Molecular mapping of wheat genes expressing resistance to the Russian wheat aphid, Diuraphis noxia (Mordvilko) (Homoptera: Aphididae)

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a serious, worldwide, economic pest of wheat (Triticum aestivum L. em. Thell). The results of our experiments described below identified microsatellite markers linked to several known genes as well as new genes expressing RWA resistance in wheat.; Wheat microsatellite marker Xgwm111 located on chromosome 7DS (short arm) is tightly linked to Dn (Diuraphis noxia) genes Dn1, Dn2, and Dn5, as well as Dnx in wheat at approximately 3.0 cM. The markers Xgwm44 and Xgwm111 are linked to Dn6 near the centromere on chromosome 7DS at 14.6 cM and 3.0 cM, respectively. This is the first report of the chromosome location of Dn6, which is either allelic or tightly linked to Dn1, Dn2, Dn5, and Dnx . The chromosome arm locations of markers Xgwm44 and Xgwm111 (and the linked genes) were confirmed to be chromosome 7DS by di-telosomic and nulli-tetrasomic analyses. Xgwm106 and Xgwm337 flanked Dn4 on chromosome 1DS at 7.4 cM and 12.9 cM, respectively. Xgwm635 (near the distal end of 7DS) clearly marked the location of a previously suggested resistance gene in PI 294994, here designated as Dn8. Xgwm642 , in a defense gene-rich region of chromosome 1DL, marked another new gene (Dn9) from PI 294994. A third new gene ( Dny) from the Chinese wheat Lin-Yuan207, was localized on chromosome 1DL between Xgdm111 and Xgwm337.; A single dominant resistance gene in PI 222666, PI 222668, PI 47545, and one of two dominant genes in PI 225245 were linked to Xgwm44 and Xgwm111 on chromosome 7DS. A single dominant resistance gene in PI 151918 was linked to Xgwm106 on chromosome 1DS.; A new type of molecular marker-based inheritance, semi-codominant inheritance, was demonstrated in a wheat segregating population. The mechanism proposed for this inheritance is the competitive PCR amplification of the primer-matched DNA template of one parent over the primer-mismatched DNA template of another parent due to sequence mutation in the primer binding sites.; Genetic maps of the above Dn genes and linked markers were constructed for wheat chromosomes 1D and 7D. These markers will be useful in marker-assisted breeding for RWA-resistant wheat.