In vitro clonal multiplication of Pterocarpus santalinus L. was achieved using mature nodal explants of a 10-year-old elite quality tree. Combinations of serial transfer technique and incorporation of antioxidants (250mg/l L-ascorbic acid and 50mg/l citric acid) into the culture medium helped to minimize medium browning and improve explant survival during shoot sprouting. About 70% of explants were sprouted on Murashige and Skoog (MS) liquid medium containing 4.4 mu M 6-benzyladenine (BA). The explant harvest period also influenced the bud break and shoot sprouting in nodal explants. The combination of 4.4 mu M BA and 2.2 mu M thidiazuron (TDZ) was found to be the most suitable growth regulator for obtaining the highest percentage of nodal segment sprouting (74%-75%), the number of secondary shoots per primary shoot (two or three), the shoot length (5-6cm), the number of new nodal segments generated per active explant (four or five), and the multiplication coefficient (3.5) within 6 weeks. Repeated subculturing of nodal explants obtained from shoot cultures enabled continuous production of healthy axillary shoots. At the end of the sixth passage, about 90% of nodal explants produced five or six healthy green shoots, each being about 6.6cm long with six or seven nodes. Multiplication coefficient was also increased from the first subculture (5.4) to the sixth subculture (8.3). The best rooting response was achieved on solidified half-strength MS medium supplemented with 4.9 mu M indole-3-butyric acid (IBA). About 70% of the micropropagated plantlets were established successfully in 20-cm pots containing a mixture of soil and farmyard manure (4:1 ratio) and formed new leaflets.
