Virulence variation within the Ug99 lineage

Race Ug99 of Puccinia graminis f. sp. tritici, recognized for possessing virulence to Sr31, was first reported in Uganda in 1999 (Pretorius et al., 2000). Based on the North American stem rust nomenclature system of 16 differential lines (Roelfs and Martens, 1988; Roelfs et al., 1993), Ug99 is identified as race TTKS (Wanyera et al., 2006). Isolates with virulence similar to Ug99 were identified in collections from Kenya and Ethiopia since 2005 and from Yemen since 2006. More recently, the race was confirmed to be present in Iran (www.fao.org/). Ug99 is projected to migrate to other major wheat growing regions in the Middle East, and south and west Asia following a pathway similar to the migration route of a Yr9-virulent race of stripe rust (Puccinia striiformis) (Singh et al., 2006). The present study reports virulence variation observed within the TTKS stem rust race group.