The short awn 2 (lks2) and dense spike 1 (dsp1) genes are unique to East Asian barley. These two spikerelated morphological genes are important because they may be involved in stable production and local adaptation. As a first step of their positional cloning, molecular mapping was conducted in 98 F 2 plants derived from a cross between Karafuto Zairai and Aizu Hadaka 3. The dsp1 gene was mapped to the proximal region of the short arm of chromosome 7H. The lks2 gene was located on the long arm of 7H and flanked by ESTbased markers k04151 and k06123, with distances of 0.5 cM in the proximal side and 1.0 cM in the distal side. Both k04151 and k06123 shared homology to rice genes on chromosome 6 that were separated with the physical distance of 5.6 Mbp. In this interval, rice-barley microsynteny was exploited for marker enrichment. Of 57 rice genes attempted, 15 (26.3%) yielded polymorphic EST-based markers. Breakdown of collinearity was found in the candidate region of lks2, suggesting occurrence of structural changes in the chromosome region harboring lks2 during divergence of barley and rice from a common ancestor.

The hulled or naked caryopsis character of barley is an important agronomic trait because of the direct link to its use. A single recessive gene, nud, located on the long arm of chromosome 7H, controls the naked caryopsis character. Previously, linked amplified fragment length polymorphism (AFLP) bands from bulked segregant analysis were screened, and the nud gene was mapped in a population of 151 F 2 plants. In the present study, the aim was to construct a high-resolution map of the nud gene towards its positional cloning. Two AFLP bands were converted into sequence-characterized amplified region (SCAR) markers (sKT5 and sKT9), and a previously reported SCAR marker sKT3 was improved for more reliable detection of polymorphism. A total of 2380 segregants derived from five cross-combinations were analysed, and the nud gene was flanked by sKT3 and sKT9, at the 0.6-cM proximal and the 0.06-cM distal side, respectively. The SCAR markers developed in this study should be useful for marker-assisted selection in naked barley breeding employing crosses between naked and hulled accessions.