Medicinal and Aromatic Plants—Industrial Profiles


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TEA TREE BREEDING
145
source of genetic improvement, however genetic gains are usually less than for other
strategies. Also, mass selection has a greater potential for inbreeding as the identity of
the propagation population is unknown.
2.
Method of mating (open or controlled). The full pedigree of both parents is maintained
with controlled pollination to maximise genetic gain. The cost, time and skill required
however can be prohibitive.
3.
Type of breeding population (single, multiple, nucleus or interspecific). The main
breeding population for each strategy is usually established from open pollinated
seed that has been collected from a large number of unrelated trees in natural stands
or plantations. This is to maximise the likelihood of genetic variation from which to
make selections. A single breeding population is the cheapest to establish. This
population may be thinned to become a seed orchard to supply improved seed for the
next generation or is used as a source of selected material that is propagated vegetatively
or as seed from controlled crossing to a separate seed orchard. Multiple populations
subdivide a breeding population to meet possible future selection needs while avoiding
the possibility of inbreeding. Nucleus breeding concentrates on selecting a small
nucleus population from the main breeding population. From this nucleus, improved
seed or clones are then produced. Interspecific breeding maintains a breeding
population of each parent species which is to be crossed. Outstanding individuals of
each species are then crossed to produce hybrids which are usually propagated as
clones.
4.
Method of mass propagation (seed or clones). Seed production is relatively inexpensive
while cloning, although expensive, offers some increase in genetic gain.
CASE STUDY: IMPROVEMENT OF MELALEUCA ALTERNIFOLIA
An outline of the breeding strategy and breeding plan undertaken by CSIRO Forestry and
Forest Products, Canberra and NSW Agriculture, Wollongbar for improving both the amount
and quality of oil yield in M. alternifolia is given below. The main breeding objective is to
increase oil yields in new plantations by 30% in five years (by 1998) with a 60% increase at
the conclusion of the first generation of breeding, about year 2001.
Breeding Strategy
In addition to maximising genetic gain, a breeding strategy for M. alternifolia must reflect
aspects of the tea tree industry. Although, the industry is expanding rapidly, the commercial
use of this Australian species is still relatively recent and limited. This limits the funding
available to the industry for research.
A simple breeding strategy was therefore adopted for this species where the use of limited
resources was matched to achievable goals. The strategy consists of two parts, interim
activities and the main breeding component (
Figure 3
).
The first incorporates interim measures to provide some short-term modest improvements
by provision of seed from a natural seed stand (SS) and best provenances (Natural stands).
The quality and quantity of oil produced from the progeny trials are to be used to identify
the best provenances.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

GARY BAKER
146
Figure 3 Flow chart representing the breeding strategy to supply progressively improved seed and
cuttings of M. alternifolia for plantation production
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

TEA TREE BREEDING 147
The main strategy, which is designed to give substantial genetic gain, uses recurrent
selection with open pollination in a single population. This population serves as a progeny
trial and finally as a seedling seed orchard (SSO). This simple strategy has been used very
successfully in improvement programmes for Eucalyptus (Eldridge et al. 1993), as it has
achieved large genetic gain without excessive cost. The strategy also has the added flexibility
to allow some limited controlled pollination in the seed orchards (CSO and SSO) and
vegetative propagation in the progeny trials and clonal trials (CT) to meet any specific
needs of the industry.
The first activity in the main strategy is to collect open pollinated seed (
Plates 13

