Different glyphosate phytotoxicity of seeds and seedlings of selected plant species

The aim of this study was to compare the physiological responses of six plant species (popular crops or plants recommended as indicators of soil pollution) to a wide range of glyphosate concentrations (0, 1, 3, 7, 10, 40, 80, 120, 180, 240, 400, 750, 1,000, 1,500, 1,700 and 2,000 μM). Percent germination, root length, seedling dry mass and myo-inositol content, as well as seedling leachate electroconductivity were determined in Lepidium sativum, Sinapis alba, Sorghum saccharatum, Brassica napus, Lupinus luteus and Avena sativa. Percent seed germination, seedling dry mass and electroconductivity of seedling leachates were not clearly affected by the herbicide and could not be used as indicators of its phytotoxicity. An metabolite induced by abiotic stresses in many plants, myo-Inositol, was very strongly stimulated by glyphosate at doses above 10 or 40 μM, depending on plant species. The sensitivity of analyzed plants to glyphosate, as manifested by root length, differed clearly. In Avena sativa the relationship between root length and glyphosate concentration was fairly linear over a wide range of herbicide doses (up to 240-400 μM). The most distinct drop in root growth at low herbicide doses was visible in Sorghum saccharatum. The results show that a mild stress affecting root length may not clearly modify seedling myo-inositol levels, that respond distinctly to stronger stresses. Not all indicator plants are equally suitable for analysis of biological activity of glyphosate residues. Sorghum saccharatum seems particularly sensitive.