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Physiology and Biochemistry

Effects of Catechin in Culture and in Cotton Seedlings on the Growth and Polygalacturonase Activity of Rhizoctonia solani. R. E. Hunter, Research Plant Pathologist, Agricultural Research Service, U. S. Department of Agriculture, National Cotton Pathology Research Laboratory, College Station, TX 77840, Present address: Southeastern Fruit and Tree Nut Laboratory, P.O. Box 87, Byron, GA 31008; Phytopathology 68:1032-1036. Accepted for publication 31 January 1978. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-1032.

Cotton seedlings became more resistant to soreshin disease, which is incited by Rhizoctonia solani, as they aged from 5 to 14 days after planting. The concentration of catechins in hypocotyls of seedlings also was directly related to seedling age. The growth of three R. solani isolates was inhibited by (+)-catechin in a basic salts solution containing either sucrose or sodium polypectate (NaPP); inhibition of growth was directly related to catechin concentration. Thus, catechins present in seedling hypocotyls of cotton may contribute to the age-related resistance to soreshin through inhibition of pathogen growth. Polygalacturonase (PGase) activity in the NaPP medium was inhibited by (+)-catechin in cultures of the slightly virulent isolates C70 and W18, but not in cultures of the more virulent isolate 63SD2. When PGase activity of 63SD2 was expressed per unit of fungal growth, PGase activity was directly correlated with catechin concentration of the culture medium. This suggests that catechin may have induced PGase synthesis.

Additional keywords: seedling disease, pectic enzymes, polyphenols, disease resistance, Gossypium hirsutum.