Rapidly expanding host range for Puccinia psidii sensu lato in Australia

Abstract

A rust affecting Myrtaceae was recently detected in New South Wales, Australia. Based on urediniospore morphology and host range, it was identified as Uredo rangelii, a taxon regarded as a member of the eucalyptus/ guava rust (Puccinia psidii sensu lato) complex, although confusion currently surrounds its taxonomy. The exotic rust was given the common name of myrtle rust to distinguish it from eucalyptus/guava rust. The more recent discovery of teliospores in NSW that match those of P. psidii sensu stricto indicates the rust in Australia is a strain (with tonsured urediniospores) of P. psidii s.l. Outside Australia, P. psidii has a wide host range within Myrtaceae, being reported from 129 species in 33 genera, and is very damaging in South and Central America-including in eucalypt plantations in Brazil-the Caribbean and in Florida and Hawaii. To ascertain the potential threat to forestry in Australia posed by the introduced rust, we tested key forestry species, as well as key known hosts of eucalyptus/ guava rust, in artificial inoculation experiments. We showed that several species of Eucalyptus are susceptible (viz. E. pilularis, E. cloeziana, E. agglomerata and E. grandis), as is Melaleuca quinquenervia. Observations during testing revealed a lengthened latent period (from inoculation until pustule formation and eruption) of four to five weeks during winter. Here we also report on observations on new hosts from surveys in NSW under the emergency response that followed the detection of the exotic rust, and surveys in NSW and Queensland following the cessation of the emergency response. In Australia, P. psidii s.l. has currently been found on 107 host species in 30 genera during surveys, including species in Angophora, Asteromyrtus, Tristaniopsis, Ugni, Uromyrtus and Xanthostemon. Species under cultivation (in nurseries and gardens) that are severely affected include Gossia inophloia, Agonis flexuosa, Syzygium jambos and S. anisatum while species that are severely damaged in native bushland include Rhodamnia rubescens, Rhodomyrtus psidioides, Choricarpia leptopetala and Melaleuca quinquenervia.

A unique genotype of the rust pathogen, Puccinia psidii, on Myrtaceae in South Africa

“…In Hawaii and Australia, by contrast, a single genotype that infects multiple hosts occurs (Carnegie and Lidbetter 2012;Graça et al 2013;Loope 2010;Sandhu et al 2015;Zhong et al 2011), indicative of an introduced pathogen. Additionally, the genetic diversity of P. psidii in Brazil is reported to be much higher than that in Australia and Hawaii Machado et al 2015).…”

Impacts of the invasive fungusAustropuccinia psidii(myrtle rust) on three Australian Myrtaceae species of coastal swamp woodland

“…Very little is known about the current level of impact of A. psidii on native species populations or the long term impacts A. psidii may have on species survival and plant communities in Australia (Carnegie & Cooper 2011;Carnegie & Lidbetter 2012).…”

“…Variability in susceptibility and impact of A. psidii has been identified for some Myrtaceae, for example Melaleuca quinquenervia and several Eucalyptus species (Grac ßa et al 2011;Pegg et al 2014b). Some of the most susceptible species are the rainforest species of the east coast -Rhodamnia rubescens and Rhodomyrtus psidioides -and the wetland keystone species M. quinquenervia (Carnegie & Lidbetter 2012;Carnegie et al 2016). Keystone species are especially important given that they can be ecological engineers, provide ecological services and be a source of food and shelter for many organisms (Westaway 2016).…”

“…Defoliation and seedling dieback are observed symptoms in this species as well as reduced flower production and death (Pegg et al 2014a). Individuals of M. quinquenervia are now recorded as severely affected by A. psidii in Australian eastern native woodlands (Carnegie & Cooper 2011;Carnegie & Lidbetter 2012). Variability exists in the susceptibility within the species, with some individuals presenting resistance (Rayamajhi et al 2010).…”

“…Austropuccinia psidii is commonly called 'myrtle rust', although other common names are 'eucalyptus rust' and 'guava rust'. Austropuccinia psidii exclusively attacks species of the Myrtaceae family (Coutinho et al 1998;Glen et al 2007), infecting a wide range of species, greater than most of the known rusts (Grgurinovic et al 2006;Carnegie & Lidbetter 2012). Austropuccinia psidii infects the young growing tissues of plants such as newly developed leaves, floral buds, fruits and coppice (Coutinho et al 1998;Glen et al 2007).…”