Major genes for resistance to powdery mildew were analysed in 24 Czechoslovakian wheat cultivars and, in part, in their parents. For this purpose individual isolates of the pathogen, able to differentiate host lines with known resistance genes, were selected. Eight of nineteen winter wheat cultivars do not possess any major resistance gene. Three cultivars have one and seven have two genes. One cultivar carries a combination of three genes {Pm2, Pm4b, Pm8). The most common resistance genes are Pm4b, Pm5 and Pm8. Pm2 is once combined with Pm6. Only one of five spring cultivars lacked a major resistance gene. Mlk is once present alone and twice combmed with Pm5. There is one spring cultivar with a novel combination of three genes: Pml, Pm5 and another gene needing further characterization. The observations are discussed with additional results of parent lines and further information on pedigrees.

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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.

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