Variation in 8-ketotrichothecenes and zearalenone production by Fusarium graminearum isolates from corn and barley in Korea

A total of 214 Fusarium graminearum isolates were obtained from corn and barley which were collected from Kangwon province and the southern part of Korea, respectively, and were tested for 8-ketotrichothecenes and zearalenone (ZEA) production on rice grains. The incidences of trichothecene production by 105 isolates of F. graminearum from corn were 59.0% for deoxynivalenol (DON), 37.1% for 15-acetyldeoxynivalenol(15-ADON), 13.3% for 3-acetyldeoxynivalenol (3-ADON), 7.6% for 3,15-diacetyldeoxynivalenol (3,15-DADON), 20.0% for nivalenol (NIV), 6.7% for 4-acetylnivalenol (4-ANIV), and 1.0% for 4,15-diacetylnivalenol (4,15-DANIV). DON chemotypes frequently produced 15-ADON as the major isomer rather than 3-ADON and 9 of the 61 DON chemotypes produced low levels of NIV. On the other hand, the incidences of trichothecene production of 109 isolates by F. graminearum from barley were 24.8% for DON, 72.5% for NIV, 62.4% for 4-ANIV, and 10.1% for 4,15-DANIV. Of these isolates, 78 were NIV chemotypes and only one isolate produced DON and 3-ADON as major toxins. In addition, 26 of the 78 NIV chemotypes produced low levels of DON. ZEA was frequently produced by the trichothecene-producing isolates and the incidences of ZEA were 51.4% and 31.2% for the isolates from corn and barley, respectively. There was a great regional difference in trichothecene production by F. graminearum isolates between corn- and barley-producing areas in Korea.     

Natural occurrence of Fusarium mycotoxins (trichothecenes and zearalenone) in barley and corn in Korea.

Barley is produced in four provinces, Chonbuk, Chonnam, Kyungbuk, and Kyungnam, and corn is mainly produced in the Kangwon province in Korea. The natural occurrence of Fusarium mycotoxins was surveyed in 39 barley and 46 corn samples from different areas. Five 8-ketotrichothecenes, namely deoxynivalenol (DON), nivalenol (NIV), 4-acetylnivalenol (4-ANIV), 3-acetyldeoxynivalenol (3-ADON), and 4,15-diacetylnivalenol (4,15-DANIV), and zearalenone (ZEA) were detected in barley. DON, NIV, and ZEA were the major contaminants in barley, with mean levels of 170, 1,011, and 287 ng/g, respectively. On the other hand, DON, 15-acetyldeoxynivalenol (15-ADON), NIV, 4-ANIV, 4,15-DANIV, and ZEA were detected in corn samples. DON and 15-ADON were the major contaminants in corn, with mean levels of 310 and 297 ng/g, respectively. The survey indicated that the natural occurrence of monoacetyl-DON and the ratios of NIV to DON in two cereals were different. In addition, this is the first report of the natural occurrence of 4,15-DANIV in cereals.     

Production of trichothecene mycotoxins byFusarium graminearum andFusarium culmorum on barley and wheat

Wheat cultivars (Stoa, MN87150, SuMai-3, YMI-6, Wheaton) and barley cultivars (Robust, Excel, Chevron, M69) were inoculated in the field with isolates ofFusarium graminearum andF. culmorum. The diseased (Fusarium head blight) kernels were analyzed for deoxynivalenol (DON), 15-acetyldeoxynivalenol (15-ADON) and nivalenol (NIV).F. culmorum produced all three trichothecenes on all cultivars tested whereasF. graminearum only produced DON and 15-ADON. There was no well defined correlation between DON production in the host and resistance although the data tended to favor SuMai-3 as having definitive resistance to bothF. graminearum andF. culmorum.Minnesota Agricultural Experiment Station, Paper No. 20 279.     

