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Rural Industries
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Dr Prinsley has been with RIRDC for five years, having worked previously for the Bureau of Resource Sciences and, before that, for the Commonwealth Secretariat in London. Currently she is General Manager (Research) at RIRDC, with responsibility for the Agribusiness, Trade and Sustainable Farming Systems portfolio.
In addition to the Tea Tree Industry program, she manages the Agroforestry and Farm Forestry, Human Capital, Communications & Information Systems and Cashews programs.
Dr Prinsley plays an active role in the rural industries policy sector. She is a member of the Rural Women's Advisory Group to the Secretary of the Department of Primary Industries (DPIE), and on the National Selection Panel for the DPIE Farm Forestry Program. She is also engaged in work with international research organisations.
Dr Prinsley has expertise in research and development and is an experienced manager. She is committed to making research work for producers.
"The RIRDC/ATTIA Tea Tree Industry Program aims to help the industry improve its national and international competitiveness", she says. "At the same time, we want to ensure that it retains its image of environmental friendliness, particularly since this is a key marketing tool."
Tea tree oil quality and yield from Melaleuca alternifolia varies dramatically between areas of seed origin (provenances), according to research conducted under the RIRDC/ATTIA Tea Tree Oil Research and Development Program.
The finding has important implications for the tea tree oil industry: improvements in productivity through the selective breeding of high yielding trees will help keep the industry competitive and improve its profitability.
This is the rationale behind a collaborative project involving the Rural Industries Research and Development Corporation, NSW Agriculture, the Australian Tea Tree Industry Association and CSIRO Forestry and Forest Products. The project aims to:
Phase 1 of the project commenced in May 1993. In this phase, the
team set out to:
Progeny trials
The main activity of Phase 1 was the establishment of three progeny trials in northern NSW. The main progeny trial was to be converted to a seedling seed orchard while the two other trials were to be managed to test the coppicing ability of the various families.
Seed was collected from 199 individual trees (23 provenances representing 13 regions) across M. altemifolia's natural range. These were supplemented by five seedlots obtained from commercial seed collectors supplying seed to the industry and by four seedlots (obtained from two nurseries) reputed to give superior performance. Two provenances of the related species M. linariifolia were also tested.
Between 20 and 24 seedlings germinated from each seedlot were planted in a latinised row-column design, with 4 replications at each of the three trial sites. A single buffer row of trees surrounded the experiments.
Measuring the differences
After 16 months, a number of parameters were measured, including height, plant shape, twig length, leaf length and insect damage. A biomass equation was determined and used to give an estimate of yield of oven dry biomass by family. Family oil yields and oil qualities were determined in two experiments (the coppice trials) at 19 months and in the third experiment (the seedling seed orchard) at 25 months.
The coppice trials were harvested in September 1995 after 20 months to test coppicing ability.
Differences between provenances
There was a wide variation in estimated oil yield at both the provenance and family level. The best performing provenance gave a first harvest yield some 3 times greater than the industry standard seed and double the yield from selected seed obtained from two nurseries. The cineole content of oil obtained from the best provenance averaged less than 3%.
Estimates of individual heritabilities for the key oil traits of concentration, cineole % and terpinen-4-ol %, were high, suggesting that substantial improvement in these traits could be achieved through selective breeding. On the other hand, heritabilities for height and basal diameter. traits closely correlated with leaf biomass, were low, indicating that only modest gains might be achieved by selection for leaf yield.
The researchers noted an apparent lack of genetic correlation (either negative or positive) between growth traits such as basal diameter and oil concentration. This means that a breeding strategy should be able to improve leaf biomass and oil concentration simultaneously.
The project continues
The second phase of this project commenced in 1996. It continues to develop the seedling seed orchard, which has a key role to play in the future production of highly improved seed. The Australian tea tree oil industry has started to see the benefits of this work with the release this year of seed from selected wild provenances. These seedlots will be replaced gradually by seed orchard seed of high quality from 1999 onwards.
The full report, "Improving tea tree yield and quality through
breeding and selection", is available from RIRDC on 02 6272 4819.
funding from RIRDC/ ATTIA Tea Tree Industry Program will assist the development of a tea tree industry in North Queensland.
