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Adult Plant Resistance of Thatcher Wheat to Stem Rust. N. R. X. Nazareno, Former graduate student, Department of Plant Pathology, now research plant pathologist, Instituto Agronomical do Paraña, Caixa Postal 1331, 86100 Londrina Paraña, Brasil; 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 71:181-185. Accepted for publication 27 June 1980. 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, 1981. DOI: 10.1094/Phyto-71-181.

No relationship was found between the independent Sr genes for seedling resistance and the adult plant resistance of Thatcher wheat, as measured by rust severity. Pyramids of seedling resistance genes Sr5, Sr12, Sr16, and SrTc did not improve resistance to stem rust. The performance of some progeny lines with both Sr12 and SrTc was similar to Thatcher’s, and this suggests that the factor(s) involved in the adult plant resistance of Thatcher might be related to this Sr gene combination. The adult plant resistance of Thatcher was sensitive to inoculum density. Although this character had been selected successfully under heavy inoculum density at the end of the season, the resistance was most apparent at stage 24 (early milk). Under light inoculum density, however, the greatest difference existed in the terminal disease severities.

Additional keywords: Puccinia graminis, race-specific resistance.