ACHLYA

CLASSIFICATION OF ACHLYA​

Kingdom :- Mycota

Division :- Eumycota

Sub-division :- Mastigomycotina

Class :- Oomycetes

Order :- Saprolegniales

Family :- Saprolegniaceae

Genus :- Achlya

GENERAL CHARATERSTICS OF ACHLYA​

• The species are aquatic and occur in a variety of water reservoirs.
• The thallus is eucarpic, filamentous, coenocytic, slender, white and much branched.
• Hyphae are broader at the base and gradually taper towards the apex.
• The basal cluster of hyphae forms holdfast. However, special organs of attachment are absent.

STUDY OF ASEXUAL REPRODUCTIVE STRUCTURES – ZOOSPORANGIA

• Zoosporangia produce asexual reproductive cells
  called zoospores.
• Each zoosporangium is an elongated, clavate or cylindrical structure. It is separated from rest of the hyphae by a septum at its base and opens by an apical pore.
• Zoospores are biflagellate and are released through apical pore. Zoospores aggregate around the pore and become encysted. (Cysts are liberated after a period of rest in the form of reniform biflagellated zoospores and are known as secondary zoospores). Zoospores germinate and give rise to new mycelium.
• In Achlya cymose branching of the hyphae occurs during the development of new zoosporangia, lateral zoosporangia growing out, below the primary and proliferation being absent.

STUDY OF SEXUAL REPRODUCTIVE STRUCTURES – OOGONIA AND ANTHERIDIA

• 1. Sexual reproduction is oogamous. Most of the species are monoecious, but a few species are dioecious (e.g. A. ambisexualis, A. bisexualis).
• Oogonia are either terminal or intercalary. Antheridia arise either from the main hyphae, from second~ ones (diclinous), from the oogonial branches or from oogonial cell (androgynous).
• Oogonia are spherical with a septum at its base. The wall of the oogonium may be smooth (e.g. A. racemosa) or spinous (e.g. A. colorata).
• Each oogonium has 1-8 eggs (or oospheres) and rarely upto 50. Each egg ( oosphere) is surrounded by a thin delicate wall, contains dense cytoplasm and a single nucleus.
• The antheridia are narrow, branched and multinucleate. Each is cut off from rest of the hyphae by a septum at its base.
• Antheridia grow closely applied to oogonium, send fertilization tubes which penetrate the oogonial wall and fertilize the eggs.
• At this stage oogonium contains many thick walled oospores.

IDENTIFICATION

• Kingdom – Mycota
  1. Chlorophyll absent
  2. Reserve food glycogen
  3. Cell wall of fungal cellulose.
• Division – Eumycota
  1. A definite cell wall present.
• Sub-division :- Mastigomycotina 
  1. Presence of motile spores or zoospores.
• Class :- Oomycetes
  1.  Usually mycelial (aseptate).
  2. Zoospores biflagellate.
• Order – Saprolegniales
  1. Mycelial thallus extensive and without conspicuous holdfast portion
  2. Sporangia cylindrical.
• Family – Saprolegniaceae
  1. Oogonium with many eggs and lack periplasm.
• Genus – Achlya
  1. Some or all zoospores encysting at the mouth of zoosporangium
  2. Zoosporangia not proliferating.