Characterisation of<Emphasis Type="Italic">fusarium graminearum</Emphasis> and<Emphasis Type="Italic">F. culmorum</Emphasis> isolates by mycotoxin production and aggressiveness to wheat

A total of 27Fusarium culmorum isolates from Germany and 41F. graminearum isolates from Kenya were investigated for aggressiveness and mycotoxin production on wheat ears. In addition, ergosterol content of the kernels from ears inoculated withF. graminearum was determined and theF. culmorum isolates were tested for mycotoxin productionin vitro. For both pathogens, isolates markedly differed in aggressiveness. 59% and 37% of theF. culmorum isolates produced NIV and DON, respectively,in vivo andin vitro. The DON-producing isolates also produced 3-acDONin vitro. The more aggressive isolates produced mainly DON while the less aggressive isolates produced mainly NIV. 12% and 85% of theF. graminearum isolates produced NIV and DON, respectively. The highly aggressive isolates produced higher amounts of DON, aggressiveness being highly correlated to DON content in the kernels. NIV-producing isolates were less aggressive. Ergosterol content of kernels was moderately correlated to aggressiveness but highly correlated to DON content. Disease severity was associated with kernel weight reduction.     

Wheat-infectingFusarium species in Poland — their chemotypes and frequencies revealed by PCR assay

ThreeFusarium species:F. graminearum, F. culmorum andF. cerealis were identified in laboratory cultures and in sporodochia from spikelets of scabby wheat. SCAR (sequence characterized amplified region) primers were used to identifyFusarium species and nivalenol (NIV) and deoxynivalenol (DON) chemotypes within species in laboratory cultures and field collected heads harvested in 2006. Results from PCR analyses confirmed preliminary identifications of species on the basis of examination of macroconidia under a light microscope and identification of cultures on agar media. NIV and DON (3Ac-DON and 15Ac-DON) chemotypes were identified using PCR assay. Among samples and isolates ofF. graminearum, the 15Ac-DON chemotype dominated, and among those whereF. culmorum was identified, the 3Ac-DON chemotype prevailed. Only 5 of the 41 isolates ofF. graminearum tested, displayed the NIV chemotype. An increase in the frequency ofF. graminearum and a decrease in the frequency ofF. culmorum were found during 1998 to 2006.     

Susceptibility of Barley Cultivars and Lines to Fusarium Infection and Mycotoxin Accumulation in Kernels

Heads of 12 barley genotypes (8 cultivars and 4 lines) were inoculated with conidial suspension of the following single isolates: F. culmorum no. 3, F. graminearum no. 122 and F. sporotrichioides no. ATCC 62 360. The number of kernels per head. 1000 Kernel weight and yield have been calculated for each genotype. Seed samples collected at harvest were analysed for each genotype. Seed samples collected at harvest were analysed for several trichothecene mycotoxins and zearalenone.The mycotoxin concentrations (mg/kg) in barley kernels inoculated with F. graminearum were as follows. deoxynivalenol (DON) 0.1 to 5.4 (av. 2.3). 3-acetyldeoxy-nivalenol (3-AcDON) 0.0–0.2 (av. 0.1), 15-acetyldeoxynivalenol (15-AcDON) 0.0–0.7 (av.0.2), nivalenol (NIV) 0.0–0.8 (av. 0.3). zearalenone (ZEA) 0.0–0.1 (av. 0.0); F. culmorum: DON 0.6 to 12.0 (av. 5.3), 3-AcDON 0.1 to 1.0 (av. 0.6). 15-AcDON nd. NIV 0.1–0.7 (av. 0.3). ZEA 0.1–0.5 (av. 0.2). F. sporotrichioides T-2 toxin 2.4–13.9 (av. 6.0), HT-2-toxin 0.1–0.8 (av.0.3) and neosolaniol 0.2–1.5 (av.0.7).     

