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

Abstract

SummaryGlyphosate 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 ED 90 values ranged between 354 and 610 g a.i. ha−1. Five populations had ED 90 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 ED 50 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.

The costs of human-induced evolution in an agricultural system

“…Glyphosate resistant weeds are already found on almost every continent 20 but are not yet present in the UK. However, English farmers are increasingly reliant on glyphosate to control herbicideresistant black-grass and as a result there has been a dramatic increase in its use 42 , ramping 30 . In the US, widespread glyphosate resistance is already a reality and the scale of the problem dwarfs that being faced with black-grass in England.…”

Molecular mechanisms of adaptive evolution revealed by global selection for glyphosate resistance

“…The recent appearance of glyphosate‐resistant populations of A. palmeri in Brazil with EPSPS gene duplication hints at the potential for intercontinental spread of resistance mutations, mediated by seed movement (Küpper et al ., ). Experiments have demonstrated that glyphosate‐sensitive populations of L. rigidum (Busi & Powles, ) and Alopecurus myosuroides (Davies & Neve, ) harbor heritable standing variation for glyphosate insensitivity, although this additive genetic variation may be distinct from the mechanisms of resistance selected in field‐evolved resistant weed populations. Selection for glyphosate resistance and susceptibility in diverse lines of Ipomoea purpurea also demonstrated heritable standing genetic variation for glyphosate insensitivity (Debban et al ., ).…”

The First Cases of Evolving Glyphosate Resistance in UK Poverty Brome (Bromus sterilis) Populations

“…The reduced sensitivity of the suspected resistant populations was greater than reported in a number of previous studies that have identified significant variation in glyphosate response in sensitive weed populations. Davies and Neve (2017) reported ED 90 values in UK blackgrass (Alopecurus myosuroides Huds.) ranging from 354 to 610 g ha − 1 .…”