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Molecular Phylogenetic Analyses of Biological Control Strains of Trichoderma harzianum and Other Biotypes of Trichoderma spp. Associated with Mushroom Green Mold

A polymerase chain reaction-amplified DNA containing the internal transcribed spacer (ITS)-1, 5.8S, and ITS-2 regions of the nuclear ribosomal DNA transcriptional unit was sequenced for 81 isolates of Trichoderma spp. associated with mushroom culture or used for biological control of plant pathogens. Phylogenetic analyses revealed that the biocontrol isolates were more closely related to an isolate of T. harzianum biotype 1 (Th1) than to the aggressive biotypes 2 and 4. Th1 has been isolated from mushroom compost but is not the cause of widespread green mold epidemics that have occurred during the last 12 years in Europe and North America. Three isolates of T. harzianum obtained from shiitake (Lentinula edodes; Shi1B and S3-96) and maitake (Grifola frondosa; Mai1) substrates were placed within the biocontrol group. We also found evidence suggesting that some isolates of T. harzianum originally identified as Th4 from Pennsylvania are more closely related to Th2 from Europe. Finally, considering the wide range in sequence distribution of our samples, we propose that the consensus sequence found in this investigation be used as the reference sequence for further studies involving the identification and taxonomy of T. harzianum.