André Comeau

Effect of Trichothecenes Produced by Fusarium graminearum during Fusarium Head Blight Development in Six Cereal Species

Fusarium head blight (FHB) is a complex cereal disease associated with trichothecene production; these mycotoxins are factors of aggressiveness in wheat. Six species (bread and durum wheat, triticale, rye, barley and oats) were submitted to point inoculations with two isogenic strains of Fusarium graminearum; a wild strain (Tri5 +) produced trichothecenes and the mutated strain (Tri5 −) did not. The trichothecene-producing strain was generally more aggressive than the non-producing strain, but this varied according to crop species. The difference in aggressiveness was less pronounced in rye, a very resistant species. High resistance levels were observed in oats due to the large spacing between florets. In six-row barley, despite the existence of a moderate Type II resistance, the fungus was often observed to move externally from one floret to another within the dense spike, without penetrating the rachis. Bread wheat had low resistance to the trichothecene-producing strain and good resistance to the non-producing strain. Triticale responded to the strains in a similar way but was somewhat more resistant to both: symptoms on the spikelets and rachis of the triticales were restricted to below the point of inoculation. Durum wheat was susceptible to the trichothecene-producing strain and only moderately resistant to the non-producing strain, which was able to cause serious damage only to this species. Our study confirmed that the role of trichothecenes in FHB pathogenesis differs among species. The failure of the trichothecene non-producing F. graminearum strain to spread within the inflorescence of wheat, triticale, rye and barley, and the significant reduction of spread in the durum wheat spike strongly suggested that trichothecenes are a major determinant of fungal spread and disease development in Triticeae.

Phytotoxicity of eight mycotoxins associated with the fusariosis of wheat spikelets.

The study of eight mycotoxins from Fusarium spp. at concentrations ranging from 0 to 4.3 mg/L for deoxynivalenol, 3-acetyldeoxynivalenol, nivalnol, and a culture filtrate, and from 0 to 14.3 mg/L for T2 toxin, HT2 toxin, diacetoxyscirpenol, and zearalenone, demonstrate that trichothecenes are phytotoxic. The inhibition of coleoptile elongation by each trichothecene is well described by a linear equation and these compounds show differences in phytotoxicity. Deoxynivalenol and 3-acetyldeoxynivalenol are 2.5 times more toxic than T2 toxin, 8 times more toxic than HT2 toxin, and 13 times more toxic than diacetoxyscirpénol. The culture filtrate, which contains deoxynivalenol and 3-acetyldeoxynivalenol, is the most toxic to the coleoptile. A mixture of four purified trichothecenes, deoxynivalenol, 3-acetyldeoxynivalenol, T2 toxin, and nivalénol, revealed differences in trichothecene susceptibility among 11 wheat cultivars. Moreover, reduction of coleoptile elongation of these cultivars was correlated with scabsusceptibility (r = 0.74; P = 0.0068).The study of eight mycotoxins from Fusarium spp. at concentrations ranging from 0 to 4.3 mg/L for deoxynivalenol, 3-acetyldeoxynivalenol, nivalnol, and a culture filtrate, and from 0 to 14.3 mg/L for T2 toxin, HT2 toxin, diacetoxyscirpenol, and zearalenone, demonstrate that trichothecenes are phytotoxic. The inhibition of coleoptile elongation by each trichothecene is well described by a linear equation and these compounds show differences in phytotoxicity. Deoxynivalenol and 3-acetyldeoxynivalenol are 2.5 times more toxic than T2 toxin, 8 times more toxic than HT2 toxin, and 13 times more toxic than diacetoxyscirpenol. The culture filtrate, which contains deoxynivalenol and 3-acetyldeoxynivalenol, is the most toxic to the coleoptile. A mixture of four purified trichothecenes, deoxynivalenol, 3-acetyldeoxynivalenol, T2 toxin, and nivalenol, revealed differences in trichothecene susceptibility among 11 wheat cultivars. Moreover, reduction of coleoptile elongation of these cultivars was correlated with scab...

Comparison of media for their aptitude in wheat anther culture

Different media were evaluated with anthers of five spring wheat (Triticum aestivum L.) genotypes for their ability to produce embryos and green plants in anther culture. Our first experiment showed that the addition of a combination of 19 amino acids significantly increased the number of embryos and green plants obtained. The mean number of green plants per 100 anthers for the two genotypes in this experiment, HY320 and B723, went from 28.2 without amino acids in the medium, to 46.7 with addition of amino acids. Our second experiment with the genotypes HY320, Wim and Laval-19 showed that liquid medium with Ficoll is more efficient for anther culture (9.9 green plants/100 anthers) than solid (0 green plants), gelationous media (2.5 green plants/100 anthers) or liquid medium with Membrane Rafts (0 green plants; Hoechst Celanese Corp.). Our third experiment revealed that the effect of replacement of sucrose by maltose varied with the genotype of the donor plant. Maltose partially inhibited the androgenesis of three responsive genotypes, HY320, Wim and Reliance (40.3 green plants/100 anthers instead of 43.9 with sucrose), while maltose significantly increased the androgenesis of the recalcitrant genotype Laval-19 (10.8 green plants/100 anthers instead of 5.4 with sucrose). An amino acid x maltose interaction was also observed. Amino acids without maltose increased androgenesis, but the addition of maltose to the amino acid-enriched medium eliminated this positive effect of the amino acids.

