In vitro morphogenesis of Sorghum bicolor (L.) Moench:: Efficient plant regeneration from shoot apices

An efficient and reproducible plant regeneration system has been developed from shoot apices of aseptically germinated seedlings of sorghum. After four passages of culture at two-week intervals on MS basal medium containing 2 or 4 mg/L BA, the shoot apices produced multiple shoot clumps, each capable of regenerating more than 100 shoots, via an intensive differentiation of both axillary and adventitious buds. When the shoot apices were cultured on MS medium supplemented with 0.5 mg/L 2,4-D and 2 or 4 mg/L BA, a highly efficient differentiation of adventitious buds was initiated from enlarged apical domes and thickened leaf bases of the shoot apices six weeks after inoculation. Over 200 shoots were induced from a shoot apex eight weeks after culture. Somatic embryos were produced directly from the enlarged and organized apical domes of primary and secondary shoots without apparent callus formation after subsequent subcultures of the multiple shoot clumps on MS medium with 0.5 mg/L 2,4-D and 2 or 4 mg/L BA. All 18 sorghum genotypes tested followed a similar differentiation and regeneration pattern at a high frequency. Most of the multiple shoots and somatic embryos developed into fertile plants after rooting on IBA-containing MS medium and transfer to greenhouse.