''Pythium'' is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...

oomycete Oomycota forms a distinct phylogenetic lineage of fungus-like eukaryotic microorganisms, called oomycetes (). They are filamentous and heterotrophic, and can reproduce both sexually and asexually. Sexual reproduction of an oospore is the resul ...

s. They were formerly classified as

fungi A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from ...

. Most species are

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclud ...

parasites Parasitism is a Symbiosis, close relationship between species, where one organism, the parasite, lives on or inside another organism, the Host (biology), host, causing it some harm, and is Adaptation, adapted structurally to this way of lif ...

, but ''

Pythium insidiosum ''Pythium insidiosum'' is a species of ''Pythium'' and a member of the class oomycota. ''Pythium insidiosum'' is mainly found in standing water and occasionally soil. Unlike most ''Pythium'' species, which are generally pathogens of terrestrial ...

'' is an important

pathogen In biology, a pathogen ( el, πάθος, "suffering", "passion" and , "producer of") in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ ...

animal Animals are multicellular, eukaryotic organisms in the Kingdom (biology), biological kingdom Animalia. With few exceptions, animals Heterotroph, consume organic material, Cellular respiration#Aerobic respiration, breathe oxygen, are Motilit ...

s, causing

pythiosis Pythiosis is a rare and deadly tropical disease caused by the oomycete ''Pythium insidiosum''. Long regarded as being caused by a fungus, the causative agent was not discovered until 1987. It occurs most commonly in horses, dogs, and humans, with ...

. The feet of the fungus gnat are frequently a vector for their transmission.

Morphology

;Hyphae: ''Pythium'' species, like others in the family

Pythiaceae Pythiaceae is a family of water moulds. The family includes serious plant and animal pathogens in the genus '' Pythium''. The family was circumscribed by German mycologist Joseph Schröter in 1893. Lifecycle *Live on land ( terrestrial), and in ...

, are usually characterized by their production of

coenocytic A coenocyte () is a multinucleate cell which can result from multiple nuclear divisions without their accompanying cytokinesis, in contrast to a syncytium, which results from cellular aggregation followed by dissolution of the cell membranes insid ...

hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one or ...

e without septations. ;Oogonia: Generally contain a single

oospore An oospore is a thick-walled sexual spore that develops from a fertilized oosphere in some algae, fungi, and oomycetes. They are believed to have evolved either through the fusion of two species or the chemically-induced stimulation of mycelia, ...

. ;Antheridia: Contain an elongated and club-shaped

antheridium An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...

Ecological importance

''Pythium''-induced

root rot Root rot is a condition in which anoxic conditions in the soil or potting media around the roots of a plant cause them to rot. This occurs due to excessive standing water around the roots. It is found in both indoor and outdoor plants, although ...

is a common crop disease. When the organism kills newly emerged or emerging seedlings, it is known as

damping off Damping off (or damping-off) is a horticultural disease or condition, caused by several different pathogens that kill or weaken seeds or seedlings before or after they germinate. It is most prevalent in wet and cool conditions. Symptoms There ar ...

, and is a very common problem in fields and greenhouses. Thus there is tremendous interest in genetic host resistance, but no crop has ever developed adequate resistance to ''Pythium''. This disease complex usually involves other pathogens such as ''

Phytophthora ''Phytophthora'' (from Greek language, Greek (''phytón''), "plant" and (), "destruction"; "the plant-destroyer") is a genus of plant-damaging oomycetes (water molds), whose member species are capable of causing enormous economic losses on cro ...

'' and ''

Rhizoctonia ''Rhizoctonia'' is a genus of fungi in the order Cantharellales. Species form thin, effused, corticioid basidiocarps (fruit bodies), but are most frequently found in their sterile, anamorphic state. ''Rhizoctonia'' species are saprotrophic, but ...

