Pythium

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For the ancient city named Pythium, see Pythion.

Pythium

Scientific classification

Kingdom:	Eukaryota
(unranked)	Chromista
Phylum:	Heterokontophyta
Class:	Oomycetes
Order:	Peronosporales
Family:	Pythiaceae
Genus:	Pythium

Species

See text.

Pythium is a genus of parasitic Oomycota. It is also known as water mold pythium.

1 Morphology
2 Ecological Importance
- 2.1 References
3 See also

[edit] Morphology

Hyphae

Pythium, like others in the family Pythiaceae, are usually characterized by their production of coenocytic hyphae, hyphae without septations.

Zoosporangia

The zoosprorangia of Pythium release via a vesicle. There have two types of hyphae, known as nematosporangia, and sphaerosporangia.

Oogonia

Generally contain a single oospore with periplasm.

Antheridia

Contain an elongated and club-shaped antheridium.

[edit] Ecological Importance

Pythium root rot is a common crop disease caused by a genus of organisms call "Pythium". These are commonly called water moulds. Pythium damping off is a very common problem in fields and greenhouses where the organism kills newly emerged seedlings (Jarvis, 1992).

Many Pythium species, along with their close relatives, Phytophthora species are plant pathogens of economic importance in agriculture] Pythium spp. are very generalistic and unspecific in their host range - that is, they infect a large range of hosts (Owen-Going, 2002) - while Phytophthora spp. are more specific, i.e. Phytophthora infestans only infect tomatoes and potatoes.

For this reason, Pythium spp. are more devastating in the root rot they cause in field crops, because crop rotation alone will often not eradicate the pathogen (nor will fallowing the field, as Pythium spp. are also good saprotrophs, and will survive for a long time on decaying plant matter).

However, the damage Pythium spp. does in field crops is limited to the area affected, because the motile zoospores need ample surface water to travel long distances as the capillaries formed by soil particles act as a natural filter. In hydroponic systems inside greenhouses, where extensive monocultures of plants are maintained in plant nutrient solution (containing nitrogen, potassium, phosphate, and micronutrients) that is continuously recirculated to the crop, Pythium spp. cause extensive and devastating root rot (Jarvis, 1992; Owen-Going, 2002, Owen-Going et al., 2003). The root rot affects entire operations (tens of thousands of plants, in many instances) within two to four days (Owen-Going, 2002, Owen-Going et al., 2003).

The species Pythium oligandrum is a parasite of fungi, as well as other water molds.

[edit] References

Jarvis, W.R. 1992. Managing diseases in greenhouse crops. APS Press, St. Paul, Minn.
Owen-Going, T.N. 2002. Etiology and epidemiology of Pythium root rot in bell pepper (Capsicum annuum L.) in commercial-scale and small-scale hydroponic systems. M.Sc. thesis, University of Guelph, Guelph, Ontario.
Owen-Going, T.N.; Sutton, J.C.; Grodzinski, B. 2003. Relationships of Pythium isolates and sweet pepper plants in single-plant hydroponic units. Canadian Journal of Plant Pathology, 25:155-167.

[edit] See also

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