Gamma Irradiation Alters in vitro Regeneration Efficiency of Rice (Oryza sativa L.) Cultivar BRRI dhan92

Abstract

Tissue culture, combined with gamma irradiation, is an important biotechnological approach for creating genetic variation in rice, particularly for shortening the life cycle of a high-yielding indica rice. The main objective of this study was to establish an effective in vitro regeneration protocol from calli derived from mature seeds, and to evaluate the effects of gamma irradiation on callus survival, as well as shoot and root development and plant establishment. Optimal callus induction occurred on Murashige and Skoog (MS) medium with 5.0 mg/L of 2,4-D, yielding a 66.67% rate. Shoot regeneration peaked at 76.67% with a combination of 0.5 mg/L NAA, 1.2 mg/L Kinetin, and 4.0 mg/L BAP in the basal MS medium. Notably, increased gamma irradiation doses resulted in decreased survival and regeneration rates. Lower doses resulted in longer survival and shoot regeneration. The control group (0 Gy) had the longest survival and shoot regeneration period, but the 6 Gy-irradiated calli had the highest overall rates of survival, shoot regeneration and plant establishment. They were superior to all other groups, including the control, except that 22 Gy-irradiated calli achieved better root induction. The optimal dose of gamma irradiation for BRRI dhan92 calli was determined to be 6 Gy, while the lethal dose for 50% callus survival (LD50) was approximately 24.9 Gy. Later, the in vitro regenerated plantlets were acclimatised and grown under field conditions. The developed protocols offer great promise for rice improvement through in vitro regeneration and mutation breeding techniques. Further studies are needed for molecular validation and field evaluation of subsequent generations to confirm trait stability.