Puccinia emaculata (switchgrass rust)

Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Basidiomycota
Subphylum	Pucciniomycotina
Class	Pucciniomycetes
Order	Pucciniales
Suborder	Uredinineae
Family	Pucciniaceae
Genus	Puccinia

Scientific Name

Puccinia emaculata

Scientific Name Synonyms

Aecidium pammelii

Uredo panici-urvilleani

Common Name

Switchgrass rust

Author:Tom Creswell, Purdue University

Reviewed by:Name, Organization

Pathogen

Symptoms begin as light yellow flecking or discoloration on the leave or culms. These spots later develop into brown lesions as spores of the rust fungus emerge through the leaf epidermis.

T. Frazier, et. al describe the urediniospores as brown, round, and averaging 26.08 ± 1.67 μm long and 24.65 ± 1.66 μm wide. The teliospores are two-celled, oblong to ellipsoid in shape, and averaged 32.23 ± 3.07 μm in length. The apical cell width averaged 17.6 ± 1.83 μm and the basal cell width averaged 15.08 ± 1.75 μm. T. Frasier, et. al designed two primers for use in identifying the pathogen (5′-CCAGTAACGGCGAGTGAAGAG-3′ and 5′-CGACTTCCATGGCCACCGTGCGGCTGTCT-3′) based on the 18S rDNA sequence of P. emaculata.

Hirsch, et. al describe the teliospores as dark brown, two-celled, oblong to ellipsoid, and 33 ± 3.5 μm long with an apical cell width of 17.5 ± 2.7 μm and basal cell width of 16.2 ± 2.8 μm (reported as mean ± standard deviation, n = 25). Pedicles were colorless to light brown and measured 25.4 ± 9.2 μm (n = 25)

Symptoms and Signs

Symptoms begin as light yellow flecking or discoloration on the leaves or culms. These spots later develop into brown lesions as spores of the rust fungus emerge through the leaf epidermis. The dark brown pustules containing urediniospores are arranged loosely in rows following leaf veins. Later in the summer infected leaves produce erumpent fissures with masses of dark brown teliospores.

Ecology and Spread

Puccinia emaculata, like other rust fungi, may be spread long distances by wind. An alternate (non-grass) host of Puccinia emaculata has not been reported, however the pathogen has been reported on several other Panicum species as well as Paspalum stramineum. (Farr, et.al)

Geographic Distribution

Puccinia emaculata appears to be widespread on switchgrass (Panicum virgatum) in the US, with reports from at least 10 US states as well as in Mexico (Farr,et.al; Creswell personal communication).

Management

Management options are limited but several projects focused on breeding for resistance are ongoing.

Diagnostic procedures

Confirmation is by direct microscopic examination of sproulating tissues containing urediniospores and/or teliospores matching the description of Puccinia emaculata.

Resources and References

• http://dx.doi.org/10.1094/PDIS-09-12-0814-PDN: First Report of Puccinia emaculata Infection on Switchgrass in Virginia

T. Frazier, Z. Shen, and B. Zhao, Department of Horticulture, Virginia Tech, 301 Saunders Hall, Blacksburg 24061; and E. Bush, Department of Plant Pathology, Physiology, and Weed Science, Virginia Tech, 101G Price Hall, Blacksburg 24061

• http://dx.doi.org/10.1094/PDIS-94-3-0381B: First Report of Rust Caused by Puccinia emaculata on Switchgrass in Arkansas

R. L. Hirsch, D. O. TeBeest, and B. H. Bluhm, Department of Plant Pathology, Division of Agriculture, University of Arkansas, Fayetteville 72701; and C. P. West, Department of Crop, Soil, and Environmental Science, Division of Agriculture, University of Arkansas, Fayetteville 72701

• BioEnergy Research: http://link.springer.com/article/10.1007%2Fs12155-012-9263-6/fulltext.html. June 2013, Volume 6, Issue 2, pp 458-468, Characterization of the Rust Fungus, Puccinia emaculata, and Evaluation of Genetic Variability for Rust Resistance in Switchgrass Populations
• S.R. Uppalapati, D.D. Serba, Y.Ishiga, L.J. Szabo, S. Mittal, H.S. Bhandari, J.H. Bouton, K. S. Mysore, M. C. Saha
• Farr, D.F., & Rossman, A.Y. Fungal Databases, Systematic Mycology and Microbiology Laboratory, ARS, USDA. Retrieved January 23, 2014, from http://nt.ars-grin.gov/fungaldatabases/

Acknowledgements

• National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30818 as part of "Diagnostic Image Series Development for Supporting IPM in the North Central Region" (USDA-NIFA-RIPM-003349)