Taxonomy

Domain	Bacteria
Phylum	Proteobacteria
Class	Gammaproteobacteria
Order	Enterobacteriales
Family	Enterobacteriaceae
Genus	Pantoea
Species	Pantoea stewartii

Scientific Name

Pantoea stewartii ssp. stewartii

Common Name

Stewart's wilt

Author: John Bonkowski, Bacheline Joseph, Deanna Bayo, University of Florida

Reviewed by:Name, Organization

Pathogen

Pantoea stewartii is a nonmotile, facultative anaerobic, gram negative, rod-shaped bacterium that causes Stewart’s wilt and leaf blight disease on maize (particularly sweet corn), flint, dent, flower, and popcorn [7].

Symptoms and Signs

The corn flea beetle (Chaetocnema pulicaria) is the primary vector for the causal agent of Stewart’s wilt. Throughout the growing season, the vector may infect susceptible plants causing one of two phases of the disease to develop depending on the life stage of the plant at the time of infection. The two stages of the Stewart’s wilt infection include the seedling wilt phase and the leaf blight phase [4]. The seedling phase occurs when Pantoea stewartii is transmitted to seedlings by the first generation of vectors in the spring. This is the most damaging stage of infection because it can eventually lead to plant death. Water-soaked lesions occur when the bacterium colonizes the intercellular spaces of leaf tissues. The plant becomes systemically infected, and will wilt rapidly. Further spread of the pathogen results in premature, bleached, and dead tassels. Pale-green to yellow longitudinal streaks with irregular or wavy margins will form parallel to venation on leaves. Leaves eventually dry out and turn brown [7]. If ears are produced, kernels may appear shriveled.

The more common leaf blight stage develops following infections of mature plants and typically appears after tassels form. Gray-green to yellow-green lesions form streaks along the veins of leaves. These lesions develop at the sites where the corn flea beetle fed and may spread to the rest of the leaf. In severe cases of the disease, the entire leaf may dry up and die, becoming straw colored and necrotic. The leaf blight phase does not generally lead to death of plant, but it will predispose the plant to secondary invaders [7].

Ecology and Spread

The principal host of Pantoea stewartii is maize, especially sweetcorn. Other hosts include black bent, Job’s tears, orchardgrass, crabgrass, tumble panic grass, smooth witchgrass, smooth-stalked meadow grass, Sudan grass, eastern gamagrass, and wheat [4]. The bacterium overwinters in the gut of the adult corn flea beetle [7]. In the spring, the pathogen is spread when the emerging adult beetles feed on the plant seedlings. Later in the season, the next generation of the corn flea beetles spreads the pathogen from plant to plant [5]. The Stevens-Boewe forecast predicts the risk of Stewart’s wilt based on average winter temperatures. More flea beetles are likely to survive a mild winter with average temperatures above freezing (average daily December-February temperatures greater than 33°F). Higher vector survival over the winter results in increased risk of Stewart’s wilt in the spring. Average temperatures below freezing reduce beetle survival (average daily temperature less than 27°F December-February), and thus disease is likely to be less severe in the spring [4].

Forecast can be found at https://www.apsnet.org/publications/apsnetfeatures/Pages/StewartsWilt.aspx.

Geographic Distribution

Europe

Austria, Greece, Poland, Romania, and Russia (European).

Asia

China (Henan), Malaysia (Peninsular), Thailand, Vietnam.

North America

Canada (Alberta, British Columbia, Ontario), Mexico, United States of America (Connecticut, Illinois, Indiana, Iowa, Kentucky, Louisiana, Missouri, Nebraska, New York, North Dakota, Ohio, Pennsylvania, Wisconsin).

Central America and Caribbean

Costa Rica, Puerto Rico.

South America

Brazil (São Paulo), Guyana, Peru (coast) [1].

Management

Management of any pathogen is often dependent upon both cultural and chemical options. Consult your local extension specialist or agent for recommendations relevant to your particular host and state. Remember: the label is the law.

Diagnostic Procedures

Procedures/Media	Result for Pantoea stewartii
Oxidase	Negative; no color change
Urease	Negative; no color change
Kings medium B	Negative; nonfluorescent
Nutrient agar	Yellow colonies
Yeast extract-dextrose CaCO3 medium	Yellow to orange flat colonies
Sucrose peptone agar	Positive; mucoidal, fluidal
Hypersensitive Response	Tomato: Negative; no necrosis
	Tobacco: Variable; must be grown on Ivanoff’s media liquid medium first (7)
Crystal violet pectate medium	Negative; no pitting is observed

One way to determine if signs of the causal agent of Stewart’s wilt are present in corn is to observe the leaf tissue under a microscope. In maize a cross sectional cut of the stem and leaves will exude yellow bacterial slime oozing from the vascular bundles. Laboratory tests used to determine the presence this pathogen include enzyme-linked immune assay (ELISA), polymerase chain reaction (PCR), biochemical tests, and pathogenicity tests (7).

ELISA kit

https://orders.agdia.com/InventoryD.asp?loc=IN&collection=PSA%2052000&attribute_Size=288

PCR

Wilson, W. J., M. Wiedmann, H.R. Dillard, and C. A. Batt. 1994. Identification of Erwinia sterwatii by a ligase chain reactionassay. Appl. Environ. Microbiol. 60:278-284.

Selected References

1. CABI and EPPO. Data Sheets on Quarantine Pest: Pantoea stewartii subs. stewartii. European Plant Protection Organization. Online: http://www.eppo.int/QUARANTINE/bacteria/Pantoea_stewartii/ERWIST_ds.pdf.

2. Gottwald, T.R., Graham, J. H. 2000. Compendium of Citrus Diseases. 2nd ed. American Phytopathological Society, St. Paul, MN. 5-7.

3. CABI and EPPO. Distribution Maps of Plant Diseases: Pantoea stewartii (Smith) Mergaert et al. Online: http://www.cabi.org/dmpd/FullTextPDF/2009/20093074276.pdf.Plant and Insect Diagnostic Clinic. Stewart's Wilt. Iowa State University. Online: http://www.ipm.iastate.edu/ipm/info/plant-diseases/stewarts-wilt.

4. Plantwise Technical Factsheet. Bacterial Wilt of Maize. Plantwise Knowledge Base. Online: http://www.plantwise.org/KnowledgeBank/Datasheet.aspx?dsid=21939.

5. Roper, C. M. 2011. Pantoea stewartii subsp. stewartii: lessons learned from a xylem-dwelling pathogen of sweet corn. Molecular Plant Pathology 12:628-637.

6. Schaad, N. W., Jones, J. B., Chun W., ed. 2001. Laboratory Guide for Identification of Plant Pathogenic Bacteria. 3rd ed. The American Phytopathological Society, St. Paul, NM.

7. White, D.G., ed. 1999. Compendium of Corn Diseases. 3rd ed. The American Phytopathological Society, St. Paul, MN. 3-4.

Resources and References

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)