Cape Byron is home to the last wild population of this native tree
CAPE Byron Conservation Area is home to the last wild stand of native guavas in Australia.
The species was once common along the east coast between Gympie to Newcastle, but a fungal plant disease known as myrtle rust has decimated its population.
Scientists from the Australian Government's National Environmental Science Program have been monitoring the guava at Byron Bay and 65 other sites in New South Wales and Queensland since the disease arrived in Australia in 2010.
Lead scientist Dr Rod Fensham from The University of Queensland said the plants have died at every site except near the Byron Bay lighthouse where about 10 plants remain. But they are not in good health.
"Myrtle rust is a highly contagious and deadly plant disease," said Dr Fensham.
"It produces trillions of microscopic spores which are carried by the wind allowing it to quickly reach new areas.
"It is particularly catastrophic for many rainforest species like the native guava, and could change the nature of some of our rainforests.
"Containment and eradication responses have so far been unsuccessful.
"To prevent the extinction of the species we are working with nurseries and gardens to establish rescue populations away from myrtle rust affected areas."
Dr Fensham said 80 native guavas were now "thriving" across two gardens run by the Toowoomba Regional Council.
"This is an important step to prevent the extinction of this species but ultimately we want to see this and other affected species returned to their natural habitats," he said.
"To achieve this it will be critical to find and propagate strains of these plants that are more resistant to myrtle rust.
"This kind of selection process is something that the nursery industry has a lot of expertise in, and we are working with commercial nursery partners on this goal."
The Australian Government's Chief Environmental Biosecurity Officer, Ian Thompson, said myrtle rust is one of the most significant native plant diseases to enter Australia.
"This research has highlighted the existing and potential impact of myrtle rust on many native species and underlines the importance of working to prevent new diseases entering and establishing in Australia," Mr Thompson said.
The study has just been published in the scientific journal Trends in Ecology and Evolution.