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Ultrastructural Changes in Pepper Cells in a Compatible Interaction with Phytophthora capsici. D. R. Jones, Postdoctorate Research Fellow, Agriculture Canada, Research Institute, University Sub Post Office, London, Ontario, Canada N6A 3K0; W. G. Graham(2), and E. W. B. Ward(3). (2)(3)Electron Microscopist, and Plant Pathologist, respectively, Agriculture Canada, Research Institute, University Sub Post Office, London, Ontario, Canada N6A 3K0. Phytopathology 64:1084-1090. Accepted for publication 7 March 1974. DOI: 10.1094/Phyto-64-1084.

Invasion of pepper fruit tissues was detected 4 h after suspensions of Phytophthora capsici zoospores were injected into cavities of ripening fruit of sweet pepper (Capsicum frutescens). Cells in the immediate vicinity of invading intercellular hyphae possessed highly lobed nuclei with prominent nucleoli. Where hyphae had penetrated into cell walls, the adjacent host cytoplasm usually was dense with ribosomes. Parallel layers of rough endoplasmic reticulum were common ultrastructural features and often surrounded degenerating chloroplasts. Six hours after zoospore injection, the cytoplasm of these layers of cells was disorganised by invading hyphae, while cells deeper in the fruit tissue near the apices of advancing intercellular hyphae had ribosome-saturated cytoplasm with rough endoplasmic reticulum layers. These responses were associated with low, noninhibitory levels of the phytoalexin capsidiol, previously found in this compatible interaction.