Dr Mariana Campos, Murdoch University
Myrtle rust (Austropuccinia psidii) is a serious pathogen which has a myriad of hosts among Australian native and industry plant species. This pathogen has not yet been detected in Western Australia (WA), despite there being suitable habitat for its establishment. The current strategy in WA regarding myrtle rust is to ‘keep an eye out’ for susceptible species and ban on importation of incoming Myrtaceae material. However, this strategy could be supplemented by: (1) a formal surveillance plan for WA; and (2) local testing preparedness.
Austropuccinia psidii (commonly known as myrtle rust) is a rust fungus with 524 hosts in the Myrtaceae family identified to date, which is native to Brazil and neighbouring countries, and was introduced to Australia in 2010.
The state of Western Australia is currently free of myrtle rust, despite having regions identified as climatically suitable for its establishment in previous modelling. Western Australia’s flora is rich in Myrtaceae, with 1959 taxa – 84 of which are known to be susceptible to myrtle rust, but many more likely to be susceptible once the testing is undertaken or the pathogen enters the state.
The recognised pathways of introduction of myrtle rust to Western Australia are wind (including cyclonic winds) and the movement of people and their clothing via roads, airports, or ports. Animals are possible vectors of myrtle rust spores, but the travel distances needed to bring the rust to Western Australia from known infested sites precludes most species from being vectors into the state, with migratory birds being a notable exception. Finally, the high-risk pathway of nursery and cut flower trade has been regulated since 2011, with no Myrtaceous species movement from other States and territories into Western Australia.
Myrtle rust surveillance and detection has so far relied heavily on opportunistic visual inspections or surveillance efforts that are not nationally coordinated or formally structured. Detection of leaf lesions or sporulation implies that the disease is already established, and in such cases, eradication or control may be beyond reach. Molecular diagnostics of myrtle rust have to date focused on confirmation of visual diagnostics and identifying the strain of myrtle rust rather than being used as a surveillance tool.
Our research aims were to: develop a Surveillance Plan for Western Australia overlapping climate suitability, host species, and pathways; and to develop a forensic-level assay for the detection and identification of myrtle rust that could be used in eDNA sampling.
The Surveillance Plan was developed, including consultation with key stakeholders in the state, and includes the background information and practical guidance for officers to deploy it before the arrival of myrtle rust to the state. Within it are approaches for visual and eDNA surveillance, including a highly sensitive and fast molecular assay that can detect as few as 1-10 copies of DNA in a sample.
The Surveillance Plan and molecular assay assist Western Australia’s preparedness against Austropuccinia psidii and, used in conjunction with the State’s Contingency Plan, give the state an advantage for achieving early detection and rapid response against a pathogen that is a known risk to biodiversity, and consequently, to ecosystem processes.