Anatomy of a Tolerant Chrysanthemum Cultivar Infected withFusarium oxysporumf. sp.chrysanthemi

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Abstract
Plants of C. morifolium ''Mandalay'' were inoculated with F. 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 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 apparently were not the major reason for the tolerance of this cultivar.

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