Use of the volatile trichodiene to reduce Fusarium head blight and trichothecene contamination in wheat

Fusarium graminearum is the primary cause of Fusarium head blight (FHB), one of the most economically important diseases of wheat worldwide. FHB reduces yield and contaminates grain with the trichothecene mycotoxin deoxynivalenol (DON), which poses a risk to plant, human and animal health. The first committed step in trichothecene biosynthesis is formation of trichodiene (TD). The volatile nature of TD suggests that it could be a useful intra or interspecies signalling molecule, but little is known about the potential signalling role of TD during F. graminearum-wheat interactions. Previous work using a transgenic Trichoderma harzianum strain engineered to emit TD (Th + TRI5) indicated that TD can function as a signal that can modulate pathogen virulence and host plant resistance. Herein, we demonstrate that Th + TRI5 has enhanced biocontrol activity against F. graminearum and reduced DON contamination by 66% and 70% in a moderately resistant and a susceptible cultivar, respectively. While Th + TRI5 volatiles significantly influenced the expression of the pathogenesis-related 1 (PR1) gene, the effect was dependent on cultivar. Th + TRI5 volatiles strongly reduced DON production in F. graminearum plate cultures and downregulated the expression of TRI genes. Finally, we confirm that TD fumigation reduced DON accumulation in a detached wheat head assay.     

Tri16 is required for esterification of position C-8 during trichothecene mycotoxin production by Fusarium sporotrichioides

We previously characterized Tri1, a gene required for hydroxylation of the C-8 position during trichothecene mycotoxin biosynthesis in Fusarium sporotrichioides NRRL 3299. Sequence analysis of the region surrounding Tri1 revealed a gene, named Tri16, which could encode an acyltransferase. Unlike the wild-type parent strain NRRL 3299, which accumulates primarily T-2 toxin along with low levels of diacetoxyscirpenol (DAS) and neosolaniol (NEO) and trace amounts of 8-propionyl-neosolaniol (P-NEO) and 8-isobutyryl-neosolaniol (B-NEO), mutants containing a disruption of Tri16 were blocked in the production of the three C-8 esterified compounds T-2 toxin, P-NEO, and B-NEO and accumulated the C-8-hydroxylated compound NEO along with secondary levels of DAS. These data indicate that Tri16 encodes an acyltransferase that catalyzes the formation of ester side groups at C-8 during trichothecene biosynthesis. We also report the presence of a Tri16 ortholog in Gibberella pulicaris R-6380 that is likely linked to a presumably inactive ortholog for Tri1.     

Patterns of mycotoxin production by Fusarium gmminearum isolated from Argentine wheat

Fusarium graminearum was isolated from several wheat samples of the 1985/86 Argentine crop, taken from lots that had suffered extensive invasion by this fungus. Previous chemical analysis of the cereal, had revealed contamination with deoxynivalenol (DON), but the presence of the other mycotoxins could not be excluded with certainty, due to the low sensitivity of the analytical methodology employed.Twenty four F. graminearum isolates were grown on white corn with 50% water, for 21 days at 28 °C, or in liquid medium (Sucrose 3%, Peptone 0,1% and Yeast Extract 0,1%) for 7 days at 28 °C without shaking, and tested for the production of mycotoxins. Eight isolates (33% of the total) were found to produce toxins in one or both media. Toxins detected were: DON (6 isolates), 15-AcetylDON (5), 3-AcetylDON (2) and Zearalenone (3). No traces of Nivalenol, Fusarenon-X or other trichothecenes were found.These results suggest that strains of F. graminearum, prevailing in Argentine wheat-growing regions, might belong to the DON/AcetylDON chemotype, since no organisms of the Nivalenol/Fusarenon-X chemotype were detected in this study.     

