EFFICIENT IN-VITRO SHOOT-REGENERATION SYSTEMS IN CASSAVA (MANIHOT-ESCULENTA CRANTZ)

Two different protocols for in vitro regeneration of cassava using zygotic embryos and nodal axillary meristems have been developed. In both cases, buds were regenerated directly from excised explants without an intervening callus phase after a two-step culture procedure. In cotyledonary explants derived from zygotic embryos, prolific shoot formation occurred within 2-3 weeks on MS medium supplemented with 0.5-5 mg/l BAP alone or in combination with 0.1 mg/l NAA. Nodal explants with axillary meristems derived from aseptically grown seedlings or stem cuttings were used to initiate a round compact bulb-like structure on MS medium containing 10 mg/l BAP. These latter structures, when cultured on MS medium supplemented with 0.1 mg/l NAA, 1 mg/l BAP and 0.1 mg/l GA(3), produced multiple shoots. Somatic embryos isolated at the globular/torpedo stage from zygotic embryo explants were also capable of multiple shoot production on medium with 1 mg/l BAP. Rooting of regenerated shoots exceeded 95% in phytohormone-free MS medium. No change in their ploidy levels was observed. Therefore, the protocols developed should be of use in the particle gun and Agrobacterium-mediated genetic transformation of cassava.