| Summary: | Although glyphosate clearly has real and potential commercial uses as a growth regulator at low doses, its main commercial significance has been as an herbicide. An important prerequisite for low dose applications gaining significance is a high efficiency and reliability of effects. This, however, seems to be a major constraint, especially regarding the approach of increasing yield by glyphosate hormesis. Glyphosate is marketed in various formulations, but potential disparities in low dose responses are unknown. Therefore, this study evaluated the expression and reliability of hormetic effects of different glyphosate formulations as a possible means for glyphosate hormesis to be more reliably and sustainably be achieved. Four commercial products sold in Germany (Glyfos, Glyfos Supreme, Glyfos Dakar, and Roundup Speed) were evaluated in germination assays with Lactuca sativa. Experiments were conducted as dose-response assays and evaluated for root length and shikimic acid production. In bioassays with exposure of seeds, none of the commercial formulations induced hormesis, while all formulations showed a similar hormetic effect if methanol pre-treated seedlings were exposed. Evaluating the reliability of the observed hormetic effect showed that the effect could only be reproduced in one out of three repeats independent of the formulation used. Hence, results indicated that in controlled bioassays, the induction of hormesis by glyphosate is independent of the formulation used and requires a preconditioning, although this does not ensure a hormetic effect. Therefore, the reliability of glyphosate hormesis may remain a major constraint for potential practical uses of this phenomenon despite new formulations claiming a safer response.
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