This thesis reports on an investigation into variation in commercial oil traits of sets of Melaleuca alternifolia (tea tree) clones and improved seedling controls at up to three plant stockings (33,333, 22,222 and 16,667 plants/ha). The two trials examined in this work were planted in 2004 and 2006 at Bungawalbin by the Rural Industry Research and Development Corporation (RIRDC)/Australian Tea Tree Industry Association (ATTIA) tea tree breeding programme managed by the New South Wales Department of Primary Industries (NSW DPI). The main aim of these trials was to determine if there is a financial advantage to growers in replanting their existing unimproved tea tree plantations with clones rather than using improved seedlings from seed orchards established by the breeding programme. This is addressed by the development of a financial model comparing the financial aspects of planting clones vs. seedlings at two stockings (33,333 and 16,667 plants/ha)
The 2006 clonal spacing trial (CST) was assessed prior to the first harvest when trees were 12 months old. In the 2004 CST they were assessed prior to the third harvest when coppice shoots were 18 months. All surviving trees were assessed for growth traits while a sampling scheme was used to estimate dry weights of key tree components associated with off-paddock oil yield and oil characteristics of the clones and seedlings in the trials. Determinations of dry weights of key tree components, extraction of leaf oil using solvent techniques, and gas chromatographic analysis to determine quantity and quality of oils were undertaken at the Essential Oil Unit of NSW DPI.
This study showed that plant stocking can have a significant effect on the growth and oil traits of tea tree. Trees at lower stocking (wider spacing) typically have a higher leafiness score as they are given more space and there is less competition for light. But they also had lower oil concentrations than those at higher stockings (narrow spacing). Dry weights of key tree components and oil yields of tea tree plantations on a per hectare basis were found to be greatest at the highest stocking of 33,333 plants/ha, which is typical of the stocking used in most commercial plantations of M. alternifolia for oil production.
Clones in the 2006 CST showed superiority in commercial oil traits over seedlings grown from improved seed from the breeding programme. Oil concentration of clones in this trial averaged 91.6 mg/g ODW and 86.69 mg/g ODW compared to seedlings that averaged 63.6 mg/g ODW and 55.77 mg/g ODW from the stocking of 33,333 plants/ha and 16,667 plants/ha respectively. Conversely, the three clones under trial in the 2004 CST were inferior in commercial oil traits to the improved seedling controls (averaged 75.68 mg/g ODW and 75.59 mg/g ODW cf. 81.32 mg/g ODW and 76.47 mg/g ODW), due to extraneous factors, particularly the fact that Jrooted clones had poorer growth. Consistency in 1,8-cineole content was a feature of each clone compared to greater variability amongst seedling stock. This is an advantage for marketing as the current market requires the oils’ 1,8-cineole content to be 3% or lower due to the misconception that this constituent is an irritant to skin and mucous membranes.
The variation in growth and oil traits of clones in the 2006 CST indicates that further gains in oil yields and oil quality can be achieved by deploying only the very best clones. The trial data suggested that average oil yields of 522.6 kg/ha and 356 kg/ha might be obtained from plantations established using three best clones –clone 5 (C64), clone 6 (C66) and clone 9 (C70)– at stockings of 33,333 plants/ha and 16,667 plants/ha respectively. These yields are substantially greater than the mature oil yields recorded for CSO1 (ATTIA 2B) seedlings in breeding programme yield trials (357 kg/ha at a stocking of 30,000 plants/ha). A further advantage of clones over seedlings is that clones give mature oil yields from first harvest whilst it is not until year three that seedlings give a higher, mature oil yield.
Financial analyses to evaluate the viability of replanting 20-ha tea tree plantations using elite clones and improved seedlings over a 15-year time frame were carried out. Four plantation options were modelled i.e. (1) plantations established using ATTIA 2B seedlings planted at a stocking of 33,333 plants/ha and (2) 16,667 plants/ha, (3) plantations established using the three best selected clones planted at a stocking of 33,333 plants/ha and (4) 16,667 plants/ha. Capital costs e.g. purchase of land and machinery were not included in this analysis, as all plantation options involve replacement plantations.
The financial analysis showed that, at the current oil price of $45/kg, replacement plantations of either elite clones or improved seedlings are both highly profitable irrespective of the stocking employed. The NPV of the plantation per hectare at 7% discount rate was $109,584, $65,224, $164,921 and $105,638 for plantation options 1, 2, 3 and 4 respectively.
A clonal plantation at a stocking of 33,333 plants/ha was predicted to give the greatest profit at any of the oil prices tested, followed by plantations using improved seedlings at a stocking of 33,333 plants/ha, plantations using clones at a stocking of 16,667 plants/ha, and plantations using seedlings at a stocking of 16,667 plants/ha. The break-even prices for tea tree oil production, using the production parameters in this model were $11.3/kg, $15.5/kg, $10.4/kg and $12.5/kg for plantation options 1, 2, 3 and 4 respectively.