14
)
from about 200 unrelated trees in natural stands. These families are used to establish three
progeny trials on two contrasting sites. Two of the trials are harvested annually to provide
estimates of family coppicing ability across sites. The remaining trial is used as a widely
based breeding population which is to be progressively thinned (based on family and
individual tree performance) to form the first seedling seed orchard (SSO1). Improved seed
from this first seed orchard is then used to help establish the second generation of breeding.
Each new generation is established from the best trees of the previous generation with an
infusion of new unrelated material from other promising sources. Family thinning from
150 to 100 to 50 is based on growth, oil characteristics and information from the other
progeny trials. As family numbers reduce, the increase in selection pressure results in
progressively improved seed to be used in the establishment of plantations.
The two progeny trials that complement the main breeding trial, also serve as a reserve
of genetic material should the programme need other seedling seed orchards.
Breeding Plan
Tree breeding is an expensive and long term activity. Industry associations and government
funding bodies must be prepared for a substantial and on-going financial commitment for
the breeding plan to be implemented.
Developing and then implementing the plan requires a wide-range of appropriate expertise
and cooperation between the growers, the breeders and the funding consortium.
Implementation on a cooperative basis encourages growers and breeders to share work and
capital resources. With such cooperation significant savings to the programme can be made,
particularly, at times of peak resource use, such as the growing of seedlings and establishing
field trials on grower’s properties. To assist growers to contribute to the programme, a form
of in-kind payment to the value of their contribution should be considered. The payment
may involve access to improved seed or cuttings.
Once the funding has been organised and a cooperative attitude adopted, a management
team is required to implement the breeding strategy. The team requires or needs to access
the personnel and facilities necessary to run the programme. Needs would include statistical
expertise for the design and analysis of field trials, agronomic skills and facilities for plant
propagation and field trial research and laboratory skills and equipment to determine leaf
oil quality and quantity.
The breeding plan is developed to implement the breeding strategy within the timeframe
and resources of the programme. A breeding plan for M. alternifolia would therefore
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

GARY BAKER
148
Table 1 The breeding plan activities for the first generation of improved M. alternifolia
detail the activities and resources used to achieve the major tasks of the breeding strategy.
A summary of the adopted breeding plan activities is presented in Table 1.
Crucial activities of the breeding plan involve progeny testing. Progeny trials evaluate
the performance of offspring from parents with full or partially known identity (Eldridge
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

TEA TREE BREEDING
149
et al. 1993). This evaluation achieves three important objectives: firstly, an estimation
of the breeding value of parent trees used to identify best provenances for further seed
collection; secondly, the provision of a source of selected trees for cuttings or improved
seed if the trial is thinned to a seed producing orchard and finally, an estimation of the
genotype by environment interaction and other genetic parameters for predicting genetic
gain.
The justification for a breeding programme is the genetic gain realised in improved
plantations and the financial returns on the programme investment (Eldridge et al. 1993).
Well designed yield trials are an important aspect of the breeding plan as they demonstrate
how much gain has been realised when progeny from the breeding programme are compared
to other sources.
SUMMARY
The range of variation in oil traits for M. alternifolia, together with the high heritability for
oil concentration and moderate heritability for growth, indicate that considerable gains can
be made from breeding programmes.
A breeding programme can achieve initial genetic gain in M. alternifolia plantations
through choosing seed from the best provenances. Then on-going gains are made by selecting
trees in the best provenances, mass producing their seed in seed orchards and selecting a
few outstanding trees for vegetative propagation.
The breeding programme detailed in the case study capitalises on the large initial gain
achievable from provenance choice and later improvement by recurrent selection and mating
in each future generation.
ACKNOWLEDGEMENTS
This chapter has been written as part of my activities as project officer for the research
project “The Improvement of Australian Tea Tree Through Selection and Breeding”.
This project is jointly funded by the Rural Industries Research and Development
Corporation (RIRDC) and the Australian Tea Tree Industry Association (ATTIA).
Institutional support is provided by NSW Agriculture and CSIRO. Their funding and
support is gratefully acknowledged. I also thank my colleagues John Doran, Ian
Southwell and Robert Lowe for their commitment to the project and for their comments
on this chapter.
REFERENCES
Allard, R.W. (1960) Principles of Plant Breeding, Wiley, New York.
Baker, G.R. (1996) The improvement of Australian tea tree through selection and breeding. Unpublished
Milestone Report for Project DAN-151A—30/11/96. For the Rural Industries Research and
Development Corporation, Canberra and NSW Agriculture, Wollongbar, NSW.
Baker, G.R. (1997) The improvement of Australian tea tree through selection and breeding. Unpublished
Milestone Report for Project DAN-151A—30/11/97. For the Rural Industries Research and
Development Corporation, Canberra and NSW Agriculture, Wollongbar, NSW.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

