Pathotype Tracker – Where is Ug99?

Ug99 Race Group Summary September 2021

Status Summary: Ug99 Lineage – September 2021

Race TTKSK (Ug99) was the first known race of P. graminis f. sp. tritici with virulence to the stem rust resistance gene Sr31. It also possesses virulence to a wide range of resistance genes of wheat origin, plus others of alien origin. The pathogen is changing rapidly and fifteen known variants have been identified within the Ug99 lineage of wheat stem rust. The Ug99 race group is present in 14 countries, with Iraq being the most recent country in which the Ug99 race group was detected (Nazari et al 2021 – see map).The latest variants are: PTKSK, detected in South Africa in 2017 (Terefe et al., 2018);  TTKSF+, detected in South Africa and Zimbabwe from samples collected in 2010 (Pretorius et al. 2012); TTHST (collected in Kenya 2013, Newcomb et al in prep); TTKTT, TTKTK. PTKTK and TTHSK (Patpour et al 2015, Fetch et al., 2016) – all collected in Kenya in 2014. A new variant TTKTT+ was detected in Kenya in 2019, this has additional virulence on Sr8155B1. Another new variant, TTHTT has been detected in samples from Kenya in 2020.  Acquired virulence to additional important Sr genes, notably Sr24 and Sr36, is known from Kenya (Sr24, Sr36), Egypt (Sr24), Eritrea (Sr24), Ethiopia (Sr24, Sr36), Mozambique (Sr24), Rwanda (Sr36, Sr24), South Africa (Sr24),Tanzania (Sr24, Sr36), Uganda (Sr24, Sr36) and Zimbabwe (Sr24). Race TTKST, carrying combined Sr31 + Sr24 virulence, caused epidemics in Kenya in 2007. Ug99 races carrying combined Sr31 + Sr24 virulence are spreading rapidly throughout Africa and it is considered likely that they will spread further in the future. In addition, virulence to the SrTmp gene has now been acquired by the latest variants detected in Kenya (i.e., race TTKTT, race TTKTT+,  race TTKTK, race PTKTK and race TTHTT). At least one of these variants (TTKTK) appears to spreading rapidly, also being detected in 2014 in Egypt, Eritrea, Rwanda and Uganda (Patpour et al., 2015).

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), Eritrea (2012), Rwanda (2014), Egypt (2014)
TTKSF     -Sr31 2000 South Africa (2000), Zimbabwe (2009), Uganda (2012)
TTKST   Ug99 + Sr24 +Sr31, +Sr24 2006 Kenya (2006), Tanzania (2009), Eritrea (2010), Uganda (2012), Egypt (2014), Rwanda (2014)
TTTSK   Ug99 + Sr36 +Sr31, +Sr36 2007 Kenya (2007), Tanzania (2009), Ethiopia (2010), Uganda (2012), Rwanda (2014)
TTKSP     -Sr31, +Sr24 2007 South Africa (2007)
PTKSK     +Sr31, -Sr21 2007 [Uganda (1998/9)?], Kenya (2009), Ethiopía (2007), Yemen (2009), South Africa (2017)
PTKST     +Sr31, +Sr24, -Sr21 2008 Ethiopia (2007), Kenya (2008), South Africa (2009), Eritrea (2010), Mozambique (2010), Zimbabwe (2010)
TTKSF+     -Sr31, +Sr9h 2012 South Africa (2010), Zimbabwe (2010)
TTKTT     +Sr31, +Sr24, +SrTmp 2015 Kenya (2014), Iraq (2019)
TTKTK     +Sr31, +SrTmp 2015 Kenya (2014), Egypt (2014), Eritrea (2014), Rwanda (2014), Uganda (2014)
TTHSK     +Sr31, -Sr30 2015 Kenya (2014)
PTKTK     +Sr31, -Sr21, +SrTmp 2015 Kenya (2014)
TTHST     +Sr31, -Sr30, +Sr24 2015 Kenya (2013)
TTKTT+     +Sr31, +Sr24, +SrTmp, +Sr8155B1 2019 Kenya (2019)
TTHTT     +Sr31, -Sr30, +Sr24, +SrTmp 2020 Kenya (2020)

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