The
              Report

No. 73: Using clones to establish 
tea tree plantations

RESEARCHER DETAILS
This is a discussion paper prepared for the RIRDC/ATTIA Tea Tree Breeding Committee by John Doran of CSIRO Forestry and Forest Products (phone 02 6281 8319, fax 02 6281 8312, email john.doran@ffp.csiro.au and Gary Baker of NSW Agriculture, with the economic analyses provided by Peter Chudleigh and Sarah Simpson of Agtrans Research.

Mass vegetative propagation of plants selected for desirable traits has long been practiced in horticulture and for some crop plants including a few forest trees.

Cloning is the quick way to access and maintain genetic gain. However, biological constraints, such as the plant materials ability to give high multiplication rates, and additional costs associated with vegetative propagation compared to seedling stock have limited the usefulness of cloning for most forest trees.

Tropical eucalypts such as Eucalyptus grandis, E. camaldulensis and various superior hybrid lines are now routinely propagated as rooted cuttings for plantation establishment in many parts of the world including Australia, Brazil, China, Congo, India, Morocco and South Africa. In Brazil alone some 45,000 ha of clonal eucalypt plantations are being planted each year, indicating that this technology has become a well established reality (Griffi n and Rivelli 1993).

Several studies have demonstrated that Melaleuca alternifolia, like the tropical eucalypts described above, is suitable for mass vegetative propagation by cuttings, using selected genotypes of high root-striking ability (e.g. Sachs et al. 1990, Whish 1992). Despite this and the potential for markedly increasing yields of oil of consistent quality through the use of clones, adoption of the technology in the tea tree industry has been slow.

Only one large plantation scheme in northern Queensland has used them to any extent at a cost per rooted cutting of 37 cents (L. Williams pers comm. 1998).

The main stumbling block to wider use of clones in the tea tree industry is cost. Clones cost up to four times more to produce than seedlings. However, there are other perceived or real problems. A common notion is that clones do not develop a stable root system making them susceptible to damage during harvesting. A large number of genetically distinct clones will be required to minimise risk of pests and diseases thus adding to the cost of producing clones. They also need more care during planting than routine seedling stock. Similar problems applied in silviculture of cloned eucalypts and have been addressed by selecting suitable genotypes not prone to these problems and planting monoclonal blocks of several clones to maintain genetic diversity across the plantation estate.

As the tea tree industry faces a period of intense competition for markets and falling oil prices, effi ciency of production could be vital to economic survival in the industry. It was the aim of this study to demonstrate that the use of clones in plantation establishment is a viable means of improving the effi ciency of production because, although clones cost more than seedlings, their higher oil yields can more than offset the higher cost of establishment.

Materials and Methods

Plant material: Source – Plants for biomass and oil yield determination were 15-month-old coppice regrowth from a 4.8-year-old progeny trial with 204 open pollinated M. alternifolia families established at Wyrallah in January 1994 at a stocking of about 20,000 plants per ha. Each family was represented by 20 plants (5 trees per plot x 4 replications). Sample details -Immediately before the fourth harvest in November 1998, all plants of the families described below were harvested into bags for assessment of leaf biomass and oil concentration –

• four families (49, 125, 129, 132) that were the highest ranked of 204 families in a second-year family selection index for growth, survival, coppicing ability and oil characteristics over three planting sites.

• four industry standards that serve as the controls in these experiments. These seed sources were acquired from commercial seed collectors supplying seed to the industry in 1993.

Estimating leaf biomass and oil concentration:

Each sample (individual tree) was air dried and kept in storage for several months prior to processing. Leaf biomass was estimated by hand stripping the leaves, discarding woody material and winnowing to remove most of the twigs and bark. The leaves with some impurities still present were then oven dried at 48°C for 48 hours and weighed. Weighted bulks of 100 g of leaves (and small twigs) were prepared to represent each family (i.e. the four selected families and the four industry standards). Fifty gram sub-samples of each were steam distilled using standard methods to provide oil concentration data while other sub-samples wereused to estimate the percentage (based on weight) of impurities (largely small twigs and bark) in each sample and to check on moisture content. These measures were used to estimate average oil yield per tree by family. Sub-samples of leaves from two trees from each of the four selected families, that had yielded the greatest amount of leaves, were given identical treatment but their individual identity was retained.

Economic analyses:

Break even analysis for tea tree clones (see Table 3) were carried out using the assumptions summarised in Table 2 for four scenarios. Clarke et al. (1999) estimated that average oil yields in the industry currently fall within the range of 150–200 kg/ha/year. For this analysis a yield of 175 kg/ha/year is assumed. Scenario A represents the current situation of 8 c per seedling. Scenario B represents a price of 10 c per seedling produced from ATTIA seed from selected provenance which gives an estimated 30% gain (227.5 kg/ha). Scenarios C and D represent a price of 37 cents per cutting with a yield increase of 100% and 200% respectively. A price sensitivity analysis was also undertaken (Table 4).

Results

Estimates of the total oil yield per plant for selected individuals amongst the best four families, the family average and the overall average for the four industry standards are given in Table 1. The potential improved yields from using selected clones over routine seedlots and seed of selected provenances were the basis for the economic analyses of mature tea tree plantations given in Tables 2 to 4.

Table 1. A comparison of the leaf biomass and yield of oil per plant between selected trees of the best families, average data for the same families and the overall means of the four industry standards included as controls in a 4.8-year-old progeny trial of M. alternifolia near Wyrallah, NSW.


 

Table 1. (continued)

* Provenance code from Table 4.4 in Doran et al. 1997 ** The estimates of oil concentration used in these calculations are likely to be lower than if based on fresh leaves. Here, the leaves were stored for several months under fl uctuating conditions of temperature and humidity and then oven dried at 48°C for 48 hours, prior to oil extraction. Despite this, oil concentration estimates were within normal ranges (4.1 to 6.7% W/W%, DW of leaf ) and, a s all families were equally affected, comparisons between families were assumed to be valid.
 

