In vitro propagation and secondary product production by Merwilla plumbea (Lindl.) Speta

Merwilla plumbea is a popular but threatened traditional medicinal plant sold at herbal markets in South Africa. It produces bioactive compounds and contributes to Traditional African Medical systems for the treatment of various diseases. Due to high demand, the plant is recommended for commercial cultivation. We investigated in vitro propagation and secondary compound production in in vitro cultures of M. plumbea, cultivated on Murashige and Skoog (Physiol Plant 15:473–497, 1962) medium supplemented with various plant growth regulators [PGRs: adenine sulphate (Ads), benzyladenine (BA), 2-isopentenyladenine (2iP), meta-topolin (mT), meta-topolin riboside (mTR), thidiazuron (TDZ), kinetin (Kin) and naphthaleneacetic acid (NAA)] and organic elicitors [casein hydrolysate (CH), glutamine (GM), haemoglobin (HB), mebendazole (MBZ), trimethoprim (TMP), yeast extract (YE) and yeast malt broth (YMB)]. A combination of 20 μM GM, 0.45 μM TDZ and 0.054 μM NAA produced the highest number of adventitious shoots per explant (30.6 shoots/explant) after 12 weeks of culture. The regenerated shoots were rooted and the plantlets successfully acclimatized. The total phenolic, flavonoid, gallotannin and condensed tannin contents were determined. The highest levels of flavonoids (50.97 μg CTE/g in shoots) and gallotannins (99.55 μg GAE/g in shoots) were recorded in combinations of 200 mg l−1 YE, 0.45 μM TDZ and 0.054 μM NAA and 100 mg l−1 YMB, 0.45 μM TDZ and 0.054 μM NAA. These increases were around 3- to 16-fold higher than in naturally-grown plants. This system offers the possibility to use in vitro culture techniques for mass propagation, secondary metabolite and pharmacological studies.