Deoxynivalenol, acetyl deoxynivalenol, and zearalenone formation by Canadian isolates of Fusarium graminearum on solid substrates

Attempting to Create a Pathway to 15-Deacetylcalonectrin with Limited Accumulation in Cultures of Fusarium Tri3 Mutants: Insight into Trichothecene Biosynthesis Machinery

The compound 15-deacetylcalonectrin (15-deCAL) is a common pathway intermediate in the biosynthesis of Fusarium trichothecenes. This tricyclic intermediate is metabolized to calonectrin (CAL) by trichothecene 15-O-acetyltransferase encoded by Tri3. Unlike other trichothecene pathway Tri gene mutants, the Δtri3 mutant produces lower amounts of the knocked-out enzyme's substrate 15-deCAL, and instead, accumulates higher quantities of earlier bicyclic intermediate and shunt metabolites. Furthermore, evolutionary studies suggest that Tri3 may play a role in shaping the chemotypes of trichothecene-producing Fusarium strains. To better understand the functional role of Tri3p in biosynthesis and evolution, we aimed to develop a method to produce 15-deCAL by using transgenic Fusarium graminearum strains derived from a trichothecene overproducer. Unfortunately, introducing mutant Tri3, encoding a catalytically impaired but structurally intact acetylase, did not improve the low 15-deCAL production level of the ΔFgtri3 deletion strain, and the bicyclic products continued to accumulate as the major metabolites of the active-site mutant. These findings are discussed in light of the enzyme responsible for 15-deCAL production in trichothecene biosynthesis machinery. To efficiently produce 15-deCAL, we tested an alternative strategy of using a CAL-overproducing transformant. By feeding a crude CAL extract to a Fusarium commune strain that was isolated in this study and capable of specifically deacetylating C-15 acetyl, 15-deCAL was efficiently recovered. The substrate produced in this manner can be used for kinetic investigations of this enzyme and its possible role in chemotype diversification.

Effect of pydiflumetofen on Gibberella ear rot and Fusarium mycotoxin accumulation in maize grain

In Ontario, Canada, Fusarium graminearum Schwabe causes Gibberella ear rot (GER) in maize, resulting in the accumulation of mycotoxins, mainly deoxynivalenol (DON), DON-3-glucoside (DON-3G) and zearalenone (ZEN) in infected kernels. Fungicides can be an important tool for managing GER and DON and other Fusarium mycotoxins in maize. Until recently, all fungicides available to growers were triazoles, thus no resistance management strategy through fungicide use was possible. In this study, a novel carboxamide fungicide active ingredient (pydiflumetofen) was evaluated against conventional triazole fungicides and mixtures for: (1) effectiveness on mycotoxins (2) optimal application timing; and (3) efficacy of application, with and without an insecticide, under natural and inoculated-misted conditions. The best timing for fungicide application was at full silk, resulting in the highest reduction of GER symptoms and lowest accumulation of F. graminearum mycotoxins in harvested grain. DON and DON-3G concentrations were reduced by at least 50% with a fungicide application at full silk. Fungicide treatments did not affect fumonisin concentrations in grain. Pydiflumetofen (94 g active ingredients (AI)/ha) and fungicides containing pydiflumetofen (75-94 g AI/ha) were similar to standard triazole fungicides (prothioconazole at 200 g AI/ha and metconazole at 90 g AI/ha) for reducing GER and F. graminearum mycotoxins under misted-inoculated plots and commercial field conditions; as a result, we expect pydiflumetofen to be competitive with triazole-only chemistries in the marketplace, which should delay the onset of fungicide resistance.

A plant biostimulant made from the marine brown algae Ascophyllum nodosum and chitosan reduce Fusarium head blight and mycotoxin contamination in wheat

Fusarium head blight (FHB) caused by Fusarium graminearum is a disease that results in yield loss and mycotoxin contamination in wheat globally. This study assessed the effect of a plant biostimulant prepared from a brown macroalga Ascophyllum nodosum (Liquid Seaweed Extract; LSE) alone and in combination with chitosan in controlling Fusarium. Wheat seedlings drenched with LSE and chitosan in combination showed reduced severity of F. graminearum infection on leaves as evidenced by a significant reduction in necrotic area and fewer number of conidia produced in the necrotic area. Gene expression studies showed that the combination of LSE and chitosan amplified the response of pathogenesis-related genes (TaPR1.1, TaPR2, TaPR3, TaGlu2) in wheat seedlings infected with Fusarium spores above that observed for the individual treatments. The combination treatments were more effective in enhancing the activity of various defense related enzymes such as peroxidase and polyphenol oxidase. FHB studies on adult plants showed a reduction of bleached spikes in wheat heads treated with the combination of LSE and chitosan. Mycotoxin content appeared to be correlated with FHB severity. Combination treatments of LSE and chitosan reduced the levels of mycotoxins deoxynivalenol and sambucinol in wheat grains. Systemic disease resistance appears to be induced by LSE and chitosan in response to F. graminearum in wheat by inducing defense genes and enzymes.

Why RGB Imaging Should be Used to Analyze Fusarium Graminearum Growth and Estimate Deoxynivalenol Contamination

Size-based fungal growth studies are limited because they do not provide information about the mold’s state of maturity, and measurements such as radius and diameter are not practical if the fungus grows irregularly. Furthermore, the current methods used to detect diseases such as Fusarium head blight (FHB) or mycotoxin contamination are labor-intensive and time consuming. FHB is frequently detected through visual examination and the results can be subjective, depending on the skills and experience of the analyzer. For toxin determination (e.g., deoxynivalenol (DON), the best methods are expensive, not practical for routine. RGB (red, green and blue) imaging analysis is a viable alternative that is inexpensive, easy to use and seemingly better if enhanced with statistical methods. This short communication explains why RGB imaging analysis should be used instead of size-based variables as a tool to measure growth of Fusarium graminearum and DON concentration.

