Morphological variation in Tricyrtis hirta plants regenerated from heavy ion beam-irradiated embryogenic calluses

In order to induce horticulturally valuable mutants in the Liliaceous ornamental Tricyrtis hirta, embryogenic calluses of this species were irradiated with (12)C(+6) ion beams. Morphological characterization was performed on 35, 37 and 15 plants regenerated from calluses irradiated with 5, 10 and 20 Gy ion beams, respectively, and on 10 plants from non-irradiated calluses after 3 years of cultivation in pots. No plants were regenerated from calluses irradiated with 50 Gy ion beams. There were no large differences in the mean values of leaf length, leaf width, soil and plant analyzer development (SPAD) value of leaves, flower length and flower diameter between the control (division-derived plants from the mother plant of the embryogenic calluses) and the irradiation treatments at different doses. On the other hand, the mean number of shoots per plant increased, and the mean shoot length and the mean number of nodes per shoot decreased in the irradiation treatments. The mean number of flowers per plant was increased in the 20 Gy irradiation treatment. For most morphological characteristics investigated, the variation spectrum widened with increase in the irradiation dose. Several horticulturally attractive variations such as dwarfism, slender and deep green leaves, and large flowers were observed in regenerants from the irradiation treatments, and these variations were stable after additional 2 years of cultivation in pots or garden. Thus mutation induction by heavy ion beam irradiation of embryogenic calluses is a valuable tool for improving horticultural value of T. hirta.