SECONDARY SOMATIC EMBRYOGENESIS AND PLANT-REGENERATION IN CASSAVA

Somatic embryos isolated from mature seed-derived cotyledon cultures of cassava (Manihot esculenta Crantz) underwent direct secondary somatic embryogenesis or plant development under appropriate incubation conditions. Isolated somatic embryos were subjected to a two-stage culture procedure similar to that which induced their development on cotyledon explants. This involved incubation for 24-30 days on Murashige and Skoog basal medium supplemented with 2-8 mgl-1 2,4-dichlorophenoxyacetic acid (2,4-D) (Stage I medium) before transfer to medium supplemented with 0.01 mgl-1 2,4-D and 0.1 mgl-1 6-benzylamino purine (BAP) (Stage II medium). Under these conditions, secondary somatic embryos developed directly from the cotyledons and shoot-tip regions of primary somatic embryos by a developmental process morphologically very similar to that occurring on zygotic cotyledon explants. Apical shoot extension of adventitious root formation occurred when somatic embryos were isolated from parental cultures and incubated on Stage II medium. Somatic embryo-derived plants growing in greenhouse conditions appeared morphologically normal when compared with non-regenerated plants.