Detection of ribosomal RNA genes in apple (Malus × domestica) using fluorescence in situ hybridization

The locations of the 18S-5.8S-25S and 5S ribosomal RNA genes (rDNAs) on the chromosomes in the seedlings obtained from open-pollination of apple ‘Sensyu’ (Malus × domestica Borkh.) were determined using fluorescence in situ hybridization (FISH). 18S-5.8S-25S and 5S rDNA probes were labeled with biotin and hybridization signals were detected using a fluorescein isothiocyanate (FITC)-avidin conjugate on the chromosomes counterstained with DAPI. The 18S-5.8S-25S rDNA signals were detected in the telomeric positions of eight chromosomes among 34. These sites were located on two long, two relatively long, two medium, and two relatively short chromosomes. The two 5S rDNA sites were located at centromeric positions of relatively short chromosomes which do not possess 18S-5.8S-25S rDNA sites. The numbers and positions of rDNA sites were stable among the seedlings.