''. Pythium wilt is caused by

zoospore A zoospore is a motile asexual spore that uses a flagellum for locomotion. Also called a swarm spore, these spores are created by some protists, bacteria, and fungi to propagate themselves. Diversity Flagella types Zoospores may possess one or mo ...

infection of older plants, leading to biotrophic infections that become necrotrophic in response to colonization/reinfection pressures or environmental stress, leading to minor or severe wilting caused by impeded root functioning. Many ''Pythium'' species, along with their close relatives ''

'', are

plant pathogens Plant pathology (also phytopathology) is the scientific study of diseases in plants caused by pathogens (infectious organisms) and environmental conditions (physiological factors). Organisms that cause infectious disease include fungi, oomyc ...

of economic importance in agriculture. ''Pythium'' spp. tend to be very generalistic and unspecific in their large range of hosts, 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 Crop rotation is the practice of growing a series of different types of crops in the same area across a sequence of growing seasons. It reduces reliance on one set of nutrients, pest and weed pressure, and the probability of developing resistant ...

alone often does not eradicate the pathogen as ''Pythium'' spp. are also good saprotrophs, and survive for a long time on decaying plant matter. In field crops, damage by ''Pythium'' spp. is often limited to the area affected, as the motile zoospores require ample surface water to travel long distances. Additionally, the capillaries formed by soil particles act as a natural filter and effectively trap many zoospores. However, in hydroponic systems inside

greenhouse A greenhouse (also called a glasshouse, or, if with sufficient heating, a hothouse) is a structure with walls and roof made chiefly of Transparent ceramics, transparent material, such as glass, in which plants requiring regulated climatic condit ...

s, where extensive

monoculture In agriculture, monoculture is the practice of growing one crop species in a field at a time. Monoculture is widely used in intensive farming and in organic farming: both a 1,000-hectare/acre cornfield and a 10-ha/acre field of organic kale are ...

s of plants are maintained in plant nutrient solution (containing

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

potassium Potassium is the chemical element with the symbol K (from Neo-Latin ''kalium'') and atomic number19. Potassium is a silvery-white metal that is soft enough to be cut with a knife with little force. Potassium metal reacts rapidly with atmosphe ...

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phospho ...

, and

micronutrient Micronutrients are nutrient, essential dietary elements required by organisms in varying quantities throughout life to orchestrate a range of physiological functions to maintain health. Micronutrient requirements differ between organisms; for exam ...

s) that is continuously recirculated to the crop, ''Pythium'' spp. cause extensive and devastating root rot and is often difficult to prevent or control. The root rot affects entire operations (tens of thousands of plants, in many instances) within two to four days due to the inherent nature of hydroponic systems where roots are nakedly exposed to the water medium, in which the zoospores can move freely. Various ''Pythium'' populations have been known to have resistance to

mefenoxam Metalaxyl is an acylalanine fungicide with systemic function. Its chemical name is methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate. It can be used to control ''Pythium'' in a number of vegetable crops, and ''Phytophthora'' in peas. Metalaxy ...

since the 1980s and

metalaxyl Metalaxyl is an acylalanine fungicide with systemic function. Its chemical name is methyl N-(methoxyacetyl)-N-(2,6-xylyl)-DL-alaninate. It can be used to control ''Pythium'' in a number of vegetable crops, and ''Phytophthora'' in peas. Metalaxyl ...

since 1984. 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 Biological control or biocontrol is a method of controlling pests, such as insects, mites, weeds, and plant diseases, using other organisms. It relies on predation, parasitism, herbivory, or other natural mechanisms, but typically also invo ...

agents.

Species

*'' Pythium acanthicum'' *'' Pythium acanthophoron'' *'' Pythium acrogynum'' *''

Pythium adhaerens ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *'' Pythium amasculinum'' *'' Pythium anandrum'' *'' Pythium angustatum'' *''

Pythium aphanidermatum ''Pythium aphanidermatum'' is a soil borne plant pathogen. ''Pythium'' is a genus in the class Oomycetes, which are also known as water molds. Oomycetes are not true fungi, as their cell walls are made of cellulose instead of chitin, they are d ...

