Detection of Virulence to Wheat Stem Rust Resistance Gene Sr31 in Puccinia graminis. f. sp. tritici in Uganda

In much of the world, resistance to stem rust in wheat, caused by Puccinia graminis f. sp. tritici, is based at least in part on the gene Sr31. During February 1999, high levels of stem rust infection were observed on entries in wheat (Triticum aestivum) grown in a nursery at Kalengyere Research Station in Uganda. Because several of the rusted entries were known to carry the 1BL-1RS chromosome translocation containing the Sr31, Lr26, and Yr9 genes for rust resistance, virulence to Sr31 was suspected. Urediniospores, collected in bulk from rusted stems of seven entries containing Sr31, were suspended in light mineral oil and sprayed on primary leaves of 7-day-old seedlings of South African wheat cv. Gamtoos (=Veery #3, pedigree: Kvz/Buho‘S’//Kal/BB). Plants were kept overnight at 19 to 21°C in a dew chamber before placement in a greenhouse at 18 to 25°C. After ≈14 days, urediniospores were collected from large, susceptible-type stem rust pustules and subsequently increased on Gamtoos, which served as a selective host for the new rust culture, designated Pgt-Ug99. Pathogenicity of Pgt-Ug99 was studied in seedling tests of available wheats containing Sr31, as well as other stem rust differential lines. All seedling tests were conducted at least three times in independent inoculations. Isolate Pgt-Ug99 was not virulent to Avocet‘S’/Yr9 (Australian line containing Sr26) or Oom Charl (South African cultivar) but was virulent to the other Sr31 testers: Alondra ‘S’, Bobwhite, Chokka, Clement, Federation/Kavkaz, Gamtoos, Grebe, Kavkaz, Letaba, Line E/Kavkaz, RL6078, and Veery ‘S’. Virulence to Sr31 (infection types [ITs] 3-3 to 3++4) was clearly contrasted by the low reactions (ITs 0; to 1) produced by UVPgt53, a South African pathotype avirulent to Sr31. According to the reactions of the differential lines, Pgt-Ug99 is avirulent to Sr21, -22, -24, -25, -26, -27, -29, -32, -33, -34, -35, -36, -39, -40, -42, and -43, Agi, and Em and virulent to Sr5, -6, -7b, -8a, -8b, -9b, -9e, -9g, -11, -15, -17, -30, -31, and -38. Virulence to the T. ventricosum-derived gene Sr38, which is linked to Lr37 and Yr17 and occurs in cultivars from Australia, the United Kingdom, and the United States, was not known previously (1). Both Pgt-Ug99 and UVPgt53 produced a continuum of ITs (; to 2+3) on Petkus rye (obtained from the USDA-ARS National Small Grains Collection, Aberdeen, ID), the original Sr31 donor source. Pgt-Ug99 did not appear more virulent than UVPgt53 on Petkus. All triticales tested, as well as oat cv. Overberg, were highly resistant to Pgt-Ug99. According to McIntosh et al. (1), Huerta-Espino mentioned a Sr31-virulent culture from Turkey, but this could not be confirmed. Should the Sr31-virulent pathotype migrate out of Uganda, it poses a major threat to wheat production in countries where the leading cultivars have resistance based on this gene. Reference: (1) R. A. McIntosh et al. 1995. Wheat Rusts: An Atlas of Resistance Genes. Kluwer Academic Publishers, Dordrecht, the Netherlands.

