Synchytrium
Synchytrium:-
1. Classification:-
Kingdom:- Myceteae
Division:- Mastigomycota
Sub division:- Haplomastigomycotina
Class:- Chytridiomycetes
Order:- Chytridiales
Family:- Synchytriaceae
Genus:- Synchytrium
2. Important Species:-
i. S. endobioticum
ii. S. fulgens
iii. S. australe
iv. S. anemones
v. S. cajani
vi. S. phaseoli-radiati
vii. S. cyperi
viii. S. fistulosus
ix. S. luffae
x. S. indicum
xi. S. meliloti
3. Habit and Habitat:-
> Synchytrium is a soil borne fungus which do not possess mycelium and is designated as holocarpic.
> It is worldwide in distribution, occurring in tropical, temperate and arctic zones.
> It has been found present even at higher altitudes of above 11000 ft.
> All the species are parasitic and infect algae, mosses, ferns and most commonly flowering plants.
> It causes Black wart disease in Potato. As a result potato tubers are affected and become malformed due to formation of warts on them.
> There are 200 species of Synchytrium, but about 60 species have been reported from India.
> The most common species is S. endobioticum, well known for disease on potato. It mainly infects solanaceous plants.
4. Thallus structure:-
> The body of the fungus is composed of a single uninucleate cell with definite cell wall.
> The fungus resides in the potato tuber in most part of its life cycle and produces many uniflagellate motile zoospores. These zoospores are the carrier of fresh infection in healthy tubers.
> The fungus induces the host tissue to multiply in number and to grow in size. Due to this, many warts develop in the tubers; hence the disease is known as wart disease.
> Although, wart is more common disease in Europe. Fortunately, it is not found in our country, but it has been reported from Darjeeling district of W. Bengal.
> Warts on infected tubers burst at later stage and release putrid liquid as exudates. This liquid contains zoospores in large number having single posterior flagellum. They swim in the film of water and move to other potato tubers.
5. Reproduction:-
a. Asexual reproduction:-
> The fungus completes its life mostly in host tissue in the form of resting sporangium.
> It remains in the soil for a very little period.
> In the spring season, uniflagellate zoospores are released from the infected tubers and swim to healthy tubers through water.
> The zoospores come in contact with the new host epidermal cell and dissolve the wall. They enter into the host epidermal cell leaving their flagellum outside.
> In the host cell, the protoplasm of the zoospore increases in size with large nucleus. Now, it becomes rounded having thick brown wall. This is called as summer spore.
> The host cell becomes enlarged and hypertrophied. The surrounding cells of infected cell form a rosette of cells around the infected cell.
> The summer spore now comes to the lower half of the cell and germinates. Its nucleus divides mitotically into 32 small nuclei. This multinucleate structure is called prosorus.
> Prosorus at the later stage becomes segmented into 4-9 multinucleate chambers, each having many nuclei.
> Now, the nuclei of each segment divides repeatedly into about 200-300 nuclei.
> Each segment of the prosorus develops into a sporangium.
> The protoplast of the each sporangium with a nucleus metamorphoses into a zoospore with a single posterior flagellum. These zoospores are released outside the tuber.
b. Sexual reproduction:-
> Under dry weather when water is scarce, the sporangium behaves like a gametangium.
> Many uninucleate uniflagellate gametes are produced from each segment. These are called as planogametes, which are similar to zoospores but, smaller in size.
> Uniflagellate planogamete, when comes out from gametangium, meet with another gamete and fuses with it.
> Fertilization takes place by karyogamy and zygote is formed.
> Each zygote has two flagella, shared by two individual mating gametes.
> The biflagellate zygote swims in the water film for some time and then it withdraws flagella. Now it settles on the host surface. Then it pierces the host wall by dissolving it and enters into the host epidermal cell.
> The protoplast of the zygote settles in the bottom of the cell. It enlarges and becomes thick walled and converts into a resting sporangium.
> The surrounding cells of the infected cell get activated to divide repeatedly giving rise to a rosette of cells.
> The resting sporangium becomes dormant in the winter. It becomes active in the next spring season.
> In the spring season, large numbers of granules appear which act as zoospore primordia.
> Meiosis was not observed, by Curtis ((1921), but it is assumed that there is reduction division during the formation of zoospores.
> Zoospores are released outside the host cell.