The genetic relationship between barley leaf rust resistance genes located on chromosome 2HS

Four seedling leaf rust resistance genes (Rph14, Rph15, Rph16 and Rph17) described in barley are located on chromosome 2HS. A fifth, present in barley accession HOR 1063, was reported to map to the same region as Rph16. A comprehensive analysis of the allelic relationship between Rph14, Rph15, Rph17 and RphHOR1063 was undertaken. Two additional genotypes (HOR 15560 and Zhu 4) that were initially thought to carry Rph16 were also included. While no segregation was observed in F-2 populations derived from crosses between PI 584760 (carrying Rph14), PI 355447 (carrying Rph15), Zhu 4 and HOR 1063, the lines did exhibit differential reactions across 10 Australian Puccinia hordei pathotypes. This suggests that the Rph14 locus may be complex. An evaluation of F-3 populations confirmed that resistance genes in Zhu 4 and in HOR 1063 were allelic to both Rph14 and Rph15, however A susceptible line was found among F-3 progeny of the cross PI 584760/PI 355447, suggesting that Rph14 and Rph15 may be independent. Rph17 and the gene present in HOR 15560 were shown to be independent of each other and of Rph14 and Rph15. The response of HOR 15560 across an array of P. hordei pathotypes revealed that it possesses the same specificity as Rph1. Because the resistance in Zhu 4 and HOR 1063 were shown to be allelic to Rph14, they should be designated Rph14.am and Rph14.an, respectively.