Molecular systematics of Helicoma, Helicomyces and Helicosporium and their teleomorphs inferred from rDNA sequences

Abstract

Three genera of asexual, helical-spored fungi, Helicoma, Helicomyces and Helicosporium traditionally have been differentiated by the morphology of their conidia and conidiophores. In this paper we assessed their phylogenetic relationships from ribosomal sequences from ITS, 5.8S and partial LSU regions using maximum parsimony, maximum likelihood and Bayesian analysis. Forty-five isolates from the three genera were closely related and were within the teleomorphic genus Tubeufia sensu Barr (Tubeufiaceae, Ascomycota). Most of the species could be placed in one of the seven clades that each received 78% or greater bootstrap support. However none of the anamorphic genera were monophyletic and all but one of the clades contained species from more than one genus. The 15 isolates of Helicoma were scattered through the phylogeny and appeared in five of the clades. None of the four sections within the genus were monophyletic, although species from Helicoma sect. helicoma were concentrated in Clade A. The Helicosporium species also appeared in five clades. The four Helicomyces species were distributed among three clades. Most of the clades supported by sequence data lacked unifying morphological characters. Traditional characters such as the thickness of the conidial filament and whether conidiophores were conspicuous or reduced proved to be poor predictors of phylogenetic relationships. However some combinations of characters including conidium colour and the presence of lateral, tooth-like conidiogenous cells did appear to be predictive of genetic relationships.

• Acanthostigma
• aero-aquatic
• Dothideomycetes
• Drepanospora
• freshwater fungi
• mitosporic fungi
• Thaxteriella
• Tubeufia
• phylogeny

CKM Tsui is grateful to the Croucher Foundation for the award of a postdoctoral fellowship. NSERC is thanked for an operating grant to Mary Berbee. TRF/BIOTEC Programme for Biodiversity Research and Training grants BRT 143016 and BRT 145006 supported freshwater fungal research in Thailand. Dr Daiske Honda and Rinka Yokoyama (Konan University, Japan) arranged a collection trip in Kobe. We express appreciation to R.J. Bandoni (UBC) and Amy Rossman (USDA) for cultures and Keith Seifert (Agri-Canada, Ottawa) and two anonymous reviewers for critical comments on the draft manuscript. Drs Goos and Goh provided advice during the course of investigation. FH and NYBG provided type and authentic specimens for identification and confirmation. SeaRa Lim, Patrik Inderbitzin and the Media group and Electron Microscopy unit at UBC are thanked for technical assistance.