Adult plant resistances toPuccinia reconditaf. sp.triticiin wheat

Abstract

Tests with adult plants in the greenhouse confirmed virulence in Australasian populations of Puccinia recondita f. sp. tritici for the adult plant resistance genes Lr12, Lr13, and Lr22b. Virulence for Lr22b has been very common since at least the early 1960s, and it is likely that this gene will be of limited use in breeding for leaf rust resistance. The frequencies of virulence for Lr12 and Lr13 declined during the period 1989–92. Virulence for Lr12 probably originated in northern New South Wales and/or Queensland following the release of cultivar ‘Timgalen’ in 1967. Pathotypes virulent for this gene predominated in this region during 1975–87, after which they were gradually replaced by an apparently more aggressive group of pathotypes avirulent for Lr12. The gene Lr13, in combination with certain seedling resistance genes, remained effective against all pathotypes isolated in pathogenicity surveys conducted before 1992. It is proposed that Lr12 could be deployed in a similar manner. Six genes conferring adult plant resistance to wheat leaf rust were placed into four groups on the basis of the earliest growth stage at which they could be detected under controlled greenhouse conditions. Lr13 was detected in primary seedling leaves of plants inoculated 2 weeks after sowing. Resistances conferred by other genes were detected in plants inoculated 3 weeks after sowing (Lr37), 5 weeks after sowing (Lr12, Lr22a, and Lr35), or 9 weeks after sowing (Lr22b).