Genetic and physical localization of a leaf rust susceptibility gene in barley.

Key message: Fine mapping of the leaf rust susceptibility gene Sph1 identified a receptor-like kinase-encoding gene as a candidate and provided user-friendly markers for barley breeding. Caused by the biotrophic fungal pathogen Puccinia hordei, leaf rust is one of the important foliar diseases in barley. Although a few dominant genes for leaf rust resistance have been identified and cloned in barley, resistance conferred by major genes has been frequently defeated by the pathogen. A recessive resistance was identified in a spring barley accession using the P. hordei isolate VA90-34 which is virulent to most of major resistance genes. To localize this recessive resistance (hereafter named Susceptibility to P. hordei 1 or Sph1 indicating that the dominant allele confers disease susceptibility), we conducted fine mapping with an F₂ population and molecular markers in the present study. The Sph1 gene was anchored near the telomere of the short arm of chromosome 3H, delimited within an ⁓560 kb region in the dominant parent. Of the six predicted genes in the Sph1 region, a gene encoding putative receptor-like kinase was selected as a candidate for functional validation. Therefore, our study provides a high-resolution genetic map and candidate for Sph1, building a foundation for the cloning of this important gene.