In this article we will discuss about the nature of conidia and other spores of deuteromycetes.
The Deuteromycetes possess several different spore forms of which mention may be made of conidia, blastospores and chlamydospores.
Conidia:
Conidia vary greatly in size, shape, number of septations, wall thickness, colour, etc., as do the cells of the conidiophores which bear them. Such differences serve to separate the numerous form-genera and form-species among the Deuteromycetes. In general, conidia are produced in chains and are then said to be catenulate.
The youngest conidium is always the latest one formed and the oldest conidium is always on the far, or distal end of the chain (Fig. 301E). But cases of development of solitary conidia are also not infrequent (Fig. 301B, C & F).
A superficially similar but quite different type of chain formation is exhibited when conidia are not cut off from the conidiophores, but are developed from them by a process of budding. The conidia may form globular clusters at the ends of the conidiophores, or the conidia become surrounded by a mass of slime, which binds the conidia into a rounded mass giving the fungi a very characteristic appearance (Fig. 301D).
Some form-genera develop two- or more-celled conidia. The mode of septation may be only transverse or both transverse and longitudinal. Correspondingly the conidia may be thick- or thin-walled. Again some of the Deuteromycetes produce more than one type of conidia in the same thallus.
Conidia which are small spherical, oval, slightly elongated are usually single-celled or with one-septate, are called micro- conidia. Whereas, conidia which are large, usually multi-celled are called macro- conidia. The micro-conidia may be spherical, elliptical pyriform or clavate.
The macro-conidia may be divided into two or more cells by transverse septations and may appear fusiform or long crescent-shaped. Conidia may be thick- or thin-walled having surface smooth or warty and may be extremely variable in shape from globose, oval, cylindrical, clavate, filamentous thread-like, filamentous spirally coiled, to stellate or irregular in shape.
They may be hyaline to bright- or dark-coloured.
Conidia are also named in accordance with their shape or structure, nature of septation and number of cells in a conidium. There may be: one-celled conidia, amerospores (Fig. 302A); two-celled conidia didymospores (Fig. 302D); conidia having two or more transverse septa, phragmospores (Fig. 302B); conidia possessing septa both lengthways and crossways, dictyospores (Fig. 302C); long, thread- or worm-like conidia are scolecospores (Fig. 302G); conidia being rolled-up or corkscrew-like cylindrical generally septate are, helicospores (Fig. 302E); and staurospores (Fig. 302F), when conidia are star-like having three or more arms.
Other Spores of Deuteromycetes:
Besides conidia other types of spores are frequently encountered in the Deuteromycetes. These spores are often referred to as thallospores. Thallo- spores are asexual spores formed by transformation of existing cells of the thallus, and are set free by decay or disarticulation of the parent hyphae, not by a process of active cutting-off (abstraction).
This is clearly a type of natural fragmentation of the mycelium. Thallospores may be terminal or intercalary.
There are three principal types of thallospores:
blastospores, chlamydospores and arthrospores.
Blastospores:
These are round or oval cells that are budded off from the parent cells, enlarge and reproduce themselves, likewise by budding (Fig. 303A). They are rather common in unicullular form-genera. There are also mycelial forms which produce blastospores.
Chlamydospores:
These are thick-walled, non-deciduous, intercalary (intercalary chlamydospores) or terminal (terminal chlamydospores) spores made by the rounding up of cells of the somatic hyphae (Fig. 303B). In some cases they may also be formed on the side of the hyphae and are then said to be lateral chlamydospores. These are the resting spores that remain viable after the remainder of the somatic hyphae has died and disintegrated.
Arthrospores:
These are the spores that are formed by segmentation of the somatic hyphae, resulting in the cutting off of rectangular, somewhat thick-walled separate cells (Fig. 303C).