Tea tree oil production is a relatively new industry on the Atherton Tablelands; interest in it arose initially from the desire to find alternative crops to tobacco. The Production systems currently used are based on information obtained from the NSW experience. However, given differences in climate and soil types, it is essential that the findings of research in NSW be adapted to North Queensland conditions.
The RIRDC/ATTIA Project ,"Development of the North Oueensland Tea Tree Industry' ",'(DAQ-184A) set out to: facilitate the rapid development of a knowledge base on the production of tea tree oil in the Mareeba Dimbulah Irrigation Area on the Atherton Tablelands; to develop guidelines for irrigation scheduling to maximise oil yield and quality; and establish a gene pool of selected superior plants.
Information was gathered from key researchers, and a soil moisture monitoring system was used to investigate tea tree water requirements. Data were collected on oil quality and yield and the factors affecting it. For example, it was determined that mature tea trees use 0.8-1.0 times the pan evaporation rate. This is equivalent is equivalent to a total water requirement of I OML/ha/year, or 7.5ML/h ear when rainfall is subtracted. Several seedlines were identified as having superior yield and quality characteristics.
This information was presented to growers via a number of extension techniques. It has also been compiled into the project's final report to RIRDC, which will be available shortly on 02 6272 4819.
The first, titled 'Tea tree oil as an alternative topical decolonisation agent for inpatients with methicillin-resistant Staphylococcus aureus', will be conducted jointly by scientists at the University of Newcastle and the University of Western Australia. Should the tea tree oil be effective, the results of the study will assist in the national and international registration of
tea tree oil as a medical product, especially as an antiseptic hand wash and body wash in hospitals.
The second project under development, titled 'The antiviral activity of tea tree oil in vitro', will be conducted by researchers at the University of Western Australia. It aims to develop and validate methods suitable for testing the antiviral activity of tea tree oil in vitro, and to use these methods to assess the oil's potential as a topical antiviral therapeutic agent.
Tea tree oil is used as an antimicrobial, antiseptic oil or formulated into value-added creams, shampoos, soaps, mouthwashes and toothpastes. It has a wide range of applications for which the marketplace is potentially enormous.
However, several factors are hindering the broadening of the tea tree oil market base. These include restrictions on the claims that can be made for the product on labels: this would be removed if tea tree oil gained entry into specific Food and Drug Administration monographs in the US.
Another major factor is the misconception regarding the presence of cincole in tea tree oil. Sectors of the marketplace regard this chemical as a skin irritant; many tea tree oils on the world market are considered to contain unacceptably high levels of cineole.
But few data exist to support claims of skin irritancy. Thus, in 1994, a project was commenced to provide data on this, to test the antimicrobial activity of the oil at various concentrations of cineole and to determine the highest acceptable limit for cineole in tea tree oil.
The project, which was completed late in 1996, was a collaborative effort between the Rural Industries Research and Development Corporation, the NSW Department of Agriculture, the University of Western Sydney and the Australian Tea Tree Industry Association. It involved a multidisciplinary team with expertise in microbiology, dermatology and essential oil chemistry.
Methods
Standard clinical procedures were used to test cineole and tea tree oil for skin irritancy. Twenty-five human subjects were subjected to occlusive patch testing applied to the upper arm or back for five days per week for three consecutive weeks. The patch was removed at 24 hour intervals and any skin reaction noted. Subjects reacting allergically to the test substances were withdrawn from the irritancy trial and were used in further testing for allergic reaction to individual components or fractions.
More than 20 strains of bacteria were used to test numerous tea tree oils with varying levels of cineole concentration for antimicrobial activity.
Results
Skin irritancy
Table 1 shows that no evidence of skin irritancy to cineole or tea tree oil (formulated at a concentration of 1:3 in soft white paraffin) was found among subjects at concentrations in the range 0.0-28.8% cineole. Thus, it can be concluded that tea tree oil in concentrations of up to 25% (by weight) containing cineole in concentrations of up to 28% is not a skin irritant. Some concern had been raised previously about the irritancy of neat tea tree oil; investigations are planned to test this.
