11th Class Biology Biological Classification And System Of Classification / जैविक वर्गीकरण और वर्गीकरण की प्रणाली Important Features of Classes

(1) Phycomycetes (Oomycetes/Algal fungi) : It is also called lower fungi, mycelium is coenocytic. Hyphal wall may contain chitin or cellulose (e.g., Phytophthora). Asexual reproduction occurs with the help of conidio-sporangia. Under wet conditions they produce zoospores. Under dry conditions, the sporangia directly function as conidia. Zoospores have heterokont flagellation (one smooth, other tinsel). Sexual reproduction is oogamous. It occurs by gametangial contact where male nucleus enters the oogonium through a conjugation tube. The fertilized oogonium forms oospore. e.g., Saprolegnia, Albugo (Cystopus), Phytophthora, Phythium, Sclerospora, Peronospora, Plasmopara.

(2) Zygomycetes (Conjugation fungi) : Mycelium is coenocytic. Hyphal wall contains chitin or fungal cellulose. Motile stage is absent. Spores (Sporangiospores/aplanospores) are born inside sporangia. Sexual reproduction involve fusion of coenogametes through conjugation (Gametangial copulation). It produces a resting diploid Zygospore. On germination, each zygospore forms a germ sporangium at the tip of a hypha called promycelium e.g., Mucor, Rhizopus, Pilobolus, Abscidia, Saksenea.

(3) Ascomycetes (Sac fungi) : These are unicellular as well as multicellular fungi. In the latter, mycelium is septate. The asexual spores formed in chains are called conidia. The spores are formed exogenously, i.e., outside sporangium. They detach from the parent and form new mycelia. Sexual reproduction is through ascospores, which are formed endogenously (within the mycelium) in a sac like structure called ascus (pl. asci). The gametes involved in sexual reproduction are nonmotile compatible and are generally represented as + and –. The fusion of gametes is followed by reductional division that produces haploid ascospores. The fruiting body called ascocarp.

The ascocarp are of four types :

(i) Cleistothecium : It is an ovoid or spherical fruiting body which remains completely closed e.g., Aspergillus.

(ii) Perithecium : It is a flask shaped fruiting body which opens by a single pore called ostiole. e.g., Neurospora.

(iii) Apothecium : It is a saucer-shaped fruiting body. The asci constitute the fertile zone called hymenium e.g., Peziza.

(iv) Ascostroma : It is not a distinct fruiting body. It lacks its own well defined wall. The asci arise directly with a cavity (locule) of stroma. It is also called as pseudothecium e.g., Mycosphaerella.

(4) Basidiomycetes (Club fungi) : They are the most advanced fungi and best decomposers of wood. These are called club fungi because of a club shaped end of mycelium known as basidium. They have septate multinucleated mycelium. Septa possess central dolipores and Lateral clamp connections. The sexual spores called basidiospores are generally four in number. They are produced outside the body (exogenuous) unlike ascomycetes where they are endogenous. Two compatible nuclei fuse to form zygote, which undergoes meiosis and forms four basidiospores. The fruiting body containing basidia is a multicelular structure called basidiocarp. The common members are edible mushrooms (Agaricus), smut (Ustilago) and rust (Puccinia).

(5) Deuteromycetes (Fungi imperfecti) : The group include all those fungi in which sexual or perfect stage is not known. Mycelium is made of septate hyphae. Asexual reproduction commonly occur by means of conidia. e.g., Alternaria solani, Fusarium, Gibberella, Colletotrichum falcatum, Helminthosporium oryzae, Cercospora personata.