Mycotoxigenic potential of fungi isolated from freshly harvested Argentinean blueberries

Alternaria alternata, A. tenuissima, Fusarium graminearum, F. semitectum, F. verticillioides, Aspergillus flavus, and Aspergillus section Nigri strains obtained from blueberries during the 2009 and 2010 harvest season from Entre Ríos, Argentina were analyzed to determine their mycotoxigenic potential. Taxonomy status at the specific level was determined both on morphological and molecular grounds. Alternariol (AOH), alternariol monomethyl ether (AME), aflatoxins (AFs), zearalenone (ZEA), fumonisins (FBs), and ochratoxin A (OTA) were analyzed by HPLC and the trichotecenes deoxynivalenol (DON), nivalenol (NIV), HT-2 toxin (HT-2), T-2 toxin (T-2), fusarenone X (FUS-X), 3-acetyl-deoxynivalenol (3-AcDON), and 15-acetyl-deoxynivalenol (15-AcDON) by GC. Twenty-five out of forty two strains were able to produce some of the mycotoxins analyzed. Fifteen strains of Aspergillus section Nigri were capable of producing Fumonisin B₁ (FB₁); two of them also produced Fumonisin B₂ (FB₂) and one Fumonisin B₃ (FB₃). One of the F. graminearum isolated produced ZEA, HT-2, and T-2 and the other one was capable of producing ZEA and DON. Two A. alternata isolates produced AOH and AME. Four A. tenuissima were capable of producing AOH and three of them produced AME as well. One Aspergillu flavus strain produced aflatoxin B₁ (AFB₁), aflatoxin B₂ (AFB₂), and aflatoxin G₁ (AFG₁). To our knowledge, this is the first report showing mycotoxigenic capacity of fungal species isolated from blueberries that include other fungi than Alternaria spp.     

Chemotyping of Fusarium graminearum and F. culmorum Isolates from Turkey by PCR Assay

Fusarium graminearum and F. culmorum are the major causal agents of Fusarium head blight in Turkey. They produce trichothecenes such as deoxynivalenol (DON), nivalenol (NIV) and their several acetylated derivatives, 3-acetyldeoxynivalenol (3-ADON) and 15-acetyldeoxynivalenol (15-ADON). In this study, a total of thirty-three isolates of F. graminearum and F. culmorum were collected from various regions and three different hosts. They were identified by amplification of tri5 gene cluster. Totally 32 isolates, 21 of F. culmorum and 11 of F. graminearum, were determined as DON chemotype, while only one F. graminearum isolate (1F) was detected as a NIV. A 282 base pair (bp) band for tri13 gene and also ranging from 458 to 535 bp bands for tri7 gene were amplified in all DON producers’ genomes. Further analysis of DON chemotype based on tri3 gene amplification showed that all isolates of F. graminearum displayed 15-ADON sub-chemotype. They yielded a 863 bp amplicon. Similarly, 3-ADON sub-chemotype was identified in F. culmorum’ isolates except F13. As a result of tri3 gene assay, it was produced a 583 bp fragment in these twenty isolates. It is the first report that a F. graminearum isolate depicts NIV chemotype in agricultural regions of Turkey. According to our findings, DON chemotype is predominating in our country. Also, it is presented that most of the F. graminearum isolates have 15-ADON sub-chemotype, while all F. culmorum’s belong to 3-ADON which possess full length amplicon of tri7 gene.     

Trichothecene production by Fusarium species isolated from grain and pasture throughout New Zealand

Liquid cultures of 200 Fusarium isolates selected to represent the most common species found in autumn pasture (70 isolates) and in grain (130 isolates) grown in New Zealand were analysed for trichothecenes and related compounds. Production of butenolide, cyclonerodiol derivatives and culmorins was also measured. The principal trichothecenes produced were derivatives of either nivalenol (NIV), deoxynivalenol (DON) or scirpentriol (Sctol), in order of frequency. The principal trichothecene producing species were F. crookwellense, F. culmorum and F. graminearum. Isolates of the first two species were predominantly NIV-chemotypes with one or two isolates respectively as Sctol-chemotypes. F. graminearum showed equal quantities of NIV- and DON-chemotypes, with the DON-chemotypes producing primarily 15-acetyldeoxynivalenol (15-ADON).     

