Pathogenic variation ofRhynchosporium secalisin Alberta

Abstract

Leaf samples with scald symptoms were taken from various barley cultivars in 1997 and 1998 at nine locations in Alberta for examination of pathogenic variability. Two hundred and fifty-six single-spore isolates of Rhynchosporium secalis were differentiated into 52 pathotypes using 12 differentials, which consisted of seven accessions with major resistance genes and five commercial cultivars. Fifty-two percent of isolates were virulent on cv. Harrington only (pathotype 1); five pathotypes, consisting of close to 25% of isolates, were virulent only on 4 of 5 commercial cultivars; and about 45 pathotypes, consisting of about 25% of isolates, were virulent on commercial cultivars and accessions. No differential was resistant to all pathotypes, and many pathotypes were represented by single isolates. There was a difference in pathotype diversity and complexity among locations in Alberta. Calmar, Lacombe, and Edmonton sites comprised the greatest number of pathotypes that were virulent on up to seven differentials; at the Beaverlodge, Carstairs, Stettler, and Westlock sites, pathotype 1 comprised more than 60% of total isolates with a few other pathotypes. The Trochu and Vegreville sites were intermediate in the number of pathotypes. Discriminant analysis based on the reactions of the 12 differentials also showed divergence in R. secalis virulence among locations. Pathogenic variability associated with location in Alberta is important in the context of breeding for resistance and use of the most resistant cultivars by producers.Résumé : En 1997 et 1998 en Alberta, des échantillons de feuille avec des symptômes de rhynchosporiose furent récoltés sur divers cultivars d'orge à neuf endroits en vue d'examiner la variabilité pathogène. Deux cent cinquante-six isolats monosporiques du Rhynchosporium secalis furent différenciés en 52 pathotypes à l'aide de 12 populations différentielles, dont sept obtentions possédant des gènes de résistance majeurs et cinq cultivars commerciaux. Cinquante-deux pour cent des isolats étaient virulents seulement sur le cv. Harrington (pathotype 1); cinq pathotypes englobant presque 25% des isolats étaient virulents seulement sur 4 des 5 cultivars commerciaux et environ 45 pathotypes englobant environ 25% des isolats étaient virulents sur les cultivars commerciaux et sur les obtentions. Aucune des plantes différentielles n'étaient résistante à tous les pathotypes et plusieurs pathotypes étaient représentés par des isolats uniques. Il y avait une différence dans la diversité et la complexité des pathotypes entre les emplacements en Alberta. Les sites de Calmar, de Lacombe et d'Edmonton comprenaient le plus grand nombre de pathotypes virulents sur jusqu'à sept populations différentielles ; aux sites de Beaverlodge, de Carstairs, de Stettler et de Westlock, le pathotype 1 comprenait jusqu'à plus de 60% du total des isolats et incluait seulement quelques autres pathotypes. Les sites de Trochu et de Vegreville étaient intermédiaires quant au nombre de pathotypes. Une analyse discriminante basée sur l...

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