Botanic Gardens Trust, Sydney, Australia

Fungal leaf spot on eucalypts

Dr Brett Summerell – Director, Science and Public Programs

Like all plants the eucalypts (Eucalyptus, Corymbia and Angophora species) are affected by a range of plant pathogens. While root rot diseases are the most important diseases there are an enormous number of species of fungi that cause leaf spot diseases on most of the species of eucalypts. Over the past 5 years Royal Botanic Gardens & Domain Trust scientists have been working with Professor Pedro Crous at the Centraalbureau voor Schimmelcultures in the Netherlands to isolate and describe the species of fungi that cause these diseases. Most of these species are members of the genus Mycosphaerella or are closely related to this genus and it is remarkable the number of new species that have been discovered from different species of eucalypts. While it might be expected that there would only be a few species causing disease across the majority of eucalypts there seems to be a very close association between particular species of fungi and each species of eucalypt indicating a close evolutionary relationship between the plant and the fungus, probably as a result of co-evolution of the host plant and fungus.  

Documenting the fungi causing these diseases is extremely important. The diseases are especially important during the establishment of young plants and consequently are very important in forestry and rehabilitation programs. The increasing use of eucalypts in overseas countries has resulted in new associations between pathogens and some species of eucalypts, so for biosecurity it is essential to have a full knowledge of the pathogens that occur both in Australia and overseas. Finally, because these diseases are so sensitive to environmental variations, knowledge of the species is essential to understand changes that may occur as a result of climate change. Hiding from the heat in the caves in Chillagoe after collecting leaf spot fungi from Cairns to Chillagoe. The species highlighted in the photographs is a new fungal species, Cibiessia nontigens, isolated from Eucalyptus terteticornis, from the front yard of Dr Brett Summerell, one of the Trust scientists working on this project. This highlights how little we know about the diversity of species of fungi in Australia.