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Tolerance to Leaf Rust in Susceptible Wheat Cultivars. J. J. Roberts, Research agronomist, USDA-ARS, and assistant professor of agronomy, Purdue University, West Lafayette, IN 47907; L. T. Hendricks(2), and F. L. Patterson(3). (2)Agricultural research technician, USDA-ARS, Purdue University, West Lafayette, IN 47907; (3)Professor of agronomy, Purdue University, West Lafayette, IN 47907. Phytopathology 74:349-351. Accepted for publication 14 October 1983. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1984. DOI: 10.1094/Phyto-74-349.

Studies of leaf rust tolerance were conducted under controlled conditions in the greenhouse using ten cultivars of winter wheat (Triticum aestivum) and races 76 and 82 of Puccinia recondita. Split-plot trials were used, subjecting one plant of each pair of plants of each cultivar in each replication to a massive inoculation of urediniospores to ensure severe, reasonably uniform infection. Cultivars were inoculated at the same stage of growth. Comparisons were made of the effect of leaf rust on grain yield, numbers and weights of kernels, and stem or leaf elongation. The greatest total mean loss over all cultivars (56%) occurred when inoculations were made before plants headed. Mean losses were about 15% when plants were inoculated after heading. These greenhouse studies confirmed field observations that cultivars of apparently equal susceptibility to leaf rust differ significantly in the magnitude of yield losses sustained. Fulhard, the most tolerant cultivar, had a high level of protection against yield losses due to rust. The tolerance of Kanqueen, although less than that of Fulhard, may still be of importance. Butler was tolerant when inoculated after heading, but not when inoculated before heading. Seneca was just the opposite, tolerant when inoculated before heading, but not when inoculated after heading. Riley and Purdue Sel 45 were consistently intolerant, regardless of growth stage when inoculated. Tolerant cultivars, but not intolerant ones, were markedly stunted by rust. This was also demonstrated in the seedling stage, but no inheritance information was found in tests of F₁ or F₂ generation materials. The data support a hypothesis that the relative tolerance of a cultivar may vary with maturity of the plant or tiller inoculated. The levels of tolerance demonstrated in these studies are of potential economic importance, but practical breeding methods for transferring tolerance to superior new cultivars must still be developed.