Surprisingly, the effect of phytoregulators on in vitro G. changii
was negligible. The results showed that application of both PAA and
BAP did not increase the growth rate of G. changii in tested concentration
combinations. Highest daily growth rate of 6.04 ± 1.03%
day−1 was observed in control explants (Fig. 1c). A lot of research
has been carried out on the application of phytoregulators in the
red algal species but the use of phytoregulators still remains indistinctly.
Kinetin proved to be most efficient in the growth of G.
tenuistipitata while G. perplexa best response was observed with
combination of IAA, 2,4-D and kinetin (Yokoya et al., 2004). Hayashi
et al. (2008) and Yong et al. (2014a) reported the positive response
of Kappaphycus alvarezii towards the addition phytoregulators in
the culture media. However, with the practice of G. changii in the
present study, the effect was not significant. Similar result was
observed in G. textorii which does not response to phytoregulators
(Huang and Fujita, 1997). The effects of other phytoregulators
and their combination with wider range of concentrations on the
growth of Gracilaria species are worth to be investigated in future.