Cytogenetic diversity of the diploid Korean wild Chrysanthemum (Asteraceae) inferred from genome size variations and chromosomal distributions of 5 S and 18 S rDNAs.

BACKGROUND

The genus Chrysanthemum (Asteraceae) consists of a series of polyploids, ranging from diploid (2x) to decaploid (10x), with a basic chromosome number of x = 9. They vary widely within and among species owing to natural hybridization and polyploidization in natural habitats, and this has made recognizing the taxonomic boundaries among them difficult. Karyotype analysis has been played a powerful methodology to investigate the cytogenetic difference of the plant species but it was not applicable to define the species boundary and discuss their relationship of the Korean Chrysanthemum because of unstable karyotypes within the species. In this study, 28 natural diploid populations of the Korean Chrysanthemum, which were identified based on their morphological characteristics, were collected from their natural habitats to understand their cytogenetic relationships at the diploid level. We measured the genome size and compared the karyotype and distribution pattern of two ribosomal DNAs (rDNAs) using FISH (fluorescence in situ hybridization).

RESULTS

The results confirmed that C. zawadskii populations had smaller 1 C values than C. boreale and C. indicum did even for infraspecific variations. FISH analysis showed that 5 S and 18 S rDNA genes were present in one and two pairs (cytotype I) in the diploid populations of C. zawadskii regardless of the differences observed in individual karyotypes. In contrast, one pair of 5 S rDNA genes was commonly observed on different chromosomes in C. boreale, C. indicum, and their intermediate-type populations. In the case of the 18 S rDNA genes, two major types with three or four pairs on the short arms were observed (cytotypes II and IV), and an additional signal was detected in a few individuals (cytotype III). In total, five cytotypes were identified in the diploid Korean Chrysanthemum, including cytotype V, which was observed in only one individual of C. indicum with colocalized 5 S and 18 S rDNA signals on chromosome 4.

CONCLUSIONS

Consequently, we concluded that C. zawadskii with white ray flowers was cytogenetically distinguished from C. boreale and C. indicum, whereas there were no distinctive features between C. boreale and C. indicum with yellow ray flowers.