| The studies include three related parts. The first one was concerned with the study on regeneration of calli derived from ray flowers and tabular flowers of three summer-flowering Chrysanthemum morifolium cultivars with small inflorescences, named 'Golden lotus', 'White dwarf' and 'Red dwarf respectively. The second one studied the effects of gamma rays on the browning and differentiation capacity of calli derived from different explants of three cultivars. The last one was variation analysis of regeneranis from tabular-flower-derived calli of 'Golden lotus' treated with 10, 15 and 20 Gy gamma rays, respectively using RAPD.The results are as follows.Firstly, both genotype and types of explants greatly influence induction and differentiation rate of calli and mean buds per callus. As far as Chrysanthemum morifolium 'Golden lotus' was concerned, induction and differentiation rate of calli and mean buds per callus were the highest among the three cultivars. Its tabular-flower-derived calli induction rate, differentiation rate and mean buds per callus were 74.25%, 30.61% and 4.91, and those of ray-flower-derived calli were 61.71%, 27.28% and 3.82, respectively. While the data of 'Red dwarf were the lowest , the tabular-flower-derived calli induction rate, differentiation rate and mean buds per callus were 72.50%, 19.03% and 0.61, and those of the ray-flower-derived callus were 58.39%, 11.02%, and 0.27, respectively. Callus differentiation rate of three cultivars had a significant difference at level of 5%, and so did mean buds per callus at level of 1%. Tabular flowers were superior to ray flowers in the capacities of callus induction and differentiation. Take 'White dwarf as an example, its induction and differentiation rate of tabular-flower-derived calli and mean buds per callus were 71.66%, 21.10% and 2.53, while those of ray-flower-derived callus were 57.33%, 13.21% and 1.68, respectively.Secondly, 60Co gamma ray has an great influence upon browning and differentiation capacity of calli derived from different explants of the three cultivars. As the doses of gamma ray increased from 0 , 10, 15 to 20 Gy, the browning rate of the calli rose, and differentiation capacity decreased gradually. When the dose of gamma ray was 15 Gy, all the calli of 'Red dwarf' lost differentiation capacity, and so did the ray-flower-derived calli of'White dwarf. When the dose was 20Gy, 'White dwarf lost differentiation capacity, and differentiation capacity of'Golden lotus' was lower than that of the control. Compared withthe control, its differentiation rate of tabular-derived calli and mean buds per callus decreased by 42.89% and 71.49%, and those of ray-flower-derived calli by 52.35% and 68.12%,respectively. In addition, tabular-flower-derived calli was more sensitive to gamma rays than ray-flower-derived calli, thus the latter was easier to brown and lose differentiation capacity than the former. What's more, as far as sensitivity to gamma rays was concerned , the calli of 'Red dwarf ' were most susceptible to gamma ray among the three cultivars, and ray-flower-derived calli more than tabular-flower-derived calli.Finally, RAPD is an effective molecular means to identify the variation of genomic DNA of regenerants quickly and reliably. The results showed that the variation range of genomic DNA of plants regenerated from inrradiated calli was proportional to the dose of gamma rays. In other words, the higher the dose of gamma ray used , the wider the variation range of the genomic DNA of plants was. In comparison with the control, the variation coefficient of the genomic DNA of plants, which produce from tabular-flower-derived calli of 'Golden lotus" irradiated with the dose of 10, 15 and 20 Gy gamma rays, was 0.223,0.335 and 0.393, respectively. A batch of mutant plants had been screened through RAPD technique. And the phenotypic characteristics of these plants are under observation in the field.
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