Endosperm Culture of Coconut

Abstract

The growth and differentiation of endosperm tissue of coconut cv. Samoan Dwarf in vitro were described. Endosperm tissues produced callus profusely without any enclosing embryo. Explants formed callus three weeks after culture. Callogenesis occurred in over 95% of all treatments. There was no significant difference in callogenesis between fruit sources, antipodal and micropylar tissues, 2, 4- dichlorophenoxyacetic acid (2, 4-D) and 4-amino-3, 5, 6 - trichloropicolinic acid (picloram) as well with 6 - benzylaminopurine (BAP). Auxin and cytokinin were not necessary to initiate callogenesis. Growth rate was influenced by fruit source and concentration of 2, 4-D and picloram but not by endosperm region of fruit, two types of auxin (2, 4-D and picloram) and addition of BAP. Growth rate of tissues increased substantially between 9 to 25 weeks but decreased by 31 weeks of culture. 2, 4-D and picloram (10-3M) inhibited growth rate in the beginning. The growth rate of the control was greater than other treatments at 31 weeks after culture. Tissue (endosperm and callus) browning occurred but did not inhibit tissue growth. In growth, tissue color changed from yellowish white, brown to black from which new yellowish white callus was produced. Callus structure changed from compact to friable after several transfers. Morphogenesis occurred in endosperm callus of antipodal tissue initially treated with 10-6M picloram after 2 1 weeks of culture. This "organ" was elongate, opaque and grew slowly. Its shape changed from triangular with several lumps on the surface to cylindrical after 14 months. Morphogenesis also occurred on endosperm callus treated with 207.04x10-6M picloram after 17 months. Histological study of endosperm callus showed structures which resembled proembryos, embryos with suspensors, promeristemoids and meristemoids. While "organ-like" structure showed a meristematic layer with a dermal layer, cortex-like region and central vascular tissue; there were many small protuberances which resembled embryoids and shoot with tunica and corpus. Callogenesis and morphogenesis (shoot organogenesis) occurred in coconut endosperm in vitro.