A callogenesis protocol for Melaleuca alternifolia
was developed in this study. The effects of different types of auxins,
activated charcoal and combination of 2,4-dichlorophenoxyacetic acid (2,4-D)
and kinetin at various concentrations on the callus induction from leaf
explants of M. alternifolia were investigated in order to determine
the optimum callus induction and maintenance medium. The callus growth
curve under the best callus maintenance medium was also studied. Calli
were induced from leaf explants cultured on Murashige and Skoog (MS) medium
incorporated with 1, 3 and 5 mg L-1 of 2,4-D, Indole-3-butyric
Acid (IBA), Naphthaleneacetic acid (NAA) or picloram as well as MS medium
with the combination of 3 mg L-1 2,4-D and 1, 2 or 3 mg L-1
kinetin, respectively. The calli developed from different types of plant
growth regulators were varied in their morphological appearances. The
maximum callogenesis response was obtained using the MS medium supplemented
with 3 mg L-1 2,4-D. The control medium and the medium incorporated
with NAA did not produce any callus. Addition of activated charcoal at
0.05 and 0.1% did not assist in the callogenic response, though it helped
in removing the pigments and phenolic compound accumulations in the culture
medium. The calli initiated from the best induction medium could not be
maintained in the fresh new medium containing the same auxin composition.
However, calli were successfully maintained in MS medium containing the
combination of 3 mg L-1 2,4-D and 2 mg L-1 kinetin.
The callus maintained in this treatment showed a sigmoid growth pattern
and reached maximum the growth rate after three to five weeks upon cultivation.