Allelic interactions defining Raphanus raphanistrum AHAS resistance level: strong vs weak target-site AHAS resistance alleles.

Background: Chlorsulfuron resistance and genetic dominance was evaluated in Raphanus raphanistrum genotypes homozygous (122-RR, 376-RR), heterozygous (122-RS, 376-RS) and compound heterozygous (122-R/376-R) for the target-site resistance mutations Ala-122-Tyr and Asp-376-Glu in the AHAS (acetohydroxyacid synthase) gene.

Results: At the AHAS level, 122-RR and 122-RS plants exhibited significantly higher I values than 376-RR and 376-RS plants, respectively. However, plants of the compound heterozygous genotype (122-R/376-R), showed no difference in AHAS activity compared to the 122-RS genotype but lower activity than the 122-RR genotype, and showed a nearly 400-fold greater I value than both genotypes (376-RR and 376-RS) carrying the 376-Glu allele.

Intergenerational consequences of an auxin-like herbicide on plant sensitivity to a graminicide mediated by a fungal endophyte.

In agroecosystems, herbicides are the predominant anthropogenic selection pressure for agriculture weed species. While weeds are the primary target, herbicides can have adverse impacts on non-target plant beneficial microorganisms. We aimed to investigate the influence of a foliar endophytic fungus (Epichloë occultans) on the sensitivity of Lolium multiflorum to a graminicide herbicide (diclofop-methyl) during both plant ontogeny and progeny.

Challenging glyphosate resistance EPSPS P106S and TIPS mutations with soybean competition and glyphosate: implications for management.

Background: Eleusine indica (L.) Gaertn. (goosegrass) is a major weed in global cropping systems.

A novel EPSPS Pro-106-His mutation confers the first case of glyphosate resistance in Digitaria sanguinalis.

Background: Digitaria sanguinalis has been identified as a species at high risk of evolving herbicide resistance, but thus far, there are no records of resistance to glyphosate. This weed is one of the most common weeds of summer crops in extensive cropping areas in Argentina. It shows an extended period of seedling emergence with several overlapping cohorts during spring and summer, and is commonly controlled with glyphosate.

A dinitroaniline herbicide resistance mutation can be nearly lethal to plants.

Background: Lolium rigidum is the most important weed in Australian agriculture and pre-emergence dinitroaniline herbicides (e.g., trifluralin) are widely and persistently used for Lolium control.

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.

Contrasting plant ecological benefits endowed by naturally occurring resistance mutations under glyphosate selection.

Concurrent natural evolution of glyphosate resistance single- and double-point EPSPS mutations in weed species provides an opportunity for the estimation of resistance fitness benefits and prediction of equilibrium resistance frequencies in environments under glyphosate selection. Assessment of glyphosate resistance benefit was conducted for the most commonly identified single Pro-106-Ser and less-frequent double TIPS mutations in the gene evolved in the global damaging weed . Under glyphosate selection at the field dose, plants with the single Pro-106-Ser mutation at homozygous state (P106S-rr) showed reduced survival and compromised vegetative growth and fecundity compared with TIPS plants.

Fitness of Herbicide-Resistant Weeds: Current Knowledge and Implications for Management.

Herbicide resistance is the ultimate evidence of the extraordinary capacity of weeds to evolve under stressful conditions. Despite the extraordinary plant fitness advantage endowed by herbicide resistance mutations in agroecosystems under herbicide selection, resistance mutations are predicted to exhibit an adaptation cost (i.e.

Do plants pay a fitness cost to be resistant to glyphosate?

We reviewed the literature to understand the effects of glyphosate resistance on plant fitness at the molecular, biochemical and physiological levels. A number of correlations between enzyme characteristics and glyphosate resistance imply the existence of a plant fitness cost associated with resistance-conferring mutations in the glyphosate target enzyme, 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS). These biochemical changes result in a tradeoff between the glyphosate resistance of the EPSPS enzyme and its catalytic activity.

The power and potential of genomics in weed biology and management.

There have been previous calls for, and efforts focused on, realizing the power and potential of weed genomics for better understanding of weeds. Sustained advances in genome sequencing and assembly technologies now make it possible for individual research groups to generate reference genomes for multiple weed species at reasonable costs. Here, we present the outcomes from several meetings, discussions, and workshops focused on establishing an International Weed Genomics Consortium (IWGC) for a coordinated international effort in weed genomics.

The role of plant size in the selection of glyphosate resistance in Sorghum halepense.

Background: The effect of plant size (seedlings versus young plants versus adult plants) on the phenotypic level of glyphosate resistance and selection intensity (SI) in Sorghum halepense with and without a reduced glyphosate translocation resistance mechanism was evaluated.

Results: Resistance parameters [the 50% lethal dose (LD ) and the dose required to cause a 50% reduction in plant growth (GR )] in adult plants were notably higher than in seedlings regardless of the resistance status. However, under similar plant size increases, populations comprised of glyphosate-resistant (R) individuals showed higher survival and growth when glyphosate treated compared with glyphosate-susceptible (S) plants.

A double EPSPS gene mutation endowing glyphosate resistance shows a remarkably high resistance cost.

A novel glyphosate resistance double point mutation (T102I/P106S, TIPS) in the 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) gene has been recently identified for the first time only in the weed species Eleusine indica. Quantification of plant resistance cost associated with the TIPS and the often reported glyphosate resistance single P106S mutation was performed. A significant resistance cost (50% in seed number currency) associated with the homozygous TIPS but not the homozygous P106S EPSPS variant was identified in E.

