Evolution of generalist resistance to herbicide mixtures reveals a trade-off in resistance management

Abstract

Intense selection by pesticides and antibiotics has resulted in a global epidemic of evolved resistance. In agriculture and medicine, using mixtures of compounds from different classes is widely accepted as optimal resistance management. However, this strategy may promote the evolution of more generalist resistance mechanisms. Here we test this hypothesis at a national scale in an economically important agricultural weed: blackgrass (Alopecurus myosuroides), for which herbicide resistance is a major economic issue. Our results reveal that greater use of herbicide mixtures is associated with lower levels of specialist resistance mechanisms, but higher levels of a generalist mechanism implicated in enhanced metabolism of herbicides with diverse modes of action. Our results indicate a potential evolutionary trade-off in resistance management, whereby attempts to reduce selection for specialist resistance traits may promote the evolution of generalist resistance. We contend that where specialist and generalist resistance mechanisms co-occur, similar trade-offs will be evident, calling into question the ubiquity of resistance management based on mixtures and combination therapies.

Target-Site and Non-target-Site Resistance Mechanisms Confer Multiple and Cross- Resistance to ALS and ACCase Inhibiting Herbicides in Lolium rigidum From Spain

“…Non-target-site resistance is a generalist resistance mechanism that develops independently from TSR, a specialist resistance mechanism that confers resistance to only one herbicide SoA, with several grasses exhibiting both classes of resistance ( Comont et al, 2020 ). EMR is one of the best-known mechanisms under-pinning NTSR and confers broad spectrum resistance to multiple herbicide SoA in weeds ( Ghanizadeh and Harrington, 2017 ; Gaines et al, 2020 ).…”

“…GSTs are known to detoxify herbicides through catalyzing their conjugation with glutathione (GSH) ( Cummins et al, 2013 ; Gaines et al, 2020 ). In Alopecurus myosuroides , the constitutive level of a glutathione transferase phi (F) class 1 protein ( AmGSTF1 ) was significantly higher in multiple herbicide resistance populations than in sensitive populations ( Comont et al, 2020 ). The biochemistry of AmGSTF1 and its transgenic expression in Arabidopsis thaliana showed that this protein has a functional role in regulating NTSR that extends beyond the glutathione conjugation of herbicides ( Cummins et al, 1999 , 2013 ).…”

Cytochrome P450 Herbicide Metabolism as the Main Mechanism of Cross-Resistance to ACCase- and ALS-Inhibitors in Lolium spp. Populations From Argentina: A Molecular Approach in Characterization and Detection

“…Resistance to multiple herbicides emerges as a challenge for current and future weed management. Chemical control practices that seek to reduce selection for specialist resistance traits may promote the evolution of generalist resistance ( Comont et al, 2020 ). The study of metabolic resistance mechanisms and the elucidation of a molecular basis is a difficult and arduous process but a better understanding of these generalist mechanisms will reinforce comprehension of the evolution of weed populations in response to selection pressures and contribute to the development of weed management strategies to delay resistance ( Nandula et al, 2019 ).…”

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

“…AmGSTF1 levels in protein samples were quantified by ELISA using specific sheep antibodies raised against AmGSTF1 in 96well plates (Comont et al, 2020). Briefly, 96-well plates were coated with the primary antiserum (S909-D, diluted to 1 µg/ml in phosphate-buffered saline (PBS) for 16-18 h at 4 • C. Plates were washed four times with wash buffer [PBS with 0.1% (v/v) Tween 20 (Sigma Aldrich)] before black-grass protein (100 µg) extracts were applied.…”