Anthracnose Leaf Blight and Stalk Rot of Sorghum

Anthracnose Leaf Blight and Stalk Rot of Sorghum


Anthracnose is caused by the fungus Colletotrichum graminicola (Ces.) G.W. Wils., teleomorph Glomerella graminicola Politis. When this disease occurs on sorghum it is commonly divided into three categories based on where symptoms develop on the plant. The three categories are: leaf anthracnose, panicle and grain anthracnose and anthracnose stalk rot. Cultivated hosts include sorghum, sudan grass, wheat, oats, rye and barley. The fungus also has several grass hosts. Those hosts of importance in Nebraska are crabgrass, Johnson grass, orchard grass 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 Johnson grass. 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 seed. 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 not 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


Colletotrichum graminicolaproduces 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 wide border that is varies in shade from red or orange to purple or tan. 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 (setae) and conidiospores form in the acervulus. Conidiospores appear creamy to pinkish color when they are present in large numbers and serve as the source of inoculum for secondary infection. Leaf infection may also appear as a midrib infection. This type of infection is characterized by elongated elliptical lesions that vary in color from red to purple to black. Acervuli may also be present in these lesions. Leaf and midrib infections may occur independently of each other or together in which case yield loss increases. Leaf anthracnose generally occurs at growth stage 50 or later. If plants are infected early in the growing season, damping off may occur or plants may be stunted, yellow and tiller poorly.

Panicle and grain anthracnose occurs on mature plants. Spores of C. graminicola produced from the leaf blight stage are splashed by rain or irrigation water to the panicle (inflorescence) and initiate infection. Initial lesions are water-soaked and turn tan or purple with age. They are elliptical or bar shaped and occur just below the epidermis. If the panicle is split lengthwise, areas of red discolored infected tissue can be seen interspersed with healthy white tissue. Black acervuli may be produced in infected tissue and extend on to seed produced on the panicle. Infected panicles are lightweight, may exhibit some degree of sterility and mature early. Infected seed is discolored, germinates poorly and may produce plants that succumb to seedling blight.

The stalk rot phase of anthracnose is very similar to the panicle infection phase. Infection may occur at anytime during the growing season but symptom development is most common on mature plants. Infection occurs when conidia from the leaf blight stage are splashed or wind blown to the stalks. The initial symptom of stalk infection is a water-soaked discoloration of rind tissue in the lower internodes. Lesions take on a reddish discoloration and infected tissue is interspersed with healthy tissue. External infections are characterized by irregular bleached areas that are surrounded by a red border (host pigmentation).

Plant Health Management

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.