By Murali Putty, EMLab P&K Analyst
Trichoderma is a genus of asexual fungi, predominantly found in soil. Where known, all species currently have the ascomycete genus Hypocrea as their sexual stage. Trichoderma is also found in or on damp wood, grains, citrus fruit, tomatoes, sweet potatoes, paper and textiles. Three species of Trichoderma: T. viride, T. harzianum, and T. koningii, are usually found in indoor environments on building materials such as wallpaper, tiles, wallboard, and wood. Generally, Trichoderma species require high water activity.
Colonies are cream-colored in the beginning, later becoming green due to abundant sporulation. Conidiophores are septate, hyaline and loosely branched. Main branches of the conidiophores produce lateral side branches. All primary and secondary branches arise at 90° angles with respect to the main axis. Phialides are flask-shaped, and may be densely clustered on the main axis, or solitary. Conidia are typically smooth, pale green, spherical to ellipsoidal, measuring 3-5 x 2-4 µm, and occurring in slimy heads. Trichoderma spores generally disseminate through rain, insects, water splash, and wind.
Figure 1: Microscopic photo of Trichoderma with conidiophores and conidia.
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On spore traps, conidia resemble Penicillium and Aspergillus spores, but Trichoderma forms sticky clumps of conidia with a distinctive green pigment, rather than occurring in chains. Typical green spore clumps are identified as Trichoderma. On direct exam tape lift samples, they are readily identifiable. Trichoderma is very distinctive in culture, producing rapidly growing, floccose colonies which are white, yellow-green or bright green in colors. Certain species can grow very quickly, often outgrowing other fungal genera in the culture media. Trichoderma are typically fast growing at 25-30°C, but will not grow at 35°C. Some species of Trichoderma (e.g. T. viride) produce a characteristic coconut odor.
The mycelium of Trichoderma can produce a wide variety of enzymes, including cellulases (degrade cellulose) and chitinases (degrade chitin). Because of its ability to produce chitinases, Trichoderma can be a parasite of other fungi. For example, Trichoderma can parasitize the fruiting bodies and mycelia of certain mushroom-forming fungi. Several strains of Trichoderma have been developed as biocontrol agents against plant pathogenic fungi. Examples include its application for control of botrytis rot on apple and strawberry crops.
Trichoderma species are efficient producers of many extracellular enzymes. They are used commercially for degradation of complex polysaccharides. They are frequently used in the food and textile industries for these purposes. For example, cellulases from these fungi are used in denim fabrics to give rise to the soft, whitened fabric: stone-washed denim. The enzymes are also used in poultry feed to increase the digestibility of hemicelluloses from barley and other crops. For many years, the ability of these fungi to increase the rate of plant growth and development, including their ability to cause the production of more robust roots, has been demonstrated. Certain strains are known to increase the numbers of deep roots. These deep roots cause crops such as corn and ornamental plants such as turfgrass, to become more resistant to drought.
Trichoderma can be a particular problem in the mushroom cultivation industry, causing green mold disease of mushrooms. When the mushroom is parasitized, it develops a green mold over the surface, making the mushroom ugly and deformed, as well as causing significant yield losses for the industry. Trichoderma is also known to be the causal agent of green mold rot of onion. Human infections include: pulmonary, peritonitis in a dialysis patient, and a perihepatic infection in a liver transplant patient. It is considered as an emerging opportunist in immunocompromised persons. Inhalation of the conidia or the microbial volatile organic compounds (MVOC) may cause symptoms similar to those of Stachybotrys reactions.
1. Barron, G.L. 1968. The Genera of Hyphomycetes from Soil. The Williams and Wilkins Company, Baltimore. Pp 306-307.
2. De hoog, G.S., J. Guarro, J. Gene, and M.J. Figueras. 2000. Atlas of Clinical Fungi, 2nd ed. CBS, Utrecht. Pp. 943-953.
3. Cleaning Industry Research Institute: Soil Fungus Condiophore and Conidia (Trichoderma sp.)
4. EMLab P&K Fungal Library: Trichoderma
5. Environmental Reporter: Trichoderma
6. Wikipedia: Trichoderma
7. Tom Volk's Fungi Collection: Trichoderma viride
8. Cornell University: Trichoderma
This article was originally published on April 2010.