Recovery of cassava (Manihot esculenta Crantz) plants from culture of immature zygotic embryos

An embryo culture protocol using immature cassava seeds has been developed to enhance successful seed germination and reduce time for population estab lishment. Embryonic axes were excised from seeds 40 days after pollination and placed on 1/3 MS medium supplemented with growth factors. Fruits were e ither air-dried at 20 degrees C to aid dehiscence, or dissected immediately after harvest. Culture of embryonic axes from seeds obtained from mature f ruits (90 days after pollination) served as control. Average percent germin ation and plantlet recovery rate were higher for embryos cultured from non air-dried immature seeds than from air-dried immature seeds. Immature seeds that were air-dried before germination had greater than or equal to 50% re duction in germination rate and greater than or equal to 75% reduction in p lantlet recovery rate, indicating that cassava immature zygotic embryos are susceptible to osmotic pressure changes. Genotypic effects were observed i n shoot elongation, formation of internodes, and vigor of cultures from bot h mature and immature seeds. The high percentage of plants recovered from i mmature seeds through embryo culture opens up opportunities for genetic sto ck development in cassava that has been previously unexplored.