Table 2. Assumptions used against each scenario in a break even economic analysis of mature tea tree plantations established using seedlings or clones giving increasing levels of genetic gain in yields over routine seedling planting stock (Scenario A represents the current situation of 8 c per seedling, with a yield of 175 kg/ha. Scenario B represents a price of 10 c per seedling produced from ATTIA seed from selected provenance which gives a 30% gain (227.5 kg/ha). Scenario's C and D represent a price of 37 cents per cutting with a yield increase of 100% and 200% respectively.


 
 

Table 3.Break even economic analysis of mature tea tree plantations established using seedlings or clones giving increasing levels of genetic gain in yields over routine seedling planting stock (Scenario A).

NA: Not applicable
 

Table 4.Sensitivity of economic indicators to oil price for the four scenarios.


 
 

Discussion

Potential gains in oil yield through use of selected clones:

The industry standards (controls) gave an average oil yield per plant of 5 g. The overall The industry standards (controls) gave an average oil yield per plant of 5 g. The overall estimate of oil yield per plant for the four best families was 9 g, or nearly double that of the industry standards.Variation within individual families and the industry standards was very large, as expected when using open pollinated seedlots. Individual oil yields for the two best trees per family ranged from 14 g to 24 g per tree.While the gain estimates presented here are based on the evaluation of limited numbers of trees, they are very similar to data from other work done in support of the case for clonal plantations of M. alternifolia (e.g. C. Ubergang pers comm. 1991,Williams et al. 1998).

In practice, a five fold increase in plantation oil yield over routine seedling stock from using clone G/132/Tree 1 is unlikely to be achieved in full. The advantage displayed by outstanding individual trees in a progeny trial is not fully realised when such individuals are cloned and deployed in block plantings, even assuming good development of the root systems of cuttings, because of stronger inter-plant competition in the fast-growing monoclonal blocks (C. Harwood pers comm. 1999). In the economic analyses, therefore, the effects on returns of 100% and 200% yield increases through the use of clones were determined, with 100% gain considered conservative. They are compared to the results using the best quality seed presently available from the RIRDC/ ATTIA tea tree improvement program which is expected to produce a 30% gain over previous industry standards.

Economic analyses:

The economic analyses showed that, even under a relatively modest level of gain from using clones with 100% gain in yield, growers would better the internal rate of return (IRR) of using the best seed currently available from the RIRDC/ATTIA tea tree improvement program (Table 3). For this scenario, the cost of rooted cuttings could rise to $0.66 each before the investment became less profi table (at a 10% discount rate) than one based on seedlings from selected provenances (Scenario B), and for Scenario D (200% gain in oil yield) the cost per cutting could rise to $1.46.

The sensitivity of IRR to oil prices (Table 4) indicates that if oil price falls below $25 then the large gains in yield which could potentially be delivered by clonal plantations will be needed for profi table production.

If nurseries generally can produce rooted cuttings of M. alternifolia at 37 cents each, as done in northern Queensland, then growers would be well advised to consider the clonal option carefully.

Future Work

The potential of significantly improving yields and the economics of growing tea tree in plantations has been demonstrated by this study. The RIRDC/ATTIA tree improvement program has undertaken preliminary work towards selecting a suite of high oil-yielding tea tree clones with potential for use in clonal programs. What is needed now is industry interest and support to screen these preliminary selections for characteristics like rooting ability in the nursery and durability under field conditions including root structure. Yield trials should also be established to accurately quantify gains from using selected clones as an alternative to seedling stock. It is important to note that clonal programs complement rather than replace traditional breeding activities. Typically, genetic gain is achieved progressively through long-term breeding programs employing well-planned recurrent selection and mating, starting with a suitable base population. A set of clones for mass vegetative propagation, selected at some point in the continuum, will soon be made obsolete by new genotypes produced by the breeding program. Thus the two activities, breeding and mass vegetative propagation, need to move forward together. Breeding produces the genetic gain and cloning, if a viable option, maximises the capture of that genetic gain in the production population.

Acknowledgments

The RIRDC/ATTIA tea tree breeding project and Australian Plantations are thanked for providing the progeny trial which was sampled in this study. Bob Lowe of NSW Agriculture assisted in collecting the plant material.

References

Clarke, B., Bialowas, A. and Mullen, J. (1999). Economics of tea tree oil production Northern Rivers, NSW. Paper to 1999 Annual Tea Tree Symposium. Wollongbar Agricultural Institute. NSW Ag: Wollongbar.

Doran, J.C., Baker, G.R., Murtagh, G.J. and Southwell, I.A. (1997). Improving tea tree yield and quality through breeding and selection. RIRDC Research Paper Series No 97/53. RIRDC: Canberra.

Griffin, A.R. and Rivelli, J. (1993). A comment on clonal eucalypt plantations. Eucalyptus Improvement and Silviculture No. 1993/1: 1.

Whish, J.P.M. (1992). The selection and propagation of high oil yield tea trees. Report to the Commonwealth of Australia's National Teaching Company Scheme, Agreement #12167. University of New England: Armidale.

Williams, L.R., Stockley, J.K., Yan, W. and Home, V.N. (1998). Essential oils with high antimicrobial activity for therapeutic use. The International Journal of Aromatherapy 8: 30-40.

Sachs, R.M., Lee, C.I., Cartwright, S.A., Reid, M.S. and Smith, C. (1990). Melaleuca alternifolia: new crop for California? California Agriculture 44: 27-29.
 

Other RIRDC new plants reports: