The Effects of Myrtle Rust on Post-Fire Regeneration of Myrtaceae in Australia

Abstract

Fire is an important factor influencing the evolution, structure and composition of Australia's native vegetation. Australia's many fire-adapted species regenerate en masse after fire, with a proliferation of new epicormic shoots and seedlings. Given Austropuccinia psidii (myrtle rust) mainly infects new growth, post-fire emergence of new epicormic shoots and seedlings is ideal for the development of the disease, leading to further loss of plants along with subsequent increase of fungal inoculum in the region. Extreme fire events across New South Wales and Queensland in 2019–2020 and subsequent vegetation regeneration across a wide area provided ideal conditions for disease epidemics. Surveys for myrtle rust were conducted across rainforest, coastal heath and woodland environments from south-eastern NSW to south-east Queensland 6–12 months post-fire. Myrtle rust was identified in all regions and ecosystems surveyed apart from areas in south-eastern NSW. Of the 73 Myrtaceae species surveyed in areas other than southern NSW, 44 were found with myrtle rust symptoms, ranging from small spots and limited damage to severe blighting, dieback and death of reshooting trees and seedlings. Monitoring plots were established for some of the more susceptible species, with monthly assessments conducted to determine impact levels and decline rates. The most severely impacted species were Rhodamnia rubescens and Uromyrtus australis, with infections of reshoots causing dieback. Infection of Melaleuca quinquenervia and M. nodosa reshoots and seedlings impeded recovery of populations, causing seedling and tree deaths and reducing flower set and subsequent seed production.