Allodiploid nature of Allium wakegi Araki revealed by genomic in situ hybridization and localization of 5S and 18S rDNAs.

Allium wakegi Araki could be originated from cross hybridization between close relatives of a form of A. cepa and A. fistulosum. Chromosomes of each parental haploid set were identified in the chromosome complement of A. wakegi by genomic in situ hybridization using probes of the total, parental genomic DNAs of A. cepa and A. fistulosum, respectively. The results of GISH suggested significant differentiation of genomic DNAs between these closely related species. Allium cepa had two 5S rDNA loci at the interstitial regions of the short arms of small chromosome pair (the 7th pair) and A. fistulosum had one locus at the interstitial region of the homologous short arms. Allium wakegi had two chromosomes carrying one and two 5S rDNA loci which appeared to correspond to those of A. fistulosum and A. cepa, respectively. Chromosomes carrying 18S rDNA loci originated from those of both A. cepa and A. fistulosum were also observed in the chromosome complement of A. wakegi.