Race Evolution in TTKS (Ug99) Lineage & Implications to Resistance Breeding Yue Jin, USDA-ARS
Ug99 First reported in Uganda in 1999 --Pretorius et al. 2000 Plant Dis 84:203 • Virulent on Sr31 Sr31 is located on 1BL.1RS translocation. Also carries Lr26, Yr9. Increased adaptation and higher yield. As a result, widely spread in wheat worldwide. Helped to reduce stem rust population worldwide. • Virulence to Yr9, originated in the eastern Africa in mid 80s, caused worldwide epidemics.
TTKS In 2002 and 2004, CIMMYT nursery planted in Njoro, Kenya were severely infected by stem rust. In 2005, we identified Kenyan isolates from 2004 were race TTKS. • --Wanyera, Kinyua, Jin, Singh 2006 Plant Dis 90:113
Broad virulence of TTKS to North American spring wheat • US spring wheat CVs of the Northern Great Plains, known to have broad-based resistance to stem rust, were mostly susceptible (84%). • 500 CIMMYT CVs released since 1950’s, 84% were susceptible. Conclusion: Ug99 possesses a unique virulence combination that renders many resistance genes ineffective. Jin & Singh, 2006, Plant Dis:90:476-480
Projected potential pathways for Ug99 based on the migration of Yr9 virulence Singh et al. 2006. CAB Review 1, 54
Ug99 migration 2007 2006 2006 2003? 2005 Singh et al. 2008. Advances in Agronomy v98 2001? 2004 1998
Evolution of the TTKS lineage Sr24- Sr31+ Sr36- TTKSK Our data point to: Sr24+ Sr31+ Sr36- Sr24- Sr31+ Sr36+ TTKST TTTSK Jin et al. 2008. Plant Dis. 92:923-926 Jin et al. 2009. Plant Dis. (in Press)
Ramification of Sr24/Sr36 virulence to US Wheat based on testing of 2007 elite breeding germplasm % of resistance to Type Entry TTKSK TTKST TTTSK (Ug99) Sr24v Sr36v Hard red spring 89 21% 12% 21% Hard red winter 416 29% 15% 28% Soft red winter 377 27% 25% 11% Western wheat 60 3% 3% 3% Total 942 26% 18% 19%
The good news • Phil and Luther are both working on it already! • Li Huang, PSPP, is starting to map genes for resistance • Fungicide trials have already started • Communication and education ramping up!