FISH PHYSICAL MAPPING OF DNA SEQUENCES ASSOCIATED WITH RWA RESISTANCE IN WHEAT AND BARLEY

¹ Soil & Crop Sciences Department, Colorado State University, Fort Collins, CO
² Department of Agronomy & Range Science, University of California, Davis, CA
³ CSIRO, Department of Plant Industry, GPO BOX 1600, Canberra, ACT 2601, Australia

The Russian Wheat Aphid (RWA) has become an important insect pest in several wheat growing regions of the world. As many as 10 different, non-allelic RWA resistance genes are thought to exist, whereas molecular markers exist for a few of these genes. We mapped the Dn2 and Dn4 RWA resistance genes on chromosomes 7DL and 1DS, respectively, using RFLP and microsatellite markers. The closest markers to the Dn2 and Dn4 genes are the WMS437-1 microsatellite marker (2.9 cM), and the ABC156 RFLP marker (13.0 cM), respectively. Mapping of the Dn7 gene on chromosome 1RS is underway. The physical location of these RWA resistance genes is unknown. Fluorescence in situ hybridization (FISH) provides a direct method for visualizing the chromosomal location of DNA sequences. BAC clones containing marker sequences associated with the Dn2 and Dn4 genes were identified by screening BAC libraries of Triticum monoccocum and T. tauschii, and these BAC clones were used as probes for FISH. We will present the results of FISH physical mapping using these BAC clones on wheat and barley metaphase chromosomes as well as a comparison of the genetic and physical maps of these genomic regions.