Dissection of Wheat Stem Rust Resistance in the Montenegrin Landrace PI362698

The emergence and spread of the Ug99 lineage of the wheat stem rust pathogen, Puccinia graminis f. sp. tritici, in eastern Africa has stimulated research focused toward the discovery and mapping of Ug99 resistance in common wheat, Triticum aestivum. A source of wheat stem rust resistance was identified in the spring wheat landrace PI362698. PI362698 exhibits resistance to multiple Ug99-lineage races and many North American races at seedling and adult plant stages. Recombinant inbred populations were developed by crossing the susceptible line LMPG-6 with a single plant selection of PI362698 to identify loci associated with stem rust resistance via QTL mapping using the Illumina iSelect 90K wheat assay. Adult plant field trials of the populations in Kenya, detected significant QTLs on chromosomes 2B, 3B, and 7D using single-trait and multiple-trait multiple interval mapping. Sr57 has been shown to be present in the PI362698 and is linked to the chromosome 7D QTL. The additional QTLs are thought to be Sr12 on chromosome 3B and a second recessive gene needed for Sr12-mediated resistance on chromosome 2B. Chi-square analysis of race TTKSK resistance for the F₃ families suggests the phenotype is controlled by two recessive genes acting in complementation at seedling stages. Furthermore, the previous model and a three gene model involving two recessive genes with the addition of an enhancing effect from Sr57 are both supported via Chi-square analysis of field trials of the advanced populations. Future work will focus on the validation of the QTLs located on chromosome 2B and 3B.