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

Abstract

Exotic fungal pathogens can substantially affect individuals and populations of susceptible native plant species, potentially resulting in changes in community structure and composition. Austropuccinia psidii (myrtle rust) is a pathogenic fungus native to South America that affects species in the plant family Myrtaceae. The pathogen was introduced accidentally to Australia and first detected in NSW in April 2010. Ecological impacts have been poorly studied in the native range of A. psidii and even less in its Australian introduced range. In order to assess the potential impact of A. psidii on coastal swamp woodland, two glasshouse experiments were conducted using three co-occurring species: Melaleuca quinquenervia, Leptospermum laevigatum and Baeckea linifolia. Plants of each species were grown individually (Experiment 1) and in mixed species assemblages (Experiment 2), with half inoculated with A. psidii and the other half remaining as controls. Infection level was assessed and impact on seedling survival and growth recorded. In both experiments L. laevigatum and M. quinquenervia seedlings were heavily infected and showed high degrees of susceptibility with negative effects on growth (height, biomass and number of leaves). In contrast, no B. linifolia seedling presented visible symptoms of disease, although seedlings showed reduced growth. Melaleuca quinquenervia seedlings had greater infection levels and suffered greater growth reductions than L. laevigatum in both experiments. However, there was no significant difference in the relative abundance of the three species in the mixed-species experiment. This study provides a better understanding of the potential impacts of A. psidii in this vegetation community and has significant implications for the conservation and management of Australian Myrtaceae-dominated plant communities generally.

Plant architecture, growth and biomass allocation effects of the invasive pathogen myrtle rust (Austropuccinia psidii) on Australian Myrtaceae species after fire

“…It has been suggested that the between‐species variation may be a result of different susceptibilities, while the within‐species variation may be explained by differing climatic conditions, resource availability and number of re‐infection events between studies (Smith ). Also consistent with our results, Fernandez Winzer et al () reported that branching was not altered by A. psidii after a single inoculation event in the three coastal woodland species mentioned above. Because of this, it can be suggested that increased branching may only occur after successive reinfections of seedlings (that is, over a longer time period) or in plants at more advanced stages in their development (Fernandez Winzer et al ).…”

“…Also consistent with our results, Fernandez Winzer et al () reported that branching was not altered by A. psidii after a single inoculation event in the three coastal woodland species mentioned above. Because of this, it can be suggested that increased branching may only occur after successive reinfections of seedlings (that is, over a longer time period) or in plants at more advanced stages in their development (Fernandez Winzer et al ).…”

“…For some of our study species, we found that A. psidii reduced the maximum height of the plants, but did not increase branching, in terms of either stem number or biomass. Fernandez Winzer et al () reported similar decreases in the height of infected plants for three coastal woodland species. Interestingly, these species showed considerable between‐ and within‐species variation ( B. linifolia : 15–30%; L. laevigatum : 15–30%; M. quinquenervia : 38–45%) in their height decreases, consistent with our study species (between: 0–25%, within: 7–14%).…”

“…Thereafter, plants from the different treatments were kept in two separate glasshouses (experimental units), with the same climatic conditions as described previously, to ensure no cross‐contamination occurred. Ideally, we would have used at least two glasshouses per treatment (see Fernandez Winzer et al ) or individual structures within each glasshouse to avoid pseudoreplication (e.g. Yahdjian & Sala ; Rondanini et al ).…”

Biases in the metabarcoding of plant pathogens using rust fungi as a model system

“…Rust fungi (Pucciniales) constitute one of the largest groups of plant pathogens, with about 7,800 described species (Helfer, ), and some rust species can have large economic and ecological impacts. For example, myrtle rust ( Austropuccinia psidii ) is currently decimating a wide range of Myrtaceae around the world (Fernandez Winzer, Carnegie, Pegg, & Leishman, ; Glen, Alfenas, Zauza, Wingfield, & Mohammed, ), such as the endemic Eugenia koolauensis in Hawai‘i and the endemic Rhodamnia rubescens in native forests in Australia (Carnegie et al, ). Coffee leaf rust ( Hemileia vastatrix ) is substantially damaging Coffee plantations worldwide (Talhinhas et al, ).…”