Allergic responses
Three panellists withdrew during the course of the investigation because they responded with allergy to the oil. These three were used for a further investigation to test each of the oil's major constituents. One of the panellists reacted to a-terpinene, present at around 1 0% in normal oil, while all three reacted to samples of sesquiterpene hydrocarbon and one reacted to a sesquiterpene alcohol fraction.
From these results, the researchers concluded that, for these three panellists, the most potent allergens occur in the sesquiterpene hydrocarbon fraction. The elimination of the most allergenic fractions in tea tree oils would be desirable: the sesquiterpenoid fraction would be relatively easy to remove without affecting the bioactivity of the oil.
Antimicrobial activity
The antimicrobial activity of the oil samples used in the irritancy trials was measured as minimum inhibitory concentration (MIC) to allow comparison with other studies. Kill-rate experiments were also performed to provide information about the rate of inactivation of various microorganisms.
The data collected indicate that within the range of 1.5-28.8% the concentration of cineole in tea tree oil has no impact on antimicrobial activity. Although there was a slight
trend towards marginally higher MIC values for some organisms for the two oils with the highest cincole levels, these oils also had relatively low concentrations of terpinen-4-ol. Overall, the results suggest that even at the limits of the standard (ie minimum of 30% terpinen-4-ol and maximum of 15% 1,8-cineole), the antimicrobial activity is not compromised.
Implications
The results of this research have major implications for the industry. Some years ago, oils with 5-10% cineole were perfectly acceptable in the marketplace. In recent years, though, buyers have been seeking oils with less than 5% and sometimes less than 3% cineole. Possible reasons for why the market has gone to such extremes include:
This research shows clearly that there are no grounds for promoting
low cineole oils other than for avoiding low terpinen-4-ol oils. If all
buyers could be convinced of this more tea tree oil could be offered for
sale, providing a yield boost to many producers.
Aid for marketing
The results of the project should aid the marketing of tea tree oil. It documents: 1) the absence of skin irritancy for formulated preparations; 2) the non-allergenic nature of most tea tree oil constituents; 3) methods for the removal of some possible allergens; 4) a wider range of tea tree 011-susceptible microorganisms; 5) specific MIC values for a range of oils; and 6) enhanced MIC values for specific oils.
The full report, "Why cineole is not detrimental to
tea tree oil", is available from RIRDC on 02 6272 4819 (or fax 02
6272 5877).
TABLE
1: Concentration, composition and responses for 1,8-cineole and
tea tree oil formulations
tested for skin irritancy on human subjects
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Irritancy scorec
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(%) in oil |
(%) in oil |
(n=25)c |
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In late 1994, a chloropyrifos residue was detected in a batch of tea tree oil. Consequently, all pesticide permits for unregistered chemicals (fluvalinate and chloropyrifos) were withdrawn by the NSW Department of Agriculture.
Only one valid pesticide remains registered in that state: methomyl, which has no residual activity.
The discovery of pesticide residues in tea tree oil has caused the industry to re-evaluate its marketing options. The industry body has adopted a policy of zero residues to enhance its 'clean, green' image.
But what are the implications for pest management? Several insect pests have the potential to reduce tea tree oil yields substantially, jeopardising the viability of the industry. Clearly, a pest management strategy is needed that does not require the wholesale use of chemicals.
This was the objective of a recently completed project supported by the Rural Industries Research and Development Corporation and the NSW Department of Agriculture. It set out to develop an effective and sustainable pest management strategy for the tea tree's major defoliating pest, the pyrgo beetle (Paropsistema tigrina).
Methods
The project proceeded on two main fronts: the field and the laboratory. Laboratory work included the screening of 31 chemical compounds against pyrgo larvae and the determination of the upper threshold temperatures for the survival of eggs and larva.
The effects of weather and climate on the development of pyrgo beetles were studied in four commercial plantations at Cudgen, Ballina, Bungawalbyn and Grafton. Chemicals were used at all four sites to control pests, but trial blocks at each were left unsprayed to allow population monitoring.
