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Kauri Foe – Phytophthora agathidicida 

Updated: Jun 5

Everyone has heard about kauri dieback, but how many of you are familiar with the fiendish organism responsible: Phytophthora agathidicida?   

Phytophthora is a genus of oomycetes, containing around 200 species commonly called “water molds” because they can be distributed by water and were thought to be related to fungi (turns out they aren’t!). Phytophthora’s resemblance to fungi is an example of convergent evolution, when nonrelated organisms evolve similar features or behaviours independently of one another.  

Phytophthora are plant pathogens – they infect and kill plants. Most are host specific; meaning that each species is adapted to infect a specific plant host. They are responsible for some of the most well-known historical crop losses, such as the Irish potato famine, which was caused by Phytophthora infestans and resulted the death of over a million people.  

Like most scientific names, this one has a deeper meaning: Phytophthora is derived from the Greek words for ‘plant destroyer’, while agathidicida is the genus name of kauri ‘agathis’ and the latin word ‘cida’, meaning ‘to kill’. This means that the species name Phytophthora agathidicida directly translates to “plant destroyer kauri killer”. Phytophthora agathidicida is host specific to kauri – it can only infect kauri trees. 

This little beastie has a cunning method of murder. It infects via the roots of the plant and, like the hair in your shower drain, clogs up the vascular system of the tree. The tree can then no longer move water and nutrients from the ground to the canopy, and slowly starves to death. While P. agathidicida is making itself comfortable in the root system, it continues to reproduce and send out spores into the surrounding soil, lying in wait until wandering feet come along to deliver it to its next victim.  

What makes kauri dieback the ultimate foe? Phytophthora have cell walls made of cellulose, like the plants they infect. This makes it incredibly challenging to kill the Phytophthora within an infected plant. We do not yet have the technology to differentiate between the two and kill one without killing the other. This is why kauri dieback mitigation is focused on the prevention of infection. Once a kauri tree is infected, there is nothing we can do.  

We can all help stop the spread of kauri dieback by using cleaning stations on feet, wheels, and paws, staying on track, and keeping dogs on lead.   


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