The ability to detoxify the mycotoxin deoxynivalenol colocalizes with a major quantitative trait locus for Fusarium head blight resistance in wheat

We investigated the hypothesis that resistance to deoxynivalenol (DON) is a major resistance factor in the Fusarium head blight (FHB) resistance complex of wheat. Ninety-six double haploid lines from a cross between 'CM-82036' and 'Remus' were examined. The lines were tested for DON resistance after application of the toxin in the ear, and for resistances to initial infection and spread of FHB after artificial inoculation with Fusarium spp. Toxin application to flowering ears induced typical FHB symptoms. Quantitative trait locus (QTL) analyses detected one locus with a major effect on DON resistance (logarithm of odds = 53.1, R2 = 92.6). The DON resistance phenotype was closely associated with an important FHB resistance QTL, Qfhs.ndsu-3BS, which previously was identified as governing resistance to spread of symptoms in the ear. Resistance to the toxin was correlated with resistance to spread of FHB (r = 0.74, P < 0.001). In resistant wheat lines, the applied toxin was converted to DON-3-O-glucoside as the detoxification product. There was a close relation between the DON-3-glucoside/DON ratio and DON resistance in the toxin-treated ears (R2 = 0.84). We conclude that resistance to DON is important in the FHB resistance complex and hypothesize that Qfhs.ndsu-3BS either encodes a DON-glucosyl-transferase or regulates the expression of such an enzyme.     

Marker-assisted characterization of Asian wheat lines for resistance to Fusarium head blight

The major quantitative trait locus (QTL) on 3BS from Sumai 3 and its derivatives has been used as a major source of resistance to Fusarium head blight (FHB) worldwide, but resistance genes from other sources are necessary to avoid complete dependence on a single source of resistance. Fifty-nine Asian wheat landraces and cultivars differing in the levels of FHB resistance were evaluated for type II FHB resistance and for genetic diversity on the basis of amplified fragment length polymorphism (AFLP) and simple sequence repeats (SSRs). Genetic relationships among these wheat accessions estimated by cluster analysis of molecular marker data were consistent with their geographic distribution and pedigrees. Chinese resistant landraces had broader genetic diversity than that of accessions from southwestern Japan. The haplotype pattern of the SSR markers that linked to FHB resistance quantitative trait loci (QTLs) on chromosomes 3BS, 5AS and 6BS of Sumai 3 suggested that only a few lines derived from Sumai 3 may carry all the putative QTLs from Sumai 3. About half of the accessions might have one or two FHB resistance QTLs from Sumai 3. Some accessions with a high level of resistance, may carry different FHB resistance loci or alleles from those in Sumai 3, and are worth further investigation. SSR data also clearly suggested that FHB resistance QTLs on 3BS, 5AS, and 6BS of Sumai 3 were derived from Chinese landrace Taiwan Xiaomai.     

In vitro assessment of Fusarium head blight spp. on wheat cultivars

Aggressiveness in four isolates of Fusarium head blight (FHB) species (F. culmorum, F. solani, F. verticillioides and F. equiesti) was studied in vitro on six wheat cultivars using a modified Petri-dish test. Results showed differences between cultivars inoculated with FHB isolates and control for three aggressiveness criteria: germination rate reduction, standardised area under disease progress curve (AUDPC_standard), and coleoptile length reduction. Regarding AUDPC_standard and Petri-dish aggressiveness index, significant differences were detected among fungal isolates. The other two aggressiveness criteria: germination rate reduction and coleoptile length reduction did not distinguish between FHB isolates. The Petri-dish test was repeatable and stable method to assess aggressiveness of four FHB species for all tested wheat cultivars. The current study confirmed the suitability of in vitro modified Petri-dish method to be used as fast and reliable test to analyse aggressiveness in FHB species.     

Genetic dissection of a major Fusarium head blight QTL in tetraploid wheat

The devastating effect of Fusarium head blight (FHB) caused by Fusarium graminearum has led to significant financial losses across the Upper Midwest of the USA. These losses have spurred the need for research in biological, chemical, and genetic control methods for this disease. To date, most of the research on FHB resistance has concentrated on hexaploid wheat (Triticum aestivum L.) lines originating from China. Other sources of resistance to FHB would be desirable. One other source of resistance for both hexaploid wheat and tetraploid durum wheat (T. turgidum L. var. durum) is the wild tetraploid, T. turgidum L. var. dicoccoides (T. dicoccoides). Previous analysis of the `Langdon'-T. dicoccoides chromosome substitution lines, LDN(Dic), indicated that the chromosome 3A substitution line expresses moderate levels of resistance to FHB. LDN(Dic-3A) recombinant inbred chromosome lines (RICL) were used to generate a linkage map of chromosome 3A with 19 molecular markers spanning a distance of 155.2 cM. The individual RICL and controls were screened for their FHB phenotype in two greenhouse seasons. Analysis of 83 RICL identified a single major quantitative trait locus, Qfhs.ndsu-3AS, that explains 37% of the phenotypic or 55% of the genetic variation for FHB resistance. A microsatellite locus, Xgwm2, is tightly linked to the highest point of the QTL peak. A region of the LDN (Dic-3A) chromosome associated with the QTL for FHB resistance encompasses a 29.3 cM region from Xmwg14 to Xbcd828.     

