Ug99 is a lineage of wheat stem rust (Puccinia graminis f. sp. tritici), which is present in wheat fields in several countries in Africa and the Middle East and is predicted to spread rapidly through these regions and possibly further afield, potentially causing a wheat production disaster that would affect food security worldwide.[1] In 2005 the noted green revolution pioneer Norman Borlaug brought great attention to the problem, and most subsequent efforts can be traced to his advocacy.[2] It can cause up to 100% crop losses and is virulent against many resistance genes which have previously protected wheat against stem rust.
Although Ug99-resistant varieties of wheat do exist,[2] a screen of 200,000 wheat varieties used in 22 African and Asian countries found that only 5-10% of the area of wheat grown in these countries consisted of varieties with adequate resistance.[1]
The original race of Ug99, which is designated as 'TTKSK' under the North American nomenclature system, was first detected in Uganda in 1998[3] and first characterised in 1999[3] (hence the name Ug99) and has since been detected in Kenya, Ethiopia, Eritrea, Sudan, Yemen, Iran, Tanzania, Mozambique, Zimbabwe, South Africa,[4] and Egypt. There are now 15 known races of Ug99.[5] They are all closely related and are believed to have evolved from a common ancestor, but differ in their virulence/avirulence profiles and the countries in which they have been detected.[1]
Geneticsedit
Ug99 is the product of a type of somatic nuclear exchange event which has not been observed in other stem rust races.[6] During this event and thereafter the nuclei have not experienced recombination.[6]
Gene resistanceedit
Ug99 and its variants differ from other strains of the Black Stem Rust (BSR) pathogen due to their ability to overcome resistance genes in wheat that have been durable against the BSR pathogen for decades.[7] These resistant Sr genes, of which 50 are known, give wheat different resistances to stem rust.[3] The virulence in Uganda was virulent against Sr31 and is specific to Ug99.[3] The massive losses of wheat that have occurred have been devastating, but in recent years the wheat rust epidemic has been effectively controlled through selection and breeding for additional Sr genes.[3] (In the decades since, however, Sr31-virulence has evolved in other strains in other locations.[8] Patpour et al., 2022 finds it in Spain and Siberia.)[8]
United States Department of Agriculture (USDA) researchers are testing genes to determine their Ug99 resistance, which will ultimately aid in the development of wheat varieties that will be able to fight off the rust. Resistance has been identified in a small number of spring wheat land races from North America - 23 out of 250 races with adult plant resistance, 27 out of 23,976 SNPs conveying APR, and only 9 races having seedling resistance.[9] This resistance was present without the Ug99 pathogen challenge being present in NA to drive its selection.[9] USDA has studied winter wheat land races where resistance is more probable.[10]
In addition to the research being conducted by the USDA, The United Kingdom’s Department for International Development (DFID) along with Bill & Melinda Gates Foundation, announced in February 2011 that they will be granting $40 million to a global project led by Cornell University to combat virulent strains of Ug99.[11] The five-year grant to the Durable Rust Resistance in Wheat (DRRW) project supported attempts to identify new resistance genes as well as reproduce and distribute rust resistant wheat seeds to farmers.[11]
There has been a continuous process of development of new resistant cultivars and failure of those cultivars.[12] This demonstrates the need for continuous improvement.[12]
As of 2020[update] modern molecular and molecular genetics techniques are identifying quantitative trait loci (QTLs), particular cellular structures, and individual R genes more efficiently than ever before.[13] These will be needed given the continuing severe, worldwide threat Ug99 poses.[13][1]
