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Tech & Science Invasive fungus myrtle rust is pushing Australia's native trees toward extinction

07:35  04 december  2019
07:35  04 december  2019 Source:   abc.net.au

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Australia must roll out an emergency national response to an invasive plant disease that is rapidly pushing at least four plant species to imminent extinction , experts have told Guardian Australia . Myrtle rust , first found at a New South Wales nursery in 2010, attacks trees in the myrtaceae family.

Myrtle rust is pushing already threatened native Australian Myrtaceae closer to extinction , notably Gossia gonoclada, and Rhodamnia angustifolia and changing species composition of rainforest understories, and Richmond birdwing butterfly numbers are under threat from an invasive flower

a bird sitting on a tree branch: The yellow spots and discoloured leaves of this red lilly pilly are signs the invasive fungus myrtle rust has infected it. (Supplied: Geoff Pegg)© Provided by ABC NEWS The yellow spots and discoloured leaves of this red lilly pilly are signs the invasive fungus myrtle rust has infected it. (Supplied: Geoff Pegg)

While cane toads creep across northern Australia and down the eastern coastline, a far more insidious invasive species is ravaging our native trees.

Scientists warn rapid extinctions of some of our most well-known tree species are on the cards if myrtle rust, an invasive, disease-causing fungus, is not rapidly brought under control.

Myrtle rust, or Austropuccinia psidii, has caused extensive dieback of trees including lilly pillies, paperbarks, box brush and tea trees.

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Myrtle rust (Puccinia psidii) is a fungus that causes disease in plants in family Myrtaceae. It is one of a complex of fungal pathogens known as eucalyptus or guava rusts . Australian scientists have been greatly alarmed by these rusts since they were first reported causing serious disease in eucalypt

Invasive species are a serious threat to the native biodiversity of Australia and are an ongoing cost to Australian agriculture. Numerous species arrived with European colonisation of Australia and

The areas most affected are wet forest environments, such as coastal heath, paperbark wetlands and rainforests, along the east coast of Australia, said Bob Makinson, a conservation botanist with the Australian Network of Plant Conservation.

"We know that at least four species are in what can only be termed catastrophic decline," Mr Makinson said.

"The critical endangered status that's been afforded to three of those species in New South Wales means that they are in danger of extinction in the near future.

"Those species are on the way out."

Native guava (Rhodomyrtus psidioides) and brush turpentine (Rhodamnia rubescens) are two of the four tree species most at risk from myrtle rust.

"Those species were widespread and had no conservation concern prior to 2010, when myrtle rust was first detected," Mr Makinson said.

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Austropuccinia psidii ( myrtle rust ) is an invasive fungus native to South America that infects the young growing tissues of species in the Myrtaceae family, one of the dominant plant families in Australia . To date, 360 native species from 49 genera have been found to be susceptible in

Invasive fungi Guava rust Eucalyptus rust Biodiversity Environmental monitoring Ecological impacts Extinction The disease it causes is variably known as guava rust , eucalyptus rust or myrtle rust . Prior to reaching Australia , the known host range for P. psidii was 129 species in 33 genera of

"But in the short space of just nine and a half years have gone to critically endangered status."

Myrtle rust is now established along the east coast of Australia and at several locations in Tasmania and the Northern Territory, but has not yet reached Western Australia.

The 'pinnacle of pathogens'

Myrtle rust is recognisable by its yellow and orange spores on tree leaves and branches.

These spores are carried by wind, and when they land on a suitable host — trees in the family Myrtaceae — they can infect it within 12 hours.

Sometimes the only sign trees are infected is isolated brown spots on their leaves, and some plants can survive with this level of infection.

More severely infected plants look burnt and this level of infection can cause plant death.

Plant pathologist Geoff Pegg called myrtle rust the "pinnacle of pathogens" at a recent Ecological Society of Australia conference in Launceston.

