mainly via a hypersensitive foliar reaction involving major Pm genes in a gene-for-gene interaction (Bennett, Powdery mildew of wheat (Triticum aestivum L.), caused by Blu-1984; Chen and Chelkowski, 1999; Hsam and Zeller, meria graminis DC f. sp. tritici Em. Marchal, occurs annually in 2002). Thirty major gene loci have been identified to eastern North America resulting in reduced grain yield and end-use quality in susceptible cultivars. The objectives of this study were to G. Srnić, Pioneer Hi-Bred International, Inc., 7300 NW 62nd Avenue, lar markers of genes for resistance to powdery mildew

Powdery mildew of wheat (Triticum aestivum L.) is a major fungal disease caused by Blumeria graminis DC f. sp. tritici A microsatellite linkage map was developed for the T. monococcum‐derived powdery mildew resistant gene present in the North Carolina germplasm line NCBGT96A6 (NCA6). Genetic analysis of F2‐derived lines from the cross NCA6 × ‘Saluda’ indicated a single gene controlled powdery mildew resistance. Four microsatellite markers linked to the NCA6 Pm gene mapped to chromosome 7AL. The most likely order was Xcfa2123‐0.9 cM–Xbarc121‐1.7 cM resistance gene/Xcfa2019‐3.0 cM‐Xgwm332 A detached‐leaf test indicated the disease reaction response of the NCA6 Pm gene was different from the five known alleles at the Pm1 locus on 7AL. Deletion interval mapping showed a large physical to genetic distance ratio for these microsatellite marker loci. This may be due to suppressed recombination between the introgressed T. monococcum segment and the homologous region of the T. aestivum cultivar Saluda. Our results suggested that the NCA6 Pm gene is likely a novel source of resistance to powdery mildew but additional allelism studies are needed to establish the relationship between this locus and the other known Pm loci on 7AL.

Powdery mildew is an economically important disease in wheat (Triticum aestivum L.). NC97BGTAB10 contains powdery mildew resistance introgressed from wild emmer wheat (T. turgidum subsp. dicoccoides). The objectives of this research were to genetically characterize the powdery mildew resistance in NC97BGTAB10, identify SSR markers closely linked to the resistance gene, and provide evidence that the gene is novel. One hundred thirty nine F2:3 lines from the cross NC97BGTAB10/Saluda were evaluated in the field and greenhouse for reaction to powdery mildew. Resistance was controlled by a single gene. Bulked segregant analysis identified a polymorphism between the resistant and susceptible bulks on chromosome 2BL. The population was genotyped with SSR markers that were specific to chromosome 2B and a linkage map was developed. The SSR marker Xwmc445 mapped 7 cM proximal to the resistance gene and no marker could be mapped distal to the gene. It was concluded that the resistance gene lies in the distal tip of chromosome 2BL. The powdery mildew resistance genes Pm33 and MlZec1 have also been mapped to the region. A detached leaf test with two powdery mildew isolates indicated the resistance gene in NC97BGTAB10 was different from MlZec1. No allelism test could be conducted to determine the relationships between the resistance genes in NC97BGTAB10, Pm33 or MlZec1 at this time. Thus, the resistance gene in NC97BGTAB10 was given the temporary designation MlAB10.

Powdery mildew is a major fungal disease in wheat, especially in cool maritime climates. A novel Aegilops tauschii Coss.-derived wheat powdery mildew resistance gene present in the germplasm line NC96BGTD1 was genetically characterized as a monogenic trait in field trials using F¿-and F^-derived lines from a NC96BGTD1 x 'Saluda' cross. Simple sequence repeat (SSR) markers were used to map and tag the resistance gene present in NC96BGTD1. Two dominant SSR markers flanking the resistance gene were identified. Xgwm635 mapped 5.5 and 8.3 cM distal to the resistance gene in the Fg and F^ generations, respectively. Xgpw328 mapped 16.2 cM proximal to the resistance gene in the f^ and 13.6 cM proximal to the resistance gene in the F^ generation. These SSR markers were previously mapped to the short arm of chromosome 7D and their positions were confirmed using Chinese Spring aneuploid and deletion stocks. Significant segregation distortion was observed in the F^ generation with markers distal to the resistance gene showing a preference for the A. tauschii alíeles while markers proximal to the resistance gene showed less significant preference for Saluda alíeles. Only the adult plant resistance gene Pm38 has been mapped to the short arm of chromosome 7D but to a more proximal position than the gene in NC96BGTD1. The resistance gene described herein should be temporarily designated MlNCDl.].]. Maxwell,