Te Herenga Waka-Victoria University of Wellington has won approval for a new DNA test to detect Phytophthora agathidicida in soil, the pathogen that causes kauri dieback in New Zealand's native kauri trees.
Known as the oDNA assay, the test was developed by a university research team led by Associate Professor Monica Gerth. It is designed to provide a faster, lower-cost way to identify the pathogen and, with an added laboratory step, measure how much is present in a soil sample.
Phytophthora agathidicida, often shortened to PA, is a soil-borne pathogen that infects kauri through their roots. With no cure available, controlling the disease depends on early detection and steps to reduce spread through contaminated soil carried on footwear, equipment, vehicles, and animals.
Unlike existing methods, which require the pathogen to be grown in a laboratory before testing, the new assay isolates oospores directly from soil. These oospores are a durable survival stage of the pathogen and can remain in soil for years after infected roots die back.
Researchers said extracting DNA from the spores takes about a day, after which detection and quantification can be completed within a few hours. This allows results to be delivered sooner than established testing approaches used in kauri protection work.
Jade Palmer developed the first versions of the test during her PhD, while Emily Hocking led in-house refinement and compiled blinded samples used in validation. The work began in 2021 and has now reached a stage where the test can be used more widely.
Independent review
Before approval for wider use, Tiakina Kauri commissioned an independent review involving international experts and testing in several laboratories using blinded soil samples. The findings showed the test correctly identified known positive samples and produced no false positives.
The review examined whether the test could be applied consistently across the kauri protection programme. Tiakina Kauri, the management agency within Biosecurity New Zealand responsible for the National PA Pest Management Plan, said the approval adds another diagnostic tool to national biosecurity work.
Field testing also formed part of the development process. Earlier versions of the assay were trialled and refined with Te Roroa in Northland, where the iwi's Kauri Ora team tested prototypes with the aim of creating a version robust enough to run in its own laboratory.
Associate Professor Gerth said the need for an accessible test has long been clear. "With no cure currently available, protecting kauri depends on finding the pathogen early and taking action to stop its spread. Our new test makes monitoring kauri health easier than ever, offering a simple, rapid, and affordable testing option," she said.
The assay targets the part of the pathogen's lifecycle most closely linked to long-term persistence in soil. "As kauri roots die back from infection, the pathogen releases oospores into the soil-tough, long-lived survival spores that can persist for years and spread the disease further," Gerth said.
She added: "Because oospores are central to how PA spreads, they're also an ideal target for detection. The new test, known as the oDNA (oospore DNA) assay, isolates these oospores directly from soil samples, rather than requiring the pathogen to be grown in a laboratory first, as current methods do."
Practical use
The assay can be used as a basic presence-or-absence test or as a quantitative tool. That second use could help land managers and researchers monitor whether interventions are reducing pathogen levels over time.
"In its simplest form, our test provides a quick and reliable yes-or-no answer on whether PA is present in the soil. With an additional step in the lab, it also gives us quantitative data on how much of the pathogen is there, allowing us to track disease progression and monitor whether management actions are working. That's something that hasn't been available before," Palmer said.
For Te Roroa, access to reliable diagnostics has been a practical issue in local disease management. "One of the biggest challenges in managing this soil pathogen is having access to accurate, reliable diagnostic testing," said Taoho Patuawa, Te Roroa Kauri Ora Science and Innovation Lead.
He added: "This assay provides a rapid and highly specific tool for detecting Phytophthora agathidicida in soil, helping identify new incursions while also giving us greater confidence in monitoring the effectiveness of management interventions designed to protect kauri."
Tiakina Kauri said surveillance, including soil sampling and tree health assessments, informs both management decisions and enforcement of protective rules under the national pest management plan. Some kauri forests remain free of PA, making early detection and containment an important part of preserving those areas.
Mike Hogg, Tiakina Kauri Manager, said the approval reflects an effort to adopt new diagnostic approaches while maintaining robust processes for wider management use. "Our surveillance work, including soil sampling and kauri health assessments, helps to inform management and legislation to protect kauri. To date, PA has not been detected in all kauri forests, and ensuring the survival of kauri depends on all of us taking action to stop it spreading. The new test will help us achieve that," he said.
The test is now available directly through the university team, which is also supporting community-based laboratories, including with Te Roroa iwi. "Mana whenua, councils, and community groups have been asking for a test that's faster and more affordable, without compromising on reliability. We're proud to deliver a rigorously validated, highly sensitive test that does exactly that. We're excited to now put it into action to help protect kauri health," Gerth said.