Chapter 5 Chemical Basis for Weed Suppressive Activity of Sorghum 1
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Agnes M . Rimando , Isabelle A. Kagan , Franck E . Dayan , Mark A. Czarnota , and Leslie A. Weston 2
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Natural Products Utilization Research Unit, Agricultural Research Service, U.S. Department of Agriculture, P.O. Box 8048, University, MS 38677 Department of Horticulture, University of Georgia, Georgia Experiment Station, Griffin, G A 30223 Department of Floriculture and Ornamental Horticulture, Cornell University, Ithaca, NY 14853
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The weed suppressive activity of Sorghum species has been associated with phytotoxic compounds that are exuded from the roots, and contain primarily sorgoleone (1). The concentration of 1 ranges from about 40 to 800 μg/mg root extract, based on quantitative analysis of seven genetically different Sorghum accessions. Minor constituents were isolated, including novel resorcinolic lipids. Analogues of 1 with the aliphatic side chain varying in number of carbon and double bonds have also been isolated by thin layer-argentation chromatography. The minor constituents that have been tested inhibit photosystem II electron transport, indicating that they contribute to weed suppressive activity of Sorghum. In studying the biosynthesis of 1, 2- C-acetate was found to also get incorporated into 4,6-dimethoxy-2-[(8'Z,11'Ζ)-8',11' 14'pentadecatrienyl]-1,3-benzenediol, providing significant information on the possibility of altering the biosynthesis of 1 to a more phytotoxic and stable methylated resorcinolic lipid. 13
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© 2005 American Chemical Society
In Semiochemicals in Pest and Weed Control; Petroski, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 2005.
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Introduction Several Sorghum spp. are used as cover crops due to their weed suppressive activity (e.g. /, 2). Because of its potential use in agriculture as a source of natural pesticides, we have undertaken studies to understand the chemical and biochemical aspects underlying the plant growth inhibiting properties of sorghum. We have focused on root exudates, based on reports that they contain phytotoxic compounds (5, 4, 5), which consist of approximately 85 - 90% (w/w) sorgoleone (1) ( 3>
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