Anthracnose of Cereals

Host and  Symptoms. C. graminicola is a fungal pathogen that colonizes and infects many turfgrass e.g., Bluegrass, Ryegrass, fescue. In addition to the grasses, C. graminicola also infects many grain crops such as barley, wheat, sorghum and corn. The fungus can infect many different parts of the corn plant, typically the kernels, tassels, roots, leaves, stalk and husks. The most common area of infection is the stalk. C. graminicola produces three major symptom types: leaf blight, stalk rot and top die-back. The leaf blight is characterized by round yellowing water soaked lesions on the leaves. These lesions usually occur early in the season and are how this pathogen is distinguished from other diseases. Top die-back is the necrosis of the top leaves and stalk of the corn. This occurs around the same time as grain formation. The stalk rot phase becomes prominent during the late reproductive stages of the corn life cycle. It is characterized by blackening of the pith tissue in the stalk and also of the rind, beginning at the nodes closest to the soil. Along with these symptoms, seedling blight and post emergence damping off are also found.
Disease Cycle. In the spring, fruiting structures (acervuli) form from corn residue and produce spores (conidia) that are dispersed by wind blown raindrops and splashing. Conidial spores infect young plants through the epidermis or stomata. Anthracnose develops rapidly in cloudy, overcast conditions with high temperatures and humidity. In optimal environmental conditions, conidia can germinate in as little as 6–8 hours in 100% humidity. Initial necrotic spots or lesions can be seen within 72 hours after infection by conidia. Lower leaves that develop lesions provide conidial spores and cause secondary infections on the upper leaves and stalk. Vascular infections primarily occur from wounds caused by stalk-boring insects, such as the larvae of the European corn borer, allowing for conidia to infect and colonize the xylem. From this, anthracnose top die back (vascular wilt) or stalk rot can occur. In the fall, C. graminicola survives as a saprophyte on corn leaf residue. The pathogen can also overwinter on corn stalks as conidia in an extracellular secretion. The secretion prevents conidia from desiccating and protects them from unfavorable environmental conditions. Overwintering on corn residue serves as a vital source of primary inoculum for the leaf blight phase in the spring. The cycle will start all over again when susceptible corn seedlings emerge from the ground in the spring.