**2.2.1 Source of explant**

*In vitro* cultures of *Dioscorea rotundata* ("Pona"), accession number PS 98 013 were obtained from the *in vitro* gene bank of the Department of Botany, University of Ghana, Legon, where the plants were maintained under long-term slow growth conditions at 18ºC. Cultures were multiplied and sub-cultured at six-week intervals on Murashige and Skoog (MS) medium (Murashige and Skoog 1962) with 2.5 μM kinetin, 20 mg l-1 L-cysteine, 2% (0.056 M) sucrose, 0.7% agar, and maintained under a 16 h photoperiod (40 μ mol m-2 s-1) at 25±1°C.