Sr35 confers resistance to all other severe Pgt races and the original Ug99.[14] Salcedo et al., 2017 finds its Avr target, AvrSr35.[14] Races virulent on Sr35 benefit from nonfunctionalization of AvrSr35 by insertion of a mobile element.[14]
Racesedit
There are 15 races of Ug99, which (under the North American nomenclature system) have the designations TTKSK, TTKSF, TTKST, TTTSK, TTKSP, PTKSK, PTKST, TTKSF+,[4] TTKTT, TTKTK, TTHSK, PTKTK, TTHST, TTKTT+, and TTHTT.[5] They are all closely related and are believed to have evolved from a common ancestor.[1]
Discovered in Kenya in 2006[16] was the first Ug99 race found to be virulent against Sr gene Sr24.[1][16] TTKST is now the predominant stem rust race in Kenya.[1]Virulent on Sr31.[5]
First detected in Kenya in 2014.[5] Also detected in Iraq in 2019, the first such detection in the country.[5] Found in Nepal in 2023.[22]Virulent on Sr31, Sr24, and SrTmp.[5]
Because stem rust (as with many fungi) spreads its spores across long distances with the help of natural air currents, containment is difficult.[28] Advances in fluid mechanics which are commonly used for meteorology have also aided Ug99 dispersal prediction.[28] This is especially important for inter-continental, intermittent spread, such as from Eastern South Africa to Western Australia.[28]
Chinaedit
Although Ug99 has not yet reached China,[29] other stem rust races already have,[29] and an effort is under way to marry resistance against present races with future needs for resistance against Ug99 whenever it arrives.[29]
Lebanonedit
Although Sr5, Sr21, Sr9e, Sr7b, Sr11, Sr6, Sr8a, Sr9g, Sr9b, Sr30, Sr17, Sr9a, Sr9d, Sr10, SrTmp, Sr38, and SrMcN are no longer effective in Lebanon, Sr11, Sr24, and Sr31 still are which is diagnostic for the absence of Ug99 from Lebanon.[30]
Low-levels of TTKTT were detected in Nepal in 2023, but surveillance has not revealed any propagation in the region.[31] As of 2013[update] it was the US Director of National Intelligence's assessment that Ug99 would arrive in South Asia soon, in the following few years. This was expected to cause worldwide supply disruptions because, although productivity was growing in Eastern Europe and could theoretically fill that gap, governments worldwide had shown a readiness to forbid exports.[32]
• Pretorius, Z. A.; Singh, R. P.; Wagoire, W. W.; Payne, T. S. (2000). "Detection of Virulence to Wheat Stem Rust Resistance Gene Sr31 in Puccinia graminis. f. sp. tritici in Uganda". Plant Disease. 84 (2). American Phytopathological Society: 203. doi:10.1094/pdis.2000.84.2.203b. ISSN 0191-2917. PMID 30841334. S2CID 73469939.
• Singh, Ravi P.; Hodson, David P.; Huerta-Espino, Julio; Jin, Yue; Bhavani, Sridhar; Njau, Peter; Herrera-Foessel, Sybil; Singh, Pawan K.; Singh, Sukhwinder; Govindan, Velu (8 September 2011). "The Emergence of Ug99 Races of the Stem Rust Fungus is a Threat to World Wheat Production". Annual Review of Phytopathology. 49 (1). Annual Reviews: 465–481. doi:10.1146/annurev-phyto-072910-095423. ISSN 0066-4286. PMID 21568701. S2CID 24770327.
• Singh, Ravi P.; Hodson, David P.; Huerta-Espino, Julio; Jin, Yue; Njau, Peter; Wanyera, Ruth; Herrera-Foessel, Sybil A.; Ward, Richard W. (2008). "Will Stem Rust Destroy the World's Wheat Crop?". Advances in Agronomy. Vol. 98. Elsevier. pp. 271–309/xiii+422. doi:10.1016/s0065-2113(08)00205-8. ISBN 9780123743558. ISSN 0065-2113. S2CID 55174564.
^ abcdefghHodson, D. P.; Grønbech-Hansen, J.; Lassen, P.; Alemayehu, Y.; Arista, J.; Sonder, K.; Kosina, P.; Moncada, P.; Nazari, K.; Park, R. F.; Pretorius, Z. A.; Szabo, L. J.; Fetch, T.; Jin, Y. "Tracking the Wheat Rust Pathogens" (PDF). 2012 Borlaug Global Rust Initiative Technical Workshop Proceedings. Borlaug Global Rust Initiative. Archived (PDF) from the original on October 5, 2019. Retrieved 28 November 2012.
