IDENTIFYING THE CORRECT DOSE OF GAMMA-RAYS FOR IN VITRO MUTATION OF ROSE CULTIVARS

Rose (Rosa hybrid) is one of the most important flower crops in the world and as a cut flower has great economical value in the world. Mutation breeding is an established method for crop improvement and has played a major role in the development of many new flower color/shape mutant cultivars in ornamentals. The in vitro culture of vegetatively propagated crops in breeding programs has proven to be a valuable method to produce desired variation and to rapidly multiply the selected mutants. In the present research effect of different doses of gamma-rays on axillary buds of two rose cultivars were investigated. Gamma ray in vitro irradiation was carried out in order to induce mutation and select mutants. Axillary buds of two rose cultivars (Rosa hybrid ‘Apollo’ and ‘Maroussia’) grown on MS proliferation medium, supplemented with 2 µM BAP were exposed to gamma irradiation (0, 20, 30, 40, 50, 60, 70, 80, 90 and 100 Gray). 45 days after irradiation, percentage of survived explants was determined to assess LD₅₀. Number of green leaves developed and length of plantlets were also recorded. The LD₅₀ was determined on survival rate and calculated at 67 and 66 Gy in ‘Mourossia’ and ‘Apollo’ respectively. As related to the other recorded parameters, the doses that caused 50% reduction in height in ‘Apollo’ and ‘Maroussia’ were 70 and 68 Gy respectively (Table 2). Thus, the most appropriate treatment dose for these cultivars can be indicated between 60 to 70 Gy. This dose range provided sufficient survival rates and plant growth, basic requirements for performing a successful mutant selection. These results are valuable in planning a breeding program based on mutation induction in roses.