Deciphering the evolution of herbicide resistance in weeds
TL;DR: Recent advances in understanding the genetic bases and evolutionary drivers of herbicide resistance that highlight the complex nature of selection for this adaptive trait are reviewed.
About: This article is published in Trends in Genetics.The article was published on 2013-11-01. It has received 453 citations till now.
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TL;DR: Current evidence suggests that insect and weed evolution may outstrip the authors' ability to replace outmoded chemicals and other control mechanisms, and it is necessary to address the mix of ecological, genetic, economic, and sociopolitical factors that prevent implementation of sustainable pest management practices.
Abstract: Resistance to insecticides and herbicides has cost billions of U.S. dollars in the agricultural sector and could result in millions of lives lost to insect-vectored diseases. We mostly continue to use pesticides as if resistance is a temporary issue that will be addressed by commercialization of new pesticides with novel modes of action. However, current evidence suggests that insect and weed evolution may outstrip our ability to replace outmoded chemicals and other control mechanisms. To avoid this outcome, we must address the mix of ecological, genetic, economic, and sociopolitical factors that prevent implementation of sustainable pest management practices. We offer an ambitious proposition.
280 citations
TL;DR: This Perspective describes how polygenic adaptation can be studied using a framework of ‘adaptive architecture’ that unifies principles from the traditionally disparate fields of quantitative genetics and molecular population genetics.
Abstract: Most adaption processes have a polygenic genetic basis, but even with the recent explosive growth of genomic data we are still lacking a unified framework describing the dynamics of selected alleles Building on recent theoretical and empirical work we introduce the concept of adaptive architecture, which extends the genetic architecture of an adaptive trait by factors influencing its adaptive potential and population genetic principles Because adaptation can be typically achieved by many different combinations of adaptive alleles (redundancy), we describe how two characteristics — heterogeneity among loci and non-parallelism between replicated populations — are hallmarks for the characterization of polygenic adaptation in evolving populations We discuss how this unified framework can be applied to natural and experimental populations Increased capacities for sequencing and genotyping are enabling a more comprehensive understanding of the genetics of adaptation for diverse species In this Perspective, Barghi, Hermisson and Schlotterer describe how polygenic adaptation can be studied using a framework of ‘adaptive architecture’ that unifies principles from the traditionally disparate fields of quantitative genetics and molecular population genetics
211 citations
TL;DR: A conceptual framework allowing to define ecological engineering options based upon ecosystem services of weeds and pollinators is presented and it is shown that weed abundance can reduce crop yields, thus inducing conflict with farmers, but weed abundance enhances regulating services by ensuring the survival of honeybees in the absence of oil seed crops.
Abstract: Agricultural intensification has led to the decrease of the diversity of wild and domestic pollinators For instance, honeybees declined by 59 % in 61 years in the USA About 35 % of major crops in the world depend on pollination services, and 3–8 % of world crop production will disappear without pollinators Indeed, pollination provides several ecosystem services such as enabling crop and honey productions, regulating weeds and other cultural services Agricultural intensification has also decreased weed diversity by about 50 % in 70 years because massive herbicide sprays have reduced the competition between weeds and crops Nevertheless, weeds are at the basis of agricultural foodwebs, providing food to many living organisms In particular, weeds provide flowers for pollinating insects including honey and wild bees Here, we review the decline of weeds and bees We discuss the effect of bees and pollination on crop production We describe the complex interactions between bee pollinators, eg honey and wild bees, and landscape habitats such as crop fields and semi-natural elements For that, we focus on spatial and temporal effects on flower resources We show that weed abundance can reduce crop yields, thus inducing conflict with farmers But weed abundance enhances regulating services by ensuring the survival of honeybees in the absence of oil seed crops Weed abundance also enhances pollination services and, in turn, honey yield for the benefit of beekeepers Weed abundance has also improved the survival of wild flora and the socio-cultural value of landscapes, a major request from the public From those findings, we present a conceptual framework allowing to define ecological engineering options based upon ecosystem services of weeds and pollinators
209 citations
Cites background from "Deciphering the evolution of herbic..."
...Growers currently use a lower number of herbicides (Delye et al. 2013) increasing the selection pressure on weeds and hence increasing the number of resistant weeds which can survive the application of herbicides by a variety of mechanisms (Powles and Yu 2010; Beckie and Tardif 2012)....
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TL;DR: While the science of ACCase herbicide resistance has progressed significantly over the past 10 years, several avenues remain to be explored for a better understanding of resistance to this important mode of action.
