Pyramiding stem rust resistance genes to race TTKSK (Ug99) in wheat

There has not been a major wheat stem rust epidemic in Canada since 1954. The detection of race TTKSK, with virulence to Sr31 and most other stem rust resistance genes in wheat, presents a threat to the wheat crop worldwide. Single disease resistance genes are usually effective for only several years before the pathogen changes genetically to overcome the resistance. To produce more durable resistance to race TTKSK, as well as to leaf rust and Fusarium head blight (FHB), we produced pyramided lines with several resistance genes. A population of 68 doubled haploids was produced from the hybrid 'AC Cadillac' (SrCad, Lr34)/'Carberry' (Lr34, Fhb1) x 'RL5405' (Sr33)/'Carberry' (Lr34, Fhb1). A total of 16 combinations of variable numbers of the four genes were recovered by marker assisted selection. The most notable combination with four of the genes was Sr33, SrCad, Lr34 and Fhb1. Two such lines were recovered. All pyramided lines with Lr34 and SrCad or Sr33 were resistant to race TTKSK, while two control wheat varieties 'Shaw' and 'Little Club' were susceptible. The two pyramided lines (SrCad-Sr33-Lr34-Fhb1) were relatively more resistant than the lines containing only one gene for stem rust resistance. The pyramided lines with Lr34 showed good resistance to leaf rust races 12-3 MBDS and TDBG. The pyramids with Fhb1 did not show a lowered expression of Fusarium head blight.