NUCLEAR RIBOSOMAL INTERNAL TRANSCRIBED SPACER PHYLOGENY AND HOST DIVERSITY IN THE COELOMYCETE PHOMOPSIS

Species concepts in Phomopsis are based primarily on host association because morphological and cultural characters are generally insufficient for species diagnosis. Increasingly, there are reports that some species of Phomopsis are not host restricted but are capable of infecting several or more taxonomically unrelated host genera. Phylogenetic analysis of nuclear ribosomal DNA internal transcribed spacer sequences (ITS1 and ITS2) for 43 North American and Caribbean strains of Phomopsis isolated from diverse plant hosts and geographic origins resolved three clades, provisionally termed groups A, B, and C. Group A consists of isolates from shrubs and trees originating primarily from eastern North America. Group B includes isolates from woody and herbaceous plants that originate from tropical to subtropical regions and produce paraphyses among their conidiogenous cells. Group C occurs primarily on herbaceous plant hosts, including agricultural field crops, and is widely distributed throughout temperate to subtropical North America. Isolates from Europe and Asia may be significantly different in ITS sequences compared with North American isolates. The diversity of host taxa associated with terminal clades in the ITS phylogeny suggests that either Phomopsis species infect more than one host or host switching occurs frequently during speciation.