''Pythium aphanidermatum'' is a soil borne

plant pathogen 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 ...

. '' 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 Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wall ...

instead of

chitin Chitin ( C8 H13 O5 N)n ( ) is a long-chain polymer of ''N''-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chit ...

, they are

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

in their vegetative state, and they form

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 (lacking crosswalls). Also, they reproduce asexually with motile biflagelette

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 ...

s that require water to move towards and infect a host. Sexually, they reproduce with structures called antheridia,

oogonia An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in larg ...

, and oospores.

Hosts

''Pythium aphanidermatum'' has a wide host range, and can have an economic impact on the cultivation of

soybean The soybean, soy bean, or soya bean (''Glycine max'') is a species of legume native to East Asia, widely grown for its edible bean, which has numerous uses. Traditional unfermented food uses of soybeans include soy milk, from which tofu an ...

beets The beetroot is the taproot portion of a beet plant, usually known in North America as beets while the vegetable is referred to as beetroot in British English, and also known as the table beet, garden beet, red beet, dinner beet or golden beet ...

, peppers,

chrysanthemum Chrysanthemums (), sometimes called mums or chrysanths, are flowering plants of the genus ''Chrysanthemum'' in the family Asteraceae. They are native to East Asia and northeastern Europe. Most species originate from East Asia and the center ...

cucurbits The Cucurbitaceae, also called cucurbits or the gourd family, are a plant family consisting of about 965 species in around 95 genera, of which the most important to humans are: *''Cucurbita'' – squash, pumpkin, zucchini, some gourds *''Lagena ...

cotton Cotton is a soft, fluffy staple fiber that grows in a boll, or protective case, around the seeds of the cotton plants of the genus ''Gossypium'' in the mallow family Malvaceae. The fiber is almost pure cellulose, and can contain minor perce ...

and turf-grasses, however, because ''P. aphanidermatum'' requires warmer temperatures, it is often seen in greenhouses and has a large impact in poinsettia production. It is a major cause of root rot in

papaya The papaya (, ), papaw, () or pawpaw () is the plant species ''Carica papaya'', one of the 21 accepted species in the genus ''Carica'' of the family Caricaceae. It was first domesticated in Mesoamerica, within modern-day southern Mexico and ...

production in subtropical areas. While this is almost exclusively a

, there is one documented case of ''P. aphanidermatum'' infecting a human being injured in the

Afghanistan conflict War in Afghanistan, Afghan war, or Afghan civil war may refer to: *Conquest of Afghanistan by Alexander the Great (330 BC – 327 BC) *Muslim conquests of Afghanistan (637–709) *Conquest of Afghanistan by the Mongol Empire (13th century), see al ...

Symptoms

''Pythium aphanidermatum'' is responsible for pre- and post-emergence damping off. Pre-emergence damping off is when the seed is infected prior to

germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, fer ...

. This can result in poor or no germination, and is observable as a browning or rotting of the seed. Post-emergence damping off takes place after germination and results in a thinning, water-soaked stem near the plant collar, which eventually causes the collapse of the plant. ''P. aphanidermatum'' can also cause root rot. Symptoms of root rot include stunted growth, chlorotic leaves, leaf drop, and wilting. The infection begins at the root tip, and can cause the infected region to lose its protective outer layer, exposing the inner root to other pathogens

Disease cycle

''Pythium aphanidermatum'' overwinters in the soil as oospores,

e and/or

sporangia A sporangium (; from Late Latin, ) is an enclosure in which spores are formed. It can be composed of a single cell or can be multicellular. Virtually all plants, fungi, and many other lineages form sporangia at some point in their life cy ...

. Oospores can produce a germ tube and infect the plant directly, or, if the environment is favorable (that is an adequate amount of water is present), the oospore may produce sporangia, which in turn produce motile, biflagallete zoospores that swim to the host plant, encyst, and germinate. This infection can occur on seeds, which can rot, or produce a weak seedling. If it infects the roots of a seedling, the

mycelium Mycelium (plural mycelia) is a root-like structure of a fungus consisting of a mass of branching, thread-like hyphae. Fungal colonies composed of mycelium are found in and on soil and many other substrate (biology), substrates. A typical single ...

will grow throughout the plant tissue, releasing digestive enzymes which break down plant cell walls allowing the pathogen to absorb the nutrients, effectively killing the plant over time. ''P. aphanidermatum'' is a polycyclic disease A polycyclic plant pathogen has several life cycles during a season, meaning it can reinfect the host plant, or travel to another plant. After infection, several things can happen that spreads the infection: 1)More asexual structures form, including

sporangiophore {{Short pages monitor