Importance de l’intéraction entre les cultivars de blé et les souches du Fusarium graminearum dans l’évaluation de la résistance à la fusariose de l’épi

Des expériences factorielles ont été réalisées au champ à deux stations, le campus de l'Université Laval en 1991 et 1992 et la ferme de Saint-Louis-de-Pintendre en 1992 et 1993, pour préciser si le développement de la fusariose de l'épi du blé est influencé par l'interaction entre les cultivars et les souches du Fusarium graminearum. Neuf souches du F. graminearum ont été inoculées à onze cultivars de blé (Triticum aestivum) et un cultivar de triticale (x Triticosecale) représentatifs de la gamme de sensibilité à cette maladie au Québec. L'analyse de la variance combinée a mis en évidence des interactions significatives entre les cultivars, les souches et les environnements. Les interactions cultivars x souches et cultivars x environnements expliquent une faible proportion de la somme des carrés totale et n'entraînent pas de modifications majeures dans le classement moyen de la sensibilité des cultivars. Concernant l'interaction cultivars x souches, le classement moyen de la sensibilité des cultivars, notamment Casavant et Concorde, variait avec les souches. Cette recherche contre pour la première fois que l'importance relative des différentes interactions entre les souches, les cultivars et les environnements est comparable dans l'évaluation de la résistance à la fusariose de l'épi du blé.Factorial experiments were carried out in the field at the campus of Universite Laval in 1991 and 1992, and Saint-Louis-de-Pintendre station in 1992 and 1993. The objective was to specify if wheat scab development caused by Fusarium graminearum is significantly affected by cultivar x strain interactions. Eleven wheat (Triticum aestivum) cultivars and one triticale (x Triticosecale) cultivar representing the range of sensitivity to this disease in Quebec were inoculated with nine strains of F. graminearum. Significant interactions between cultivars, strains and environments were shown by the results of a combined analysis of variance. Cultivar x strain and cultivar x environment interactions explained a small proportion of the total sum of squares and did not have a strong impact on cultivar average ranking by environment or strain. However, the examination of cultivar x strain interactions revealed that the rank of cultivars such as Casavant and Concorde changed when different strains were compared. This research shows for the first time that all interactions involving cultivars, strains and environments have a similar impact on wheat scab resistance screening

Importance de l’intéraction entre les cultivars de blé et les souches du Fusarium graminearum dans l’évaluation de la résistance à la fusariose de l’épi

Des expériences factorielles ont été réalisées au champ à deux stations, le campus de l'Université Laval en 1991 et 1992 et la ferme de Saint-Louis-de-Pintendre en 1992 et 1993, pour préciser si le développement de la fusariose de l'épi du blé est influencé par l'interaction entre les cultivars et les souches du Fusarium graminearum. Neuf souches du F. graminearum ont été inoculées à onze cultivars de blé (Triticum aestivum) et un cultivar de triticale (x Triticosecale) représentatifs de la gamme de sensibilité à cette maladie au Québec. L'analyse de la variance combinée a mis en évidence des interactions significatives entre les cultivars, les souches et les environnements. Les interactions cultivars x souches et cultivars x environnements expliquent une faible proportion de la somme des carrés totale et n'entraînent pas de modifications majeures dans le classement moyen de la sensibilité des cultivars. Concernant l'interaction cultivars x souches, le classement moyen de la sensibilité des cultivars, notamment Casavant et Concorde, variait avec les souches. Cette recherche contre pour la première fois que l'importance relative des différentes interactions entre les souches, les cultivars et les environnements est comparable dans l'évaluation de la résistance à la fusariose de l'épi du blé.Factorial experiments were carried out in the field at the campus of Universite Laval in 1991 and 1992, and Saint-Louis-de-Pintendre station in 1992 and 1993. The objective was to specify if wheat scab development caused by Fusarium graminearum is significantly affected by cultivar x strain interactions. Eleven wheat (Triticum aestivum) cultivars and one triticale (x Triticosecale) cultivar representing the range of sensitivity to this disease in Quebec were inoculated with nine strains of F. graminearum. Significant interactions between cultivars, strains and environments were shown by the results of a combined analysis of variance. Cultivar x strain and cultivar x environment interactions explained a small proportion of the total sum of squares and did not have a strong impact on cultivar average ranking by environment or strain. However, the examination of cultivar x strain interactions revealed that the rank of cultivars such as Casavant and Concorde changed when different strains were compared. This research shows for the first time that all interactions involving cultivars, strains and environments have a similar impact on wheat scab resistance screening

Ophiostoma ulmi DNA naturally introgressed into an isolate of Ophiostoma novo-ulmi is clustered around pathogenicity and mating type loci

