Molecular phylogenetic support from ribosomal DNA sequences for origin of Helminthosporium from Leptosphaeria-like loculoascomycete ancestors

Internal transcribed spacer (ITS) regions and 5.8S rDNA were PCR-amplified and sequenced for 17 isolates of Helminthosporium solani, cause of the pota to disease silver scurf, and for 10 other isolates obtained from culture co llections as Helminthosporium spp. Of these, five isolates had been incorre ctly identified as Helminthosporium spp. and belonged in the genera Cochlio bolus (anamorphs Bipolaris, Curvularia), Cladosporium, and Pyrenophora (ana morph Drechslera). Sequence alignment and analyses of ITS regions and 5.8S rDNA of four true Helminthosporium species and more than 45 fungi formerly grouped in the genus Helminthosporium s. l. revealed that the segregated He lminthosporium species did not group with Helminthosporium s. s. Three spec ies of Helminthosporium s. s. (H. solani, type species H. velutinum, and H. chlorophorae) grouped tightly and were most closely related to the teleomo rph Leptosphaeria bicolor For H. solani and H. velutinum, 18SrDNA sequences were also determined. Phylogenetic analyses of the 18S rDNA sequences of 3 3 euascomycetous species confirmed the close relationship of H. solani and H. velutinum to L. bicolor and placed Helminthosporium in the Pleosporales with 100% parsimony bootstrap support. Helminthosporium asterinum did not g roup closely with the other species of Helminthosporium s. s., but was as c losely related to discomycetes in the Leotiales as to other true Helminthos porium spp. Review of type material revealed that H. asterinum could be exc luded from the genus Helminthosporium based on morphology.