Taxonomy

Domain	Eukarya
Kingdom	Fungi
Phylum	Ascomycota
Subphylum	Pezizomycotina
Class	Dothideomycetes
Subclass	Pleosporomycetidae
Order	Pleosporales
Family	Pleosporaceae
Genus	Bipolaris

Scientific Name

Bipolaris maydis

Scientific Name Synonyms

Helminthosporium maydis

Cochliobolus heterostrophus

Common Name

southern corn leaf blight and stalk rot

Author: Juliana Pereira, University of Florida

Reviewed by: Jeffrey Rollins, University of Florida

Pathogen

Bipolaris maydis, also known as Drechslera maydis or Cochliobolus heterostrophus, causes Southern corn leaf blight (SCLB) and stalk rot (1). There are three races of this pathogen (race O, race T, and race C). Race T no longer considered a threat since the transition to normal cytoplasm corn (2).

Symptoms and Signs

SCLB results in the development of leaf lesions. Lesion size can range from a barely visible speck up to 1.27cm in width and 3.8cm in length (1), depending on which pathogen isolate is present. The elongated lesions along the veins are tan in color (2) and can have purplish to brown borders (1). The lesions reduce the photosynthesis leaf surface area compromising the plant normal physiology (3).

Ecology and Spread

Spores and mycelium of the pathogen survive the winter on plant debris. Wind and water splash then disperse the spores to corn the next growing season. Favorable environmental conditions for disease and symptom development are temperatures between 22-30°C accompanied with high humidity. Primary lesions act as a source of secondary inoculum after successful infection and colonization (1,3). Spores can germinate within six hours if there is free water on the leaves and temperatures are favorable (1). The sexual phase is rarely observed in the field, but can be induced in the laboratory. When in sexual phase pseudothecium is produced (3).

Geographic Distribution

The disease is a concern in all tropical and temperate regions of corn crops. Race C is found only in China (3).

Management

Bury crop residues.
Rotate fields for at least one year with crops other than corn.
Use resistant hybrids.
Start transplants with disease free seeds.
Use fungicides to prevent disease at or before the time vines begin to touch within the row.
Do not save seeds from fields where Bipolaris maydis has been observed.
Consult your local extension specialist for legal and efficacious fungicide products available in your state. Remember, the label is the law and the product applicator is responsible for reading and following all chemical labeling.

Diagnostic Procedures

The diagnosis is based on the fungal morphology. The spindle-shaped, dark brown color, and septated conidia can be easily visualized under microscope and it is characteristic of this species. The dimension of the conidia is 15-20 × 70-160 µm (3).

This fungus will grow well on common culture media such as PDA.

Resources and References

1. Department of Crop Sciences. 1997. Common leaf blights and spots of corn. RPD No. 202. University of Illinois Extension. https://ipm.illinois.edu/diseases/rpds/202.pdf

2. http://cropdisease.cropsci.illinois.edu/corn/southerncornleafblight.html

3. http://maizedoctor.cimmyt.org/in

Acknowledgements

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)