Abstract: Resistance to acetyl-CoA carboxylase herbicides is documented in at least 43 grass weeds and is particularly problematic in Lolium, Alopecurus and Avena species. Genetic studies have shown that resistance generally evolves independently and can be conferred by target-site mutations at ACCase codon positions 1781, 1999, 2027, 2041, 2078, 2088 and 2096. The level of resistance depends on the herbicides, recommended field rates, weed species, plant growth stages, specific amino acid changes and the number of gene copies and mutant ACCase alleles. Non-target-site resistance, or in essence metabolic resistance, is prevalent, multigenic and favoured under low-dose selection. Metabolic resistance can be specific but also broad, affecting other modes of action. Some target-site and metabolic-resistant biotypes are characterised by a fitness penalty. However, the significance for resistance regression in the absence of ACCase herbicides is yet to be determined over a practical timeframe. More recently, a fitness benefit has been reported in some populations containing the I1781L mutation in terms of vegetative and reproductive outputs and delayed germination. Several DNA-based methods have been developed to detect known ACCase resistance mutations, unlike metabolic resistance, as the genes remain elusive to date. Therefore, confirmation of resistance is still carried out via whole-plant herbicide bioassays. A growing number of monocotyledonous crops have been engineered to resist ACCase herbicides, thus increasing the options for grass weed control. While the science of ACCase herbicide resistance has progressed significantly over the past 10 years, several avenues provided in the present review remain to be explored for a better understanding of resistance to this important mode of action.
174 citations
TL;DR: This review is both a retrospective (what have the authors missed?) and prospective (where are they going?) examination of weed control and technology, particularly as it applies to herbicide-resistant weed management (RWM).
Abstract: This review is both a retrospective (what have we missed?) and prospective (where are we going?) examination of weed control and technology, particularly as it applies to herbicide-resistant weed management (RWM). Major obstacles to RWM are discussed, including lack of diversity in weed management, unwillingness of many weed researchers to conduct real integrated weed management research or growers to accept recommendations, influence or role of agrichemical marketing and governmental policy and lack of multidisciplinary research. We then look ahead to new technologies that are needed for future weed control in general and RWM in particular, in areas such as non-chemical and chemical weed management, novel herbicides, site-specific weed management, drones for monitoring large areas, wider application of 'omics' and simulation model development. Finally, we discuss implementation strategies for integrated weed management to achieve RWM, development of RWM for developing countries, a new classification of herbicides based on mode of metabolism to facilitate greater stewardship and greater global exchange of information to focus efforts on areas that maximize progress in weed control and RWM. There is little doubt that new or emerging technologies will provide novel tools for RMW in the future, but will they arrive in time?
162 citations
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TL;DR: Despite a clear increase in pesticide use, crop losses have not significantly decreased during the last 40 years, however, pesticide use has enabled farmers to modify production systems and to increase crop productivity without sustaining the higher losses likely to occur from an increased susceptibility to the damaging effect of pests.
Abstract: Productivity of crops grown for human consumption is at risk due to the incidence of pests, especially weeds, pathogens and animal pests. Crop losses due to these harmful organisms can be substantial and may be prevented, or reduced, by crop protection measures. An overview is given on different types of crop losses as well as on various methods of pest control developed during the last century.Estimates on potential and actual losses despite the current crop protection practices are given for wheat, rice, maize, potatoes, soybeans, and cotton for the period 2001–03 on a regional basis (19 regions) as well as for the global total. Among crops, the total global potential loss due to pests varied from about 50% in wheat to more than 80% in cotton production. The responses are estimated as losses of 26–29% for soybean, wheat and cotton, and 31, 37 and 40% for maize, rice and potatoes, respectively. Overall, weeds produced the highest potential loss (34%), with animal pests and pathogens being less important (losses of 18 and 16%). The efficacy of crop protection was higher in cash crops than in food crops. Weed control can be managed mechanically or chemically, therefore worldwide efficacy was considerably higher than for the control of animal pests or diseases, which rely heavily on synthetic chemicals. Regional differences in efficacy are outlined. Despite a clear increase in pesticide use, crop losses have not significantly decreased during the last 40 years. However, pesticide use has enabled farmers to modify production systems and to increase crop productivity without sustaining the higher losses likely to occur from an increased susceptibility to the damaging effect of pests.The concept of integrated pest/crop management includes a threshold concept for the application of pest control measures and reduction in the amount/frequency of pesticides applied to an economically and ecologically acceptable level. Often minor crop losses are economically acceptable; however, an increase in crop productivity without adequate crop protection does not make sense, because an increase in attainable yields is often associated with an increased vulnerability to damage inflicted by pests.
