Interpopulation variability and adaptive potential for reduced glyphosate sensitivity in Alopecurus myosuroides

Glyphosate use in the United Kingdom has more than
doubled in the last 20 years. Much of this increase is
driven by efforts to control herbicide resistant weeds,
particularly Alopecurus myosuroides, prior to crop drilling. There is precedent for evolution of glyphosate
resistance in similar situations, raising concerns over
the sustainability of glyphosate use in the UK. We used
dose–response experiments to examine variation in
glyphosate sensitivity amongst 40 field-collected
A. myosuroides populations. No populations were resistant to glyphosate, but ED90 values ranged between 354
and 610 g a.i. ha
1
. Five populations had ED90 values
significantly higher than the unexposed control population collected from a site at Rothamsted Research with
no previous glyphosate exposure. Recurrent selection
experiments were performed to determine whether
variation in glyphosate sensitivity had a heritable basis.
Following two rounds of selection, five of six field populations evolved significantly reduced sensitivity to glyphosate, with R/S ratios, based on estimated ED50
values, ranging from 1.2 to 1.5. These results confirm
that there is a heritable basis to variation in glyphosate
sensitivity. The response to selection was modest.
Evolved populations were not highly resistant to glyphosate, although some twice-selected individuals survived recommended field rates. These results do not
represent definitive proof of the potential of
A. myosuroides to evolve glyphosate resistance,
although they do indicate caution is needed when considering the sustainability of increased glyphosate use
to control this herbicide resistance-prone species.