At the Cudgen site, the efficacy of four insecticides and a biocide treatment, applied at two different rates, was also assessed. Treatments were replicated ten times across ten rows. Trees were sprayed past the point of runoff and shielded to reduce drift. Foliar samples were also collected to determine the presence or absence of chemical residues.
Results
The effect of temperature
The optimum temperatures for pyrgo are in the range 25-30'C. Exposure of pyrgo beetle eggs to a temperature of 35'C for 72 hours prevented hatching, while shortterm exposures (2-6 hours) at 38-40'C reduced hatching to less than 15%. Egg-laying was negligible outside the temperature range of 15-35'C. In the laboratory, egg-laying resumes after the beetles feed on new flush for 5-7 days at 25'C and 80% humidity.
The exposure of larvae to 40'C for four hours caused 100% mortality. Exposure to 35'C temperatures for the same duration had no effect, but when exposure was extended to six hours more than 65% of larvae were killed. An eight hour exposure killed 100% of larvae.
Data from these trials were used in a mathematical model that accurately accounted for population development observed at the four field sites.
Efficacy of chemicals against pyrgo
Several synthetic pyrethroids were effective against small pyrgo beetle larvae at significantly lower concentrations than the currently registered treatment (methomyl) and gave higher mortality than the vegetable or mineral oils, fertilisers and soaps tested in the laboratory.
Of the oils tested in the lab, the petroleum oil DC Tron had a lower LD50 rate than Synetrol, Codacide, pure canola oil, Eco oil and pure olive oil. Pure tea tree oil had a lower LD50 rate than Eco oil, which contains a tea tree oil derivative. Tea tree and olive oil, with an emulsifier (Tween 201), were effective at lower concentrations than the commercial oil products of Synetrol, Codacide and Eco oil.
At Cudgen, the location of a field insecticide trial, high egg mortality was observed, due initially to predatory bugs and coccinellids and later to cannibalism by adult pyrgo and larval parasitism. Other pyrgo larvae collected for laboratory work were consistently parasitised by tachinids (Anagonia spp?).
Ichneumonid hyperparasites were also found. According to the report's authors, parasites can play a major role in pyrgo control but do not curtail feeding by the infected larvae.
Field results demonstrated that the synthetic pyrethroids were more effective in pyrgo control than was the currently registered methomyl treatment. Vegetable and petroleum oils had some short-term value and no residual activity.
The timing of insecticide applications for pyrgo control is crucial. For insect control, a chemical with residual activity would be desirable, but this conflicts with the industry's policy of zero residues.
Detecting pyrgo in the field
A simple technique for detecting the movement of pyrgo adults into and out of plantations was tried and found to be successful. Yellow sticky traps placed about 2 metres at) over the ground proved easier to monitor and more accurate than the on-plant counting of beetles, eggs or larvae.
Pyrgo are not distributed evenly across a plantation; the strongly aggregated distribution pattern raises the possibility of site-specific treatment. The yellow sticky traps catch beetles before the commencement of egg-laying, giving managers an early warning of potential problems and indicating where the problem is likely to occur.
Better monitoring, fewer chemicals
While this research suggests that chemical insecticides are most effective against the pyrgo beetle, it also points out ways to minimise the need to use them. When combined, the monitoring technique and weather-based pyrgo development modelling remove the guesswork from decision-making about pyrgo control.
For a relatively small outlay, growers could establish colour traps and basic weather stations on their farms to improve pest monitoring and prediction, leading ultimately to better targeted control programs. This would reduce the need for broadscale application of pesticides, leading in turn to diminished environmental risks and lower costs for pest control.
The full report of project DAN-9]A: "Controlling pyrgo beetle in tea tree", is available from RIRDC on phone 6272 4819.
The potential for residues is high and the issue warrants investigation in its own right. The strategic management of pests which minimises the need for the widespread use of chemicals should be encouraged and needs to be developed further.
Washing One's Hands in the Good Oil
Scientists at the University of Western Australia are involved in an ongoing project funded by the RIRDC/ATTIA Tea Tree Industry Program. The project, titled The antimicrobial activity of tea tree oil (UWA-24A), commenced in 1994.
