ALS resistance in bromes identified in the UK
One population of great brome (Anisantha diandra), meadow brome (Bromus commutatus) and three populations of sterile brome (Anisantha sterilis) have been shown to be resistant to ALS-inhibiting herbicides (mesosulfuron+ iodosulfuron and pyroxsulam) in the UK.
The results were published in Pest Management Science this month. One population of rye brome (Bromus secalinus) was shown to have increased tolerance to ALS-inhibiting herbicides.
The type of resistance was identified as a point mutation at Trp-574 in meadow brome but NTSR/EMR in the other brome species.
These results originate from an AHDB project: 211200059 – Investigating the distribution and presence, and potential for herbicide resistance of UK brome species in arable farming. This AHDB project runs from March 2017 to February 2021. Funding is £218,000 (£183,000 to ADAS & £35,000 to Rothamsted Research), plus £10,000 each in-kind from BASF, Bayer, Monsanto (now Bayer), Corteva & UPL.
What does this mean for UK farmers?
The good news is that all brome populations tested were sensitive to propaquizafop, although resistance to propaquizafop and cycloxydim in sterile brome were identified in Germany in 2012.
Additionally, all bromes tested were still controlled by 360g a.i/ha of glyphosate although some populations showed increased tolerance at this rate. All populations were well controlled by 540g a.i/ha of glyphosate the recommended field rate for annual grass weeds.
The results indicate that although ALS resistance is evolving in brome populations other modes of action can be used to control these populations in a diverse rotation but growers should be alert to the risk of rapid herbicide resistance evolution to other modes of action in UK bromes.
Full abstract from the paper
Authors: Laura R Davies, Nawaporn Onkokesung, Melissa Brazier‐Hicks, Robert Edwards and Stephen Moss (2020) Detection and characterisation of resistance to acetolactate synthase inhibiting herbicides in Anisantha and Bromus species in the United Kingdom. Pest Management Science.
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 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. In 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 levels of an orthologue of the glutathione transferase phi (F) class 1 (GSTF1) protein, a functional biomarker of non‐target site resistance (NTSR) in Alopecurus myosuroides. NTSR was further evidenced 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.