Predicting impact of Austropuccinia psidii on populations of broad leaved Melaleuca species in Australia

Melaleucaeae is the second largest angiosperm tribe in Australia containing more than 330 species. Most Melaleuca species are endemic to Australia and are found in a wide variety of habitats. The Melaleuca leucadendra complex, including M. leucadendra, M. quinquenervia and M. viridiflora, are dominant components of the tropical and sub-tropical biota of Australia. All three species are known to be susceptible to Austropuccinia psidii (myrtle rust), which was first detected in Australia in 2010 and is now widespread in the eastern states and the Northern Territory. In this study we examined variability in susceptibility to A. psidii within populations of M. quinquenervia, M. leucadendra and M. viridiflora using in-vitro assessments of seedlings from provenances across the native range of the three species. We identified wide variation in susceptibility to A. psidii between M. quinquenervia, M. leucadendra and M. viridiflora, among provenances within these species as well as within provenances. Further studies on larger populations of these Melaleuca species addressing the long-term impacts of repeated infection in native ecosystems are needed to not only help predict but also limit impact. Regaining lost genetic diversity within some of these species populations may require human intervention