Detection and characterization of resistance to acetolactate synthase inhibiting herbicides in Anisantha and Bromus species in the United Kingdom

Abstract

BACKGROUND: Anisantha and Bromus spp. are widespread and difficult to control, potentially due to the evolution of herbicide resistance. In this study, UK populations of four brome species have been tested for the early development of resistance to acetolactate synthase (ALS)-inhibiting herbicides commonly used in their control.RESULTS: Glasshouse assays confirmed reduced sensitivity to ALS-inhibiting herbicides in single populations of A. diandra, B. commutatus and B. secalinus, and in three populations of A. sterilis. By contrast, all 60 brome populations tested were sensitive to the ACCase-inhibiting herbicide propaquizafop and glyphosate. Dose-response with two ALS herbicides showed broad-ranging resistance in the A. diandra, A. sterilis and B. commutatus populations. In the B. commutatus population, this was associated with a point mutation in the ALS enzyme conferring target site resistance (TSR). Additionally, resistant populations of A. sterilis and B. commutatus populations contained enhanced amounts of an orthologue of the glutathione transferase phi (F) class 1 (GSTF1) protein, a functional biomarker of nontarget site resistance (NTSR) in Alopecurus myosuroides. There was further evidence of NTSR as these plants also demonstrated an enhanced capacity to detoxify herbicides.CONCLUSION: This study confirms the evolution of resistance to ALS inhibiting herbicides in brome species in the UK by mechanisms consistent with the evolution of both TSR and NTSR. These findings point to the need for increased vigilance in detecting and mitigating against the evolution of herbicide resistance in brome species in Northern Europe.

Non-target Site Herbicide Resistance Is Conferred by Two Distinct Mechanisms in Black-Grass (Alopecurus myosuroides)

“…After 24 h, leaf material (n = 5) was collected, dried, and then frozen in liquid nitrogen prior to storage at -80 • C. Samples were ground in liquid nitrogen and extracted with 80% methanol (750 µl, Sigma Aldrich) overnight at 4 • C, prior to centrifugation (4,500×g, 4 • C, 5 min). The supernatant (5 µl) was analyzed on a Waters Xevo G2-XS QTof mass spectrometer following electrospray ionization (Waters Ltd., Wilmslow, United Kingdom) as described (Davies et al, 2020). The chlorotoluron and fenoxaprop acid metabolites were identified from their reference spectra, with metabolites quantified based on calibration curves prepared from the respective parent herbicides…”

“…To test for enhanced herbicide metabolism in the resistant black-grass plants, metabolism studies with the herbicides chlorotoluron and fenoxaprop acid were performed with all three NTSR and the HS populations over 24 h. These herbicides were selected as they undergo different routes of metabolism, with chlorotoluron being detoxified by ring hydroxylation catalyzed by CYPs, whereas fenoxaprop acid is acted on by GSTs, to form the S−(6−chlorobenzoxazole−2−yl)−glutathione (CBO-SG) conjugate. For each set of plants, the levels of the two parent herbicides and their respective primary detoxification products were determined in the leaves using a high-performance liquid chromatography (HPLC)-MS method (Davies et al, 2020). With chlorotoluron, as compared with the HS population, levels of parent herbicide were depleted in both the NTSR1 and NTSR2 plants, and this was accompanied by an increased accumulation of hydroxylated chlorotoluron (Figures 2C,D).…”

Enhanced metabolism and target gene overexpression confer resistance against acetolactate synthase‐inhibiting herbicides in Bromus sterilis

“…In addition to the CytP450s, glutathione‐ S ‐transferase (GSTs), glycosyltransferases and ABC transporters are also known to be involved with NTSRs 23 . Resistant populations of Bromus sterilis from the United Kingdom showed elevated amounts of an orthologue of the glutathione transferase phi (F) class 1 protein 24 …”

“…23 Resistant populations of Bromus sterilis from the United Kingdom showed elevated amounts of an orthologue of the glutathione transferase phi (F) class 1 protein. 24 Recently, farmers in the Czech Republic have also reported of resistance to ALS-inhibiting herbicides in Bromus sterilis biotypes. The recommended doses of pyroxsulam have failed to control this weed species in winter wheat fields of the Czech Republic.…”

Plant pest surveillance: from satellites to molecules

“…Poor weed control due to herbicide resistance incurs significant costs; for example, herbicide resistant black-grass (Alopecurus myosuroides) has been associated with U.K. wheat production losses of 1 million tonnes per year [75]. The quick and reliable diagnosis of herbicide resistance is, therefore, an essential step to improve weed control and minimise adverse effects on crop production and the farm economy [76,77]. For instance, the early detection of a protein biomarker, black-grass glutathione-s-transferase phi (F) 1 and its orthologues in rye-grass (Lolium rigidum), barren brome (Bromus sterilis), and meadow brome (Bromus commutatus) using LFAs confirmed the existent of herbicide resistance in these species [78].…”