25 Oct 2018

Myrtle rust research

From Our Changing World, 9:06 pm on 25 October 2018

Drone-mounted cameras to detect dying trees from the air.

Screening thousands of seedlings to determine which succumb and which might hold the genetic code for resistance.

Better ways to save seeds.

When it comes to myrtle rust, researchers are looking at anything and everything that might help in the fight to keep New Zealand plants and ecosystems healthy.

Seedlings from species such as pohutukawa are being tested to see how susceptible - or resistant - they are to myrtle rust.

Seedlings from species such as pohutukawa are being tested to see how susceptible - or resistant - they are to myrtle rust. Photo: RNZ / Alison Ballance

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In late May 2017, myrtle rust was detected for the first time on mainland New Zealand. Tiny orange spores of this invasive plant fungi had blown across from Australia.

The Ministry for Primary Industries responded by trying to control the outbreak. This involved many people physically looking for the small distinctive rust-coloured pustules that form on the leaves of infected myrtle plants.

It was time-consuming and labour intensive, and although tens of thousands of at-risk plants were checked, millions of hectares of native bush remained unchecked.

Lower and upper surface of same pōhutukawa (Metrosideros) leaf. Red/brown lesions with pustules on top; orange/yellow pustules underneath.

Lower and upper surface of same pōhutukawa (Metrosideros) leaf. Red/brown lesions with pustules on top; orange/yellow pustules underneath. Photo: MPI

In the months following the first detection, infected plants were found across the North Island and the top of the South Island.

By September 2018, 776 infected properties had been found, including five sites on conservation land. This number continues to rise, especially during warmer humid months.

The Department of Conservation has been urgently collecting seeds from the 40-or-so native myrtle species, including manuka, to put in a seed bank as an insurance policy.

In April 2018, MPI admitted that efforts to control myrtle rust had failed. The new focus was to be community management and research into the disease, which continues to spread.

Jules Freeman, Julia Soewarto, Becky Ganley and Katrin Webb are carrying out research into the impact of myrtle rust on native plants.

Jules Freeman, Julia Soewarto, Becky Ganley and Katrin Webb are carrying out research into the impact of myrtle rust on native plants. Photo: RNZ / Alison Ballance

Eyes in the sky

Scion is one of a number of organisations collaborating on better understanding myrtle rust and its future impacts.

One of their goals is to develop better ways of detecting myrtle rust, both at the level of individual plants and at a landscape scale.

“It’s always a challenge because myrtle rust is hard to spot,” says Katrin Webb.

This research is in its early phases, but the researchers are beginning to think about new remote sensing methods as well as novel sensors and cameras, that could be deployed by unmanned aerial vehicles (UAVs). This would allow large areas of forest to be monitored.

Becky Ganley says that surveillance is about more than just determining if the pathogen is present. “So you’ll pick up the dieback which we expect to see in a few years, so that’s the health monitoring that goes on.”

“Are we losing tracts of pohutukawa or ramarama? Or are the forests actually quite healthy?”

Seedlings of manuka, ramarama and pohutukawa (pictured) are being exposed to myrtle rust in the lab to see if they succumb to the disease.

Seedlings of manuka, ramarama and pohutukawa (pictured) are being exposed to myrtle rust in the lab to see if they succumb to the disease. Photo: RNZ / Alison Ballance

The search for resistance

Becky says that a key focus of Scion’s research is looking at the susceptibility of native Myrtaceae species to myrtle rust.

Researchers from Scion and its collaborators, such as Plant and Food Research and Manaaki Whenua Landcare Research have gathered seeds from a range of native myrtle species such as manuka, pohutukawa and ramarama. Key commercial species such as feijoa and eucalyptus are also being tested.

Seeds were collected at different sites around the country. This means the scientists can test different genetic stocks that might differ in how susceptible they are to the disease.

The team is hoping to find some variants that are resistant to myrtle rust. Once these are identified, geneticists can look for genes that might control this resistance.

The actual lab testing can’t take place in New Zealand, as the rust is still considered to be an unwanted organism.

The New Zealand researchers have sent seeds to Australia and South Africa, where they can be germinated and then artificially exposed to the pathogen.

Australia has the same myrtle rust strain as New Zealand, while South Africa has a different strain. The question is whether these strains have the same impact on plants.

The plan is to also send seeds to Uruguay, to test against another strain of the disease.

“So at the end of it we’ll have this picture of how resilient this material will be against at least three different strains of the disease,” says Becky.

Back in New Zealand, seedlings raised from the same batches of seeds will be put out into the wild to see if they naturally succumb to myrtle rust, and whether rates of infection vary at different locations.

Low seed germination rates

Becky says they have been surprised and a little alarmed at the low germination rate of the native myrtle species.

“This is quite concerning when you think about the ecological impacts of myrtle rust,” says Becky. “So if it’s going to be hit by a pathogen, and it has a low germination rate, that could be a big issue for the future.”

More research

Manaaki Whenua Landcare Research has just received a five-year $13-million research grant from the Ministry of Business, Innovation and Employment’s 2018 Endeavour Fund for “Beyond myrtle rust: Next-generation tools to 'engineer' forest ecosystem resilience to plant pathogens.”

Find out more about myrtle rust

Listen to the full podcast to hear about the impact of myrtle rust in New Caledonia, and to hear about exciting new genetic research being used in the search for genes that influence resistance.

Check out Our Changing World’s feature on myrtle rust to learn about the disease, and hear about its impacts in Hawaii, Australia and on New Zealand’s Raoul Island.