'' *'' Pythium apleroticum'' *'' Pythium aquatile'' *'' Pythium aristosporum'' *'' Pythium arrhenomanes'' *'' Pythium attrantheridium'' *'' Pythium bifurcatum'' *'' Pythium boreale'' *'' Pythium buismaniae'' *'' Pythium butleri'' *'' Pythium camurandrum'' *'' Pythium campanulatum'' *'' Pythium canariense'' *'' Pythium capillosum'' *'' Pythium carbonicum'' *''

Pythium carolinianum ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *'' Pythium catenulatum'' *''

Pythium chamaehyphon ''Pythium'' is a genus of parasitism, parasitic oomycetes. They were formerly classified as fungus, fungi. Most species are plant parasitism, parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet ...

'' *'' Pythium chondricola'' *'' Pythium citrinum'' *'' Pythium coloratum'' *'' Pythium conidiophorum'' *'' Pythium contiguanum'' *'' Pythium cryptoirregulare'' *'' Pythium cucurbitacearum'' *'' Pythium cylindrosporum'' *'' Pythium cystogenes'' *''

Pythium debaryanum ''Pythium debaryanum'' is a species of water mould in the family Pythiaceae. It is known as a plant pathogen on many kinds of wild and cultivated plants, including peanut, beet, eucalyptus, tobacco, and pine trees. The plants develop damping off ...

'' *'' Pythium deliense'' *'' Pythium destruens'' *'' Pythium diclinum'' *'' Pythium dimorphum'' *'' Pythium dissimile'' *'' Pythium dissotocum'' *'' Pythium echinulatum'' *'' Pythium emineosum'' *'' Pythium erinaceum'' *'' Pythium flevoense'' *'' Pythium folliculosum'' *''

Pythium glomeratum ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *''

Pythium graminicola ''Pythium graminicola'' is a plant pathogen infecting cereals. Host and symptoms ''Pythium graminicola'' infects a wide range of hosts, including: bent grass, turmeric, cotton, barley, wheat, rice, beans, peas, and sugarcane. In particular ' ...

'' *'' Pythium grandisporangium'' *''

Pythium guiyangense ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *'' Pythium helicandrum'' *'' Pythium helicoides'' *'' Pythium heterothallicum'' *'' Pythium hydnosporum'' *'' Pythium hypogynum'' *'' Pythium indigoferae'' *'' Pythium inflatum'' *''

'' *'' Pythium intermedium'' *''

Pythium irregulare ''Pythium irregulare'' is a soil borne oomycete plant pathogen. Oomycetes, also known as "water molds", are fungal-like protists. They are fungal-like because of their similar life cycles, but differ in that the resting stage is diploid, they h ...

'' *'' Pythium iwayamae'' *'' Pythium jasmonium'' *'' Pythium kunmingense'' *'' Pythium litorale'' *'' Pythium longandrum'' *'' Pythium longisporangium'' *'' Pythium lutarium'' *'' Pythium macrosporum'' *'' Pythium mamillatum'' *'' Pythium marinum'' *'' Pythium marsipium'' *''

Pythium mastophorum ''Pythium mastophorum'' is a plant pathogen infecting pocketbook plants (''Calceolaria crenatiflora ''Calceolaria crenatiflora'' is a species of flowering plant in the pocketbook plant genus ''Calceolaria'', family Calceolariaceae. It is nat ...

'' *'' Pythium megacarpum'' *'' Pythium middletonii'' *'' Pythium minus'' *'' Pythium monospermum'' *'' Pythium montanum'' *'' Pythium multisporum'' *''

Pythium myriotylum ''Pythium myriotylum'' is a soil-borne oomycete necrotroph that has a broad host range, this means that it can infect a wide range of plants. Hosts and symptoms ''Pythium myriotylum'' is a causal agent of soft root rot in economically important ...

'' *'' Pythium nagaii'' *'' Pythium nodosum'' *''

Pythium nunn ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *'' Pythium oedochilum'' *'' Pythium okanoganense'' *''

Pythium oligandrum ''Pythium oligandrum'' is an oomycete. It is a parasite of many fungi and other oomycetes including '' Botrytis'', ''Fusarium'' and ''Phytophthora''. It has been licensed as a biocontrol agent in the form of an oospore soil treatment, which redu ...

