The development of winter 6-row malting barley varieties is an objective of the OSU program. Our winter germplasm is quite susceptible to Barley Yellow Dwarf Virus (BYDV). We recently released the spring 2-row variety Orca, which carries the Yd2 gene for BYDV resistance. The objective of this project is to transfer the Yd2 gene from Orca to the winter varieties Strider and Kold. We proposed to use molecular markers tightly linked to the Yd2 locus to facilitate the introgression of this gene from the spring to the winter germplasm pool. In 1998, six-row plants were selected in F₂ populations derived from crosses of Orca x Kold and Orca x Strider. DNA was extracted from these plants for genotyping with molecular markers YLM and HVM27 linked to the Yd2 locus on chromosome 3 (3H). In order to encourage natural infection by BYDV-infected aphids, the F₃ families tracing to selected F₂ plants were planted one month before the usual planting date in the Fall of 1998. Unusually low temperatures in December 1998, led to significant winter injury, leading to the loss of approximately 30% of the F₃ families in each of the two populations. The Dhn2 locus on chromosome 7 (5H) is reported to be linked to a major low temperature tolerance QTL. We will, accordingly, extend our genotyping to include the Dhn2 locus. Integration of our phenotype data (visual rating of BYDV symptoms on F₂ plants and F₃ families; quantification of BYDV infection in F₃ families via ELISA; and visual rating of winter survival in F₃ families) with our genotype data (allelic structure of each F₂ plant at the YLM, HVM27, and Dhn2 loci) will allow us to predict the genotypes of F₃ phenotypic selections and assess the utility of the marker loci as tools for introgressing alleles from spring to winter germplasm.