Comparison of Somatic Chromosomes in Dendranthema Species and F1 Hybrids in Korea

Dendranthema species and F₁ hybrids from the different habitats in Korea were collected to investigate the variation of their somatic chromosomes. The results in this study revealed series of polyploidy in Dendranthema from diploids (2n=2x=18) up to octoploids (2n=8x=72) with the basic chromosome number x=9. Some of the F₁ hybrids have also intraspecific polyploids as well as aneuploids. Due to Dendranthema has shown to comprise series of polyploidy (2x, 4x, 6x, 8 x), it was possible that polyploidy (2x, 4x, 5x, 6x) individuals also produced in F₁ hybrid progeny. Mostly the range of variation was found as diploid (2n=2x=18) individuals with D. boreale, D. makinoi and D. lineare, irrespective of whether they occurred together with tetraploid (2n=4x=36) of D. indicum, D. zawadskii ssp. lucidum, D. zawadskii ssp. latilobum var. leiophyllum, D. japonicum, and hexaploid (2n=6x=54) of D. indicum for. albescens, D. zawadskii ssp. acutilobum, D. zawadskii ssp. acutilobum var. tenuisectum, D. zawadskii ssp. acutilobum var. alpinum, D. zawadskii ssp. naktongense, D. zawadskii ssp. yezoense, D. zawadskii ssp. latilobum and octoploids (2n=8x=72) of D. zawadskii ssp. coreanum. Number of chromosomes in different species suggests that the hybridization between individuals had repeatedly occurred not only in D. zawadskii complex, but also in D. boreale and D. indicum. As morphological characteristic, intermediate individuals between D. zawadskii complex and D. indicum suggests that the hybridization occurred with different species respectively.
Artificial reciprocal crosses between D. japonicum (2n=36, tetraploid) and D. indicum for albescens (2n=54, hexaploid) were made and produced F₁ hybrid (2n=45, pentaploid). The cytogenetic investigation in Dendranthema has been largely directed to ascertain chromosome numbers and the descriptions of chromosome morphology.