Three linked genes responsible for resistance respectively to stem rust, to leaf rust, and to powdery mildew are located on chromosome 7B of Hope wheat. The gene for stem rust resistance, operative in seedling and adult plant stages, is recessive and is designated Br17. The incompletely dominant gene for resistance to leaf rust, designated Lr14, showed 18% recombination with sr17, whilst in two different crosses recombination estimates of 6·0 and 2·5%, respectively, were obtained for the recessive gene for mildew resistance and Br17. All three genes were found to be present in a high proportion of Hope and H·44 derivatives. The gene Br 1'7 is apparently ineffective in conferring resistance to North American and pre.1954 Australian stem rust strains. Its incorporation into several cultivars selected for resistance to these strains presumably resulted from gene interactions or linkage with genes for resistance to other diseases.
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Abstract A recombinant inbred line (RIL) population derived from the cross Arina/Forno was field tested for 2 years against Puccinia graminis f. sp. tritici under artificially created epidemic conditions. Both parents showed intermediate adult plant stem rust responses and the RIL population showed continuous variation for this trait. Composite interval mapping identified genomic regions controlling low stem rust response on chromosomes 5B and 7D consistently across all experiments. These genomic regions were named QSr.Sun-5BL and QSr.Sun-7DS and explained on an average 12% and 26% of the phenotypic variation in adult plant stem rust response, respectively. QSr.Sun-5BL mapped close to Xglk0354 and was contributed by Arina. The Lr34-linked markers csLV34 and swm10 were closely associated with QSr.Sun-7DS suggesting the involvement of Lr34 in controlling adult plant stem rust response of cultivar Forno. Additional minor and inconsistent QTLs explaining variation in adult plant stem rust response were identified on chromosome arms 1AS and 7BL. The QTL located on chromosome 7BL corresponded to the stem rust resistance gene Sr17 carried by cultivar Forno. A seedling stem rust resistance gene carried by Arina, SrAn1, was ineffective under field conditions and was mapped on the long arm of chromosome 2A. Genotypes carrying combinations of QSr.Sun-5BL and QSr.Sun-7DS based on positive alleles of the respective closest marker loci Xglk0354 and XcsLV34 or Xswm10 exhibited a lower response than either parent indicating an additive effect of these genes. Transfer of these genes into cultivars carrying Sr2 would provide a more effective and durable resistance against the stem rust pathogen. Markers csLV34 and/or swm10 could be used in marker assisted selection of QSr.Sun-7DS in breeding programs.