Stopping kauri dieback in its tracks
Leader: Dr Monica Gerth, Victoria University
‘A biosecurity team of 4.7 million’ is the first of five strategic direction statements in the draft Biosecurity 2025 Direction Statement for New Zealand.
The National Science Challenge for NZ’s Biological Heritage is funding two new programmes, including this one, to enlist the public’s help in dealing with the very worrying disease killing our kauri trees.
Selected native plant extracts may be able to attract and kill the spores of Phytophthora agathidicida – the pathogen causing kauri dieback, according to researchers.
Victoria University of Wellington researcher Dr Monica Gerth is leading a BioHeritage Challenge project that aims to find disease-fighting science solutions by combining a biochemical approach with Mātauranga Māori (Māori knowledge).
A major way kauri dieback disease spreads is by free swimming zoospores in soil. With their long flagella and rudders, these spores can swim through water-logged soil at amazing speeds of up to 0.7 metres per hour. Once they find their target kauri roots, they encyst and initiate an infection that eventually starves the tree to death.
The question at the heart of their research is: what is it about kauri roots that attracts the zoospores? These spores seem to find the smell of kauri as alluring as coffee is to humans. Dr Gerth and her team will identify the chemical signals from kauri and other native plants that attract, repel or generally disrupt the 'homing' ability of zoospores - and then, in collaboration with Dr. Amanda Black (Lincoln University), they will test the effect of these compounds on the movement of zoospores through soils.
The overall goal of their research is to provide new tools to protect New Zealand's kauri forests. For instance, zoospore repellents could potentially be applied around kauri trees to deter the spores. Long term, the general principles of their research may also be applied to the battle against other plant pathogens.
Understanding the interactions between P. agathidicida and its host plant kauri is an essential step in developing disease control strategies. The overall goal of this research is to prevent P. agathidicida from spreading to uninfected trees. Our hypothesis is that infection can be prevented by interfering with the chemotactic responses of this pathogen. Some Phytophthora species, such as the pine pathogen P. pluvialis, produce airborne spores that infect leaves. In contrast, P. agathidicida and other root rot Phytophthora use motile zoospores to infect the roots of their hosts. Phytophthora zoospores can travel great distances in waterlogged soil, and once they have located a host’s root, they encyst on the surface to initiate infection. Although chemotaxis is clearly an important part of Phytophthora pathogenesis (and a prerequisite for infection by some species), this behaviour in P. agathidicida remains almost completely uncharacterised. Here, we will investigate critical aspects of P. agathidicida chemotaxis and how this contributes to its movement through landscapes.
Mātauranga Māori offers important insights for this research, as native plants are almost certainly important sources of naturally occurring chemo-attractants or repellents. As part of our proposed project, we will seek to build research collaborations with kaitiaki and other experts in ngahere kauri, building on Dr. Amanda Black's strong connections to Iwi, kaitiaki and Māori researchers, and the Kauri Dieback Programme Tāngata Whenua Rōpū. This will also help us to ensure that any treatment or methodology is compatible with tikanga. As a first step, we have undertaken a formal consultation with our local Iwi, Ngāi Tahu, via their Research Consultation Committee. The Ngāi Tahu Committee supports our proposed research, noting that it is “of interest and importance” and that “any work to aid in its [i.e. kauri’s] health and proliferation is very important”. Our next steps will be to liaise with Far North Iwi and hapū to develop more of a research partnership approach based on sites suggested by them.
Overall, successful implementation of our research has the potential to prevent the spread of kauri dieback, and stop the loss of these culturally and environmentally important trees. These benefits are encapsulated both within the Challenge Mission and the Vision Mātauranga Taiao (environmental sustainability) theme.
Lawrence, S.A., Armstrong, C.B., Patrick, W.M. and Gerth, M.L. 2017. High-throughput chemical screening identifies compounds that inhibit different stages of the Phytophthora agathidicida and Phytophthora cinnamomi life cycles. Frontiers in Microbiology DOI: 10.3389/fmicb.2017.01340
The collaborative effort to address kauri dieback includes the Ministry for Primary Industries, the Department of Conservation, Auckland Council, Northland Regional Council, Waikato Regional Council, Bay of Plenty Regional Council and Tāngata Whenua. We are working together as one team to ensure the integrity of kauri ecosystems remains, to protect high value kauri areas and iconic kauri trees.
This project is DOC's on the ground response to the disease killing kauri trees in the North Island. It aims to control the human spread of kauri dieback on public conservation land.
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