Tackling maize fusariosis: in search of Fusarium graminearum biosuppressors

This review presents biocontrol agents employed to alleviate the deleterious effect of the pathogen Fusarium graminearum on maize. The control of this mycotoxigenic phytopathogen remains elusive despite the elaborate research conducted on its detection, identification, and molecular fingerprinting. This could be attributed to the fact that in vitro and greenhouse biocontrol studies on F. graminearum have exceeded the number of field studies done. Furthermore, along with the variances seen among these F. graminearum suppressing biocontrol strains, it is also clear that the majority of research done to tackle F. graminearum outbreaks was on wheat and barley cultivars. Most fusariosis management related to maize targeted other members of Fusarium such as Fusarium verticillioides, with biocontrol strains from the genera Bacillus and Pseudomonas being used frequently in the experiments. We highlight relevant current techniques needed to identify an effective biofungicide for maize fusariosis and recommend alternative approaches to reduce the scarcity of data for indigenous maize field trials.

An impact of Deoxynivalenol produced by Fusarium graminearum on broiler chickens

Deoxynivalenol (DON) is a major mycotoxin from the trichothecene family of mycotoxins produced by Fusarium fungi that cause disease in grains. Food and feed contaminated with DON cause a variety of adverse health effects in humans and farm animals. However, the fermentation conditions of DON for toxicological study remain to be optimised. Deoxynivalenol levels were increased in a constant temperature of 20°C after fermentation for 7 and 14 days compared with cycling temperatures between 10-20°C and 15-20°C. We have established that optimum conditions for DON production on rice-based medium is constant temperature at 20°C. In feeding experiments, the villus height and the ratio of villus height and crypt depth were reduced in the duodenum of DON-fed broiler chickens, whereas a mycotoxin degradation agent efficiently reversed the abnormal morphology of the small intestine in the DON-fed broilers. The expression of pro-inflammatory gene, COX-2, was induced in the spleen and bursa of Fabricius of DON-fed broilers. This effect was alleviated in the presence of mycotoxin degradation agent. DON produced in solid-state fermentation is able to cause toxic effects in broilers and induce an abnormal morphology of the small intestine, particularly the duodenum.

Fusarium graminearum in Stored Wheat: Use of CO₂ Production to Quantify Dry Matter Losses and Relate This to Relative Risks of Zearalenone Contamination under Interacting Environmental Conditions

Zearalenone (ZEN) contamination from Fusarium graminearum colonization is particularly important in food and feed wheat, especially during post-harvest storage with legislative limits for both food and feed grain. Indicators of the relative risk from exceeding these limits would be useful. We examined the effect of different water activities (a_w; 0.95–0.90) and temperature (10–25 °C) in naturally contaminated and irradiated wheat grain, both inoculated with F. graminearum and stored for 15 days on (a) respiration rate; (b) dry matter losses (DML); (c) ZEN production and (d) relationship between DML and ZEN contamination relative to the EU legislative limits. Gas Chromatography was used to measure the temporal respiration rates and the total accumulated CO₂ production. There was an increase in temporal CO₂ production rates in wetter and warmer conditions in all treatments, with the highest respiration in the 25 °C × 0.95 a_w treatments + F. graminearum inoculation. This was reflected in the total accumulated CO₂ in the treatments. The maximum DMLs were in the 0.95 a_w/20–25 °C treatments and at 10 °C/0.95 a_w. The DMLs were modelled to produce contour maps of the environmental conditions resulting in maximum/minimum losses. Contamination with ZEN/ZEN-related compounds were quantified. Maximum production was at 25 °C/0.95–0.93 a_w and 20 °C/0.95 a_w. ZEN contamination levels plotted against DMLs for all the treatments showed that at ca. <1.0% DML, there was a low risk of ZEN contamination exceeding EU legislative limits, while at >1.0% DML, the risk was high. This type of data is important in building a database for the development of a post-harvest decision support system for relative risks of different mycotoxins.

Influence of temperature, water activity and incubation time on fungal growth and production of ochratoxin A and zearalenone by toxigenic Aspergillus tubingensis and Fusarium incarnatum isolates in sorghum seeds

The major objective of this study was to describe the effect of water activity and temperature on radial growth and production of ochratoxin A (OTA) and zearalenone (ZEA) on sorghum grains of three Aspergillus tubingensis and three Fusarium incarnatum isolates. The water activity range was 0.91-0.99 a_w for F. incarnatum isolates and 0.88-0.99 a_w for A. tubingensis isolates. Temperatures of incubation were 15, 25 and 37°C for both species. Mycotoxin production was determined after 7, 14, 21 and 28days depending on the growth rate of the six isolates. Maximum growth rates (mm/day) were observed at 37°C and 0.99 a_w for A. tubingensis isolates and at 0.99 a_w and 25°C for F. incarnatum isolates. A. tubingensis was able to grow at 15°C only at the highest a_w levels (0.97 and 0.99 a_w). However, at this temperature F. incarnatum grew at 0.94 a_w. Optimum ochratoxin A production was observed at 0.97 a_w×37°C whereas optimal conditions for ZEA production varied from one isolate to another. Moreover, isolates of F. incarnatum from Tunisia do not require high a_w and temperature levels to yield maximum levels of ZEA. In general, our results showed that there is no correlation between the growth and production of ZEA in the case of F. incarnatum. This is the first study on the water activity and temperature effect on growth rate and ZEA production of F. incarnatum. Our results show that sorghum grains not only support growth but also OTA and ZEA production by A. tubingensis and F. incarnatum, respectively.

Distribution of deoxynivalenol, zearalenone, and their respective modified analogues in milling fractions of naturally contaminated wheat grains

Mycotoxins are among the most abundant contaminants in food and feed worldwide. Therefore, in the EU maximum levels are established, e.g. for the frequently occurring Fusarium toxins deoxynivalenol (DON) and zearalenone (ZEA). Additional to DON and ZEA, modified mycotoxins are present in naturally contaminated grain products contributing significantly to the exposure of humans and animals with mycotoxins. Up to now data on the spatial distribution of many (masked) mycotoxins in the kernels of wheat are missing. The aim of the present study was to investigate the amounts of DON and ZEA as well as their most abundant derivatives DON-3-glucoside (DON-3G), 3- and 15-acetyl-DON, ZEA-14- and 16-glucoside and ZEA-14-sulphate (ZEA-14S) in mill fractions of naturally contaminated wheat batches using HPLC-MS/MS. The investigated distribution pattern in ten milling fractions is comparable among the three investigated different wheat batches. Interestingly, DON and DON-3G were found to be present to similar amounts in all fractions. In bran, the levels were only slightly higher than in the endosperm. By contrast, for ZEA and ZEA-14S a significantly higher amount of toxin is located in the fibre-rich fractions. The relative mass proportion of DON-3G comprises for only between 2.9 and 11.2% of the free DON, while the relative mass proportion of ZEA-14S is estimated to even exceed the amount of free ZEA in certain fractions. Acetylated DON derivatives and ZEA-glucosides were only detected in low amounts. The experimental results show that a significant reduction of the ZEA and ZEA-14S level in wheat flour is feasible by applying milling technology strategies. However, the almost evenly distribution of DON and DON-3G in all fractions does not allow for the technological removal of relevant toxin amounts. Furthermore, the relative share of masked forms was higher for ZEA derivatives than for the DON conjugates in the investigated wheat lots.