'' *'' Pythium oopapillum'' *'' Pythium ornacarpum'' *'' Pythium orthogonon'' *''

Pythium ostracodes ''Pythium'' is a genus of parasitism, parasitic oomycetes. They were formerly classified as fungus, fungi. Most species are plant parasitism, parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet ...

'' *'' Pythium pachycaule'' *'' Pythium pachycaule'' *'' Pythium paddicum'' *''

Pythium paroecandrum ''Pythium paroecandrum'' is a plant pathogen infecting carrots and impatiens. References External links Index FungorumUSDA ARS Fungal Database Water mould plant pathogens and diseases Carrot diseases Ornamental plant pathogens and dise ...

'' *'' Pythium parvum'' *'' Pythium pectinolyticum'' *'' Pythium periilum'' *'' Pythium periplocum'' *''

Pythium perniciosum ''Pythium perniciosum'' is a plant pathogen infecting strawberries and poinsettias. References External links Index FungorumUSDA ARS Fungal Database Water mould plant pathogens and diseases Water mould strawberry diseases Ornamental pl ...

'' *'' Pythium perplexum'' *'' Pythium phragmitis'' *'' Pythium pleroticum'' *'' Pythium plurisporium'' *''

Pythium polare ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *'' Pythium polymastum'' *''

Pythium porphyrae ''Pythium porphyrae'', is a parasitism, parasitic species of oomycete in the family Pythiaceae. It is the cause of red rot disease or red wasting disease, also called ' () in Japanese language, Japanese. The Botanical name, specific epithet '' ...

'' *'' Pythium prolatum'' *'' Pythium proliferatum'' *'' Pythium pulchrum'' *'' Pythium pyrilobum'' *'' Pythium quercum'' *'' Pythium radiosum'' *'' Pythium ramificatum'' *'' Pythium regulare'' *'' Pythium rhizo-oryzae'' *''

Pythium rhizosaccharum ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but '' Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are freque ...

'' *'' Pythium rostratifingens'' *'' Pythium rostratum'' *''

Pythium salpingophorum ''Pythium'' is a genus of parasitism, parasitic oomycetes. They were formerly classified as fungus, fungi. Most species are plant parasitism, parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet ...

'' *'' Pythium scleroteichum'' *'' Pythium segnitium'' *'' Pythium spiculum'' *'' Pythium spinosum'' *''

Pythium splendens ''Pythium splendens'' is a plant pathogen. It is a potentially useful organism for the synthesis of large amounts of eicosapentaenoic acid, which is a polyunsaturated fatty acid Polyunsaturated fatty acids (PUFAs) are fatty acids that contain ...

'' *'' Pythium sterilum'' *'' Pythium stipitatum'' *'' Pythium sulcatum'' *'' Pythium tardicrescens'' *'' Pythium terrestris'' *'' Pythium torulosum'' *'' Pythium tracheiphilum'' *''

Pythium ultimum ''Pythium ultimum'' is a plant pathogen. It causes the damping off and root rot diseases of hundreds of diverse plant hosts including corn, soybean, potato, wheat, fir, and many ornamental species. ''P. ultimum'' belongs to the peronosporal ...

'' ** ''Pythium ultimum'' var. ''ultimum'' *'' Pythium uncinulatum'' *'' Pythium undulatum'' *'' Pythium vanterpoolii'' *'' Pythium viniferum'' *'' Pythium violae'' *'' Pythium volutum'' *''

Pythium zingiberis ''Pythium'' is a genus of parasitic oomycetes. They were formerly classified as fungi. Most species are plant parasites, but ''Pythium insidiosum'' is an important pathogen of animals, causing pythiosis. The feet of the fungus gnat are frequent ...

'' *'' Pythium zingiberum'' '' Globisporangium sylvaticum'' was formerly placed here as ''Pythium sylvaticum''

Morphology

Ecological importance

Species

See also

References

Further reading