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Cytokinin Activity in Plasmodiophora brassicae-Infected Cabbage Tissue Cultures. M. N. Reddy, Postdoctoral Fellow, Department of Plant Pathology, University of Wisconsin, Madison 53706; P. H. Williams, Associate Professor, Department of Plant Pathology, University of Wisconsin, Madison 53706. Phytopathology 60:1463-1465. Accepted for publication 28 April 1970. DOI: 10.1094/Phyto-60-1463.

On modified Murashige and Skoog's medium containing 0.5 mg/liter of α-naphthalene acetic acid and 1 mg/liter of kinetin, the dry wt of Plasmodiophora brassicae-infected cabbage tissue cultures doubled every 3 days; whereas that of noninfected tissues doubled every 5 days. Noninfected tissues had an absolute requirement for exogenous auxin and kinetin; whereas infected tissues required only an exogenous auxin but not kinetin. Extracts from infected tissue cultures grown on kinetin-free media contained cytokinin activity based on tobacco callus growth, barley leaf senescence, and barley root inhibition bioassays. Three components having cytokinin activity in the tobacco pith bioassay could be isolated from infected callus grown on kinetin-free medium.