Fusarium Head Blight Epidemics Research Articles

Systematics, Phylogeny and Trichothecene Mycotoxin Potential of Fusarium Head Blight Cereal Pathogens

Summary Economically devastating outbreaks and epidemics of Fusarium head blight (FHB) or scab of wheat and barley have occurred worldwide over the past two decades. Although the primary etiological agent of FHB was thought to comprise a single panmictic species, Fusarium graminearum, a series of studies we conducted over the past decade, employing genealogical concordance/discordance phylogenetic species recognition (GCPSR) 1) , revealed that this morphospecies comprises at least 16 phylogenetically distinct species (referred to hereafter as the F. graminearum species complex ＝FGSC). Results of a multilocus molecular phylogeny, based on maximum parsimony and maximum likelihood analyses of 12 combined genes comprising 16.3 kb of aligned DNA sequence data, suggest that the different species groups within the FGSC radiated in Asia, North America, South America, Australia and/or Africa. The significant biogeographic structure of these lineages, together with evidence of disjunct species in Asia and North America, are consistent with widespread allopatric speciation within the FGSC. In contrast to the results obtained using GCPSR, morphological species recognition using conidial characters and colony morphology was only able to distinguish 6 species and 3 species groups among the 16 species within the FGSC, highlighting the need for sensitive molecular diagnostic tools to facilitate species identifi cation. A validated multilocus genotyping assay was developed to address the need for species determination and trichothecene toxin chemotype prediction, and this assay has been extraordinarily useful in the discovery of novel FGSC species represented in our global FHB surveys. Ongoing molecular and phenotypic analyses are being conducted to elucidate the full spectrum of FHB pathogen diversity, their trichothecene toxin potential and biogeographic distribution. Increased understanding of the distribution and agricultural signifi cance of variation within the FGSC is needed for the development of novel disease and mycotoxin control strategies, including improvements in agricultural biosecurity designed to limit the introduction and spread of non-indigenous FHB pathogens.

Genetic and Malt Quality Diversity of East Asian Two-Rowed Barley Accessions in Relationship to North American Malting Barley

Because of epidemics of Fusarium head blight (FHB; caused by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schwein.) Petch]) in the northern Great Plains of the United States and Canada in the past two decades, malting barley breeders have been forced to use nonadapted barley (Hordeum vulgare L.) accessions as sources of FHB resistance. Many of the resistant accessions are from East Asia, and limited information is available on their genetic diversity and malt quality. The objectives of this study were to determine the genetic diversity among 30 East Asian accessions and two North American cultivars. Genetic diversity was based on 49 simple-sequence repeat markers. All accessions were tested for barley grain brightness; protein content; 1,000-kernel weight; malting loss; fine-grind malt extract; content of plump kernels, free amino nitrogen, soluble protein, and wort β-glucan; the Kolbach index (i.e., the ratio of malt soluble protein to malt total protein); α-amylase activity; diastatic power; wort color; and wort viscosity. A few accessions had equal quality compared with Harrington and Conlon barley for individual traits but not for all. Qing 2, Mokkei 93–78, and Nitakia 48 could be excellent sources for increased malt extract; Nitakia 48 is a possible source for low wort viscosity; and Mokkei 93–78 and Nitakia 48 are putative sources of low β-glucan content. The cluster analyses also implied that the malt quality of an accession cannot be predicted based on the country where it was developed.

Variability in Fusarium Head Blight Epidemics in Relation to Global Climate Fluctuations as Represented by the El Niño-Southern Oscillation and Other Atmospheric Patterns

