*3.2. Effects of Auxin with Optimal Concentration of BA*

In another set of experiments, the effectiveness of the optimum concentration of BA in combination with concentrations of 0, 0.1, 0.5, 2.5, or 5.0 μM of auxins (i.e., IAA or NAA) for the induction and proliferation of shootlets was assessed (Table 4). The better multiplication response was obtained from a shoot section of *P. amboinicus* grown on medium with 5.0 μM BA and 2.5 μM NAA (Figure 1C). On this media, 97.1 percent of the explants generated 19.3 shootlets (Table 4). However, NAA concentrations over 2.5 μM, along with optimal BA concentration, reduced the frequency of shoots with non-degenerative callusing from the explants. When IAA was coupled with BA, it improved the morphogenic response but produced fewer shootlets than BA with NAA in the growth medium. The maximum number of shootlets, 15.3 and 12.2, was observed from each shoot section on 5.0 μM BA or Kin supplied medium containing 2.5 μM of IAA, respectively (Table 4).


**Table 4.** Combined effect of 6-benzyladenine (BA) or kinetin (Kin) with α-naphthalene acetic acid (NAA) or indole-3-acetic acid (IAA) on shoot regeneration from axillary node explants of *Plectranthus amboinicus*.

Data are expressed as mean ± SE recorded after 8 weeks of culture on shoot induction medium. Different letters in each column indicate significant differences among treatments according to Tukey's honestly significant difference test (Tukey's HSD) at a *p*-value of less than 0.05.
