Project leader, Organisation
Geoff Pegg, Queensland Department of Agriculture and Fisheries
While fire is considered an important selection agent in the development of Australia’s native flora (Gill 1975), the development of new epicormic and young seedlings en-masse are ideal for the development and spread of A. psidii. The impact A. psidii might have on regeneration following disturbance such as fire has long been considered a risk this pathogen posed prior to arrival in Australia, with consequences for forest structure and survival of dependent fauna and understory plants (Grgurinovic et al. 2006). Assessments in Australia since detection have identified significant impacts, including regeneration following disturbance events (Carnegie & Pegg 2018).
The impact A. psidii might have on regeneration following disturbance such as fire has long been considered a risk this pathogen posed prior to arrival in Australia, with detrimental consequences for forest structure and survival of dependent fauna and understory plants. Assessments in Australia since detection have identified significant detrimental impacts due to the fungus, including adverse effects on regeneration following disturbance events. Recent extreme fire events have resulted in significant impacts on a range of different ecosystems, with widespread epicormic and seedling regeneration now occurring or about to commence, creating ideal conditions for spread and impact of rust. This project aimed to determine the impact myrtle rust is having on species and ecosystem regeneration.
Monitoring plots were established in coastal heath and woodland ecosystems focused on species showing levels of susceptibility during initial surveys (see previous reports – Fire and Rust | Australian Network for Plant Conservation (anpc.asn.au). Plots were monitored monthly to determine impact of repeated A. psidii infection on fire affected reshooting trees of selected species. These species were Melaleuca quinquenervia and M. nodosa, Eucalyptus pilularis and Leptospermum trinervium. Monitoring plots were established in Yarringully Nature Reserve, Double Duke State Forest and Bundjalung National Park.
Impact from A. psidii infection was identified on all species monitored as part of this study. Impacts ranged from minor leaf spotting, periods of shoot and foliage dieback to reshoot and whole tree death. Flowering was also impacted, particularly the Melaleuca species, M. nodosa and M. quinquenervia. The level of impact and the duration of infection differed significantly between species assessed. Post fire recovery of M. nodosa was severely impacted by myrtle rust with repeated infection resulting in dieback, reduced flowering and death, particularly the small tree form. Only a few trees within the sites assessed produced multiple flowers/seed capsules. The influence of this reduced flowering rate on pollination processes is unknown as is the viability of seed produced on trees showing field tolerance.
While some site variation was observed when assessing the impact of A. psidii infection on fire affected M. quinquenervia, at all sites repeated infection resulted in dieback, reduced flowering and was associated with tree death. In some cases, A. psidii appeared to be the sole cause of tree death following repeated attack on the reshoots. The low numbers of trees producing flowers across the study sites appears alarming but in saying this, longer-term monitoring is required to see if this changes over time.
While the study identified many susceptible individuals within the species of Melaleuca assessed, it also identified individuals showing field resistance, producing flower and seed. Perhaps, this provides an opportunity to selectively collect germplasm for propagation and use in regeneration plantings and long-term conservation.
The Progress Report can be found here, including lots of great images on the impact of myrtle rust on post-fire recovery of native species.