Target‐site mutations conferring resistance to glyphosate in feathertop Rhodes grass (<i>Chloris virgata</i>) populations in Australia

404

287

Glyphosate is the most widely used and successful herbicide discovered to date, but its utility is now threatened by the occurrence of several glyphosate-resistant weed species. Glyphosate resistance first appeared in Lolium rigidum in an apple orchard in Australia in 1996, ironically the year that the first glyphosate-resistant crop (soybean) was introduced in the USA. Thirty-eight weed species have now evolved resistance to glyphosate, distributed across 37 countries and in 34 different crops and six non-crop situations. Although glyphosate-resistant weeds have been identified in orchards, vineyards, plantations, cereals, fallow and non-crop situations, it is the glyphosate-resistant weeds in glyphosate-resistant crop systems that dominate the area infested and growing economic impact. Glyphosate-resistant weeds present the greatest threat to sustained weed control in major agronomic crops because this herbicide is used to control weeds with resistance to herbicides with other sites of action, and no new herbicide sites of action have been introduced for over 30 years. Industry has responded by developing herbicide resistance traits in major crops that allow existing herbicides to be used in a new way. However, over reliance on these traits will result in multiple-resistance in weeds. Weed control in major crops is at a precarious point, where we must maintain the utility of the herbicides we have until we can transition to new weed management technologies. © 2017 Society of Chemical Industry.

Section: Mechanisms Of Resistancesupporting

confidence: 76%

Overview of glyphosate‐resistant weeds worldwide

Heap¹,

Duke

2017

404

287

“…In addition, the S C. barbata population showed LD 50 value (545 g ae ha −1 ) close to the standard dose, evidencing a certain innate tolerance level in this species. Sensitive populations of C. elata , C. ciliata , C. truncata and C. virgata also recorded high degrees of tolerance to glyphosate with LD 50 ranging from 515 to 1385 g ae ha −1 of glyphosate . Taking into account that controlling a weed population requires at least twice its estimated LD 50 , the standard dose of 720 g ae ha −1 used is not enough to control the S C. barbata population (Fig.…”

Section: Discussionmentioning

confidence: 99%

From tolerance to resistance: mechanisms governing the differential response to glyphosate in Chloris barbata

Bracamonte

Silveira

Cruz

et al. 2018

“…Most reported EPSPS mutations conferring glyphosate resistance in weeds have been a single base pair alteration from the Pro106 amino acid to Ala, Leu, Ser, or Thr . In some instances, two different mutations at the Pro106 position have occurred in glyphosate‐resistant weed populations . Also, novel mutations in EPSPS that confer evolved glyphosate resistance in weeds have been reported, including a Thr102Ser substitution in coat buttons ( Tridax procumbens L.) and a double amino acid substitution (Thr102Ile + Pro106Ser) in goosegrass [ Eleusine indica (L.) Gaertn.]…”

Section: Resultsmentioning

confidence: 99%

Physiological and molecular analysis of glyphosate resistance in non‐rapid response Ambrosia trifida from Wisconsin

Wilson

Takano

Horn

et al. 2019

BACKGROUND We previously identified a glyphosate‐resistant A. trifida phenotype from Wisconsin USA that showed a non‐rapid response to glyphosate. The mechanism of glyphosate resistance in this phenotype has yet to be elucidated. We conducted experiments to investigate non‐target‐site resistance and target‐site resistance mechanisms. The roles of glyphosate absorption, translocation, and metabolism in resistance of this phenotype have not been reported previously, nor have EPSPS protein abundance or mutations to the full‐length sequence of EPSPS. RESULTS Whole‐plant dose–response results confirmed a 6.5‐level of glyphosate resistance for the resistant (R) phenotype compared to a susceptible (S) phenotype. Absorption and translocation of 14C‐glyphosate were similar between R and S phenotypes over 72 h. Glyphosate and AMPA concentrations in leaf tissue did not differ between R and S phenotypes over 96 h. In vivo shikimate leaf disc assays confirmed that glyphosate EC50 values were 4.6‐ to 5.4‐fold greater for the R than S phenotype. Shikimate accumulation was similar between phenotypes at high glyphosate concentrations (>1000 μM), suggesting that glyphosate entered chloroplasts and inhibited EPSPS. This finding was supported by results showing that EPSPS copy number and EPSPS protein abundance did not differ between R and S phenotypes, nor did EPSPS sequence at Gly101, Thr102, and Pro106 positions. Comparison of full‐length EPSPS sequences found five nonsynonymous polymorphisms that differed between R and S phenotypes. However, their locations were distant from the glyphosate target site and, therefore, not likely to affect enzyme‐glyphosate interaction. CONCLUSION The results suggest that a novel mechanism confers glyphosate resistance in this A. trifida phenotype. © 2019 Society of Chemical Industry