ABSTRACT

Santalum macgregorii (sandalwood), which is endemic to the southern part of Papua New Guinea (PNG), has been heavily exploited for its fragrant heartwood and is classified as threatened across its natural range. Domestication and smallholder agroforestry offer the means to preserve remaining diversity. This study was undertaken to understand the extent of remaining natural variation to support the species’s conservation and domestication. We evaluated morphological, heartwood and essential oil characters in 126 S. macgregorii trees in five populations (districts) in PNG’s Central, Gulf and Western provinces. The heartwood oil of this species is characterised by extreme tree-to-tree variation in key fragrant compounds. Proportions of individual compounds range from negligible to high for (Z)-α-santalol (0.5–51%), (Z)-β-santalol (0–24.2%), (Z)-nuciferol (0–40.5%) and (Z)-lanceol (0–72%). Despite the wide variation found within populations, an ordination of seven oil constituents revealed broad provenance-based variation in which trees from the eastern provinces (i.e. Central and Gulf) were more influenced by (Z)-nuciferol content and the trees from the Western Province site were more strongly influenced by (Z)-lanceol. The driver of this variation was the different associations between oil constituents, with (Z)-α- and (Z)-β-santalol both negatively correlated with (Z)-nuciferol for sites in the eastern provinces and (Z)-lanceol in Western Province. No evidence of distinct chemotypes was found, with continuous variation demonstrated across all major oil constituents. Of the trees surveyed with a basal diameter of >10 cm, 79% had heartwood. Mean heartwood percentage was 15.8% of basal area, with no significant differences between sites. Significant tree-to-tree variation in heartwood percentage (0–61%) was found. A modest positive correlation was found between stem and heartwood diameter (r = 0.39). Heartwood percentage and heartwood oil quality varied independently and, therefore, independent selection of these traits may be required for their simultaneous improvement. The population in Western Province is non-contiguous with those in the eastern part of the species distribution. It also has a distinct phenotype based on oil composition, leaf shape, flower colour and potential reproductive failure. It is possible that sandalwood in Western Province is more closely related to the proximal populations of S. lanceolatum in Cape York Peninsula, Queensland, than the more distant populations of S. macgregorii in PNG. While these phenotypic features do not necessarily discriminate a new species, molecular genetic research is required to determine the potential existence of a cryptic species of sandalwood. The implications of the variation found in S. macgregorii are discussed with respect to its domestication and conservation.

摘要

巴布亚新几内亚（PNG）南部特有的檀香（Santalum macgregorii）（檀香木）因其香气浓郁的心材而被大量开采，在其自然范围内被列为濒危物种。驯化和小农农林业为保持剩余的多样性提供了手段。进行这项研究是为了了解保留自然变异的程度，以支持该物种的保护和驯化。我们评估了126 S. macgregorii的形态，心材和精油特性巴布亚新几内亚，海湾和西部省份的五个人口（区）中的树木。该树种的心材油的特征在于主要香气化合物的树与树之间存在极大差异。（Z）-α-檀香醇（0.5–51％），（Z）-β-檀香醇（0–24.2％），（Z）-核苷（0–40.5％）和（Z）喷枪（0–72％）。尽管在种群中发现了很大的差异，但对七个石油成分的排序显示出基于物源的广泛差异，其中东部省份（即中部和海湾）的树木受（Z）-核苷含量的影响更大，而西部省份的树木则受到更大的影响（Z）-lanceol对位点的影响更大。造成这种变化的原因是石油成分之间的关​​联不同，东部省份的（Z）-α-和（Z）-β-檀香醇与（Z）-核苷的含量呈负相关，而西部省份的（Z）-lanceol则呈负相关。没有发现明显的化学型的证据，所有主要油成分均表现出连续变化。接受调查的基径大于10厘米的树木中有79％具有心材。平均心材百分比为基面积的15.8％，各部位之间无显着差异。发现树木之间心材百分比的显着差异（0–61％）。发现茎与心材直径之间存在适度的正相关（79％的人有心材。平均心材百分比为基面积的15.8％，各部位之间无显着差异。发现树木之间心材百分比的显着差异（0–61％）。发现茎与心材直径之间存在适度的正相关（79％的人有心材。平均心材百分比为基面积的15.8％，各部位之间无显着差异。发现树木之间心材百分比的显着差异（0–61％）。发现茎与心材直径之间存在适度的正相关（r = 0.39）。心材百分比和心材油品质独立变化，因此，可能需要对这些性状进行独立选择以同时改善它们。西部省份的人口与物种分布东部的人口不连续。根据油的成分，叶的形状，花的颜色和潜在的生殖衰竭，它也具有独特的表型。西部省份的檀香木可能与昆士兰州约克角海角半岛的S. lanceolatum的近缘种群比更远的S. macgregorii种群更密切相关。在PNG中。尽管这些表型特征不一定能区分新物种，但仍需要进行分子遗传学研究来确定檀香隐性物种的潜在存在。关于其驯化和保存，讨论了在Macgregorii中发现的变异的含义。