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Field Resistance to the Ug99 Race Group of the Stem Rust Pathogen in Spring Wheat Landraces

July 2013 , Volume 97 , Number  7
Pages  882 - 890

M. Newcomb, United States Department of Agriculture–Agricultural Research Service (USDA-ARS), Small Grains and Potato Germplasm Research Unit, Aberdeen, ID, 83210; M. Acevedo, Department of Plant Pathology, North Dakota State University, Fargo, 58108; H. E. Bockelman, USDA-ARS, Small Grains and Potato Germplasm Research Unit; G. Brown-Guedira, USDA-ARS, Eastern Regional Genotyping Laboratory, Raleigh, NC, 27695; B. J. Goates and E. W. Jackson, USDA-ARS, Small Grains and Potato Germplasm Research Unit; Y. Jin, USDA-ARS, Cereal Disease Laboratory, University of Minnesota, St. Paul, MN, 55108; P. Njau, Kenya Agricultural Research Institute, Njoro, Kenya; M. N. Rouse, USDA-ARS, Cereal Disease Laboratory; D. Singh, Plant Breeding Institute, The University of Sydney, NSW, Australia; R. Wanyera, Kenya Agricultural Research Institute; and J. M. Bonman, USDA-ARS Small Grains and Potato Germplasm Research Unit

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Accepted for publication 30 October 2012.

Wheat landraces provide a source of genetic variability for breeding. The emergence and spread of highly virulent races of the stem rust pathogen (Ug99 race group of Puccinia graminis f. sp. tritici) threaten wheat production globally. Spring wheat landraces were screened for resistance in eight field seasons at the Kenya Agricultural Research Institute, Njoro, where the Ug99 race group has become endemic. Accessions showing resistance in one season were retested and screened with molecular markers associated with resistance genes Sr2, Sr24, Sr36, and Lr34/Yr18; two height-reducing genes; and a photoperiod insensitivity allele. Of 2,509 accessions tested, 278 were categorized as resistant based on results from at least two seasons. Of these resistant accessions, 32 were positive for one or more markers for Sr2, Sr36, Rht-B1b, or Rht-D1b, indicating that they do not fit the definition of “landrace” because these genes were likely introduced via modern breeding practices. Thus, 246 resistant “landrace” accessions were identified. Of countries with more than five tested accessions, Afghanistan, Iran, Portugal, Ethiopia, Uzbekistan, Greece, Tajikistan, Bosnia and Herzegovina, and Serbia had at least 10% of tested accessions that were resistant to the Ug99 race group. Future research will characterize the resistance to determine its novelty and incorporate novel genes into improved lines.

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, 2013.