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GENOMICS, MOLECULAR GENETICS & BIOTECHNOLOGY

A High-Density Map and PCR Markers for Russian Wheat Aphid Resistance Gene Dn7 on Chromosome 1RS/1BL

Dep. of Soil and Crop Science, Colorado State Univ., Fort Collins, CO 80523-1170. All authors contributed equally to this study

^* Corresponding author (nlapitan{at}lamar.colostate.edu).

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.

Abbreviations: AFLP, Amplified fragment length polymorphism • MAS, Marker-assisted selection • PCR, Polymerase chain reaction • RFLP, Restriction fragment length polymorphism • RWA, Russian wheat aphid • SSR, Simple sequence repeats • 1RS, rye chromosome 1R short arm.