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Leaf and Sprout Infection of Potato by Verticillium albo-atrum. C. C. Thanassoulopoulos, Fellow, North Atlantic Treaty Organization, Department of Botany and Plant Pathology, Michigan State University, East Lansing, 48823, Present address of senior author: Phytopathological Station, Patras, Greece; W. J. Hooker, Professor, Department of Botany and Plant Pathology, Michigan State University, East Lansing, 48823. Phytopathology 60:196-203. Accepted for publication 13 August 1969. DOI: 10.1094/Phyto-60-196.

Evidence was obtained histologically that hyphae of Verticillium albo-atrum penetrated potato leaves directly into the epidermis. Small, bronze-colored areas surrounded darkened centers. Later, the leaf became generally chlorotic. Hyphae first intracellular soon became intercellular also. Mesophyll tissue was quickly invaded sometimes within 24 hr. From inoculated leaves, invasion of the vascular elements of petioles was demonstrated histologically and by isolation. Further systemic spread of the fungus from the leaf lamina to the stem and to the tuber was shown by isolation. Direct penetration through epidermal cells of young sprouts preceded granulation and death of the protoplast. Necrosis of apical and leaf primordial meristems extended close to the vascular elements.