PYTHIUM: CHARACTERISTICS, SPECIES, REPRODUCTION, NUTRITION - BIOLOGY - 2024

Pythium is a genus of oomycetes that contains many phytopathogenic species of economic importance in agriculture, since they cause the disease known as root rot in various plants. Some species are saprophytic and one of them affects different species of animals, including man, causing the disease known as pythiosis.

The species of this genus are characterized, among other things, by presenting a coenocytic mycelium, being able to reproduce vegetatively (asexually) as well as sexually, producing a single oosphere per oogonium, presenting an elongated antheridium and producing flagellated zoospores.

Pythium debaryanum culture. Taken and edited from: Tashkoskip.

Currently the genus is represented by more than 120 species around the world. Parasitic plant species do not show specificity for their host and are difficult to eradicate, since in addition to attacking various plant species, they are capable of surviving as saprophytes on decomposing plant matter.

characteristics

The species of the genus Pythium all possess coenocytic hyphae, hyaline in appearance, without transverse septa. The sporangium can be globose or filamentous. A characteristic of these oomycetes is that the zoospores do not develop directly in the sporangium, but in a vesicle that derives from the discharge tube of the sporangium.

The oogonium can be smooth or ornate, and the antheridium can be paragynous or hypogynous. Inside the oogonium a single oospore is formed, which can occupy its entire interior (plethoric) or a space may remain between the walls of the oogonium and the oospore (apletoric).

Taxonomy and representative species

- Taxonomy

The taxonomy of oomycetes is complex both at the level of the higher and lower taxonomic categories. According to traditional taxonomy, these organisms were considered fungi, however, they have recently undergone various rearrangements due to molecular and biochemical studies.

According to these results, some authors place them in the Protista Kingdom, while others place them, together with the Chrysophyta and Phaeophyta algae, within the Chromista Kingdom, Pseudofungi Subdivision. Lastly, they have also been located in the Straminipila Kingdom.

The genus Pythium is located within the Order Pythiales, Class Pythiaceae. This genus was originally described by Pringsheim in 1858, who selected P. monospermum as the type species.

The internal ordering of the genus has also undergone numerous changes, with the description of various subgenera, or the inclusion or exclusion of species. Currently, taxonomists consider that there are two morphologically distinguishable groups based on the shape of the sporangium.

On the one hand, there are the species that present a filamentous sporangium, while in the other group the sporangium is globose, which suggests that new intrageneric studies should be carried out to elucidate the phylogenetic relationship between both groups.

- Representative species

Pythium aphanidermatum

A nonspecific phytopathogenic species that frequently appears in greenhouse crops, it is responsible for the disease known as damping-off, root and stem rot, or fruit blight that affects many families and genera of plants.

The disease mainly affects plants in their early stages of development. In tobacco seedlings, for example, it causes growth retardation, chlorotic or partially necrotic leaves, as well as a diminished root system, with darker, necrotic roots.

It is also responsible for the disease known as grass burn or cottony burn, which affects the grass of golf courses, sports stadiums, parks and gardens. This disease is most active in the hottest seasons, with night temperatures above 20 ° C.

Pythium debaryanum

It is the causal agent of the disease known as soft seed rot, which can attack the plant at any stage of its cycle, but is more frequent in the sowing stage, before and after germination. Causes seedling drop, as well as seed rot.

In the newly germinated seeds and in the smallest plants, it causes the total destruction of the host, but the more developed plants can survive showing as symptoms of the disease a change in the color of some leaves, which turn yellow.

Pythium insidiosum

It is a pathogen that causes pythiosis, a pyogranulomatous disease of the skin characterized by being diffuse, with multiple foci, exudative, and progressing very rapidly. As this species lacks chitin and ergosterol in the cell wall and membrane, it cannot be controlled by antifungal agents that inhibit their production.

It affects various species of vertebrates, including dogs, cats, sheep, horses, cattle, migratory birds, and even man. It is considered an emerging disease.

Other species

References

1. AJ van der Plaats-Niterink (1981). Monograph of the genus Pythium. Studies in Mycology.
2. S. Uzuhashi, M. Tojo & M. Kakishima (2010). Phylogeny of the genus Pythium and description of new genera. Mycoscience.
3. JA Cardona, M. Vargas & S. Perdomo (2012). Frequency of presentation of Bovine Cutaneous Pythiosis (Pythium insidiosum) in three cattle farms in Córdoba, Colombia. CES Journal of Veterinary Medicine and Zootechnics.
4. Exploring what Pythium is… In FungiAlert. Recovered from: fungialert.es
5. Pythium. On Wikipedia. Recovered from: en.wikipedia.org
6. CALevesque & AW de Cock (2004) Molecular phylogeny and taxonomy of the genus Pythium. Mycological Research.
7. What is Pythium? Department of plant pathology and environmental microbiology. Recovered from: plantpath.psu.edu.