Myrtle rust – impact on native Myrtaceae and associated plant communities

Austropuccinia psidii (myrtle rust) has long been considered a significant threat to Australian plant industries and ecosystems. A. psidii was detected for the first time in Australia in April 2010, on the central coast of New South Wales. The distribution of A. psidii continues to expand, with detections extending from Tasmania, along the eastern coast of Australia to Cape York Peninsula, and most recently in the Tiwi Islands and Northern Territory. The current host list for Australia includes 347 species from 57 genera. A. psidii severely affects key species in natural ecosystems, including threatened species with restricted natural ranges as well as widespread species with a broad native range (e.g. Rhodomyrtus psidioides and Rhodamnia rubescens). Our studies have demonstrated severe impacts of myrtle rust on plant communities and the potential for A. psidii to negatively affect Australia’s biodiversity in the short- and long-term. A. psidii has caused significant disturbance in wet sclerophyll environments, where Myrtaceae dominate the rainforest understorey, and regeneration of coastal heath following wildfire. Significant dieback caused by repeated A. psidii infection has seen once dominant species in severe decline with little evidence of potential for regeneration. Impacts on keystone species such as Melaleuca quinquenervia include tree death, decline in tree vigour and reduced flowering rates, with additional decline associated with interactions with insect damage. Continued monitoring programs are required to identify species and plant communities at greatest risk. The implementation of a disease screening and tree breeding program may be required for some species as without human intervention regaining lost genetic diversity within these species populations may not be possible. Already, as a direct result of myrtle rust impacts, two species have been recommended for legislative listing as being critically endangered.