Bacterial leaf streak (BLS), caused by Xanthomonas translucens pv. undulosa (Xtu), is an important disease of wheat worldwide. The best way to control this disease in the field is the use of resistant cultivars. Although source of resistance is lacking in wheat, several triticale accessions have high levels of resistance. However, resistance in triticale has not be investigated. The main objective of this project was to map the BLS-resistance gene in triticale. A high density genetic linkage map was constructed in a triticale recombinant inbred line population covering all wheat and rye chromosomes. QTL mapping revealed a single locus on the chromosome 5R significantly associated with resistance to BLS. The resistance reaction of F1 hybrids indicated the dominance resistance. This is the first study to map a major resistance gene to BLS and will facilitate the introgression of this rye-derived BLS resistance into wheat genome through molecular marker-assisted chromosome engineering.