Comparative RFLP mapping of Hordeum vulgare and Triticum tauschii

Hordeum vulgare (barley) and Triticum tauschii are related, but sexually incompatible, species. This study was conducted to determine the extent of homology between the genomes of barley and T. tauschii using a common set of restriction fragment length polymorphism (RFLP) markers. Results showed that >95% of low-copy sequences are shared, but 42% of the conserved sequences showed copy-number differences. Sixty-three loci were mapped in T. tauschii using RFLP markers previously mapped in barley. A comparison of RFLP marker order showed that, in general, barley and T. tauschii have conserved linkage groups, with markers in the same linear orders. However, six of the seven linkage groups of T. tauschii contained markers which mapped to unrelated (i.e., non-homoeologous) barley chromosomes. Additionally, four of the T. tauschii linkage groups contained markers that were switched in order with respect to barley. All the chromosome segments differing between T. tauschii and barley contained markers that were detected by multi-copy probes. The results suggest that the observed differences between the T. tauschii and barley genomes were brought about by duplications or deletions of segments in one or both species. The implications of these findings for genetic mapping, breeding, and plant genome evolution are discussed.