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Symptom Response and Colonization as Measures of Resistance in Chrysanthemum Cultivars Inoculated with Fusarium oxysporum f. sp. chrysanthemi. N. L. Fisher, Research Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. T. A. Toussoun, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Plant Dis. 67:376-378. Accepted for publication 23 September 1982. Copyright 1983 American Phytopathological Society. DOI: 10.1094/PD-67-376.

Sixteen cultivars of Chrysanthemum morifolium were tested for susceptibility to wilt caused by Fusarium oxysporum f. sp. chrysanthemi. Symptomatology was rated according to a scale of 05, and variation from resistant to susceptible was noted among cultivars, with variation in symptom type and location on the plant. Colonization of plant stems was a more consistent assay of susceptibility than were symptoms. Results suggest a standardized assay technique to minimize variability in plant responses. The susceptible cultivars Yellow Delaware and Royal Trophy were indexed at regular intervals on the stem to determine the rate and pattern of colonization by Fusarium. In single-stemmed and branched plants, colonization increased with time and was discontinuous in 14% of the plants sampled. The fungus was found in the vascular system of symptomless plants, as well as in those expressing symptoms.