FISH Karyotype Comparison of Platycodon grandiflorus (Jacq.) A. DC. ‘Jangbaek’ and Its Colchicine-Induced Tetraploid ‘Etteumbaek’

Genome sequencing has been going on major medicinal plants, including Platycodon grandiflorus, which is commonly used as a functional food and medicinal resource in Korea. Molecular cytogenetic studies using fluorescence in situ hybridization (FISH) show the chromosomal organization of specific DNA sequences. We analyzed the FISH karyotypes of P. grandiflorus ‘Jangbaek’ and a colchicine-induced tetraploid cultivar ‘Etteumbaek’ using 5S and 45S rDNA probes. As a result, ‘Jangbaek’ had chromosome length ranging from 2.34 ± 0.13 to 3.99 ± 0.197 μm with its karyotypic formula of 2n = 2x = 18 = 16m + 2sm (two satellites) whereas ‘Etteumbaek’ had chromosome length of 2.37 ± 0.08 to 4.20 ± 0.16 μm and a karyotypic formula of 2n = 4x = 36 = 24m + 12sm (four satellites). A pair of 5S rDNA signals observed interstitially in chromosome 3 and the co-localization of 5S and 45S rDNA signals occupying the nucleolar-organizing region (NOR) of chromosome 6 was observed in the diploid cultivar ‘Jangbaek’. Doubling of both signals co-localized in the NOR of chromosome 6 were observed in the colchicine induced tetraploid cultivar. However, the tetraploid revealed a modified positioning of 5S rDNA signals on chromosome 3 interstitially, with observable vague dispersed signals in one chromosome of chromosomes 1 and 5. This result will be useful for further breeding program and chromosomal backbone for the Platycodon genome analysis.