On the Karyotypes of Garden Chrysanthemums, Chrysanthemum morifolium Ramat.

Abstract

To elucidate the karyomorphological character and mechanism of the appearance of aneuploidy in garden chrysanthemums, karyotype analysis was made by using 17 cultivars and one strain of chrysanthemum which differ in use, flower size, and flower type.
1. Size and shape of chromosomes. 1) The longest chromosome in each cultivar was 3.95.8 μm (av. 4.9 μm) and the shortest was 1.73.3 μm (av. 2.6μm). 2) The shape was classified into four types by the position of centromere; medium (m), sub-median (sm), subterminal (st), and terminal (t). Since the morphological variation of chromosomes was narrow, it was difficult to detect an indicator chromosome. 3) One to seven satellite chromosomes per chromosome set were observed in 77.8% of given cultivars; usually one to four and rarely were there five to seven.
2. As for the position of centromere, most chromosomes were the m type, followed by sm, st, and t types. A possible relationship between the frequency of occurrence of the m type chromosomes and use or flower size of garden chrysanthemum was recognizable in some cases. The karyotype component of garden chrysanthemums showed obvious hybridity in all cultivars.
3. Judging from the above results, the heterozygous karyotype seems to be closely related to the occurrence of aneuploidy in garden chrysanthemums. Moreover, the genomic makeup of the aneuploidy differed among the cultivars of garden chrysanthemum.