Rapid Determination of Glyphosate Injury to Plants and Identification of Glyphosate-Resistant Plants

Drift of glyphosate may cause injury to nontarget plant species. Herbicidal damage caused by glyphosate may be attributed to the herbicides that inhibit acetohydroxyacid synthase (AHAS) or acetyl CoA carboxylase (ACCase), because the time taken to show herbicidal damage and the visual injury symptoms caused by these three types of herbicides are similar. Glyphosate inhibits the bio- synthesis of aromatic amino acid biosynthesis which causes accumulation of shikimate in plants. A modified, simpler method of extraction and assay for detection of shikimate in plants has been adapted from previously published procedures. With this assay, rapid accumulation of shikimate was observed in glyphosate-sensitive plants that have been treated with glyphosate. Furthermore, the accumulation of shikimate in herbicide-sensitive plants was only due to glyphosate and not due to an AHAS or an ACCase inhibitor. Therefore, high levels of shikimate in a damaged plant indicate glyphosate injury. With this assay, no accumulation of shikimate was seen in a glyphosate-resistant variety of soybean. Therefore, lack of accumulation of shikimate in a glyphosate-treated weed or crop species indicates that the plant is resistant to glyphosate. Nomenclature: Glyphosate, N-(phosphonomethyl)glycine; imazaquin, 2-(4,5-dihydro-4-methyl-4-(1- methylethyl)-5-oxo-lH-imidazol-2-yl)-3-quinolinecarboxylic acid; sethoxydim, 2-(1-(ethoxyimi- no)butyl)-5-(2-(ethylthio)propyl)-3-hydroxy-2-cyclohexen-1-one; soybean, Glycine max L.; corn, Zea