Cross-spectral analysis was used to characterize the relationship between climate variability, represented by atmospheric patterns, and annual fluctuations of Fusarium head blight (FHB) disease intensity in wheat. Time series investigated were the Oceanic Niño Index (ONI), which is a measure of the El Niño-Southern Oscillation (ENSO), the Pacific-North American (PNA) pattern and the North Atlantic Oscillation (NAO), which are known to have strong influences on the Northern Hemisphere climate, and FHB disease intensity observations in Ohio from 1965 to 2010 and in Indiana from 1973 to 2008. For each climate variable, mean climate index values for the boreal winter (December to February) and spring (March to May) were utilized. The spectral density of each time series and the (squared) coherency of each pair of FHB-climate-index series were estimated. Significance for coherency was determined by a nonparametric permutation procedure. Results showed that winter and spring ONI were significantly coherent with FHB in Ohio, with a period of about 5.1 years (as well as for some adjacent periods). The estimated phase-shift distribution indicated that there was a generally negative relation between the two series, with high values of FHB (an indication of a major epidemic) estimated to occur about 1 year following low values of ONI (indication of a La Niña); equivalently, low values of FHB were estimated to occur about 1 year after high values of ONI (El Niño). There was also limited evidence that winter ONI had significant coherency with FHB in Indiana. At periods between 2 and 7 years, the PNA and NAO indices were coherent with FHB in both Ohio and Indiana, although results for phase shift and period depended on the specific location, climate index, and time span used in calculating the climate index. Differences in results for Ohio and Indiana were expected because the FHB disease series for the two states were not similar. Results suggest that global climate indices and models could be used to identify potential years with high (or low) risk for FHB development, although the most accurate risk predictions will need to be customized for a region and will also require use of local weather data during key time periods for sporulation and infection by the fungal pathogen.

Deoxynivalenol and nivalenol in commercial wheat grain related to Fusarium head blight epidemics in southern Brazil

A three-year (2006–2008) survey on commercial wheat grain was conducted aimed at quantifying the intensity of Fusarium head blight epidemics related to kernel quality and levels of deoxynivalenol (DON) and nivalenol (NIV). Grain samples, obtained from 38 municipalities throughout the state of Rio Grande do Sul, Brazil, were assessed visually for Fusarium-damaged kernels (FDK) and chemically using liquid chromatography–mass spectrometry (LC–MS/MS). Overall FDK mean levels were 15.5%, not differing among the years. Co-contamination was predominant (59/66) across samples and overall mean levels of DON and NIV were 540 and 337μg/kg, respectively. When the levels of both mycotoxins were added together (DON+NIV), a higher correlation with FDK was found (R=0.36, P<0.01), compared to single toxin data. For the first time, the presence of NIV in levels comparable to DON is reported from a multi-year regional epidemiological survey in the country which should be of concern to the small grains industry.

The Spread of a Released Clone of Gibberella zeae from Different Amounts of Infested Corn Residue.

Corn residue is a significant source of inoculum for epidemics of Fusarium head blight (FHB) in wheat and barley, but little is known about the influence of different amounts of corn residue on FHB. We monitored the spread of a released clone of Gibberella zeae (Fusarium graminearum), causal agent of FHB, from small 0.84-m-diameter research plots containing 45, 200, or 410 g of infested corn stalk pieces in winter wheat and barley fields in Virginia over 3 years (2008 to 2010). The fungus was recaptured through the collection of wheat and barley spikes at 0 and 3 m from the source and the released clone was identified in heterogeneous background populations using amplified fragment length polymorphisms. Results showed a slightly greater intensity of recovery of the clone at a greater distance when more infested residue was present. Plots containing larger amounts of inoculum (410 g) generally resulted in a smaller decline of recovery of the clone at 3 m from the source, indicating a greater spread from the larger inoculum source. The clone was also recovered at distances ≥18 m from inoculum sources. Larger amounts of corn residue generally had less influence on clone recovery in plots containing a moderately resistant wheat cultivar than those containing a susceptible wheat cultivar.