Forward selection for multiple resistance across the non-selective glyphosate, glufosinate and oxyfluorfen herbicides in Lolium weed species.

Background: In the Mediterranean area, Lolium species have evolved resistance to glyphosate after decades of continual use without other alternative chemicals in perennial crops (olive, citrus and vineyards). In recent years, oxyfluorfen alone or mixed with glyphosate and glufosinate has been introduced as a chemical option to control dicot and grass weeds.

Results: Dose-response studies confirmed that three glyphosate-resistant Lolium weed species (L.

Directional selection for flowering time leads to adaptive evolution in Raphanus raphanistrum (Wild radish).

Herbicides have been the primary tool for controlling large populations of yield depleting weeds from agro-ecosystems, resulting in the evolution of widespread herbicide resistance. In response, nonherbicidal techniques have been developed which intercept weed seeds at harvest before they enter the soil seed bank. However, the efficiency of these techniques allows an intense selection for any trait that enables weeds to evade collection, with early-flowering ecotypes considered likely to result in early seed shedding.

Effect of herbicide resistance endowing Ile-1781-Leu and Asp-2078-Gly ACCase gene mutations on ACCase kinetics and growth traits in Lolium rigidum.

The rate of herbicide resistance evolution in plants depends on fitness traits endowed by alleles in both the presence and absence (resistance cost) of herbicide selection. The effect of two Lolium rigidum spontaneous homozygous target-site resistance-endowing mutations (Ile-1781-Leu, Asp-2078-Gly) on both ACCase activity and various plant growth traits have been investigated here. Relative growth rate (RGR) and components (net assimilation rate, leaf area ratio), resource allocation to different organs, and growth responses in competition with a wheat crop were assessed.

Glyphosate resistance in Echinochloa colona: phenotypic characterisation and quantification of selection intensity.

Background: A population of Echinochloa colona infesting agricultural fields in the northern region of Western Australia evolved glyphosate resistance after 10 years of glyphosate selection. This study identified two phenotypic (susceptible S versus resistant R) lines from within a segregating glyphosate-resistant population. Estimation of survival, growth and reproductive rates of the phenotypes in response to glyphosate selection helped to characterise the level of resistance, fitness and the selection intensity for glyphosate in this species.

Expanding the eco-evolutionary context of herbicide resistance research.

The potential for human-driven evolution in economically and environmentally important organisms in medicine, agriculture and conservation management is now widely recognised. The evolution of herbicide resistance in weeds is a classic example of rapid adaptation in the face of human-mediated selection. Management strategies that aim to slow or prevent the evolution of herbicide resistance must be informed by an understanding of the ecological and evolutionary factors that drive selection in weed populations.

Herbicide resistance modelling: past, present and future.

Computer simulation modelling is an essential aid in building an integrated understanding of how different factors interact to affect the evolutionary and population dynamics of herbicide resistance, and thus in helping to predict and manage how agricultural systems will be affected. In this review, we first discuss why computer simulation modelling is such an important tool and framework for dealing with herbicide resistance. We then explain what questions related to herbicide resistance have been addressed to date using simulation modelling, and discuss the modelling approaches that have been used, focusing first on the earlier, more general approaches, and then on some newer, more innovative approaches.

Herbicide-resistant weeds: from research and knowledge to future needs.

Synthetic herbicides have been used globally to control weeds in major field crops. This has imposed a strong selection for any trait that enables plant populations to survive and reproduce in the presence of the herbicide. Herbicide resistance in weeds must be minimized because it is a major limiting factor to food security in global agriculture.

Inheritance of evolved resistance to a novel herbicide (pyroxasulfone).

Agricultural weeds have rapidly adapted to intensive herbicide selection and resistance to herbicides has evolved within ecological timescales. Yet, the genetic basis of broad-spectrum generalist herbicide resistance is largely unknown. This study aims to determine the genetic control of non-target-site herbicide resistance trait(s) that rapidly evolved under recurrent selection of the novel lipid biosynthesis inhibitor pyroxasulfone in Lolium rigidum.

No fitness cost of glyphosate resistance endowed by massive EPSPS gene amplification in Amaranthus palmeri.

Amplification of the EPSPS gene has been previously identified as the glyphosate resistance mechanism in many populations of Amaranthus palmeri, a major weed pest in US agriculture. Here, we evaluate the effects of EPSPS gene amplification on both the level of glyphosate resistance and fitness cost of resistance. A.

Glyphosate resistance in Sorghum halepense and Lolium rigidum is reduced at suboptimal growing temperatures.

Background: Glyphosate resistance in populations of the C(4) perennial Sorghum halepense (Johnsongrass) and C(3) annual Lolium rigidum (rigid ryegrass) has evolved and been documented in many cropping areas around the globe. In S. halepense and in the majority of reported cases in L.

ALS herbicide resistance mutations in Raphanus raphanistrum: evaluation of pleiotropic effects on vegetative growth and ALS activity.

Background: Gene mutations that endow herbicide resistance may cause pleiotropic effects on plant ecology and physiology. This paper reports on the effect of a number of known and novel target-site resistance mutations of the ALS gene (Ala-122-Tyr, Pro-197-Ser, Asp-376-Glu or Trp-574-Leu) on vegetative growth traits of the weed Raphanus raphanistrum.

Results: The results from a series of experiments have indicated that none of these ALS resistance mutations imposes negative pleiotropic effects on relative growth rate (RGR), photosynthesis and resource-competitive ability in R.