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Pathological Changes in Ultrastructure: Tobacco Roots Infected with Phytophthora parasitica var. nicotianae. Penelope Hanchey, Former Research Associate, Department of Plant Pathology, University of Kentucky, Lexington 40506, Present address of senior author: Department of Botany and Plant Pathology, Colorado State University, Fort Collins 80521; Harry Wheeler, Professor, Department of Plant Pathology, University of Kentucky, Lexington 40506. Phytopathology 61:33-39. Accepted for publication 27 July 1970. DOI: 10.1094/Phyto-61-33.

Within 3 hours after inoculation of roots of a resistant burley tobacco, line L-8, with zoospores of a virulent isolate (race 0) of Phytophthora parasitica var. nicotianae, a hypersensitive type of response was evident in epidermal and adjacent cortical cells. Necrotic cells with coagulated protoplasm were found in advance of the fungus. In one susceptible combination, Burley 21 inoculated with zoospores of race 1, less drastic effects on ultrastructure were evident in advance of the fungus. In this case, injury in advance may have been caused by either a higher amount of infection than that which occurred with other susceptible combinations or by a slight resistant reaction by the host. In two other susceptible combinations (Burley 21 and race 0; L-8 and race 1), changes in advance of the pathogen were not observed. The earliest effects in these susceptible combinations were a swelling of the endoplasmic reticulum and the formation of structures on cell walls. Some of the structures resembled cell wall lesions in victorin-treated oats, whereas others resembled structures termed sheath, collar, papilla, and lomasome described in other diseased plants. Their occurrence together support the previous suggestion that all such structures may be similar in origin and function. Later effects included increased vesicular activity by the Golgi apparatus and a decreased electron density of the vacuoles. Changes in vacuolar density may have resulted from effects on membrane permeability.