What is kauri dieback disease?
Phytophthora agathidicida, the pathogen that causes kauri dieback disease, was only discovered in 2009, and formally named in 2015 (previously it was known as Phytophthora taxon Agathis). The pathogen can sense a kauri tree’s roots, and swim towards them using a tail-like flagella.
There is no cure for kauri dieback disease, and the disease kills most if not all the kauri it infects. It can be spread by just a pinhead of soil, and although there are physical symptoms, you can't tell just by looking whether a tree is infected or not. Kauri dieback disease is threatening kauri with functional extinction. But kauri will be saved – by people like you.
Kauri dieback disease infects new trees in seven steps:
1: Oospores (resting spores) are introduced into an area of kauri, typically by human activity, but also by animals such as pigs. It only takes a pinhead of soil to move enough oospores to spread the disease.
2. The oospores germinate to form sporangia (a structure which produces zoospores).
3. Zoospores are released during and immediately after rain.
4. The zoospores swim (propelled by their tails) through moisture in the soil towards a kauri’s roots, where they attach themselves to the outside. They then germinate to produce mycelia (branded tubular structure) which infects the root. The tree’s fate is now sealed.
5. The mycelia spreads through the root system to attack the tissues at the base of the kauri’s trunk (eventually stopping the transport of nutrients and water to the canopy).
6. More sporangia are formed from where there are areas of infected root. These sporangia release more zoospores during and after rain, ensuring that it is only a matter of time before any other kauri in the vicinity are infected.
7. More oospores form within the tree's infected tissue. These are released into the soil as that tissue decays.