Taxonomy and phylogeny of the Fusarium dimerum species group

Abstract

The morphospecies Fusarium dimerum, known only from its anamorph, comprises at least 12 phylogenetically distinct species. Analyses of the large subunit ribosomal DNA (LSU rDNA) show they are taxa of the Nectriaceae (Hypocreales), related to F. domesticum and form a phylogenetically distinct clade within Fusarium. Fusarium dimerum, for which no herbarium material could be located, is characterized by macroconidia with a single, median septum, according to the original description and illustration. Fusarium lunatum (= F. dimerum var. violaceum) forms similar but longer macroconidia and purple, catenate or clustered chlamydospores. Fusarium delphinoides sp. nov., F. biseptatum sp. nov., F. penzigii sp. nov., F. nectrioides comb. nov. (= F. dimerum var. nectrioides) and two unnamed Fusarium spp. produce macroconidia with mostly two or rarely three septa. The name F. dimerum, which originally was applied to a fungus from a citron, is used for a taxon including isolates causing infections in immunocompetent and immunocompromised patients. Fusarium nectrioides, F. delphinoides, F. penzigii and F. biseptatum are known from soil and dead plant substrata or rarely as agents of trauma-related eye infections of humans. Fusarium lunatum is an inhabitant of the cladodes of species within the cactus genera Opuntia and Gymnocalycium. Its unnamed closest sister taxon, which also forms 1-septate macroconidia and purple, clustered chlamydospores, was isolated from a human sinus. Fusarium delphinoides is a pathogen of the cactus-like African species Hoodia gordonii (Apocynaceae). Phylogenetic analyses based on combined sequences of the internal transcribed spacer region, LSU rDNA and partial sequences of the elongation factor 1-alpha and beta-tubulin genes identified a clade of several species producing predominately 2-septate macroconidia as the reciprocally monophyletic sister of F. dimerum. The basal sister group of the two aforementioned clades includes Fusarium lunatum and two undescribed species, all of which form 1-septate macroconidia.

• β-tubulin gene
• DNA barcoding
• Hoodia pathogens
• Hypocreales
• internal transcribed spacer region
• large subunit of ribosomal DNA
• microcodes
• Microdochium
• morphology
• opportunistic human pathogens
• phylogeny
• translation elongation factor 1 α

We gratefully acknowledge the assistance of the curators and staff of the herbaria B, BM, BR, C, CGE, E, G, GE, GZU, K, M, NY, PAD, PAV, PC, PR, PRM, RO, S, STR, TAES, UPS and W. We also thank Walter Gams (Baarn, the Netherlands) for kindly correcting the Latin diagnoses and Wally Marasas and two annonymous reviewers for their critical comments on earlier drafts of this paper. H.-J.S. is specifically grateful for the assistance of Arien van Iperen (CBS, Utrecht, the Netherlands), who provided technical assistance, and Johannes Z. Groenewald (CBS) and Stacy Sink (USDA, ARS, NCAUR), who provided DNA sequences. The vast majority of the morphological data in this study were collected at CBS; some figures were made at the Department of Biology at the Biotechnical Faculty of the University of Ljubljana. A part of this work was supported by program SYNTHESYS NL-TAF-364 made available by the European Community. The mention of trade products or firm names does not imply that they are recommended or endorsed by the institutions and organizations hosting the authors of this paper over similar products or other firms not mentioned.