Seasonal, genetic and economic analysis of Eucalyptus bosistoana essential oil. (2022)
Type of ContentTheses / Dissertations
Degree NameDoctor of Philosophy
The New Zealand Dryland Forest Initiative (NZDFI) is working to establish naturally durable eucalyptus plantations in New Zealand. The prioritized species is Eucalyptus bosistoana. A central focus is to identify high performing genetic material in a network of breeding trials. Although, heartwood is the main envisaged product, leaves could be used to produce essential oil as a by-product of these plantations. Essential oil quality is mainly determined by oil chemistry. The phytochemical composition of foliage can also have an effect on browsing damage and consequently tree health and profitability of such plantations.
Chapter 1 gives an introduction in the history, chemistry, production and global market of eucalyptus essential oils. A review of NZDFI’s durable eucalyptus species indicated that E. bosistoana could be a species suitable for essential oil production.
The development of an appropriate method for oil analysis is described in chapter 2. Of the three extractive methods tested, namely accelerated solvent extraction (ASE), hydro- distillation and microwave solvent extraction (MSE), MSE was selected for this work due to its convenience. Ten major compounds (1,8-cineole, limonene, α-terpineol, α-pinene, aromadendrene, β-myrcene, caryophyllene, trans-pinocarveol, ocimene, linalool) were identified in the GC chromatograms of the eucalyptus oils. Chemical analyses of NZDFI’s species E. argophloia, E. globoidea, E. tricarpa, E. quadrangulata and E. sideroxylon and New Zealand’s commercially grown E. nitens confirmed that E. bosistoana has the highest oil yield (15.8 µL/g) and 1,8-cineole percentage (62%). The data also suggested the essential oil of E. bosistoana is different to that of the closely related E. argophloia.
Chapter 3 investigates the seasonal variation of essential oil composition in mature and immature E. bosistoana leaves. Leaf oil was monitored for 2 years. The highest oil yield (average 16.7 µL/g) and percentage of 1,8-cineole (average 67.1%) were obtained from the leaves collected during summer while they were lowest during winter. Mature leaves contained a significantly higher (p ≤ 0.01) proportion of 1,8-cineole in (60.9%) than immature leaves (44.6%). Total oil yield ranged from 3.0 to 27.0 µL/g (fresh) in mature leaves and from 5.0 to 26.7 µL/g (fresh) in immature leaves. Oil quality and quantity were comparable to literature reports.
Genetic control of oil traits was investigated in chapter 4. Mature leaves of 8 year old E. bosistoana were collected from 1901 trees representing 85 families from one breeding trial. 20 Compounds were quantified in these samples. Data on tree height and insect defoliation (health scores) were also available for 72 families in this trial. Heritability estimates (h2) of the quantified essential oil compounds ranged from 0.06 to 1.14, with the most abundant compounds 1,8-cineole, aromadendrene and unidentified compound 8 showing the highest h2 of 0.78, 1.14 and 0.59, respectively. Total oil content had moderate 0.25 heritability.
The negative correlation between total oil content and 1,8-cineol concentration at the phenotypic and genetic level (rp = -0.44 and rg = -0.70, respectively) implied that families with a higher quality oil have less oil in the leaves. 1,8-cineole was genetically strongly negatively correlated with myrcene (rg = -0.74), α-pinene (rg = -0.71), linalool (rg = -0.90), aromadendrene (rg = -0.94), trans-pinocarveol (rg = -0.75) and unknown compounds 3 (rg = -0.91), 6 (rg = - 0.83), 8 (rg = -0.88) and 9 (rg = -0.75). 19 Families had breeding values consistent with the standard commercial oil quality requirement of over 60% 1,8-cineole. The results show that planting stock could be selected from the E. bosistoana breeding programme which would aid essential oil production, as it is done for other eucalyptus species, i.e. E. polybractea.
Oil traits did not correlate with tree height or insect defoliation and these traits were also not heritability in this assessment. However, the small number of individuals (n = 3) assessed for those two traits was likely contributing to this results. Additional work is needed to investigate the correlation of those traits with oil characteristics.
Chapter 5 considers economic aspects of essential oil production from New Zealand grown E. bosistoana. Leaf biomass was estimated using published allometric equations for other eucalypt species and validated with available E. bosistoana data. This indicated E. bosistoana leaf biomass could be comparable to that of E. globulus. A sensitivity analysis indicated that biomass, genetics, seasonal variation and fluctuations in oil prices were equally important on the viability of an essential oil operation. Potential small- (400 t fresh leaf/year) and large-scale (2000 t fresh leaf/year) oil production would be supported by NZDFI’s envisaged planting programme of 5,000 ha regional catchments. Small-scale oil production could be initiated using the leaves from thinning operations, and expand into a large-operation over time when trees will be harvested. Lastly, based on the operational costs of a domestic small-scale essential oil producer, oil value from E. bosistoana would exceed the cost of production.
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