Effects of Growth Stage and Temperature on Components of Resistance to Leaf Rust in Wheat Genotypes with Lr26. Z. A. Pretorius, Department of Plant Pathology, University of the Orange Free State, Bloemfontein 9300, South Africa. G. H. J. Kemp, Grain Crops Research Institute, Bethlehem 9700, South Africa. Plant Dis. 74:631-635. Accepted for publication 16 November 1989. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/PD-74-0631.

In a qualitative assessment of the reactions of seedlings of wheat cultivars Kavkaz (Lr26+) and Veery (Lr26+) to an isolate of Puccinia recondita f. sp. tritici virulent to Lr26, only Kavkaz exhibited a lower infection type at increased temperatures. Quantitative evaluations indicated that seedlings with and without Lr26 responded similarly to leaf rust infection. The latent period in flag leaves of Kavkaz, Gamtoos (Veery 3), and RL6078 (Thatcher:Lr26) was longer than in the leaf rust-susceptible cultivar Thatcher. These differences were more pronounced at 12–18 C than at 24–28 C. Fewer and smaller uredinia developed on flag leaves of certain Lr26 carriers than on susceptible cultivars. On the basis of uredinium size, a postanthesis loss of adult-plant resistance occurred in Gamtoos. Temperature did not influence the density of uredinia on wheat genotypes with Lr26, but higher temperatures restricted the size of uredinia on flag leaves of RL6078. Lr26 produces certain characteristics in the adult plant, but expression of the gene appears to be influenced by genetic background, age of leaf tissue, and temperature.