Genetic Mapping of Intermediate-Host Resistance of Barley to Wheat Stripe Rust

Wheat stripe rust, caused by pathogen Puccinia striiformis f. sp. tritici (Pst) is a major pathogen of wheat. While the deployment of genetic resistance remains the most effective method to combat this pathogen, many known resistance genes have been overcome by new races of Pst. In contrast, cultivated barley (Hordeum vulgare ssp. vulgare) and its wild relative (Hordeum vulgare ssp. spontaneum) are predominantly resistant to Pst and it is possible that this type of intermediate-host resistance could provide a more durable source of resistance to Pst. We identified accessions of cultivated and wild barley susceptible to Pst and developed populations to map the genetic basis of resistance to wheat stripe rust within barley. Within the cross between the Pst susceptible barley cultivar Russell and the resistant Steptoe, we identified a primary QTL on chromosome 4HL and a minor effect locus 5H. We also found three accessions of wild barley susceptible to Pst and with them mapped another locus conferring resistance to Pst on the distal region of chromosome arm 7HL and designated it as Rps6. This locus was also detected in the cultivated barley ‘Tamalpais’ and the Chinese barley ‘Y12’, suggesting it is another important component of barley resistance to Pst. High density genetic mapping with more than 10,000 gametes placed Rps6 within a 0.06 cM region, but revealed no candidate genes. Further work will refine the genetic position of the loci on 4H and 5H and a dedicated positional cloning effort in barley will be required to identify Rps6.