Somatic embryogenesis and plantlet formation in Santalum album and S. spicatum

Abstract

important species because they produce essential oil in the heartwood which is used extensively in the incense A reproducible system for somatic embryogenesis and perfumery industry (Loneragan, 1990; Rao and and plantlet formation of sandalwood has been Bapat, 1995). Santalum spicatum natural stands are developed. A high frequency (100%) of somatic depleted since the rate of regeneration cannot keep pace embryos were induced directly from various explants with the rate of harvesting. Sandalwood harvesting, which in MS (Murashige and Skoog, 1962) medium with thidi- usually involves removing the entire tree, may have azuron (1 or 2 mM) or indirectly in medium containing resulted in a critical loss of genetic diversity and valuable 2,4-D plus thidiazuron. Within 8 weeks, white globular agronomic characters. Techniques for vegetative propagasomatic embryos or friable embryogenic tissue tion of WA sandalwood are not yet available. developed on cultured explants. In S. album the globu- In addition to conserving and regenerating the indigenlar somatic embryos were transferred to MS medium ous species, Indian sandalwood, which contains a higher supplemented with IAA (6 mM) and kinetin (1 mM) where oil content, is being evaluated as a potential plantation they developed further, multiplied and maintained species in the Ord river region of Western Australia friable embryogenic tissue. After 15‐30 d, mature (Applegate and McKinnell, 1993). However, S. album is somatic embryos (1‐2 mm) with well-developed cotyle- susceptible to many pests, such as fungi, nematodes (Rai, dons were separated and subcultured on to medium 1990), and spike diseases caused by micoplasma containing GA 3 (6 mM) for germination. Once germin- (Parathasarathy and Venkatesan, 1982). ated, elongated somatic embryos (10‐20 mm long) Conventional breeding of sandalwood for introgression grew further in MS supplemented with lower GA 3 of new genetic information can be an expensive and (3 mM). In S. spicatum, the addition of casein hydrolys- diYcult task because of their long generation time, sexual ate and coconut milk was necessary for plantlet devel- incompatibility and heterozygous nature (Rugkhla, opment from somatic embryos. From histological 1997). In vitro regeneration techniques can be used to studies, it appeared that primary somatic embryos clone superior lines, and are needed for Agrobacteriumarose from single cells or had a multicellular origin mediated gene transfer techniques and for protoplast from the epidermis or cortical parenchyma. Secondary fusion. Regeneration via somatic embryogenesis of S. somatic embryos and friable embryogenic tissue dif- album can be achieved from hypocotyl, nodal and endoferentiated from groups of proembryogenic cells from sperm explants (Bapat and Rao, 1979; Lakshmi Sita a superficial layer of the primary somatic embryos. et al., 1979; Rao and Bapat, 1992). Preliminary results on somatic embryogenesis of