No abstract

SummaryThree 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.

Two techniques used for genetic transfer of stem rust resistance from einkorn (T. monococcum) to hexaploid wheat are described. Success of direct interspecific hybridization between wheat and einkorn was confined to the wild form, and is attributed to differences in survival and development of F 1 hybrids rather than crossability between the two species or germination of hybrid grains. Meiotic pairing between A genome chromosomes in interspecific hybrids was shown to be significantly lower in AABD than in AAB hybrids. These two interspecific hybrids also showed a different distribution pattern of functional female gametes.

SummaryA dominant gene conditioning resistance to certain stem rust strains each with unusual genes for avirulence was located on chromosome ID. It was found to be widespread among bread wheats, and is present in many Australian cultival's, some of which possess no resistance to strains of wheat stem rust prevalent in the field. Pathogenic tests indicated that it was identical with a gene described previously by North American investigators. As it is different from any of the previously catalogued genes in wheat for stem rust resistance the designation Sr18 is proposed.

SummaryThe dominant gene for physiological resistance in the wheat cultivar Uruguay to certain Australian strains of leaf rust was located on chromosome 5D by the F2 method of monosomic analysis. The gene responsible for resistance in the cultivar Transfer was confirmed to be on chromosome 6B. Possible mechanisms producing aberrant F2 ratios involving Transfer in crosses with certain susceptible cultivars are discussed.