Unfertilized ovaries isolated from immature female flowers of coconut (Cocos nucifera L.) were tested as a source of explants for callogenesis and somatic embryogenesis. The correct developmental stage of ovary explants and suitable in vitro culture conditions for consistent callus production were identified. The concentration of 2,4-dichlorophenoxyacetic acid (2,4-D) and activated charcoal was found to be critical for callogenesis. When cultured in a medium containing 100 microM 2,4-D and 0.1% activated charcoal, ovary explants gave rise to 41% callusing. Embryogenic calli were sub-cultured into somatic embryogenesis induction medium containing 5 microM abscisic acid, followed by plant regeneration medium (with 5 microM 6-benzylaminopurine). Many of the somatic embryos formed were complete with shoot and root poles and upon germination they gave rise to normal shoots. However, some abnormal developments were also observed. Flow cytometric analysis revealed that all the calli tested were diploid. Through histological studies, it was possible to study the sequence of the events that take place during somatic embryogenesis including orientation, polarization and elongation of the embryos.

Cassava flowering with emphasis on flowering pattern, morphology and phenology; pollen biology on viability and dimorphism, and histology on male and female gametophyte development are demonstrated. Reduced pollen viability at anthesis and the existence of pollen tri-morphism are the key findings.

Conditions for induction of androgenesis in coconut cv. Sri Lanka Tall were studied. Anthers collected from inflorescences at four maturity stages were given heat (38°C) or cold (4°C) pretreatments for 1, 3, 6 and 14 days, either prior to or post inoculation. Three different basal media and different anther densities were also tested. Androgenesis was observed only in anthers collected from inflorescences 3 weeks before splitting (WBS) and after a heat pretreatment at 38°C for 6 days. Modified Eeuwens Y 3 liquid medium supplemented with 100 lM 2,4-dichlorophenoxyacetic acid (2,4-D), 0.1% activated charcoal and 9% sucrose was effective in inducing an androgenic response. The lowest anther density tested, 10 per petri plate, was found to be the optimal density. When androgenic calli or embryos were subcultured to Y 3 medium containing 66 lM 2,4-D, followed by transfer to Y 3 medium without plant growth regulators and finally to Y 3 medium containing 5 lM 6-benzyladenine (BA) and 0.35 lM gibberellic acid (GA 3 ), plantlets regenerated at a frequency of 7%. Histological study indicated that the calli and embryos originated from the inner tissues of the anthers. Ploidy analysis of calli and embryos showed that they were haploid. This is the first report of successful androgenesis yielding haploid plants from coconut anthers.

The effect of growth regulators on induction of androgenesis in coconut was investigated using seven different growth regulators at various concentrations and combinations. Three auxins (1-naphthalene acetic acid-NAA, indoleacetic acid-IAA, picloram) and three cytokinins (2-isopentyl adenine-2-iP, kinetin, zeatin) were tested either alone or in combination with 2,4-dichlorophenoxyacetic acid (2,4-D), using modified Eeuwens Y3 liquid medium as the basal medium. Among the tested auxins, 100 lM NAA in combination with 100 lM 2,4-D enhanced the production of calli/embryos (123) whereas IAA and picloram showed negative and detrimental effects, respectively, for androgenesis induction over 100 lM 2,4-D alone. Kinetin and 2-iP enhanced the production of calli/ embryos when 100 lM 2,4-D was present in the culture medium. Both cytokinins at 10 lM yielded the highest frequencies of embryos (113 and 93, respectively) whereas zeatin (1 or 2.5 lM) had no impact on microspore embryogenesis. When calli/embryos (produced from different treatments in different experiments) were subcultured in somatic embryo induction medium (Y 3 medium containing 66 lM 2,4-D), followed by maturation medium (Y 3 medium without growth regulators) and germination medium (Y 3 medium containing 5 lM-6-benzyladenine-BA and 0.35 lM gibberellic acid-GA 3 ), plantlets were regenerated at low frequencies (in most treatments ranging from 0% to 7%).