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Australia has the highest rate of vertebrate mammal extinction in the world, and invasive species are our number one threat. Myrtle rust is pushing already threatened native Australian Myrtaceae closer to extinction , notably Gossia gonoclada, and Rhodamnia angustifoliaand changing species

Myrtle rust is pushing already threatened native Australian Myrtaceae closer to extinction , notably Gossia gonoclada, and Rhodamnia angustifolia and changing species composition of rainforest understories, and Richmond birdwing butterfly numbers are under threat from an invasive flower

"Initially we thought that [myrtle rust infection] would be mainly in areas where we have regeneration — so seedlings," said Dr Pegg, who works in forest production and protection with the Queensland Department of Agriculture and Fisheries.

"But we've actually seen the decline of mature trees, so over-storey species 80 to 100 years old.

"We're losing the lower branches first and the plants just struggling to survive by having only the top of the canopy still alive. But it's eventually succumbing as well."

Over 350 species of Myrtaceae can be suitable hosts to myrtle rust, and it's not clear why, according to Dr Pegg.

"[Myrtaceaea] is such a diverse thing, some species have spiny little leaves, and others have massive fleshy leaves, and there just doesn't seem to be difference in terms of their susceptibility," he said.

The invasive rust also targets fruit and flowers and with repeated infection of new growth over time, trees are no longer able to reproduce and eventually die.

Fire and rust

At one of Dr Pegg's study sites in Lennox Head in northern New South Wales, Myrteacea species that once dominated the site did not regenerate after fire.

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Myrtle Rust is a major new threat to Australia ’ s flora. This information hub has been developed by the ANPC to contribute to response capabilities here in Australia and overseas. Myrtle Rust reviewed: the impacts of the invasive pathogen Austropuccinia psidii on the Australian environment.

Uredo rangelii, commonly known as myrtle rust , is a fungal plant pathogen native to South America that affects plants in the family Myrtaceae. It is a member of the fungal complex called the guava rust (Puccinia psidii) group.

"The prickly melaleuca, Melaleuca nodosa, was once dominant and grew in thickets, now we only find one or two individuals within those thickets, and it's been swamped by acacias and banksias," he said.

With huge bushfires burning throughout Australia this spring, and predictions of more frequent and intense fires due in some part to climate change, will the threat of myrtle rust increase?

"It may significantly impact on regeneration of some Myrtaceae as the forests recover from fire," Dr Pegg said.

"Because you get a massive amount of regenerating seedlings which is susceptible to myrtle rust, you will potentially get a rapid increase in spores, increase in the number of plants infected and severity of impact on species."

Eucalypts OK, for now

Myrtle rust is not yet affecting eucalypts to the same extent as other Myrtaceae groups, but that could change, Mr Makinson said.

"Myrtle rust has different strains, and there are two strains in South America, which are strongly eucalypt associated and have caused major economic damage in the eucalypt plantations over there," he said.

"If either of those strains or indeed any others were to arrive in Australia the effects could be quite dire."

Action plan not yet taken up

In mid-2018 a roadmap for the conservation response to myrtle rust was drawn up by a group of concerned scientists, led by Mr Makinson, with support the Department of Environment and Energy and the previous Plant Biosecurity Cooperative Research Centre.

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Myrtle rust is just one example of the invasive pests – weeds, animals and pathogens – that are cutting a swathe through Australia ’ s unique native flora and fauna. Invasives are the major driver of species loss, so if we're worried about extinction we should worry about invasives .

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Collecting germplasm — cuttings or seeds — from Myrtaceae is one of the actions recommended, as there aren't any safe refuges due to myrtle rust dispersal via wind.

Samples collected could be used to identify plants that are more resistant or tolerant to the rust, which could be used to breed resistant lines of those species for putting back out into the wild to reinforce surviving populations or as reintroductions where extinction has occurred.

However, Mr Makinson said this plan is yet to be taken up or resourced.

"This is an existential threat to plant family of great ecological significance in Australia and indeed have commercial significance too," he said.

"One would hope that a vigorous reaction to the arrival of one strain in Australia would would emerge and would prepare us better for future strains that might arise as well."

In a statement, a spokesperson for the federal environment minister Sussan Ley said the draft action plan was being finalised by the Australian Plant Biosecurity Science Foundation following public consultation.

The statement also said that two of the four species of Myrtaceae currently in "catastrophic decline" due to myrtle rust in New South Wales and Queensland have been prioritised for assessment under the Environment Protection and Biosecurity Conservation Act.

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