Detection of the onset of crop stress induced by glyphosate using chlorophyll fluorescence measurements

In this study, Chlorophyll Fluorescence (ChlF) was used to assess and detect the onset of crop injury from glyphosate, the most widely used herbicide. Thirty-six pots of non-glyphosate-resistant soybean (cultivar FM955LL) were randomly divided into three groups and treated with different doses of glyphosate solutions. The three treatment groups were CTRL group (with no glyphosate treatment), 0.25X group (treated with 0.217 kg·ae/ha solution of glyphosate), and 0.5X group (treated with 0.433 kg·ae/ha solution of glyphosate). The Kautsky effect parameters were acquired in the experiment by using a chlorophyll fluorimeter. Reflectance-based indices, which were potentially related to ChlF, were also calculated from leaf reflectance spectra acquired using an integrating sphere apparatus coupled with a spectroradiometer. These data were processed and analyzed to study their response to the glyphosate treatments. Results indicate that four Kautsky effect parameters, Fv, Fv/Fm, Area, and PI, are parameters sensitive to glyphosate treatment, showing significant differences among the three groups at and beyond 48 Hours After Treatment (HAT). Moreover, ChlF-related spectral indices, R₆₇₅·R₆₉₀/R₆₈₃² and R₆₉₀/R₆₅₅, are shown to be useful in detection of the glyphosate injury, though they are shown less effective compared with the Kautsky effect parameters. Results presented in this paper demonstrate that ChlF is effective in detecting the onset of glyphosate-induced leaf injury, and has the potential to be further developed into practical use.