EFFECTS OF ACUTE AND CHRONIC GAMMA IRRADIATION ON IN VITRO GROWTH OF Stevia rebaudiana Bertoni
Stevia rebaudiana Bertoni is a perennial herb that belongs to the family of Asteraceae. It is a natural sweetener plant known as sweet leaf, which is estimated to be 300 times sweeter than cane sugar. In this study, micropropagation and in vitro mutagenesis of this natural herb was successfully conducted. It was found that shoot tips on MS medium supplemented with 1 mg/l Kinetin showed the highest shoot induction and multiplication after 3 weeks of culture (5.50±1.95a). Radiosensitivity test was conducted to identify the dose that killed 50% of the irradiated explants (LD50) for in vitro stevia shoots and to select effective doses to be used for the in vitro mutagenesis. Shoot tips were irradiated with acute and chronic gamma radiation at 0, 10, 20, 30, 40, 60, and 80Gy. At 60 Gy and 80 Gy, all treated shoot tips were not survived. In this study, LD50 for the stevia was estimated at 29 Gy for acute irradiation and 45 Gy for chronic irradiation. The effective doses were selected at 10, 20, 30 and 40 Gy. These selected doses were applied for the in vitro mutagenesis of the stevia shoots.