DISCUSSION OF ASEXUAL REPRODUCTION IN FUNGI

Fungi, unlike most other organisms, often possess the means of reproducing without sex. Although sexual reproduction has the advantage of facilitating genetic recombination and diversity it usually involves the slow and energetically costly production of accessory structures. As well, finding a compatible mate is often difficult or impossible.

A typical fungal life cycle can be seen as starting at the onset of a new growing season, such as at the end of winter or the coming of seasonal rains. At this time the fungus colonizes its substrate and begins to occupy it with hyphae. The new season often provides an abundance of substrate but in a discontinuous manner so that the fungus cannot just grow from one place to the next. This difficulty is overcome by many fungi through the production of asexual spores. Asexual spores are "cheap" to produce and therefore can be made in large quantities. As the season progresses, fungi produce these masses of asexual spores and thereby colonize new substrata which in turn serve as new bases for spore production. Thus the early stages of colonization may be modest and scattered but the later stages may resemble an out-of-control forest fire.

As the growing season comes to an end the fungi will usually begin to initiate sexual reproduction and its attendent spores. At this time they will have the nutrient reserves and the time to carry out the more complex sexual process. The spores produced by sexual reproduction may often survive a dormant period and then be released when the new growing season commences. This stage, and the asexual stages that precede it, are well-known to naturalists who use these as a basis for their outings.

The importance of asexual reproduction in fungal life histories is great and is reflected in the diversity of its forms. All groups of fungi possess asexual reproduction and carry it out within the limits of their genetic makeup. The subject is broad and of great importance to humans, hence it is treated in some detail on these pages. It also receives even closer attention on our Moulds web pages.

Our treatment here considers three means of asexual reproduction in fungi:

1. Sporangia - the spores are produced within a cell and are released when the cell breaks open

2. Conidia - spores that occur externally on the cells that produce them

3. Sclerotia - masses of fungal tissue with a hard rind produced by the aggregation of hyphae. Sclerotia are not spores

These three catagories cover nearly all types of asexual reproduction in fungi. There are a few intermediates but these are rare and of little importance.