Ug99

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Resistance to Stem Rust Race TTKSK Maps to the rpg4/Rpg5 Complex of Chromosome 5H of Barley

Race TTKSK (Ug99) of the wheat stem rust pathogen (Puccinia graminis f. sp. tritici) is a serious threat to both wheat and barley production worldwide because of its wide virulence on many cultivars and rapid spread from eastern Africa.

Steffenson,B. J.; Jin,Y.; Brueggeman,R. S.; Kleinhofs,A.; Sun,Y.
Phytopathology
Year: 
2009
Volume: 
99
Issue: 
10.0
Start Page: 
1135.0
Other Page(s): 
1141.0

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

Wheat stem rust (Puccinia graminis f. sp. tritici) race TTKSK (Ug99), with virulence to the majority of the world's wheat (Triticum aestivum) cultivars, has spread from Uganda throughout eastern Africa, Yemen, and Iran. The identification and spread of variants of race TTKSK with virulence to additional stem rust resistance genes has reminded breeders and pathologists of the danger of deploying major resistance genes alone. In order to protect wheat from this rapidly spreading and adapting pathogen, multiple resistance genes are needed, preferably from improved germplasm. Preliminary screening of over 700 spring wheat breeding lines and cultivars developed at least 20 years ago identified 88 accessions with field resistance to Ug99. We included these resistant accessions in the stem rust screening nursery in Njoro, Kenya for two additional seasons. The accessions were also screened with a bulk of North American isolates of P. graminis f. sp. tritici in the field in St. Paul, MN. In order to further characterize the resistance in these accessions, we obtained seedling phenotypes for 10 races of P. graminis f. sp. tritici, including two races from the race TTKSK complex. This phenotyping led to the identification of accessions with either adult-plant or all-stage resistance to race TTKSK, and often North American races of P. graminis f. sp. tritici as well. These Ug99 resistant accessions can be obtained by breeders and introgressed into current breeding germplasm.

Rouse,M. N.; Wanyera,R.; Njau,P.; Jin,Y.
Plant Disease
Year: 
2011
Volume: 
95
Issue: 
6.0
Start Page: 
762.0
Other Page(s): 
766.0

Identification and Evaluation of Sources of Resistance to Stem Rust Race Ug99 in Wheat

The race Ug99 of Puccinia graminis f. sp. tritici causing stem rust disease of wheat was initially identified in Uganda in 1998. It was designated as TTKSK based on the North American nomenclature and has caused periodic losses to wheat crops in East Africa. Ug99 has recently moved out of Africa to Yemen and West Asia.

Njau,Peter N.; Jin,Yue; Huerta-Espino,Julio; Keller,Beat; Singh,Ravi P.
Plant Disease
Year: 
2010
Volume: 
94
Issue: 
4.0
Start Page: 
413.0
Other Page(s): 
419.0

First Report of a Puccinia graminis f. sp. tritici Race Virulent to the Sr24 and Sr31 Wheat Stem Rust Resistance Genes in South Africa

Isolates of Puccinia graminis f. sp. tritici belonging to the Ug99 race group are virulent to a broad spectrum of resistance genes, rendering most of the world's wheat germplasm susceptible to stem rust (3). Following the initial detection of Ug99 (TTKSK, North American [NA] race notation) in Uganda, virulence to the widely used Sr31 resistance gene has been reported from Kenya, Ethiopia, Sudan, and Iran (2,3). In November 2009, a wheat genotype suspected to carry Sr31 showed a susceptible response to stem rust in a disease nursery (29°08′05.02′′S, 30°38′29.18′′E), inoculated with race TTKSP, near Greytown in KwaZulu-Natal, South Africa.

Pretorius,Z. A.; Bender,C. M.; Visser,B.; Terefe,T.
Plant Disease
Year: 
2010
Volume: 
94
Issue: 
6.0
Start Page: 
784.0
Other Page(s): 
784.0

Sources of Resistance to Stem Rust Race Ug99 in Spring Wheat Germplasm

Wheat stem rust (Puccinia graminis f. sp. tritici) race TTKSK (Ug99), with virulence to the majority of the world's wheat (Triticum aestivum) cultivars, has spread from Uganda throughout eastern Africa, Yemen, and Iran. The identification and spread of variants of race TTKSK with virulence to additional stem rust resistance genes has reminded breeders and pathologists of the danger of deploying major resistance genes alone. In order to protect wheat from this rapidly spreading and adapting pathogen, multiple resistance genes are needed, preferably from improved germplasm. Preliminary screening of over 700 spring wheat breeding lines and cultivars developed at least 20 years ago identified 88 accessions with field resistance to Ug99. We included these resistant accessions in the stem rust screening nursery in Njoro, Kenya for two additional seasons. The accessions were also screened with a bulk of North American isolates of P. graminis f. sp. tritici in the field in St. Paul, MN. In order to further characterize the resistance in these accessions, we obtained seedling phenotypes for 10 races of P. graminis f. sp. tritici, including two races from the race TTKSK complex. This phenotyping led to the identification of accessions with either adult-plant or all-stage resistance to race TTKSK, and often North American races of P. graminis f. sp. tritici as well. These Ug99 resistant accessions can be obtained by breeders and introgressed into current breeding germplasm.

