Disease Forms - Phytophthora Dieback

Question 1

What is Phytophthora Dieback?

Answer 1

A soil-borne water mould that produces an infection which causes a plant condition of root rotting/dieback. The most common strain of the pathogen in WA is P. cinnamomi.

Question 2

How does the disease work?

Answer 2

The pathogen spends its life in the soil & plant tissue; causing root rot in susceptible plants - preventing the uptake of water and nutrients. During dry soil conditions, the pathogen can remain dormant as its preferred mode of transport is water.

Question 3

What are the symptoms of the disease?

Answer 3

Root rot, decreased fruit size, discolouring, lack of water/nutrients, leaf curling.

Question 4

Outline its lifecycle.

Answer 4

• Resides in soil/plant tissue.
• Zoospores penetrate healthy host.
• Infection begins at root tips; progressing through the root system.
• Zoospores produce mycelial threads on the roots.
• Sporangia & chlamydospores form on mycelia.
• Zoospores release sproangia - travel in water of soil to new hosts.
• Chlamydospores can remain dormant in harsh consitions - ready to germinate in moist conditions.

Question 5

Where is the disease distributed?

Answer 5

Common in southern Australia, found in areas recieving over 400mm of rain a year (Jurien - Esperence).

Question 6

How does it spread?

Answer 6

• In sloping areas it can spread fast in surface/sub-surface water flows.
• Speads slower uphill/flatground as root to root contact is minimal.
• Human Activity - redistributing soils in different locations, spreading the pathogen.
• Soil that is warm/moist provide the best conditions for spores.

Question 7

Which plants does the pathogen kill?

Answer 7

• 40% of WA native flora (jarrah, banksias, grass trees and zamia palms).
• 50% of endangered flora found in the south-west ecoregion.

Question 8

How do we manage the disease/prevention?

Answer 8

• Cleaning stations to avoid transport of contaminated soil.
• Cleaning footwear and washing down vehicles and equipment.
• Use of dieback free construction materials.
• Seasonal and permanent road and trail closures.
• Information signs and education.

Question 9

Outline a particular treatment for dieback.

Answer 9

Phosphite - a biodegradable fungicide that protects the plants from the pathogen.
By boosting the plant’s natural defence systems.
Low amounts sprayed on plants to avoid pollution via. the water table. (Soil bound).
Needs to enter the plants’ water transport system to be effective.

Question 10

What is the role of ‘The Departments of Parks & Wildlife’ in fighting the pathogen?

Answer 10

• Detecting and identifying new Phytophthora species.
• Investigating the susceptibility of Western Australian plants to Phytophthora.
• Investigating ways to reduce the spread of Phytophthora dieback.
• Researching and understanding the long-term impacts of Phytophthora.