Abstract
The stimulatory effect of different concentrations of thidiazuron (TDZ) on in vitro shoot proliferation in an important medicinal shrub, Cassia alata L. (Ringworm Bush or Senna) was investigated. Multiple shoots were induced from cotyledonary node (CN) explants derived from 15-d-old axenic seedlings on Murashige and Skoog (MS) medium fortified with different concentrations of TDZ. The shoot-forming capacity of CN explants (90% response) was influenced by TDZ concentration (0.5, 1.0, 2.5, 5.0, 7.5, or 10.0 mu M). The highest frequency of shoot regeneration (95%), the maximum mean number of shoots per explant (9.2 +/- 0.2), and the greatest shoot length (2.6 +/- 0.1 cm) were obtained on MS medium fortified with 7.5 mu M TDZ after 4 weeks of culture. Prolonged exposure of CN explants to TDZ had an adverse affect on the developing shoots. To avoid this, cultures were transferred to TDZ-free MS medium, or to a medium fortified with various concentrations of 6-benzyladenine (BA) for further multiplication, proliferation, and elongation of induced shoots. The highest mean number of shoots per explant (18.9 +/- 1.1) and shoot length (4.7 +/- 0.1 cm) were achieved when TDZ-exposed explants were then sub-cultured for 6 weeks on MS medium containing 1.0 mu M BA. In vitro-rooting of shoots was optimal on full-strength MS medium containing 0.5 mu M indolebutyric acid (IBA), which gave the highest mean number of roots per shoot (7.2 +/- 0.2) and the greatest root length (2.6 +/- 0.1 cm). Well-rooted plantlets were hardened-off successfully and acclimatised in Thermocol (TM) cups containing sterile Soilrite (TM). These plantlets were then transferred to earthenware pots containing garden soil and maintained in a greenhouse, with a survival rate of 85%.