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Cytology and Histology

Histopathology of the Chrysanthemum Cultivar Bonnie Jean Infected with Chrysanthemum Stunt Viroid. Laurie T. Morelli, Former graduate research assistant, Department of Plant Pathology, Fusarium Research Center, The Pennsylvania State University, University Park 16802; Paul E. Nelson(2), and R. K. Horst(3). (2)Professor, Department of Plant Pathology, Fusarium Research Center, The Pennsylvania State University, University Park 16802; (3)Professor, Department of Plant Pathology, Cornell University, Ithaca, NY 14853. Phytopathology 77:655-660. Accepted for publication 29 July 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/Phyto-77-655.

Plants of Chrysanthemum morifolium ‘Bonnie Jean’ were inoculated with chrysanthemum stunt viroid. At 7-day intervals portions of stems and leaves and entire shoot meristems were fixed, dehydrated, embedded, sectioned, and stained to examine changes in the anatomy of infected plants. Apical leaves were checked for the presence of the viroid by polyacrylamide gel electrophoresis and ethidium bromide staining. Infected plants were stunted and developed a pronounced curvature of the stem. There was disruption and dysfunction of the actively dividing cambial initials resulting in the replacement of portions of the xylem and phloem with hypertrophied and hyperplastic tissue. In most stem sections, the vascular cambium was distorted and necrotic. Other anatomical changes included areas of cell hypertrophy and dark staining intercellular material in the cortex. In some cases, the unicellular epidermal layer was replaced by a multicellular layer or by cavities containing wound gum and pectin. In leaf tissue, the palisade cells and upper and lower epidermal cells were necrotic. In the apical meristems, there was a breakdown of individual cells in the rib meristem or groups of cells in vertical files extending through the tunica-corpus region into the rib meristem.