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— Major genes for resistance to the wheat powdery mildew pathogen, Erysiphe graminis f sp tritici, were analysed in 35 French wheat cultivars and in part in their parents. Cultivars were tested with a set of differential pathogen isolates which had specific interactions for each host line. The results were supplemented by cytological investigations and by consideration of pedigrees. Eighteen cultivars showed susceptible reactions. The remainder formed 9 groups with 1 or 2 resistance genes. Of the 5 known resistance genes present, Pm2 was the most common (in 5 culti-vars), followed by Pm4b and Pm6 (each present in 4 cultivars), Pm5 (3 cultivars) and Pm8 (2 cultivars). In addition, an unknown resistance, tentatively designated Mlar, was identified in 3 cultivars. Triticum aestivum = common wheat / Erysiphe graminis f sp tritici = wheat powdery mildew / resistance genes Résumé — Identification des gènes de résistance à l'oïdium chez le blé tendre (Triticum aestivum L). II. Culti-vars français. Des gènes majeurs de résistance à l'agent de l'oïdium du blé Erysiphe graminis f sp tritici ont été re-cherchés chez 35 cultivars français de blé, et quelques-uns de leurs parents. Les cultivars ont été testés avec un ensemble d'isolats différentiels présentant des interactions spécifiques sur chaque lignée hôte. Les résultats ont été complétés par des observations cytologiques et par une analyse des généalogies. Dix huit cultivars ont montré des réactions de sensibilité. Les autres forment 9 groupes possédant 1 ou 2 gènes de résistance. Des 5 gènes de résis-tance connus présents chez les cultivars étudiés, Pm2 apparaît le plus fréquemment (chez 5 cultivars) suivi de Pm4b et Pm6 (chacun présent chez 4 cultivars), Pm5 (3 cultivars) et Pm8 (2 cultivars). De plus, un gène de résistance in-connu a été identifié chez 3 cultivars, nommé provisoirement Mlar. Triticum aestivum = blé / Erysiphe graminis f sp tritici = oïdium / gènes de résistance

A total of 59 old wheat cultivars grown in Germany prior to 1960 were tested for mildew response using a collection of 12 differential isolates of Erysiphe graminis DC f. sp. tritici Marchal (Blumeria graminis (DC) Speer f. sp. tritici). Nineteen cultivars did not possess any major resistance gene and 25 were characterized by susceptible or intermediate responses. Fifteen cultivars revealed isolate-specific response patterns that could not be attributed to known major resistance genes or gene combinations. Many of the old German cultivars inherited a mildewresistance gene from the Canadian cultivar 'Garnet", which is tentatively designated Ml-Ga. Cultivars 'Bretonischer Bartweizcn" (designated MlBr) and 'Adlungs Alemanncn" (designated Ml-Ad) appeared to carry unknown resistance genes.Among 18 winter wheat cultivars released in the former GDR, eight showed susceptibility to all isolates used. Cv. 'Borenos" carries resistance gene Pm3c. Five cultivars possess gene Pm4b. two cultivars gene pm5 and one cultivar a combination of genes Pm2 and Pm4h. Cultivar 'Zentos" was resistant to almost all Isolates used. Its resistance might be conditioned by different unknown major resistance genes.

A total of 26 common wheat cultivars and advanced breeding hnes grown in China were tested with a set of 11 differential powdery-mildew isolates. Seven cultivars were susceptible. Another seven cultivars showed the response pattern of resistance gene Pm2., either individually or in combination with genes Pm3d or Pm4a. Five cultivars expressed the resistance of gene Pm4b singly or in combination with Pm6. Another four cultivars exhibited the response patterns of genes Pm5, Pm6 and Pw5, respectively. Three cultivars, which included one breeding hne with a pair of substituted chromosomes from Haynaldia villosa, presumably carrying the resistance gene Pm2\, showed resistance-response patterns to all the isolates tested.