RphMBR1012 is a novel barley leaf rust resistance gene designated as Rph30

<title>Abstract</title> <p> Barley leaf rust, caused by <italic>Puccinia hordei</italic> Otth., is an important disease affecting barley production worldwide. The identification and deployment of novel resistance genes/alleles is the most economical and environmentally sustainable strategy. Two seedling resistance genes, <italic>Rph</italic> _{<italic>MBR1012</italic>} and <italic>Rph4,</italic> were previously mapped to the distal region of chromosome 1HS, however, their genetic relationship remained unclear. In this study, donor lines of each gene were crossed, and their F₂, F ₃ and advanced F₄ progenies were used for allelism analysis. Phenotypic assessment of 177 F ₂ plants, 71 F ₃ families and 90 F _3:4 families using <italic>P</italic> . <italic>hordei</italic> isolate AUS220, avirulent to both genes, demonstrated that <italic>Rph</italic> _{<italic>MBR1012</italic>} is genetically independent of <italic>Rph4</italic> . Genetic mapping with 5,702 markers in the F _3:4 population localized both genes <italic/> to the distal region of chromosome 1HS, spanning 18.7 cM and 10.6 cM, respectively. These intervals correspond to physical regions of 14.7 Mb and 11.8 Mb in the Morex v3 genome, and 15.7 Mb and 13.8 Mb in the Maximus genome. The diagnostic value of eight co-segregating markers was assessed across a diverse panel of 143 barley genotypes with the KASP marker <italic>QBS217</italic> showing the highest predictive accuracy (96.48%), although no marker achieved 100% diagnostic reliability. These results confirm that <italic>Rph</italic> _{<italic>MBR1012</italic>} represents a distinct resistance locus, which is here designated <italic>Rph30</italic> , in accordance with the rules and numbering system of barley gene nomenclature. The characterization of this novel resistance gene provides valuable resources for marker-assisted selection and gene pyramiding to improve durability of BLR resistance. </p>