Pythium

Class: Oomycetes

Order: Peronosporales

Family: Pythiaceae

Genus: Pythium

Pythium is a mold of cosmopolitan distribution and consisting of about 45 species which maybe aquatic or terrestrial inhabits. It is facultative parasite on fresh water algae and seedling of many plants like mustard, papaya, tobacco, beans, ginger, etc. it also occurs saprophytic ally in moist soil. Pythium infects the host plant by the wounds. It is also responsible for the “damping- off” disease of seedling. It is also causes “soft rot”,”root rot” etc. it is also involved in decay and decomposition of the plant remains in the soil.

The mycelium of Pythium appears as a white fluffy growth consisting of slender, branched, aseptatic coenocytic hyphae without rhizoids. In the host plant mycelium is both inter and intra cellular without hysteria formation. The cell wall is made up of fungal cellulose and the cytoplasm consists of , many nuclei and other membrane bound organelles like, the mitochondria, ribosome’s, endoplasmic reticulum etc. Reserved food materials are in the form of oil droplets and glycogen.

REPRODUCTION
Reproduction in Pythium is both asexual and sexual.

ASEXUAL REPRODUCTION
It is by the formation of biflagellate zoospore inside zoosporangia both at the tip of the sporangiopore. The sporangium is globule with an epical papilla. Some spices have filamentous or elongated sporangia, which are the same diameter of the hyphae and are they form indistinguishable from hyphae. The sporangiopore maybe simple or in branched. In some spices the sporangia germinates directly into new hyphae and hence they are called cornidium.

SEXUAL REPRODUCTION
It is oogamous and occurs in the formation of terminal oval or spherical oogonium and an elongated antheridium from adjacently on the same mycelium. Fertilization of the female gamete in the oogonium is by the male single functional nucleus in the antheridium which results in the formation of thick walled oospores.

ECONOMIC IMPORTANCE
Pythium dibaryanun causes the “damping-off” tobacco and chilies seedlings.
P. aphanidermatum causes soft rot of apple, papaya and beans.
P.myriotylum causes rhizome rot of ginger.
Pythium is also responsible for decomposition of organic matter in the soil

Posted in: Microbiology