Survey of mycotoxins in corn distillers' dried grains with solubles from seventy-eight ethanol plants in twelve States in the U.S. In 2011

Fuel ethanol co-products known as distillers' dried grains with solubles (DDGS) are a significant source of energy, protein, and phosphorous in animal feed. Fuel ethanol production may concentrate mycotoxins present in corn into DDGS. One hundred and forty one corn DDGS lots collected in 2011 from 78 ethanol plants located in 12 states were screened for the mycotoxins deoxynivalenol (DON), 15-acetyldeoxynivalenol (15-ADON), 3-acetyldeoxynivalenol (3-ADON), nivalenol (NIV), and zearalenone (ZON). DON ranged from <0.50 to 14.62 μg g-1, 15-ADON ranged from <0.10 to 7.55 μg g-1, and ZON ranged from <0.10 to 2.12 μg g-1. None of the DDGS lots contained 3-ADON or NIV. Plants in OH had the highest levels of DON overall (mean of 9.51 μg g-1), and plants in NY, MI, IN, NE, and WI had mean DON levels >1 and <4 μg g-1. Twenty six percent (36/141) of the DDGS lots contained 1.0 to 5.0 μg g-1 DON, 2% (3/141) contained >5.0 and <10.0 μg g-1 DON, and 3% (4/141) contained >10.0 μg g-1 DON. All DDGS lots contaminated with unacceptable levels of DON evaded detection prior to their commercial distribution and were likely sold as feed products.

Recent progress regarding the bioactivities, biosynthesis and synthesis of naturally occurring resorcinolic macrolides

Macrolides, which comprise a family of lactones with different ring sizes, belong to the polyketide class of natural products. Resorcinolic macrolides, an important subgroup, possess interesting structures and exhibit a wide variety of bioactivities, such as anti-tumor, anti-bacteria, and anti-malaria activities, etc. This review summarizes progress in isolation, bioactivity studies, biosynthesis, and representative chemical syntheses of this group of macrolides in recent decades, encompassing 63 naturally occurring macrolides published in 120 articles.

Early detection of toxigenic Fusarium graminearum in wheat

Fusarium graminearum (Schwabe) contaminates agricultural crops and commodities with trichothecenes, mostly deoxynivalenol and its acetyl-derivatives. Current techniques available to detect final mycotoxin contamination products usually require an extended time lag between sampling and the corresponding report, and include different clean-up steps and eventually derivatisation. This study was aimed to develop a methodology to detect toxigenic F. graminearum prior to mycotoxin production. Headspace solid-phase microextraction coupled to capillary gas chromatography is shown to be useful to predict the potential of trichothecene mycotoxin formation by detecting the presence of F. graminearum at early stages of fungal growth in wheat cultivars, based on the detection of trichodiene (TRI), the volatile intermediate of trichothecenes. We showed that TRI is a useful marker to detect toxigenic Fusarium in wheat spikes from live plants, regardless of the actual development of Fusarium head blight (FHB). This is the first predictive methodology for FHB and trichothecene occurrence in field-collected samples. It might be a useful tool to help to prevent the risk of mycotoxin contamination.

Characterization and mycotoxigenic potential of Fusarium species in freshly harvested and stored sugar beet in Europe

Based on a 2-year field trial at two locations in Lower Saxony (Germany), 395 Fusarium isolates belonging to 13 species were collected from more than 3,000 sugar beet roots that were apparently healthy at harvest. In a comparative screen, subsamples were analyzed for Fusarium infection directly after harvest and after different storage conditions. Depending on the storage duration, a different species composition was observed. F. redolens was predominant in freshly harvested beets, while F. culmorum, F. cerealis, and F. graminearum comprised 50.0% (2006) and 84.8% (2007) of the Fusarium mycoflora of sugar beets subjected to long-term pile storage. Randomly selected isolates of all species detected were tested for pathogenicity to sugar beet, but only isolates of F. graminearum and F. sambucinum caused severe root symptoms. Overall, 34 isolates of all species detected were characterized for their mycotoxin profile in rice culture to determine potentially produced toxins for future analysis of sugar beet. A total of 26 Fusarium mycotoxins were detected by liquid chromatography-tandem mass spectrometry, including trichothecenes, zearalenone, and especially high amounts of beauvericin, enniatins, and moniliformin. Further work is required to analyze the natural occurrence of these mycotoxins in sugar beet.

Comparative mycotoxin profiles of Gibberella zeae populations from barley, wheat, potatoes, and sugar beets

Gibberella zeae is one of the most devastating pathogens of barley and wheat in the United States. The fungus also infects noncereal crops, such as potatoes and sugar beets, and the genetic relationships among barley, wheat, potato, and sugar beet isolates indicate high levels of similarity. However, little is known about the toxigenic potential of G. zeae isolates from potatoes and sugar beets. A total of 336 isolates of G. zeae from barley, wheat, potatoes, and sugar beets were collected and analyzed by TRI (trichothecene biosynthesis gene)-based PCR assays. To verify the TRI-based PCR detection of genetic markers by chemical analysis, 45 representative isolates were grown in rice cultures for 28 days and 15 trichothecenes and 2 zearalenone (ZEA) analogs were quantified using gas chromatography-mass spectrometry. TRI-based PCR assays revealed that all isolates had the deoxynivalenol (DON) marker. The frequencies of isolates with the 15-acetyl-deoxynivalenol (15-ADON) marker were higher than those of isolates with the 3-acetyl-deoxynivalenol (3-ADON) marker among isolates from all four crops. Fusarium head blight (FHB)-resistant wheat cultivars had little or no influence on the diversity of isolates associated with the 3-ADON and 15-ADON markers. However, the frequency of isolates with the 3-ADON marker among isolates from the Langdon, ND, sampling site was higher than those among isolates from the Carrington and Minot, ND, sites. In chemical analyses, DON, 3-ADON, 15-ADON, b-ZEA, and ZEA were detected. All isolates produced DON (1 to 782 microg/g) and ZEA (1 to 623 microg/g). These findings may be useful for monitoring mycotoxin contamination and for formulating FHB management strategies for these crops.

