Botanic Gardens Trust, Sydney, Australia


Eucalyptus Rust a Major Threat

The Australian native flora includes approximately half of the world’s 147 genera and 3000 species of the myrtle family, the Myrtaceae. More Australian native plant species belong to this family than any other plant family. They are dominant species in many of our natural ecosystems, from tall forests to swamps and wetlands. Furthermore our major industrial tree species are all myrtaceous species.

A current and alarming threat to the Myrtaceae is Eucalyptus rust, a plant disease recently introduced into the country. Since its first report in NSW central coast in April 2010, the rust has now spread throughout the eastern coast of the continent, infecting more than 150 myrtaceous species in more than 40 genera, including the iconic Eucalyptus, Callistemon, Melaleuca and Syzygium. While management operations were activated across jurisdictions and governments, the rust was officially declared non-eradicable at the end of 2010.

Eucalyptus rust, also known as Myrtle rust or Guava rust depending on the strain, is caused by the rust fungus, Puccinia psidii, which originated in South and Central America. The rust mainly infects young shoots and stems of susceptible plants, forming rusty pustules which produce a multitude of spores. Although the disease does not usually kill mature trees, it is extremely destructive to young plants and today its full devastating impact to our natural ecosystems is only beginning to be realised.

Puccinia psidii resembles in many ways the rusts that infect many cereals causing devastating crop losses worldwide. However, its true relationship with other rust fungi is ambiguous, casting doubt as to its proper name and, hence, its biological affiliations. While various government agencies (e.g. CSIRO, NSW DPI, universities) are conducting research on different aspects of this pathogen in order to better understand how to combat this devastating disease, the Royal Botanic Gardens and Domain Trust’s plant pathology team is collaborating with eminent international scientists (Dr Wolfgang Maier, Germany; Prof Mike Wingfield, South Africa) to work out the evolutionary relationships of this fungus with other rust fungi. Information on such relationships leads to more efficient disease management in terms of diagnostics, quarantine and understanding plant-host associations.

Dr Edward Liew and Dr Marlien van der Merwe are leading this study to unravel evolutionary information about this rust fungus encrypted in its DNA. The approach involves sequencing and analysing specific fragments of DNA extracted from this organism and its relatives.

This work is partly funded by the Australian Department of Agriculture, Fisheries and Forestry and a private donor to the Foundation and Friends of the Gardens.


Dr Ed Liew examining a Eucalyptus rust specimen

Eucalyptus rust on turpentine - the bright yellow pustules contain a multitude of rust spores

Eucalyptus rust on coppice growth of Eucalyptus elata