GARY BAKER
150
Brophy, J.J., Davies, N.W., Southwell, I.A., Stiff, I.A. and Williams, L.R. (1989) Gas chromatographic
quality control for oil of Melaleuca, terpinen-4-ol type (Australian tea tree). Journal of Agriculture
and Food Chemistry, 37, 1330–1335.
Brophy, J.J. and Lassak, E.V. (1992) Steam volatile leaf oils of some Melaleuca species from Western
Australia. Flavour and Fragrance Journal, 7, 27–31.
Bryant, L.H. (1950) Variations in oil yield and oil composition in some species of eucalypts and tea
trees. Technical Notes, Forestry Commission (Division of Wood Technology) NSW, 4, 6–10.
Byrnes, N.B. (1986) A revision of Melaleuca L. (Myrtaceae) in northern and eastern Australia, 3.
Austrobaileya, 2, 254–273.
Butcher, P.A. (1994) Genetic diversity in Melaleuca alternifolia: Implications for breeding to improve
production of Australian tea tree oil. PhD. Thesis, Australian National University.
Butcher, P.A., Bell, J.C. and Moran, G.F. (1992) Patterns of genetic diversity and nature of the breeding
system in Melaleuca alternifolia. Australian Journal of Botany, 40, 365–375.
Butcher, P.A., Doran, J.C. and Slee, M.U. (1994) Intraspecific variation in leaf oils of Melaleuca
alternifolia (Myrtaceae). Biochemical Systematics and Ecology, 42, 419–430.
Butcher, P.A., Matheson, A.C. and Slee, M.U. (1996) Potential for genetic improvement of oil production
in Melaleuca alternifolia and M. linariifolia. New Forests, 42, 419–430.
Campbell, A.J. and Maddox, C.D.A. (1996) Insect pest management in tea tree. Final Report for the
Rural Industries Research and Development Corporation, Canberra.
Colton, R.T. and Murtagh, G.J. (1990) Tea-tree oil—plantation production. Agfact P6.4.6, NSW
Agriculture and Fisheries, Sydney.
Cotterill, P.P. and Dean, C.A. (1990) Successful Tree Breeding with Index Selection. CSIRO, Melbourne.
Cotterill, P.P. and Jackson, N. (1981) Index selection with restrictions in tree breeding. Silvae Genetica,
30, 2–3.
Dean, C.A., Cotterill, P.P. and Cameron, J.N. (1983) Genetic parameters and gains expected from multiple
trait selection of radiata pine in eastern Victoria. Australian Forest Research, 13, 271–278.
Doran, J.C. (1992) Breeding strategy for genetic improvement of Melalecua alternifolia. Report to
Australian Tea Tree Industry Association and Rural Industries Research and Development
Corporation. CSIRO, Canberra.
Doran, J.C., Baker, G.R., Murtagh, G.J. and Southwell, I.A. (1997) Improving tea tree yield and quality
through breeding and selection. Rural Industries Research and Development Corporation Research
Paper Series No. 97/53, RIRDC, Canberra.
Drinnan, J. (1996) Tea tree research in North Queensland. Tea Tree Oil Symposium. August 1996
Abstracts. Wollongbar Agricultural Institute, Wollongbar, NSW, pp. 3–4.
Drinnan, J. (1997) Tea tree research in North Queensland. Tea Tree Oil Symposium. August 1997
Abstracts. Wollongbar Agricultural Institute, Wollongbar, NSW, p. 5.
Eldridge, K., Davidson, J., Harwood, C. and van Wyk, G. (1993) Eucalypt Domestication and Breeding,
Oxford University Press, Oxford.
Hanson, W.D. (1963) Heritability. In W.D.Hanson and H.F.Robinson (eds.), Statistical Genetics and
Plant Breeding, No. 982 (National Academy of Sciences Publication), (National Research Council,
Washington), pp. 125–140.
Hartney, V.J. and Svensson, J.G.P. (1992) Micropropagation of superior clones of Melaleuca alternifolia.
In Breeding Strategy for Genetic Improvement of Melaleuca alternifolia, (Report to Australian Tea
Tree Industry Association and Rural Industries Research and Development Corporation), Appendix
A, Canberra.
Lassak, E.V. and McCarthy, T. (1983) Australian Medicinal Plants, Methuen, Australia.
Maddox, C.D.A. (1996a) Aspects of the biology of Paropsisterna tigrina (Chapuis) the major pest
species of Melalecua alternifolia (Cheel). MSc. Thesis, University of Queensland.
Maddox, C.D.A. (1996b) NSW Agriculture, unpublished results.
Moncur, M.W. (1997) CSIRO Canberra, unpublished results.
Penfold, A.R., Morrison, F.R. and McKern, H.H.G. (1948) Studies in the Myrtaceae and their essential
oils. Part 1. The seasonal variations in yield and cineole content of Melaleuca alternifolia Cheel. In
Researches on Essential Oils of the Australian Flora, Part 1 (Museum of Technology and Applied
Science, Sydney), pp. 5–7.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

