Morphology of Sclerotium coffeicola, a tropical foliar pathogen

Abstract

Sclerotium coffeicola, the cause of target-spot disease of coffee, is reported from Venezuela for the first time. Target spot is a foliar disease characterized by large brown lesions composed of a series of concentric rings. Columnar bundles of hyphae (propagules) form on the undersides of the leaves. Orange sclerotia are produced on infected host tissues and in culture. Hyphal septa are sparse and are of the dolipore type. The sclerotia develop from loose aggregations of interwoven hyphae that become more compact as the sclerotia mature. As the sclerotia develop, most interior hyphae enlarge into inflated, thin-walled cells that are interspersed with scattered, broad, thin-walled hyphae. Circular areas of pseudoparenchymatous cells form in the periphery of the sclerotia where they secrete liquid droplets. The outermost layer or two of cells have slightly thickened walls and are pigmented, but the interior of the sclerotium remains white. The entire sclerotium is covered by two thin layers of an amorphous material.