Understanding herbicide resistance in grass weeds using metabolic fingerprinting

Abstract

Herbicide resistance is a major concern in agriculture. Resistance falls into two categories; target-site resistance (TSR) or non-target-site resistance (NTSR). Enhanced metabolic resistance (EMR) which leads to a decrease in the phytotoxicity of the herbicide is the main type of NTSR in grass weeds. Resistant black-grass (Alopecurus myosuroides), which is a competitive wheat weed widely distributed in the UK and Western Europe, has a negative impact on crop yields causing significant economic losses every year. This thesis aims to demonstrate that Tandem Liquid Chromatography – Mass Spectrometry (LC-MS) can be used to identify herbicide metabolites and their fragments in complex matrices with the objective to use the metabolic fingerprints to develop a new diagnostic tool for NTSR grass-weeds. Different MS instruments, low or high resolution, with chromatography or direct injection were tested towards different plant samples treated with herbicides with different chemistries in order to determine optimal LC-MS conditions. Herbicide feeding assays were also carried out over a range of characterised plant systems and were analysed to determine metabolism levels and its correlation with NTSR traits. Treatments of wheat, sensitive and resistant black-grass with individual and mixture doses of herbicides, suggested that there was competition for the detoxification enzymes, especially cytochrome P450s. In conclusion, this thesis demonstrated that multiple herbicides and their metabolites can be resolved and identified using high resolution LC-MS over a relatively short run time. LC-MS has the power to form the basis of a high throughput analytical technique that can characterise different weed populations based on their metabolism profile and help to further elucidate the favoured routes of primary metabolism in NTSR black-grass