Tri13 and Tri7 Determine Deoxynivalenol- and Nivalenol-Producing Chemotypes of Gibberella zeae

Gibberella zeae, a major cause of cereal scab, can be divided into two chemotypes based on production of the 8-ketotrichothecenes deoxynivalenol (DON) and nivalenol (NIV). We cloned and sequenced a Tri13 homolog from each chemotype. The Tri13 from a NIV chemotype strain (88-1) is located in the trichothecene gene cluster and carries an open reading frame similar to that of Fusarium sporotrichioides, whereas the Tri13 from a DON chemotype strain (H-11) carries several mutations. To confirm the roles of the Tri13 and Tri7 genes in trichothecene production by G. zeae, we genetically altered toxin production in 88-1 and H-11. In transgenic strains, the targeted deletion of Tri13 from the genome of 88-1 caused production of DON rather than NIV. Heterologous expression of the 88-1 Tri13 gene alone or in combination with the 88-1 Tri7 gene conferred on H-11 the ability to synthesize NIV; in the latter case, 4-acetylnivalenol (4-ANIV) also was produced. These results suggest that Tri13 and Tri7 are required for oxygenation and acetylation of the oxygen at C-4 during synthesis of NIV and 4-ANIV in G. zeae. These functional analyses of the Tri13 and Tri7 genes provide the first clear evidence for the genetic basis of the DON and NIV chemotypes in G. zeae.     

Nivalenol and 15‐acetyldeoxynivalenol Chemotypes of Fusarium graminearum Clade Species are Prevalent on Maize throughout China

Fusarium graminearum clade species are among the main causative agents of Gibberella ear rot (GER) in maize and responsible for the various trichothecene mycotoxins accumulated in contaminated maize grains. In this study, a total of 620 isolates from diseased maize ears collected from 59 districts in 19 provinces throughout China, previously identified morphologically as Fusarium graminearum clade, was genetically characterized at the species level based on SCAR (Sequence Characterized Amplified Region) and for their potential capability of mycotoxin production using the genetic chemotyping assay. The results showed that 359 isolates were F. asiaticum (SCAR 5), which consisted of 97% nivalenol (NIV)‐chemotypes, 0.8% 3‐acetyldeoxynivalenol (3‐ADON)‐producing isolates and 2.2% 15‐acetyldeoxynivalenol (15‐ADON) producers, whereas the remaining 261 isolates were identified as F. graminearum sensu stricto (SCAR 1), all of which produced 15‐ADON mycotoxins. This high proportion of NIV producers present in F. asiaticum is different from the chemotype patterns in F. asiaticum populations isolated from wheat and barley, where DON and its acetylated chemotypes were the predominant mycotoxins. Moreover, the majority of NIV producers (59.1%) and all the 3‐ADON‐producing strains were derived from the warmer regions in southern China, whereas most of the 15‐ADON‐producing strains (78.4%) were isolated from the colder regions in northern China. Our study is the first report of NIV chemotypes of F. asiaticum and 15‐ADON chemotypes of F. graminearum sensu stricto that were associated with the GER of maize in China.     

Mycological survey of Korean cereals and production of mycotoxins by Fusarium isolates

The fungal species isolated from Korean cereals (barley, polished barley, wheat, rye, and malt) were Alternaria spp., Aspergillus spp., Chaetomium spp., Drechslera spp., Epicoccum sp., Fusarium spp., and Penicillium spp., etc. The number of Fusarium strains isolated was 36, and their ability to produce Fusarium mycotoxins on rice was tested. Nivalenol (NIV) was produced by Fusarium graminearum (7 of 9 isolates), Fusarium oxysporum (3 of 10 isolates), and Fusarium spp. (7 of 15 isolates). Of 15 isolates of Fusarium spp., 6 formed deoxynivalenol (DON). Fusarenon-X and 3-acetyl-DON were produced by most NIV- and DON-forming isolates, respectively. Zearalenone was produced by 3 isolates of F. graminearum, 1 isolate of Fusarium equiseti, and 11 isolates of Fusarium spp. T-2 toxin was not produced by any Fusarium isolates. The highest concentrations of mycotoxins produced by Fusarium isolates were 77.4 (NIV), 5.3 (DON), 138.3 (fusarenon-X), 40.6 (3-acetyl-DON), and 23.2 (zearalenone) micrograms/g.     

Mycological survey of Korean cereals and production of mycotoxins by Fusarium isolates.

