*3.3. Effects of Basal Medium Strength and pH*

In addition, varying strengths (one-quarter; one-third; half; and full MS) of basal medium were evaluated when combined with 5 μM BA and 2.5 μM NAA in order to get the best response for in vitro propagation and mass multiplication of *P. amboinicus* from nodal sections (Figure 2). Substantial differences were observed between the strengths of the medium used in this set of experiments. From the results, it was evidenced that the explants responded better in the MS basal medium supplied with the full strength of macro and micro-salts and vitamins. Shoot sections grown on MS basal media containing onequarter macro and micro-salts as well as vitamins generated fewer shootlets. In subsequent studies, different pH values of MS basal medium (4.7, 5.2, 5.7, and 6.2) were employed to examine their influence on in vitro morphogenesis (Figure 3).

The pH 5.7 basal medium was shown to be optimal for the induction and proliferation of shoots, but the highly and severely acidic basal medium had a detrimental effect on in vitro shoot proliferation. The MS basal medium, which was supplied with full strength macro and micro-salts, vitamins, 5 μM BA, 2.5 μM NAA, and pH 5.7, provided the best response in terms of percent shoot induction (97.1) and number of shoots (19.3), according to the data collected throughout the investigation (Figure 3). The clusters of shootlets that formed were either sub-cultured onto new medium for further proliferation or individually transplanted into auxin-containing media for rhizogenesis.

**Figure 2.** Effect of MS medium strength with optimized concentration of 6-benzyladenine (BA) 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. Bars denoted with different letters 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 3.** Effect of different pH of the MS medium with optimized concentration of 6-benzyladenine (BA) 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. Bars denoted with different letters 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.
