Embedded Files
Phylum Oomycota
Phylum Oomycota
The oomycetes, or water molds, are a group of fungal-like protists, that are more closely related to diatoms and brown algae. This group plays an important role in the decomposition and recycling of decaying matter. They are also known for causing well-known plant diseases such as downy mildew and root rot. In addition, the genus Phytophthora causes Sudden Oak disease, Ink Disease in American Chestnut (Castanea dentata), and the infamous Potato blight that caused massive starvation (Irish Potato Famine) in Ireland in the 1800s.
Ecology & form
Ecology & form
Terrestrial and aquatic (marine and freshwater)
Saprotrophic & parasitic
Non-photosynthetic; store glycogen
Filamentous with cellulosic cell walls (similar to plants)
Oomycetes are able to reproduce asexually
They produce flagellated asexual zoospores which can easily spread through wet and saturated soils
Asexual production of zoospores probably lead to the catastrophic and rapid blight of potatoes during the 1840s
Geologic Range
Geologic Range
Neoproterozoic(?) or Cretaceous - present
Reproduction
Reproduction
Water molds have a diplontic life cycle
They are oogamous, in which they possess oogonia (with eggs) & antheridia (with sperm)
Diversity
Diversity
~500 species
e.g., Saprolegnia, Phytophthora, Cryphonectria
Above: Downy mildew, caused by a water mold (oomycete); powdery mildew is caused by a true fungus (ascomycete)
Above: Potato blight, Phytophthora infestans
Above: sudden oak disease, Phytophthora ramoru
Above: Ink Disease (Cryphonectria) in American chestnut
Above: an oogonium of a water mold
Below: crown infection of summer squash
Additional Resources
Additional Resources
Previously unreported 'plant destroyers' detected in Minnesota (Phys.org 4Aug2025)
└Rajtar et al. (2025) Surveys of nurseries, forests and waterways in Minnesota revealed the presence of 14 new records of Phytophthora species
How Phytophthora affects urban linden trees (Phys.org 4Jun2025)
└Absalom et al. (2025) Impact of Phytophthora Disease on the Growth, Physiology and Ecosystem Services of Common Lime (Tilia × europaea) Street Trees
How to tackle new strains of potato blight and avoid another great famine (Phys.org 20May2025)
Study analyzes potato-pathogen 'arms race' after Irish potato famine (Phys.org 5Aug2024)
└Coomber et al. (2024) Evolution of Phytophthora infestans on its potato host since the Irish potato famine
Water mold evolution could help farmers fight potato blight (Science Daily 31Jan2014)
└Dong et al. (2025) Effector Specialization in a Lineage of the Irish Potato Famine Pathogen
Zoospore discharge of Phytophthora (YouTube 24Aug2010)
Genomics helps identify the strain of Phytophthora responsible for Potato Famine (NPR 22May2013)
Google Sites
Report abuse