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Histopathology of Carnation Infected with Fusarium oxysporum f. sp. dianthi. Barbara White Pennypacker, Research Assistant, Department of Plant Pathology, The Pennsylvania State University, University Park 16802; Paul E. Nelson, Professor, Department of Plant Pathology, The Pennsylvania State University, University Park 16802. Phytopathology 62:1318-1326. Accepted for publication 25 May 1972. DOI: 10.1094/Phyto-62-1318.

Carnations, cultivar Improved White Sim, were inoculated with three isolates of Fusarium oxysporum f. sp. dianthi and examined histologically. Fusarium oxysporum f. sp. dianthi isolates from Pennsylvania (A-31), California (A-15), and Denmark (A-80) were used. Isolates A-31 and A-15 caused vascular plugging, hypertrophy and hyperplasia of xylem parenchyma cells, xylem parenchyma cell disintegration, and the formation of vascular cavities. Isolate A-80 incited more cell proliferation in the xylem parenchyma and less vascular cavity formation than did A-15 and A-30. No tyloses were seen in the xylem vessel elements regardless of the isolate used. No conidia were observed in advance of the mycelium in xylem vessel elements. Absence of conidia in advance of mycelium in the xylem vessel elements is probably the primary reason for the success of culture indexing as a control measure for Fusarium wilt of carnation.