Genes for the biosynthesis of the fungal polyketides hypothemycin from Hypomyces subiculosus and radicicol from Pochonia chlamydosporia

Gene clusters for biosynthesis of the fungal polyketides hypothemycin and radicicol from Hypomyces subiculosus and Pochonia chlamydosporia, respectively, were sequenced. Both clusters encode a reducing polyketide synthase (PKS) and a nonreducing PKS like those in the zearalenone cluster of Gibberella zeae, plus enzymes with putative post-PKS functions. Introduction of an O-methyltransferase (OMT) knockout construct into H. subiculosus resulted in a strain with increased production of 4-O-desmethylhypothemycin, but because transformation of H. subiculosus was very difficult, we opted to characterize hypothemycin biosynthesis using heterologous gene expression. In vitro, the OMT could methylate various substrates lacking a 4-O-methyl group, and the flavin-dependent monooxygenase (FMO) could epoxidate substrates with a 1',2' double bond. The glutathione S-transferase catalyzed cis-trans isomerization of the 7',8' double bond of hypothemycin. Expression of both hypothemycin PKS genes (but neither gene alone) in yeast resulted in production of trans-7',8'-dehydrozearalenol (DHZ). Adding expression of OMT, expression of FMO, and expression of cytochrome P450 to the strain resulted in methylation, 1',2'-epoxidation, and hydroxylation of DHZ, respectively. The radicicol gene cluster encodes halogenase and cytochrome P450 homologues that are presumed to catalyze chlorination and epoxidation, respectively. Schemes for biosynthesis of hypothemycin and radicicol are proposed. The PKSs encoded by the two clusters described above and those encoded by the zearalenone cluster all synthesize different products, yet they have significant sequence identity. These PKSs may provide a useful system for probing the mechanisms of fungal PKS programming.

A guanylyl cyclase-like gene is associated with Gibberella ear rot resistance in maize (Zea mays L.)

Gibberella ear rot, caused by the fungal pathogen Fusarium graminearum Schwabe, is a serious disease of maize (Zea mays L.) grown in northern climates. The infected maize grain contains toxins that are very harmful to livestock and humans. A maize gene that encodes a putative 267-amino acid guanylyl cyclase-like protein (ZmGC1) was characterized and shown to be associated with resistance to this disease. The putative ZmGC1 amino acid sequence is 53% identical and 65% similar to AtGC1, an Arabidopsis guanylyl cyclase. The Zmgc1 coding sequence is nearly identical in a Gibberella ear rot-resistant line (CO387) and a susceptible line (CG62) but several nucleotide sequence differences were observed in the UTRs and introns of the two alleles. Using a 463 bp probe derived from the CG62 allele of Zmgc1 and a recombinant inbred (RI) mapping population developed from a CG62 x CO387 cross, six Zmgc1 restriction fragment length polymorphism (RFLP) fragments (ER1_1, ER1_2, ER1_3, ER1_4, ER1_5, and ER5_1) were mapped on maize chromosomes 2, 3, 7, and 8. Markers ER1_1 and ER5_1 on chromosomes 7 and 8, respectively, were significantly associated with Gibberella ear rot resistance, each in three different environments. The amount of Zmgc1 transcript in ear tissues increased more quickly and to a greater extent in the resistant genotype compared to the susceptible genotype after inoculation with F. graminearum. Zmgc1 is the first guanylyl cyclase gene characterized in maize and the first gene found to be associated with Gibberella ear rot resistance in this plant.

Molecular mapping of QTLs for resistance to Gibberella ear rot, in corn, caused by Fusarium graminearum

Gibberella ear rot, caused by the fungus Fusarium graminearum Schwabe, is a serious disease of corn (Zea mays) grown in northern climates. Infected corn is lower yielding and contains toxins that are dangerous to livestock and humans. Resistance to ear rot in corn is quantitative, specific to the mode of fungal entry (silk channels or kernel wounds), and highly influenced by the environment. Evaluations of ear rot resistance are complex and subjective; and they need to be repeated over several years. All of these factors have hampered attempts to develop F. graminearum resistant corn varieties. The aim of this study was to identify molecular markers linked to the genes for resistance to Gibberella ear rot. A recombinant inbred (RI) population, produced from a cross between a Gibberella ear rot resistant line (CO387) and a susceptible line (CG62), was field-inoculated and scored for Gibberella ear rot symptoms in the F4, F6, and F7 generations. The distributions of disease scores were continuous, indicating that resistance is probably conditioned by multiple loci. A molecular linkage map, based on segregation in the F5 RI population, contained 162 markers distributed over 10 linkage groups and had a total length of 2237 cM with an average distance between markers of 13.8 cM. Composite interval mapping identified 11 quantitative trait loci (QTLs) for Gibberella ear rot resistance following silk inoculation and 18 QTLs following kernel inoculation in 4 environments that accounted for 6.7%-35% of the total phenotypic variation. Only 2 QTLs (on linkage group 7) were detected in more than 1 test for silk resistance, and only 1 QTL (on linkage group 5) was detected in more than 1 test for kernel resistance, confirming the strong influence of the environment on these traits. The majority of the favorable alleles were derived from the resistant parent (CO387). The germplasm and markers for QTLs with significant phenotypic effects may be useful for marker-assisted selection to incorporate Gibberella ear rot resistance into commercial corn cultivars.

