Chromosomal location of powdery mildew resistance genes in Triticum aestivum L. (common wheat). 2. Genes Pm2 and Pm19 from Aegilops squarrosa L

Two mildew resistant accessions of diploid Aegilops squarrosa and their hexaploid synthetics derived from crosses with mildew susceptible Triticum durum cultivars were tested with differential isolates of Erysiphe graminis f. sp. tritici and their responses were compared with the response patterns of 16 wheat cultivars or lines possessing known mildew resistance genes. Resistance in the A. squarrosa accession ‘Braunschweig BGRC 1458’ was conditioned by the dominant gene Pm2 . This gene confers the same response pattern with a set of mildew isolates when present at the diploid species level or in a hexaploid synthetic with T. durum . It was located on wheat chromosome 5D. The resistance gene in the A. squarrosa accession ‘Gatersleben AE 457/78’ showed a different response pattern in the hexaploid synthetic line ‘XX 186’ tested with mildew isolates compared with that of the diploid. Its response pattern was also different from all other wheats with named genes for resistance to powdery mildew. The gene, localized on chromosome 7D in the synthetic ‘XX 186’, was designated Pm19 .