Exploring risks of evolution of resistance to glyphosate in UK weeds

Globally, glyphosate use has increased very significantly since the introduction and widespread adoption of genetically-modified (GM) glyphosate-resistant crops. In the UK, these crops are not currently grown, yet glyphosate use in agricultural situations has increased substantially in recent years as resistance to other herbicides has proliferated and reduced soil cultivation systems have been adopted. Evolved resistance following repeated use of glyphosate has now been reported in 19 weed species across six continents, including in France, Italy and Spain. To date, no evolved resistance to glyphosate has been reported in UK weed species. In the past, the majority of herbicide resistance research has been reactive - suspected resistance to a herbicide is reported and efforts are made to confirm and characterise the resistance trait after the fact. A number of converging factors including increasing glyphosate use, the potential future introduction of GM glyphosate-resistant crops to the UK, reports of glyphosate resistance in other European countries and changes to EU pesticide legislation make it timely to ask - what are the future risks of glyphosate resistance evolution in major UK weeds? The project will commence with a UK-wide collection of seed populations of major UK weeds with known and contrasting glyphosate use histories. The project will likely focus on Alopecurus myosuroides (black-grass), though other weeds will also be included. A series of glasshouse-based glyphosate dose response assays will be performed to determine the glyphosate sensitivity of collected populations and to relate this sensitivity to glyphosate use histories. It is not expected that high levels of glyphosate resistance will be detected in populations. However, the project will test the hypothesis (supported by previous research by the main supervisor) that gradual reductions in the sensitivity of populations, related to past use histories, are a precursor to major phenotypic resistance (failure of commercial herbicide applications). This phenomenon, sometimes referred to as 'creeping resistance' has often been speculated on, though never unequivocally demonstrated and offers the intriguing and practically significant possibility of an early warning system for glyphosate resistance. In order to further test this hypothesis, black-grass populations showing evidence of reduced sensitivity to glyphosate will be chosen for glasshouse-based selection experiments. These experiments will expose populations to recurrent multi-generational selection with commercially-applied doses of glyphosate to determine if it is possible to select for major phenotypic resistance. These experiments will provide 'proof of principle' for the early warning system for glyphosate resistance. Where it has been possible to select for resistance, appropriate molecular genetic and physiological techniques will be used to determine the mechanism of resistance. Glyphosate dose response and plant growth analyses will also be performed on evolved resistant populations to determine the fitness consequences of evolved resistance in the presence and absence of glyphosate. Based on the knowledge and understanding gained from these empirical studies, existing population-based simulation models of herbicide resistance evolution will be modified to explore the risks associated with current and likely future glyphosate use in the UK. Management strategies to mitigate these risks will be evaluated using computer simulation and recommendations will be made for proactive management to reduce the likely future incidence of glyphosate resistance in the UK.