Pythium

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Pythium
Scientific classification
Domain: Eukaryota
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Oomycetes
Order: Peronosporales
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 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.

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.

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.

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 (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).

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.

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.

See also


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