Fighting a deadly fungus
It is so small that it is invisible to the naked eye. Yet this microscopic fungus poses such a serious a threat that it has been identified by the Federal Government as one of Australia's five national threatening processes.Phytophthora cinnamomi, better known as the pathogen that causes the dieback disease in plants, is the fungus in question.Along with the fox, the rabbit, the goat and long line fishing, this fungus has the dubious honour of being deemed so dangerous that every state and territory in Australia is required to formulate a national plan of action to combat its threat.Phytophthora cinnamomi may be invisible to the naked eye but its impact is clear for all to see. Yellow, shriveled trees and shrubs dying by the hectares testify to the devastating effect of this fungus.The affected species are often colourful flowering shrubs while the resistant species are often less attractive. It is not only plant species that are at risk -- entire ecosystems are affected in terms of the bird and animal life that
depend on those plants.In Australia, it is WA that is hardest hit by the fungus. Up to 80 per cent of the Stirling Ranges are infected, along with many areas of the State's sandplains and Jarrah forest. This is because the State has many plant communities with species susceptible to the disease.The spread of the dieback disease was unfortunately exacerbated in the days before the fungus was identified as the cause of the problem. In areas where trees had been killed, councils were encouraged to collect gravel for road
building activities. This led to the spread of Phytophthora cinnamomi into previously uninfected areas.However, quarantine measures have since been put in place. Nowadays, there are restrictions on movement through Phytophthora cinnamomi-affected areas and all vehicles moving in and out of contaminated areas are required to be washed down.Work conducted by the WA Department of Conservation and Land Management (CALM) has also shown that the chemical phosphite, which switches on plant resistance to the deadly fungus, has potential to control the disease in native plant communities.The work of Dr Bryan Shearer of CALM, who is also an adjunct Associate Professor in the Division of Science and Engineering at Murdoch, has shown that shrubs can be sprayed or misted with phosphite and large trees can be injected with the chemical. These treatments stop the spread of the fungus in infected plants and restricts infection in non-infected plants. Therefore, the chemical gives scientists a "breathing space" during which more effective control measures can be developed, particularly for the protection of rare and endangered species.Most Effective Use
The effect of phosphite on different plant species, however, has not been fully researched, nor has the most effective use of the chemical.
And this is where the team of biological scientists from Murdoch University, headed by Dr Giles Hardy, has stepped in. Under a project funded by the Minerals and Energy Research Institutions of Western Australia (MERIWA), the Australian Research Council (ARC) and several mining companies including Alcoa of Australia, Worsley Alumina, TiWest, Sons of Gwalia and Renaissance Gold Company, Murdoch University is investigating the use of phosphite to treat Phytophthora cinnamomi.
The mining companies funding the project are specifically interested in a set of operational guidelines for using phosphite. Such guidelines would be useful because the companies sometimes have to use the chemical given that their operations pose the risk of spreading Phytophthora cinnamomi.The team consists of about ten core members, including project leaders Dr Giles Hardy, Associate Professor Bernie Dell and Head of Plant Sciences, Associate Professor Jen McComb.Some of the questions the team is investigating include the best time to spray, the most effective rates of spray, its effect on different plant species and the long-term impact on the ecosystem of using the spray.According to Dr Hardy, the spray comprises a relatively simple non-toxic compound but there are many questions surrounding its optimal use, potentially detrimental side effects and its long term efficacy."It's one of those damned if you do and damned if you don't decisions," explained Dr Hardy."You're damned if you don't use it because you've got species disappearing around you as a result of the fungus and you're damned if you do use it because all the science hasn't been done yet."But at the moment it is the only tool we have against the disease and we are going to have to make some pretty important decisions as to how we are going to use phosphite in Western Australia."
Cheaper Dieback TreatmentGiven that phosphite will need to be applied to extensive areas, Murdoch's research was also important in identifying the most cost-effective way of using the chemical.
Murdoch was awarded the research grant of approximately $600,000 for this project based on the strength of its previous research into Jarrah dieback disease. It had also already developed a good working relationship with several mining companies on other projects.The mining companies sponsoring the project have made available tracts of vegetation within their mining leases for the Murdoch team to conduct their field trials.The availability of such sites is important. It is difficult to do work with Phytophthora cinnamomi as the disease cannot be introduced into areas free of the pathogen for the purpose of experiments.However it is possible to do so in the mining sites because the area is to be mined once experiments are completed. Furthermore, the fungus is placed under the bark of trees, which are later cut off and destroyed at the end of the experiment. This prevents the pathogen from getting into the soil.Mining sites where Murdoch is currently conducting such field trials include Renaissance Gold Company's site in Eneabbea, TiWest's site at Cataby and Alcoa's sites at Huntley and Jarrahdale.The trials are not due to be completed for another year but Dr Hardy and his team have already come up with some significant results.Preliminary results indicate that phosphite is effective in a range of plant species and families, and that one rate of spray is also effective across these species.These answers are useful, but Dr Hardy cautions that there are still more questions. What happens to the fungus after being exposed to the chemical over time? Will it develop a resistance to the spray? Is the fungus prevented from producing spores?"A lot of the work we have already done is indicating that we need to do a lot more work on the biology and ecology of the organism," said Dr Hardy."We need to do all this before we make any broad statements about the long term use of the chemical on native plant communities." |
| Inoculating trees with Phytophthora cinnamomi by inserting the fungus under the bark. |
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Dr Giles Hardy School of Biological Sciences and Biotechnology Telephone (08) 9360 6272 email g-hardy@central.murdoch.edu.au |
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