Phytophthora cinnamomi

Phytophthora cinnamomi is a soil-borne water mould that produces an infection which causes a condition in plants called "root rot" or "dieback".

P. cinnamomi infects the roots by zoospores entering the root behind the root tip. Zoospores need water to swim through the soil, therefore infection is most likely in moist soils. Mycelia (or hyphae) grow throughout the root absorbing carbohydrates and nutrients, destroying the structure of the root tissues, "rotting" the root, and preventing the plant from absorbing water and nutrients. Early symptoms of infection include wilting, yellowing and retention of dried foliage and darkening of root color. Infection often leads to death of the plant, especially in dry summer conditions when plants way be water stressed .

In Australia P. cinnamoini infects a number of native plants, causing damage to forests and removing habitats for small mammals. Of particular concern is the infection and dieback of threatened species, including plants from the genera Banksia, Darwinia, Grevillea, and Verticordia .

Damage to forests suspected to be caused by P. cinnamoni was first recorded in the United States about 200 years ago. Infection is the cause of sudden death of a number of native tree species, including American Chestnut, Littleleaf disease of Shortleaf Pine (Pinus echinata), Christmas tree disease in nursery grown Fraser Fir (Abies fraseri), while oaks are affected from South Carolina to Texas.

It has devastated forests of Ohi'a lehua (Metrosideros polymorpha) on the Hawaiian Islands. P. cinnamomi is also a problem in Colima, Mexico killing several native oak species and other susceptible vegetation in the surrounding woodlands.

In addition to damage to native woodlands, P. cinnamoni can also infect fruit trees, nut trees and other ornamental plants. Research has shown that P. cinnamoini can infect club mosses , ferns, cycads, conifers, cord rushes, grasses, lilies and a large number of species from many dicotyledonous families. This is a remarkble range for a plant pathogen and highlights the effectiveness of P. cinnamomi as an aggressive primary pathogen.

References

• Botanic Gardens Trust. Phytophthora root rot — fact sheet.
• Department of Envoronment and Heritage, South Australia Phytophthora cinnamomi causing dieback in plants.
• Environment Australia. Threat Abatement Plan for Dieback Caused by the Root-rot Fungus Phytophthora cinnamomi, 2001.
• Hansen, E. Phytophthora in North American forests.
• Zentmyer, G.A., 1980. Phytophthora cinnamomi and the Diseases it Causes, Monograph no. 10, APS Press, St Paul, Minnesota, US.