Glyphosate applied at low doses can stimulate plant growth.
BACKGROUND
Glyphosate blocks the shikimic acid pathway, inhibiting the production of aromatic amino acids and several secondary compounds derived from these amino acids. Non-target plants can be exposed to low doses of glyphosate by herbicide drift of spray droplets and contact with treated weeds. Previous studies have reported that low doses of glyphosate stimulate growth, although these data are very limited. The objective of this study was to determine the effects of low glyphosate doses on growth of a range of plant species.


RESULTS
Growth of maize, conventional soybean, Eucalyptus grandis Hill ex Maiden, Pinus caribea L. and Commelia benghalensis L. was enhanced by 1.8-36 g glyphosate ha(-1). Growth of glyphosate-resistant soybean was unaffected by any glyphosate dose from 1.8 to 720 g AE ha(-1). The optimum doses for growth stimulation were distinct for plant species and tissue evaluated. The greatest stimulation of growth was observed for C. benghalensis and P. caribea. Shikimic acid levels in tissues of glyphosate-treated soybean and maize were measured and found to be elevated at growth-stimulating doses.


CONCLUSIONS
Subtoxic doses of glyphosate stimulate the growth of a range of plant species, as measured in several plant organs. This hormesis effect is likely to be related to the molecular target of glyphosate, since the effect was not seen in glyphosate-resistant plants, and shikimate levels were enhanced in plants with stimulated growth.
Velini
Edivaldo D
ED
São Paulo State University, Faculty of Agronomic Sciences, Experimental Station Lageado, Laboratory of Weed Science, Botucatu, SP, Brasil CEP 18603-970 PB 237, Brazil. velini@uol.com.br
Alves
Elza
E
Godoy
Maria C
MC
Meschede
Dana K
DK
Souza
Reginaldo T
RT
Duke
Stephen O
SO
D005998:Glycine / Q000008:administration & dosage / Q000031:analogs & derivatives*; D053209:Herbicide Resistance / Q000235:genetics; D006540:Herbicides / Q000008:administration & dosage*; D063245:Plant Development; D010944:Plants / Q000187:drug effects*; D030821:Plants, Genetically Modified / Q000187:drug effects; D013025:Glycine max / Q000187:drug effects / Q000235:genetics / Q000254:growth & development; D000097797:Glyphosate
D005998:Glycine; D006540:Herbicides; D000097797:Glyphosate