PRODUCTION AND CHARACTERISTICS OF CHROMOS OME-DOUBLED PLANTS OF SMALL-FLOWERED GARDEN CHRYSANTHEMUM, DENDRANTHEMA X GRANDIFLORUM (RAMAT) KITAM CV YS BY COLCHICINE TREATMENT OF CULTURED SHOOT TIPS

Small-flowered garden chrysanthemum cv. YS is unique in that it has th e smallest chromosome number (2n = 36) among chrysanthemum cultivars, Although cv. YS has a potential as a breeding parent, it has low polle n fertility. To improve pollen fertility, chromosome-doubled plants of cv. YS were produced and their characteristics investigated. 1. Shoot tips were cultured on solid MS medium containing 0.05 similar to 0.2% colchicine for 12 similar to 48 hrs. Chromosome numbers of root-tip c ells in 68 regenerated plants were counted one month after potting. Si x plants, which regenerated in the treatments with 0.2% colchicine for 24 or 48 hrs, were regarded as chromosome-doubled plants (the first e xamination). 2. Six months after potting, a second examination of two plants of the above six revealed that the chromosome numbers differed between root- and shoot-tip cells. Out of 156 plants propagated from t he six plants by crown division, 96 chromosome-doubled planes were sel ected after counting the chromosomes in the root-tip cells. From the a bove 96 plants, 78 were selected after chromosome counting both root- and shoot-tip cells (the third examination). 3. Examination of the chr omosome-doubled plants of cv. YS cultivated in unheated greenhouse rev ealed that in comparison with cv. YS, the propagules were: 1) obviousl y dwarfed, the number of branches, leaves and flower buds reduced, and the first flowering dates were late; 2) the pollen fertility was cons iderably improved; and 3) the size of the pollen grains and stomata we re equal.