Submitted to: American Chemical Society Symposium Series
Publication Type: Book / chapter
Publication Acceptance Date: 9/13/2004
Publication Date: 6/3/2005
Citation: Rimando, A.M., Kagan, I., Dayan, F.E., Czarnota, M.A., Weston, L.A. 2005. Chemical Basis for Weed Suppressive Activity of Sorghum. In: American Chemical Society Symposium Series: Semiochemicals in Pest and Weed Control. Petroski, R.J., Tellez, M.R. and Behle, R.W., Editors. Washington, DC. American Chemical Society. 906:59-70. Interpretive Summary: Sorghum species exude constituents from its roots that cause suppression of weeds. The main constituent is sorgoleone, making up to about 80% of the exudates, based upon quantitative analysis of seven genetically different Sorghum accessions. Minor constituents have been isolated from the exudates which also demonstrated phytotoxic activity, indicating that they contribute to the weed suppressive activity of Sorghum. One compound was more phytotoxic than sorgoleone when tested in a lettuce germination assay. This provides information on the possibility of altering the biosynthesis of sorgoleone to a more phytotoxic and stable compound.
Technical Abstract: 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 ug/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 inhibited photosystem II electron transport, indicating that they contribute to weed suppressive activity of Sorghum. In studying the biosynthesis of 1, 2-13C-acetate was found to also get incorporated into 4,6-dimethoxy-2-[(8'Z,11'Z)-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.