Optimization of Gamma Radiation Dose for Induction of Genetic Variation in Sugarcane (Saccharum spp) Callus and Regenerated Shoot Cultures

Callus cultures were established in three commercial sugarcane varieties viz., CoJ 64, CoJ 83 and CoJ 86 from spindle explants on MS + 2,4-D (4 mg l⁻¹) + BAP (0.5 mg l⁻¹) medium. Shoots were regenerated from two-month-old calli on MS + BAP (0.5 mg l⁻¹) medium. Callus and callus derived shoots were treated with gamma (γ) radiation at 20, 40, 60 and 80 Gray (Gy). Per cent shoot regeneration from γ-irradiated calli in the three varieties ranged from 90 to 93.8 at 20 Gy, 83.3 to 87.5 at 40 Gy, 30 to 36.4 at 60 Gy and 0 at 80 Gy. Upon irradiating shoots, subsequent shoot proliferation in the three varieties ranged from 90.9 to 93.1% at 20 Gy, 82.6 to 84.0% at 40 Gy and 27 to 32.3% at 60 Gy, whereas 80 Gy dose was 100% lethal. Thus, 60 Gy dose of γ-radiation was found to be optimum for carrying out mutagenesis of both callus and callus derived shoots. In the field, different irradiated clones of the same variety exhibited huge variability with respect to number of canes, cane girth, cane height and sucrose content.