Taxonomy

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

Scientific Name

Puccinia polysora

Common Name

southern corn rust

Author: Juliana Pereira, University of Florida

Reviewed by: Jeffrey Rollins, University of Florida

Pathogen

Southern corn rust is caused by the fungal pathogen Puccinia polysora. Although this is the most devastating rust of the three rusts that affect corn, it is of minor importance in the USA (4). It is an important disease of corn in tropical areas. The damage to the plant is due to the loss of photosynthetic leaf area (3). The disease progressively worsens as the plant develops. This pathogen also infects other hosts including silver plume grass (Saccharum [Erianthus] apopecuroides), eastern gamagrass (Tripsacum dactyloides), Tripsacum lanceolatum, T. laxum, and T. pilorum (1).

Symptoms and Signs

Puccinia polysora produces dense uredial pustules on the surfaces of the corn leaves, leaf sheaths, and stalks. The uredia are small, 0.2-2.0 mm long nad circular to oval in shape (4). The color is orange-red to light cinnamon brown (1). The rust symptoms occur when the uredia break open and sporulate. The rust affects the lower leaves more than leaves further up the plant (4). Pustules of P. polysora are not as powdery initially as those produced by Puccinia sorghi (Common corn rust). Also, the development of dark colored teliospores around the pustule occurs later in the season than those of common corn rust (1).

Ecology and Spread

Favorable environmental conditions for disease development are altitude less than 700 meters, temperatures between 25 and 35 degrees Celsius, and high humidity. The uridiospores are the only type of spores known for this pathogen life cycle. Urediniospores are responsible for primary and secondary inoculum (3). These urediniospores spread via wind. Urediniospore germination and penetration requires free water on the surface of the corn leaves (1). The spores are able to survive in plant debris, which is an important source for the disease spread (3).

Geographic Distribution

The disease can be found in almost all the tropical and subtropical regions in the globe, such as Africa, Southeast Asia, Australia, and southern regions of the Americas (3).

Management

Till fields in the fall to bury crop residue.
Rotate fields for at least one year with crops other than corn.
Plant corn varieties that are less susceptible to the pathogen.
Analyze the right place and the right time to plant.
Use fungicides to prevent disease and before significant damage.
Consult your local extension specialist for legal and efficacious fungicide products available in your area. Remember, the label is the law and the product applicator is responsible for reading and following all chemical labeling.

Diagnostic Procedures

It is necessary to use PCR to differentiate between P. polysora and P. sorghi because symptoms and fungal morphology of this disease are extremely similar to those of common corn rust (2).

Resources and References

1. Babadoost, M. 1991. Common and southern rust of sweet corn. RPD No. 965. University of Illinois Extension. https://ipm.illinois.edu/diseases/rpds/965.pdf

2. Crouch, J. A., and Szabo, L. J. 2011. Real-time PCR detection and discrimination of the southern and common corn rust pathogens Puccinia polysora and Puccinia sorghi. Plant Dis. 95:624-632.

3. http://maizedoctor.cimmyt.org/index.php/en/pests-and-diseases/243?task=view

4. http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=45850

Acknowledgments

National Institute of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2011-41530-30708 as part of "Diagnostic Image Series Development for Supporting IPM in the Southern Region" (USDA-NIFA-RIPM-003351)

Puccina polysora