Weed species within cereal crop rotations can serve as alternative hosts for Fusarium graminearum causing Fusarium head blight of wheat

Fusarium graminearum is the main causal agent of Fusarium head blight (FHB) of small grain cereals, but the importance of weeds in the FHB disease cycle and the establishment of F. graminearum in agroecosystems are still not fully understood. The objective of this study was to determine the potential role of weeds present within cereal crop rotations as alternative hosts. F. graminearum was isolated from different organs of asymptomatic weeds sampled from six fields with cereal-crop rotations in Lithuania for two consecutive years (2015 and 2016). The fungi were identified using morphological and molecular methods. Out of 57 weed species that were investigated, 41 (71.9%) harboured F. graminearum isolates. Twenty five weed species were identified as new, previously undocumented, hosts. The majority (73.3%) of the isolates of F. graminearum from this study belonged to the 15ADON genotype while a smaller proportion (23.4%) belonged to the 3ADON genotype. All F. graminearum isolates that were assessed induced FHB symptoms on artificially inoculated spring wheat tested in the field.     

Effects of Fusarium culmorum head blight on mycotoxin accumulation and yield traits in barley doubled haploids

The susceptibility of barley doubled haploids (DH) to Fusarium head blight (FHB) was investigated. Heads of 24 DH lines (11 two-rowed and 13 six-rowed) derived from F₁ Maresi (two-rowed) × Pomo (six-rowed) hybrids were inoculated with a conidial suspension of the single isolate IPO348-01 of Fusarium culmorum. The experiment was carried out in three consecutive years (1996–98) in one location. The number of kernels per ear, 1000-kernel weight and kernel weight per ear were recorded in inoculated and control plots. In the infected kernels nivalenol (NIV) content and deoxynivalenol (DON) content were determined. The effects of genotype, year and genotype-year interaction on reduction of yield traits were significant. For mycotoxin content only genotype and year effects were found to be important. The average NIV concentration in kernels of inoculated lines ranged from 0.15 mg/kg in the two-rowed line MP7 to 6.36 mg/kg in the six-rowed line MP113. A low accumulation of DON was observed in the studied population (from 0.01 to 0.20 mg/kg). Generally, no significant differences in mycotoxin content were found between two-rowed and six-rowed genotypes. The line MP7 was found to be superior — with the lowest mycotoxin accumulation, and reduction in yield traits. Environmental conditions (years) affected DON and NIV level in kernels; however, the tendency to a lower or higher accumulation of mycotoxin in individual lines was stable over the years.     

Evaluation of genetic diversity of Fusarium head blight resistance in European winter wheat

Genetic diversity in relation to Fusarium head blight (FHB) resistance was investigated among 295 European winter wheat cultivars and advanced breeding lines using 47 wheat SSR markers. Twelve additional wheat lines with known FHB resistance were included as reference material. At least one SSR marker per chromosome arm, including SSR markers reported in the literature with putative associations with QTLs for FHB resistance, were assayed to give an even distribution of SSR markers across the wheat genome. A total of 404 SSR alleles were detected. The number of alleles per locus ranged from 2 to 21, with an average of 8.6 alleles. The polymorphism information content of the SSR markers ranged from 0.13 (Xwmc483) to 0.87 (Xwmc607), with an average of 0.54. Cluster analysis was performed by both genetic distance-based and model-based methods. In general, the dendrogram based on unweighted pair-group method with arithmetic averages showed similar groupings to the model-based analysis. Seven clusters were identified by the model-based method, which did not strictly correspond to geographical origin. The FHB resistance level of the wheat lines was evaluated in field trials conducted over multiple years or locations by assessing the following traits: % FHB severity, % FHB incidence, % diseased kernels, in spray inoculation trials, and % FHB spread and % wilted tips, in point inoculation trials. Association analysis between SSR markers and the FHB disease traits detected markers significantly associated with FHB resistance, including some that have not been previously reported. The percentage of variance explained by each individual marker was, however, rather low. Haplotype analysis revealed that the FHB-resistant European wheat lines do not contain the 3BS locus derived from Sumai 3. The information generated in this study will assist in the selection of parental lines in order to increase the efficiency of breeding efforts for FHB resistance.     

