Susceptibility of native New Zealand Myrtaceae to the South African strain of Austropuccinia psidii: A biosecurity threat

Abstract

Austropuccinia psidii, cause of myrtle rust, has spread globally where Myrtaceae occur. Multiple strains of A. psidii have been identified, including a unique strain found only in South Africa. The South African strain is a biosecurity concern for species of Myrtaceae worldwide. This is because preliminary testing of South African Myrtaceae suggests it could have a wide host range, and thus has the potential to be invasive. In this study, we assessed the ability of the South African strain to infect other species of Myrtaceae by testing the susceptibility of New Zealand provenance Myrtaceae. Seedlings of four native New Zealand Myrtaceae species (Metrosideros excelsa, Leptospermum scoparium, Kunzea robusta, and Kunzea linearis) were artificially inoculated in South Africa with a single‐uredinium isolate of the South African strain. Fourteen days after inoculation, uredinia, and in many cases telia, had developed on the young leaves and stems of all four host species, which led to shoot tip dieback in the more severe cases. When comparisons were made between the species, K. robusta was the least susceptible to the South African strain of A. psidii, while L. scoparium and M. excelsa were the most susceptible. While only a limited number of seed families were tested, only a small proportion of the seedlings showed resistance to infection by the South African strain. This preliminary testing highlights the potential invasive risk the South African strain poses to global Myrtaceae communities, including New Zealand Myrtaceae.

Ecological importance of the Myrtaceae in New Zealand's natural forests

“…The warm, oceanic climates of NZ are not only associated with a greater Myrtaceae importance, but also favour the spread of myrtle rust (Beresford et al, 2018; Narouei‐Khandan et al, 2020). After the myrtle rust incursion, a cautious conservation approach was taken where all NZ Myrtaceae were considered vulnerable to myrtle rust and listed with a threatened status (de Lange et al, 2018), although we now know the degree of vulnerability differs among species (Smith et al, 2020; Sutherland et al, 2020; Soewarto et al, 2021). Warmer areas have a higher abundance and richness of Myrtaceae, adding to concerns that myrtle rust may have significant impacts on the conservation of at‐risk species (Fensham & Radford‐Smith, 2021; McCarthy et al, 2021b) and the functional integrity of NZ ecosystems.…”

“…The unique combinations of functional traits, and substantial contributions to CWM functional traits by Myrtaceae compared to co‐occurring woody families in NZ forests and shrublands, highlights the potential impacts of Myrtaceae loss due to the spread of myrtle rust. However, the effect of myrtle rust on forest community composition and ecosystem processes cannot be definitively predicted yet, due to unknown differences among and within species in their susceptibility to the pathogen (Smith et al, 2020; Soewarto et al, 2021) and gaps in species level functional trait values for a range of NZ species. Modelling potential shifts in forest community structure and community‐level functional trait composition based on large‐scale, long‐term demographic studies allied with more comprehensive trait data that capture regional trait variation will improve our understanding of the functional roles of Myrtaceae, and the potential consequences of Myrtaceae loss in forest and shrubland ecosystems (Hill et al, 2019).…”

Approaches to Forecasting Damage by Invasive Forest Insects and Pathogens: A Cross-Assessment

“…An example where such assays can be misleading involves the pine wood genetic lineages and variants with different characteristics, and the diverse genotypes in natural pathogen and insect populations. For example, Meterosideros spp., native to New Zealand, are potentially threatened by the myrtle rust pathogen A. psidii, which has several races (Toome-Heller et al 2020, Soewarto et al 2021. Screening a diversity of Meterosideros and other Myrtaceae provenances to specific pathogen genotypes outside New Zealand can provide a robust estimate of the potential impact.…”

Early Detection of Myrtle Rust on Pōhutukawa Using Indices Derived from Hyperspectral and Thermal Imagery

“…Due to its impact, and the threat of invasion into new areas by strains currently restricted in range [13], biosecurity restrictions on the movement of Myrtaceae and infected Remote Sens. 2024, 16, 1050 2 of 27 plants are recommended.…”