• Scheben, Armin; Verpaalen, Brent; Lawley, Cynthia T.; Chan, Chon‐Kit K.; Bayer, Philipp E.; Batley, Jacqueline; Edwards, David (2019-01-28). "CropSNPdb: a database of SNP array data for Brassica crops and hexaploid bread wheat". The Plant Journal. 98 (1). John Wiley & Sons: 142–152. doi:10.1111/tpj.14194. ISSN 0960-7412. PMID 30548723. S2CID 56486847. Society for Experimental Biology (SEB).
• Bajgain, Prabin; Jin, Yue; Tsilo, Toi J.; Macharia, Godwin K.; Reynolds, Susan E.; Wanyera, Ruth; Anderson, James A. (2020-05-14). "Registration of KUWNSr, a wheat stem rust nested association mapping population". Journal of Plant Registrations. 14 (3). John Wiley & Sons, Inc.: 467–473. doi:10.1002/plr2.20043. ISSN 1936-5209. S2CID 219423451.
^ abMcCandless, Linda (February 27, 2011). "$40M grant to fight wheat pathogen that threatens global food security". Cornell Chronicle. Retrieved October 5, 2019.
• Wessels, Elsabet; Prins, Renée; Boshoff, Willem H. P.; Zurn, Jason D.; Acevedo, Maricelis; Pretorius, Zacharias A. (2019). "Mapping a Resistance Gene to Puccinia graminis f. sp. tritici in the Bread Wheat Cultivar 'Matlabas'". Plant Disease. 103 (9). American Phytopathological Society: 2337–2344. doi:10.1094/pdis-10-18-1731-re. ISSN 0191-2917. PMID 31306087. S2CID 146090970.
• Fetch, Thomas; Park, Robert; Pretorius, Zacharias; Depauw, Ronald (2021). "Stem rust: its history in Kenya and research to combat a global wheat threat". Canadian Journal of Plant Pathology. 43 (sup2). Taylor & Francis: S275–S297. doi:10.1080/07060661.2021.1902860. ISSN 0706-0661. S2CID 233672540.
• Pretorius, Zacharias A.; Prins, Renée; Wessels, Elsabet; Bender, Cornel M.; Visser, Botma; Boshoff, Willem H.P. (2020-11-26). "Accomplishments in wheat rust research in South Africa". South African Journal of Science. 116 (11/12). Academy of Science of South Africa: 1–8. doi:10.17159/sajs.2020/7688. ISSN 1996-7489. S2CID 229382857.
^ abDeng, Yiwen; Ning, Yuese; Yang, Dong-Lei; Zhai, Keran; Wang, Guo-Liang; He, Zuhua (2020-10-05). "Molecular Basis of Disease Resistance and Perspectives on Breeding Strategies for Resistance Improvement in Crops". Molecular Plant. 13 (10). Cell Press: 1402–1419. doi:10.1016/j.molp.2020.09.018. ISSN 1674-2052. PMID 32979566. S2CID 221955936.
• Jin, Yue; Szabo, Les J.; Pretorius, Zacharias A.; Singh, Ravi P.; Ward, R.; Fetch, T. (2008). "Detection of Virulence to Resistance Gene Sr24 Within Race TTKS of Puccinia graminis f. sp. tritici". Plant Disease. 92 (6). American Phytopathological Society: 923–926. doi:10.1094/pdis-92-6-0923. ISSN 0191-2917. PMID 30769714. S2CID 55431333.
