HIGH FREQUENCY CALLUS INDUCTION AND PLANT REGENERATION FROM SHOOT TIP EXPLANTS OF SORGHUM BICOLOR L. MOENCH Original Article

Objective: Sorghum bicolor is a relatively recalcitrant crop that is less amenable to in vitro manipulation by tissue culture and transformation techniques. In this study, a robust protocol was developed for attaining high frequency callus induction and plant regeneration from the shoot tip explants of Sorghum bicolor. Methods: The shoot tips were cultured in the presence of 2,4-dichlorophenoxyacetic acid (2,4-D) alone, and in combinations with benzylaminopurine, kinetin and 1-napthaleneacetic acid at varying concentrations in Murashige Skoog (MS) media to determine the optimal media for callus induction. Further, thidiazuron (TDZ) in the concentration range of 0.1-2.0 mg/L was supplemented in MS media to study its effect on plant regeneration. Results: The highest frequency of embryogenic callus (74.8%) was obtained on MS medium supplemented with 2.0 mg/L of 2,4-D and 0.5 mg/L of kinetin. The embryogenic calli on transfer to regeneration medium supplemented with 1.0 mg/L of thidiazuron (TDZ) in MS media showed the highest regeneration of shoots with 12.2 (mean) shoots per embryogenic callus. The histochemical analysis of callus showed the formation of shoot apex from the meristematic centres of calli. The regenerated shoots were rooted on half-strength MS medium containing 1.0 mg/L of Indole-3butyric acid (IBA). The well rooted plantlets developed after 2 weeks were subjected to hardening and acclimatization with a survival frequency of 68%. The in vitro regenerated plants were observed to be phenotypically similar to in vivo plants. Conclusion: The development of rapid and reproducible in vitro regeneration protocols would enable the isolation and characterization of secondary metabolites from sorghum under controlled environment that could be evaluated for their pharmacological efficacy.