Examination of Trichoderma phylogenies derived from ribosomal DNA sequencedata

Ribosomal DNA sequences were assessed for their usefulness in distinguishin g among Trichoderma isolates and for their robustness in resolving their ph ylogenetic relationships. DNA sequences from the D2 region of the 28S rRNA gene were determined for so Trichoderma isolates representing seven species . Eight distinct sequence types existed, and were mostly consistent with gr oupings based on morphology. Sequence variability within the D2 region alon e was not sufficient to provide a reliable phylogeny. Sequences from the IT S1, 5.8S and ITS2 regions were subsequently determined for 18 of the isolat es. Eight distinct ITS sequence types were detected among these 18 isolates . The ITS sequence types were generally consistent with morphology, ITS1 se quence data supported the identification of the Th3 T. harzianum group of M uthumeenakshi et ai. (1994) as T. atroviride. The data also confirmed that the biocontrol strains of this study were different from those causing dise ase problems in the mushroom industry in Europe and North America. Results from the phylogenetic analysis stress the importance of testing the robustn ess of data used to predict phylogenies. Two ITS sequence data sets for the same group of isolates produced significantly different phylogenies. Congr uence analysis detected that T. inhamatum (GJS90-90) was corrupting tree to pologies and 'first order pruning' was performed by removing its sequence f rom the two ITS data sets. Subsequent differences in the topologies of prun ed ITS1 and ITS2 trees were attributed to a lack of phylogenetic informatio n in the ITS2, sequence region. Although ITS sequences successfully differe ntiated among morphologically distinct isolates within Trichoderma, it did not provide a sufficient phylogenetic signal to resolve all of their relati onships.