• Singh, Ravi P.; Hodson, David P.; Huerta-Espino, Julio; Jin, Yue; Bhavani, Sridhar; Njau, Peter; Herrera-Foessel, Sybil; Singh, Pawan K.; Singh, Sukhwinder; Govindan, Velu (8 September 2011). "The Emergence of Ug99 Races of the Stem Rust Fungus is a Threat to World Wheat Production". Annual Review of Phytopathology. 49 (1). Annual Reviews: 465–481. doi:10.1146/annurev-phyto-072910-095423. ISSN 0066-4286. PMID 21568701. S2CID 24770327.
• Sparks, Donald L. (2008). Advances in Agronomy. Vol. 98. London: Elsevier. pp. xiii+422. ISBN 978-0-08-088814-9. ISSN 0065-2113. OCLC 302357009. : 281
• Singh, Ravi P.; Hodson, David P.; Jin, Yue; Lagudah, Evans S.; Ayliffe, Michael A.; Bhavani, Sridhar; Rouse, Matthew N.; Pretorius, Zacharias A.; Szabo, Les J.; Huerta-Espino, Julio; Basnet, Bhoja R.; Lan, Caixia; Hovmøller, Mogens S. (2015). "Emergence and Spread of New Races of Wheat Stem Rust Fungus: Continued Threat to Food Security and Prospects of Genetic Control". Phytopathology. 105 (7). American Phytopathological Society: 872–884. doi:10.1094/phyto-01-15-0030-fi. ISSN 0031-949X. PMID 26120730. S2CID 205345605.
^ abcd
This review...
Singh, Ravi P.; Hodson, David P.; Huerta-Espino, Julio; Jin, Yue; Bhavani, Sridhar; Njau, Peter; Herrera-Foessel, Sybil; Singh, Pawan K.; Singh, Sukhwinder; Govindan, Velu (8 September 2011). "The Emergence of Ug99 Races of the Stem Rust Fungus is a Threat to World Wheat Production". Annual Review of Phytopathology. 49 (1). Annual Reviews: 465–481. doi:10.1146/annurev-phyto-072910-095423. ISSN 0066-4286. PMID 21568701. S2CID 24770327.
...cites this study:
Visser, B; Herselman, L; Park, RF; Karaoglu, H; Bender, CM; Pretorius, Z (2010). "Characterization of two new Puccinia graminis f. sp. tritici races within the Ug99 lineage in South Africa". Euphytica. 179: 119–127. doi:10.1007/s10681-010-0269-x. S2CID 6176783.
^Terefe, T.; Pretorius, Z. A.; Visser, B.; Boshoff, W. H. P. (2019). "First Report of Puccinia graminis f. sp. tritici Race PTKSK, a Variant of Wheat Stem Rust Race Ug99, in South Africa". Plant Disease. 103 (6). American Phytopathological Society: 1421. doi:10.1094/pdis-11-18-1911-pdn. ISSN 0191-2917.
^Randhawa, Mandeep S.; Singh, Ravi P.; Dreisigacker, Susanne; Bhavani, Sridhar; Huerta-Espino, Julio; Rouse, Matthew N.; Nirmala, Jayaveeramuthu; Sandoval-Sanchez, Maricarmen (2018-11-30). "Identification and Validation of a Common Stem Rust Resistance Locus in Two Bi-parental Populations". Frontiers in Plant Science. 9. Frontiers Media: 1788. doi:10.3389/fpls.2018.01788. ISSN 1664-462X. PMC6283910. PMID 30555507.
^Pretorius, Z. A.; Szabo, Les J.; Boshoff, W. H. P.; Herselman, L.; Visser, B. (2012). "First Report of a New TTKSF Race of Wheat Stem Rust (Puccinia graminis f. sp. tritici) in South Africa and Zimbabwe". Plant Disease. 96 (4). American Phytopathological Society: 590. doi:10.1094/pdis-12-11-1027-pdn. ISSN 0191-2917. PMID 30727416.
