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Physiology and Biochemistry

Terpenoid Accumulation in Hypocotyls of Cotton Seedlings During Aging and After Infection by 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 of senior author: Southeastern Fruit and Tree Nut Laboratory, P. O. Box 87, Byron, GA 31008; J. M. Halloin(2), J. A. Veech(3), and W. W. Carter(4). (2)(3)(4)Research Plant Physiologists, and Research Plant Pathologist, respectively, Agricultural Research Service, U. S. Department of Agriculture, National Cotton Pathology Research Laboratory, College Station, TX 77840. Phytopathology 68:347-350. Accepted for publication 21 September 1977. Copyright 1978 The American Phytopathological Society, 3340 Pilot Knob Road, St. Paul, MN 55121. All rights reserved.. DOI: 10.1094/Phyto-68-347.

The resistance of cotton seedlings to Rhizoctonia solani increased between 5 and 12 days after planting. Concentrations of the terpenoids desoxyhemigossypol, desoxy-6-methoxyhemigossypol, hemigossypol, 6-methoxyhemigossypol, gossypol, 6-methoxygossypol, and 6,6-dimethoxygossypol were higher in extracts of healthy hypocotyls of 12-day-old cotton seedlings than in those of 5-day-old seedlings. The concentration of each compound in hypocotyls of either age increased even more for the first 48 hr after inoculation with R. solani. However, rates of postinfection increases in concentrations of the compounds were not significantly different between 5- and 12-day-old seedlings. Terpenoid compounds may be involved in the age-related increased resistance of cotton seedlings to R. solani because of differences in concentrations occurring before infection or in total concentrations present after infection. However, the toxicity of the terpenoid compounds to R. solani must be thoroughly tested before it is known whether they play an active part in the age-related resistance.

Additional keywords: Gossypium, seedling disease, phytoalexins, disease resistance, hemigossypol, gossypol, soreshin.