Oomycetes - Rankinrui

Japanese: 卵菌類 - らんきんるい

A biflagellate fungus with one wing-shaped and one tail-shaped flagellum at the front or side of the reproductive cell (zoospore). In sexual reproduction, the antheridium comes into contact with the oophorum, and the fertilization tube extends to the egg cell and fuses with it, but the zygote develops thick walls and becomes a dormant oospore. This type of fungus lives both in water and on land, and can be saprophytic or parasitic.

In unicellular or simple intracellular parasitic mycelia, the entire vegetative body becomes a zoosporangium or angiosperm (called holocytic). Many others are mycelia formed from branched tubular hyphae containing multiple nuclei, and at the time of reproduction, the tips of the hyphae are separated by septa to become zoosporangia or other organelles (called sporangial). In terrestrial angiosperm parasitic fungi, the mycelium that invades between cells creates knobby or branched haustoria inside the host cell to absorb nutrients, and forms sporangia with stalks that protrude from the stomata. These are called sporangia, which detach from the stalk and are dispersed by air currents or rainwater. If there is water at the time of germination, they produce zoospores, but if there is no water, they produce germ tubes and grow into mycelium.

[Hironori Terakawa]

Classification

(1) Paramecium: The whole-fruiting hyphae parasitize on Spirogyra or crab eggs, etc., and produce several chains of zoosporangia or oophores with antheridia and a single egg.

(2) Saprolegnia: Some are unicellular organisms that parasitize diatoms, and some, like the Thraustochytrids, produce roots on their tiny bodies, but most are saprophytic tubular mycelium.

(3) Sphaerothecales: These fungi grow in fresh water and have constrictions at almost equal intervals in their hyphae. They have rhizoids at the base of the hyphae. The ootheca usually contains a single egg.

(4) Pythia order: There are amphibious and terrestrial species, and most of them are saprophytic underground. A few parasitize algae and insects, and the Phytophthora species preys on rotifers. Phytophthora species parasitize agricultural crops, producing conidiophores.

(5) Commeliales: These parasitize agricultural crops, grapes, etc., and produce conidiophores. The oophores contain a single egg, and when the oospores germinate, zoosporangia form at the end of the germ tube.

[Hironori Terakawa]

[Reference items] | Fungi | Mizumoldi

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

Japanese:

生殖細胞（遊走子）の前端か側面に、羽型と尾型の鞭毛(べんもう)各1本をもつ二鞭毛の菌類。有性生殖では造精器が生卵器に接触し、受精管を卵細胞まで伸ばして接合するが、接合子は厚壁を生じ、休眠する卵胞子となる。この種の菌は水中と陸上にすみ、腐生も寄生もみられる。

　細胞内寄生の単細胞性、ないし簡単な菌糸では、その栄養体全体が遊走子嚢(のう)または生卵器・造精器になる（全実性という）。その他の多くのものは、多核を含む管状の菌糸が分岐した菌糸体であり、生殖時には菌糸の先端部が隔壁で仕切られて遊走子嚢その他になる（分実性という）。陸上被子植物類寄生菌では、細胞間に侵入した菌糸体が宿主細胞内にこぶ状か分岐した吸器をつくって栄養を吸収し、気孔から突き出して柄(え)のある胞子嚢を形成する。これは分生胞子嚢といわれ、柄から離れて気流や雨水によって散布され、発芽時に水があれば遊走子を生ずるが、水がない場合は発芽管を生じて菌糸体に成長する。

［寺川博典］