Assembly and Annotation of the Tetraploid Salsola tragus (Russian thistle) Genome.

This report presents two phased chromosome-scale genome assemblies of allotetraploid Salsola tragus (2n=4x=36) and fills the current genomics resource gap for this species. Flow cytometry estimated 1C genome size was 1.319 Gbp.

Metabolism of 2,4-D in plants: comparative analysis of metabolic detoxification pathways in tolerant crops and resistant weeds.

The commercialization of 2,4-D (2,4-dichlorophenoxyacetic acid) latifolicide in 1945 marked the beginning of the selective herbicide market, with this active ingredient playing a pivotal role among commercial herbicides due to the natural tolerance of monocots compared with dicots. Due to its intricate mode of action, involving interactions within endogenous auxin signaling networks, 2,4-D was initially considered a low-risk herbicide to evolve weed resistance. However, the intensification of 2,4-D use has contributed to the emergence of 2,4-D-resistant broadleaf weeds, challenging earlier beliefs.

Confirmation and characterization of the first case of acetolactate synthase (ALS)-inhibitor resistance in Japanese brome (Bromus japonicus) in the US.

Background: Japanese brome (Bromus japonicus Thumb.) is one of the problematic annual weeds in winter wheat (Triticum aestivum L.) and is generally controlled by acetolactate synthase (ALS) inhibitors.

Enhanced metabolic detoxification is associated with fluroxypyr resistance in .

Auxin-mimic herbicides chemically mimic the phytohormone indole-3-acetic-acid (IAA). Within the auxin-mimic herbicide class, the herbicide fluroxypyr has been extensively used to control kochia (). A 2014 field survey for herbicide resistance in kochia populations across Colorado identified a putative fluroxypyr-resistant (Flur-R) population that was assessed for response to fluroxypyr and dicamba (auxin-mimics), atrazine (photosystem II inhibitor), glyphosate (EPSPS inhibitor), and chlorsulfuron (acetolactate synthase inhibitor).

The nexus between reactive oxygen species and the mechanism of action of herbicides.

Herbicides are small molecules that act by inhibiting specific molecular target sites within primary plant metabolic pathways resulting in catastrophic and lethal consequences. The stress induced by herbicides generates reactive oxygen species (ROS), but little is known about the nexus between each herbicide mode of action (MoA) and their respective ability to induce ROS formation. Indeed, some herbicides cause dramatic surges in ROS levels as part of their primary MoA, whereas other herbicides may generate some ROS as a secondary effect of the stress they imposed on plants.

Nontarget-site resistance due to rapid physiological response in 2,4-D resistant Conyza sumatrensis: reduced 2,4-D translocation and auxin-induced gene expression.

Background: Resistance to 2,4-Dichlorophenoxyacetic acid (2,4-D) has been reported in several weed species since the 1950s; however, a biotype of Conyza sumatrensis showing a novel physiology of the rapid response minutes after herbicide application was reported in 2017. The objective of this research was to investigate the mechanisms of resistance and identify transcripts associated with the rapid physiological response of C. sumatrensis to 2,4-D herbicide.

Recurrent Selection of with a Herbicide Mixture Reduces Progeny Sensitivity.

Herbicide mixtures are used to increase the spectrum of weed control and to manage weeds with target-site resistance to some herbicides. However, the effect of mixtures on the evolution of herbicide resistance caused by enhanced metabolism is unknown. This study evaluated the effect of a fenoxaprop-p-ethyl and imazethapyr mixture on the evolution of herbicide resistance in using recurrent selection at sublethal doses.

Identification of a Novel 2,4-D Metabolic Detoxification Pathway in 2,4-D-Resistant Waterhemp ().

A 2,4-dichlorophenoxyactic acid (2,4-D)-resistant population of (common waterhemp) from Nebraska, USA, was previously found to have rapid metabolic detoxification of the synthetic auxin herbicide 2,4-D. We purified the main 2,4-D metabolites from resistant and susceptible plants, solved their structures by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS), and synthesized the metabolites to determine their toxicity. Susceptible plants conjugated 2,4-D to aspartate to form 2,4-D-aspartic acid (2,4-D-Asp), while resistant plants had a unique metabolic profile where 2,4-D was hydroxylated into 5-OH-2,4-D, followed by conjugation into a sugar metabolite (2,4-D-5--d-glucopyranoside) and subsequent malonylation into 2,4-D-(6'--malonyl)-5--d-glucopyranoside.

Survey of ACCase and ALS resistance in winter annual grasses identifies target-site and nontarget-site imazamox resistance in Secale cereale.

Background: Early detection of herbicide resistance in weeds is crucial for successful implementation of integrated weed management. We conducted a herbicide resistance survey of the winter annual grasses feral rye (Secale cereale), downy brome (Bromus tectorum), and jointed goatgrass (Aegilops cylindrica) from Colorado winter wheat production areas for resistance to imazamox and quizalofop.

Results: All samples were susceptible to quizalofop.

The safener isoxadifen does not increase herbicide resistance evolution in recurrent selection with fenoxaprop.

Safeners are chemical compounds used to improve selectivity and safety of herbicides in crops by activating genes that enhance herbicide metabolic detoxification. The genes activated by safeners in crops are similar to the genes causing herbicide resistance through increased metabolism in weeds. This work investigated the effect of the safener isoxadifen-ethyl (IS) in combination with fenoxaprop-p-ethyl (FE) on the evolution of herbicide resistance in Echinochloa crus-galli under recurrent selection.

