What is Phytophthora cinnamomi?


Photograph showing microscope image of the release of zoospores from sporangia.

Photograph shows release of microscopic zoospores
from sporangia

Phytophthora cinnamomi belongs to a group of micro-organisms known as water moulds. Water moulds were once included in the fungi kingdom and, as a result, Phytophthora dieback  has been called a fungus in earlier interpretation literature. Water moulds have a motile or animal-like stage which fungi do not. As the name water mould suggests, it requires moist conditions to thrive. Its food source is the root and basal stem tissue of living plants. Phytophthora dieback grows as microscopic sized filaments (mycelium) within susceptible host plants. It consumes the host plant causing lesions (areas that appear rotten). This weakens or kills the plants by reducing or stopping the movement of water and nutrients within the plant.

Phytophthora cinnamomi may reproduce through production of microscopic spores. Two types of spores, zoospores and chlamydospores, are most likely to be formed in Tasmania:
  1. Zoospores are released in very large numbers under moist soil conditions. They have flagella (tails), which are used to propel the spore through the soil water towards other plant roots. The movement of water down slope, through or over the soil, can also passively disperse these spores over considerable distances. Zoospores are attracted by the root secretions of some plants. They then penetrate the root, germinate and the cycle repeats itself.
  2. Chlamydospores are larger, long-lived spores with thick protective walls. These spores can withstand dry conditions for months, germinating when warm moist soil conditions re-occur. They are one of the mechanisms the fungus has developed to help it survive adverse conditions. These spores may survive being transported long distances in dry soil.

The Phytophthora cinnamomi may also spread through mycelial growth along roots and spread between closely connecting plant roots within the soil.


Diagram showing generalised life cycle of Phytophthora cinnamomi.

Life Cycle of Phytophthora cinnamomi