The fungal species isolated from Korean cereals (barley, polished barley, wheat, rye, and malt) were Alternaria spp., Aspergillus spp., Chaetomium spp., Drechslera spp., Epicoccum sp., Fusarium spp., and Penicillium spp., etc. The number of Fusarium strains isolated was 36, and their ability to produce Fusarium mycotoxins on rice was tested. Nivalenol (NIV) was produced by Fusarium graminearum (7 of 9 isolates), Fusarium oxysporum (3 of 10 isolates), and Fusarium spp. (7 of 15 isolates). Of 15 isolates of Fusarium spp., 6 formed deoxynivalenol (DON). Fusarenon-X and 3-acetyl-DON were produced by most NIV- and DON-forming isolates, respectively. Zearalenone was produced by 3 isolates of F. graminearum, 1 isolate of Fusarium equiseti, and 11 isolates of Fusarium spp. T-2 toxin was not produced by any Fusarium isolates. The highest concentrations of mycotoxins produced by Fusarium isolates were 77.4 (NIV), 5.3 (DON), 138.3 (fusarenon-X), 40.6 (3-acetyl-DON), and 23.2 (zearalenone) micrograms/g.     

Geographic distribution of phylogenetic species of the <Emphasis Type="Italic">Fusarium graminearum</Emphasis> species complex and their 8-ketotrichothecene chemotypes on wheat spikes in Iran

Isolates of the Fusarium graminearum species complex (FGSC, n = 446) were collected from wheat spikes from northern and western regions of Iran with a history of Fusarium head blight (FHB) occurrences. The trichothecene mycotoxin genotypes/chemotypes, the associated phylogenetic species, and geographical distribution of these isolates were analyzed. Two phylogenetic species, Fusarium asiaticum and F. graminearum, were identified and were found to belong to sequence characterized amplified region (SCAR) groups V and I. Isolates from F. asiaticum species lineage 6 were within SCAR group V, whereas F. graminearum species lineage 7 were of SCAR group I. Of the 446 isolates assayed, 274 were F. asiaticum species predominantly of the nivalenol (NIV) genotype, while other isolates were either deoxynivalenol (DON) plus 3-acetyldeoxynivalenol (3-AcDON) or DON plus 15-acetyldeoxynivalenol (15-AcDON) genotype. Based on Tri7 gene sequences, a new subpopulation of 15-AcDON producers was observed among F. asiaticum strains in which 11-bp repeats were absent in the Tri7 sequences. The trichothecene chemotype was confirmed and quantified by high-performance liquid chromatography (HPLC) in 46 FGSC isolates. Isolates produced NIV (33.4–108.2 μg/g) and DON (64.7–473.6 μg/g) plus either 3-AcDON (51.4–142.4 μg/g) or 15-AcDON (24.1–99.3 μg/g). Among FGSC isolates, F. asiaticum produced the highest levels of trichothecenes. Using BIOCLIM based on the climate data of 20-year during 1994–2014, modelling geographical distribution of FGSC showed that F. asiaticum was restricted to warmer and humid areas with a median value of mean annual temperature of about 17.5 °C and annual rainfall of 658 mm, respectively (P < 0.05). In contrast, F. graminearum (only 15-AcDON producers) was restricted to cooler and drier areas, with a median value of the mean annual temperature of 14.4 °C and an annual rainfall of 384 mm, respectively (P < 0.05). Based on climate parameters at anthesis, the recorded distribution of F. graminearum and F. asiaticum was similar to that based on BIOCLIM parameters. Therefore, geographic differences on the wheat-growing areas in Iran have had a significant effect on distribution of FGSC and their trichothecene chemotypes.     

