An Event Preceding Genome Differentiation in the A Genome Populations of Scilla scilloides

Hybrids between A genome diploid plants from the Chinese and Korean populations of the Scilla scilloides complex were found. Molecular cytogenetic examination and genome size measurement showed that the hybrids were composed of two distinguishable A genomes. Genomic in situ hybridization (GISH) using mixed probes of both parental genomic DNAs could distinguish the chromosomes of each A genome in the chromosome spreads of hybrid plants. This suggests that the A genome plants of the two populations differ at the genomic DNA level. The genome size of the Korean population was 1.2–1.3 times larger than that of the Gansu population according to the area of chromosome set and fluorescence intensity in flow cytometry (FCM). Despite these cytological differences, the hybrids showed normal chromosome pairing in meiosis of pollen mother cells (PMCs), suggesting that the genomes of these two populations still belong to the same genome in terms of classical cytogenetics. Despite these genomes belonging to the same A genome, molecular signs of genome differentiation in the A genome were also found in the 5S rDNA spacer region. Southern blot hybridization of this spacer region from several populations showed that the three A genome populations were distinct from one another. Additionally, in a sequence analysis of a part of matK gene and ITS1, the three A genome populations showed population-specific sequence variations. These results suggest that the A genome populations of S. scilloides is just in the process of genome differentiation.