Mapping Ug99 Stem Rust Resistance Gene from Aegilops tauschii Accession TA1642.

The stem rust fungus Puccinia graminis f. sp. tritici Pers. is a persistent threat to wheat production and a cause of severe crop epidemics in the past.  Races of stem rust, especially TTKSK (Ug99), with virulence to important stem rust resistance genes, pose new threats to reduce wheat yields in the future.  Aegilops tauschii, the D genome progenitor of wheat, is a valuable source for novel resistance genes.  Populations for this study were developed by crossing stem rust susceptible T. aestivum KS05HW14 with stem rust resistant Ae. tauschii TA1642 then backcrossing with KS05HW14 (KS05HW14/TA1642//KS05HW14).  Phenotyping for stem rust resistance was carried out in 240 BC₁F₂ individuals and 170 BC₁F_2:3 families.  BC₁F_2:3 families were inoculated with QFCSC, QTHJC, and TTKSK (Ug99) and the resistance response scored using the Stakman scale (Stakman et al 1962).  Bulked segregant analysis (BSA) using 67 simple sequence repeat (SSR) markers from the D genome was carried out.  The marker WMC111 differentiated resistant and susceptible bulks indicating the gene conferring stem rust resistance is located distally on the short arm of the 2D wheat chromosome.  KASPar markers from chromosome 2DS were mapped to refine the genetic map location.  To more closely map this gene, additional markers in the distal region of chromosome 2DS are in development.