New leaf rust resistance genes in barley and their allelic and linkage relationships with other Rph genes

The inheritance of leaf rust resistance was investigated in four barley accessions (PI 531840, PI 531841, PI 531849, and PI 584760) that were resistant to isolates of Puccinia hordei with wide virulence combinations. Crosses were made between the resistant barley lines and barley lines with genes Rph1 to Rph12 (except for Rph8) to determine the allelic and linkage relationships with known Rph genes. F-2 populations were evaluated for leaf rust reaction at the seedling stage. An incompletely dominant gene was identified in accessions PI 531841 and PI 584760, and a completely dominant gene was identified in PI 531849. The resistance gene in PI 531841 is an allele at the Rph2 locus or a closely linked locus. This gene also is present in accession PI 531840. A linkage was detected between this gene and Rph5 with recombination fractions of 33.8 +/- 3.8 and 17.0 +/- 3.5%, respectively, in crosses of 'Magnif' with PI 531841 and PI 531840. The Rph genes in PI 531849 and PI 584760 were not allelic at any of the previously reported Rph loci. Locus symbols Rph13 and Rph14 are recommended for the leaf rust resistance loci in PI 531849 and PI 584760, respectively. A linkage was detected between Rph13 and Rph9 with a recombination fraction of 30.4 +/- 4.5%.