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Identification of Resistance to Races of Puccinia graminis f. sp. tritici with Broad Virulence in Triticale (×Triticosecale)

Plant Disease ◽

10.1094/pdis-05-12-0459-re ◽

2013 ◽

Vol 97 (4) ◽

pp. 479-484 ◽

Cited By ~ 9

Author(s):

P. D. Olivera ◽

Z. A. Pretorius ◽

A. Badebo ◽

Y. Jin

Keyword(s):

South African ◽

Stem Rust ◽

Triticum Turgidum ◽

Puccinia Graminis ◽

Wheat Stem Rust ◽

Cereal Rye ◽

Infection Types ◽

Stem Rust Resistance Genes ◽

Moderately Resistant ◽

Excellent Source

Triticale (×Triticosecale), an amphiploid of wheat (mainly Triticum turgidum) and cereal rye (Secale cereale), is an excellent source of resistance to wheat stem rust, caused by Puccinia graminis f. sp. tritici. A collection of 567 triticale accessions originating from 21 countries was evaluated at the seedling stage for reaction to races of P. graminis f. sp. tritici with broad virulence, including TTKSK, TRTTF, and TTTTF. A high frequency (78.4%) of accessions was resistant to race TTKSK, with low infection types ranging from 0; to X. A selection of 353 TTKSK-resistant accessions was evaluated for reaction to three South African isolates of P. graminis f. sp. tritici with single and/or combined virulences to stem rust resistance genes SrSatu, Sr27, and SrKw present in triticale. Genes SrSatu, Sr27, and SrKw were postulated to be present in 141 accessions and contributed to TTKSK resistance. The remaining 212 resistant accessions may possess uncharacterized genes or combinations of known genes that could not be determined with these isolates. These accessions were further evaluated for resistance to races TTKST, TPMKC, RKQQC, RCRSC, QTHJC, QCCSM, and MCCFC. Resistance remained effective across the entire set of races in the majority of the accessions (n = 200), suggesting that the resistances are effective against a broad spectrum of virulence. In all, 129 (79.6%) resistant accessions with noncharacterized genes were resistant to moderately resistant in field stem rust nurseries at Debre Zeit (Ethiopia) and St. Paul (Minnesota). Results from evaluating F2 populations derived from resistant–susceptible crosses revealed that resistance to TTKSK in triticale was conferred mostly by single genes with dominant effects.

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Races of Puccinia graminis Identified in the United States During 2003

Plant Disease ◽

10.1094/pd-89-1125 ◽

2005 ◽

Vol 89 (10) ◽

pp. 1125-1127 ◽

Cited By ~ 28

Author(s):

Y. Jin

Keyword(s):

United States ◽

Resistance Genes ◽

Stem Rust ◽

Rust Resistance ◽

The United States ◽

Stem Rust Resistance ◽

Puccinia Graminis ◽

Wheat Stem Rust ◽

Stem Rust Resistance Genes ◽

Rust Resistance Genes

Stem rust of small grain cereals, caused by Puccinia graminis, is a major disease of wheat, barley, and oat. In order to effectively utilize stem rust resistance in the improvement of small grain cereals, it is necessary to monitor the virulence composition and dynamics in the stem rust population. Races of P. graminis from barberry, wheat, barley, and oat were surveyed across the United States during 2003. Aecial infections on barberry were primarily due to P. graminis f. sp. secalis, as inoculations using aeciospores failed to produce infection on wheat and oat. Race QFCS of P. graminis f. sp. tritici was the most common race identified from wheat and barley. Race QFCS has virulence on stem rust resistance genes Sr5, 8a, 9a, 9d, 9g, 10, 17, and 21 that are used for race identification. Race TTTT was identified in 2003. This race possesses virulence to all 16 stem rust resistance genes present in the wheat stem rust differentials and should be targeted in breeding for stem rust resistance. Race QFCN appeared to be a new race in the U.S. stem rust population. Races QCCJ and MCCF were identified, but at low frequencies. Seven races of P. graminis f. sp. avenae were identified from oat, and races NA-27, NA-29, and NA-67 were the predominant races. Race NA-76 was identified for the first time in the United States.