Genetic Diversity and Fitness of Fusarium graminearum Populations from Rice in Korea

Fusarium graminearum is an important fungal pathogen of cereal crops and produces mycotoxins, such as the trichothecenes nivalenol and deoxynivalenol. This species may be subdivided into a series of genetic lineages or phylogenetic species. We identified strains of F. graminearum from the Republic of Korea to lineage, tested their ability to produce nivalenol and deoxynivalenol, and determined the genetic composition and structure of the populations from which they were recovered. Based on amplified fragment length polymorphism (AFLP), PCR genotyping, and chemical analyses of trichothecenes, all 249 isolates from southern provinces belonged to lineage 6, with 241 having the nivalenol genotype and 8 having the deoxynivalenol genotype. In the eastern Korea province, we recovered 84 lineage 6 isolates with the nivalenol genotype and 23 lineage 7 isolates with the deoxynivalenol genotype. Among 333 lineage 6 isolates, 36% of the AFLP bands were polymorphic, and there were 270 multilocus haplotypes. Genetic identity among populations was high (>0.972), and genotype diversity was low (30 to 58%). To test the adaptation of lineage 6 to rice, conidial mixtures of strains from lineages 3, 6, and 7 were inoculated onto rice plants and then recovered from the rice grains produced. Strains representing lineages 6 and 7 were recovered from inoculated spikelets at similar frequencies that were much higher than those for the strain representing lineage 3. Abundant perithecia were produced on rice straw, and 247 single-ascospore isolates were recovered from 247 perithecia. Perithecia representing lineage 6 (87%) were the most common, followed by those representing lineage 7 (13%), with perithecia representing lineage 3 not detected. These results suggest that F. graminearum lineage 6 may have a host preference for rice and that it may be more fit in a rice agroecosystem than are the other lineages present in Korea.Fusarium graminearum (teleomorph: Gibberella zeae) causes head blight of small grains, including rice, wheat, and barley (23). The fungus was first reported on rice in Italy by Cattaneo (4) as Botryosphaeria saubinetii Niessland. This rice disease has since been recorded in other countries, including Brazil, China, India, Japan, Nepal, and Uganda (11, 31). The disease usually does not cause heavy damage, but under conditions that favor disease development, e.g., high humidity, it may be severe. Chung et al. (7) found that an isolate from wheat could infect rice and other plants and also could cause a postemergence blight in rice. Wheat isolates of F. graminearum can cause significant disease on rice, but under greenhouse conditions no trichothecenes were detected in the infected rice florets (14). In addition, Nepalese rice contained no detectable contamination with trichothecenes even though F. graminearum occurs in Nepal (11).The fungus can produce the 8-ketotrichothecene mycotoxins nivalenol (NIV) and deoxynivalenol (DON). Most of the biosynthetic genes for the synthesis of 8-ketotrichothecenes are tightly linked in the TRI gene cluster (9). TRI7 and TRI13 are required for acetylation and oxygenation of the oxygen at C-4 to produce NIV and 4-acetyl nivalenol (4-ANIV), respectively, from DON. PCR-based methods to identify polymorphisms in both genes were developed as simple, reliable diagnostic tools for differentiating strains with DON and NIV chemotypes (20, 21). There are regional differences in the distribution of the two chemotypes. Maize and wheat in North America and Europe commonly are contaminated with DON (9), while strains with NIV chemotypes are commonly recovered from cereal crops in Asia (15, 17). In the Republic of Korea, strains with the DON chemotype often cause maize ear rot, while strains with the NIV chemotype commonly are recovered from barley (17, 35). A severe epidemic of Fusarium head blight on wheat and barley occurred in 1963 in southern Korea (5, 6). Humans and farm animals consuming moldy cereals exhibited typical signs of trichothecene intoxication involving vomiting, dizziness, nausea, abnormal pain, and diarrhea (9). The natural occurrence of NIV and DON has been reported in barley and maize in Korea (17, 35, 41), but there have been few surveys of Fusarium mycotoxins in Korean rice.O''Donnell et al. (30) divided F. graminearum into seven phylogenetic lineages based on the genealogical concordance of six genes. The phylogenetic separation has been used to raise these seven and four additional lineages to species status (36). The geographic location often influences the lineage present, e.g., lineage 7 is the most common in the United States, and lineage 6 dominates in China. Lineage and trichothecene chemotype are not correlated (45), and the lineages are morphologically cryptic. Members of all lineages are cross-fertile with strains belonging to lineage 7 and in some cases with strains of other lineages (1, 2, 19, 25), a pattern that suggests that the members of all of the lineages belong to a single biological species.Studies of F. graminearum populations have been made in different geographic regions, e.g., China (12), Europe (42), the United States (48, 49), and Argentina (34). Populations of F. graminearum have high levels of genotypic diversity, which suggests that recombination occurs regularly in F. graminearum populations. Most studies have focused on populations from wheat, barley, and corn, and there is little information on F. graminearum populations from rice.Severe epidemics of Fusarium head blight of rice occurred in August 2001 after heavy rainfall during the rice flowering period in southern Korea. Lesions on or discoloration of the glumes were common, with infected grains first appearing to be white and later yellow, salmon, or carmine. Sometimes the entire seed was colonized. Infected grains were lightweight, shrunken, and brittle. Our objectives in the present study were (i) to determine the frequency at which F. graminearum occurs in plants with rice head blight; (ii) to determine the number and relative frequency of the F. graminearum lineages present; and (iii) to evaluate the strains for their sexual fertility, genetic relatedness, virulence, and toxin-producing abilities. Our working hypotheses were that sexually fertile strains from lineage 6 would dominate in the population and that these strains would be the most aggressive toward rice. We expected most of the lineage 6 strains to produce NIV and for there to be a high level of genetic variation, as assessed by neutral (amplified fragment length polymorphism [AFLP]) markers. We evaluate here F. graminearum population diversity in Korea and provide new information on the pathogenic capabilities of strains belonging to several of the known lineages of this very widespread fungal species.     

