ABSTRACT
Variation in Deuteromycetous and Ascomycetous fungi has been of great interest to researchers since at least the 1920s (Brierly, 1931; Hansen, 1938) and is an issue about which everyone working with these fungi soon becomes aware. For example, strains in culture may change in morphology, lose ability to sporulate normally, or suffer altered or lost pathogenicity. Such alterations are well documented and the literature frequently has been reviewed (Hastie, 1981; Kistler and Miao, 1992; Parmenter et al., 1963). Trichoderma and Gliocladium spp. are no exception in this regard. While teleomorphic stages of these fungi are known (see Volume 1, Chapter 2), most strains have no known sexual stages. Therefore, the genetic events that occur in these fungi during vegetative growth and reproduction are of primary importance in considerations of phenotypic expression of characters. Further, the nature of the changes that occur and their interactions within the thallus probably have substantial impacts on appropriate taxonomy of these fungi, on their abilities to adapt to changing environmental conditions, and on their interactions with other organisms, including plants, other microbes, and other strains of Trichoderma and Gliocladium.