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Prevalence and Distribution of Common Barberry, the Alternate Host of Puccinia graminis, in Minnesota

Plant Disease ◽

10.1094/pd-89-0159 ◽

2005 ◽

Vol 89 (2) ◽

pp. 159-163 ◽

Cited By ~ 12

Author(s):

P. D. Peterson ◽

K. J. Leonard ◽

J. D. Miller ◽

R. J. Laudon ◽

T. B. Sutton

Keyword(s):

United States ◽

Stem Rust ◽

Active Sites ◽

The United States ◽

Puccinia Graminis ◽

Alternate Host ◽

Wheat Stem Rust ◽

State Program ◽

Cereal Production ◽

Active Class

A federal and state program operated from 1918 until the 1980s to eradicate common barberry (Berberis vulgaris), the alternate host of Puccinia graminis, from the major areas of cereal production in the United States. Over 500 million bushes were destroyed nationally during the program, approximately 1 million in Minnesota. Some sites in Minnesota where barberry bushes were destroyed remained in the “active” class when eradication was phased out in the 1980s. Active sites were defined as those on which there was still a possibility of emergence of barberry seedlings or sprouts arising from the parent bush. In the present study, from 1998 to 2002, 72 of the approximately 1,200 active sites in Minnesota were surveyed. Areas within 90 m of mapped locations of previously destroyed bushes were searched carefully at each site. Reemerged barberry plants were found on 32 sites. The reproductive status and GPS coordinates were recorded for each reemerged bush. More than 90% of the barberry bushes were found in counties with less than 400 ha of wheat per county, mostly in southeastern Minnesota, but one bush was found in a major wheat-producing county in northwestern Minnesota. Reemergence of barberry may serve as a source of new wheat stem rust races in future epidemics.

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First Report of a New TTKSF Race of Wheat Stem Rust (Puccinia graminis f. sp. tritici) in South Africa and Zimbabwe

Plant Disease ◽

10.1094/pdis-12-11-1027-pdn ◽

2012 ◽

Vol 96 (4) ◽

pp. 590-590 ◽

Cited By ~ 45

Author(s):

Z. A. Pretorius ◽

L. J. Szabo ◽

W. H. P. Boshoff ◽

L. Herselman ◽

B. Visser

Keyword(s):

South Africa ◽

South African ◽

Stem Rust ◽

Infection Type ◽

Puccinia Graminis ◽

Nucleotide Polymorphisms ◽

Wheat Stem Rust ◽

Letter Code ◽

Formed Part ◽

Sr Gene

Seven races have been described in the Ug99 race group of Puccinia graminis f. sp. tritici (2). Ug99-related races previously recorded in South Africa are TTKSF, TTKSP, and PTKST (4). In December 2010, severe stem rust infection of the winter wheat cv. Matlabas was observed for the first time in South Africa. Race analysis using the 20 North American (NA) stem rust differential lines and letter code system classified the race as TTKSF. In comparative infection studies in a greenhouse, cv. Matlabas seedlings were susceptible (infection type [IT] 4) to isolate UVPgt61/1 (TTKSF+) collected from Afrikaskop in the eastern Free State, whereas the cultivar was resistant (IT 1 to 2) to stem rust isolates 2013 (TTKSF), UVPgt55 (TTKSF), UVPgt59 (TTKSP), and UVPgt60 (PTKST). Isolate 2013 represents the original collection of race TTKSF in South Africa (1). In addition to the NA differentials, no variation in the IT range of seedlings of lines with Sr7a, 8b, 12, 13, 14, 16, 18, 19, 22, 25, 26, 27, 28, 29, 32, 33, 34, 35, 39, 41, 42, 43, 44, Em, R, Tt2, and Satu was observed between UVPgt61/1 and UVPgt55. With the exception of cv. Matlabas, ITs of 106 South African cultivars likewise did not differentiate UVPgt61/1 and UVPgt55. Seedling IT studies were conducted at least twice. Microsatellite analysis (4) showed that all single pustule isolates established from the original Matlabas isolate formed part of the Ug99 group. When characterized with selected single nucleotide polymorphisms (SNPs), all single pustule isolates shared an identical genotype that differed from UVPgt55 (TTKSF), a foreign introduction into South Africa (1,3). SNP genotype analysis suggests that UVPgt61/1 is genetically dissimilar to UVPgt55, as is Zim1009, another TTKSF+ isolate that was collected from Birchenough in Zimbabwe. Studies are underway to determine the identity of the defeated Sr gene in Matlabas and the cultivar has been added to the South African stem rust differential set. TTKSF+ is the eighth race detected in the Ug99 group. Since no other cultivars or advanced lines were found to carry the Matlabas gene, it is unlikely that race TTKSF+ will threaten wheat production in South Africa. However, the occurrence of a new Ug99-related race emphasizes the variability within this internationally important group. References: (1) W. H. P. Boshoff et al. Plant Dis. 86:922, 2002. (2) R. F. Park et al. Euphytica 179:109, 2011. (3) B. Visser et al. Mol. Plant Pathol. 10:213, 2009. (4) B. Visser et al. Euphytica 179:119, 2011.

