Taxonomic re-evaluation of three related species of Graphium, based on morphology, ecology and phylogeny

Abstract

Two fungi associated with bark beetles, Graphium pseudormiticum (described in 1994) and Rhexographium fimbriisporum (described in 1995), have two micromorphological characters in common. Both species produce conidia with conspicuous basal frills, and the conidia align in chains, despite being produced in slime. The association of G. pseudormiticum with the pine bark beetle, Orthotomicus erosus, and the association of R. fimbriisporum with the spruce bark beetle, Ips typographus, suggest ecological differences between the two fungal species. Analyses of micromorphology and phylogenetic analyses of aligned 18S and ITS sequences suggest that these two species are congeneric and should be classified in Graphium but that they represent distinct species. A collection of strains tentatively identified as Graphium spp., isolated from Ips typographus on Picea abies, Ips cembrae on Larix decidua and Tomicus minor on Pinus sylvestris in Austria share the same unusual basal conidial frills and conidial chains. Isolates from spruce were identified as G. fimbriisporum and those from pine as G. pseudormiticum. The strains from Ips cembrae on Larix decidua, distinguished by the reddish color of their colonies, microscopic structures and molecular characteristics, are described as the new species Graphium laricis sp. nov., and the close relationship of this species with the other two species is confirmed.

• conidium development
• Graphium
• Ips spp
• Larix
• phylogeny
• Picea
• Pinus
• Rhexographium

This study was significantly enhanced and to some extent motivated by cultures collected from galleries of Ips cembrae on larch in Scotland. We are deeply grateful to Dr. Derek B. Redfern, formerly of the pathology branch of Forest Research, Northern Research Station, Roslin, Scotland, who assisted M.J.W. and T.K. in making these collections. We also thank Keith Seifert and Scott Redhead for advice on many aspects of this study and critical reviews of early versions of our manuscript, as well as Dr. M. Morelet and PPRI (South Africa) for providing us with the type specimens of R. fimbriisporum and G. pseudormiticum, respectively. The financial assistance of the National Research Foundation (NRF), the THRIP initiative of the Department of Trade and Industry (DTI), and members of the Tree Pathology Co-operative Programme, South Africa, as well as a Strategic Grant from the Natural Sciences and Engineering Research Council of Canada (NSERC) to C. Breuil, the University of British Columbia, Vancouver, Canada, is sincerely appreciated. T.K. received financial support from the Forest Ecosystem Restoration (SF008) Special Research Program, financed by the Austrian Science Foundation and the Austrian Ministry of Agriculture and Forestry. This paper is part of a broader study of ophiostomatoid fungi on insect-infested spruce and larch in Austria and Scotland.