Assessment of two nondestructive assays for detecting glyphosate resistance in horseweed (<i>Conyza canadensis</i>)

Koger, Clifford H.; Shaner, Dale L.; Henry, W. Brien; Nadler-Hassar, Talia; Thomas, Walter E.; Wilcut, John W.

doi:10.1614/ws-05-010r

Cited by 28 publications

(9 citation statements)

References 30 publications

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“…As a consequence, in the R biotypes, a physiological process actively pumping glyphosate into vacuole and/or into apoplast environment occurs within 3 and 7 DAT. This resistance mechanism observed for C. bonariensis appears to be the same as in C. canadensis (Koger et al. , 2005) and L. multiflorum (Perez‐Jones et al.…”

Section: Discussionmentioning

confidence: 62%

Physiological and molecular bases of glyphosate resistance in Conyza bonariensis biotypes from Spain

et al. 2008

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Summary The physiological and molecular bases of glyphosate resistance in one susceptible (S) and four resistant (R) Conyza bonariensis biotypes (sampled in orchards from Andalusia, Spain) were investigated. Resistance index (RI) values of the four R biotypes ranged between 2.9 and 5.6. The main physiological difference between S and R biotypes was the dissimilar mobility of glyphosate in the whole plant. In R biotypes, the herbicide was translocated less from leaves to culm and root, and more from culm to leaves compared with the S biotype. The upward mobility of glyphosate via xylem suggests that the herbicide may be sequestered to the apoplast or the vacuole. The hypothesis of an insensitive 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS) was provisionally discarded on the basis of shikimate accumulation in R plant tissues after glyphosate treatment. At the molecular level, the relative abundance of EPSPS mRNA prior to glyphosate treatment was approximately double in two R biotypes compared with the S standard and the other R biotypes. Moreover, the two R biotypes having both no translocation and doubled EPSPS mRNA levels had also the highest RI. These results suggest that two factors may be related to glyphosate resistance in the R biotypes: (i) impaired translocation and (ii) high basal EPSPS transcript levels. The comparison between these findings and earlier results on glyphosate resistance mechanism in Conyza canadensis biotypes from the USA, suggests that similar agronomic factors (repeated application of glyphosate, no crop and herbicide rotation, no tillage) have selected similar traits on different genetic pools of the resistance‐prone Conyza genus.

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Section: Discussionmentioning

confidence: 62%

Physiological and molecular bases of glyphosate resistance in Conyza bonariensis biotypes from Spain

et al. 2008

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“…Shikimate levels remained elevated at the last sampling date of 28 DAT. Elevated shikimate levels in rice as late as 28 DAT have not been reported for other species, where shikimate levels often increased by 3–7 DAT and then returned to levels in untreated plants after 7 DAT 12–15. Visual injury and measurement of shikimate levels have the potential to be used in combination for identifying glyphosate drift onto rice.…”

Section: Discussionmentioning

confidence: 99%

“…Leaf‐discs were maintained in the freezer for <1 month before measuring shikimate levels according to previously published procedures 15, 16. Vials were removed from the freezer and 1 ml of 0.25 M hydrochloric acid was added to each vial.…”

Section: Methodsmentioning

confidence: 99%

Rice (Oryza sativa) response to drift rates of glyphosate

Koger

Shaner²,

Krutz

et al. 2005

Pest Management Science

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Greenhouse and field studies were conducted to investigate response of two rice varieties, Priscilla and Cocodrie, to sub-lethal rates of glyphosate in terms of injury, shikimate accumulation and yield. In the greenhouse, more shikimate accumulated in Cocodrie than Priscilla at comparable glyphosate rates applied to plants at the three-leaf stage. In field studies, glyphosate was applied to both varieties when they were 74-cm tall and in the internode separation growth stage. Visual injury, plant height, and leaf-tissue samples for shikimate analysis were collected at 3, 7, 14, 21 and 28 days after treatment (DAT). Rice yield was also determined. Noticeable visual injury and height reduction to both varieties was observed as early as 7 and 3 DAT in Cocodrie and Priscilla, respectively. Shikimate levels in leaves began to increase in both varieties by 3 DAT in a dose-dependent manner and reached a peak between 7 and 14 DAT. Elevated shikimate levels were still detectable by 28 DAT. Similar levels of shikimate accumulated in both varieties at comparable glyphosate rates. However, glyphosate treatment at comparable rates reduced rice yields more in Cocodrie than in Priscilla. The highest rate of glyphosate reduced yield in Cocodrie by 92% whereas there was only a 60% yield reduction in Priscilla. Shikimate levels in glyphosate-treated rice were strongly correlated to yield reductions across both varieties and appeared to be a better predictor of yield reduction than was visual injury. Visual injury coupled with measured shikimate levels can be used collaboratively to identify glyphosate exposure and estimate subsequent rice yield reductions.

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“…Recent research also found that differential accumulation of shikimate between glyphosate‐resistant accessions (RR and NRR phenotypes which included the Wisconsin R phenotype) and ‐susceptible A. trifida accessions decreased at glyphosate concentrations greater than 1000 μM, suggesting that glyphosate is able to enter cells and ultimately chloroplasts where it is capable of binding to and inhibiting EPSPS . In other species, similar shikimate accumulation between resistant and susceptible biotypes at high glyphosate concentrations has been observed as well …”

Section: Resultsmentioning

confidence: 78%

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

Wilson

Takano

Horn

et al. 2019

Pest Management Science

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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

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Assessment of two nondestructive assays for detecting glyphosate resistance in horseweed (Conyza canadensis)

Cited by 28 publications

References 30 publications

Physiological and molecular bases of glyphosate resistance in Conyza bonariensis biotypes from Spain

Physiological and molecular bases of glyphosate resistance in Conyza bonariensis biotypes from Spain

Rice (Oryza sativa) response to drift rates of glyphosate

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

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