**2.2.2 Conditioning excised explants in culture (preculture)**

Yam shoot tips (~1 - 2 mm) were excised from cultures grown on MS pregrowth medium [as above, except containing 3% (0.09 M) sucrose instead of 2% sucrose] for five weeks, placed on sterilised nylon mesh, which was then positioned, explant cut side down, on fresh medium, overnight. Explants were then transferred on the mesh to semi-solid medium with higher sucrose concentrations (0.3, 0.5, 0.7 and 1.0 M, the control material continuing to be exposed to 0.09 M sucrose) in 90 mm Petri dishes for one, three, five or seven days, each followed by transfer either to growth-enhancing medium (MS complete salts with vitamins, 3% sucrose, 5 μM kinetin, 20 mg l-1 L-cysteine, 0.8% agar, 1% filter-sterilised casein hydrolysate at pH 5.7 ± 0.1), or further conditioned for cryopreservation.
