Rust fungi on panicum


Demers, J.E., Liu, M., Hambleton, S., Castlebury, L.A. (2017). Rust fungi on panicum, 109(1), 1-17.

Plain language summary

Switchgrass and other closely related grasses are cultivated for forage and as ornamentals, and in some cases as a source of cellulose for ethanol production. With increased cultivation, the incidence of major diseases caused by rust fungi has also increased. The objectives of this study were to establish a sound framework for identification of the rust species responsible for these diseases and to document host ranges more precisely, using traditional taxonomic approaches and molecular data analyses. The success of this study relied on the availability of historical biological collections; half of the herbarium specimens examined for morphological characters and sequenced for DNA barcodes were collected between 1881 and 1935. The results showed that five species infect switchgrass including two new species, rather than only two as previously reported, but not the species that has been most commonly reported which was shown to be restricted to a different host, called witchgrass. In particular, the DNA sequences that were publically available prior to this study for switchgrass rusts were found to match data for one of the new species described here. A third new species was described on a grass identified as yet only by a DNA sequence. The DNA barcodes published in this study for the rusts and their associated hosts will enable future researchers to correctly identify rust diseases on these grasses, which is critical for targeted breeding for rust resistance in biofuel crops and managing rust diseases in the field.


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.

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