Susceptibility of selected winter wheat cultivars produced in Poland to Fusarium head blight

The susceptibility of six winter wheat cultivars toFusarium head blight has beenstudied. The lowest infected plants intensity, mean degree of head damage and fusariosis index exhibited cultivar Grana which also cumulated the lowest amount of trichothecenes (DON and derivatives ). Possibility to produce NIV by Polish strains has been found.in F.graminearum.     

Inheritance of resistance to Fusarium head blight in three European winter wheat populations

Fusarium head blight (FHB) resistance is of particular importance in wheat breeding programmes due to the detrimental effects of this fungal disease on human and animal health, yield and grain quality. Segregation for FHB resistance in three European winter wheat populations enabled the identification of resistance loci in well-adapted germplasm. Populations obtained from crosses of resistant cultivars Apache, History and Romanus with susceptible semi-dwarfs Biscay, Rubens and Pirat, respectively, were mapped and analysed to identify quantitative trait loci (QTL) for FHB severity, ear emergence time and plant height. The results of the present study together with previous studies in UK winter wheat indicated that the semi-dwarfing allele Rht-D1b seems to be the major source for FHB susceptibility in European winter wheat. The high resistance level of the cultivars Romanus and History was conditioned by several minor resistance QTL interacting with the environment and the absence of Rht-D1b. In contrast, the semi-dwarf parents contributed resistance alleles of major effects apparently compensating the negative effects of Rht-D1b on FHB reaction. The moderately resistant cultivar Apache contributed a major QTL on chromosome 6A in a genome region previously shown to carry resistance loci to FHB. A total of 18 genomic regions were repeatedly associated with FHB resistance. The results indicate that common resistance-associated genes or genomic regions are present in European winter wheats.     

Suppression of wheat Fusarium head blight by novel amphiphilic aminoglycoside fungicide K20

K20 is a novel amphiphilic aminoglycoside capable of inhibiting many fungal species. K20's capabilities to inhibit Fusarium graminearum the causal agent wheat Fusarium head blight (FHB) and to this disease were examined. K20 inhibited the growth of F. graminearum (minimum inhibitory concentrations, 7.8–15.6 mg L^?1) and exhibited synergistic activity when combined with triazole and strobilurin fungicides. Application of K20 up to 720 mg L^?1 to wheat heads in the greenhouse showed no phytotoxic effects. Spraying wheat heads in the greenhouse with K20 alone at 360 mg L^?1 lowered FHB severity below controls while combining K20 with half–label rates of Headline (pyraclostrobin) improved its disease control efficacy. In field trials, spraying K20 at 180 mg L^?1 and 360 mg L^?1 combined with half-label rates of Headline, Proline 480 SC (prothioconazole), Prosaro 421 SC (prothioconazole + tebuconazole), and Caramba (metconazole) reduced FHB indices synergistically. In addition, the K20 plus Proline 480 SC combination reduced levels of the mycotoxin deoxinivalenol by 75 % compared to the control. These data suggest that K20 may be useful as a fungicide against plant diseases such as FHB particularly when combined with commercial fungicides applied at below recommended rates.     

Molecular mapping of QTL for Fusarium head blight resistance introgressed into durum wheat

Key message

The major QTL for FHB resistance from hexaploid wheat line PI 277012 was successfully introgressed into durum wheat and minor FHB resistance QTL were detected in local durum wheat cultivars. A combination of these QTL will enhance FHB resistance of durum wheat.

Abstract

Fusarium head blight (FHB), caused by Fusarium graminearum, is a devastating disease of durum wheat. To combat the disease, great efforts have been devoted to introgress FHB resistance from its related tetraploid and hexaploid wheat species into adapted durum cultivars. However, most of the quantitative trait loci (QTL) for FHB resistance existing in the introgression lines are not well characterized or validated. In this study, we aimed to identify and map FHB resistance QTL in a population consisting of 205 recombinant inbred lines from the cross between Joppa (a durum wheat cultivar) and 10Ae564 (a durum wheat introgression line with FHB resistance derived from the hexaploid wheat line PI 277012). One QTL (Qfhb.ndwp-2A) from Joppa and two QTL (Qfhb.ndwp-5A and Qfhb.ndwp-7A) from 10Ae564 were identified through phenotyping of the mapping population for FHB severity and DON content in greenhouse and field and genotyping with 90K wheat Infinium iSelect SNP arrays. Qfhb.ndwp-2A explained 14, 15, and 9% of the phenotypic variation, respectively, for FHB severity in two greenhouse experiments and for mean DON content across the two greenhouse environments. Qfhb.ndwp-5A explained 19, 10, and 7% of phenotypic variation, respectively, for FHB severity in one greenhouse experiment, mean FHB severity across two field experiments, and mean DON content across the two greenhouse experiments. Qfhb.ndwp-7A was only detected for FHB severity in the two greenhouse experiments, explaining 9 and 11% of the phenotypic variation, respectively. This study confirms the existence of minor QTL in North Dakota durum cultivars and the successful transfer of the major QTL from PI 277012 into durum wheat.

