31 May 2022

Media release from Bioheritage National Science Challenge

Background

Myrtle rust, caused by the fungal pathogen Austropuccinia psidii, was first detected on mainland New Zealand in May 2017, having arrived on the wind from Australia. Over the last five years the disease has spread across much of the North Island and the top parts of the South Island. It has been found as far afield as Greymouth, Christchurch and, most recently, the Chatham Islands.

Since arriving in New Zealand, 17 of our 27 Myrtaceae have been confirmed as being susceptible. Of these, our Lophomyrtus species (ramarama and rohutu) as well as swamp maire/maire tawake have been particularly hard hit.

Research

The initial response to the myrtle rust incursion was to eliminate the pathogen. However, with the constant threat of reintroduction of spores on the wind, this proved impossible. After a year, government resources turned to research. In the last five years there have been many milestones that kiwi researchers have achieved or contributed to.

We have identified susceptibility and resistance of our taonga species: This was some of the earliest work on myrtle rust in the New Zealand context. Key Myrtaceae species were sent to Australia to test the susceptibility of our plants. This revealed that many of our species would be susceptible to myrtle rust and gave an early indication of the higher susceptibility of our Lophomyrtus species. Susceptibility has continued to be studied in the lab and the field and has highlighted the threat of myrtle rust on ramarama and swamp maire.  Also, researchers have identified susceptibility of our native Myrtaceae to strains of the disease that are not yet present in New Zealand.
Key organisations: Plant & Food Research, Scion, Better Border Biosecurity (B3), Plant Health Australia, Queensland Department of Agriculture and Fisheries, New South Wales Department of Primary Industries–Forestry, Manaaki Whenua Landcare Research, The University of the Sunshine Coast, Ngā Rākau Taketake.

The pathogen’s genome was assembled: In 2020, a trans-Tasman group of scientists sequenced the genome of Austropuccinia psidii, the fungus responsible for the disease myrtle rust. New Zealand and Australian researchers have been using the genome to understand how pathogen genes and which host genes are interacting at the earliest points in the infection process. For example, researchers have been able to express and purify the first Austropuccinia psidii effector protein. Work such as this will progress our understanding of how myrtle rust occurs and help find new strategies to stop its spread.
Key organisations: Plant & Food Research, University of Sydney, Australian National University, Agriculture Victoria Department of Jobs, Precincts and Regions, Queensland Department of Agriculture and Fisheries, University of Canterbury

Climate models now inform disease predictions: Modeling has been applied to myrtle rust in several ways.  A suite of tools and information to help plant nurseries manage myrtle rust outbreaks has been released by New Zealand Plant Producers Inc (NZPPI). This suite includes a beta version of the Myrtle Rust Climate Model app to enable plant producers to anticipate when myrtle rust is most likely to develop in their nurseries and so implement prevention practices. Modeling activities have also revealed where current climate patterns may be inhospitable for myrtle rust. These areas may provide a natural refuge from disease.
Key organisations: NZPPI, Plant and Food Research, NIWA

Novel approaches to finding solutions have been developed: Researchers across the board have used modern technology and innovative approaches to learn more about our Myrtaceae, the disease, and the ecosystems them both occupy. For example, PhD student Sarah Sale is using lab-on-a-chip technology to test the forces exerted by the fungus. The lab-on-a-chip platform can be used to measure the impacts of different microorganisms, bioactive compounds or potential fungicides on the fungus and see how they impact growth and penetrative force.
Key organisations: University of Canterbury, Plant and Food Research, MBIE. Funding for Sarah’s project is primarily from the MBIE Endeavour programme, Beyond Myrtle Rust, with additional funding from the MacDiarmid Institute, Rutherford Discovery Fellowship, BIC and Science for Technological Innovations.

Social science tools have shed light on how people engage with myrtle rust: From research into the uptake of the iNaturalist platform to the exploration of creatively engaging the public in myrtle rust, there have been numerous efforts to bring society into the biosecurity equation.
Key organisations: Beyond Myrtle Rust, Ngā Rākau Taketake

Future work

While much of the research above has tangible results already, there is much more work to be done. One piece of research that is still underway is the identification of native microbes in plants and soil that may help in the fight against myrtle rust.

It is important to note that Ngā Rākau Taketake funding runs out this year and the Beyond Myrtle Rust programme ends in one year’s time. Without additional funds, this work will be halted well before we have a complete picture of the damage that could be caused by this disease and without knowing what preventative tools we could have developed had time and funding allowed. This is a critical moment in myrtle rust research and continuing to understand this disease is critical for protecting our many taonga Myrtaceae. This pathogen has caused the functional extinction of myrtaceace species over ranges greater than 1,000 km on the East Coast of Australia as well as localised extinction of ramarama in the Aotearoa.