Investigating the origins and evolution of a glyphosate-resistant weed invasion in South America.

The global invasion, and subsequent spread and evolution of weeds provides unique opportunities to address fundamental questions in evolutionary and invasion ecology. Amaranthus palmeri is a widespread glyphosate-resistant (GR) weed in the USA. Since 2015, GR populations of A.

Genomic-based epidemiology reveals independent origins and gene flow of glyphosate resistance in Bassia scoparia populations across North America.

Genomic-based epidemiology can provide insight into the origins and spread of herbicide resistance mechanisms in weeds. We used kochia (Bassia scoparia) populations resistant to the herbicide glyphosate from across western North America to test the alternative hypotheses that (i) a single EPSPS gene duplication event occurred initially in the Central Great Plains and then subsequently spread to all other geographical areas now exhibiting glyphosate-resistant kochia populations or that (ii) gene duplication occurred multiple times in independent events in a case of parallel evolution. We used qPCR markers previously developed for measuring the structure of the EPSPS tandem duplication to investigate whether all glyphosate-resistant individuals had the same EPSPS repeat structure.

Can new herbicide discovery allow weed management to outpace resistance evolution?

While herbicides are the most effective and widely adopted weed management approach, the evolution of multiple herbicide resistance in damaging weed species threatens the yield and profitability of many crops. Weeds accumulate multiple resistance mechanisms through sequential selection and/or gene flow, with long-range and international transport of herbicide-resistant weeds proving to be a serious issue. Metabolic resistance mechanisms can confer resistance across multiple sites of action and even to herbicides not yet discovered.

A needle in a seedstack: an improved method for detection of rare alleles in bulk seed testing through KASP.

Background: Amaranthus palmeri is an aggressive and prolific weed species with major impact on agricultural yield and is a prohibited noxious weed across the Midwest. Morphological identification of A. palmeri from other Amaranthus species is extremely difficult in seeds, which has led to genetic testing for seed identification in commercial seed lots.

Synthetic auxin herbicides: finding the lock and key to weed resistance.

Synthetic auxin herbicides are designed to mimic indole-3-acetic acid (IAA), an integral plant hormone affecting cell growth, development, and tropism. In this review, we explore target site genes in the auxin signaling pathway including SCF, Aux/IAA, and ARFs that are confirmed or proposed mechanisms for weed resistance to synthetic auxin herbicides. Resistance to auxin herbicides by metabolism, either by enhanced cytochrome P450 detoxification or by loss of pro-herbicide activation, is a major non-target-site resistance pathway.

Dicamba resistance in kochia from Kansas and Nebraska evolved independently.

Background: Evolution and spread of resistance to glyphosate in kochia [Bassia scoparia (L.) A.J.

Coexpression Clusters and Allele-Specific Expression in Metabolism-Based Herbicide Resistance.

In the last decade, Amaranthus tuberculatus has evolved resistance to 2,4-dichlorophenoxyacetic acid (2,4-D) and 4-hydroxyphenylpyruvate dioxygenase inhibitors in multiple states across the midwestern United States. Two populations resistant to both mode-of-action groups, one from Nebraska (NEB) and one from Illinois (CHR), were studied using an RNA-seq approach on F2 mapping populations to identify the genes responsible for resistance. Using both an A.

Evolution of EPSPS double mutation imparting glyphosate resistance in wild poinsettia (Euphorbia heterophylla L.).

The evolution of glyphosate resistance (GR) in weeds is an increasing problem. Glyphosate has been used intensively on wild poinsettia (Euphorbia heterophylla L.) populations for at least 20 years in GR crops within South America.

The quick and the dead: a new model for the essential role of ABA accumulation in synthetic auxin herbicide mode of action.

This article comments on: 2020. Transcriptomics in reveals rapid photosynthetic and hormonal responses to auxin herbicide application. Journal of Experimental Botany 3701–3709.

Mechanisms of evolved herbicide resistance.

The widely successful use of synthetic herbicides over the past 70 years has imposed strong and widespread selection pressure, leading to the evolution of herbicide resistance in hundreds of weed species. Both target-site resistance (TSR) and nontarget-site resistance (NTSR) mechanisms have evolved to most herbicide classes. TSR often involves mutations in genes encoding the protein targets of herbicides, affecting the binding of the herbicide either at or near catalytic domains or in regions affecting access to them.

Trp2027Cys mutation evolves in Digitaria insularis with cross-resistance to ACCase inhibitors.

Sourgrass (Digitaria insularis) is one of the most problematic weeds in South America because glyphosate resistance is widespread across most crop production regions. Acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides have been intensively used to manage D. insularis, which substantially increased selection pressure for this class of herbicides.

Herbicide drift exposure leads to reduced herbicide sensitivity in Amaranthus spp.

While the introduction of herbicide tolerant crops provided growers new options to manage weeds, the widespread adoption of these herbicides increased the risk for herbicide spray drift to surrounding vegetation. The impact of herbicide drift in sensitive crops is extensively investigated, whereas scarce information is available on the consequences of herbicide drift in non-target plants. Weeds are often abundant in field margins and ditches surrounding agricultural landscapes.

Omics Potential in Herbicide-Resistant Weed Management.

The rapid development of omics technologies has drastically altered the way biologists conduct research. Basic plant biology and genomics have incorporated these technologies, while some challenges remain for use in applied biology. Weed science, on the whole, is still learning how to integrate omics technologies into the discipline; however, omics techniques are more frequently being implemented in new and creative ways to address basic questions in weed biology as well as the more practical questions of improving weed management.