Temperature and water activity effects on growth and temporal deoxynivalenol production by two Argentinean strains of Fusarium graminearum on irradiated wheat grain

The objective of this study was to determine the effects of water activity (a(W); 0.900-0.995), temperature (5, 15, 25 and 30 degrees C), time of incubation (7-49 days) and their interactions on mycelial growth and deoxynivalenol (DON) production on irradiated wheat grain by two strains of Fusarium graminearum isolated from wheat ears in Argentina. Optimal a(W) levels for growth were in the range 0.950-0.995 with a temperature optima of 25 degrees C. Maximum growth rates were obtained at the highest a(W) (0.995) and 25 degrees C for both strains. No growth was observed at 5 degrees C regardless of the a(W) levels assayed. Both strains were able to growth at the lowest a(W) assayed (0.900), although the temperature ranges allowing growth at this minimal a(W) was 15-25 degrees C. DON was produced the most rapidly (7 days) when incubated at 25 degrees C and 0.995 a(W). All other conditions required 7-14 days before DON was produced on grain. Maximum amounts of DON for both strains were produced at the highest a(W) treatment (0.995) after 6 weeks at 30 degrees C. The range of DON concentrations varied considerably (5 to 140,000 ng g(-1)) depending on a(W) and temperature interaction treatments. Production of DON occurred over a narrower range of a(W) (0.995-0.95) than that for growth (0.995-0.90). DON was more rapidly produced at 25 degrees C but the maximum amount produced was at 30 degrees C. Two-dimensional profiles of a(W) x temperature were developed from these data to identify areas where conditions indicate a significant risk from DON accumulation.

Relationships Between Weather Conditions, Agronomic Practices, and Fermentation Characteristics with Deoxynivalenol Content in Fresh and Ensiled Maize

The deoxynivalenol (DON) content of maize silage was determined in samples collected at harvest and after ensiling in 2001 and 2002 from 30 to 40 Pennsylvania dairies. Information on cultural practices, hybrid maturity, planting, and harvest date was collected from each site. Site-specific weather data and a corn development model were used to estimate hybrid development at each site. Correlation analysis was used to assess the relationship between weather data, hybrid development, cultural practices and preharvest DON. Fermentation characteristics (moisture, pH, and so on) of ensiled samples were measured to study their relationship to postharvest DON contamination. No significant difference (P ≤ 0.05) was noted between the numbers of samples containing DON in 2001 and 2002, although concentration was higher in 2002 samples. A positive correlation was observed between DON concentration of harvest samples and daily average temperature, minimum temperature, and growing degree day during tasselling, silking, and milk stages. A negative correlation was observed between daily average precipitation at blister stage and DON concentration in harvest samples. Samples from no-till or minimum-till locations had higher DON concentrations than moldboard or mixed-till locations. Harvest samples had higher DON concentration than ensiled samples, suggesting that some physical, chemical, or microbiological changes, resulting from ensiling, may reduce DON in storage.

Processing and purity assessment of standards for the analysis of type-B trichothecene mycotoxins

The lack of reliable, certified calibrant solutions for the Fusarium mycotoxins deoxynivalenol (DON), 3-acetyl-DON (3-Ac-DON), 15-acetyl-DON (15-Ac-DON) and nivalenol (NIV) is a serious drawback in the already problematic area of trichothecene analysis. For this reason, purified DON, 3-Ac-DON, 15-Ac-DON and NIV standards were processed, the conditions required for their isolation and purification were optimised, and the crystalline toxins were thoroughly characterised. Several complimentary analytical methods were used to evaluate the identities of the mycotoxins and the types and amounts of impurities; results obtained from 1H and 13C NMR spectra, as well as from IR-spectra, were in agreement with the literature. Elemental analysis revealed that the isolated NIV occurs as monohydrate. If this is not known it results in a weighing error of approximately 5%. Differential scanning calorimetry (DSC) was only successful for 15-Ac-DON, as the other trichothecenes decomposed during measurements. No traces of chloride, nitrate and sulphate were found by means of ion chromatography (IC). As expected UV absorption spectra for DON, NIV, 3-Ac-DON and 15-Ac-DON yielded lambda(max) values of 216, 217, 217 and 219 nm, respectively. Minor peaks due to impurities were observed by high performance liquid chromatography (HPLC) with UV detection. The main impurity peak in the DON sample was identified by LC-tandem mass spectroscopy (LC-MS/MS) as 4,7-dideoxy-NIV (7-deoxy-DON), which occurs at levels of approximately 1.4%. Gas chromatography (GC) was performed, coupled with either an electron capture detector (ECD), a flame ionisation detector (FID), or a mass spectrometric detector (MS); however, derivatisation prior to GC analysis makes the estimation of impurities difficult. LC-MS/MS was found to be unsuitable for quantifying levels of impurities. It can be concluded that high-purity (>97%) B-trichothecene standards were successfully processed and fully characterised for the first time.

Influence of environmental factors on the biosynthesis of type B trichothecenes by isolates of Fusarium spp. from Spanish crops

Various species of Fusarium can produce trichothecene mycotoxins that contaminate food commodities and can represent a risk for human and animal health. In this paper, a full factorial design was applied to study the influence of incubation temperature, water activity (a(w)) and type of isolate on the production of deoxynivalenol (DON), nivalenol (NIV) and 3-acetyldeoxynivalenol (3-AcDON) in corn kernel cultures by three isolates of Fusarium graminearum and three isolates of Fusarium culmorum from crops grown in Spain. The tested temperatures were 15, 20, 28 and 32 degrees C. The a(w)-values were 0.960, 0.970 and 0.980. Moisture of cultures (within the studied range) did not affect significantly production of trichothecenes; however, the temperature affected significantly mycotoxin production and the optimal values were 28, 20 and 15 degrees C for DON, NIV and 3-AcDON, respectively. Four additional isolates of F. graminearum and two additional isolates of F. culmorum were examined for production of these mycotoxins at the optimal temperatures. Of the seven isolates of F. graminearum, four produced DON (0.88-3.97 microg/g), seven produced NIV (1.53-124 microg/g), and three produced 3-AcDON (0.65-10.6 microg/g). Of the five isolates of F. culmorum, four produced DON (1.20-4.93 microg/g), four produced NIV (6.94-701 microg/g), and four produced 3-AcDON (0.83-7.70 microg/g). Practically all isolates seem to belong to the NIV-chemotype. This is the first study done with regard to interaction between strain and ecological variables on type B trichothecene production by isolates of these two species from crops grown in Spain.

