Micropropagation of coconut from epicotyl tissues: a histological study

Clonal propagation of coconut was attempted using epicotyl tissues. Calloids were successfully initiated in more than 65% of the cultures in Hornung's (1995) medium. Formation, maturation, and germination of somatic embryos were attained by adding thidiazuron (TDZ) in the regeneration media, and then replacing it with 6-benzylaminopurine (6-BAP), Maintenance of the cultures in modified Branton & Blake's (1983) medium with 6-BAP enhanced regeneration of individual and fused plantlets (10.29%) 18-24 mo after initial culture. The onset of callogenesis was associated with the periclinal division of provascular cells leading to a meristematic zone organized in a cambium-like zone. Callus growth was ensured by periclinal mitosis in this cambium-like zone. Fragmentation of this meristematic zone resulted to the formation of meristematic nodules. These nodules, considered as proembryos, produced cotyledons and became somatic embryos that germinated later. Individualization of single cells from superficial layers of the leaf primordia was also noted from the embryogenic calloids induced from epicotyl tissues. This unicellular pathway of somatic embryogenesis would represent an attractive pathway for genetic transformation studies in coconut. (Résumé d'auteur