It aims to produce scientifically valid and publishable data relating antimicrobial activity of oil against bacteria; the mechanism of action of, and of resistances to, tea tree oil; and the efficacy of the various components of tea tree oil.
Preliminary results indicate that tea tree oil may be useful in removing transient skin flora while
suppressing but maintaining resident flora. In a paper published recently in the American Journal of' Infection Control, researchers suggest that given the antimicrobial activity of tea tree oil observed during the project, particularly against transient bacterial pathogens, the potential exists tea tree oil to be used in hospitals for hygienic hand disinfection.
The final report of this project be produced later this year.
Favourable conditions for weed growth often exist in tea tree plantations. The location of many such plantations on the north coast of NSW offers a generally warm and moist climate that is ideal for numerous weed species. Weeds are also favoured by the waterlogging frequently present in such plantations because this may reduce access for weed control activities. Past and present agricultural practices often mean that weeds are already present in the soil seed bank or on adjacent land.
Weed control has been identified by growers in the tea tree industry as a significant concern, both because of a lack of knowledge about the effect of weeds on oil yield and because no consensus has yet emerged on the most effective weed control practices.
Surveying the situation
In 1991, a collaborative project between the University of Sydney and NSW Agriculture, with funding from RIRDC, was set up to address the issue of weed control in tea tree plantations.
As a first step, a survey of growers covering 28 tea tree plantations ranging in size from 0.4 to 400 hectares was carried out. Its purpose was to identify production trends and to obtain as much objective information as possible on the influence of weeds on tea tree cultivation.
The survey showed that a wide range of chemical and non-chemical weed control methods were used in 1992 (the year of the survey). These methods included herbicide application, cultivation, and other practices such as hand-hoeing, mowing/slashing and grazing.
Field experiments
Field experiments at five sites were then carried out to:
Pot trials were used to supplement the field trials.
How do weeds affect the mature yield of regrowing plantation tea trees?
Tea tree plantations at the five experimental sites were harvested and allowed to regenerate with and without weed control. Several parameters of weeded and unweeded plots were assessed.
Herbaceous weed interference reduced mature leaf biomass yield of regrowth plantation tea tree by 9-47% across all sites, with an average reduction of 27%. This suggests that the competitiveness of regrowth tea tree is more akin to young established trees rather than tree seedlings (which have yield losses of more than 50%).
A decrease in leaf oil concentration in the presence of weeds was only detected in one out of eight regrowth cycles. Similarly, there was little evidence of a weed effect on tea tree oil chemical composition.
How can weed competition be minimised?
Weed competition, particularly for nitrogen but also for potassium and phosphorous, was demonstrated to be IMDortant late in the tea tree regrowth cycle, while early competition due to shading can also be significant. Thus, weed management should aim to minimise early shoot competition and late root competition.
Ten different weed control techniques were tested using a randomised complete block design with four replicates. The techniques were:
Herbicides were the most effective of the techniques tested. However,
there are risks associated with the use of herbicides: for example, they
may have a negative effect on tea tree growth, and they may also pose environmental
and health hazards and leave residues in products.
Of the non-chemical weed control techniques tested, regular cultivation provided the best results. The factor most limiting its effectiveness was lack of machinery access due to waterlogging. Other limiting factors included selection for perennial weeds which reproduce vegetatively and the difficulty of cultivating within tree rows or in closely spaced hedges.
Aside from reducing weed competition, cultivation may also favour tea tree growth in the short term through improved soil penetrability for root growth, increased rainfall infiltration and increased mineralisation of nutrients from soil aeration. There may be negative effects on growth in the longer term through damage to trees and soil structure.
Mowing was not an effective weed control technique. Perennial grasses with lateral vegetative growth are favoured by mowing and become increasingly dominant. The high root density of these grasses and the regular promotion of vigorous regrowth with each mowing favours strong competition with tea tree for soil nitrogen.
The full report of project US-20A: Weed control alternatives in tea
tree plantations, is available from RIRDC on phone 02 6272 4819.
Last updated: 17 November 1998
Copyright © RIRDC
http://www.rirdc.gov.au/pub/teatree97.htm