Genetic Delimitation of rym2 and a New Barley Yellow Mosaic Virus (BaYMV)‐Specific Resistance Gene Rym19 in Cultivated Barley ( Hordeum vulgare L.)

The soil‐borne yellow mosaic virus disease, caused by infection of barley yellow mosaic virus (BaYMV) and barley mild mosaic virus (BaMMV), poses a persistent and serious threat to autumn‐sown barley ( Hordeum vulgare L.) in East Asia and Europe. Identifying and deploying resistance genes is crucial for protecting barley from viral infections, particularly against pathogenic isolates that have overcome existing resistance in commercial cultivars. In this study, we performed genetic mapping using a double haploid (DH) population generated via microspore culture from F 1 hybrids of two parental lines, ‘Mihori Hadaka 3’, which carries the recessive resistance gene rym2 and the Chinese malting barley variety ‘Dan 2’. This population was genotyped using a complexity‐reduced target‐enrichment assay. Through QTL mapping and linkage analysis with newly developed KASP markers, we identified two resistant genes, rym2 , located within the physical interval 156.9–438.9 Mb spanning the peri‐centromeric region on chromosome 7H and a new resistant gene that was tentatively designated Rym19 from ‘Dan 2’ on chromosome 5H spanning the peri‐centromeric region as well, within the interval 33.3 to 437.4 Mb. The gene rym2 was known for conferring resistance to multiple BaMMV/BaYMV isolates, whereas the Rym19 conferred race‐specific resistance against BaYMV; however, it was less effective in mechanical inoculation. In summary, this work reports the genetic mapping of both the broad‐spectrum resistance gene rym2 on chromosome 7H and a BaYMV‐specific resistance gene Rym19 on chromosome 5H, establishing a foundation for future fine mapping and cloning of these genes, as well as marker‐assisted selection from their respective donor accessions for barley resistance breeding.