Plant Cell, Tissue and Organ Culture 69: 65–70, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. 65 Direct somatic embryogenesis from mature embryos of sandalwood V. Ravishankar Rai ∗ & Jen McComb 1 Department of Studies in Applied Botany and Biotechnology, University of Mysore, Manasagangotri, Mysore, India 570 006; 1 Biological Sciences, Murdoch University, Perth, WA 6150, Australia ( ∗ requests for offprints; Fax: +91-821-518835; E-mail: rrai33@hotmail.com) Received 17 January 2001; accepted in revised form 12 September 2001 Key words: zygotic embryo, repetitive embryogenesis, Santalum album L. Abstract Plants were regenerated from mature zygotic embryos of sandalwood (Santalum album L.) through direct somatic embryogenesis. Somatic embryos were formed directly without any intervening callus phase on zygotic embryos plated on Murashige and Skoog (MS) medium containing thidiazuron or benzylaminopurine. Individual somatic embryos were then isolated and transferred to MS medium without cytokinin on which they formed secondary embryos in repetitive cycles with or without the addition of indole acetic acid to the medium. Conversion of somatic embryos into plantlets was achieved by isolating somatic embryos with distinct cotyledons and reculturing them onto half-strength MS medium with GA 3 (1.4 μM). Recovered plantlets were acclimatised and grown in the greenhouse. This is the first report on in vitro regeneration via direct somatic embryogenesis of sandalwood. Abbreviations: BAP – 6-benzylamino purine; GA 3 – gibberellic acid; IAA – indole-3-acetic acid; IBA – indole-3- butyric acid; KN – kinetin; MS medium – Murashige and Skoog (1962) medium; TDZ – thidiazuron Introduction Somatic embryogenesis has many potential advant- ages for mass propagation and genetic improvement of hardwood forest trees (Merkle, 1995). The method offers fast multiplication of high value clones for re- forestation and provides a means of gene transfer and the production of new plants from transformed cells for the mass production of transgenic trees. Indian sandalwood (Santalum album L.) is closely tied to the culture and economies of many Asian coun- tries. It has been valued for its perfumed wood and oils for thousands of years. However, spike disease and widespread smuggling have left India’s sandal- wood stands dangerously depleted. Efforts are now needed to increase the area of cultivation and to im- prove productivity with the aim of sustainable supply (Srinivasan et al., 1997). Early attempts to develop somatic embryogenesis for sandalwood propagation focussed on indirect em- bryogenesis using hypocotyl, nodal and endosperm explants (Rao and Rangaswamy, 1971; Bapat and Rao, 1974; Lakshmi Sita et al., 1979, 1980). How- ever, when somatic embryos were obtained through callus, the conversion or germination of these em- bryos into plantlets was problematic (Rao and Bapat, 1995). An efficient and highly reliable method for the regeneration of plants from explants is essential for sandalwood. This report describes the successful induction of somatic embryogenesis from mature zygotic embryos of sandalwood without involving a callus phase and a large number of plants regenerated in this way from somatic embryos have been established in the soil in a greenhouse. Materials and methods Plant material and culture conditions A 50- to 60-year-old elite tree of S. album was selected from which the dried and mature fruits were collected.