ADULT-PLANT RESISTANCES TO PUCCINIA-RECONDITA F-SP TRITICI IN WHEAT

Tests with adult plants in the greenhouse confirmed virulence in Austr alasian 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 tha t this gene will be of limited use in breeding for leaf rust resistanc e. 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 'Timg alen' 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, rem ained effective against all pathotypes isolated in pathogenicity surve ys conducted before 1992. It is proposed that Lr12 could be deployed i n a similar manner. Six genes conferring adult plant resistance to whe at leaf rust were placed into four groups on the basis of the earliest growth stage at which they could be detected under controlled greenho use 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 wee ks after sowing (Lr12, Lr22a, and Lr35), or 9 weeks after sowing (Lr22 b).