Gotowa bibliografia na temat „Santalum austrocaledonicum”

Santalum austrocaledonicum Vieill. (Santalaceae) is a small tree endemic to New Caledonia and Vanuatu, well-known for the highly priced aromatic oil of its heartwood (Nasi & Ehrhart 1996). In New Caledonia, sandalwood grows on Loyalty Islands, the Isle of Pines and Grande-Terre (Bottin et al. 2006). The tree produces single-seeded fleshy drupes, which turn dark-red at maturity. Sandalwood seeds are dormant because of their hard coat and germinate only on physical scarification, or after removing the coat (Chauvin & Ehrhart 1998). In natural habitats, such seeds need further processing to relieve dormancy and promote germination, within a period where there is a good chance of successful seedling establishment (Murdoch & Ellis 2000).

Les îles océaniques constituent de véritables « laboratoires naturels » pour comprendre l'impact des forces évolutives sur la biodiversité. Les effets de dérive génétique et l'impact de la sélection naturelle apparaissent d'autant plus exacerbés que les îles sont isolées et soumises à de forts gradients environnementaux. Notre étude associe des marqueurs moléculaires neutres et des caractères liés à l'adaptation afin d'évaluer l'influence de ces différentes forces dans le contexte insulaire de Nouvelle-Calédonie sur l'espèce forestière Santalum austrocaledonicum. L'étude des microsatellites nucléaires et chloroplastiques montre une différenciation nette des populations des petites îles Loyauté et un isolement par la distance au sein de l'île la plus vaste, Grande Terre. En outre elle met en évidence un déficit en hérérozygotes au sein de certaines populations pouvant être attribué à une sous-structuration spatiale ou un régime de reproduction autogame. La variation de la taille des feuilles et des graines, caractères liés à l'adaptation, résulte des effets de dérive mais aussi de la sélection naturelle provoquée par des contrastes environnementaux notamment par des différences de pluviométrie. De même la composition chimique du bois de coeur, analysée par chromatographie, subirait, en plus de la dérive, une pression sélective exercée par le cortège d'insectes et de champignons phytophages. Cette étude exploratoire permet de dégager de nombreuses perspectives de recherche relevant des questions évolutives en milieu insulaire. Sur un plan opérationnel, elle permet de définir des unités de gestion de l'espèce associant caractères
adaptatifs et variables moléculaires.

[Truncated abstract] An investigation into the causes of heartwood and essential oil content of Australian plantation sandalwood, Santalum album was undertaken. Genetic diversity of 233 S. album, five S. austrocaledonicum and fifteen S. macgregorii trees growing in the Forest Products Commission arboretum, Kununurra WA, was assessed using nuclear and chloroplast RFLPs. Santalum spicatum was chosen as an out-group. Nuclear genetic diversity of the S. album collection was very low, with observed and expected heterozygosity levels of 0.047. This was lower than the results previously reported in the literature for trees in India, however a different technique was used. Based on allelic patterns, the collection was able to be categorised into 19 genotypes; each representing some shared genetic origin. Some groups were highly redundant with 56 trees being represented, while others were populated by just one tree. The essential oil yield and heartwood contents of trees from these genetic groups were compared. Yields were highly variable both within and between groups of trees which share a common genetic history, suggesting a significant environmental component was contributing to the observed phenotype, despite identical soil and climatic conditions. Ancestral lineages were tested using chloroplast RFLPs, although a lack of shared mutations between species made this difficult. Only one S. album tree originating from Timor was resolved using nuclear RFLPs, with the other trees being grouped with material sourced from India. There was no resolution of Indian S. album from Timorese using chloroplast RFLPs, however one S. album tree grown from Indian seed possessed a single unique mutation. The low genetic diversity of the Australian S. album collection is likely to be a combination of incomplete seed sourcing and highly restricted gene flow during the evolution of the species. Combined with information gathered on the phylogeny of the genus by other researchers, S. album is postulated to have originated from an over-sea dispersal out of northern Australia or Papua New Guinea 3 to 5 million years ago. Essential oil yield and composition was assessed for 100 S. album trees growing in the collection, ranging in age from 8 to 17 years. Oil content of heartwood ranged from 30 mg g-1 to 60 mg g-1, and the transition zone 36 mg g-1 to 90 mg g-1. Sapwood contained almost no sesquiterpene oils. Despite the highly variable total oil yields, the chemical profile of the oil did not vary, suggesting there was limited genetic diversity within this region of the genome. Strong, positive correlations existed between v sesquiterpenoids in the essential oil of S. album. ... These represent the first TPS genes to be isolated from sandalwood and will enable further elucidation of oil biosynthesis genes. This thesis compiles a three-pronged approach to understanding the underlying causes of oil yield variation in S. album. As a species for which so little is known, the research presented here provides a major leap forward for tree improvement, breeding and silviculture. Hence the best of Santalum album research is presented.

