In this article we will discuss about:- 1. Introduction to Zygomycetes 2. Distinctive Features of Zygomycetes 3. Classification.
Introduction to Zygomycetes:
The class zygomycetes derives its name from the thick-walled resting spores, the zygospores formed as a result of the complete fusion of the protoplasts of two equal or unequal gametangia. It comprises 450 species which are grouped under 70 genera.
They all are terrestrial molds which show a wide range in their habit. Most of them are saprobes. Among these some are soil saprophytes and others coprophilous (growing on dung).
The parasitic species include pin molds which attack fungi, insects or protozoa. Some are facultative weak parasites (Rhizopus sexualis) of higher plants. A few are specialized parasites of animals. A very few occur as obligate parasites of other Zygomycetes.
The mycelium is well developed. When young it lacks cross walls but the old hype may be septate. Septa also appear in connection with development of reproductive bodies or to seal off injuries.
Distinctive Features of Zygomycetes:
1. The hyphal walls are chiefly composed of chitinchitosan.
2. The motile cells are completely absent in the life cycle.
3. Asexual reproduction typically takes place by means of non-motile sporangiospores commonly produced in large numbers within sporangia. Sometimes the entire sporangium functions as a single spore in the same manner as the conidium.
4. Chlamydospore formation is of frequent occurrence.
5. Sexual fusion involves gametangial copulation.
6. The thick-walled sexually produced zygospore formed by the complete fusion of the protoplasts of two gametangia is a resting structure.
7. The zygospore germinates to produce a hypha, the promycelium which bears a terminal sporangium.
Economically the zygomycetes are of significant importance. Some of them are used in the fermentation of food items while a few others are employed to produce enzymes, acids, etc. Saprophytic species spoil our food stuffs. Some zygomycetes are important mycorrhizal fungi and a few others are human pathogens.
Some of the zygomycetes are of great interest for having developed peculiar methods of spore dispersed. “Fungus shotgun” of spore dispersal of Pilobolus and forceful propulsion of the asexual spores of the Entomophthorales are the common examples. Animal trapp-mechanism of the zoopagales is of common interest.
Classification of Zygomycetes:
Traditionally the class comprises 3 orders:
Mucorales, Entomophthorales and Zoopagales. Benjamin (1979) divided the class into 7 orders namely, Mucorales, Demorgaritales, Kickxellales, Endogonales, Entomophthorales, Zoopagales and, Harpellales.
Dube (1993), modifying the original classification of Ainsworth (1973) recognises following three orders under the class Zygomycetes:
Chiefly Saprophytes, some weak parasites on plants, a few endoparasites of vertebrates; mycelium extensive, asexual reproduction by sporangiospores or rarely by conidia Zygospore wall may be formed by modification of gametangial walls.
Typically parasitic on animals; rarely saprophytes, mycelium- limited. Asexual reproduction by sporangia turned conidia or true conidia; conidia discharged forcibly, gametangial wall not transformed to Zygospore wall.
Typically parasite on animals, rarely saprophytes, mycelium present with complicated haustoria. A sexual reproduction by conidia which are passively discharged; gametangial wall not transformed to Zygospore wall. Of these, Mucorales have been discussed in some detail.