Abstract:
In vitro culture technology is the only means for vegetative multiplication of coconut.
A protocol has been developed for plant regeneration in vitro from various tissues of
coconut variety 'Sri Lanka Tall'. Despite this success, the plant regeneration
efficiency is far from adequate and further refinement is needed Therefore the
objective of this study was to analyze the plant regeneration process at cellular level
and gain a better understanding of possible causes of low plant regeneration
efficiency.
Plumules excised from mature zygotic embryos were used for the study
Callogenesis, somatic embryogenesis and plant regeneration were achieved using
the protocol developed previously. Cultures were fixed at weekly intervals for
histological studies.
Fifty percent explants produced callus. Thirty percent of callus produced somatic
embryos and five percent regenerated plants. Histological analysis revealed that
meristematic cells were formed by the division of provascular cells of plumular
leaves. These cells were arranged in a cambium-like zone, breaking up of which
gave rise to proembryos of multicellular origin. Alternatively, protodermal cells
produced highly embryogenic cells, which could form proembryos of unicellular origin
Under the culture conditions established, only proembryos of multicellular origin
developed into somatic embryos. Among the developed somatic embryos, complete
(bipolar) as well as incomplete (embryos without shoot pole) somatic embryos were
present.
The study revealed that the response of coconut variety Sri Lanka Tall to culture
conditions developed were comparable to those observed in culture systems of other
coconut varieties and oil palm. The presence of bipolar structures confirmed that
plant regeneration occurred through somatic embryogenesis. The occurrence of
incomplete embryos might be one of the main reasons for low plant regeneration
efficiency. Further studies are needed to improve bipolar somatic embryo formation
and unicellular proembryo development.
