*3.1. Effects of Cytokinin on Shoot Induction*

Only 1–2 shoots were formed by the sterile nodal segments of *P. amboinicus* cultured on cytokinin-free medium, which were used as a control. Adding BA or Kin to the basal medium, on the other hand, significantly increased the number of shoots that sprouted from the cultivated shoot segments. Nodal segments of *P. amboinicus* respond quite differently in vitro depending on the cytokinin type and concentration used (Table 3). The cultures were carefully investigated at periodic intervals (sub-culture) to see if any morphogenic alterations in the nodal sections had occurred. It was determined that all tested concentrations of both BA and Kin cytokinins, i.e., 0.5, 2.5, 5.0, or 10 μM, enhanced the induction and proliferation of shoots. Within ten days of culture, the latent axillary bud swelled, and after four weeks, it differentiated into numerous microshoots (Figure 1A,B). In general, of the different concentrations of BA and Kin tested, the number of shootlets increased with increasing the concentration from 0.5 to 5.0 μM. In contrast, concentrations of BA and Kin in the media more than 5.0 μM resulted in fewer shoots with non-degenerative callusing (slight) from the cut ends of each explant. When compared to Kin, BA was shown to be more effective for the induction and proliferation of shootlets. The MS basal medium combined with 5.0 μM of BA exhibited the greatest number of 7.5 shootlets per explant in 79.3 percent of cultures.


**Table 3.** Effect of 6-benzyladenine (BA) and kinetin (Kin) 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.

**Figure 1.** (**A**) Initiation of shoots from axillary node explants of *Plectranthus amboinicus*. (**B**) Multiple shootlets of *P. amboinicus* after 4 weeks of culture. (**C**) Proliferated multiple shoots of *P. amboinicus* after 8 weeks of culture. (**D**) Rooted *P. amboinicus* shoot after 4 weeks of transfer on the rooting media.
