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Ultrastructure of Chrysanthemum Stunt Virus-Infected and Stunt-Free Mistletoe Chrysanthemum. Roger H. Lawson, Pathologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705; Suzanne S. Hearon, Microbiologist, Plant Science Research Division, ARS, USDA, Beltsville, Maryland 20705. Phytopathology 61:653-656. Accepted for publication 6 January 1971. DOI: 10.1094/Phyto-61-653.

The American source of Chrysanthemum morifolium ‘Mistletoe’ infected with chrysanthemum stunt virus (CSV) shows chlorotic spots on leaves of plants grown in the greenhouse in both summer and winter. Chlorotic spots are also present on fully expanded leaves of CSV-free American Mistletoe in the greenhouse in summer, but the spots disappear from expanding leaves in winter. Chlorotic spots on leaves of CSV-infected and CSV-free American Mistletoe were not modified with the addition of supplemental iron chelate. A source of CSV-free Mistletoe from Great Britain shows a few chlorotic leaf spots on unexpanded and fully expanded leaves in summer, but not in winter. No viruslike particles were observed in chlorotic spotted or green leaf tissue of CSV-infected Mistletoe. Chloroplasts in chlorotic leaf tissue from CSV-infected and CSV-free plants contain electron-dense inclusions resembling phytoferritin. Inclusions were also observed in chloroplasts of palisade and mesophyll cells from green tissue of CSV-infected plants, but were less numerous than in chlorotic tissue. No inclusions were observed in these cells in green tissue from healthy plants.