Phylogeny and taxonomy of the Ophiostoma piceae complex and the Dutch elm disease fungi

The Ophiostoma piceae complex forms a monophyletic group of insect-dispersed pyrenomycetes with synnemata (Pesotum) and micronematous (Sporothrix) synanamorphs. Other species of Ophiostoma outside of the O. piceae complex that form synnemata lack the Sporothrix state. The nine recognized species within the O. piceae complex are delimited by synnema morphology, growth rate at 32 C, mating reactions and sequences of the internal transcribed spacer (ITS) region of the rDNA operon. Phylogenetic analysis of the ITS region suggests two major clades in the complex, one that causes bluestain in primarily coniferous hosts and the other on primarily hardwood hosts. In the coniferous group are O. piceae, O. canum, O. floccosum and the recently described O. setosum (anamorph Pesotum cupulatum sp. nov.). In the hardwood group are O. querci, O. catonianum, and the Dutch elm disease fungi: O. ulmi, O. novo-ulmi and O. himal-ulmi. Restriction fragment length polymorphisms of the ITS region are shown to be a convenient diagnostic tool for delimiting these species.