Identification and mapping of adult-onset sensitivity to victorin in barley

Victoria blight of oats caused by the fungus Cochliobolus victoriae is of distinct interest due to the link between Victoria blight susceptibility and crown rust resistance. C. victoriae-susceptible oats were introduced into the USA as a source of the Pc2 gene for resistance to the crown rust fungus Puccinia coronata. A dominant gene (Vb) in these oats was found to condition susceptibility to Victoria blight disease and sensitivity to the C. victoriae toxin called victorin. Numerous genetic approaches to separate Vb from Pc2 have failed, suggesting that Pc2 and Vb share identity. Because Victoria blight has only been described in allohexaploid oat, which has a poorly characterized genome of 11,300 Mb, molecular genetic investigations of Vb in oat are not practical. Previously we identified a presumed Vb ortholog in Arabidopsis, called LOV. LOV confers victorin sensitivity and susceptibility to C. victoriae, and encodes a coil-coil-nucleotide-binding site-leucine-rich repeat (CC-NBS-LRR) protein. Analysis of cereal DNA databases reveals a large array of CC-NBS-LRR genes, but no obvious LOV ortholog. Identifying a cereal ortholog of LOV will require identification and subsequent mapping of victorin sensitivity in a genetically tractable cereal plant. In this work, we surveyed barley for victorin sensitivity and identified adult-onset sensitivity to victorin in eight barley accessions. Evaluation of a doubled haploid (DH) population derived from the cross of sensitive x insensitive parents revealed a single quantitative trait locus (QTL) for victorin sensitivity in a resistance-gene-rich region on the short arm of chromosome 1H. Furthermore, enhanced victorin sensitivity observed in some DH lines suggests a background-dependent enhancement of victorin sensitivity.