Estimating the Risk of a Crop Epidemic From Coincident Spatio-temporal Processes

Fusarium Head Blight (FHB), or “scab,” is a very destructive disease that affects wheat crops. Recent research has resulted in accurate weather-driven models that estimate the probability of an FHB epidemic based on experiments. However, these predictions ignore two crucial aspects of FHB epidemics: (1) An epidemic is very unlikely to occur unless the plants are flowering, and (2) FHB spreads by its spores, resulting in spatial and temporal dependence in risk. We develop a new approach that combines existing weather-based probabilities with information on flowering dates from survey data, while simultaneously accounting for spatial and temporal dependence. Our model combines two space-time processes, one associated with pure weather-based FHB risks and the other associated with flowering date probabilities. To allow for scalability, we model spatiotemporal dependence via a process convolutions approach. Our sample-based approach produces a realistic assessment of areas that are persistently at high risk (where the probability of an epidemic is elevated for extended time periods), along with associated estimates of uncertainty. We conclude with the application of our approach to a case study from North Dakota.

A Model‐based Assessment of the Impacts of Climate Variability on Fusarium Head Blight Seasonal Risk in Southern Brazil

AbstractThe frequency of Fusarium head blight (FHB) outbreaks increased considerably in many countries in the last two decades. We used a crop‐disease model to assess the impacts of climate variability over a 50‐year period at Passo Fundo, Rio Grande do Sul, Brazil. Thirty individual simulation runs of a wheat model were performed for each year by varying planting dates from 1 June to 30 June. For each simulation, an FHB risk index was estimated with the disease model using the heading date simulated by the crop model. A seasonal FHB risk index was estimated by averaging the 30 indices each year. Our simulation results showed that climate at Passo Fundo became favourable to FHB after the 1980s following a period of less favourable conditions for epidemics in the 1960s and 1970s. The risk for FHB was higher for the later planting dates in the most recent decades. Consideration of sea surface temperature (SST) anomalies (deviations from long‐term mean values) in the Tropical Pacific Ocean allowed the separation of groups of years with frequently low FHB risk (negative SST anomalies, La Niña like years) and years with frequently high FHB risks (positive SST anomalies – El Niño like years, and near‐normal SST – neutral years). Southern Atlantic SST anomalies were then included to separate years with different FHB risks in El Niño‐like years and Neutral years. However, the consideration of these anomalies did not result in an improvement. Our results suggest that increased spring rainfall linked to warm sea surface temperature in the Pacific after the 1980s was associated with higher frequency of FHB epidemics in southern Brazil.

Fusarium head blight of barley in China

Fusarium head blight (FHB) is a widespread and destructive disease of barley (Hordeum vulgare) in China. Extensive research on FHB of barley has been conducted in China over the past 50 years, but most of the research publications are written in Chinese and are not accessible to readers outside China. At least 16 Fusarium species pathogenic to barley have been identified in China, with F. graminearum (teleomorph Gibberella zeae) considered the primary cause of FHB. Severe FHB epidemics have occurred since 1952, particularly in regions in the lower and middle reaches of the Yangtze River. The mycotoxins deoxynivalenol, nivalenol, zearalenone, T-2, and fumonisin have been associated with FHB epidemics in barley, and many cases of mycotoxicosis have been reported. An integrated management strategy has been employed to mitigate FHB. Six-row cultivars have mostly been replaced by two-row cultivars in southern China. New barley cultivars are generally short in stature, mature early, and have the potential to withstand rainstorms in early spring. Barley accessions with different levels of resistance to FHB have been identified and used in barley breeding programs in China and elsewhere in the world. Forecasting models with high levels of accuracy have been used for decades to assess the risk of FHB epidemics. Application of fungicides is recommended as a control measure when necessary. Also recommended are cultural practices to reduce the risk of FHB epidemics. If all these control measures fail, decontamination methods that have been developed are employed to save Fusarium -infected barley kernels for use as feed.

