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Status Summary: Ug99 Lineage – May 2010
Ug99 is unique as it is the only known race of P. graminis f. sp. tritici with virulence to the stem rust resistance gene Sr31. It also possesses virulence to virtually all the resistance genes of wheat origin, plus others of alien origin. The pathogen is changing rapidly and seven known variants have been identified within the Ug99 lineage of wheat stem rust. All are considered to be single step mutations. Acquired virulence to additional important Sr genes, notably Sr24 and Sr36, is known from Kenya (Sr24, Sr36), Ethiopia (Sr24), South Africa (Sr24) and Tanzania (Sr24, Sr36). Race TTKST, carrying combined Sr31 + Sr24 virulence, caused epidemics in Kenya in 2007.
Ug99 Lineage: Proposed Evolutionary Summary
Summary Table – Ug99 lineage Race a | | Common Alias | Key Virulence (+) or Avirulence (-) * | Year of Identification | Confirmed Countries (year) | TTKSK | | Ug99 | +Sr31 | 1999 | Uganda (1998/9), Kenya (2001), Ethiopia (2003), Sudan (2006), Yemen (2006), Iran (2007), Tanzania (2009) | TTKSF | | | -Sr31 | 2000 | South Africa (2000), Zimbabwe (2009) | TTKST | | Ug99 + Sr24 | +Sr31, +Sr24 | 2006 | Kenya (2006), Tanzania (2009)
| TTTSK | | Ug99 + Sr36 | +Sr31, +Sr36 | 2007 | Kenya (2007), Tanzania (2009) | TTKSP | | | -Sr31, +Sr24 | 2007 | South Africa (2007) | PTKSK | | | +Sr31, -Sr21 | 2007 | [Uganda (1998/9)?], Kenya (2009), Ethiopía (2007) | PTKST | | | +Sr31, +Sr24, -Sr21 | 2008 | Ethiopia (2007), Kenya (2008), South Africa (2009) |
a Some uncertainty exists over the reaction of the Sr21 gene (this influences the initial code letter being “T” (+Sr21) or “P” (-Sr21). Current table presents most plausible races
* Only key Sr genes are indicated, not the complete virulence/avirulence profile |
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