Sandalwood (Santalum spp.) is a commercially important forest product that has been traded for many centuries. The trade has been based on the exploitation of wild stands of the wood, but as supplies have dwindled interest in its cultivation has been increasing within agroforestry systems, both as an industrial crop and a small scale product. More recently, interest has increased in the domestication of the more commercially valuable species. Recent studies in Vanuatu into Santalum austrocaledonicum have identified individuals with high oil yield and quality that can form the basis of a breeding programme. A lack of appropriate knowledge of the reproductive biology within the genus and the capacity for clonal propagation has hindered progress towards genetic improvement. This situation has led to this study, which has the following objectives: (i) to determine the amenability of cuttings for propagation for S. austrocaledonicum; and (ii) elucidate key features of the reproductive biology of S. austrocaledonicum and other Santalum species that can inform their breeding and domestication. Method To develop an effective method for the vegetative propagation of clonal sandalwood (S. austrocaledonicum), a series of four experiments were conducted. In these experiments I evaluated the effects of cutting (genotype, type of cutting, and leaf area,) and environmental (exogenous auxin, rooting media, and light intensity) treatments on adventitious root initiation and development (mean root number and length) in leafy stem cuttings using non-mist propagators. The results demonstrated that S. austrocaledonicum seedlings can be successfully propagated by cuttings. Genotype: Cuttings taken from genotypes from the island of Erromango outperformed those from Tanna for all three measures of rooting across all experiments. In experiment 2, for instance, the level of adventitious root induction in Erromango genotypes ranged from 63 to 92% and those from Tanna 0 to 6%. Significant variation was also found among genotypes from Erromango, with genotype 'j-erro' demonstrating greater root induction compared with others across three of the four experiments. Cutting Type: Cuttings taken from the apical and medial stem positions on the stockplant outperformed those taken from basal stems across the two clones examined. In a complementary experiment (4th), apical cuttings were found to have significantly greater rooting percentage than medial cuttings across the three clones. Leaf area: The effect of leaf area (400 vs. 800mm²) was not significant for adventitious root induction, root number or root length. The proportion of leaves retained by the cutting during propagation positively influenced the percentage of cuttings that form adventitious roots. Significantly greater rooting percentage was found in cuttings with no leaf abscission (85%), followed by quarter (71%), half (48%), three quarters (35%) and all (21%) leaves abscised. This result indicates that the retention of some of the leaves is important in propagation by cuttings of this species. IBA: The application of the exogenous auxin (3000, 4000 & 8000 ppm indole- 3-butyric acid) did not have a significant effect on adventitious root induction, mean root number and length when compared with the control (0 IBA). Rooting Media: I examined the effect of three rooting media 1. Gravel-5mm (29% Air Filled Porosity AFP), 2. Vermiculite and Perlite at 1:1v/v (46% AFP) and 3. Vermiculite, Perlite and Peat 2:2:1v/v/v (42% AFP). No significant differences in percent adventitious root induction or mean root number were found between these three media. The mean length of the roots was, however, significantly shorter in the gravel medium compared with the other two media. Light Intensity in the propagator: The effect of four different mean daily light levels (116, 86, 56 and 48 μmol m⁻² s⁻¹) in the propagator on cutting performance (mean root number and mean root length) was examined. The level of light had a significant effect on the percentage of cuttings with adventitious root induction. The influence of light on root induction was not consistent among clones, with a significant interaction found between light and clone. The greatest percentage of root induction was found for a mean daily light level of 86 μmol m⁻² s⁻¹ across all clones, which was achieved in a propagator positioned under 50% high-set shade with an additional 25% shade cloth over the top of the propagator. No significant effect of propagator light level was found for the mean number of roots or mean root length. Reproductive Biology: To understand the breeding system in sandalwood (Santalum species), two experiments were undertaken. In these experiments I evaluated floral phenology in five species (S. lanceolatum, S. austrocaledonicum, S. album, S. macgregorii and S. yasi), and controlled hybridisation between three species (S. lanceolatum, S. austrocaledonicum and S. album) of sandalwood. Floral Phenology: Systematic investigation of S. lanceolatum, S. austrocaledonicum, S. album, S. macgregorii and S. yasi has found that flowers in all species open rapidly (over 3-4 hrs), primarily in the morning. Flower life of an unpollinated flower varies significantly among the species, with mean days of flower life ranging from 24 hours (S. macgregorii) to 8.7 days (S. album). Full closing of flowers after opening was displayed among some of the species. S. lanceolatum (12-24 hrs), S. austrocaledonicum (12-36 hrs) and S. macgregorii (up to 12 hrs) closed after opening, while S. album and S yasi remained open. A change in colour of the tepals was observed in S. album S. yasi and S. magregorii. The tepals changed from white to pink after opening in S. album (19-24 hrs) and S. yasi (4-12hrs), and then changed progressively to dark red/purple. In S. macgregorii, the flower bud turned pink just before opening, and changed colour to red/purple after flower opening. Breeding system of Santalum lanceolatum: Self- and intraspecific crosscompatibility was examined in 13 genotypes of S. lanceolatum, and interspecific crosscompatibility between S. lanceolatum with each of S. austrocaledonicum and S. album. A total of 20% of genotypes formed seed after self-pollination. Conversely, a total of 62% of genotypes pollinated with outcross (intraspecific) pollen set seed. S. lanceolatum was found to be cross compatible with both S. austrocaledonicum or S. album. However, although the percentage of seed set was similar between intra- (7.5%) and interspecific (7.6%) crosses, the germination of seeds produced through interspecific pollination was greater (S. album = 114% (some seeds producing 2 seedlings), and S. austrocaledonicum = 70%) than those produced through intraspecific (41%) pollinations. The implications of this breeding system on both the domestication of sandalwood as well as the genetic conservation issues surrounding introduction of a foreign species into a natural population are discussed.