What is the mechanism of glyphosate resistance?
We now know of two mechanisms of glyphosate resistance in annual ryegrass in Australia. Most of the resistant annual ryegrass populations are the result of limited translocation of glyphosate within the plant. In plants with this resistance mechanism, glyphosate preferentially collects in the leaf tips, leaving much lower concentrations at the growing points. These plants are therefore able to quickly grow away from any glyphosate damage. The second mechanism is through mutations within the EPSPS target site that allow a modest degree of resistance to glyphosate. Plants with this mechanism are typically less resistant to glyphosate than those with the translocation mechanism. They are also more heavily damaged by glyphosate and show the effects for longer. In annual ryegrass, it is possible to get both mechanisms in the same plants. These plants are highly resistant to glyphosate.
