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Exciting developments in Beyond Myrtle Rust research

May 2022 marks the five-year anniversary of the arrival of myrtle rust in Aotearoa New Zealand. The Beyond Myrtle Rust research programme began in 2018, just over a year into the incursion. The programme has built on pre-incursion research from both Australia and New Zealand and has provided a solid foundation of fundamental knowledge about the disease. We spoke with Mahajabeen Padamsee, programme leader at Manaaki Whenua – Landcare Research, about new research developments that she’s excited about.

Reproduction may be driven by microclimates

Myrtle rust is caused by the fungal pathogen Austropuccinia psidii. The fungus usually reproduces asexually (i.e., it clones itself) but it is capable of sexual reproduction.

Until recently, researchers weren’t sure what caused the fungus to shift from asexual reproduction to sexual reproduction. However, new data is being analyzed that may shed light on the cause of that shift.

“It will be interesting to see if temperature and microclimates play a role in whether the fungus reproduces sexually or asexually,” says Padamsee.

Researchers are hoping to use this information to understand the likelihood of increased genetic variation in the fungus, which would allow it to adapt to local conditions.


Refined understanding of impacts to our ecosystems

Before the arrival of myrtle rust, not much was known about our Myrtaceae.

“People know some of the plants, like pōhutukawa and mānuka especially, but we really didn’t have any idea about the associations of our plants with other organisms,” says Padamsee.

Myrtaceae, like many plant families, are associated with a variety of microorganisms and fungi.

“Our research is enhancing our knowledge of what relies on these plants,” says Padamsee. “The inter-species interactions that surround Myrtaceae are so much more complex that we thought.”

Another finding is that the impact of disease varies among species and across the landscape. While ramarama (Lophomyrtus bullata) in the East Cape have already been hit hard, the disease is progressing more slowly on other plants and on ramarama in other areas.

“It gives us some hope that once we do find ways to preserve the trees or control the severity of the disease that we might have enough time to change the trajectory of the disease,” says Padamsee.


Novel ways to protect plants

Beyond Myrtle Rust is at the bleeding edge of developing ways to protect our Myrtaceae. From genetics to bioengineering, novel approaches are being employed to find ways to strengthen our plants and weaken the disease.

One of these approaches is in the field of native biocontrol agents. Researchers are on the hunt for microorganisms that live in partnership with plants that could help hosts survive the spread of myrtle rust.

“One of our researchers has been able to isolate a few species of bacteria and fungi that may have an antagonistic effect on the disease,” says Padamsee.

In a recent experiment, the researcher has attempted to transfer the microbiome of older leaves to younger leaves.

“Myrtle rust infects new plant growth, especially new leaves,” says Padamsee. “When new leaves are produced, they don’t have much of a microbiome.”

As leaves age, they acquire bacteria and fungi from the environment and from the plant.

“Providing new growth with a more mature, more developed microbiome could really affect the trajectory of this disease,” says Padamsee.


Continued collaboration

Padamsee highlights that the strengths of the programme are derived from the many collaborations and organizations that support it.

“That’s the real strength of myrtle rust research in New Zealand. We’re all working towards the collective good.”

Alby Marsh (Māori Relationship Advisor, Te Raranga Ahumāra at Plant & Food Research) with the help of other programmes has been working to empower mana whenua by giving them tools to protect plants in their own rohe. Marsh also works to build linkages with communities in the Pacific Islands.

“We’re hoping people will use controls that they may have developed over the centuries for other diseases and apply those controls to myrtle rust,” says Padamsee.

Beyond Myrtle Rust gives back to the local and global community by hosting a webinar series featuring myrtle rust research taking place across the globe.

“Most of the webinars get 100-150 people actively participating and if you’ve missed one, they are all available on the webinar link,” says Padamsee.

Padamsee believes that engaging with a wide variety of people, from local gardeners to international researchers, is the best way to protect our plants from disease.

“The thing about myrtle rust is you’re never going to cure it,” says Padamsee. “But these collaborations are our best shot at controlling the disease, so these plants have the best chance of survival.”