Molecular changes at Rrn loci in barley (Hordeum vulgare L.) hybrids with H-bulbosum (L.)

Southern blots of restriction fragments of genomic DNAs from Hordeum vulgar e (L.), H. bulbosum (L.), and interspecific hybrids and their derivatives w ere hybridized with rDNA probe to identify locus-specific modifications at Rrn loci. H. bulbosum rDNA revealed a single EcoRV site per repeat compared with two sites in H. vulgare rDNA repeats. H. bulbosum accessions possesse d at least two rDNA repeat lengths, indicating heterozygosity at the Rrn lo cus. Hybrids possessed both H. vulgare and H. bulbosum rDNA repeats. Two of the hybrid derivatives possessed bulbosum-specific Sau3AI and HaeIII rDNA fragments, while amphiploid and doubled haploid derivatives lacked H. bulbo sum rDNA repeat units and (or) fragments. Two hybrid derivatives, one amphi ploid and a doubled haploid derived from the same parental combination, lac ked the vulgare Rrn(2)-specific 9.0-kb rDNA repeat. This is the first concl usive evidence for the elimination of vulgare genetic material in vulgare-b ulbosum hybrids. The ratios of 9.0- to 9.9-kb vulgare repeats and H. vulgar e to H. bulbosum rDNA repeats indicate partial loss of the vulgare-specific 9.0-kb rDNA repeat among the hybrids. Differences in MboI and Sau3AI fragm ents and the ratios of 9.0 to 9.9 kb vulgare rDNA repeats revealed differen tial methylation at Rrn(1) and Rrn(2) loci. Hybrids and derivatives showed differential distribution of methylation of EcoRI, Bg/II, and SacI sites at the Rrn(1) locus. Two of the hybrid derivatives exhibited extensive CpG-bi ased methylation. Data presented here are indicative of the differences in the onset of events triggered by the interaction of the component genomes a nd enabled detection of differential methylation among Rrn loci, loss of H. vulgare genetic material, and development of doubled haploids with the Rrn (1) locus.