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ARS Home Midwest Area St. Paul, Minnesota Cereal Disease Lab Docs







Emerging virulent stem rust race (Ug99)headline bar   **The emerging virulent stem rust race (Ug99) and vulnerability of wheat in the U.S. and worldwide.**  Yue Jin (yuejin@umn.edu) USDA-ARS, Cereal Disease Laboratory  New virulence in East Africa In a nursery in Uganda, Africa in 1999, susceptible type stem rust pustules (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 of Ug99 in Kenya in 2005. *Sr31* is 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 *Yr9* are also on the 1B/1R translocation. Stem rust vulnerability of wheat worldwide--the Sr31 factor  Stem rust resistance geneSr31 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).The use of the rust resistance gene Sr31 might have hindered the use of other *Sr*resistance genes (masking effect)--resulted in a genetic uniformity of narrowly based resistance in a large magnitude.  Environments in East Africa that may have contributed to new races  Wheat production in the highlands (>2000m or higher).Wheat is present year-around due to staggered plantings and volunteer plants.Daily dews and mild temperatures permit continued survival of the fungus and re-infections on host plants.  Potential migration routes for Ug99  The current know status of Ug99 in east Africa (courtesy of R. Singh, CIMMYT).    The potential migration routes for Ug 99 based on prevailing air-flows and regional wheat production areas. Route A via Arabian peninsular, Middle-East, and South Asia is considered to have a higher probability (courtesy of R. Singh, CIMMYT).     Current research emphasis  ? Screening U.S. wheat in Kenya against Ug99 ? Characterizing sources of resistance ? Mapping effective resistance genes--ARS Genotyping Labs    **Results of 2006 Kenyan stem rust screening****Country****Number of entries****%  R or MR**Bangladesh843.6Nepal1051.9Pakistan1055.7China1181.7Iran1002.0Khazakstan863.5Russia352.9India AKJ1009.0Turkey8518.8U.S. HRS-breeding9722.7CIMMYT-combined88625.5Canada23338.2Australia5246.2    **Characterization of resistance to TTKS** - postulation of genes **** **Characterization of resistance to TTKS** -inheritance   ****    Cross#of F2 plants with ITH0: Compl. rec. genesH0: SuppressorParent 1Parent 2IT ;1IT 2IT X-IT 3IT 4c2P (>c2)c2P (>c2)ChrisCSA1122661.210.272<0.010.982AC BarrieMarquis61340.920.3370.050.822Bonza 65CSA14990.370.543<0.010.954ThatcherCSA32700.380.5370.010.911ChrisAC Barrie2814ChrisThatcher19255ChrisKeene32025490.010.9290.050.816   Effectiveness of Sr genes to TTKS **Not effective****Effective (including moderate levels)****No data**  **Origin****Resistance genes*********Triticum aestivum******5, 6, 7a, 7b, 8a, 8b, 9a, 9b, 9f, 15, 16, 18, 19, 20, 23?, 28, 29, 30, 41, 42, Tmp*, Wld-1******T. turgidum*****2, 9d, 9e, 9g, 11, 12, 13*, 14, 17*****T. monococcum******21, 22, 35******T. timopheevi******36*, 37******T. speltoides******32, 39******T. tauschii******33, 45******T. comosum******34?******T. ventricosum******38?******T. araraticum******40******Thinopyrum elongatum******24*, 25, 26, 43**********Th. intermedium******44******Secale cereale******27*, 31, 1RS-Am**** Virulence known to occur in other races  Resistance to TTKS in US & CIMMYT wheat -Based on seedling & 2005 Kenyan nursery results  Class05KENadult% resist.(?20MS)06TTKSseedling% resist.(?IT 2)GenesHRS-breeding lines & cvs10312Stoa-type, Chris-type, Sr24HRS-germplasm466198982UnknownHRW-breeding lines1213136846Sr24, 1RS-Am, Tmp, 36, unk.SRW-breeding lines922714822Sr36, 24, 1RS-Am, Tmp, unkCIMMYT-breeding lines25001127089Sr24, 25, synthetic, APR, unk.  Current status of stem rust in North AmericaThe pathogen population in the U.S. has been very stable!QFCS (>90% of isolates) 2003-06RCRS & QFCS (>90% of isolates) 1998-2002TPMK 1971-97QCCJ 1989-93QFCS 1978-83, 88-94Inter-related factors contributed to the stability:Widespread use of resistant cultivarsReduction in pathogen population sizeA lack of sexual recombination (eradication of alternate host barberry)The bottleneck of overwinteringOpportunities for improving SR resistance in U.S. wheatEffective resistance genes, Sr2, 13, 24, 36, Tmp, 1RS-Am, and unknown genes are in adapted U.S. germplasm, and could be used as a packages:Hard red winter wheat:Sr2, 6, 24, Tmp, 1RS-AmSoft red winter wheat:Sr2, 6, 24, 31, 36Hard red spring wheat:Sr2, 6, Wld-1,Thatcher-derivedOpportunity to deploy and maintain some diversity of stem rust resistance among different classes of wheat.Opportunity to utilize the overwintering "bottleneck".ChallengesCompeting resources with FHB, stripe rust, etc.Perspectives on the need for Sr resistance in the Southeast and southern Plains.Research efforts in stem rust worldwide is declining, including Canada, Australia, and US.Genetic uniformity due to developing FHB resistance?Re-emergence of barberries in the Midwest?Other resources:Global Rust Initiativehttp://www.globalrust.org/Jin, Y., and Singh, R. P. 2006. Resistance in U.S. wheat to recent eastern African isolates of Puccinia graminis f. sp. tritici with virulence to resistance gene Sr31.  Plant Dis. 90:476-480./ARSUserFiles/50620500/Cerealrusts/US_resis.pdfRust ARS, Cooperators Fight New Strain of Wheat Stem/is/pr/2006/060201.htm


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