ABSTRACT
The genera Trichoderma and Gliocladium have long been associated with biological control phenomena, usually because of their presence in suppressive soils or on the root systems of surviving plants among diseased ones. Another conspicuous attribute is the ability of many species within these two genera to act as parasites of other fungi, some of which are plant pathogens (Baker, 1990; Chet, 1987; Cook and Baker, 1983; Howell, 1990; Papavizas, 1985). Although mycoparasitism is usually the first phenomenon that excites the attention of the observer, further investigation often reveals that secondary metabolites with antifungal and/or antibacterial activity are also produced by the biocontrol agent. The antimicrobial compounds produced by Trichoderma and Gliocladium constitute a rather diverse group with respect to structure and function (Taylor, 1986), and the group contains both volatile and nonvolatile compounds. A number of these antibiotic compounds have been related to biocontrol activity, but none has proven to be the sole arbiter of success or failure in a biocontrol system. More than likely, antibiosis is only one mechanism among the many that constitute a much more complex system, the end product of which is biological control. The entire range of secondary metabolites produced by these two genera and their structure and function are treated in detail in Volume 1, Chapter 8 and will not be addressed here. The purpose of this chapter is to acquaint the reader with the kinds of antibiotics produced by Trichoderma and Gliocladium spp. that have been associated with disease control, what the effects of environment are on their production and activity, how they act as mechanisms in the biocontrol process, and how genetic manipulation of these biocontrol agents can be used to enhance their antibiotic activity or reduce their phytotoxicity.
