Santalum yasi is a high-value hemiparasitic tree endemic to Fiji, Niue and Tonga. It has been overexploited for its oil-yielding heartwood and is now threatened. Remaining stands lack genetic diversity and are likely to be suffering from inbreeding depression, although the species still has significant genetic diversity overall. We argue that the best way to conserve this species is through an active domestication program that will adequately sample and conserve the genetic base in ex situ and circa situm plantings. The approach to S. yasi tree-breeding can be characterised as a low-input strategy involving the early use of molecular markers for population parameter determination. Longterm success will have strong interdependent links with the conservation of the remaining genetic resources. A strategy based on recurrent selection and breeding for key traits-including heartwood volume and oil yield per year, oil quality and environmental adaptability related to cyclone resistance and the tolerance of pests and diseases-is recommended. The establishment of genetic conservation stands based on collections of the species throughout its natural range in Fiji and Tonga has commenced. Challenges associated with the conservation and domestication of S. yasi are discussed. These include the advanced age required before oil characterisation can be undertaken; the need to assess genotype-host-plant interactions; and the need for comparatively sophisticated equipment and destructive harvesting to carry out oil assessments. Capacity development of professional staff in the Pacific Islands is an additional prerequisite for implementing an effective strategy. Research into the variation and heritability of heartwood formation and oil characteristics, and a better understanding of the breeding biology of S. yasi and geneflow between it and exotic Indian sandalwood (S. album), are high priorities. It will be more than a decade-probably around 20 years-before S. yasi individuals in planned, well-designed trial plantings have sufficient heartwood development to enable oil-trait assessment. Establishment of such trials is an immediate priority. In addition to this long-term activity, we recommend a simple interim strategy that promotes high genetic diversity of seedling-based planting stock. This can be implemented using a combination of gene conservation stands, progeny trials that can be culled to seedling seed orchards, and genetically diverse community-based seed stands. The strategy will both provide a safeguard against the further loss of diversity and promote wide outcrossing. Releasing fragmented populations from inbreeding depression is expected to increase general vigour.

Santalum yasi, a sandalwood native to Fiji and Tonga, is a tree crop of significant economic potential for these countries. Development of a plantation industry underpinned by a breeding program is a high priority for industry development. Gathering information on heartwood development, oil yield and oil composition is a critical step for the domestication and tree breeding of the species. Oil yield and composition were determined for 86 Santalum core samples using gas chromatography and combined gas chromatography/mass spectrometry. Most (67) cores were from the lower boles of individual trees of S. yasi, with smaller samples of S. album and S. album × S. yasi, both of which are also commonly grown in Fiji and Tonga, and S. austrocaledonicum was included for comparison. Although the ages of the trees were unknown, they are likely to have been between 10 and 20 years. Relationships among traits, including solvent-extracted oil yield, oil composition, lower bole diameters under and over bark, and heartwood diameter, were examined. Yield was highly variable (0.05-11.8%) and only weakly correlated with underbark diameter at 30 cm above ground. Oil yield and percent composition of santalol oil components were strongly positively correlated. For those trees with oil yields >1% w/w, the oil composition was generally favourable relative to the international standard for S. album oil, with large proportions of santalols, particularly β-santalol. The study confirms that both harvesting and selection for genetic improvement of S. yasi trees younger than 20 years old are likely to be suboptimal, with unreliable heartwood and oil development. Further study of heartwood and oil development, both within individual trees and among genotypes in common-garden trials with known genetics and controlled environments and hosts, is a high priority. The development of an international standard for S. yasi, supporting the growth of a niche market for the product, is also recommended.