First Resistance Mechanisms Characterization in Glyphosate-Resistant Leptochloa virgata

Abstract

Leptochloa virgata (L.) P. Beauv. is an annual weed common in citrus groves in the states of Puebla and Veracruz, Mexico limiting their production. Since 2010, several L. virgata populations were identified as being resistant to glyphosate, but studies of their resistance mechanisms developed by this species have been conducted. In this work, three glyphosate-resistant populations (R8, R14, and R15) collected in citrus orchards from Mexico, were used to study their resistance mechanisms comparing them to one susceptible population (S). Dose-response and shikimic acid accumulation assays confirmed the glyphosate resistance of the three resistant populations. Higher doses of up to 720 g ae ha-1 (field dose) were needed to control by 50% plants of resistant populations. The S population absorbed between 7 and 13% more 14C-glyphosate than resistant ones, and translocated up to 32.2% of 14C-glyphosate to the roots at 96 h after treatment (HAT). The R8, R14, and R15 populations translocated only 24.5, 26.5, and 21.9%, respectively. The enzyme activity of 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) was not different in the S, R8 and R14 populations. The R15 Population exhibited 165.9 times greater EPSPS activity. Additionally, this population showed a higher EPSPS basal activity and a substitution in the codon 106 from Proline to Serine in the EPSPS protein sequence. EPSPS gene expression in the R15 population was similar to that of S population. In conclusion, the three resistant L. virgata populations show reduced absorption and translocation of 14C-glyphosate. Moreover, a mutation and an enhanced EPSPS basal activity at target-site level confers higher resistance to glyphosate. These results describe for the first time the glyphosate resistance mechanisms developed by resistant L. virgata populations of citrus orchards from Mexico.

Overview of glyphosate‐resistant weeds worldwide

“…Reduced movement of glyphosate into plant cells from the plant epidermis (herbicide uptake) can contribute to weed resistance to glyphosate. This mechanism has been invoked for some glyphosate‐resistant biotypes of S. halepense , L. multiflorum , D. insularis , C. eleta and Leptochloa virgata . Reduced uptake can be the result of chemical and/or morphological changes in the leaf cuticle or to changes in leaf shape or orientation that reduces the interception of herbicide spray …”

“…This mechanism has been invoked for some glyphosate-resistant biotypes of S. halepense, 44 L. multiflorum, 45 D. insularis, 46 C. eleta 47 and Leptochloa virgata. 48 Reduced uptake can be the result of chemical and/or morphological changes in the leaf cuticle 49 or to changes in leaf shape or orientation that reduces the interception of herbicide spray. 45 One reason that glyphosate is such an effective herbicide is that it is readily translocated from leaves to meristems.…”

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

“…Twenty plants per population were treated with one drop (1 μL plant −1 ) of solution on the adaxial surface of the first or second leaf. The plants were handled according to Alcántara-de la Cruz et al 5 at 24, 48, 72 and 96 h after treatment (HAT) (five plants per population at each time evaluated in a completely random design). Radioactivity of 14 C was analyzed by liquid scintillation spectrometry in a scintillation counter (Beckman LS-6500, Beckman Coulter Inc.) for 10 min per sample.…”

“…Veracruz (Gulf of Mexico) is the main producer of this citrus fruit, but to cover the large volume of exports, its production has been extended to states with similar environmental characteristics, such as Colima, Guerrero, Michoacán and Oaxaca (Pacific Coast) . Tropical rainfall conditions allow continuous Persian lime production all year round, but also favor the emergence of weeds, such as Bidens pilosa , Eleusine indica and Leptoclhoa virgate , which have been identified as being resistant to glyphosate. They do not have a great impact on yield, but weeds can make cultivation difficult .…”

New Case of False-Star-Grass (Chloris distichophylla) Population Evolving Glyphosate Resistance

“…Glyphosate resistance in weeds includes two different mechanisms: (1) outside the site of action, called NTSR (non-target-site resistance), which plays an important role in the differences between the absorption, translocation, and vacuole sequestration of the glyphosate applied to resistant (GR) and sensitive (GS) populations of the same species [10,26,27] and (2) involved in protein binding (EPSPS), called TSR (target-site resistance), where the important role is played by the EPSPS, where target-site alterations are due to target-site mutations [10,23] or target-site gene amplifications [22,28] in glyphosate-resistant populations.…”