Radiosensitivity of in-vitro Cultured Calotropis gigantea Plants to Gamma Irradiation

Gamma irradiation has become an important tool in in-vitro propagation, especially for mutation breeding in clonally propagated crops. This study investigates the radiosensitivity of Calotropis gigantea plants in in-vitro culture exposed to gamma irradiation. The experiment was conducted at the tissue culture laboratory of the University of Colombo Institute for Agro-Technology and Rural Sciences under a Complete Randomized Design with 5 treatments and 15 replicates per treatment. Mature seeds of C. gigantea were exposed to surface sterilization and germinated in half-strength MS medium supplemented with 0.5 mg/L BAP. After germination, hypocotyl segments were separated and used as explants. Explants were inoculated into induction medium containing 2.5 mg/L BAP and 0.1 mg/L NAA. The cultures were exposed to four gamma irradiation doses such as 100 Gy, 125 Gy, 150 Gy, and 175 Gy, with 0 Gy as a control, using a Cobalt-60 research irradiator. The effects of gamma irradiation on plant survivability, shoot number, and shoot length were recorded over six weeks. The results indicated that gamma irradiation significantly reduced the survivability, shoot number, and shoot length in a dose-dependent manner (P≤ 0.05). At the lowest dose of 100 Gy, survivability decreased to 69.30%, while at the highest dose of 175 Gy, it dropped to 29.84%. Similarly, shoot number and shoot length also showed a significant reduction with increasing doses, with the control plants exhibiting the highest values. The LD50 value was estimated at 138.2 Gy, suggesting that doses near this threshold are sufficient to induce variability without significantly impairing regenerative capacity in-vitro. These findings highlight the potential of gamma irradiation in mutation breeding, but also emphasize the need for caution with higher doses. The results suggest that for Calotropis gigantea, irradiation doses above 138 Gy may significantly hinder regeneration, making lower doses more appropriate for genetic variation.