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Resistance

Greenhouse Evaluation of the Adult Plant Resistance of Sr2 to Wheat Stem Rust. S. D. Sunderwirth, Former graduate student, Department of Plant Pathology, University of Minnesota, St. Paul, Present address: plant pathologist, Société Coopérative Agricole de la région de Froissy (Oise) France; A. P. Roelfs, research plant pathologist, Cereal Rust laboratory, Agricultural Research, Science and Education Administration, U.S. Department of Agriculture, University of Minnesota, St. Paul 55108. Phytopathology 70:634-637. Accepted for publication 12 December 1979. 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, 1980. DOI: 10.1094/Phyto-70-634.

Plants of the wheat cultivars Hope, Hopps, and H-44 (possessing resistance gene Sr2) and Line E, and McNair 701 (susceptible) were inoculated in a settling tower at four growth stages; ie, first-node, second-node, boot, and anthesis. The resistance to Puccinia graminis f. sp. tritici conditioned by Sr2 was non-race specific to the races 15-TLM, 15-TNM, and 151-QSH, and was characterized by reductions in number, size, and location of uredia. The resistance was best expressed after anthesis. A reduction in number of uredia (compared to those formed on a susceptible host) occasionally occurred as early as the second-node stage. Uredial numbers on plant lines with Sr2 were significantly lower than those of susceptible hosts at the boot stage. At anthesis, the greatest reduction in uredial numbers on lines with Sr2 occurred on the peduncle, but not on the spike. A reduction in uredial size usually was apparent on plants inoculated after the boot stage. The greatest reduction in size of uredia occurred on the peduncle and on the internode directly beneath it, but not on the spike or the lower internodes. The infection types on the peduncle and internode below the peduncle generally decrease in size, with the type 4 infections occurring nearest to the nodes and the type 0 two-thirds of the way up or one-third of the way down the internode.