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

Abstract

Internal transcribed spacer (ITS) regions and 5.8S rDNA were PCR-amplified and sequenced for 17 isolates of Helminthosporium solani, cause of the potato disease silver scurf, and for 10 other isolates obtained from culture collections as Helminthosporium spp. Of these, five isolates had been incorrectly identified as Helminthosporium spp. and belonged in the genera Cochliobolus (anamorphs Bipolaris, Curvularia), Cladosporium, and Pyrenophora (anamorph 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 Helminthosporium species did not group with Helminthosporium s. s. Three species of Helminthosporium s. s. (H. solani, type species H. velutinum, and H. chlorophorae) grouped tightly and were most closely related to the teleomorph Leptosphaeria bicolor. For H. solani and H. velutinum, 18SrDNA sequences were also determined. Phylogenetic analyses of the 18S rDNA sequences of 33 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 group closely with the other species of Helminthosporium s. s., but was as closely related to discomycetes in the Leotiales as to other true Helminthosporium spp. Review of type material revealed that H. asterinum could be excluded from the genus Helminthosporium based on morphology.

Key Words:

• ascomycete phylogeny
• Bipolaris
• Cochliobolus
• Drechslera
• Exserohilum
• H. solani
• H. velutinum
• internal transcribed spacers
• Pleosporales
• Pyrenophora
• rDNA
• Setosphaeria