Spores There are many different kinds of spores. Those that come from mold mycelia asexually are called conidia Ð a round ball containing a genetically identical fragment of the parent fungus. Acospores are different because they are formed when the nuclei of two different spores in the same species merge. Basidiospores come from parasite fungi such as “rusts” and are often multicellular. Spores either single or multicelled, vary greatly in shape and wall ornamentation by the species. All spores, however, are small Ð they rarely exceed 100 microns and most are less than 20 microns2 . Spores also carry distinctive surface features that can cause allergic reactions, e.g., spikes, hooks, thorns, etc. adorn spore surfaces. Each species of mold produces a distinctive spore. Spore produced asexually are called conidia (conidium, singular) whereas spore produced sexually are called ascospores if produced by the main spore group, Ascomycetes. Conidia are genetically identical to the parent cell, whereas ascospores are genetically different.
For reproductive strategy, Fungi depend on wind and air for dispersing its “seed” and therefore each fungi produces a lot of spore. For example, the fungus responsible for corn smut produces about 25 billion spores per ear of corn. The wheat rust fungus produces about 10 billion spore per acre of moderately diseased plants and has been estimated to produce spore at the rate of 350,000 per second Ð up to 5.4 trillion per year. In short, every active Fungi or mold colony produces millions of spore which contaminate the air within any enclosed space.
For dispersal strategy, Fungi produce very small “seed” (spore) that stay aloft for a very long time. Even in absolute still air, an average-sized spore of about 20 microns in diameter will fall at the rate of about seven feet per minute. In fact, fungi spores are lifted up and moved by the slightest draft and conceivably stay aloft indefinitely Ð if, for example, windows in an apartment are left open. Professor C.M. Christensen at the University of Minnesota measured spore dispersal within an office building by using a marker fungus, a fungus with a distinctive color not normally found in the region. Five minutes after a culture dish was opened on the first floor, spore of the same fungus were detected on the fourth floor. Five minutes later, spore were falling on the fourth floor in amounts of thousands per square yard.4
For survival strategy, Fungi produce almost indestructible spore that survive a long time. Spore have very thick walls with dark pigmentation that defy ultraviolet light. In addition, many pathogenic spore have spiny cell walls that cause them to cling together as clumps when borne aloft. Fungi spore are capable of surviving both high and low temperatures. Many fungus colonies literally propel spore into the air by ejecting spore when water pressure builds up in the hypha stalk.