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Histopathology of Cylindrocladium Black Rot of Peanut. S. A. Johnston, Former Graduate Research Assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27607, Present address of senior author: Plant Biology Department, Cook College, P. O. Box 231, New Brunswick, New Jersey 08903; M. K. Beute, Associate Professor, Department of Plant Pathology, North Carolina State University, Raleigh 27607. Phytopathology 64:649-653. Accepted for publication 10 January 1975. DOI: 10.1094/Phyto-65-649.

Early stages of pathogenesis of peanut (Arachis hypogaea) by Cylindrocladium crotalariae involved the formation of infection cushions on the epidermis, followed by complete hyphal colonization of the cortex. Three alternative courses in pathogenesis were observed: (i), the fungus overcame host defense mechanisms, breached the periderm, and completely colonized the hypocotyl resulting in death of the plant; (ii), the host effectively limited the pathogen to the cortex and recovered from disease; or (iii), the fungus initially overcame host defense mechanism, but the host formed an additional periderm in advance of the necrosis, which limited the pathogen to colonized tissues and enabled the plant to recover from the disease. An eight-stage scheme for peanut hypocotyl pathogenesis is proposed on the basis of these observations. Exogenous nutrients enhanced pathogenesis in hypocotyls and resulted in earlier death of infected peanut plants. The fungus intercellularly penetrated the cortex of fibrous roots 24 hours after inoculation. Complete hyphal colonization and death of these roots occurred within 72 hours.