Investigating the Host-Range of the Rust Fungus Puccinia psidii sensu lato across Tribes of the Family Myrtaceae Present in Australia

Abstract

The exotic rust fungus Puccinia psidii sensu lato was first detected in Australia in April 2010. This study aimed to determine the host-range potential of this accession of the rust by testing its pathogenicity on plants of 122 taxa, representative of the 15 tribes of the subfamily Myrtoideae in the family Myrtaceae. Each taxon was tested in two separate trials (unless indicated otherwise) that comprised up to five replicates per taxon and six replicates of a positive control (Syzygium jambos). No visible symptoms were observed on the following four taxa in either trial: Eucalyptus grandis×camaldulensis, E. moluccana, Lophostemon confertus and Sannantha angusta. Only small chlorotic or necrotic flecks without any uredinia (rust fruiting bodies) were observed on inoculated leaves of seven other taxa (Acca sellowiana, Corymbia calophylla ‘Rosea’, Lophostemon suaveolens, Psidium cattleyanum, P. guajava ‘Hawaiian’ and ‘Indian’, Syzygium unipunctatum). Fully-developed uredinia were observed on all replicates across both trials of 28 taxa from 8 tribes belonging to the following 17 genera: Agonis, Austromyrtus, Beaufortia, Callistemon, Calothamnus, Chamelaucium, Darwinia, Eucalyptus, Gossia, Kunzea, Leptospermum, Melaleuca, Metrosideros, Syzygium, Thryptomene, Tristania, Verticordia. In contrast, the remaining 83 taxa inoculated, including the majority of Corymbia and Eucalyptus species, developed a broad range of symptoms, often across the full spectrum, from fully-developed uredinia to no visible symptoms. These results were encouraging as they indicate that some levels of genetic resistance to the rust possibly exist in these taxa. Overall, our results indicated no apparent association between the presence or absence of disease symptoms and the phylogenetic relatedness of taxa. It is most likely that the majority of the thousands of Myrtaceae species found in Australia have the potential to become infected to some degree by the rust, although this wide host range may not be fully realized in the field.

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

“…This suggests that it may have the potential to infect many other hosts in the sub-family Myrtoideae, including commercially important eucalypts and P. guajava. Morin et al (2012), conducted extensive host range studies of Australian Myrtaceae and concluded that there is no apparent association between the presence or absence of P.…”

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

“…Due to its halophilic nature it is usually found on sandy soils. This species has been tested and found to be susceptible to A. psidii, showing high variability within the species ranging from resistant individuals to very susceptible ones (Morin et al 2012). Shoots can be infected as well as leaves and a reduction in flower production has been observed as a result of repeated infection (Dr G. Pegg 2015, pers.…”

The genetic basis of foliar terpene yield: Implications for breeding and profitability of Australian essential oil crops

“…However, there remain significant challenges such as maintaining yields in resistant material. Under particular threat is the tea tree oil industry because Melaleuca alternifolia shows high levels of susceptibility to the rust (Morin et al 2012). Although the full effect of myrtle rust infection is not yet known, it has the potential to cause enormous losses.…”