Page Banner

United States Department of Agriculture

Agricultural Research Service

Ug99- emerging virulent stem rust races
headline bar


  In the News (provided on the BGRI website)
 3/25/2013 Virulent wheat disease threatens global food stocks (Suite 101)
3/31/2011 Saving the world a grain at a time (MN Daily)
3/29/2011 Ug99 - an educational video (BGRI)
6/2/2010 Wheat rust tracking site launched (FAO)
5/20/2010 Wheat Rust Threatens World's Wheat Crops (Suite101)
2/22/2010 Red Menace: Stop the Ug99 Fungus Before Its Spores Bring Starvation  (Wired Magazine)
10/14/2008 Report for the stem rust surveillance and management workshop held July 30-31, 2008
7/2/2008 Ug99 Workshop Summary   Summary of national workshop on new virulences in wheat and barley stem rust held March 5-6, 2008, in Baltimore, Maryland.
4/2/2008 Gates Foundation awards $26.8 million to combat Ug99.
11/02/2007 Forum—Once Again, International Cooperation Key to Saving Wheat and Barley
1/02/2007 World Wheat Supply Threatened!
1/16/2007 Dangerous wheat disease jumps Red Sea - Devastating fungal pathogen spreads from eastern Africa to Yemen, following path scientists predicted.
3/30/2007 Deadly Wheat Fungus Threatens World's Breadbaskets(Science 30:1786-1787)

An emerging virulent stem rust race and vulnerability of wheat in the U.S. and worldwide.

New virulence in East Africa

In a nursery in Uganda, Africa in 1999, susceptible type stem rust pustules (collection designated Ug99) were found on wheat lines known to have the stem rust resistance gene Sr31, a gene for which no virulence had been reported previously anywhere in the world.  Similar virulence was observed in 2001 in Kenya and 2003 in Ethiopia.   (Race identification of earlier observations prior to 2001 could not be confirmed because of a lack of samples).   Race typing (race TTKS based on Pgt system of nomenclature, see Phytopathology 78:526-533) and DNA confirmed the presence in Kenya in 2005.  Sr31is on the 1B/1R chromosomal translocation, a piece of rye chromosome that has been introduced into many wheat cultivars.  In addtion to Sr31, the leaf rust resistance gene Lr26 and the stripe rust resistance gene Yr9are also on the 1B/1R translocation.

Stem rust vulnerability of wheat worldwide--the Sr31 factor

Stem rust resistance gene Sr31 is widely utilized in wheat worldwide, particularly in the India subcontinent, China, Europe, and South America.  From the CIMMYT report: Impacts of International Wheat Breeding Research in Developing Countries, 1966-97, developing countries planted 69 million hectares (~170 million acres) of spring wheat in 1997, of which nearly 80% were planted to CIMMYT-related varieties.   Susceptibility of this material will provide little barrier to the spread of a virulent race (e.g. TTKS).




 Current research emphasis

  • Screening U.S. wheat in Kenya against stem rust race TTKS

  • Characterizing sources of resistance

  • Mapping effective resistance genes


    Germplasm evaluation

  • Stem rust resistance screening nursery data (BGRI)
  • Contact at Cereal Disease Laboratory

    Yue Jin (

    USDA-ARS, Cereal Disease Laboratory


    Other resources: 

    USDA-ARS Official Ug99 website

    Ug99 Action Plan

    Global Rust Initiative 

    RustTracker - A global wheat rust monitoring system (CIMMYT)

    Durable rust resistance in wheat (resources on rust of wheat)


    Ug99 related publications: 


    Resistance to race TTKSK of Puccinia graminis f. sp. tritici in emmer wheat.

    Identification of markers linked to the race Ug99 effective stem rust resistance gene Sr28 in wheat (Triticum aestivum L.).

    Seedling resistance to stem rust race Ug99 and marker analysis for Sr2, Sr24 and Sr31 in South African wheat cultivars and lines.

    Races of Puccinia graminis f. sp. tritici with combined virulence to Sr13 and Sr9e in a field stem rust screening nursery in Ethiopia.

    Inheritance of resistance to Ug99 stem rust in wheat cultivar Norin 40 and genetic mapping of Sr42.


    Genetics of resistance to race TTKSK of Puccinia graminis f. sp. tritici in Triticum monococcum.

    The emergence of Ug99 races of the stem rust fungus is a threat to world wheat production.

