Phosphite for the prevention of disease caused by Phytophthora species in six rare or threatened species. Will it kill or cure?

K. L. McDougall; E. C. Y. Liew

doi:10.1071/BT25020

RESEARCH ARTICLE (Open Access)

Next Contents Vol 73(5)

Phosphite for the prevention of disease caused by Phytophthora species in six rare or threatened species. Will it kill or cure?

K. L. McDougall

^A ^C ^* and E. C. Y. Liew ^B

+ Author Affiliations

- Author Affiliations

^A NSW Department of Climate Change, Energy, the Environment and Water, PO Box 733, Queanbeyan, NSW 2620, Australia.

^B Research Centre for Ecosystem Resilience, The Royal Botanic Gardens and Domain Trust, Mrs Macquaries Road, Sydney, NSW 2000, Australia.

^C Present address: School of Agriculture, Biomedicine and Environment, La Trobe University, Bundoora, Vic 3083, Australia.

^* Correspondence to: Keith.Mcdougall@latrobe.edu.au

Handling Editor: Chris Blackman

Australian Journal of Botany 73, BT25020 https://doi.org/10.1071/BT25020

Submitted: 17 March 2025 Accepted: 7 June 2025 Published: 27 June 2025

© 2025 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Phytophthora species are a significant threat to Australia’s biodiversity and many plant species are at risk of extinction as a result. For some plant species, the chemical phosphite (salts of phosphonic acid) can improve survival by activating defence mechanisms. However, phosphite at some concentrations can be phytotoxic. Uptake of and responses to phosphite vary greatly between species, so it is not possible to predict whether there will be positive or negative effects of its use. Glasshouse trials can be performed to test efficacy prior to field applications. The size of such trials can be constrained for rare or threatened species because of the difficulty of producing sufficient plants for adequate replication. In this study, we tested the effects of foliar application of phosphite on six threatened species in a glasshouse: three species were susceptible to infection by Phytophthora cinnamomi (Hibbertia circinata, Nematolepis rhytidophylla, and Phebalium squamulosum subsp. alpinum); and three species were susceptible to infection by Phytophthora gregata (Boronia deanei, Correa baeuerlenii, and Pimelea bracteata). We found that phosphite had severe phytotoxic effects on C. baeuerlenii but reduced disease and mortality of N. rhytidophylla. The effects on the other species were less equivocal. Alternative control options will be required for some species.

Keywords: chlorosis, Hibbertia, Nematolepis, phosphonic acid, Phytophthora cinnamomi, Phytophthora gregata, phytotoxicity, root pathogens.

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