Impact of trichothecenes on Fusarium head blight [Fusarium graminearum] development in spring wheat (Triticum aestivum)

>Fusarium head blight pathogens (Fusarium spp.) produce trichothecenes that have been demonstrated to play a role in the pathogenesis. To test the impact of trichothecenes on a broad range of genotypes, 18 spring wheat lines (Triticum aestivum) were inoculated with two Fusarium graminearum strains, the genetically modified GzT40 strain, which could not produce trichothecene, and the wild parental Gz3639 strain. During 3 weeks of observation, the two fungal strains showed extreme differences in aggressiveness in all but three of wheat genotypes tested. While the GzT40 mutant did not spread into the rachis, the wild-type strain quickly spread in the spike. This work confirms earlier findings that trichothecenes are a principal determinant of F. graminearum aggressiveness on most spring wheat cultivars. Therefore, trichothecenes may serve as a useful screening tool in programs breeding for resistance to Fusarium head blight of wheat.Key words: trichothecenes, deoxynivalenol, mycotoxins, Fusarium head blight, Fusarium graminearum, spring wheat, Triticum aestivum.

Identification of novel QTL for resistance to Fusarium head blight in a tetraploid wheat population

Most tetraploid durum wheat (Triticum turgidum L var. durum) cultivars are susceptible to Fusarium head blight (FHB). This study reports novel quantitative trait loci (QTL) associated with FHB resistance. A backcross recombinant inbred line (BCRIL) population was developed from the cross BGRC3487/2*DT735, and 160 lines were evaluated for resistance to Fusarium graminearum Schwabe (teleomorph Gibberella zeae (Schwein. Petch) in field trials over 3 years (2008-2010) and to a F. graminearum 3-acetyl-deoxynivalenol (3-ADON) chemotype in greenhouse trials. The population was genotyped with 948 polymorphic loci using DArT and microsatellite markers. Eleven QTL were associated with FHB resistance under field conditions on chromosomes 2A, 3B, 5A, 5B, 7A, and 7B. Two of these, QFhb.usw-3B from BGRC3487 and QFhb.usw-7A2, were consistently detected over environments. The QFhb.usw-3B QTL was in a similar position to a resistance QTL in hexaploid wheat. The combination of the two QTL reduced field index by 53.5%-86.2%. Two QTL for resistance to the 3-ADON chemotype were detected on chromosomes 1B and 4B. Both BGRC3487 and DT735 could provide new sources of FHB resistance and the combination of QTL reported here could be valuable tools in breeding FHB-resistant durum wheat.

Somatic embryogenesis and plant regeneration in Triticum aestivum x Leymus angustus F1 hybrids and the parental lines

Somatic embryos and plants were produced from cultured inflorescence and leaf segments of Triticum aestivum X Leymus anaustus F1 hybrids and the parental lines. Inflorescences showed a better capacity for somatic embryogenesis and plant regeneration than leaves. Leymus anaustus produced the highest number of embryogenic calli, while the hybrids were intermediate between this species and Triticum aestivum. Presence of 2,4-D was shown to be essential for induction and maintenance of somatic embryogenesis. Addition of five amino acids (glutamine, proline, asparagine, aspartic acid and glutamic acid) did not have any marked effect when they were used in the callus induction medium. The regenerated plants had the same morphology as the original plants. No cytological modification was observed in the examined plants.

Use of hen lysozyme for protection against bacterial contamination ofin vitro embryo cultures

SummaryCurative treatments with antibiotics and hen egg white lysozyme (HEWL) were used to salvage embryo cultures contaminated withBaccillus subtilis. The use of HEWL gave good control ofBaccillus subtilis, but no control ofErwinia. HEWL was better than antibiotics, being much less phytotoxic. The antibiotics piperacillin, ampicillin and imipenem were also found to be ineffective againstErwinia. HEWL, at a final concentration of 1 mg per mL, was used as a preventive and curative agent for routine use in embryo culture ofTriticum aestivum and other Triticeae, as it cured from 30% to 50% of bacterial contamination problems over a one year period. Standardin vitro culture precautions remained essential, as certain bacteria were not controlled by HEWL.