Fine Mapping the Un8 Locus Controlling Resistance to True Loose Smut in Barley

True loose smut of barley, caused by the basidiomycete pathogen Ustilago nuda (Jens.) Rostr. (U. nuda), is a common disease in Western Canada and the United States. Traditional breeding for resistance to true loose smut is both labor-intensive and time-consuming. Molecular marker-assisted selection (MMAS) for true loose smut resistance is one of the best examples of how markers can improve the efficiency of selection since significant increases in efficiency and accuracy are achievable. Among the true loose smut resistance genes, Un8 is the most effective and long-lived resistance. Here we report progress made in fine mapping the Un8 interval which is essential for positional cloning of the gene. A variety of strategies including synteny, gene expression data, BAC and whole-genome sequence information, were used to saturate the Un8 region. A population of 4,700 F₄ lines segregating for Un8 was used to delimit the Un8 gene to a 0.13 cM interval on chromosome 1HL, and assign it to FPC contig_546. Two sequences located close to a marker co-segregating with Un8 showed high BLAST hit scores to disease resistance genes. One sequence matched a serine/threonine protein kinase and the other matched a NBS-LRR type resistance gene. Sequencing and expression analysis of these two sequences is currently underway to determine their potential to be the Un8 gene.