The invasive fungal pathogens Ophiostoma ulmi and O. novo-ulmi have caused two successive pandemics of Dutch elm disease since the beginning of the 20th century. In nature, the highly aggressive O. novo-ulmi may hybridize with the less aggressive O. ulmi. Growth rate and molecular analyses were conducted on an unusual, moderately aggressive O. novo-ulmi isolate, AST27, carrying an introgressed pathogenicity gene, Pat1-m; on highly aggressive O. novo-ulmi isolate H327; on O. ulmi isolates Q412T and W9; and on progeny from laboratory crosses between H327 and AST27. Genetic analysis indicated that the Pat1 and Mat1 (mating type) loci were in different linkage groups corresponding to O. novo-ulmi H327 chromosomes 1 and 2, respectively. Most of the molecular differences between the nuclear genomes of H327 and AST27 occurred in the vicinity of Pat1 and Mat1. In addition, two putative quanti-tative trait loci, Mgr1 and Mgr2, which influence mycelial growth rate at 21°C and 28°C, the optima for O. novo-ulmi and O. ulmi, were linked to Mat1 and Pat1, respectively.Les champignons pathogènes envahissants Ophiostoma ulmi et O. novo-ulmi ont causé deux pandémies successives de maladie hollandaise de l’orme depuis le début du 20e siècle. On a mesuré la croissance et procédé à des analyses moléculaires chez l’isolat O. novo-ulmi AST27, modérément agressif et chez lequel le gène de pathogénie Pat1-m est introgressé; chez l’isolat O. novo-ulmi H327; chez les isolats O. ulmi Q412T et W9; ainsi que chez les descendants de croisements dirigés entre les isolats H327 et AST27. Les analyses génétiques indiquent que les loci Pat1 et Mat1 (type sexuel) sont situés sur des groupes de liaison différents qui correspondent respectivement aux chromosomes 1 et 2. Les différences moléculaires entre les génomes nucléaires des souches H327 et AST27 se retrouvent majoritairement dans le voisinage de Pat1 et de Mat1. De plus, deux loci présumés de caractères quantitatifs, Mgr1 et Mgr2, qui influencent la croissance mycélienne à 21 °C et à 28 °C (températures optimales pour O. novo-ulmi et O. ulmi) sont liés respectivement à Mat1 et à Pat1

Genetic diversity of Australian Fusarium graminearum and F-pseudograminearum

Genotypic diversity in Fusarium pseudograminearum and F. graminearum from Australia and the relationship between diversity and pathogen aggressiveness for head blight and/or crown rot of wheat were examined. Amplified fragment length polymorphism (AFLP) analysis revealed a high level of genotypic diversity within each species. Sixty-three of the 149 AFLP loci were significantly different between the two species and 70 of 72 F. pseudograminearum and 56 of 59 F. graminearum isolates had distinct haplotypes. When head blight and crown rot severity data from a recently published work on isolates representing the entire range of aggressiveness were used, only the genotypic diversity of F. pseudograminearum was significantly associated with its aggressiveness for the two diseases. Cluster analyses clearly demonstrated the polyphyletic structures that exist in both pathogen populations. The spatial diversity within F. graminearum was high within a single field, while frequent gene flow (N-m similar to 14) and a low fixation index (G(st) = 0.03) were recorded among F. pseudograminearum isolates from the adjacent states of New South Wales and Queensland. The differences in population structure between the heterothallic F. pseudograminearum (teleomorph G. coronicola) and the homothallic F. graminearum (teleomorph G. zeae) were not as pronounced as expected given their contrasting mating systems. Neither species was panmictic or strictly clonal. This points to sexual recombination in F. pseudograminearum, suggesting that ascospores of G. coronicola may also play a role in its biology and epidemiology

Mycelial compatibility reactions of Australian Fusarium graminearum and F. pseudograminearum isolates compared with AFLP groupings

Using the mycelial reactions of 435 combinations of 14 Fusarium pseudograminearum and 15 F. graminearum isolates, it was demonstrated for the first time that mycelial reactions/barrage formation cannot be clearly used to distinguish F. graminearum and F. pseudograminearum. Mutually compatible isolates produced very different patterns of compatibility with other isolates. However, about 60% of pairings between F. graminearum and F. pseudograminearum isolates were compatible, indicating common ancestry. The Mantel tests used to determine any possible associations between mycelial compatibility reactions and AFLP genotypic diversity data revealed no association between the two systems in either species. In addition, no association was found between mycelial compatibility reactions and sexual reproduction in the two species. Implications of the higher frequency of mycelial compatibility reactions observed in F. pseudograminearum than in F. graminearum are discussed

Vegetative compatibility and molecular characterization of Fusarium graminearum isolates from the State of Paraná, Brazil Compatibilidade vegetativa e caracterização molecular de isolados patogênicos de Fusarium graminearum do Estado do Paraná

Fusarium graminearum isolates causing Fusarium head blight in wheat were collected in Brazil and analyzed by random amplified polymorphic DNA (RAPD) markers and vegetative compatibility grouping (VCG). Nitrate non-utilizing mutants (nit) from each isolate were paired to verify heterokaryon formation. Three VCGs were identified among F. graminearum isolates: VCG1 included F-2, F-3 and F-4 isolates; VCG2 included F-1, F-6 and F-9 isolates; VCG3 included F-5, F-7 and F-8 isolates. Based on PCR amplification with eight different primers, the isolates showed great genetic similarity among themselves. Dendrogram analysis demonstrated two RAPD groups: Group A, consisting of isolates F-2 and F-9, and Group B, composed of the remaining isolates. Results suggest the clonal origin of F. graminearum isolates.<br>Isolados de Fusarium graminearum, obtidos de espigas de trigo com sintomas de Giberela, foram analisados pela técnica do Polimorfismo de DNA Amplificado ao Acaso (RAPD) e pelos Grupos de Compatibilidade Vegetativa (GCV). Mutantes auxotróficos (nit) de cada isolado foram pareados em todas as combinações possíveis, para a formação de heterocários. Três GCVs foram identificados: GCV1, incluindo os isolados F-2, F-3 e F-4; GCV2, incluindo os isolados F-1, F-6 e F-9; e GCV3, formado pelos isolados F-5, F-7 e F-8. Dois grupos foram identificados com base nos marcadores de RAPD: o grupo A, formado pelos isolados F-2 e F-9, e o grupo B, composto pelos demais isolados, os quais apresentaram grande similaridade entre si. Os resultados sugerem a origem clonal dos isolados de F. graminearum analisados