Ryd4 (Hb): a novel resistance gene introgressed from Hordeum bulbosum into barley and conferring complete and dominant resistance to the barley yellow dwarf virus.

Barley yellow dwarf virus (BYDV) causes high yield losses in most of the major cereal crops worldwide. A source of very effective resistance was detected within the tetraploid wild species of Hordeum bulbosum. Interspecific crosses between a resistant H. bulbosum accession and H. vulgare cv. 'Igri' were performed to transfer this resistance into cultivated barley. Backcrosses to H. vulgare resulted in offspring which carried a single subterminal introgression of H. bulbosum chromatin on barley chromosome 3HL and proved to be fully resistant to BYDV-PAV, as inferred by ELISA values of zero or close to zero and lack of BYDV symptoms. Genetic analysis indicated a dominant inheritance of the BYDV-PAV resistance factor, which we propose to denote Ryd4 ( Hb ) . The identity and effect of Ryd4 ( Hb ) are discussed in relation to other known genes for BYDV resistance or tolerance, as well as the relevance of this gene for resistance breeding in barley.