Studies on the variation of chromosome numbers in hybrids between Dendranthema shiwogiku (Kitam.) Kitam. and spray type cultivars of D. X grandiflorum (Ramat.) Kitam.

摘要

Chromosome numbers were counted in three individuals of Dendranthema shiwogiku, 16 cultivars of spray type chrysanthemum (D. Xgrandiflorum [Chrysanthemum morifolium]), 40 F1 hybrids between D. shiwogiku and a spray type cultivar, and 68 backcross (BC1) hybrids between the F1 hybrid and the spray type cultivar. Aneuploids were observed in D. shiwogiku and spray type cultivars. The chromosome numbers of F1 hybrids varied from 2n = 60 + B to 68; the average was 2n = 63.9 which is close to the heptaploid chromosome number of 63. Chromosome numbers of BC1 hybrids varied widely from 2n = 53 to 65; the average number was 2n = 59 whose ploidy was considered as the intermediate between hexaploidy and heptaploidy. Aneuploids were also observed in the progeny of each cross, and their average chromosome number was the same as the mean chromosome number of the parents. It seems that the aneuploids in spray type cultivars and heptaploid F1 hybrids are not sterile, and that their chromosomes are divided into two equal parts. Small B chromosomes, lacking the constriction, were observed in two individuals of D. shiwogiku (frequency of 67%), one spray type cultivar (6%), 13 F1 hybrids (33%) and 12 BC1 hybrids (18%). The B chromosomes were equally divided as wellas the autosomes. No correlation exists between chromosome number and diameter of the upper flower head in the spray type cultivars, F1 hybrids and BC1 hybrids, whereas a significantly negative correlation was identified between ploidy level and diameterof flower head.