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 vulgare (L.), H. bulbosum (L.), and interspecific hybrids and their derivatives were 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 possessed at least two rDNA repeat lengths, indicating heterozygosity at the Rrn locus. 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. bulbosum rDNA repeat units and (or) fragments. Two hybrid derivatives, one amphiploid and a doubled haploid derived from the same parental combination, lacked the vulgare Rrn2-specific 9.0-kb rDNA repeat. This is the first conclusive evidence for the elimination of vulgare genetic material in vulgare-bulbosum hybrids. The ratios of 9.0- to 9.9-kb vulgare repeats and H. vulgare 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 fragments and the ratios of 9.0 to 9.9 kb vulgare rDNA repeats revealed differential methylation at Rrn1 and Rrn2 loci. Hybrids and derivatives showed differential distribution of methylation of EcoRI, BglII, and SacI sites at the Rrn1 locus. Two of the hybrid derivatives exhibited extensive CpG-biased methylation. Data presented here are indicative of the differences in the onset of events triggered by the interaction of the component genomes and enabled detection of differential methylation among Rrn loci, loss of H. vulgare genetic material, and development of doubled haploids with the Rrn1 locus.