Phylogenetic relationships of Trichoderma harzianum causing mushroom green mold in Europe and North America to other species of Trichoderma from world-wide sources

Abstract

Nucleotide sequences of internal transcribed spacers (ITS-1 and ITS-2) and the 5.8 S gene of the ribosomal DNA repeat were examined in 15 lines of Trichoderma spp. Six lines representing four biotypes (Th1, Th2, Th3 and Th4) of T. harzianum associated with mushroom compost or the raw materials used in compost could be separated into two distinct groups. One group contained biotypes Th1, Th2 and Th4 while the other contained biotype Th3 and other isolates of T. harzianum/atroviride (Sect. Trichoderma) from worldwide sources. We propose that Th3 should be considered T. atroviride and not T. harzianum. Within this group, excluding gaps, nucleotide differences in ITS-1 were as much as double those of the ITS-2 region (25.6% versus 11.0%, respectively). Biotype Th3 from Ireland accounted for most of the variation in both the ITS-1 (24.3%) and ITS-2 (7.8%) data. Five nucleotide substitutions (2.5%) were found in ITS-1 sequences for the most prevalent biotypes associated with mushroom green mold (Th2 and Th4) from Canada, Ireland and the United States. Only one substitution (0.5%) was found for these biotypes for ITS-2. Four nucleotide substitutions (2.0%) were found for Th2 from Ireland compared to isolates of biotype Th4 from Canada and the United States. Only one nucleotide difference (0.5%) each for ITS-1 and ITS-2 was found among the isolates of Th4 from Canada and the United States. Thus, most of the variation in nucleotide sequences among the biotypes were present in ITS-1. Finally, Th2 accounted for the only difference found in the 5.8 S rDNA sequences of the six lines of mushroom-associated T. harzianum.