Pythium

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Pythium
Scientific classification
Domain: Eukaryota Kingdom: Chromalveolata Phylum: Heterokontophyta Class: Oomycetes Order: Pythiales Family: Pythiaceae Genus: Pythium
Species
Pythium acanthicum Pythium acanthophoron Pythium acrogynum Pythium adhaerens Pythium amasculinum Pythium anandrum Pythium angustatum Pythium aphanidermatum Pythium apleroticum Pythium aquatile Pythium aristosporum Pythium arrhenomanes Pythium attrantheridium Pythium bifurcatum Pythium boreale Pythium buismaniae Pythium butleri Pythium campanulatum Pythium canariense Pythium capillosum Pythium carbonicum Pythium carolinianum Pythium catenulatum Pythium chamaehyphon Pythium chondricola Pythium citrinum Pythium coloratum Pythium conidiophorum Pythium contiguanum Pythium cryptoirregulare Pythium cucurbitacearum Pythium cylindrosporum Pythium cystogenes Pythium debaryanum Pythium deliense Pythium destruens Pythium diclinum Pythium dimorphum Pythium dissimile Pythium dissotocum Pythium echinulatum Pythium erinaceum Pythium flevoense Pythium folliculosum Pythium glomeratum Pythium graminicola Pythium grandisporangium Pythium guiyangense Pythium helicandrum Pythium helicoides Pythium heterothallicum Pythium hydnosporum Pythium hypogynum Pythium indigoferae Pythium inflatum Pythium insidiosum Pythium intermedium Pythium irregulare Pythium iwayamai Pythium jasmonium Pythium kunmingense Pythium litorale Pythium longandrum Pythium longisporangium Pythium lutarium Pythium macrosporum Pythium mamillatum Pythium marinum Pythium marsipium Pythium mastophorum Pythium megacarpum Pythium megalacanthum Pythium middletonii Pythium minus Pythium monospermum Pythium montanum Pythium multisporum Pythium myriotylum Pythium nagaii Pythium nodosum Pythium nunn Pythium oedochilum Pythium okanoganense Pythium oligandrum Pythium ornacarpum Pythium orthogonon Pythium ostracodes Pythium pachycaule Pythium pachycaule Pythium paddicum Pythium paroecandrum Pythium parvum Pythium pectinolyticum Pythium periilum Pythium periplocum Pythium perplexum Pythium phragmitis Pythium pleroticum Pythium plurisporium Pythium polymastum Pythium porphyrae Pythium prolatum Pythium proliferatum Pythium pulchrum Pythium pyrilobum Pythium quercum Pythium radiosum Pythium ramificatum Pythium regulare Pythium rhizo-oryzae Pythium rhizosaccharum Pythium rostratifingens Pythium rostratum Pythium salpingophorum Pythium scleroteichum Pythium segnitium Pythium spiculum Pythium spinosum Pythium splendens Pythium sterilum Pythium sulcatum Pythium sylvaticum Pythium terrestris Pythium torulosum Pythium tracheiphilum Pythium ultimum Pythium uncinulatum Pythium undulatum Pythium vanterpoolii Pythium vexans Pythium viniferum Pythium violae Pythium volutum Pythium zingiberis Pythium zingiberum

Pythium is a genus of parasitic oomycete. Because this group of organisms were once classified as fungi, they are sometimes still treated as such.

Contents 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.

• Oogonia

Generally contain a single oospore

• 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 called "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). This disease complex usually involves other fungi as Phytophthora and Rhizoctonia. Pythium wilt is caused by zoospore infection of plants older than seedling stage and results in minor (sometimes barely noticeable) to severe (leading to plant death) wilting of the plants due to impeded root functioning (Bagnall, 2007)

Many Pythium species, along with their close relatives, Phytophthora species are plant pathogens of economic importance in agriculture. Pythium spp. tend to be very generalistic and unspecific in their host range. They infect a large range of hosts (Owen-Going, 2002), while Phytophthora spp. are generally more host-specific.

For this reason, Pythium spp. are more devastating in the root rot they cause in 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. do in field crops is limited to the area affectedthis is because the motile zoospores need ample surface water to travel long distances and 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 and is often difficult to prevent or control (Jarvis, 1992; Owen-Going, 2002, Owen-Going et al., 2003; Bagnall, 2007). 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) due to the inherent nature of hydroponic systems where roots are nakedly exposed to the water medium, in which the zoospores can move freely (Bagnall, 2007).

Several Pythium species, including P. oligandrum, P. nunn, P. periplocum, and P. acanthicum are mycoparasites of plant pathogenic fungi and oomycetes, and have received interest as potential biocontrol agents.

[edit] References

• Plaats-Niterink AJ van der. 1981. Monograph of the genus Pythium. Studies in Mycology, 21:1–242.
• Levesque,C.A. and de Cock,A.W. (2004) Molecular phylogeny and taxonomy of the genus Pythium. Mycological Research, 108:1363-1383
• 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.
• Bagnall, R. 2007. Control of Pythium wilt and root rot of hydroponically grown lettuce by means of chemical treatment of the nutrient solution. M. Sc Thesis, University of Pretoria, Pretoria, South Africa.

[edit] See also

• Pythiosis
• Water mould
• Oomycetes
• Phytophthora
• Damping off
• Hydroponics

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