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- Saprophytic Fungi.
- Grows in plant and animal tissues, and soils.
- Lab cultures often show a cottony-pink mycelium.
- Macronidia shape is main basis for identification.
- Causes many plant diseases, mainly root rots and vascular wilts.
- Spores dispersed by air movement and rain splash.
- Over thirty unique species within the genus have been isolated.
The picture on the left shows typical Fusarium cells.
2. TAXONOMIC DESCRIPTION
The genus Fusarium consists of species that are highly variable
due to their genetic structure and also because environmental changes can
easily cause changes in their morphology. Many Fusarium species
require specific conditions to form their optimal morphologies and also
tend to mutate rapidly, causing further difficulties in identification.
The specific shape of the Fusarium's slimy, banana-shaped, septate
macronidia is the main identifying characteristic. Some species also form
distinctly different sequences of micronidia in their aerial mycelium.
Also, some species form chlamydospores in varying patterns.
Fusarium is a genus of the hyphomycetes, formally classified
as a genus of the deuteromycetes. There are thirty species of Fusarium
that are most commonly recognized, but many additional species have been
isolated. However, due to the varying conditions under which these were
cultured and the mutational possibilities of these species, not all scientists
recognize them as unique. It cannot be stressed enough as to the myriad
of subtle and qualitative differences among Fusarium species.
The above picture shows micronidial chains in the aerial mycelium of
various species of Fusarium.
3. ISOLATION AND
Isolation of Fusarium species can be achieved from samples of
soil, running water, insects, and seeds and roots from most plants. Because
of the many difficulties in identifying the various species, an evolving
set of isolation principles is gaining favor, including the following:
1) nutrient poor media such as carnation or banana leaf agar must be used
to culture the microscopic characteristics of Fusarium for accurate
identification to be possible, 2) exposure to fluorescent light and/or
UV light is necessary for optimal macronidia growth, and 3) the potato
dextrose and potato sucrose agars commonly used in the past to culture
Fusarium species should no longer be used as the high sugar levels
in these media tend to promote mutation in many species, therefore making
accurate identification an almost impossible task.
As stated earlier, Fusarium is found to be widely distributed
in nature in various environments. There are several toxic species that
can cause disease in both plant and animals, including humans. Infection
in animals by a Fusarium rarely occurs, and most often only does
so when a break in the skin allows for the organism to enter the body.
The most common diseases associated with Fusarium are common in
plants, mainly root rots and vascular wilts of field crops such as potatoes,
tomatoes, and small grains such as wheat, oats, barley, and rye.
The above picture shows chlamydospores in clumps of Fusarium.
4. ADDITIONAL SOURCES OF INFORMATION
Joffe, Abraham Z. 1986. Fusarium Species: Their Biology and Toxicology.
John Wiley & Sons, Inc. New York. 588 pp.
Nelson, Paul E. 1983. Fusarium Species: An Illustrated Manual for Identification.
The Pennsylvania State University Press. University Park. 193 pp.
Paul, E. A. 1996. Soil Microbiology and Biochemistry. Academic Press.
San Diego. pp. 92-98.
Toussoun, T. A. A Pictoral Guide To The Identification of Fusarium Species.
The Pennsylvania State University Press. University Park. 1976. 43 pp.
5. LINKS TO OTHER SITES ON FUSARIUM
This is the ULTIMATE FUSARIUM SITE. It contains everything you could
ever want to know about this genus.
ISK Biosciences Online
This page discusses the most common plant diseases caused by Fusarium.
This page will definitely fuel your madness for fungi!