Pythium root rot is a common crop disease caused by a water mould of the same name. Pythium damping off is a very common problem in fields and greenhouses where the organism kills newly emerged seedlings (Jarvis, 1992).

Many Pythium spp., along with their close relatives, Phytophthora spp. 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 very specific, i.e. Phytophthora capsici only infect pepper (Capsicum spp.) and Phytophthora infestans only infect 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).

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.

See also

• Pythiosis
• Water mould
• Oomycetes
• Phytophthora
• Hydroponics

Pythium