Adult plant resistance (APR) to wheat stem rust has been one of the approaches for resistance breeding since the evolution of the Ug99 race group and other races. This study was conducted to dissect and understand the genetic basis of APR to stem rust in spring wheat line 'Copio'. A total of 176 recombinant inbred lines (RILs) from the cross of susceptible parent 'Apav' with Copio were phenotyped for stem rust resistance in six environments. Composite interval mapping using 762 genotyping-by-sequencing markers identified 16 genomic regions conferring stem rust resistance. Assays with gene-linked molecular markers revealed that Copio carried known APR genes Sr2 and Lr46/Yr29/Sr58 in addition to the 2NS/2AS translocation that harbors race-specific genes Sr38, Lr37, and Yr17. Three quantitative trait loci (QTLs) were mapped on chromosomes 2B, two QTLs on chromosomes 3A, 3B, and 6A each, and one QTL on each of chromosomes 2A, 1B, 2D, 4B, 5D, 6D, and 7A. The QTL QSr.umn.5D is potentially a new resistance gene and contributed to quantitative resistance in Copio. The RILs with allelic combinations of Sr2, Sr38, and Sr58 had 27 to 39% less stem rust coefficient of infection in all field environments compared with RILs with none of these genes, and this gene combination was most effective in the U.S. environments. We conclude that Copio carries several genes that provide both race-specific and non-race-specific resistance to diverse races of stem rust fungus and can be used by breeding programs in pyramiding other effective genes to develop durable resistance in wheat.
Keywords: QTL mapping; Ug99 races; adult plant resistance; genotyping-by-sequencing; wheat stem rust.