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Russian wheat aphid (RWA) [Diuraphis noxia (Kurdjumov)] is an important pest of wheat (Triticure aestivum L.) in several production areas of the world. The most effective and economical approach for controlling RWA is to use resistant cultivars. A wheat line, ST-ARS 02RWA2414-11 (2414-11), showed a high level of resistance to RWA biotype 2. Our objectives were to map the resistance gene and develop polymerase chain reaction (PCR)-based markers for marker-assisted selection (MAS). A mapping population of 212 [F.sub.2] individuals was developed from a cross of 2414-11 and the susceptible cultivar Yuma. The [F.sub.2] individuals and [F.sub.2:3] families were infested using biotype 2 RWA. The RWA resistance of 2414-11 is controlled by a single major gene, provisionally designated as Dn2414. Using standard PCR, 30 marker loci were found to be linked to Dn2414 with recombination frequencies ([theta]) of 0.00 to 0.27 and logarithm of the odds to the base 10 (LOD) scores of 7.6 to 66.1. Of the 30 markers, 26 were tightly linked to Dn2414 with [theta] [less than or equal to] 0.05. A genetic map was constructed consisting of 31 loci spanning a region of 34.7 cM. The close linkage of Dn2414 with several rye chromosome 1R short arm (1RS)-specific simple sequence repeat markers and low 0 values around the Dn2414 gene indicate that Dn2414 is located on chromosome 1RS.1BL (translocation chromosome with IRS and wheat chromosome 1B long arm). Phenotypic and marker profiles of 2414-11 and its relatives are the same as other lines known to carry Dn7. The Dn2414 gene is thus located on 1RS arm, and the large number of PCR markers will be valuable for MAS of this gene.

The Russian wheat aphid (RWA) [Diuraphis noxia (Kurdjumov)] is an economically significant insect pest of wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) in the USA. Since 1986, only one biotype existed in the USA. In 2003, a new biotype appeared which was virulent to all known resistance genes in wheat, with the exception of Dn7. Dn7 is a rye gene transferred into a wheat background via 1RS/1BL translocation. It was previously mapped; however, no PCR-based markers were developed for marker-assisted selection (MAS) and the map was sparse. This study presents a higher density map of Dn7 containing 19 markers. The markers spanning Dn7 are XHor2 and Xscb241 at distances of 1.4 and 1 cM, respectively, from Dn7. PCR markers were developed and tested on 19 wheat cultivars. Two markers which amplified rye-specific fragments proved to be useful for MAS. Xrems1303 amplified a 320-bp band only in cultivars with high-level resistance to biotype 2 and is effective for MAS of Dn7. Xib267 is linked to the susceptible locus and amplified a fragment specific for rye Petkus 1RS and would be a good marker for selecting against the susceptible locus. The value of Dn7 as a source of resistance has increased because of the broad spectrum resistance it provides against several biotypes. The markers developed in this study will be useful for facilitating the transfer of Dn7 into wheat cultivars with or without translocation chromosomes containing 1RS.

The Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), is a serious pest in wheat (Triticum aestivum L.). Four Russian triticale (X Triticosecale Wittmack) lines, PI 386148, PI 386149, PI 386150, and PI 386156, have been the most resistant triticales to the RWA in several screening tests. Resistance is controlled by a single dominant gene at a common locus in the three triticale lines PI 386148, PI 386149, and PI 386156. However, expression of these resistance genes in a wheat background and the inheritance of resistance in PI 386150 have not been determined. The objectives of this study were (i) to assess the transmission and the expression of RWA resistance in triticale x wheat hybrids, (ii) to determine the inheritance of resistance in PI 386150, and (iii) to identify the rye chromosome(s) from Secale montanum Guss. associated with RWA resistance. Advanced generations from crosses between PI 386148 triticale x 'Lamar' wheat and PI 386150 triticale x Lamar were produced and the progenies screened to determine their reaction to the RWA. All [F.sub.1] plants derived from both crosses were resistant indicating that resistance is dominant in both triticale lines. C-banding and in situ hybridization with the pSc119.1 probe, a rye-specific DNA probe, showed that chromosome [4R.sup.mon] was associated with resistance in PI 386150. The results of this study should facilitate the transfer of the resistance gene(s) from these triticale lines into wheat.