Host-Parasite Relations in the Gibberidea Disease of Helianthus strumosus

Abstract

SUMMARYDisease symptoms in Helianthus strumosus L. attacked by Gibberidea heliopsidis (Schw.) Shear are described. Distinctive black lesions occur on leaves and stems. The fungus penetrates host leaves directly through the tip cell of the smaller of two kinds of trichomes. Mycelium is almost exclusively intracellular in foliage lesions but grows both intracellularly and intercellularly in the stem cortex. The pathogen causes neither hypertrophy nor hyperplasia, and for a week or more the protoplasts of host cells in invaded areas are only mildly disrupted. Chloroplasts are quickly reduced in number and size in the presence of the fungus. Nuclei, in contrast, are durable, although sometimes deformed by hyphae in the cell. Mitochondria appear to become more numerous and are often aggregated in the vicinity of fungal strands. Electron micrographs revealed that intracellular hyphae are insulated from the host hyaloplasm by a thin sheath consisting of an encapsulation matrix covered by a membrane which seems to be an extension of the host cell plasmalemma. In a few cases, capsules were found encasing invading hyphal tips in mesophyll cells.