TEA TREE BREEDING
151
Reilly, T.L. (1991) The economics of tea tree. Tea Tree Marketing and Planning Conference, 31 October-
2 November, Ballina, NSW, pp. 30–38.
Small, B.E.J. (1981) Effects of plant spacing and season on growth of Melaleuca alternifolia and
yield of tea tree oil. Australian Journal of Experimental Agriculture and Animal Husbandry, 21,
439–442.
Southwell, I.A., Freeman, S. and Rubel, D. (1997) Skin irritancy of tea tree oil. Journal of Essential
Oil Research, 9, 47–52.
Southwell, I.A., Hayes, A.J., Markham, J. and Leach, D.N. (1993) The search for optimally bioactive
Australian tea tree oil. Acta Horticulturae, 334, 256–265.
Southwell, I.A., Markham, J. and Mann, C. (1996) Is cineole detrimental to tea tree oil? Perfumer and
Flavorist, 21, 7–10.
Southwell, I.A., Stiff, I.A. and Brophy, J.J. (1992) Terpinolene varieties of Melaleuca. Journal of
Essential Oil Research, 4, 363–367.
Standards Association of Australia, Essential oils—oil of Melaleuca, terpinen-4-ol type, 2782, Sydney.
Standards Australia (1985).
Williams, L.R., Home, V.N. and Asre, S. (1990) Selection and breeding of superior strains of Melaleuca
species to produce low cost, high quality tea tree oil. In L.R.Williams and V.N.Homes (eds.), Modern
Phytotherapy—The Clincal Significance of Tea Tree Oil and Other Essential Oils, Vol. 2, Macquaire
University, Sydney, pp. 73–91.
Williams, L.R., Home, V.N., Zhang, X. and Stevenson, I. (1988) The composition and bactericidal
activity of oil of Melaleuca alternifolia (tea tree oil). International Journal of Aromatherapy, 1,
15–17.
Whish, J.P.M. (1993) The selection and propagation of high oil-yield tea trees. Unpublished Report.
Department of Agronomy, University of New England, Armidale.
Zobel, B.J. and Talbert, J. (1984) Applied Forest Tree Improvement, Wiley, New York.
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

Plate 10 Eight months of regrowth in a highly productive plantation (A.Manciagli)
Plate 11 Forage-harvested trees are taken to the distillery in trailer-bins for oil extraction (R.Colton)
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

Plate 12 Melaleuca alternifolia leaf oil glands (A.Curtis)
Plate 13 M. alternifolia seed capsules
(J.Murtagh)
Plate 14 M. alternifolia seed (R.Colton)
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

Plate 15 Tipping mobile still (G.Davis)
Plate 16 Simple direct-fired tea tree still (L.Davis)
Plate 17 Two-pot distillery with boiler and separator in the background,
sealed mobile bin (left) and suspended bin lid (right) (R.Colton)
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