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• Patpour, M.; Hovmøller, M. S.; Justesen, A. F.; Newcomb, M.; Olivera, P.; Jin, Y.; Szabo, Les J.; Hodson, D.; Shahin, A. A.; Wanyera, R.; Habarurema, I.; Wobibi, S. (2016). "Emergence of Virulence to SrTmp in the Ug99 Race Group of Wheat Stem Rust, Puccinia graminis f. sp. tritici, in Africa". Plant Disease. 100 (2). American Phytopathological Society: 522. doi:10.1094/pdis-06-15-0668-pdn. ISSN 0191-2917. S2CID 83728264.
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^ abcdSingh, Ravi P.; Hodson, David; Huerta-Espino, Julio; Jin, Yue; Njau, Peter; Wanyera, Ruth; Herrera-Foessel, Sybil; Ward, Richard W. (2008). "Will Stem Rust Destroy The World's Wheat Crop?". Advances in Agronomy. 98. Elsevier B. V.: 272–309. doi:10.1016/S0065-2113(08)00205-8. ISBN 9780123743558. Archived from the original on 2020-11-08. Retrieved 2018-12-29.
• Patpour, M.; Hovmøller, M. S.; Shahin, A. A.; Newcomb, M.; Olivera, P.; Jin, Y.; Luster, D.; Hodson, D.; Nazari, K.; Azab, M. (2016). "First Report of the Ug99 Race Group of Wheat Stem Rust, Puccinia graminis f. sp. tritici, in Egypt in 2014". Plant Disease. 100 (4). American Phytopathological Society: 863. doi:10.1094/pdis-08-15-0938-pdn. ISSN 0191-2917.
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• Bhavani, Sridhar; Hodson, David P.; Huerta-Espino, Julio; Randhawa, Mandeep S.; Singh, Ravi P. (2019). "Progress in breeding for resistance to Ug99 and other races of the stem rust fungus in CIMMYT wheat germplasm". Frontiers of Agricultural Science and Engineering. 6 (3). Engineering Sciences Press: 210. doi:10.15302/j-fase-2019268. ISSN 2095-7505. S2CID 202011907.
• Abdelmageed, Kishk; CHANG, Xu-hong; WANG, De-mei; WANG, Yan-jie; YANG, Yu-shuang; ZHAO, Guang-cai; TAO, Zhi-qiang (2019). "Evolution of varieties and development of production technology in Egypt wheat: A review". Journal of Integrative Agriculture. 18 (3). Elsevier: 483–495. doi:10.1016/s2095-3119(18)62053-2. ISSN 2095-3119. S2CID 92749147.
• Awaad, Hassan Auda; El-Naggar, Doaa Ragheb (2021). "Developing Rust Resistance of Wheat Genotypes Under Egyptian Conditions". Mitigating Environmental Stresses for Agricultural Sustainability in Egypt. Springer Water. Cham, Switzerland: Springer International Publishing. pp. 311–370. doi:10.1007/978-3-030-64323-2_12. ISBN 978-3-030-64322-5. ISSN 2364-6934. S2CID 234309678. Page 327.
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^ abc
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^ abcWu, Xian Xin; Lin, Qiu Jun; Ni, Xin Yu; Sun, Qian; Chen, Rong Zhen; Xu, Xiao Feng; Qiu, Yong Chun; Li, Tian Ya (2020). "Characterization of Wheat Monogenic Lines with Known Sr Genes and Wheat Lines with Resistance to the Ug99 Race Group for Resistance to Prevalent Races of Puccinia graminis f. sp. tritici in China". Plant Disease. 104 (7). American Phytopathological Society: 1939–1943. doi:10.1094/pdis-12-19-2736-re. ISSN 0191-2917. PMID 32396054.
^Kumari, Safaa (2020-11-09). El Amil, Rola (ed.). (DAY 2) - Phytosanitary Safety for Transboundary pest prevention - Yellow and Black rust population variability. CGIAR Germplasm Health Webinar series. Vol. Phytosanitary Awareness Week. International Institute of Tropical Agriculture + CGIAR. Slide at 00:44:37. Archived from the original on 2021-12-15.
^"Successful surveillance results in early first detection of Ug99 in South Asia". Grainews. Retrieved 2024-04-22.