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Races of Puccinia graminis in the United States During 1997 and 1998

Plant Disease ◽

10.1094/pdis.2002.86.6.568 ◽

2002 ◽

Vol 86 (6) ◽

pp. 568-572 ◽

Cited By ~ 16

Author(s):

D. V. McVey ◽

D. L. Long ◽

J. J. Roberts

Keyword(s):

United States ◽

Stem Rust ◽

The United States ◽

Puccinia Graminis ◽

Yield Losses ◽

Wheat Stem Rust ◽

The West ◽

East Central ◽

Central Texas ◽

Wheat Lines

Wheat stem rust caused negligible yield losses in 1997 and 1998. Overwintering sites were found in central and east-central Louisiana in 1997, and in northwestern Florida, northeastern Louisiana, and central Texas in 1998. Race Pgt-TPMK predominated in 1997 with 69% of 100 isolates with race RCRS next at 11%. In 1998, race RCRS predominated with 55% of 132 isolates, and TPMK occurred at 10%. Race QFCS occurred at 8% in 1997 and 31% in 1998. Races QCCS and QTHJ were found in 1997, and races QFBS, RKMQ, RKQQ, and RCMS were found in 1998. Race QCCJ, virulent to barley with the Rpg1 gene for stem rust resistance, was not found from wheat in 1997 or 1998. No virulence was found to wheat lines with Sr 13, 22, 24, 25, 26, 27, 29, 30, 31, 32, 37, Gt, or Wld-1. Oat stem rust was found earlier in 1997 than 1998, but was more widespread in 1998. Race NA27, virulent to Pg-1, -2, -3, -4, and -8, was the predominant race in the United States in 1997 (79% of 116 isolates) and again in 1998 (79% of 116 isolates). NA16, virulent to Pg-1, -3, and -8, was found in the south (1997 and 1998), and NA5, virulent to Pg-2 and -15, and NA10, virulent to Pg-2, -3, and -15, were found in the west (1997).

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Pathogenic Variability of Wheat Stem Rust Pathogen (Puccinia graminis f. sp. tritici) in Hararghe Highlands, Ethiopia

Advances in Agriculture ◽

10.1155/2018/8612135 ◽

2018 ◽

Vol 2018 ◽

pp. 1-7

Author(s):

Arif Abrahim ◽

Temam Hussein ◽

Ayele Badebo

Keyword(s):