Resistance to Fusarium head Blight and Deoxynivalenol Accumulation in Chinese Barley

Abstract Fusarium head blight (FHB) caused by Fusarium graminearum Schwabe is a devastating barley disease world‐wide, causing significant yield losses and contaminating cereal products with mycotoxins. Barley grain contaminated with deoxynivalenol (DON) is associated with gushing and may be rejected by the malting and brewing industry. Genetically inherited resistance is the most effective option for the control of the disease. A total of 266 barley cultivars and breeding lines originating from China were evaluated for FHB resistance and concentration of DON in grain. Plants were inoculated with isolates of F. graminearum under field conditions by injecting conidia into a single spikelet of each spike. FHB symptoms were evaluated by visual inspection, and DON content was analysed by HPLC. Significant differences in FHB ratings and DON levels were observed among cultivars. Visual symptoms of FHB varied from 4.88 to 71.75% of infected spikelets 21 days after inoculation and from 7.86 to 113.33 area under the disease progress curve units (AUDPC). Twenty‐seven lines were more resistant to FHB than the control resistant cultivar Zhedar 2 and with fewer than 12% infected spikelets. Twenty‐one of the above lines originated from the area in the mid to low valley of Yangtze River, where FHB epidemics are frequent. DON levels ranged from 0.05 to 24.39 mg/kg among the tested barley lines. Correlation coefficients were significant between FHB symptom ratings and DON levels. However, there was no significant correlation between symptom rating and plant height and no significant correlation between symptom rating and heading date.

Infection of green fluorescence protein-taggedFusarium graminearumon wheat and barley spikes

Fusarium head blight (FHB), mainly caused by Fusarium graminearum, is a very serious disease in wheat and barley production area. FHB epidemics cause yield decreases and production of mycotoxin that renders the grain useless for flour and malt products. Understanding the infection mechanism of F. graminearum plays an important role for the disease control. In present study, green fluorescence protein (GFP)-tagged were infected to wheat and barley varieties by single floret injection and screened via GFP signal. Results showed similar infection pattern of F. graminearum on both wheat and barley. Pathogen geminated in the inoculated spikelets, grew on the top of ovary or between lemma and palea, and extended towards and through rachis to the adjacent spikelets to infect the whole spike. When a spike of cultivar with FHB resistance was inoculated by F. graminearum, only the injected spikelet showed symptom at 6 days past inoculation (dpi). GFP signals indicated that F. graminearum colonized only in the inoculated spikelet and stop at the compact tissue of rachilla at 6 dpi. On the contrary, the diseased spikelets were up to 5 at 6 dpi in the spike of cultivars susceptible to FHB. F. graminearum extended through compact tissue to rachis and infected to the adjacent spikelets by spreading upward and downward to adjacent florets inter- and intra-cellularly in vascular bundles and cortical tissue of the rachis.

Jasmonate and Ethylene Signaling Pathway May Mediate Fusarium Head Blight Resistance in Wheat

Fusarium head blight (FHB), caused by Fusarium graminearum Schw. [teleomorph: Gibberella zeae (Schw.) Petch], can be a devastating disease in small grains production. Understanding its molecular pathogenesis will help identifying key steps in disease development and developing a strategy for efficiently preventing FHB epidemics. As the first step toward our goal, gene expression in the FHB‐resistant wheat (Triticum aestivum L.) cultivar Sumai 3 and the FHB‐susceptible wheat landrace Y1193‐6 was profiled with Affymetrix Wheat Genome GeneChip in 24 h after inoculation by F. graminearum isolate Fg4 and compared. Twofold change [log2(signal ratio) = 1] in expression was set as the threshold for data selection. Comparing the FHB‐inoculated and the mock‐inoculated wheat spikelets in both Sumai 3 and Y1193‐6 revealed a total of 677 possible FHB‐responsive genes. Further analysis and comparison revealed that, among these FHB‐responsive genes, 69 were F. graminearum genes. Of the 608 wheat genes, 243 showed similar expression in both Sumai 3 and Y1193‐6; 281 and 79 significantly changed expression pattern only in Sumai 3 or Y1193‐6, respectively; and five had opposite expression pattern between the two wheat genotypes. Functional genomics and physiological analyses both suggested that FHB resistance in Sumai 3 involves defense pathways regulated by jasmonic acid and ethylene signaling, while salicylic acid–regulated systematic acquired resistance is insignificant in this process.