Tri13 and Tri7 determine deoxynivalenol- and nivalenol-producing chemotypes of Gibberella zeae

Gibberella zeae, a major cause of cereal scab, can be divided into two chemotypes based on production of the 8-ketotrichothecenes deoxynivalenol (DON) and nivalenol (NIV). We cloned and sequenced a Tri13 homolog from each chemotype. The Tri13 from a NIV chemotype strain (88-1) is located in the trichothecene gene cluster and carries an open reading frame similar to that of Fusarium sporotrichioides, whereas the Tri13 from a DON chemotype strain (H-11) carries several mutations. To confirm the roles of the Tri13 and Tri7 genes in trichothecene production by G. zeae, we genetically altered toxin production in 88-1 and H-11. In transgenic strains, the targeted deletion of Tri13 from the genome of 88-1 caused production of DON rather than NIV. Heterologous expression of the 88-1 Tri13 gene alone or in combination with the 88-1 Tri7 gene conferred on H-11 the ability to synthesize NIV; in the latter case, 4-acetylnivalenol (4-ANIV) also was produced. These results suggest that Tri13 and Tri7 are required for oxygenation and acetylation of the oxygen at C-4 during synthesis of NIV and 4-ANIV in G. zeae. These functional analyses of the Tri13 and Tri7 genes provide the first clear evidence for the genetic basis of the DON and NIV chemotypes in G. zeae.     

Pathogenicity of Fusarium graminearum Chemotypes Towards Corn, Wheat, Triticale and Rye

The pathogenicity of nine Fusarium graminearum isolates belonging to three different trichothecene-producing chemotypes, i.e. NIV + FUS, DON + 3-AcDON, and DON + 15-AcDON was tested on corn, wheat, triticale and rye. Although these compounds are known to have different toxicity, no difference in pathogenicity was observed among the mean values for chemotypes. However, within each chemotype there were isolates with different pathogenicity which was not correlated with the ability to produce trichothecenes in vitro. The pathogenicity of each isolate was almost the same for all tested cereals. The involvement of trichothecenes in pathogenesis was investigated in infected corn stalk tissues. All the expected trichothecenes were detected with the exception of NIV and FUS.     