Resistance Genes ◽

Stem Rust ◽

Agricultural Research ◽

Low Frequency ◽

Puccinia Graminis ◽

Total Production ◽

Rust Disease ◽

Wheat Stem Rust ◽

Pathogenic Variability ◽

Infection Types

Wheat is one of the important major crops of Hararghe Highlands. It is third in land coverage and total production after sorghum and maize. However, the wheat stem rust disease is threatening production of wheat in this region. So, this research was conducted with the following objective: to determine the population of Puccinia graminis f. sp. tritici in Hararghe Highlands. A total of 200 fields were surveyed and stem rust samples were collected and transported to Kulumsa Agricultural Research Center for race analysis. Inoculation of differentials carrying resistance genes Sr24 and Sr-Tmp indicated typical low infection types on all isolates. Isolates EH5, EH8, and EH3 from East Hararghe and WH2, WH1, and WH3 from West Hararghe showed high virulence of infection in all differential lines. Ten (10) races were identified by using Puccinia graminis tritici code system: TTGSK, PTJQK, TTSSK, TTKSK, TRSSK, and TTJQK from East Hararghe and TTTSK and TTSQK from West Hararghe zones. Race TTSSK was most frequent (25%) followed by TTKSK (25%) in East Hararghe. Race TTSSK showed 50% frequency of occurrence in West Hararghe zones. The low frequency of occurrences indicated high variability of the races in the survey areas. Therefore, monitoring of populations of pathogens is important for the national and regional research centers. Detection of pathogen virulence evolution and of currently effective resistance genes is necessary and must be applied within a system of resistance gene management.

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The Spread of Stem Rust Caused by Puccinia graminis f. sp. tritici, with Virulence on Sr31 in Wheat in Eastern Africa

Plant Disease ◽

10.1094/pd-90-0113a ◽

2006 ◽

Vol 90 (1) ◽

pp. 113-113 ◽

Cited By ~ 106

Author(s):

R. Wanyera ◽

M. G. Kinyua ◽

Y. Jin ◽

R. P. Singh

Keyword(s):

Stem Rust ◽

Rust Resistance ◽

Infection Type ◽

Single Gene ◽

Stem Rust Resistance ◽

Eastern Africa ◽

Puccinia Graminis ◽

High Infection ◽

Infection Types ◽

Sr Genes

Stem rust resistance in wheat cultivars with Sr31 has been effective and durable worldwide for more than 30 years. Isolates of Puccinia graminis f. sp. tritici with virulence to Sr31 were detected in Uganda in 1999 (1). During 2003 and 2004, a majority of current Kenyan cultivars and a large portion of CIMMYT wheat germplasm with gene Sr31 planted in Kenya were susceptible to stem rust. Six isolates collected during 2004 at different locations in Kenya were tested for virulence on the 16 North American stem rust race differentials with the following Sr genes: Sr5, 6, 7b, 8a, 9a, 9b, 9d, 9e, 9g, 10, 11, 17, 21, 30, 36, and Tmp. An extended set of designated Sr genes (Sr13, 19, 22, 24, 25, 26, 29, 31, 32, 33, 35, 37, 39, 40, 44, and Wld-1) was also tested at the seedling stage. An isolate from Uganda collected in 1999 with virulence on Sr31 was used for comparison. Urediniospores suspended in a lightweight mineral oil were inoculated onto 7-day-old seedlings. Inoculated plants were placed in a dew chamber for 14 h at 18°C in the dark and then for an additional period of 3 to 4 h placed under fluorescent light. Plants were incubated in a greenhouse at 18 ± 2°C with a photoperiod of 16 h. Infection types (IT), described by Stakman et al. (3), were assessed after 14 days postinoculation. All isolates from Kenya exhibited a low infection type (IT 0) on line W2691SrTt-1 (donor of Sr36), a low infection type (IT 2) on cv. Triumph 64 (donor of SrTmp), and high infection types (IT 3 or 4) on all other lines in the differential set (2); thus these isolates were keyed to race TTKS. The virulence pattern of the isolate collected in 1999 from Uganda was identical to that from Kenya on the differential set and on the extended set of designated Sr genes. In this study, these isolates produced a high infection type (IT 3) on Einkorn and CnSSr21Tm (a derivative of Triticum monococcum in Chinese Spring background), two sources of Sr21 used in our study, whereas the isolate with Sr31-virulence from Uganda in 1999 was reported to be avirulent on Sr21 (1). These isolates produced high infection types on single gene lines with Sr31 and winter wheat cvs. Custer, Foster, GA-Dozier, Patton, and Pioneer 26R61, which were known to carry the 1BL.1RS translocation with Sr31. These isolates were also virulent on SrWld-1, a gene used in spring wheat for its resistance to North American stem rust isolates. In addition to Sr36 and SrTmp, other stem rust resistance genes that were effective against TTKS at the seedling stage include Sr13, 22, 24, 25, 26, 27, 29, 32, 33, 35, 37, 39, 40, and 44. Cultivars, breeding germplasm, and single gene lines are currently being evaluated for adult plant reaction in Kenya. Results from this study indicated that stem rust isolates with virulence on Sr31 are now wide spread in the Eastern Africa highlands and pose a threat to wheat production in the region, as well as in other wheat production areas where Sr31 resistance is important. A rapid deployment of effective resistance genes to this race in breeding programs throughout Eastern Africa and Asia is needed to reduce this threat. References: (1) Z. A. Pretorius et al. Plant Dis. 84:203, 2000. (2) A. P. Roelfs and J. W. Martens. Phytopathology 78:526, 1988. (3) E. C. Stakman et al. U.S. Department of Agriculture. ARS E-617, 1962.