Identification by PCR of Fusarium culmorum strains producing large and small amounts of deoxynivalenol

Thirty deoxynivalenol-producing F. culmorum strains, isolated from wheat grains, were incubated in vitro and analyzed for trichothecene production. Seventeen strains produced more than 1 ppm of deoxynivalenol and acetyldeoxynivalenol and were considered high-deoxynivalenol-producing strains, whereas 13 F. culmorum strains produced less than 0.07 ppm of trichothecenes and were considered low-deoxynivalenol-producing strains. For all strains, a 550-base portion of the trichodiene synthase gene (tri5) was amplified and sequenced. According to the tri5 data, the F. culmorum strains tested clustered into two groups that correlated with in vitro deoxynivalenol production. For three high-producing and three low-producing F. culmorum strains, the tri5-tri6 intergenic region was then sequenced, which confirmed the two separate clusters within the F. culmorum strains. According to the tri5-tri6 sequence data, specific PCR primers were designed to allow differentiation of high-producing from low-producing F. culmorum strains.

Detection of trichothecenes in animal feeds and foodstuffs during the years 1997 to 2000 in Saudi Arabia

A total of 843 commercial animal feed and foodstuff samples (465 samples of agricultural commodities and 378 samples of animal feeds) from all over the Kingdom of Saudi Arabia were collected during the years 1997 to 2000 and analyzed for type A and type B trichothecenes (diacetoxyscirpenol, neosolaniol, HT-2 toxin, T-2 toxin, nivalenol, fusarenon-x, deoxynivalenol). Levels of mycotoxins detected ranged from <2 to 4,000 microg/kg deoxynivalenol, 3.25 to 500 microg/kg fusarenon-x, 3.13 to 600 microg/kg nivalenol, 3.13 to 50 microg/kg diacetoxyscirpenol, 6.25 to 200 microg/kg neosolaniol, 3.13 to 18.75 microg/kg HT-2 toxin, and 6.25 microg/kg T-2 toxin. The study reflected the need for routine surveillance of agricultural commodities to minimize potential hazards to human health.

Biosynthesis of Deoxynivalenol in Spikelets of Barley Inoculated with Macroconidia of Fusarium graminearum

This research examined the biosynthesis of deoxynivalenol (DON) and 15-acetyldeoxynivalenol (15-ADON) in barley spikelets inoculated with macroconidia of Fusarium graminearum (Group-II). Investigations were conducted to determine if these toxins were present in macroconidia of the pathogen prior to inoculating barley spikelets. Extracts of macroconidia cultured from mung bean agar were analyzed using gas chromatography-mass spectrometry. Neither DON or 15-ADON was detected in three isolates' macroconidia when compared with macroconidia-DON-matrix standards adjusted to 100, 200, 300, and 400 ng/g with a detection limit of 100 ng/g. Mean recovery of DON that was added to macroconidia was 89.5%. The same isolates were pathogenic on barley cultivars Robust (moderately susceptible) and Chevron (moderately resistant) and produced DON (0 to 3.69 ng/g) and 15-ADON (detected but not quantified) when grown in rice culture. Greenhouse experiments were performed to determine when DON and 15-ADON were detectable after inoculation and to quantify their amount in inoculated barley spikelets. The three isolates of F. graminearum were separately inoculated to a central spikelet on heads of barley cultivars Robust and Chevron. Both toxins were detected in spikelets 48 h postinoculation (PI). DON increased dramatically after 72 h and did not diminish thereafter. Accumulation of 15-ADON peaked at 72 to 120 h and decreased by 240 h PI. There were no statistical differences between cultivars or among fungal isolates for accumulation of either toxin when averaged over the time intervals. Differences of toxin accumulation at each sampling interval were significant (P < 0.0001) when averaged over isolates and cultivars. Spikelets of six cultivars and lines were sampled at inoculation and 18, 36, 54, 72, and 90 h PI. DON and 15-ADON were detected at 36 h PI, but differences among the cultivars and lines were not significant. Yield of DON in inoculated spikelets of 31 barley cultivars and lines at 72 h PI ranged from 0.14 to 1.26 μg per spikelet, and differences among the cultivars and lines were significant (P < 0.002). The data demonstrate a useful range of variability for toxin accumulation in inoculated spikelets among germ plasm in the Minnesota breeding program. Macroconidia with no detectable DON or 15-ADON could be used for in vitro studies of toxin biosynthesis. Establishing when DON and 15-ADON are synthesized facilitates studying the effects of promising fungicides, biocontrol organisms, and new or novel genetic resistance mechanisms and if or how they may prevent or delay the biosynthesis of toxins.

Determination of mycotoxins produced by Fusarium isolates from banana fruits by capillary gas chromatography and high-performance liquid chromatography

A method of analysis for trichothecenes (nivalenol, deoxynivalenol, 3- and 15-acetyldeoxynivalenol, diacetoxyscirpenol, neosolaniol, T-2 tetraol, T-2 and HT-2 toxins), zearalenone and zearalenols, and another method for determination of fumonisin B1 are described and applied to cultures of Fusarium isolated from bananas. Both methods were adapted from different techniques of extraction, clean-up and determination of these mycotoxins. The first method involves extraction with methanol-1% aqueous sodium chloride, clean-up of extracts by partition with hexane and dichloromethane, additional solid reversed-phase clean-up and analysis of two eluates by both high-performance liquid chromatography with ultraviolet detection and capillary gas chromatography. The method for fumonisin B1 implies extraction with aqueous methanol, concentration, clean-up with water and methanol on Amberlite XAD-2 column, formation of a fluorescent 4-fluoro-7-nitrobenzofurazan derivative and analysis by high-performance liquid chromatography with fluorescence detection. Both procedures give good limits of detection and recoveries, and are considered suitable for the detection and quantification of the studied toxins in corn and rice cultures of Fusarium spp. isolated from banana fruits.

