Induction of mutations for stem quality in chrysanthemum (Dendranthema grandiflora) by using gamma-ray irradiation.

Chrysanthemum (Dendranthema grandiflora) is one of the important cut flowers all over the world as well as in Korea. Dendranthema grandiflora 'Beakma' is a white standard-type cultivar developed in Korea and produces high quality cut flowers throughout the year. However, this cultivar shows hollow stems during high temperature periods in summer. The strength of the stem is decreased and causing extra care in flower handling. The objective of this study was to induce mutations without hollow space in the stem for improvement of quality in Dendranthema grandiflora 'Beakma'. In addition, the effect of radiation was investigated on the survival and growth rate of individuals. A total of 1,679 rooted cuttings were treated with different doses of gamma rays (10-50 Gy). All individuals survived regardless the irradiation-dose but the growth was decreased with an increase of radiation-dose. Particularly, plant height and internode length were remarkably decreased from 2 to 4 times at 40 and 50 Gy. The morphological characteristics of leaves, the leaf length and width were increasingly decreased, and petiole length was increased as increment of dose. The irradiated individuals were repeatedly propagated and one plant was selected as a mutant without hollow space in the stem from a total of 7,109 individual stems. The cuttings from this selected mutant were rooted for propagation and further selection. We conclude that treatment of gamma-ray can be an effective way for indution of exclusive mutations in Dendranthema grandiflora.