Chemotaxonomic diagnostics: combining sucrose-water agar with TLC to discriminate <Emphasis Type="Italic">Fusarium graminearum</Emphasis> 3-acetyl-DON and 15-acetyl-DON chemotypes

Twelve randomly-selected isolates of Fusarium graminearum that produce 3-acetyl-deoxynivalenol (3-ADON) or 15-acetyl-deoxynivalenol (15-ADON) were screened by thin-layer chromatography (TLC) for their ability to produce ADON and zearalenone (ZEA) mycotoxins when grown on water agar containing different concentrations of sucrose. The results showed the ability of the F. graminearum 3-ADON chemotype population to produce DON and ZEA at a lower concentration range of sucrose (5-7%) compared with the 15-ADON chemotype (30-40%). The former distinction allows for sucrose-water agar to be employed as a rapid and simple differential medium, where two separate sucrose-gradient concentrations discriminate 3-ADON from 15-ADON populations. In the light of the shift in sugar concentrations occurring during the process of grain formation and maturation, the difference in mycotoxin production between the two populations is discussed with respect to predicting Fusarium head blight (FHB) epidemiology and accumulation of DON and ZEA.     

Natural Occurrence of 16 Fusarium Toxins in Grains and Feedstuffs of Plant Origin from Germany

A total of 220 samples comprising cereals, cereal byproducts, corn plants and corn silage as well as non-grain based feedstuffs was randomly collected during 2000 and 2001 from sources located in Germany and analysed for 16 Fusarium toxins. The trichothecenes scirpentriol (SCIRP), 15-monoacetoxyscirpenol (MAS), diacetoxyscirpenol (DAS), T-2 tetraol, T-2 triol, HT-2 and T-2 toxin (HT-2, T-2), neosolaniol (NEO), deoxynivalenol (DON), 3-acetyldeoxynivalenol (3-ADON), 15-acetyldeoxynivealenol (15-ADON), nivalenol (NIV) and fusarenon-X (FUS-X) were determined by gas chromatography/mass spectrometry. Zearalenone (ZEA) and α- and β-zearalenol (α- and β-ZOL) were analysed by high performance liquid chromatography with fluorescence and UV-detection. Detection limits ranged between 1 and 19 μg/kg. Out of 125 samples of a group consisting of wheat, oats, corn, corn byproducts, corn plants and corn silage only two wheat samples did not contain any of the toxins analysed. Based on 125 samples the incidences were at 2–11% for DAS, NEO, T-2 Triol, FUS-X, α- and β-ZOL, at 20–22% for SCIRP, MAS, T-2 tetraol and 3-ADON, at 44–74% for HT-2, T-2, 15-ADON, NIV and ZEA, and at 94% for DON. Mean levels of positive samples were between 6 and 758 μg/kg. Out of 95 samples of a group consisting of hay, lupines, peas, soya meal, rapeseed meal and other oilseed meals, 64 samples were toxin negative. DAS, T-2 triol, NEO and FUS-X were not detected in any sample. The incidences of DON and ZEA were at 14 and 23% respectively, those of the other toxins between 1–4%, mean levels of positive samples were between 5 and 95 μg/kg.     

Cumulation of mycotoxins in maize cobs infected with<Emphasis Type="Italic">Fusarium gramihearum</Emphasis>

Maize cobs withFusarium ear rot were collected at 1986 season and five infected byFusarium graminearum were analyzed for presence of triohothecenes and zearalenone. Collected material was subsampled forFusarium damaged kernels and corresponding axial stems and healthy looking kernels. All investigated cobs contained deoxynivalenol (DON) (range 18.0–131.5 mg/kg) and zearalenone (ZEA) (range 0.38–2.17 mg/kg), in four cobs 15-acetyl-deoxynivalenol (15-AcDON) (range 5.2–6.2 mg/kg) was present and two cobs besides three all metabolites contained 3-acetyl-deoxynivalenol (3-AcD0N) (range 0.5–0.8 mg/kg).The average of individual toxins amount in axial stems: in mg/kg was equal to: DON — 110.36, ZEA — 4.57, 15-AcD0N — 16.66, and 3-AcD0N — 1.32.Fusarium damaged kernels contained in average the following amount (mg/kg) of: DON 77.00, ZEA 0.98, 15-AcD0N 3.78 and 3-AcD0N 0.06. Healthy looking kernels contained DON 1.96 mg/kg and ZEA 0.07 mg/kg only. Cooccurrence of 3-AcDON and 15-AcDON in two samples was an interesting finding. The amount of DON in total cob was highly correlated (r = 0.94) with percentage ofFusarium damaged kernels in given ear.