RA3 Thesis: Effect of phosphite on arbuscular ...

Patterson HR. 2022. Assessing the effect of phosphite treatment on arbuscular mycorrhizal fungal colonisation in kauri (Agathis australis). Unpublished Honours thesis, University of Auckland.

This thesis is not publicly available online. For further information please contact supervisor, Dr. Luitgard Schwendenmann at the University of Auckland (l.schwendenmann@auckland.ac.nz)

A poster presented at the New Zealand Ecological Society Conference, University of Otago, November 2022 has been provided.

Kauri (Agathis australis) is a keystone New Zealand tree species. Kauri are also a taonga species with an integral place in Māori culture. Kauri are threatened by Phytophthora agathidicida, an oomycete that causes kauri dieback. Currently, phosphite is the treatment used to manage the disease, and although it is an effective short-term treatment, it is not a cure. There is little research on the effect of phosphite on the arbuscular mycorrhizal fungi (AMF), which exist in a symbiotic relationship with kauri roots. AMF are integral for kauri survival in low-nutrient soil. This study investigates the effect of phosphite on AMF in the root nodules of kauri trees. Twenty trees in the Waitākere Ranges that were treated with phosphite in 2018 and 2019 were sampled. Firstly, methods of quantifying colonisation in kauri root nodules were trialled and optimised. Then, microscopy was used to quantify AMF colonisation in selected trees. Soil characteristics were assessed across the two plots, and a correlation between soil pH and colonisation rate was found. Colonisation rates in trees treated with phosphite appear comparable to pre-phosphite colonisation rates in kauri trees. This research will aid in determining how appropriate phosphite injection is as a continued treatment against kauri dieback, and in developing research methodology for working with kauri roots. Future directions include analysing sequenced root material to assess AMF diversity across the two plots.