Hyphae with frequent nodules, up to 8 µm wide, hyphal swellings in clusters, typically spherical, average 42 µm diameter. Sporangiophores thin (3 µm wide), proliferating through the empty sporangium or occasionally branched. Sporangia broadly ellipsoid to ovoid, 57 x 33 µm (up to 100 x 40 µm), no papilla, slight apical thickening, not shed. Oogonia average 40 µm diameter, wall smooth, becoming yellowish with age. Antheridia amphigynous, 21-23 x 17 µm. A full description is given in Waterhouse & Waterston (1966).
Related invasive species
- Phytophthora cinnamomi
Related Farm Practice
- Invasion
- Sapwood
- Soil
- Host plants
P. cinnamomi is a soilborne pathogen that is now widely established in many parts of the world. Initial long-range spread is likely to have been on infected nursery plants (e.g., Kenerley and Bruck, 1983;Benson and Campbell, 1985;Davison et al., 2006), and still occurs in this way. Additional long-range spread is by movement of soil and gravel infested with chlamydospores (e.g., Batini, 1977;Colquhoun and Petersen, 1994). Short-range spread is also by zoospores in drainage, seepage and irrigation water (Kinal et al., 1993;MacDonald et al., 1994). It has a very wide host range (Zentmyer, 1980) so that, once introduced into an area, it can persist on the roots of many different plants without necessarily causing symptoms on the foliage. It is a major pathogen of horticultural crops, in forestry and in natural vegetation, especially in southern Australia (Natural Resource Management Western Australia, 2013 - see http://www.dieback.net.au/pages/1382/susceptible-species). It is regarded as a key threatening process in the Australian environment (Environment Protection and Biodiversity Conservation Act, 1999), affecting both plant communities by reducing diversity, and the animal communities that depend on them.
P. cinnamomi causes a rot of fine feeder roots, and root cankers in some species, leading to dieback and death of host plants. Other symptoms include wilt, stem cankers (with sudden death of tree), decline in yield, decreased fruit size, gum exudation, collar rot (if infected through grafts near soil level) and heart rot (e.g. pineapple). A symptomless invasion of the sapwood has been reported in some species (Davison, 2011).
The host range is very wide and P. cinnamomi is the most widely distributed species of Phytophthora. Zentmyer (1983) stated there were nearly 1000 host species but, as research continues, the Project Dieback website (Natural Resource Management Western Australia, 2013) reports that over 2000 native plants are susceptible to Phytophthora dieback in Western Australia. The principal food crop hosts are avocados (root rot) and pineapples (root and heart rot);it also attacks Castanea, Cinnamomum, conifers, Ericaceae (including Rhododendron), Eucalyptus, Fagus, Juglans, Quercus and many ornamental trees and shrubs. Its recorded host range includes most of the temperate fruit trees, but these are not important hosts in practice. The impact of infection on hosts varies from symptomless infection restricted to root tissue to complete invasion of the root and stem storage tissue causing plant death (Environment Australia, 2001).