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Cytology and Histology

Anatomy of a Tolerant Chrysanthemum Cultivar Infected with Fusarium oxysporum f. sp. chrysanthemi. Barbara A. Stuehling, Former graduate research assistant, Department of Plant Pathology, Fusarium Research Center, The Pennsylvania State University, University Park 16802; Paul E. Nelson, professor, Department of Plant Pathology, Fusarium Research Center, The Pennsylvania State University, University Park 16802. Phytopathology 71:1162-1168. Accepted for publication 20 February 1981. Copyright 1981 The American Phytopathological Society. DOI: 10.1094/Phyto-71-1162.

Plants of Chrysanthemum morifolium ‘Mandalay’ were inoculated with Fusarium oxysporum f. sp. chrysanthemi, and stem portions were cultured to determine the location of the fungus. Other stem portions were fixed, dehydrated, embedded, sectioned, and stained to examine changes in the anatomy of infected plants. Stems frequently were colonized, but symptoms were limited in severity and the fungus was restricted to the xylem. Breakdown of xylem parenchyma and vessel elements; occlusion of vessel elements by gums; accumulation of pectic substances; and hypertrophy of cells surrounding, and sometimes replacing, the xylem occurred in the primary xylem. Tyloses were present in a few cases. Responses in the secondary xylem included proliferation of hypertrophied parenchyma and formation of partially differentiated tracheary elements. Hyphae of the pathogen were sparse and limited primarily to xylem vessel elements. Occasionally, other xylem cells were colonized. The hyphae were continuous in infected stems. The limited host responses to infection did not appear to be the major reason for the tolerance of this cultivar.