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Type:Water mold (Oomycete)
Conditions:Favored by wet soils
Transmission:zoospores, tools, etc.

Phytophthora (from Greek phytón, “plant” and phthorá, “destruction”, “plant-destroyer”) is a genus of plant-damaging Protists of the Oomycetes (water moulds). Heinrich Anton de Bary described it for the first time in 1875.

Phytophthora is sometimes referred to as a fungus-like organism but it is classified under a different kingdom altogether: Stramenopila (previously named Chromista). In contrast to Fungi, stramenopiles are more closely related to plants than animals. Whereas Fungal cell walls are made primarily of chitin, stramenopile cell walls are constructed mostly of cellulose.

Phytophthoras reproduce both sexually and asexually. Sporangia, zoospores, and chlamydospores are asexual. Oospores are sexual.

Symptoms and Signs

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Infection by Phytophthora leads to root rots, cankers, foliar blights, and usually results in the death of the host plant. Symptoms vary according to both the pathogen species and the host species.

Life Cycle

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Phytophthora can live for long periods in the soil without the presence of a host. During wet conditions, the zoospores swim towards host plants following chemical traces. Once a plant is infected, it cannot be "cured", but may be sustained through foliar feeding for a time, depending on the host's natural resistance.

The life cycle of Phytophthora Phytophthora is easily spread by infected tools, and is often introduced through infected nursery stock. Spores and vegetative tissues can also be spread by animals or wind.

Host Range

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Phytophthoras are mostly pathogens of dicotyledons, and are relatively host specific parasites. Many species of Phytophthora are plant pathogens of considerable economic importance. Phytophthora infestans was the infective agent of the potato blight that caused the Irish potato famine. Research beginning in the 1990s has placed some of the responsibility for European forest die-back on the activity of imported Asian Phytophthoras[1].

Species and host genera

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Plant diseases caused by this genus are difficult to control chemically, thus resistant cultivars are grown as a management strategy.

  • Cultivation: Some bacteria and fungi associated with composts can suppress the activity of soil-borne phytophthora.
  • Cultural Controls: Raised beds and other techniques to improve drainage
  • Disposal: Infected materials should not be composted


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  1. "Phytophthora: Asiatischer Pilz lässt die Bäume sterben" Süddeutschen Zeitung 11 May 2005
  2. Hawaii Extension Service
  3. Florida Extension Service
  4. APSnet
  5. "APHIS List of Regulated Hosts and Plants Associated with Phytophthora ramorum" U.S. Animal and Plant Health Inspection Services;
Phytophthora forms: A: Sporangia. B: Zoo pore. C: Chlamydospore. D: Oospore.