    Stem rust resistance in Aegilops tauschii germplasm.

    Discovery and molecular mapping of a new gene conferring resistance to stem rust, Sr53, derived from Aegilops geniculata and characterization of spontaneous translocation stocks with reduced alien chromatin.

    Sources of resistance to stem rust race Ug99 in spring wheat germplasm.

    Stem rust resistance in A-genome diploid relatives of wheat.

    A novel Robertsonian translocation event leads to transfer of a stem rust resistance gene (Sr52) effective against race Ug99 from Dasypyrum villosum into bread wheat.

    Development and characterization of wheat-Ae. searsii  Robertsonian translocations and a recombinant chromosome conferring resistance to stem rust.

    Race non-specific resistance to rust diseases in CIMMYT spring wheats.

    Targeted introgression of a wheat stem rust resistance gene by DNA marker-assisted chromosome engineering.

    International surveillance of wheat rust pathogens: progress and challenges.

    Genetic mapping of stem rust resistance gene Sr13 in tetraploid wheat (Triticum turgidum ssp. durum L.).


    Development of wheat lines having a small introgressed segment carrying stem rust resistance gene Sr22.

    Geneic maps of stem rust resistance gene Sr35 in diploid and hexaploid wheat.

    Identification of flanking markers for the stem rust resistance gene Sr6 in wheat.

    Haplotype diversity of stem rust resistance loci in uncharacterized wheat lines.

    Molecular and cytogenetic characterization of wheat introgression  lines carrying the stem rust resistance gene Sr39.

    Identification and evaluation of sources of resistance to stem rust race Ug99 in wheat.  Njau, P. N., Jin, Y., Huerta-Espino, J., Keller, B., and Singh, R. P.  2010.  Plant Disease 94:413-419.

    Resistance to stem rust race TTKSK maps to the rpg4/Rpg5complex of chromosome 5H of barley. B. J. Steffenson, Y. Jin, R. S. Brueggeman, A. Kleinhofs, and Y. Sun.  2009.  Phytopathology 99:1135-1141.

    Detection of virulence to resistance gene Sr36 within the TTKS race lineage of Puccinia graminis f. sp. tritici.  Jin, Y., Szabo, L.J., Rouse, M.N., Fetch, Jr., T., Pretorius, Z.A., Wanyera, R., Njau, P.  2009.  Plant Disease 93:367-370.

    Detection of virulence to resistance gene Sr24within race TTKS of Puccinia graminisf. sp. tritici.  Jin, Y., Szabo, L.  2008.  Plant Disease 92:923-926.

    Molecular and cytogenetic characterization of a durum wheat - Aegilopsspeltoides chromosome translocation conferring resistance to stem rust.  Faris, J.D., Xu, S.S., Cai, X., Friesen, T. L., Jin, Y.  2008.  Chromosome Research 16:1097-1105.

    Characterization of seedling infection types and adult plant infection responses of monogenic Srgene lines to race TTKS of Pucciniagraminisf. sp. tritici.  Jin, Y., Singh, R.P., Ward, R.W., Wanyera, R., Kinyua, M., Njau, P., Fetch, T., Pretorius, Z., Yahyaoui, A.  2007.  Plant Disease 91:1096-1099.

    The spread of stem rust caused by Puccinia graminisf. sp. tritici, with virulence on Sr31 in wheat in eastern Africa.  Wanyera, R., Kinyua, M.G., Jin, Y. and Singh, R.P. 2006.  Plant Dis. 90:113.

    Resistance in U.S. wheat to recent eastern African isolates ofPuccinia graminisf. sp. triticiwith virulence to resistance gene Sr31.  Jin, Y., and Singh, R.P. 2006.   Plant Dis. 90:476-480.

    Current status, likely migrations and strategies to mitigate the threat to wheat production from race Ug99 (TTKS) of stem rust pathogen.  Singh, R.P., Hodson, D.P., Jin, Y., Huerta-Espino, J. Kinyua, M.G., Wanyera, R., Njau, P. and Ward, R.W.  CAB Reviews: Perspectives in Agriculture, Veterinary Science, Nutrition and Natural Resources, 2006, 1, No. 054, 13 pp.

    ARS, Cooperators Fight New Strain of Wheat Stem Rust

  • Last Modified: 7/8/2015
    Footer Content Back to Top of Page