of resistant pathogen populations in the field. JS399-19 (experimental number; a.i. 2-cyano-3-amino-3-phenylancryic acetate) is a novel cyanoacrylate fungicide discovered and patented by the Jiangsu Branch of National Pesticide Research&Development South Center of China. To evaluate the potential risk of resistance development in MBC-resistant F. graminearum isolates to this new fungicide JS399-19, five isolates each of MBC-resistant or -sensitive, which were classified into three different sensitivity phenotypes, such as sensitive (S), moderately resistant (MR), and highly resistant (HR) to MBC, were selected to induce JS399-19-resistant mutants by selecting resistance on potato sucrose agar (PSA) plates amended with JS399-19 at 10 μg/ml. In this way, a total of 24 JS399-19-resistant mutants were obtained from all tested MBC-resistant or -sensitive isolates. All 50 single-spore progenies of each of the resistant mutants could grow normally on PSA plates amended with JS399-19 at 10 μg/ml, indicating stability of resistance to this fungicide. Also, all of the resistant mutants maintained their resistance to JS399-19 and/or MBC through eight transfers on PSA plates for 40 days and when stored on PSA slants at 4°C for 60 days. The mycelial growth and conidial production capacity were decreased in 52.4% of the resistant mutants, indicating that a fitness cost was associated with JS399-19-resistant phenotypes of F. graminearum isolates. However, most of the mutants resistant to both MBC and JS399-19 exhibited high sexual reproduction capacity and pathogenicity as their parental isolates. Nevertheless, the majority of these mutants possessed fitness levels comparable to their parents. The results on the efficacy of the two fungicides for controlling FHB incited by the fungicide-resistant mutants were generally consistent with those of the in vitro sensitivity tests. JS399-19 was effective in controlling FHB caused by MBC-resistant isolates under field conditions, while it was not effective in controlling FHB caused by isolates resistant to JS399-19 or those that were resistant to both MBC and JS399-19. Moreover, the efficacy of the mixture of MBC and JS399-19 was also significantly lower in controlling FHB caused by the isolates resistant to both MBC and JS399-19 than the efficacy against the disease caused by the sensitive isolates, the MBC-resistant isolates, or the JS399-19-resistant isolates. The results suggest that JS399-19 possessed a high risk in development of resistance in MBC-resistant and -sensitive F. graminearum isolates, and this double resistance to both of these fungicides could presumable emerge and create a major problem since both these fungicides are extensively used in China. Therefore, careful use of JS399-19 should be followed to delay resistance development in natural populations of F. graminearum, avoid unexpected control failures, and sustain the usefulness of MBC and the new product JS399-19. [ABSTRACT FROM AUTHOR]

Over 4 years, the environmental conditions and the causal agents of Fusarium head blight (FHB) disease of wheat were determined in field sites in four European countries: Hungary, Ireland, Italy, and the United Kingdom. Polymerase chain reaction-based methods were used to detect each species causing FHB and quantify its DNA (as a measurement of fungal abundance) in the samples. Canonical correspondence analysis (CCA) was used to determine the relationship of the incidence and abundance of each species with weather variables. CCA indicated that little variability in the species prevalence data was explained by the weather variables. In contrast, a greater proportion of variability in abundance data was accounted for by the weather variables. Most samples contained two or more species and statistical analysis suggested that these species tended to coexist at field sites. CCA also indicated that there were differences in the relationships of the prevalence and abundance of the six FHB species with environmental variables. Fusarium poae was associated with relatively drier and warmer conditions, whereas F. graminearum was associated with warmer/humid conditions. F. avenaceum and F. culmorum were both associated with niches of cooler/wet/humid conditions. Two Microdochium species were associated with regions of relatively cool/moderate temperatures and frequent rainfalls of short duration. The results also suggested that environmental conditions differentially affect the infection and colonization processes, and the comparative abundance of the six species. [ABSTRACT FROM AUTHOR]

Genetic control of resistance to Fusarium head blight (FHB) is quantitative, making phenotypic selection difficult. Genetic markers to resistance are helpful to select favorable genotypes. This study was conducted to determine if Fhb1 and Fhb5 present in the Sumai 3 source of FHB resistance occur in Sumai 3-derived North American spring wheat cultivars and to understand the appropriateness of using markers to select for the favorable alleles at these loci in breeding. Sumai 3-derived parents Alsen, ND3085, ND744, Carberry, and Glenn were used in crosses to generate 14 doubled haploid breeding populations. The parents and progeny were genotyped with five Fhb1 and three Fhb5 microsatellite markers. Progeny were selected based on performance relative to parents and other control cultivars in FHB nurseries near Portage la Prairie and Carman, MB. χ² and t test analyses were performed on marker and FHB data. The χ² test frequently determined the proportion of lines carrying molecular variants associated with FHB resistance increased following nursery selection for FHB. Similarly, the t test regularly demonstrated that selection for FHB resistance lowered the mean level of disease associated with resistant marker haplotypes. The study affirmed FHB resistance sources Alsen, Carberry, ND3085, and ND744 have Fhb1 and Fhb5 loci like Sumai 3, but no evidence was found that Glenn carries Fhb1 and Fhb5 resistance alleles. The results justified use of Fhb1 and Fhb5 markers for marker assisted selection in populations derived from Alsen, Carberry, ND3085, and ND744, but not Glenn. Combined or individual application of Xgwm493 and Xgwm533 in selection of genotypes carrying Fhb1, and Xgwm150, Xgwm304, and Xgwm595 for Fhb5 will enhance FHB resistance in wheat. [ABSTRACT FROM AUTHOR]

Breeding for resistance is a key task to control Fusarium head blight (FHB), a devastating disease of small cereals leading to economic losses and grain contamination with mycotoxins harmful for humans and animals. In the present work, FHB resistance of the six-rowed spring barley 'Chevron' to FHB in Germany was compared with those of adapted German spring barley cultivars. Both under natural infection conditions and after spray inoculation with conidia of Fusarium culmorum, F. sporotrichioides, and F. avenaceum under field conditions, Chevron showed a high level of quantitative resistance to the infection and contamination of grain with diverse mycotoxins. This indicates that Chevron is not only a little susceptible to deoxynivalenol-producing Fusarium spp. but also to Fusarium spp. producing type A trichothecenes and enniatins. Monitoring the initial infection course of F. culmorum on barley lemma tisst, e by confocal laser-scanning microscopy provided evidence that FHB resistance of Chevron is partially mediated by a preformed penetration resistance, because direct penetration of floral tissue by F. culmorum was observed rarely on Chevron but was common on susceptible genotypes. Alternatively, F. culmorum penetrated Chevron lemma tissue via stomata, which was unusual for susceptible genotypes. We generated double-haploid barley populations segregating for the major FHB resistance quantitative trait loci (QTL) Qrgz-2H-8 of Chevron. Subsequently, we characterized these populations by spray inoculation with conidia of F. culmorum and F. sporotrichioides. This suggested that Qrgz-2H-8 was functional in the genetic background of European elite barley cultivars. However, the degree of achieved resistance was very low when compared with quantitative resistance of the QTL donor Chevron, and the introgression of Qrgz-2H-8 was not sufficient to mediate the cellular resistance phenotype of Chevron in the European backgrounds. [ABSTRACT FROM AUTHOR]