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Markers Linked to Wheat Stem Rust Resistance Gene Sr11 Effective to Puccinia graminis f. sp. tritici Race TKTTF

Phytopathology ◽

10.1094/phyto-04-16-0165-r ◽

2016 ◽

Vol 106 (11) ◽

pp. 1352-1358 ◽

Cited By ~ 14

Author(s):

Jayaveeramuthu Nirmala ◽

Shiaoman Chao ◽

Pablo Olivera ◽

Ebrahiem M. Babiker ◽

Bekele Abeyo ◽

...

Keyword(s):

Stem Rust ◽

Rust Resistance ◽

Genetic Resistance ◽

Wheat Breeding ◽

Snp Markers ◽

Stem Rust Resistance ◽

Puccinia Graminis ◽

Wheat Stem Rust ◽

Wheat Varieties ◽

Breeding Lines

Wheat stem rust, caused by Puccinia graminis f. sp. tritici, can cause severe yield losses on susceptible wheat varieties and cultivars. Although stem rust can be controlled by the use of genetic resistance, population dynamics of P. graminis f. sp. tritici can frequently lead to defeat of wheat stem rust resistance genes. P. graminis f. sp. tritici race TKTTF caused a severe epidemic in Ethiopia on Ug99-resistant ‘Digalu’ in 2013 and 2014. The gene Sr11 confers resistance to race TKTTF and is present in ‘Gabo 56’. We identified seven single-nucleotide polymorphism (SNP) markers linked to Sr11 from a cross between Gabo 56 and ‘Chinese Spring’ exploiting a 90K Infinium iSelect Custom beadchip. Five SNP markers were validated on a ‘Berkut’/‘Scalavatis’ population that segregated for Sr11, using KBioscience competitive allele-specific polymerase chain reaction (KASP) assays. Two of the SNP markers, KASP_6BL_IWB10724 and KASP_6BL_IWB72471, were predictive of Sr11 among wheat genetic stocks, cultivars, and breeding lines from North America, Ethiopia, and Pakistan. These markers can be utilized to select for Sr11 in wheat breeding and to detect the presence of Sr11 in uncharacterized germplasm.

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The wheat Sr22, Sr33, Sr35 and Sr45 genes confer resistance against stem rust in barley

10.1101/374637 ◽

2018 ◽

Cited By ~ 3

Author(s):

M. Asyraf Md. Hatta ◽

Ryan Johnson ◽

Oadi Matny ◽

Mark A. Smedley ◽

Guotai Yu ◽

...

