The explants that had formed somatic embryos were then transferred to the germination and regeneration medium. After 2 weeks, some somatic embryo clusters developed, and some somatic embryos grew into seedlings (Figure 1b). The regeneration rate was calculated after the explants had been cultured on the medium with 4 mg/L 6-BAP for 8 weeks. The regeneration rate declined as the radiation dose increased but was approximately 60% with 67 Gy (Figure 2).