Preliminary Study on the Optimization of the Heavy-ion Dose for Mutation Breeding in Three Lilium Species

Heavy-ion beam technology is an excellent tool in mutation breeding of horticultural plants. This approach has been applied in more than twenty ornamental plants and many novel mutations and varieties have been thus obtained. In this study, dry seeds from three Lilium species (L. leichtlinii var. maximowiczii, L. cernuum, and L. amabile) were laid flat in dishes and irradiated with ¹²C⁶⁺ heavy-ion at doses of 0 (control), 10, 20, 30, 40, 50, and 100 Gy in the Heavy Ion Research Facility in Lanzhou, China. The irradiated and control seeds were soaked in water for 24h, the wings of seeds were cut, and then placed on the germination medium. There were four responses in the growth of irradiated seeds: no germination, abnormal germination, normal germination but failure of roots/bulblet formation, and normal germination with successful formation of roots/bulblet. The germination rates of all irradiated seeds first rose but then fell because some irradiated seeds did not form roots. The survival rates increased according to the records after 90 days growth and intersected with germination rates as the levels of radiation decreased. Generally speaking, the germination rates and survival rates decreased with increased radiation dose in L. leichtlinii var. maximowiczii and L. amabile. However, a saddle-shaped curve was observed in the L. cernuum. The species differed substantially in seed growth with the same radiation dose, which was likely caused by the differences in thickness of the testa. It is speculated that the appropriate doses for mutation breeding are 10-20 Gy for L. leichtlinii var. maximowiczii, 20 and 50 Gy for L. cernuum, and 40-50 Gy for L. amabile.

Acknowledgments. This work was supported by the Special Fund for Forestry Scientific Research in the Public Interest (201204609), the Program for Innovative Research Team in BJAST (IG201404N) and the BJAST Young Researcher Training Plan (201416).