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 iso- lates obtained from culture collections as Helminthos- porium spp. Of these, five isolates had been incor- rectly identified as Helminthosporium spp. and be- longed in the genera Cochliobolus (anamorphs Bipo- laris, 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. 1. revealed that the segregated Helminthosporium spe- cies did not group with Helminthosporium s. s. Three species of Helminthosporium s. s. (H. solani, type spe- cies H. velutinum, and H. chlorophorae) grouped tightly and were most closely related to the teleo- morph Leptosphaeria bicolor. For H. solani and H. ve- lutinum, 18SrDNA sequences were also determined. Phylogenetic analyses of the 18S rDNA sequences of 33 euascomycetous species confirmed the close rela- tionship of H. solani and H. velutinum to L. bicolor and placed Helminthosporium in the Pleosporales with 100% parsimony bootstrap support. Helminthos- porium 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