Cultural control practices for Fusarium head blight: Problems and solutions

Reduced tillage practices have been adopted worldwide in agriculture. The implementation of conservation tillage, leaving crop residues at the soil surface following the harvest of crops is essential to protect soils vulnerable to erosion, however these practices have contributed directly to the upsurge of Fusarium head blight of wheat and barley. While researchers have made significant progress in the identification and incorporation of genetic resistance, and in the identification and delivery of effective fungicides to cereal crops, Fusarium head blight remains a recalcitrant problem. It would seem that we can not reduce the threat of future Fusarium head blight epidemics without addressing the underlying origin of the problem, Fusarium -infested crop residues. Given the limitations of current agricultural practices, we are challenged to find ways to reduce the inoculum potential of Fusarium -infested residues without removing them from the soil surface.

The FHB challenge to irrigation wheat production in South Africa

Irrigation wheat production in South Africa is seriously impaired by the regular occurrence of Fusarium head blight epidemics. The disease was noted for the first time in 1980 and has since caused damage whenever the seasonal climatic conditions were favourable. Higher levels of disease concurred with an increase in conservation tillage and maize production in a double cropping system with wheat. Farmers are challenged by a lack of rotation summer crops and high input costs, forcing them towards reduced tillage practices. At present the disease has not been successfully controlled with fungicides and most commercial cultivars show a low level of resistance. Removal of high levels of maize residue, before the cultivation of a wheat crop, has proved effective in reducing disease. Climatic conditions during flowering are extremely unpredictable, but excessive rainfall, lower night temperatures and subsequent higher humidity seem to be key factors in the development of high infection levels. Research currently focuses on cultivar and resistance evaluation, tillage practices, climatic triggers for disease and a fungal population study.

The TRI101 story: engineering wheat and barley to resist Fusarium head blight

Fusarium head blight (FHB), caused primarily by Fusarium graminearum, is a major disease of wheat and barley in the United States and Canada. FHB epidemics have been on the increase since 1993 and have caused severe monetary damage for the growers and seed industry. Along with reduced yields, the presence of mycotoxins in moldy grain constitutes a major problem for the grain industry. These mycotoxins pose health hazards to humans and animals upon ingestion. The acute phytotoxicity of these mycotoxins and their occurrence in plant tissues correlates with their role in pathogenesis and the production of plant disease. Transgenic plants incorporating the Fusarium sporotrichioides Tri101 gene, a gene that reduces toxicity of trichothecenes, have reduced levels of disease, thus demonstrating that FHB severity and deoxynivalenol (DON) accumulation can be reduced in small grains by the introduction of a toxin-modification gene.

Evaluation of Fusarium Head Blight Resistance in Tetraploid Wheat (Triticum turgidum L.)

Durum wheat (Triticum turgidum L. subsp. durum) production in North America in recent years has been seriously threatened by epidemics of Fusarium head blight (FHB), caused mainly by Fusarium graminearum Schwabe [teleomorph Gibberella zeae (Schw.) Petch]. Deployment of FHB‐resistant cultivars has been considered the most effective and cost‐efficient strategy to combat this disease; however, progress in developing FHB‐resistant durum wheat cultivars has been hindered by a lack of effective sources of resistance. The objective of this study is to identify tetraploid wheat germplasm that could be used to enhance FHB resistance in durum wheat. We evaluated FHB reactions in 376 accessions of five cultivated subspecies of T. turgidum, including Persian wheat [T. turgidum subsp. carthlicum (Nevski) Á. Löve and D. Löve], cultivated emmer wheat [T. turgidum subsp. dicoccum (Schrank ex Schübler) Thell.], Polish wheat [T. turgidum subsp. polonicum (L.) Thell.], Oriental wheat [T. turgidum subsp. turanicum (Jakubz.) Á. Löve and D. Löve], and Poulard wheat (T. turgidum L. subsp. turgidum). We used point inoculation to evaluate resistance to the spread of infection over three greenhouse seasons and used the grain inoculum method of inoculation to evaluate putatively resistant accessions in two field locations. Preliminary evaluation data showed that 16 T. turgidum subsp. carthlicum and 4 T. turgidum subsp. dicoccum accessions consistently exhibited resistance or moderate resistance to FHB. These accessions likely carry genetic resistance to FHB and could be used directly in breeding programs to enhance FHB resistance in durum wheat.

