Rust fungi on Panicum

ABSTRACT

Rusts are economically important diseases of switchgrass (Panicum virgatum) and other Paniceae grasses. Phylogenetic analyses based on sequences of the nuc rDNA 5.8S internal transcribed spacer 2 region (ITS2), partial 28S region, and intergenic spacer region (IGS) of nuc rDNA showed that species of rust fungi infecting switchgrass are closely related within Puccinia. Variation among rbcLa sequences for the associated hosts sampled concurred with the original identifications. Five species infecting switchgrass were recognized: Puccinia graminicola (≡ Uromyces graminicola), P. pammelii (= P. panici), and the proposed new species P. amari, P. novopanici, and P. pascua. These species were distinct from P. emaculata, the species previously considered the principal rust pathogen infecting switchgrass but that was found exclusively on witchgrass (Panicum capillare) in this study. Rust fungi on switchgrass previously identified as P. emaculata were identified as the morphologically similar species P. amari, P. novopanici, and P. pammelii. The morphological species Puccinia graminicola was found to comprise three species, P. graminicola and the proposed new species P. pascua on switchgrass and P. cumminsii on Panicum sp.

KEY WORDS:

• herbarium specimens
• molecular phylogeny
• Pucciniales
• switchgrass
• warm-season grasses

ACKNOWLEDGMENTS

We thank Lindsay Garnett, Quinn Eggertson, and Sylvia Wilson for assistance with sample handling and molecular work; Cavan Allen, Scott Redhead, and John Wiersema for advice on taxonomy; and Tunesha Phipps for technical support. We also thank the US National Fungus Collections, the Canadian National Mycological Herbarium (DAOM), the Swedish Museum of Natural History (S), and the Academy of Natural Sciences of Philadelphia (PH) for curatorial assistance, access to specimens, and allowing DNA sampling, and to S for permission to reprint the photograph and line drawing associated with F28130. This work was supported by a USDA-ARS headquarters–funded postdoctoral award and the Genomics Research and Development Initiative (GRDI) of the Government of Canada.

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