SciNews

Australian scientists have declared open war on a fungal disease that is rapidly infecting the nation's iconic myrtaceous trees and shrubs.

Eucalyptus or myrtle rust is a recent invader of the Australian continent with potential to cause havoc in native forests and woodlands, and among industries that depend on native trees and shrubs.

A team of researchers in the Cooperative Research Centre for National Plant Biosecurity (CRCNPB) is currently working overtime to understand the disease, how it spreads and which species are most at risk of attack - as a basis for developing a national strategy for managing it.

Eucalyptus or myrtle rust is caused by the fungus Puccinia psidii and appears to have originated from South America. The disease affects plants in the Myrtaceae family. Biosecurity experts consider it poses a serious threat to the Australian native environment and to industries that utilise myrtaceous trees and shrubs.

The disease was first detected on the central coast of New South Wales in April 2010. By December it had spread to Queensland, and now spans a 2000 km corridor along the east coast of Australia. In December last year the Myrtle Rust National Management Group agreed it was no longer technically feasible to eradicate it.

Mike Ashton, Director of Biosecurity Queensland's Myrtle Rust Program, which is leading the CRCNPB's myrtle rust project, says myrtle rust has the potential to affect many plant species that are integral to Australia's fragile ecosystems - like eucalypts and Melaleuca.

"The disease has already been detected in several national parks and World Heritage Areas, highlighting the threat to our environment. So far more than 100 species in the Myrtaceae family have been found to be susceptible to the disease," Mr Ashton says.

Industries already impacted by myrtle rust, or likely to be, include the nursery and garden, forestry, bee, zoo, native fruit, cut flower and plant oil industries.

"There may also be a significant social impact as the disease spreads further in public parks and people's backyard gardens. There is bound to be strong community concern over the damage to a number of iconic Australian species," he says.

"Myrtle rust infects young leaves and stems on susceptible plants, and may infect floral buds and fruit. The disease kills off new shoots, stems and young leaves leading to defoliation, poor growth rates, reduced flower and seed production and ruining the appearance of native trees.

"By affecting native trees, it could also harm native animals, birds and insects that depend upon them.

"A major concern is the regeneration and even survival of particular species of native Myrtaceae. For example, the disease affects many species of Melaleuca or paperbarks which are ecologically significant in wetlands, swamps, coastal woodlands and forests. Melaleuca quinquenervia or broad-leaved paperbark, which is an important and widespread coastal species, is severely affected by this disease," he says.

CRCNPB CEO, Dr Simon McKirdy, says research into the fungus is a top priority for the Centre.

"Australia now experiences, on average, around 30 new invasions by species damaging plants and crops every year. Eucalyptus or myrtle rust is one of the worst we have ever seen, because of the wide range of native species it can attack. This is as close to a national plant health emergency as it gets" he says.

"Basically, because this disease is new to Australia, we need to determine its potential host and geographic range, and study its epidemiology and impacts in the Australian environment.

"The main focus of the CRCNBP research is to gather information on which plants are susceptible to the fungus, its natural range in Australia, and the behaviour of the disease in the Australian environment so we can better predict what the likely impacts will be," he says.

"Australian plant industries and the environment are particularly at risk from Puccinia psidii because of the large number of myrtaceous plants which are native to Australia.

"Most of these are considered ‘naïve' hosts, meaning they have never before encountered this particular disease, and may be all the more vulnerable. Over time, it is entirely possible some Australian native plants will be driven into extinction because of it."

"We simply don't yet understand the long term ecological impacts of this disease - and an important part of our research is to try to find out, so we can develop the right countermeasures and management strategies."