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Effect of the Plant Growth Retardant Pydanon on Verticillium Wilt of Cotton and Tomato. H. Buchenauer, Department of Plant Pathology, University of California, Riverside 92502, The senior author now is at Lehrstuhl für Phytopathologie und Pflanzenschutz, University of Hohenheim, Stuttgart, W. Germany; D. C. Erwin, Department of Plant Pathology, University of California, Riverside 92502. Phytopathology 66:1140-1143. Accepted for publication 9 February 1976. Copyright © 1976 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-66-1140.

Root drench treatment of cotton and tomato plants with Pydanon (200 mg/plant) before inoculation with Verticillium dahliae (microsclerotial strain) reduced the severity of foliar and vascular discoloration symptoms of Verticillium wilt. The protective effect of Pydanon was more marked than its curative effect. Foliar treatments with Pydanon (2,000 and 4,000 µg/ml) were less effective than soil treatments against Verticillium wilt. Pydanon was not toxic to growth of V. dahliae on potato-dextrose agar or to the formation of spores in a shaken synthetic nutrient solution. No ethanol-extractable antifungal compounds could be detected in xylem tissue of treated cotton plants. Pydanon interfered with gibberellic acid induction of a-amylase activity in barley endosperm.