3,821 citations
TL;DR: Aproximately 50,000 nonindigenous (non-native) species are estimated to have been introduced to the United States, many of which are beneficial but have caused major economic losses in agriculture, forestry, and several other segments of the US economy, in addition to harming the environment.
Abstract: [Extract] Aproximately 50,000 nonindigenous (non-native) species are estimated to have been introduced to the United States. Some of these are beneficial; for example, species introduced as food crops (e.g., corn, wheat, and rice) and as livestock (e.g., cattle and poultry) now provide more than 98% of the US food system, at a value of approximately $800 billion per year (USBC 1998). Other exotic species have been introduced for landscape restoration, biological pest control, sport, pets, and food processing, also with significant benefits. Some nonindigenous species, however, have caused major economic losses in agriculture, forestry, and several other segments of the US economy, in addition to harming the environment. One study reported that 79 exotic species had caused approximately $97 billion in damages during the period 1906–1991 (OTA 1993).
2,922 citations
TL;DR: Understanding resistance and building sustainable solutions to herbicide resistance evolution are necessary and worthy challenges to herbicides sustainability in world agriculture.
Abstract: Modern herbicides make major contributions to global food production by easily removing weeds and substituting for destructive soil cultivation. However, persistent herbicide selection of huge weed numbers across vast areas can result in the rapid evolution of herbicide resistance. Herbicides target specific enzymes, and mutations are selected that confer resistance-endowing amino acid substitutions, decreasing herbicide binding. Where herbicides bind within an enzyme catalytic site very few mutations give resistance while conserving enzyme functionality. Where herbicides bind away from a catalytic site many resistance-endowing mutations may evolve. Increasingly, resistance evolves due to mechanisms limiting herbicide reaching target sites. Especially threatening are herbicide-degrading cytochrome P450 enzymes able to detoxify existing, new, and even herbicides yet to be discovered. Global weed species are accumulating resistance mechanisms, displaying multiple resistance across many herbicides and posing a great challenge to herbicide sustainability in world agriculture. Fascinating genetic issues associated with resistance evolution remain to be investigated, especially the possibility of herbicide stress unleashing epigenetic gene expression. Understanding resistance and building sustainable solutions to herbicide resistance evolution are necessary and worthy challenges.
1,379 citations
TL;DR: This work argues for alternatives to the hard sweep model: in particular, polygenic adaptation could allow rapid adaptation while not producing classical signatures of selective sweeps, and discusses some of the likely opportunities for progress in the field.
887 citations
TL;DR: This work investigated recently discovered glyphosate-resistant Amaranthus palmeri populations from Georgia, in comparison with normally sensitive populations, and revealed that EPSPS genes were present on every chromosome and, therefore, gene amplification was likely not caused by unequal chromosome crossing over.
Abstract: The herbicide glyphosate became widely used in the United States and other parts of the world after the commercialization of glyphosate-resistant crops. These crops have constitutive overexpression of a glyphosate-insensitive form of the herbicide target site gene, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). Increased use of glyphosate over multiple years imposes selective genetic pressure on weed populations. We investigated recently discovered glyphosate-resistant Amaranthus palmeri populations from Georgia, in comparison with normally sensitive populations. EPSPS enzyme activity from resistant and susceptible plants was equally inhibited by glyphosate, which led us to use quantitative PCR to measure relative copy numbers of the EPSPS gene. Genomes of resistant plants contained from 5-fold to more than 160-fold more copies of the EPSPS gene than did genomes of susceptible plants. Quantitative RT-PCR on cDNA revealed that EPSPS expression was positively correlated with genomic EPSPS relative copy number. Immunoblot analyses showed that increased EPSPS protein level also correlated with EPSPS genomic copy number. EPSPS gene amplification was heritable, correlated with resistance in pseudo-F2 populations, and is proposed to be the molecular basis of glyphosate resistance. FISH revealed that EPSPS genes were present on every chromosome and, therefore, gene amplification was likely not caused by unequal chromosome crossing over. This occurrence of gene amplification as an herbicide resistance mechanism in a naturally occurring weed population is particularly significant because it could threaten the sustainable use of glyphosate-resistant crop technology.
626 citations