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Keywords:

  • herbicide tolerance;
  • intercellular changes;
  • shikimate;
  • xenobiotics;
  • vascular bundles;
  • necrosis;
  • meristems;
  • weed anatomy

Lorentz L, Beffa R & Kraehmer H (2011). Recovery of plants and histological observations on advanced weed stages after glyphosate treatment. Weed Research51, 333–343.

Summary

Some weeds treated with the recommended dose rates of glyphosate recover after the application. An explanation of this phenomenon is needed to avoid incomplete control and the potential spread of resistance. The distributions of glyphosate and of shikimate levels within treated plants were therefore analysed, and plant reactions were investigated via histological examinations. It was found that glyphosate was translocated from Amaranthus palmeri leaves to roots within 48 h following treatment. Changes in the phloem of different weed species became visible after 3 days. After 4 days, shikimate accumulation was highest in stem tips and decreased towards the base of plants. Necrosis of pith cells started at the same time. Yellowing of leaves, stem curvature and wilting were observed after 1 week. Herbicide-induced polyphenols and lignin in the intercellular space suggest that glyphosate phytotoxicity is not based solely on the shikimate pathway. It seems to be linked to the decay of vascular tissues and of pith, but not to the transport of glyphosate into apical meristems. Meristematic tissue surrounding the pith survived and gave rise to new buds in Amaranthus plants. These findings are important for the characterisation of plants that escape herbicide treatment and for the search for new control tools.