Interspecific hybridisation between Santalum album and S-spicatum

The possibility of producing inter-specific and intra-specific hybrids of Santalum album and S. spicatum was investigated. A study of the reproductive biology of the species showed that both S. album and S. spicatum are obligate out-crossing species, with pre-and post-fertilisation barriers preventing self-pollination and inter-specific pollination. Initial fruit-set was low with 70-100% fruit abscission. Reasons for failure of fruit-set included lack of fertilisation, lack of an embryo sac, and failure of endosperm development. An in-vitro culture technique was developed which could induce embryogenesis and thus 'rescue' embryos of intra-specific crosses at 3.5-6 months old, but not from putative inter-specific hybrid fruit, which abscised at 1-3 months old. Putrescine spray increased fruit-set and delayed fruit abscission for both intra-specific and inter-specific crosses. However only a few putative hybrid fruits were retained until four months after pollination; they were not harvested for ovary culture, but allowed to develop to maturity. These mature putative hybrid seeds did not germinate, but their endosperms were confirmed to be hybrid by random amplified polymorphic DNA (RAPD) analysis.