Management of soil microbial communities to enhance populations of Fusarium graminearum-antagonists in soil

Fusarium head blight (FHB), incited by Fusarium graminearum Schwabe is one of the most devastating diseases of wheat. Primary inoculum generated on crop residue is the driving force of FHB epidemics. Fusarium survival on crop residues is affected by soil microbial antagonists. The incorporation of green manures has been shown to increase the density and diversity of microbes in soils, particularly the density and the pathogen-inhibitory activity of specific bacteria and fungi. Evidence of increased streptomycete populations in soil as a response to green manure incorporation, and their negative effect on the survival of Fusarium oxysporum Schlechtendahl in soil, suggests their potential use to reduce the survival of related pathogens. There is, however, no precedent for the use of green manures to promote indigenous streptomycete populations to control FHB. This study investigated the use of green manures (sorghum–sudangrass hybrid [Sorghum bicolor (L.) Moench–S. bicolor (L.) Moench var. sudanense (Piper)] and common buckwheat [Fagopyrum esculentum (Moench)]) for reducing F. graminearum survival in association with wheat residues. Soil bacterial density, streptomycete density and the density and inhibitory activity of F. graminearum-antagonists were monitored from planting until 3 and 6 months following the incorporation of green manures in greenhouse and field experiments, respectively. The decomposition of wheat residues and survival of Fusarium in residues was also assessed. The use of green manures did not statistically impact the survival of F. graminearum in wheat residue. However, green manures promoted the development of higher densities and antagonistic abilities of F. graminearum-antagonists in soils. Additionally, streptomycete densities and F. graminearum-antagonist densities were significantly and positively correlated with reduced survival of Fusarium. The results of our study suggest that the use of green manures can enhance populations of indigenous soil microorganisms antagonistic to the survival of F. graminearum in wheat residue.

Geographic distribution and genetic diversity of Fusarium graminearum and F. asiaticum on wheat spikes throughout China

A large number of Fusarium graminearum and F. asiaticum isolates were collected from wheat spikes from all regions in China with a history of fusarium head blight (FHB) epidemics. Isolates were analysed to investigate their genetic diversity and geographic distribution. Sequence characterized amplified region (SCAR) analyses of 437 isolates resolved both species, with 21% being F. graminearum (SCAR type 1) and 79% being F. asiaticum (SCAR type 5). AFLP profiles clearly resolved two groups, A and B, that were completely congruent with both species. However, more diversity was detected by AFLP, revealing several subgroups within each group. In many cases, even for isolates from the same district, AFLP haplotypes differed markedly. Phylogenetic analyses of multilocus DNA sequence data indicated that all isolates of SCAR type 1, AFLP group A were F. graminearum, whilst isolates of SCAR type 5, AFLP group B were F. asiaticum, demonstrating that it is an efficient method for differentiating these two species. Both species seem to have different geographic distributions within China. Fusarium graminearum was mainly obtained from wheat growing in the cooler regions where the annual average temperature was 15°C or lower. In contrast, the vast majority of F. asiaticum isolates were collected from wheat growing in the warmer regions where the annual average temperature is above 15°C and where FHB epidemics occur most frequently. This is the first report of the distribution of, and genetic diversity within, F. graminearum and F. asiaticum on wheat spikes throughout China.

Forecasting of Fusarium head blight and deoxynivalenol content in winter wheat with FusaProg*