M. N. Rouse; R. Wanyera and P. Njau,; Y. Jin
Plant Disease
Year: 
2011
Volume: 
95
Issue: 
6
Start Page: 
762
Other Page(s): 
766

The spread of stem rust caused by Puccinia graminis f. sp tritici, with virulence on Sr31 in wheat in Eastern Africa.

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

Wanyera,R.; Kinyua,M. G.; Jin,Y.; Singh,R. P.
Plant Disease
Year: 
2006
Volume: 
90
Issue: 
1.0
Start Page: 
113.0
Other Page(s): 
113.0
Expert pick: 
False

Current Status, likely migration and strategies to mitigate the threat to wheat production from race Ug99 (TTKS) of stem rust pathogen

Stem or black rust, caused by Puccinia graminis tritici, has historically caused severe losses to wheat (Triticum aestivum) production worldwide. Successful control of the disease for over three decades through the use of genetic resistance has resulted in a sharp decline in research activity in recent years. Detection and spread in East Africa of race TTKS, commonly known as Ug99, is of high significance as most wheat cultivars currently grown in its likely migration path, i.e. to North Africa through Arabian Peninsula and then to Middle East and Asia, are highly susceptible to this race and the environment is conducive to disease epidemics. Identifying/developing adapted resistant cultivars in a relatively short time and replacing the susceptible cultivars before rust migrates out of East Africa is the strategy to mitigate potential losses. Although several alien genes will provide resistance to this race, the long-term strategy should focus on rebuilding the 'Sr2-complex' (combination of slow rusting gene Sr2 with other unknown additive genes of similar nature) to achieve long-term durability. A Global Rust Initiative has been launched to monitor the further migration of this race, facilitate field testing in Kenya or Ethiopia of wheat cultivars and germplasm developed by wheat breeding programmes worldwide, understand the genetic basis of resistance especially the durable type, carry out targeted breeding to incorporate diverse resistance genes into key cultivars and germplasm, and enhance the capacity of national programmes. A few wheat genotypes that combine stem rust resistance with high yield potential and other necessary traits have been identified but need rigorous field testing to determine their adaptation in target areas

Singh,R. P.; Hodson,D. P.; Jin,Y.; Huerta-Espino,J.; Kinyua,M.; Wanyera,R.; Njau,P.; Ward,R.
CAB Reviews
Year: 
2006
Volume: 
1
Issue: 
Start Page: 
1.0
Other Page(s): 
13.0

Haplotype diversity of stem rust resistance loci in uncharacterized wheat lines

Stem rust is one of the most destructive diseases of wheat worldwide. The recent emergence of wheat stem rust race Ug99 (TTKS based on the North American stem rust race nomenclature system) and related strains threaten global wheat production because they overcome widely used genes that had been effective for many years. Host resistance is likely to be more durable when several stem rust resistance genes are pyramided in a single wheat variety; however, little is known about the resistance genotypes of widely used wheat germplasm. In this study, a diverse collection of wheat germplasm was haplotyped for stem rust resistance genes Sr2, Sr22, Sr24, Sr25, Sr26, Sr36, Sr40, and 1A.1R using linked microsatellite or simple sequence repeat (SSR) and sequence tagged site (STS) markers. Haplotype analysis indicated that 83 out of 115 current wheat breeding lines from the International Maize and Wheat Improvement Center (CIMMYT) likely carry Sr2. Among those, five out of 94 CIMMYT spring lines tested had both Sr2 and Sr25 haplotypes. Five out of 22 Agriculture Research Service (ARS) lines likely have Sr2 and a few have Sr24, Sr36, and 1A.1R. Two out of 43 Chinese accessions have Sr2. No line was found to have the Sr26 and Sr40 haplotypes in this panel of accessions. DArT genotyping was used to identify new markers associated with the major stem resistance genes. Four DArT markers were significantly associated with Sr2 and one with Sr25. Principal component analysis grouped wheat lines from similar origins. Almost all CIMMYT spring wheats were clustered together as a large group and separated from the winter wheats. The results provide useful information for stem rust resistance breeding and pyramiding.

