Point Mutations and Cytochrome P450 Can Contribute to Resistance to ACCase-Inhibiting Herbicides in Three Phalaris Species

Strategic lead compound design and development utilizing computer-aided drug discovery (CADD) to address herbicide-resistant Phalaris minor in wheat fields

Wheat (Triticum aestivum) is a vital cereal crop and a staple food source worldwide. However, wheat grain productivity has significantly declined as a consequence of infestations by Phalaris minor. Traditional weed control methods have proven inadequate owing to the physiological similarities between P. minor and wheat during early growth stages. Consequently, farmers have turned to herbicides, targeting acetyl-CoA carboxylase (ACCase), acetolactate synthase (ALS) and photosystem II (PSII). Isoproturon targeting PSII was introduced in mid-1970s, to manage P. minor infestations. Despite their effectiveness, the repetitive use of these herbicides has led to the development of herbicide-resistant P. minor biotypes, posing a significant challenge to wheat productivity. To address this issue, there is a pressing need for innovative weed management strategies and the discovery of novel herbicide molecules. The integration of computer-aided drug discovery (CADD) techniques has emerged as a promising approach in herbicide research, that facilitates the identification of herbicide targets and enables the screening of large chemical libraries for potential herbicide-like molecules. By employing techniques such as homology modelling, molecular docking, molecular dynamics simulation and pharmacophore modelling, CADD has become a rapid and cost-effective medium to accelerate the herbicide discovery process significantly. This approach not only reduces the dependency on traditional experimental methods, but also enhances the precision and efficacy of herbicide development. This article underscores the critical role of bioinformatics and CADD in developing next-generation herbicides, offering new hope for sustainable weed management and improved wheat cultivation practices. © 2024 Society of Chemical Industry.

Differential Resistance to Acetyl-CoA Carboxylase Inhibitors in Rice: Insights from Two Distinct Target-Site Mutations

Weeds present a significant challenge to agricultural productivity, and acetyl-CoA carboxylase (ACCase)-inhibiting herbicides have proven to be effective in managing weed populations in rice fields. To develop ACCase-inhibiting herbicide-resistant rice, we generated mutants of rice ACCase (OsACC) featuring Ile-1792-Leu or Gly-2107-Ser substitutions through ethyl methyl sulfonate (EMS) mutagenesis. The Ile-1792-Leu mutant displayed cross-resistance to aryloxyphenoxypropionate (APP) and phenylpyrazoline (DEN) herbicides, whereas the Gly-2107-Ser mutants primarily exhibited cross-resistance to APP herbicides with diminished resistance to the DEN herbicide. In vitro assays of the OsACC activity revealed an increase in resistance to haloxyfop and quizalofop, ranging from 4.84- to 29-fold in the mutants compared to that in wild-type. Structural modeling revealed that both mutations likely reduce the binding affinity between OsACC and ACCase inhibitors, thereby imparting resistance. This study offers insights into two target-site mutations, contributing to the breeding of herbicide-resistant rice and presenting alternative weed management strategies in rice cultivation.

Distribution, frequency and molecular basis of clethodim and quizalofop resistance in brome grass (Bromus diandrus)

BACKGROUND

Brome grass (Bromus diandrus Roth) is prevalent in the southern and western cropping regions of Australia, where it causes significant economic damage. A targeted herbicide resistance survey was conducted in 2020 by collecting brome grass populations from 40 farms in Western Australia and subjecting these samples to comprehensive herbicide screening. One sample (population 172-20), from a field that had received 12 applications of clethodim over 20 years of continuous cropping, was found to be highly resistant to the acetyl-CoA carboxylase (ACCase)-inhibiting herbicides clethodim and quizalofop, and so the molecular basis of resistance was investigated.

RESULTS

All 31 individuals examined from population 172-20 carried the same resistance-endowing point mutation causing an aspartate-to-glycine substitution at position 2078 in the translated ACCase protein sequence. A wild-type susceptible population and the resistant population had similar expression levels of plastidic ACCase genes. The level of resistance to quizalofop, either standalone or in mixture with clethodim, in population 172-20 was lower under cooler growing conditions.

CONCLUSION

Target-site resistance to ACCase-inhibiting herbicides, conferred by one ACCase mutation, was selected in all tested brome plants infesting a field with a history of repeated clethodim use. This mutation appears to have been fixed in the infesting population. Notably, clethodim resistance in this population was not detected by the farmer, and a high future incidence of quizalofop resistance is anticipated. Herbicide resistance testing is essential for the detection of evolving weed resistance issues and to inform effective management strategies. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Sustainable Weed Management

Weeds are the most important biological constraint determining yield losses for field crops [...].

Comparison between the mechanisms of Clearfield ® wheat and Lolium rigidum multiple resistant to acetyl CoA carboxylase and acetolactate synthase inhibitors

Clearfield® wheat (Triticum aestivum) have helped eliminate the toughest grasses and broadleaf weeds in Spain since 2005. This crop production system includes other tolerant cultivars to the application of imidazolinone (IMI) herbicides. However, the continuous use and off-label rates of IMI herbicides can contribute to the development of resistance in Lolium rigidum and other weed species. In this research, the main objectives were to study the resistance mechanisms to acetolactate synthase (ALS) and acetyl coenzyme A carboxylase (ACCase) inhibitors in a L. rigidum accession (LrR) from a Clearfield® wheat field, with a long history rotating these IMI-tolerant crops and compare them with those present in the IMI-tolerant wheat. The resistance to ACCase inhibitors in LrR was due to point mutations (Ile1781Leu plus Asp2078Gly) of the target site gene plus an enhanced herbicide metabolism (EHM), on the other hand, in wheat accessions was due only by EHM. Mechanisms involved in the resistance to ALS inhibitors were both point mutations of the target gene and EHM in the IMI-tolerant wheat, while only evidence of mutation (Trp574Leu) was found in the multiple herbicide resistant L. rigidum accession. This research demonstrates that if crop rotation is not accompanied by the use of alternative sites of action in herbicide-tolerant crops, resistant weeds to herbicide to which crops are tolerant, can easily be selected. Moreover, repeated and inappropriate use of Clearfield® crops and herbicide rotations can lead to the evolution of multiple resistant weeds, as shown in this study, and have also inestimable environmental impacts.