Natural occurrence of Fusarium mycotoxins in field samples from the 1992 Wisconsin corn crop

Analysis of 98 moldy corn samples collected in Wisconsin between November 1992 and January 1993 for Fusarium toxins by various immunochemical assays revealed overall average mycotoxin concentrations of 305.6, 237.7, and 904.3 ng/g for type A trichothecenes (TCTCs), deoxynivalenol (DON)-related type B TCTCs (total DON), and zearalenone (ZE), respectively. A small portion (5.1%) of the samples was found to be contaminated with high levels ( > 1 microgram/g) of type A TCTCs and total DON during the whole survey. Over 40% of the samples had 100 to 1,000 ng of total DON per g, while 17% of the samples had the same levels of type A TCTCs. The analytical data were consistent with those from mycological examinations for the samples in which various toxic Fusarium spp., including F. sporotrichioides, F. poae, and F. graminearum, were found. The samples received in November 1992 had relatively low concentrations of toxin; the average levels of type A TCTCs and total DON were 9.9 and 79 ng/g, respectively. The toxin concentrations became progressively higher in the samples received in December. The average levels for the type A TCTCs and total DON increased to 920 and 335 ng/g, respectively. However, the levels of ZE were higher in the samples collected earlier. The average levels for samples collected in November and late December were 1,195 and 242 ng/g, respectively. Analysis of selected samples by high-performance liquid chromatography monitoring with an enzyme-linked immunosorbent assay revealed that T-2 toxin, HT-2 toxin, diacetoxyscirpenol, neosolaniol, and T-2 tetraol (T-2-4ol) were common in these samples. Statistical analysis revealed a weak correlation between the levels of total type A TCTCs and total DON in the samples (r = 0.18, P = 0.09), but a strong correlation between the levels of ZE and total type B TCTCs (r = 0.75, P < 0.0001) was found. The mycotoxin levels of total type A TCTCs, total DON-related type B TCTCs, and ZE in the cobs (5.2, 3.9, and 21 micrograms/g, respectively) were considerably higher than those in the kernels (1.0, 0.5, and 0.5 microgram/g, respectively). The type A toxin levels increased from a range of 14 to 35 ng/g to a range of 110 to 538 ng/g after the moldy corn samples were held at 5 degrees C for 8 days in the laboratory.

Toxin production by Fusarium species from sugar beets and natural occurrence of zearalenone in beets and beet fibers

Fifty-five Fusarium isolates belonging to nine species were collected from fungus-invaded tissue of stored sugar beets and identified as F. acuminatum (11 isolates), F. avenaceum (1 isolate), F. culmorum (1 isolate), F. equiseti (23 isolates), F. graminearum (4 isolates), F. oxysporum (1 isolate), F. solani (4 isolates), F. sporotrichioides (7 isolates), and F. subglutinans (2 isolates). All isolates were cultured on autoclaved rice grains and assayed for toxicity by feeding weanling female rats the ground-rice cultures of the isolates in a 50% mixture with a regular diet for 5 days. Fifty-eight percent of the isolates were acutely toxic to rats, 26% caused hematuria, 18% caused hemorrhages, and 29% caused uterine enlargement. In most cases, toxicity could not be accounted for by the known toxins found. The following mycotoxins were found in extracts of the rice cultures: zearalenone (22 to 6,282 micrograms/g), chlamydosporol (HM-8) (68 to 4,708 micrograms/g), moniliformin (45 to 400 micrograms/g), deoxynivalenol (10 to 34 micrograms/g), 15-acetyldeoxynivalenol (5 to 10 micrograms/g), diacetoxyscirpenol (22 to 63 micrograms/g), monoacetoxyscirpenol (21 to 26 micrograms/g), scirpenetriol (24 micrograms/g), T-2 toxin (4 to 425 micrograms/g), HT-2 toxin (2 to 284 micrograms/g), neosolaniol (2 to 250 micrograms/g), and T-2 tetraol (4 to 12 micrograms/g). F. equiseti was the predominant species found on visibly molded beets in the field. Six of 25 moldy sugar beet root samples collected in the field contained zearalenone in concentrations ranging between 12 and 391 ng/g, whereas 10 samples from commercial stockpiles were negative for zearalenone.(ABSTRACT TRUNCATED AT 250 WORDS)

[Occurrence of Fusarium strains and their mycotoxins on corn silage. 6. Formation of zearalenone and trichothecenes (type A) by indigenous Fusarium isolates]

A total of 399 indigenous Fusarium strains mainly isolated from silage maize were tested for the production of zearalenone and type A trichothecenes by thin-layer chromatography and biological assays. About 45% of the isolates examined were capable of producing different levels of zearalenone and trichothecene toxins on a cracked corn substrate. The majority of these strains (75%) produced zearalenone only and no trichothecenes type A. The results of the biological tests indicated a higher rate of toxin-positive extracts than chemical analysis. Isolates of nine out of seventeen Fusarium species examined produced one or several mycotoxins looked for. The most important toxin producers were F. culmorum and F. crookwellense (zearalenone) and F. sporotrichioides (trichothecenes type A), respectively. F. avenaceum, the species most frequently isolated from silage maize, produced neither zearalenone nor trichothecenes but avenacein Y a antibiotic compound. First results of a study of the production of type B trichothecenes have shown that indigenous F. culmorum isolates were capable of producing high levels of deoxynivalenol.

A survey on the occurrence of Fusarium mycotoxins in Bavarian cereals from the 1987 harvest

Bavarian cereals and wheat flour from the 1987 harvest were analysed for nivalenol (NIV) and deoxynivalenol (DON) using high performance liquid chromatography (HPLC) and for T-2 toxin and zearalenone (ZEA) by enzyme-linked-immunosorbent assay (ELISA). The study included 190 field samples of wheat, barley, rye and oat with visibly damaged ears, 45 samples of wheat intended for feed production and two series of wheat flour (type 550) and whole wheat flour collected in October 1987 and June 1988. The field samples examined showed a high DON contamination of wheat (87%) with an average of 3.96 mg/kg and a maximum of 43.8 mg/kg. Mean levels between 0.33 mg/kg and 0.27 mg/kg DON could be detected in barley, rye and oat. Of the wheat samples, 58% contained ZEA with a maximum of 1.560 mg/kg. The highest levels of ZEA were detected in samples which also showed high concentrations of DON. The NIV and T-2 toxin levels were comparatively low. Thirty percent of the samples showed NIV concentrations between 0.04 mg/kg and 0.29 mg/kg and 38% contained between 0.005 and 0.60 mg/kg of T-2. In the wheat samples for feed production, only DON was detected with an average of 0.190 mg/kg and a maximum of 0.75 mg/kg. The highest DON levels (0.58 mg/kg) from October 1987 were found in the wheat flour samples which were lower than the highest DON concentration (3.24 mg/kg) detected in the samples collected during June 1988. This fact was probably due to a substantial amount of non-contaminated wheat from 1986. The toxin concentrations in the whole wheat flour were not higher than in the type 550 flour.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in Deoxynivalenol, 15-Acetyldeoxynivalenol, 3-Acetyldeoxynivalenol, and Zearalenone Production by Fusarium graminearum Isolates

Of 88 isolates of Fusarium graminearum collected from soil or cereals in the United States, 49 produced 15-acetyldeoxynivalenol (15-ADON) as the major isomer; one produced 3-acetyldeoxynivalenol (3-ADON). A total of 26 isolates collected from cereals or soil in Australia, New Zealand, Norway, China, and Poland were used for comparison. Of these, 15 produced 3-ADON as the major isomer and 2 produced 15-ADON.

