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.
Highlights
Rust fungi are among the most important plant pathogens worldwide [1]
No visible symptoms were observed on four taxa inoculated with the rust: Eucalyptus grandis6camaldulensis, E. moluccana, Lophostemon confertus and Sannantha angusta (Tables 1, S1)
While many rust fungi have a host range restricted to a single plant species, there are some, such as Puccinia coronata [36], Phakopsora pachyrhizi [37] and Uromyces striatus [38], that infect a wide range of different plant species within a family
Summary
Rust fungi are among the most important plant pathogens worldwide [1]. They can cause severe damage to plants that considerably reduces biomass accumulation and reproduction. Puccinia psidii s.l. has been reported to cause severe damage in some years on Pimenta dioica (allspice) in Jamaica [22], Eucalyptus grandis [23] and Psidium guajava (guava) [24] in Brazil, Syzygium jambos (rose apple) in Hawaii [25] and Melaleuca quinquenervia in Florida [26,27] The implications of such a pathogen incursion in Australia are far-reaching because members of the family Myrtaceae are widespread across the continent and are often major components of natural plant communities [28]. This family includes the major genera Eucalyptus, Corymbia, Leptospermum, Melaleuca and Syzygium [29], all of which have been previously recorded as hosts for the disease with the exception of Leptospermum
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