Phylogeny and Taxonomy of the Ophiostoma piceae Complex and the Dutch Elm Disease Fungi

Abstract

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 0. piceae complex that form synnemata lack the Sporothrix state. The nine recognized species within the 0. 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 0. piceae, 0. canum, 0. floccosum and the recently described 0. setosum (anamorph Pesotum cupulatum sp. nov.). In the hardwood group are 0. querci, 0. catonianum, and the Dutch elm disease fungi: 0. ulmi, 0. novo-ulmi and 0. himal-ulmi. Restriction fragment length polymorphisms of the ITS region are shown to be a convenient diagnostic tool for delimiting these species.

Both mating types in the heterothallic fungus Ophiostoma quercus contain MAT1-1 and MAT1-2 genes

“…After analysis of chromatograms with Chromas Lite v. 2.01 (Technelysium Pty. Ltd.; http://www.technelysium.com.au), the sequences of all isolates were compared to the ITS sequences of authentic O. quercus isolates (De Beer et al 2003;Grobbelaar et al 2009;Harrington et al 2001). …”

“…Most species have a close association with treeinfesting bark beetles and some cause serious tree diseases (Hausner et al 1993). This is true of species in the O. piceae complex (Chung et al 2006;De Beer et al 2003;Harrington et al 2001;Kamgan et al 2008;Uzunovic et al 2000), which includes the Dutch elm disease pathogens (O. ulmi and O. novo-ulmi) that have been responsible for the death of millions of Elm trees in the Northern Hemisphere (Brasier 1990). Other species in the O. piceae complex result in blue-stain of timber and they degrade wood quality.…”

“…Other species in the O. piceae complex result in blue-stain of timber and they degrade wood quality. For example, O. quercus is responsible for significant economic losses due to sapstain in hardwoods (De Beer et al 2003;Harrington et al 2001). …”

“…For example, the Dutch elm disease pathogens and O. quercus are heterothallic (Brasier and Kirk 1993;Harrington et al 2001;Solla et al 2008) where sexual reproduction requires the interaction of two individuals of opposite mating type (Coppin et al 1997). In contrast, individuals of homothallic species (e.g., O. arduennense and O. minus) are typically self-fertile and capable of completing the sexual cycle in the absence of a second individual (Carlier et al 2006;Gorton and Webber 2000;Grobbelaar et al 2009).…”

“…Conventional mating tests are laborious and time-consuming as they involve mating all available isolates in every possible combination and subsequent assignment of mating specificities. This traditional approach has been used widely for heterothallic species of Ophiostoma (Brasier and Kirk 1993;De Beer et al 2003;Grobbelaar et al 2009;Harrington et al 2001;Zhou et al 2004). …”