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ABSTRACT
Taxonomy in Trichoderma is problematic because of the lack of reliable morphological characters. This study evaluates five morphological species using methods of isozyme analysis that allow determination of allozyme polymorphism. One hundred nine alleles were resolved at 16 putative enzyme loci among 71 strains tested. Morphological species were not characterized either by specific alleles at single loci or by specific patterns of alleles at multiple loci. Rather, most alleles were distributed among most species, and each species included several different alleles at most loci. Allele patterns were analysed by phylogenetic analysis using parsimony (PAUP). A strict consensus tree was derived from 20 equally parsimonious, shortest cladograms using Gliocladium virens as an outgroup. In the resulting cladogram, T. harzianum included a main group of strains adjacent to the outgroup and other strains distributed throughout the cladogram; this species appears to be paraphyletic. A core group of T. pseudokoningii strains appears to be monophyletic and derived directly from a T. harzianum-like ancestral group. Trichoderma hamatum included three isozymically distinct strains with close affinity to Gliocladium virens and a main group which appears to have been derived from a T. harzianum-like ancestral group independently of the core group of T. pseudokoningii. Trichoderma koningii and T. viride are not well distinguished from each other, but T. viride appears to be more derived and may have arisen from a more ancestral T. koningii type. Phylogenetic analysis of allozyme data identified isozymically similar core groups of strains within morphological species, clusters of strains from various species, and isozymically distinct strains for further study. Wide distribution of numerous aUeles among morphological species suggests that extensive genetic exchange occurs among these taxa.