High-resolution mapping ofRyd4Hb, a major resistance gene toBarley yellow dwarf virusfromHordeum bulbosum

Abstract

AbstractVirus diseases are causing high yield losses in crops worldwide. TheBarley yellow dwarf virus(BYDV) complex is responsible for one of the most widespread and economically important viral diseases of cereals. While no complete resistance gene has been uncovered in the primary genepool of barley, sources of resistance were identified in the wild relativeHordeum bulbosum, representing the secondary genepool of barley. One such locus,Ryd4Hb, has been previously introgressed into barley, and was allocated to chromosome 3H, but is tightly linked to a sublethality factor that prevents the incorporation and utilization ofRyd4Hbin barley varieties. To solve this problem, we fine-mappedRyd4Hband separated it from this negative factor. We narrowed theRyd4Hblocus to a 66.5 kbp physical interval in the barley ‘Morex’ reference genome. The region comprises one complete and one partial gene from the nucleotide-binding and leucine-rich repeat immune receptor family, typical of dominant virus resistance genes. The closest homolog to these twoRyd4Hbcandidate genes is the wheatSr35stem rust resistance gene. In addition to the fine mapping, we reduced the sublethality factor interval to 600 kbp in barley. Aphid feeding experiments demonstrated thatRyd4Hbprovides a direct resistance to BYDV rather than a resistance to its vector. The presented results, including the high-throughput molecular markers, will permit a more targeted selection of the resistance in breeding, enabling the use ofRyd4Hbin barley varieties.Key messageWe mappedRyd4Hbin a 66.5 kpb interval in barley and dissociated it from a sublethality factor. These results will enable a targeted selection of the resistance in barley breeding.