Submitted to: Plant Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/14/2016
Publication Date: 2/13/2017
Citation: Savchenko, K.G., Carris, L.M., Demers, J.E., Manamgoda, D.S., Castlebury, L.A. 2017. What causes flag smut of wheat? Plant Pathology. doi:10.1111/ppa.12657. Interpretive Summary: Fungi in the genus Urocystis cause diseases known as flag smut and occur on many different plant hosts including important food crops such as wheat. In addition to causing losses in yield, flag smut of wheat is quarantined in many countries and shipments of wheat with flag smut spores can be refused entry by those countries. In 2015, there was an outbreak of flag smut of wheat in Kansas. Using DNA sequences and spore characteristics, we were able to accurately determine the identity of the fungus causing this disease as Urocystis tritici and distinguish it from U. agropyri, which causes a similar disease on a weedy grass host. This allowed plant pathologists to rapidly determine the extent of the disease outbreak. This research will be used by extension agents, plant breeders, plant pathologists, and plant quarantine officials to implement management strategies for disease and to accurately determine the presence of flag smut of wheat in the United States and other countries.
Technical Abstract: The causal agent of flag smut of wheat is currently subject to strict quarantine regulations in many countries and is believed to have a wide host range on wild and cultivated grasses. This fungus has been classified as both Urocystis agropyri and Urocystis tritici. Urocystis agropyri was first described from Elymus repens and U. tritici was first described from wheat; however, using a morphological concept, G.W. Fischer in 1953 placed a large number of species in synonymy with U. agropyri, including U. tritici. The present study is the first attempt to clarify the taxonomy and phylogeny of flag smut pathogens of grasses using molecular analyses. The internal transcribed spacer (ITS) region of rDNA and the RNA polymerase II subunit 2 (RPB2) and translation elongation factor (TEF) protein-coding regions were used for phylogenetic reconstruction to determine the species boundaries of fresh and herbarium specimens from infected triticoid hosts. Results indicate that there are several distinct lineages of flag smut including flag smut of wheat, which is supported as a separate species, U. tritici. Sequences from specimens on E. repens, which are retained as U. agropyri, grouped in a clade distinct from those on wheat and rye. The closest relatives of U. tritici were found to be U. hispanica from Aegilops and Urocystis sp. from Thinopyrum junceiforme and Elymus trachycaulis. Recognition that U. tritici is genetically distinct from U. agropyri sensu stricto will facilitate trade through the development of accurate diagnostic tests.