First Case of Glyphosate Resistance in Bromus catharticus Vahl.: Examination of Endowing Resistance Mechanisms

Abstract

Bromus catharticus Vahl. has been used as a valuable forage crop, but it has also been noted as a weed of winter crops and an invader in several countries. In Argentina, a putative glyphosate-resistant population of B. catharticus was identified as a consequence of the lack of effective control with glyphosate in the pre-sowing of wheat. Plant survival and shikimate accumulation analysis demonstrated a lower glyphosate-sensitivity of this population in comparison to a susceptible B. catharticus population. The resistant population was 4-fold more resistant to glyphosate than its susceptible counterpart. There was no evidence of target-site mechanisms of glyphosate resistance or an enhanced capacity to metabolize glyphosate in the resistant population. However, the resistant plants showed a lower foliar retention of glyphosate (138.34 μl solution g−1 dry weight vs. 390.79 μl solution g−1 dry weight), a reduced absorption of 14C-glyphosate (54.18 vs. 73.56%) and lower translocation of 14C-glyphosate from the labeled leaf (27.70 vs. 62.36%). As a result, susceptible plants accumulated a 4.1-fold higher concentration of 14C-glyphosate in the roots compared to resistant plants. The current work describes the first worldwide case of glyphosate resistance in B. catharticus. A reduced foliar retention of herbicide, a differential rate of glyphosate entry into leaves and an altered glyphosate translocation pattern would be the most likely mechanisms of glyphosate exclusion.

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

“…Pots containing four Dgs R or Dgs S plants were used in a completely randomised design with ten replicates per glyphosate dose. Glyphosate was applied using a laboratory belt sprayer (application rate 200 L ha −1 ), as described by Yanniccari et al 21 …”

“…Pots containing four Dgs R or Dgs S plants were used in a completely randomised design with ten replicates per glyphosate dose. Glyphosate was applied using a laboratory belt sprayer (application rate 200 L ha −1 ), as described by Yanniccari et al 21 Twenty-one days after glyphosate treatment, plant survival was recorded, where 'surviving' plants showed active growth with no apparent visual injury as opposed to 'dead' plants that exhibited damaged and necrotic leaves.…”

“…Five grammes of young foliar tissue were taken from Dgs R and Dgs S plants and ground in liquid N 2 using a mortar. Enzyme extraction was carried out following the methodology described by Yanniccari et al 21 The specific EPSPS activity was measured in a reaction medium containing glyphosate at 0, 0.1, 1, 10, 100 and 1000 μM. The EPSPS enzyme reaction substrates were phosphoenolpyruvate and shikimate-3-phosphate (Sigma-Aldrich).…”

Constitutive overexpression of EPSPS by gene duplication is involved in glyphosate resistance in Salsola tragus

“…A set of 5‐cm high plants were sprayed with glyphosate at 480 g ae ha −1 as in the dose–response assay. Another group of plants were sprayed with water as control 17 . Ten plants per population and treatment were washed with distilled water at 48 and 96 HAT and flash‐frozen in liquid nitrogen immediately.…”

Non-Target Site Mechanisms Endow Resistance to Glyphosate in Saltmarsh Aster (Aster squamatus)

“…The second leaf was identified and protected with aluminum film. After this, plants were treated with glyphosate (720 g ae ha −1 ), and 30 min later, the aluminum layer was removed [ 47 ]. The labeled herbicide solution was applied to the adaxial surface of the second leaf, that had been protected with aluminum layer, of 25 plants of each saltmarsh aster population in four 0.5 µL droplets with a PB-600 repeating dispenser (Hamilton Company, Reno, NV, USA), i.e., each plant received a total of 50,000 dpm.…”