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Downscaling for higher throughput and reduced resource use – new fungicide sensitivity assay

From Forest Health News 286, December 2018.

A high-throughput bioassay to screen sensitivity of species of Phytophthora to fungicides has been developed1. The research by Scion-based Master of Science student, Shannon Hunter, uses a plate reader machine and optical density measurements to quantify the amount of mycelial growth in liquid media with various fungicide concentrations.

Phosphite was utilised in this experiment because it is used to control Phytophthora diseases in a range of horticultural crops, forest nurseries, and culturally and ecologically important plant species. In New Zealand, phosphite is used to control avocado root rot. It also has the potential to be used to protect iconic individual kauri trees from kauri dieback, caused by P. agathadicida.

Growth of Phytophthora cinnamomi mycelium after 6 days in liquid media (Ribeiros minimal media containing 0, 15, 40, 80, 200 and 500 μg ml-1 phosphite).

The new bioassay was compared to two widely used methods, dry weight and linear growth assays. Dry weight assays required cultures to be grown in liquid media (at least 20 ml) and then drying the cultures in an oven and weighing them. Linear growth assays involve growing cultures on solid media in a Petri dish and measuring the diameter of the colony.

The optical density assay developed was just as effective at measuring chemical inhibition of Phytophthora as the other two methods and it has the added benefits of requiring fewer resources and less time, providing a higher through-put of samples and allowing for multiple measurements over time.

Shannon Hunter (Scion)


1 Hunter, S.; McDougal, R.; Clearwater, M.J.; Williams, N. & Scott, P. (2018) Development of a high throughput optical density assay to determine fungicide sensitivity of oomycetes. Journal of Microbiological Methods. 154, 33-39.


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