Influence of metabolic and physical factors on production of diacetoxyscirpenol by Fusarium sambucinum Fuckel

Fusarium sambucinum Fuckel 8099-1 was grown on Czapek-Dox peptone-supplemented medium at 15 degrees C for 14 days, and the cultures were investigated for diacetoxyscirpenol (DAS) production by liquid-liquid extraction and gas chromatography. The addition of 150 mg of sorbic acid, a tricarboxylic acid cycle inhibitor, per liter stimulated both fungal growth and DAS production. Among the beta-hydroxy-beta-methylglutaryl coenzyme A precursors tested, isovaleric acid completely inhibited fungal growth and DAS production, ethyl isovalerate did not support a significant increase in DAS production, and L-leucine partially inhibited DAS production, showing that L-leucine and isovaleric acid catabolisms do not induce trichothecene biosynthesis. Solid particles (cork powder) were necessary for DAS production in stationary cultures but did not influence DAS production in shaken cultures. Shaking strongly stimulated DAS production and fungal growth.

[The occurrence of Fusarium varieties and their mycotoxins in silo corn. 3. The effect of silaging on the zearalenone content of CCM corn]

The influence of silaging on zearalenone already formed and on the growth of Fusarium culmorum in naturally contaminated CCM maize was studied. The zearalenone content remained approximately constant (13.35 +/- 2.94 mg/kg, n = 59) over the whole test period (12 weeks), whereas Fusarium culmorum could not longer be detected after 11 days. Thus the hypothesis that zearalenone survives the silaging process unchanged is experimentally strongly supported. The study confirms the view that zearalenone detected in maize silages is probably already formed in the field or during intermediate storing. Relations between the fermentation process and the toxin content of the silage could not be ascertained.

Influence of water activity and temperature on the accumulation of zearalenone in corn

The influence of water activity (aw) and temperature on the zearalenone biosynthesis in corn has been examined. Viable corn kernels were conditioned at different values of water activity (0.90, 0.95 and 0.97), inoculated with Fusarium graminearum and incubated at different temperatures. Zearalenone was determined at selected times. For the strain used, a constant temperature of 25 degrees C resulted more favorable than 15 degrees C, 20 degrees C and the combination of two weeks at 25 degrees C followed by incubation at 15 degrees C shown by other authors to increase the zearalenone accumulation. Both F. graminearum growth and zearalenone production at 25 degrees C were inhibited at water activity 0.90. At short incubation times, toxin accumulation was greater at water activity 0.97 than at water activity 0.95 (25 degrees C). This relation was inverted at longer periods of incubation. A combined effect of water activity and temperature on the zearalenone accumulation was observed.

Production of mycotoxins by Fusarium species isolated in Germany. 2. Time course of deoxynivalenol and 3-acetyldeoxynivalenol formation by Fusarium graminearum in different liquid media

Several semisynthetic liquid media were examined for the large-scale production of deoxynivalenol (DON) und 3-acetyldeoxynivalenol (AcDON) by Fusarium graminearum 183. Only in three of the eight media used could high toxin yields of DON and AcDON be detected. The maximum levels of DON in a medium according to Miller were 3 mg/l and of AcDON 32 mg/l. In glucose-yeast extract-peptone (GYEP) medium containing 1% glucose, the AcDON concentrations reached 33 mg/l and the DON yields were 19 mg/l. In a rice flour liquid medium, however, the mean levels of AcDON and DON increased to 170 mg/l and 9 mg/l, respectively. The maximum amounts observed were 480 mg/l for AcDON and 65 mg/l for DON. The addition of trifluoracetic acid sodium salt or malonic acid, which are suggested to cause an accumulation of acetyl-CoA by inhibiting enzymes of the tricarboxylic acid cycle, did not stimulate the toxin formation.

Risk assessment of the mycotoxin zearalenone

Trans-zearalenone, a resorcylic acid lactone, also known as F-2 toxin, is a nonsteroidal estrogenic mycotoxin produced by numerous species of Fusarium. As a result zearalenone is found in a number of cereal crops and their derived food products. A closely related substance "zeranol" (zearalanol) is at present being used in the United States and Canada as an anabolic agent in beef cattle. Zearalenone has been implicated in numerous incidences of mycotoxicosis in farm animals, especially pigs. In this report the health risks to Canadians due to the presence of zearalenone in food products have been evaluated. The first part of the report deals with the physicochemical aspects, mycology, laboratory production, and natural occurrence in plant products and animal products of zearalenone. The stability of zearalenone in foods and feeds, the effects of food processing, and the removal from foods and feeds by physicochemical means are also discussed. From these data the daily exposure of Canadians to zearalenone from food consumption has been estimated to be in the range of 0.05-0.10 microgram/kg b.w./day (mean and 90th percentile of eaters, respectfully) for young children, the highest consumption group on a body weight basis. The second part of the report deals with the metabolic disposition of zearalenone as well as the available toxicity data base of zearalenone in laboratory animals, farm animals, and humans. Studies in various species (rodents, rabbits, pigs, monkeys) including man have shown that zearalenone has estrogenic and anabolic activity. Its major effects are on reproduction, including reproductive organs and their function, leading to hyperestrogenism. Zearalenone has been implicated in numerous incidences of hyperestrogenism in farm animals, especially pigs. For reproductive effects a no adverse effect level (NOAEL) of 0.06 mg/kg b.w./day was estimated for the pubertal pig, the most sensitive species tested. Important differences in the biotransformation of zearalenone were noted, with greater amounts of alpha-zearalenol, the more estrogenic metabolite, formed in man and the pig compared to rodents. In addition, the biological half-life of these substances was longer in man than in other species tested. The binding of zearalenone to estrogen receptors was approximately 20-fold lower than that seen with 17 beta-estradiol in several assays.(ABSTRACT TRUNCATED AT 400 WORDS)