Keyword(s):

Resistance Genes ◽

Stem Rust ◽

Rust Resistance ◽

Stem Rust Resistance ◽

Puccinia Hordei ◽

Puccinia Graminis ◽

Golden Promise ◽

Wheat Stem Rust ◽

Potential Source ◽

Barley Leaf

SummaryIn the last 20 years, stem rust caused by the fungus Puccinia graminis f. sp. tritici (Pgt), has re-emerged as a major threat to wheat and barley cultivation in Africa and Europe. In contrast to wheat with 82 designated stem rust (Sr) resistance genes, barley’s genetic variation for stem rust resistance is very narrow with only seven resistance genes genetically identified. Of these, only one locus consisting of two genes is effective against Ug99, a strain of Pgt which emerged in Uganda in 1999 and has since spread to much of East Africa and parts of the Middle East. The objective of this study was to assess the functionality, in barley, of cloned wheat Sr genes effective against Ug99. Sr22, Sr33, Sr35 and Sr45 were transformed into barley cv. Golden Promise using Agrobacterium-mediated transformation. All four genes were found to confer effective stem rust resistance. The barley transgenics remained susceptible to the barley leaf rust pathogen Puccinia hordei, indicating that the resistance conferred by these wheat Sr genes was specific for Pgt. Cloned Sr genes from wheat are therefore a potential source of resistance against wheat stem rust in barley.

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Races of Puccinia graminis f. sp. tritici with Combined Virulence to Sr13 and Sr9e in a Field Stem Rust Screening Nursery in Ethiopia

Plant Disease ◽

10.1094/pdis-09-11-0793 ◽

2012 ◽

Vol 96 (5) ◽

pp. 623-628 ◽

Cited By ~ 47

Author(s):

P. D. Olivera ◽

Y. Jin ◽

M. Rouse ◽

A. Badebo ◽

T. Fetch ◽

...

Keyword(s):

Resistance Genes ◽

North American ◽

Stem Rust ◽

Rust Resistance ◽

The United States ◽

Stem Rust Resistance ◽

Seedling Stage ◽

Puccinia Graminis ◽

Stem Rust Resistance Genes ◽

Rust Resistance Genes

North American durum lines, selected for resistance to TTKSK (Ug99) and related races of Puccinia graminis f. sp. tritici in Kenya, became susceptible in Debre Zeit, Ethiopia, suggesting the presence of stem rust races that were virulent to the TTKSK-effective genes in durum. The objective of this study was to characterize races of P. graminis f. sp. tritici present in the Debre Zeit, Ethiopia stem rust nursery. Three races of P. graminis f. sp. tritici were identified from 34 isolates: JRCQC, TRTTF, and TTKSK. Both races JRCQC and TRTTF possess virulence on stem rust resistance genes Sr13 and Sr9e, which may explain why many TTKSK-resistant durum lines tested in Kenya became susceptible in Debre Zeit. The Sr9e-Sr13 virulence combination is of particular concern because these two genes constitute major components of stem rust resistance in North American durum cultivars. In addition to Sr9e and Sr13 virulence, race TRTTF is virulent to at least three stem rust resistance genes that are effective to race TTKSK, including Sr36, SrTmp, and resistance conferred by the 1AL.1RS rye translocation. Race TRTTF is the first known race with virulence to the stem rust resistance carried by the 1AL.1RS translocation, which represents one of the few effective genes against TTKSK in winter wheat cultivars in the United States. Durum entries exhibiting resistant to moderately susceptible infection response at the Debre Zeit nursery in 2009 were evaluated for reaction to races JRCQC, TRTTF, and TTKSK at the seedling stage. In all, 47 entries were resistant to the three races evaluated at the seedling stage, whereas 26 entries exhibited a susceptible reaction. These results suggest the presence of both major and adult plant resistance genes, which would be useful in durum-wheat-breeding programs. A thorough survey of virulence in the population of P. graminis f. sp. tritici in Ethiopia will allow characterization of the geographic distribution of the races identified in the Debre Zeit field nursery.

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