Submitted to: Phytopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/5/2009
Publication Date: 10/1/2009
Publication URL: http://hdl.handle.net/10113/37195
Citation: Steffenson, B.J., Jin, Y., Brueggeman, R.S., Kleinhofs, A., Sun, Y. 2009. Resistance to Stem Rust Pathotype TTKSK Maps to the Rgp4/Rpg5 Complex of Chromosome 5H of Barley. Phytopathology. 99:1135-1141. Interpretive Summary: Wheat stem rust (Puccinia graminis f. sp. tritici) is a serious threat to both wheat and barley production worldwide because of its wide virulence on many cultivars and rapid spread from eastern Africa. To elucidate the genetics of resistance in barley, we evaluated a population for reaction at the seedling stage, and identified a single gene in Q21861 which confers resistance to the pathotype known as TTKSK. This resistance gene co-segregated with two previous known genes for stem rust resistance. This result was confirmed through molecular analysis used to characterize resistance of the wheat stem rust pathogen and an isolate of the rye stem rust pathogen. Research is underway to resolve which genes are required for resistance to pathotype TTKSK. Simple inheritance should make a valuable source of TTKSK resistance in barley breeding programs.
Technical Abstract: The wheat stem rust (Puccinia graminis f. sp. tritici) pathotype TTKSK (original isolate synonym Ug99) is a serious threat to both wheat and barley production worldwide because of its wide virulence on many cultivars and rapid spread from eastern Africa. Line Q21861 is one of the most resistant barleys known to this pathotype. To elucidate the genetics of resistance in this line, we evaluated the Q21861/SM89010 (Q/SM) doubled haploid population for reaction to pathotype TTKSK at the seedling stage. Segregation for resistance:susceptibility in Q/SM doubled haploid lines fit a 1:1 ratio (58:71 with '2=1.31 and P=0.25), indicating that a single gene in Q21861 confers resistance to pathotype TTKSK. In previous studies, a recessive gene (rpg4) and a partially dominant gene (Rpg5) were reported to control resistance to P. g. f. sp. tritici pathotype QCCJ and P. g. f. sp. secalis isolate 92-MN-90, respectively, in Q21861. These resistance genes co-segregate with each other in the Q/SM population and were mapped to the long arm of chromosome 5H. Resistance to pathotype TTKSK also co-segregated with resistance to both rusts, indicating that the gene conferring resistance to pathotype TTKSK also lies at the rpg4/Rpg5 locus. This result was confirmed through the molecular analysis of recombinants previously used to characterize loci conferring resistance to QCCJ and 92-MN-90. The 70 kb region contains Rpg5 (an NBS-LRR-S/TPK gene), rpg4 (an actin depolymerizing-like [Adf] gene), and two other genes of unidentified function. Research is underway to resolve which of the genes are required for conferring resistance to pathotype TTKSK. Regardless, the simple inheritance should make Q21861 a valuable source of TTKSK resistance in barley breeding programs.