Microsatellite markers linked to six Russian wheat aphid resistance genes in wheat

The Russian wheat aphid (RWA), Diuraphis noxia Mordvilko, is a serious econ omic pest of wheat and barley in North America, South America, and South Af rica. Using aphid-resistant cultivars has proven to be a viable tactic for RWA management. Several dominant resistance genes have been identified in w heat, Triticum aestivum, including Dn1 in PI 137739, Dn2 in PI 262660, and at least three resistance genes (Dn5+) in PI 294994. The identification of RWA-resistant genes and the development of resistant cultivars may be accel erated through the use of molecular markers. DNA of wheat from near-isogeni c lines and segregating F-2 populations was amplified with microsatellite p rimers via PCR. Results revealed that the locus for wheat microsatellite GW M111 (Xgwm111), located on wheat chromosome 7DS (short arm), is tightly lin ked to Dn1, Dn2 and Dn5, as well as Dnx in PI 220127. Segregation data indi cate RWA resistance in wheat PI 220127 is also conferred by a single domina nt resistance gene (Dnx). These results confirm that Dn1, Dn2 and Dn5 are t ightly linked to each other, and provide new information about their locati on, being 7DS, near the centromere, instead of as previously reported on 7D L. Xgwm635 (near the distal end of 7DS) clearly marked the location of the previously suggested resistance gene in PI 294994, here designated as Dn8. Xgwm642 (located on 1DL) marked and identified another new gene Dn9, which is located in a defense gene-rich region of wheat chromosome 1DL. The locat ions of markers and the linked genes were confirmed by di-telosomic and nul li-tetrasomic analyses. Genetic linkage maps of the above RWA resistance ge nes and markers have been constructed for wheat chromosomes 1D and 7D. Thes e markers will be useful in marker-assisted breeding for RWA-resistant whea t.