Title : In search of new adjuvants: Assessing the physiological response of white quinoa (Chenopodium album L.) to dioxolane-assisted herbicide via efficiency of the photosynthetic apparatus
Global pesticide use has increased to unprecedented levels since the middle of the last century. Many papers reported that over-reliance on herbicides, especially glyphosate, is detrimental to the environment. It is also recognized that inert ingredients in pesticides can can pose phytotoxic effects or harm non-target organisms. In this frame, more attention is being paid to solutions improving the efficacy of herbicides and thereby mitigate their environmental impact. Herein, we tested a novel application of low molecular weight 1,3-dioxolanes as adjuvants dedicated to herbicides. The data suggest that these compounds diminish barriers posed by the surface tension of the formulation and cuticular wax and cell walls of the plant. By their properties, they can increase the absorption of xenobiotic active ingredients, i.e. herbicides, by the foliage. Described compounds were characterized as harmless to plants and favorably modifying the physicochemical properties of the spray solution. Thus, this study aimed to quantify the efficacy of a commercial formulation of the potassium salt of glyphosate (Roundup 360 Plus) supported by 1,3-dioxolanes on a common weed species, white quinoa (Chenopodium album L.), grown under greenhouse conditions. In order to show the differences among different adjuvant treatments significantly, the glyphosate rates applied were under the recommended doses. Three formulations were made with reduced concentrations of glyphosate (0.04, 0.12 and 0.2 L ha-1) and one of three dioxolanes at 1%(v/v)—TMD (2,2,4-trimethyl-1,3-dioxolane), DMD (2,2-dimethyl-1,3-dioxolane) and DDM ((2,2-dimethyl-1,3-dioxan-4-yl)methanol).
They were compared with a pure commercial product. Chlorophyll a fluorescence parameters and OJIP test analysis, which explores changes in photosystem II (PSII) photochemical performance, has been used as a measure of plant susceptibility to glyphosate stress and verified the effectiveness achieved by different formulations. As a result, we observed a negative effect on Chl a fluorescence parameters as well as on the shape of OJIP ChlF transients. Changes were observed for all 1,3-dioxolanes-at the lowest dose and especially at the middle dose of glyphosate. It was also partly the case for the highest dose, at which the variation was less noticeable due to the excessive herbicidal activity of glyphosate. Adding 1,3-dioxolanes to glyphosate increased herbicidal activity and had comparable effects for lower herbicide doses. Results derived from the assay based on the efficiency of the photosynthetic apparatus correlate well with increased mortality. Furthermore, this physiological response of white quinoa occurred seven days after treatment before the visible damage caused by glyphosate. In conclusion, experimental results suggest that introducing 1,3-dioxolanes to agriculture may be an opportunity to reduce herbicide load and minimize herbicide runoff pollution. The early response of photosynthetic apparatus efficiency decrease can be considered a measure of the amount of glyphosate acting after entering the plant, thus determining the effectiveness of the adjuvant. These findings suggest that the following directions for research should be conducted under field conditions. On a larger scale, other applications of these compounds would also be worth exploring.