Yu,Long-Xi; Liu,Sixin; Anderson,James; Singh,Ravi; Jin,Yue; Dubcovsky,Jorge; Brown-Guidera,Gina; Bhavani,Sridhar; Morgounov,Alexey; He,Zhonghu; Huerta-Espino,Julio; Sorrells,Mark
Molecular Breeding
Year: 
2010
Volume: 
26
Issue: 
4
Start Page: 
667
Other Page(s): 
680

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

The emergence of a new highly virulent race of stem rust (Puccinia graminis tritici), Ug99, rapid evolution of new Ug99 derivative races overcoming resistance of widely deployed genes, and spread towards important wheat growing areas now potentially threaten world food security. Exploiting novel genes effective against Ug99 from wild relatives of wheat is one of the most promising strategies for the protection of the wheat crop. A new source of resistance to Ug99 was identified in the short arm of the Aegilops searsii chromosome 3S(s) by screening wheat- Ae. searsii introgression libraries available as individual chromosome and chromosome arm additions to the wheat genome. For transferring this resistance gene into common wheat, we produced three double-monosomic chromosome populations (3A/3S(s), 3B/3S(s) and 3D/3S(s)) and then applied integrated stem rust screening, molecular maker analysis, and cytogenetic analysis to identify resistant wheat-Ae. searsii Robertsonian translocation. Three Robertsonian translocations (T3AL center dot 3S(s)S, T3BL center dot 3S(s)S and T3DL center dot 3S(s)S) and one recombinant (T3DS-3S(s)S center dot 3S(s)L) with stem rust resistance were identified and confirmed to be genetically compensating on the basis of genomic in situ hybridization, analysis of 3A, 3B, 3D and 3S(s)S-specific SSR/STS-PCR markers, and C-banding. In addition, nine SSR/STS-PCR markers of 3S(s)S-specific were developed for marker-assisted selection of the resistant gene. Efforts to reduce potential linkage drag associated with 3S(s)S of Ae. searsii are currently under way.

Liu,W. X.; Jin,Y.; Rouse,M.; Friebe,B.; Gill,B.; Pumphrey,M. O.
Theoretical and Applied Genetics
Year: 
2011
Volume: 
122
Issue: 
8
Start Page: 
1537.0
Other Page(s): 
1545.0
Expert pick: 
False

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

Stem rust (Puccinia graminis f. sp. tritici Eriks. & E. Henn.) (the causal agent of wheat stem rust) race Ug99 (also designated TTKSK) and its derivatives have defeated several important stem rust resistance genes widely used in wheat (Triticum aestivum L.) production, rendering much of the worldwide wheat acreage susceptible. In order to identify new resistance sources, a large collection of wheat relatives and genetic stocks maintained at the Wheat Genetic and Genomic Resources Center was screened. The results revealed that most accessions of the diploid relative Dasypyrum villosum (L.) Candargy were highly resistant. The screening of a set of wheat-D. villosum chromosome addition lines revealed that the wheat-D. villosum disomic addition line DA6V#3 was moderately resistant to race Ug99. The objective of the present study was to produce and characterize compensating wheat-D. villosum whole arm Robertsonian translocations (RobTs) involving chromosomes 6D of wheat and 6V#3 of D. villosum through the mechanism of centric breakage-fusion. Seven 6V#3-specific EST-STS markers were developed for screening F-2 progeny derived from plants double-monosomic for chromosomes 6D and 6V#3. Surprisingly, although 6D was the target chromosome, all recovered RobTs involved chromosome 6A implying a novel mechanism for the origin of RobTs. Homozygous translocations (T6AS.6V#3L and T6AL.6V#3S) with good plant vigor and full fertility were selected from F-3 families. A stem rust resistance gene was mapped to the long arm 6V#3L in T6AS.6V#3L and was designated as Sr52. Sr52 is temperature-sensitive and is most effective at 16 degrees C, partially effective at 24 degrees C, and ineffective at 28 degrees C. The T6AS.6V#3L stock is a new source of resistance to Ug99, is cytogenetically stable, and may be useful in wheat improvement.

Qi,L. L.; Pumphrey,M. O.; Friebe,Bernd; Zhang,P.; Qian,C.; Bowden,R. L.; Rouse,M. N.; Jin,Y.; Gill,B. S.
Theoretical and Applied Genetics
Year: 
2011
Volume: 
123
Issue: 
1.0
Start Page: 
159.0
Other Page(s): 
167.0

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