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Research vital to understand kauri killer

Research-vital-to-understand-kauri-killer

While it is somewhat removed from issues around your humble but ubiquitous pinus radiata, kauri dieback ​in our iconic native trees has the ability to have a serious impact on the future of those less salubrious species.
 
This disease is spreading and has been creating panic in so-called ‘local government’ in the Auckland region where millions of visitors are actively spreading it.
 
Fundamental research by scientists in the Bio-Protection Research Centre is uncovering how the fungus-like organism that causes kauri dieback (Phytophthora agathidicida) is such an effective killer. 
 
​​In New Zealand, kauri trees are taonga. A precious remnant of the country’s history and culture, these massive trees can live for more than 2000 years. Kauri once covered the Far North, but they were decimated in the 1700s and 1800s by felling for timber. Now only 1% of these original kauri forests remain — mostly in fragmented stands in Northland — and these are facing an ever-expanding threat from dieback disease. 
 
“Many different types of research are needed to combat this devastating disease if we want to save this precious iconic species,” says Rosie Bradshaw, Professor of Genetics at Massey University. "All around the country, an army of scientists and motivated citizens are working hard to find better ways to prevent the spread of this disease, to treat the symptoms and to understand the complexities of kauri forests and this pathogen.” 
 
Soilborne spores of the oomycete P. agathidicida infect kauri roots and damage the tissues that carry nutrients throughout the tree. While infected kauri can be treated with phosphite to delay disease development, it is not a long-term solution and its application across age classes is still to be determined. In some areas impacted by the disease, most infected kauri trees have succumbed. However, it is not known how susceptible the species is on whole. 
 
Breeding for disease resistance provides hope for the survival of this iconic species; however, to develop durable resistance, it is important to understand how P. agathidicida infects kauri trees and how the tree responds. 
 
Research by Dr Melissa Guo and colleagues at Massey University is revealing how certain proteins, called effectors, in P. agathidicida are involved in helping the pathogen cause disease or triggering a protective immune response in its plant host.
 
Using tobacco plants as a model system, Dr Guo has found two effectors that suppress the plant’s immune system, which could help the disease to spread within the plant, and eight that triggered cell death, which may offer some protection to the plants by sacrificing diseased tissues.
 
“By identifying pathogen effectors that interact with the plant, we hope to be able to identify plant immune receptors that can resist attack by Phytophthora agathidicida,” says Dr Guo. 
 
The next step is to test whether these P. agathidicida effectors have the same effect on kauri tissue. For this stage of the project, the researchers will be working closely with Scion's Healthy Trees Healthy Future (HTHF) team, who have established a collaboration with Mana Whenua that involves collecting kauri lines from different sites. 
 
“Our work represents another piece in the puzzle to understand how the host and pathogen interact with each other,” explains Professor Bradshaw. These investigations will help to characterise disease-resistant trees and help inform the breeding of trees that are less susceptible to this devastating organism. 
 
The research is funded by the Bio-Protection Research Centre and is affiliated to the HTHF research programme run at Scion. Dr Guo's work is a key implementation of the HTHF research and the first demonstration of key molecules involved in disease caused by P. agathidicida. 
 
The project is a team effort, involving researchers Prof Rosie Bradshaw, Dr Melissa Guo, Dr Pierre-Yves Dupont and Dr Carl Mesarich at Massey University, Dr Rebecca McDougal and Dr Nari Williams at Scion, and overseas collaborators at the University of Exeter and the Sainsbury Laboratory in the UK.

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