155
8. TEA TREE OIL DISTILLATION
GEOFFREY R.DAVIS
Hornsby, NSW, Australia
INTRODUCTION
This chapter considers mainly the practical aspects of steam distillation of tea tree oil, the
essential oil of Melaleuca, terpinen-4-ol type.
The definition of an essential oil which was adopted by the Standards Association of
Australia in 1968 and also by the International Standards Organisation (ISO) at the Ninth
Plenary Meeting of the Technical Committee ISO/TC54 Essential Oils, held in Lisbon,
5th–9th March, 1968, was:
Essential oils are volatile oils, generally odorous, which occur in certain plants or specified
parts of plants, recovered therefrom by accepted procedures, such that the nature and
composition of the product is, as nearly as practicable, unchanged by such procedures.
This is an important definition. It specifies clearly that the nature and composition of the
oil must be unchanged, as nearly as practicable, by the process of extracting it, and is
therefore one reason why steam distillation is an appropriate method of extraction.
Furthermore, because steam distillation has been the extraction method since the oil was
first produced, the market accepts steam distilled oil as normal oil. Oil derived by another
technique might be of slightly different chemical composition and therefore might not be
accepted by the market as normal tea tree oil.
The standards for this oil, both Australian (Standards Australia 1997) and International
(International Standards Organisation 1996), define the oil as “Essential oil obtained by
steam distillation of the foliage and terminal branchlets of Melaleuca alternifolia (Maiden
et Betche) Cheel, M. linariifolia Smith and M. dissitiflora F.Mueller as well as other species
of Melaleuca provided that the oil obtained conforms to the requirements given in this
International Standard”.
There are other methods of extracting essential oils from plants, including:
Solvent extraction followed by steam distillation of the extract.
Solvent extraction followed by vacuum distillation of the extract.
Liquid carbon dioxide extraction.
Enfleurage.
Expression from the pericarp of citrus fruits.
Use of microwaves has also been suggested.
THE DISTILLATION PROCESS
Steam distillation is the appropriate method of extraction, not only because it causes
minimum change to the composition of the oil during extraction, but also because steam is
Copyright © 1999 OPA (Overseas Publishers Association) N.V. Published by license under the Harwood Academic Publishers imprint,
part of The Gordon and Breach Publishing Group.

GEOFFREY R.DAVIS
156
readily available, cheap, not hazardous (chemically), can be used at low pressure and can
be recycled. In particular, it allows the oil to be extracted at a temperature which is constant
and low enough not to damage the oil. By using steam at atmospheric pressure, the oil will
be distilled from the plant material at a temperature slightly below that of boiling water.
This is because the vapour pressure of a two or more phase liquid mixture in which the
phases are not miscible, is equal to the sum of the partial pressures of the phases. Thus if
water boils at 100°C, a mixture of water and some other volatile liquid which is not soluble
in water, i.e. the oil, will have a higher vapour pressure than water alone, and will therefore
boil at a lower temperature (Guenther 1965).
This is a fundamental principle of steam distillation. Steam distillation is therefore the
best method of extracting the oil, both in relation to cost of extraction and quality of oil.
In this chapter, the term “still” refers to the still-pot only and not the whole unit comprising
the boiler, the pot and condenser and separator.
Pressure
Certain essential oils may be more advantageously steam-distilled at still pressures greater
than atmospheric pressure, others at lesser still pressures. Pressure distillation is achieved
by enhancing the still pressure which is then maintained independently of the boiler pressure.
Fortunately, there is no advantage in either reduced or elevated pressure in the distillation of
tea tree oil from the foliage. Thus elaborate pressure equipment or vacuum pumps are not
called for. In fact, working at other than atmospheric, particularly at raised pressure, is
likely to produce an oil of different composition from normal tea tree oil.
Solubility in Water
Some essential oils are partially soluble in water. Furthermore, some compounds in an oil
might be more soluble than others. In the case of tea tree oil, while its solubility in water is
low, the most valuable compound, terpinen-4-ol, is slightly soluble. Therefore, if tea tree oil
is extracted by steam distillation there will be some removal of terpinen-4-ol as long as
fresh steam is passed through the charge during distillation or comes into contact with oil in
the receiver.
Cohobation
The traditional technique for preventing loss of oil in the distillate water is to return the
water to the still during distillation. By so doing, the water in the system becomes saturated
with the oil, or soluble parts of it, and, being saturated, no longer absorbs oil during the
distilling process. This process is known as cohobation. In the case of some oils with soluble
components, cohobation is necessary. With tea tree oil, the loss of oil through its solubility
in water is small. Whilst cohobation is desirable, it is not essential. Cohobation, however, is
certainly desirable where the water supply is limited. It is also useful in maintaining the
water level in the still where steam is raised in the still. Where steam is raised externally,
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