Isolation and fine mapping of Rps6: An intermediate host resistance gene in barley to wheat stripe rust

A plant may be considered a nonhost of a pathogen if all known genotypes of a plant species are resistant to all known isolates of a pathogen species. However, if a small number of genotypes are susceptible to some known isolates of a pathogen species this plant maybe considered an intermediate host. Barley (Hordeum vulgare) is an intermediate host for Puccinia striiformis f. sp. tritici (Pst), the causal agent of wheat stripe rust. We wanted to understand the genetic architecture underlying resistance to Pst and to determine whether any overlap exists with resistance to the host pathogen, Puccinia striiformis f. sp. hordei (Psh). We mapped Pst resistance to chromosome 7H and show that host and intermediate host resistance is genetically uncoupled. Therefore, we designate this resistance locus Rps6. We used phenotypic and genotypic selection on F2:3 families to isolate Rps6 and fine mapped the locus to a 0.1 cM region. Anchoring of the Rps6 locus to the barley physical map placed the region on two adjacent fingerprinted contigs. Efforts are now underway to sequence the minimal tiling path and to delimit the physical region harbouring Rps6. This will facilitate additional marker development and permit identification of candidate genes in the region

Are multiple acute small subcortical infarctions caused by embolic mechanisms?

Race-specific resistance genes (Rph) for leaf rust (Puccinia hordei) are often overcome by new pathotypes with matching virulence. Adult plant resistance (APR) is considered potentially more durable for controlling barley leaf rust. Previous studies established that the cultivar Pompadour carried APR to leaf rust. A doubled haploid population (DH) of 200 lines developed from a cross Pompadour/Stirling, and the parents were phenotyped for leaf rust resistance at five field experimental sites in three agricultural zones in Australia. Using a linkage map of SSR and DArT molecular markers, a major QTL associated with the leaf rust resistance was identified on the short arm of chromosome 5H. This QTL explained between 31% and 86% of the phenotypic variation for the APR at different sites. A PCR-based molecular marker was developed and mapped at 1.6 cM to the APR gene. The present study provides new genetic material and a molecular tool for breeding new varieties with adult plant leaf rust resistance using marker-assisted selection