Induction of Small-flowered Chrysanthemum Mutant Using Neutron Irradiation

Abstract

This study was aimed to investigate the growth characteristics of neutron-irradiated small-flowered chrysanthemums, including the types and frequencies of induced mutations, as well as survival rates after irradiation, in order to clarify the effectiveness of mutation breeding through neutron irradiation. The germination rates of axillary buds in three tested varieties after neutron irradiation revealed that the median lethal dose (LD₅₀) for germination rates was 11.10–16.65 Gy for ‘17c02’, and 5.55–11.10 Gy for both ‘18c22’ and ‘Hitachi Summer Light’. Additionally, weak individuals with significantly inhibited growth were observed after irradiation. For ‘17c02’ and ‘18c22’, all germinated individuals were weak at doses of 11.10 Gy or higher, while for ‘Hitachi Summer Light’, all germinated individuals were weak at doses of 16.65 Gy or above. The irradiated individuals exhibited different tendencies in the types of mutations depending on the tested varieties and strains. From the red-flowered ‘17c02’, a large number of color mutants (138 individuals) were generated. However, no color mutants were obtained from the white-flowered ‘18c22’. From the yellow-flowered ‘Hitachi Summer Light’, seven individuals with lighter-colored flowers were obtained, indicating a broader spectrum of flower color mutations in red varieties. Additionally, from ‘Hitachi Summer Light,’ unique leaf and plant form mutants were obtained, such as those with white-colored lateral buds and individuals with variegated leaves. These mutations were characteristic and not observed in the other two varieties. As for flower shape mutations, malformed and miniaturized flowers were observed in all three tested varieties, suggesting minimal differences among them. Moreover, even under low-dose conditions, where the germination rate of axillary buds after irradiation was high at over 92%, the mutation rate remained high at 5.0–16.0%. This suggests that compared with low LET mutagens such as gamma rays, neutron irradiation can effectively produce useful mutants with less radiation damage.