Anthracnose Leaf Blight and Stalk Rot of Corn

Anthracnose Leaf Blight and Stalk Rot of Corn


Anthracnose is caused by the fungus Colletotrichum graminicola (Ces.) G.W. Wils. (teleomorph Glomerella graminicola Politis.). The disease is commonly divided into two disease sections in the literature; anthracnose leaf blight and anthracnose stalk rot and between the two phases, virtually all plant tissues may become infected. Cultivated hosts include corn, sorghum, wheat rye and barley. The fungus also has several grass hosts. Those hosts of importance in Nebraska are crabgrass, Johnsongrass, orchardgrass and red fescue. While C. graminicola has a wide host range, isolates from small grains do not infect corn and sorghum. However, corn isolates have been shown to infect sorghum and Johnsongrass. The fungus survives readily as mycelium and spores on plant debris that remains on the soil surface. Fungal viability is diminished when debris is buried. The fungus also survives between seasons in kernels. It is suspected that it overwinters as hyphae and/or stroma in the endosperm. Primary infection of leaves occurs when conidia are windblown or splashed from debris to leaves. Conidia germinate and infection occurs directly through the epidermis or through stomata. The infection process takes place readily when warm wet weather conditions prevail. Primary infection is not as clearly understood in the stalk rot phase of the disease. The confusion is partially due to the fact that stalk rot can occur in fields with very little leaf blight and little or no crop residue from the previous year. The infection may spread from leaf sheaths to stalk tissue or the disease may progress from the roots up the plant. In the latter case, the source of inoculum is suspected to be resting spores that have overwintered in buried stalk debris. In addition, the fungus may enter stalk tissue through insect feeding wounds.

Symptoms


C. graminicola produces a wide range of symptoms on corn. Leaf blight symptoms progress from lower to upper leaves and vary in size and color with host genotype. Typical symptoms on a susceptible hybrid appear as small, water soaked spots that are semitransparent and oval to elongate in shape. Spots enlarge and become tan with a border than is varying shades from yellow to reddish brown. The entire leaf may become blighted if lesions coalesce, resulting in a "fired" appearance. Dark fruiting bodies called acervuli develop on dead host tissue. When large numbers of acervuli form, they may be present in concentric rings. Black hairlike structures (seatae) and conidiospores form in the acervulus. Conidiospores serve as the source of inoculum for secondary infection. Similar lesions occur on leaf sheaths, husks and shanks. Most symptoms of a kernel infection are black longitudinal black streaks. Acervuli may form in these streaks. In cases of severe infection the entire kernel may be discolored. When infected kernels are planted the following season, the seedlings often succumb to seedling blight. The leaf blight infection on a resistant host are much less severe. Leaf lesions are usually smaller and appear as chlorotic or necrotic spots. Large spots may develop on some resistant hybrids but they do not coalesce producing extensive blighting.

The stalk rot phase of anthracnose typically exhibits both internal and external symptoms. Infection may occur at anytime during the growing season but symptom development is most common after tasseling. The initial symptom of stalk infection is a water-soaked discoloration of rind tissue in the lower internodes. Lesions begin as streaks then enlarge to oval shapes and eventually cover the entire internode. In the final stages of development lesions are dark brown to shiny black and sunken. Internal tissue associated with the lesions is also discolored. Pith either disintegrates or becomes soft and watery and lodging occurs. Another type of stalk rot, referred to as top rot occurs when the fungus invades stalk tissue above the ear. Symptoms of top rot include a grayish green discoloration of the stalk tissue and yellow or red discoloration of the leaves above the ear. Infection usually occurs earlier and lodging associated with top rot normally occurs higher on the plant as than they do with stalk rot.

Finally, C. graminicola has also been reported to cause root rot in its hosts. (Its the totally complete pathogen!)

Plant Health Management

Names and Naming

References

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Caveat

This description is presented for information only and no endorsement is intended for products listed, nor criticism meant for products not mentioned. Always consult the product label before purchasing and using any pesticide.

Material contained on the Links from the page are the responsibility of the linked page's author(s).

This page was drafted by: Jane Christensen, Department of Plant Pathology, University of Nebraska-Lincoln

Disease images were provided by: Dr. David Wysong, Department of Plant Pathology, University of Nebraska-Lincoln

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This page is authored and maintained by:
Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved. This page is maintained by:

Dr. J.E. Partridge, Department of Plant Pathology, University of Nebraska-Lincoln

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Copyright (C) 2003 J.E. Partridge, University of Nebraska-Lincoln. All Rights Reserved.