Fusarium head blight is one of the most serious cereal diseases of the world. Epidemics of Fusarium head blight can lead to a decline in grain quality and yield. In addition, grains often become contaminated with mycotoxins, which are harmful to humans and animals. In a field survey of winter wheat in Switzerland, Fusarium graminearum proved to be the most prevalent species responsible for head blight and deoxynivalenol the most common mycotoxin. To elucidate and quantify single or combined effects of cropping factors on F. graminearum infestation and to reduce the risk of mycotoxin contamination of wheat under conservation tillage, we developed the decision support system FusaProg. Our model takes into account the effects of cropping factors, previous crops, soil and straw management, as well as the F. graminearum susceptibility of the planted variety. These factors are used as driving variables and are combined with the prevailing weather conditions and growth stage in order to predict the deoxynivalenol content of a specific wheat plot before harvest. To use FusaProg as a threshold‐based tool to control F. graminearum with optimized timing of fungicide applications, forecasts of deoxynivalenol contents are conducted during the flowering period. FusaProg is an Internet‐based decision support system which not only provides information about the local and regional F. graminearum infection risks; it also forecasts plot‐specific deoxynivalenol contamination of winter wheat. In 2006, the system was evaluated by Swiss cantonal plant protection officers, and in 2007, the system will be made available to Swiss wheat producers.

Real-time PCR Quantification and Mycotoxin Production of Fusarium graminearum in Wheat Inoculated with Isolates Collected from Potato, Sugar Beet, and Wheat

ABSTRACT Fusarium graminearum causes Fusarium head blight (FHB) in small grains worldwide. Although primarily a pathogen of cereals, it also can infect noncereal crops such as potato and sugar beet in the United States. We used a real-time polymerase chain reaction (PCR) method based on intergenic sequences specific to the trichodiene synthase gene (Tri5) from F. graminearum. TaqMan probe and primers were designed and used to estimate DNA content of the pathogen (FgDNA) in the susceptible wheat cv. Grandin after inoculation with the 21 isolates of F. graminearum collected from potato, sugar beet, and wheat. The presence of nine mycotoxins was analyzed in the inoculated wheat heads by gas chromatography and mass spectrometry. All isolates contained the Tri5 gene and were virulent to cv. Grandin. Isolates of F. graminearum differed significantly in virulence (expressed as disease severity), FgDNA content, and mycotoxin accumulation. Potato isolates showed greater variability in producing different mycotoxins than sugar beet and wheat isolates. Correlation analysis showed a significant (P < 0.001) positive relationship between FgDNA content and FHB severity or deoxynivalenol (DON) production. Moreover, a significant (P < 0.001) positive correlation between FHB severity and DON content was observed. Our findings revealed that F. graminearum causing potato dry rot and sugar beet decay could be potential sources of inoculum for FHB epidemics in wheat. Real-time PCR assay provides sensitive and accurate quantification of F. graminearum in wheat and can be useful for monitoring the colonization of wheat grains by F. graminearum in controlled environments, and evaluating wheat germplasms for resistance to FHB.

Potential biocontrol agents for Fusarium head blight and deoxynivalenol production in wheat

Fusarium head blight (FHB) caused by Gibberella zeae (anamorph= Fusarium graminearum) is a devastating disease that causes extensive yield and quality losses to wheat in humid and semi-humid regions of the world. During the last 50 years, several epidemics of FHB of varying degrees of severity have occurred in Argentina. Besides the economic losses due to reduction in grain quality, the main problem is the potential mycotoxin contamination of wheat mainly with deoxynivalenol (DON). Biological control offers an additional strategy that can be used as part of an integrated management to control FHB. A survey was done to search for potential biocontrol agents (BCA) isolated from wheat anthers in Argentina. A total of 354 bacterial strains were screened in two selection steps using a index of dominance ( I D) assay considering environmental parameters such as temperature and water activity in the interaction between pathogen and antagonist. Among the evaluated strains, 22 strains (6%) were able to reduce the growth of F. graminearum. The 22 selected strains reduced the production of DON on irradiated wheat grains by 60–100%. The ability of these strains to control FHB and DON production was evaluated under greenhouse conditions. Nine strains (40.9%) significantly reduced the disease severity by 49–71% ( P⩽0.05). The DON content in spikes, produced by plants in the greenhouse trial, was significantly reduced by 32–100% compared with the control. Five strains decreased mycotoxin content to undetectable levels. From this study we identified two strains, Brevibacillus sp. BRC263 and Streptomyces sp. BRC87B, to be tested in combination for potential control of FHB.