Wild barley (Hordeum vulgare spp. spontaneum) is a source of useful genes for improving cultivated barley. Even though some breeders still select new cultivars from the progeny of elite x elite crosses, genetic variation for many key traits is limited. This may be due to evolutionary bottlenecks resulting in a relatively shallow germplasm pool. Useful genes from H. vulgare spp. spontaneum may be new alleles at described loci, or they may be entirely new genes in the sense that there is limited allelic variation at these loci in the cultivated germplasm pool. This project involves three components: characterization of diversity, development of genetic stocks, and genotypic and phenotypic characterization of the genetic stocks. Approximately 70 SSRs will be assayed on 33 H. vulgare and 21 H. vulgare spp. spontaneum accessions. Genetic similarities between genotypes will be estimated from the allele data and used as a basis for description of the germplasm array using cluster and principal component analysis tools. Recombinant Chromosome Substitution Lines (RCSLs) will be used to systematically explore the H. vulgare spp. spontaneum genome. Our objective is to identify lines that represent approximately 20 cM overlapping insertions of the H. vulgare spp. spontaneum genome in a H. vulgare background. Four H. vulgare spp spontaneum accessions were selected on the basis of genetic divergence and geographic origin and were used to develop RCSLs at cooperating laboratories. OUH602 (G. Muehlbauer, University of Minnesota), OUH640 (M. Saghai-Moroof, Virginia Polytechnic Institute), Caesarea 26-24 (I. Matus, Oregon State University) and Wadi Qilt 23-38 (A. Kleinhofs, Washington State University) were used as allele donors in backcrossing programs, with Harrington as the recurrent parent. In the case of Caesarea 26-24, 148 BC₁ plants were each crossed with the recurrent parent to generate the BC₂ generation. Approximately 560 BC₂F₅ SSD families with a defined family structure were derived. Each set of four BC₂F₅ families traces to a single BC₁ plant. Initially, 200 BC₂F₅ lines will be genotyped with 70 SSRs distributed throughout the genome to generate a graphical genotype for each line. The same four H. vulgare spp. spontaneum used to generate the RCSLs were also used to generate single cross mapping populations. Each accession was crossed with Harrington and 150 F_2:6 derived recombinant inbred lines (RILs) were developed from each cross combination. The RCSLs and RILs are available for collaborative gene discovery and manipulation projects.