Submitted to: Mycological Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 7, 2009
Publication Date: May 15, 2010
Citation: Dixon, L.J., Castlebury, L.A., Aime, M., Glynn, N.C., Comstock, J.C. 2010. Phylogenetic relationships of sugarcane fungi. Mycological Progress. 9(4):459-468. Interpretive Summary: Rust fungi are a large and diverse group of parasites that attack crop plants. Accurate knowledge of the relationships among these fungi is important for controlling the diseases they cause. In this research a rust fungus on sugarcane recently introduced into the United States was compared to another rust fungus on sugarcane. Specimens were obtained from throughout the world. Using molecular sequence data it was determined that these two species are not closely related despite the fact that they infect the same host. Knowledge of these plant pathogenic fungi will be used by agronomists and plant pathologists who are working to control the rust fungi on sugarcane.
Technical Abstract: The phylogenetic positions of Puccinia spp. infecting sugarcane (a complex hybrid of Saccharum spp.) was determined using 42 newly generated rust sequences and 25 sequences from Genbank. Rust specimens on sugarcane were collected from 161 locations in 25 countries and identified based on light microscopy. The morphology for all samples matched that of Puccinia kuehnii or P. melanocephala, the orange and brown rust pathogens of sugarcane, respectively. Nuclear ribosomal DNA sequences (rDNA) including portions of the 5.8S rDNA, the complete internal transcribed spacer 2 (ITS2) and 5’ region of the large subunit (nLSU) rDNA were obtained for each species. Despite a shared host, the two Puccinia spp. on sugarcane are not closely related within the Pucciniales. Phylogenetic analyses place P. melanocephala most closely to P. miscanthi, P. nakanishikii, and P. rufipes infecting Miscanthus sinensis, Cymbopogon citratus, and Imperata cylindrica, respectively. Puccinia kuehnii is basal to a clade of Poaceae-infecting rusts including P. agrophila, P. polysora, P. substriata, and Uromyces setariae-italicae infecting Schizachyrium spp., Zea mays, Digitaria spp., and Urochloa mosambicensis, respectively. Light and scanning electron microscopy images highlight morphological differences distinguishing the two sugarcane-infecting species.