Some of Aotearoa New Zealand’s most iconic native trees - including pōhutukawa and rātā - could be at risk from a group of two aggressive fungal pathogens Ceratocystis lukiohia and C. huliohia, if they reached the country. The pathogens were first identified on the island of Hawai‘i in 2014, with widespread death of Metrosideros polymorphia or 'Ohi'a lehua trees.
These two new pathogens are collectively called Rapid Ohia Death (ROD) and has now spread to other islands in Hawaii.
Ceratocystis includes several species capable of causing death to trees and crops, and ROD has, and continues to devastate native ʻōhiʻa forests in Hawai‘i. 'Ohi'a is closely related to pōhutukawa and rātā in the Myrtaceae family. The vectors and pathways for spread of ROD in Hawaii include bark beetles, humans, animals like cows and pigs, contaminated equipment, footwear, and dispersal of pathogen spores on the wind.
To get ahead of this potential threat, AgResearch is contributing to a research programme funded via B3 (Better Border Biosecurity) in partnership with Plant and Food Research and Scion.
AgResearch scientist Mark McNeill says the work is focused on assessing how these pathogens might enter Aotearoa New Zealand, identifying which native and productive plants could be vulnerable, and preparing detection and response tools, are also areas of research.
“There’s real concern about the damage Ceratocystis could do here—particularly to taonga species like pōhutukawa and rātā, which hold deep cultural and ecological importance,” says Mark.
“We want to understand the most likely pathways for entry, how they could spread, and how best to respond if they’re detected.”
Mark’s research colleague and collaborator Waipaina Awarau said as a precaution the research team is supporting seed collection and storage for at-risk native Myrtaceae. In partnership with hapū, seeds of pōhutukawa and rātā have been collected from key sites using culturally appropriate protocols.
Some of these seeds were sent under strict biosecurity conditions to colleagues at the United States Department of Agriculture (USDA) in Hilo, Hawai'i Island, where they were germinated and grown in high-security containment. This allowed scientists to safely expose seedlings to known Ceratocystis strains that are not present in Aotearoa New Zealand and observe their effects.
The offshore collaboration with the USDA is providing valuable data on how native species may respond to infection.
“This could be our next Myrtle rust,” says Waipaina. “We’re mapping its spread across the Pacific, and it’s a big concern. The various hapū we’ve been working with have been very receptive.
"The hapū we work with have been open and supportive. While each hapū holds their own tikanga, we maintain respectful relationships guided by protocols and information to support a shared understanding. Mātauranga Māori is place-based and is central to our approach. Ultimately, hapū are the kaitieki and decision-makers when it comes to protecting these taonga species."
While only one strain of Ceratocystis is currently present in New Zealand (affecting kūmara), related pathogens are of high international concern. Several are listed as "unwanted organisms" under New Zealand law, and the International Plant Protection Convention recognises the group as a major global risk.
“C. lukuohia, if it arrived here, could be devastating - not only ecologically but culturally,” Mark warns.
In addition to human-mediated pathways, other potential vectors are under investigation.
As part of the overall B3 project, AgResearch has set up traps in the Christchurch (pictured above), Hamilton and on the East Coast to find out which bark beetles are associated with Metrosideros. Our fellow CRIs Plant and Food Research and Scion are covering the rest of the country. In recent trapping at Christchurch Botanic Gardens, Mark recorded high populations of bark beetles, especially an ambrosia beetle called fruit-tree pinhole borer (or Xyleborinus saxesenii), closely associated with pōhutukawa and rātā. This beetle is known to be a key vector of ROD in Hawaii. Although no beetles have yet tested positive for Ceratocystis, their presence represents a plausible transmission risk.
Other risk factors unique to New Zealand include browsing animals such as possums and deer. These species can damage the roots and trunks of trees and create entry points for infection.
Community connection and Māori engagement remain at the heart of the programme.
“The support from mana whenua has been critical,” says Mark. “When we talk about the risk of losing rātā or pōhutukawa, there’s deep understanding. This is not just a Māori loss—the pōhutukawa is iconic to all New Zealanders.”
Mark and Waipaina have presented their research at the South Pacific Research Conference in Tonga, highlighting both the technical and cultural aspects of their work.
Left to right: Sulav Paudel (AgResearch), a delegate from PNG Forest Research, Mark McNeill (AgResearch) and Waipaina Awarau (AgResearch) at a recent Pacific biosecurity conference in Tonga. The event brought together researchers and officials from across the region to strengthen collaboration on biosecurity challenges.
“While the direct risk from Hawai‘i is well understood, we need to stay alert to secondary invasion routes—such as via Tonga or New Caledonia,” Mark says. “It’s not inevitable the pathogen will arrive, but vigilance is key.”
The ROD project has links with mark’s earlier B3 work on sentinel plants, linking with botanic gardens and arboreta across Australia, the UK, Europe, and the US. The research has provided Aotearoa New Zealand’s access to an global intelligence network, providing foresight into emerging threats and gives the country a head-start in biosecurity preparedness.
“Our Sentinel Plants project, run in collaboration with Botanic Gardens Conservation International and Kew Gardens, is helping formalise a UK-based monitoring network,” Mark explains. “If a new pest or pathogen starts affecting our native species overseas, we’ll know early. It’s a global early warning system. By connecting global insights with local action, we’re positioning New Zealand to respond proactively to a threat that could severely impact our iconic trees, ecosystems, and cultural heritage.”
