Molecular and morphological characterization of the willow rust fungus, Melampsora epitea, from arctic and temperate hosts in North America

Abstract

Current taxonomy places all rust fungi that occur on willow (Salix spp.) in North America in one species complex, Melampsora epitea Thüm. Characteristics of M. epitea isolates from the Canadian arctic were compared to M. epitea isolates from temperate regions of North America. Sequences from internal transcribed spacer (ITS) regions of rDNA were obtained from urediniospores from rust-infected Salix leaves collected in the Canadian arctic and in Minnesota and compared. Phylogenetic analysis of nuclear ribosomal ITS regions indicated that arctic M. epitea samples were divergent from temperate M. epitea isolates, perhaps in part because all rusts examined diverged according to host species. Four urediniospore characteristics were examined: area, circularity (shape factor), major axis length and spine density. Statistically significant (P < 0.05) differences were observed for spine density among all host species except S. nigra and S. bebbiana. However major axis length differed between these species. These results represent the first evidence that arctic and temperate Melampsora species on Salix hosts in North America have evolved distinct molecular and morphological characters.

• arctic fungal diversity
• fungal phylogenetics
• fungal taxonomy
• Melampsoraceae
• Uredinales
• willow diseases

The authors wish to thank Dr Les Szabo at the U.S.D.A. Cereal Disease Laboratory, St. Paul, Minnesota, for reviewing the paper and help with sequence alignment and phylogenetic analyses; Dr Michael Ostry, U.S. Forest Service, North Central Research Station, St. Paul, Minnesota, and Dr Kurt Leonard, Department of Plant Pathology, University of Minnesota, for comments and suggestions; and Dr Cort Anderson, University of Idaho, for help with DNA extractions. The authors also thank the Nunavut Research Institute for their co-operation, Polar Continental Shelf Project for transport in the arctic, and Monty Yank, Quttinirpaaq National Park and Parks Canada, for co-operation and interest in the project. This work was completed under Nunavut Research Institute License No. 0201102R-M and Quttinirpaaq National Park and Parks Canada Permit No. QNP-2002-004. This project serves as partial fulfillment of the requirements for Doctor of Philosophy degree at the University of Minnesota.