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Cytology and Histology

Penetration and Infection of Leaves of Black Walnut by Marssonina juglandis and Resulting Lesion Development. Steven Cline, Research assistant, Department of Plant Pathology, University of Illinois, Urbana; Dan Neely, plant pathologist, Illinois Natural History Survey, 607 E. Peabody Drive, Champaign, IL 61820. Phytopathology 73:494-497. Accepted for publication 18 October 1982. Copyright 1983 The American Phytopathological Society. DOI: 10.1094/Phyto-73-494.

Penetration and infection of black walnut (Juglans nigra) leaves by the walnut anthracnose fungus and the resulting lesion development were observed. A conidial suspension was atomized onto mature leaves. Conidia germinated terminally or subterminally within 48 hr and formed short germ tubes and/or appressoria. Penetration through epidermal cells was initiated from appressoria and was either direct or followed subcuticular growth. Papilla formation was associated with resistance to penetration. Intercellular hyphae were observed after 72 hr, while intracellular spread through epidermal cells was prominent at 144 hr. By 168 hr, the mycelium had entered the mesophyll, and host cell necrosis could be seen microscopically. Macroscopic lesions were observed at 240 hr and acervulus formation occurred after 240 hr.