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Vascular Response of Cotton to Infection by Fusarium oxysporum f. sp. vasinfectum. W. M. Bugbee, Plant Pathologist, Crops Research Division, ARS, USDA, and Research Associate, Department of Plant Pathology, University of Missouri, Cooperative Investigations, Crops Research Division, and the Missouri Agricultural Experiment Station, Portageville 63873, Present address: ARS, USDA, Department of Plant Pathology, North Dakota State University, Fargo 58102. Phytopathology 60:121-123. Accepted for publication 18 August 1969. DOI: 10.1094/Phyto-60-121.

Occlusion of xylem vessels followed by toxin formation in the cotton plant are major mechanisms of resistance to Fusarium oxysporum f. sp. vasinfectum. Tracheal fluids of Fusarium-infected stems were toxic to Fusarium or Verticillium albo-atrum only if the fluids came from occluded vessels. Resistance to Fusarium increased with host age. One resistant and one susceptible line of cotton had the same occlusion rate, but the resistant line produced more xylem vessels. It is suggested the higher capacity conductive system compensated for the relatively slow vascular occlusion rate.