BIOL/CSES 4684

FUSARIUM

SOIL MICROBIOLOGY

This webpage was created by Michael W. Cullison

1. IDENTIFYING CHARACTERISTICS

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 ECOLOGY
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
FusKey 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.

Mycology Links This page will definitely fuel your madness for fungi!