Genetic Diversity of an Australian Santalum album Collection – Implications For Tree Improvement Potential

The Forest Products Commission of Western Australia manages a sandalwood (Santalum spp.) core germplasm collection at Kununurra in the states far north. This collection serves as a significant seed source for sandalwood plantations in the area and remains an important resource for ongoing research. The collection contains S. album trees sourced from Indian arboreta, along with a few trees from West Timor, Indonesia. Also present are representatives of S. macgregorii from Papua New Guinea and S. austrocaledonicum from Vanuatu and/or New Caledonia. Despite the apparently diverse seed origins, the genetic background of many of the accessions remains vague. In this study, diversity and relatedness was assessed by nuclear and chloroplast RFLPs and a phylogeny was inferred. Nuclear RFLPs revealed very low levels of genetic diversity for a tree species, with an observed and expected heterozygosity (Ho and He) of 0.047. Nineteen genotypes were identified within the 233 S. album individuals sampled, with only one tree known to have originated from Timor being differentiated from Indian material. Other trees thought to have come from Timor grouped with those believed to be from India, indicating they were either incorrectly labelled or sourced from heavily modified populations. Despite the poor sample size, chloroplast RFLP analysis revealed no genetic distinction between the Timorese and Indian S. album, which supports the theory of human mediated seed dispersal from Timor to India. The structure of the phylogeny and associated relatedness has assisted in the establishment of seed orchards, designed to ensure maximum diversity is maintained through limiting the proximity of highly related trees. Finally, in light of these and other findings, a hypothesis concerning the evolution of S. album is proposed.