     

Inheritance of Fusarium head blight resistance in the soft red winter wheat Ernie

Fusarium head blight (FHB), caused by Fusarium graminearum Schwabe [telomorph:Gibberella zeae Schw. (Petch)], is an increasingly important disease of wheat (Triticum aestivum L.). Host-plant resistance is considered to be the most economical means of control, but a lack of unique sources of resistance has hindered efforts to breed resistant varieties. The soft red winter wheat, Ernie, has moderately high FHB resistance and is widely used in U.S. breeding programs; however, the genetics of resistance have not been studied. The objectives of this study were to estimate the genetic effects, gene numbers, and heritability for traits related to FHB resistance in Ernie through generation means analyses and variance analyses of 243 F₃-derived F₈ and F₉ recombinant inbred lines (RILs). Replicated experiments were grown in the greenhouse, inoculated with F. graminearum, and evaluated for disease spread and the FHB index (FHBI). The latter was calculated as the percentage of diseased spikelets in inoculated spikes and is often referred to as type-II resistance. Gene action for both disease spread and FHBI was primarily additive with partial dominance for low disease. Broad-sense heritabilities for spread and FHBI were 78.2% and 78.3%, respectively, while the narrow-sense heritabilities were 51.3% and 55.4%, respectively. Line-mean heritabilities from analyses of variance of RILs were 0.70 and 0.87 for spread and FHBI, respectively. A minimum of four genes conditioned both disease spread and FHBI. These results suggest that breeders should be able to enhance FHB resistance by combining the resistance in Ernie with other complementary additive sources of resistance.     

QTL mapping of Fusarium head blight resistance in three related durum wheat populations

Key message

The QTL Fhb1 was successfully introgressed and validated in three durum wheat populations. The novel germplasm and the QTL detected will support improvement of Fusarium resistance in durum wheat.

Abstract

Durum wheat (Triticum durum Desf.) is particularly susceptible to Fusarium head blight (FHB) and breeding for resistance is hampered by limited genetic variation within this species. To date, resistant sources are mainly available in a few wild relative tetraploid wheat accessions. In this study, the effect of the well-known hexaploid wheat (Triticum aestivum L.) quantitative trait locus (QTL) Fhb1 was assessed for the first time in durum wheat. Three F7-RIL mapping populations of about 100 lines were developed from crosses between the durum wheat experimental line DBC-480, which carries an Fhb1 introgression from Sumai-3, and the European T. durum cultivars Karur, Durobonus and SZD1029K. The RILs were evaluated in field experiments for FHB resistance in three seasons using spray inoculation and genotyped with SSR as well as genotyping-by-sequencing markers. QTL associated with FHB resistance were identified on chromosome arms 2BL, 3BS, 4AL, 4BS, 5AL and 6AS at which the resistant parent DBC-480 contributed the positive alleles. The QTL on 3BS was detected in all three populations centered at the Fhb1 interval. The Rht-B1 locus governing plant height was found to have a strong effect in modulating FHB severity in all populations. The negative effect of the semi-dwarf allele Rht-B1b on FHB resistance was compensated by combining with Fhb1 and additional resistance QTL. The successful deployment of Fhb1 in T. durum was further substantiated by assessing type 2 resistance in one population. The efficient introgression of Fhb1 represents a significant step forward for enhancing FHB resistance in durum wheat.

     

Family-based mapping of quantitative trait loci in plant breeding populations with resistance to Fusarium head blight in wheat as an illustration

Traditional quantitative trait loci (QTL) mapping approaches are typically based on early or advanced generation analysis of bi-parental populations. A limitation associated with this methodology is the fact that mapping populations rarely give rise to new cultivars. Additionally, markers linked to the QTL of interest are often not immediately available for use in breeding and they may not be useful within diverse genetic backgrounds. Use of breeding populations for simultaneous QTL mapping, marker validation, marker assisted selection (MAS), and cultivar release has recently caught the attention of plant breeders to circumvent the weaknesses of conventional QTL mapping. The first objective of this study was to test the feasibility of using family-pedigree based QTL mapping techniques generally used with humans and animals within plant breeding populations (PBPs). The second objective was to evaluate two methods (linkage and association) to detect marker-QTL associations. The techniques described in this study were applied to map the well characterized QTL, Fhb1 for Fusarium head blight resistance in wheat (Triticum aestivum L.). The experimental populations consisted of 82 families and 793 individuals. The QTL was mapped using both linkage (variance component and pedigree-wide regression) and association (using quantitative transmission disequilibrium test, QTDT) approaches developed for extended family-pedigrees. Each approach successfully identified the known QTL location with a high probability value. Markers linked to the QTL explained 40–50% of the phenotypic variation. These results show the usefulness of a human genetics approach to detect QTL in PBPs and subsequent use in MAS.     

Mapping of quantitative trait loci for field resistance to Fusarium head blight in an European winter wheat

Fusarium head blight (FHB) caused by Fusarium culmorum is an economically important disease of wheat that may cause serious yield and quality losses under favorable climate conditions. The development of disease-resistant cultivars is the most effective control strategy. Worldwide, there is heavy reliance on the resistance pool originating from Asian wheats, but excellent field resistance has also been observed among European winter wheats. The objective of this study was to map and characterize quantitative traits loci (QTL) of resistance to FHB among European winter wheats. A population of 194 recombinant inbred lines (RILs) was genotyped from a cross between two winter wheats Renan (resistant)/Récital (susceptible) with microsatellites, AFLP and RFLP markers. RILs were assessed under field conditions For 3 years in one location. Nine QTLs were detected, and together they explained 30-45% of the variance, depending on the year. Three of the QTLs were stable over the 3 years. One stable QTL, QFhs.inra.2b, was mapped to chromosome 2B and two QTLs QFhs.inra.5a2 and QFhs.inra5a3, to chromosome 5A; each of these QTLs explained 6.9-18.6% of the variance. Other QTLs were identified on chromosome 2A, 3A, 3B, 5D, and 6D, but these had a smaller effect on FHB resistance. One of the two QTLs on chromosome 5A was linked to gene B1 controlling the presence of awns. Overlapping QTLs for FHB resistance were those for plant height or/and flowering time. Our results confirm that wheat chromosomes 2A, 3A, 3B, and 5A carry FHB resistance genes, and new resistance factors were identified on chromosome arms 2BS and 5AL. Markers flanking these QTLs should be useful tools for combining the resistance to FHB of Asian and European wheats to increase the resistance level of cultivars.     

Structural and functional characterization of the TRI101 trichothecene 3-O-acetyltransferase from Fusarium sporotrichioides and Fusarium graminearum: kinetic insights to combating Fusarium head blight

Fusarium head blight (FHB) is a plant disease with serious economic and health impacts. It is caused by fungal species belonging to the genus Fusarium and the mycotoxins they produce. Although it has proved difficult to combat this disease, one strategy that has been examined is the introduction of an indigenous fungal protective gene into cereals such as wheat barley and rice. Thus far the gene of choice has been tri101 whose gene product catalyzes the transfer of an acetyl group from acetyl coenzyme A to the C3 hydroxyl moiety of several trichothecene mycotoxins. In vitro this has been shown to reduce the toxicity of the toxins by approximately 100-fold but has demonstrated limited resistance to FHB in transgenic cereal. To understand the molecular basis for the differences between in vitro and in vivo resistance the three-dimensional structures and kinetic properties of two TRI101 orthologs isolated from Fusarium sporotrichioides and Fusarium graminearum have been determined. The kinetic results reveal important differences in activity of these enzymes toward B-type trichothecenes such as deoxynivalenol. These differences in activity can be explained in part by the three-dimensional structures for the ternary complexes for both of these enzymes with coenzyme A and trichothecene mycotoxins. The structural and kinetic results together emphasize that the choice of an enzymatic resistance gene in transgenic crop protection strategies must take into account the kinetic profile of the selected protein.