Resistance mechanisms to 2,4-D in six different dicotyledonous weeds around the world

2,4-D resistance is increasing around the world due to both transgenic crops and resistance to other herbicides. The objective of the this study was to characterize the currently unknown mechanisms of 2,4-D resistance in five weed species from around the globe: Amaranthus hybridus (Argentina), Conyza canadensis (Hungary), Conyza sumatrensis (France), Hirschfeldia incana (Argentina) and Parthenium hysterophorus (Dominican Republic), using Papaver rhoeas (Spain) as a standard resistant (R) species. Dose-response trials using malathion and absorption, translocation and metabolism experiments were performed to unravel the resistance mechanisms. R plants produced at least 3-folds less ethylene than susceptible plants, confirming the resistance to 2,4-D, together with resistance factors >4. A. hybridus, P. hysterophorus and P. rhoeas showed both reduced translocation and enhanced metabolism. In the two Conyza sps., the only resistance mechanism found was enhanced metabolism. Malathion synergized with 2,4-D in all these species, indicating the role of cytochrome P450 in the herbicide degradation. In H. incana, reduced translocation was the only contributing mechanism to resistance. Among the six dicotyledonous weed species investigated, there was a differential contribution to 2,4-D resistance of enhanced metabolism and reduced translocation. Thus, extrapolating 2,4-D resistance mechanisms from one weed species to another is very risky, if even related.EEA BordenaveFil: Palma Bautista, Candelario. Universidad de Córdoba. Departamento de Química Agrícola y Edafología; EspañaFil: Rojano Delgado, Antonia María. Universidad de Córdoba. Departamento de Química Agrícola y Edafología; EspañaFil: Dellaferrera, Ignacio Miguel. Universidad Nacional del Litoral. Facultad de Ciencias Agrarias; ArgentinaFil: Dellaferrera, Ignacio Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET); ArgentinaFil: Rosario, Jesús M. Universidad de Córdoba. Departamento de Química Agrícola y Edafología; EspañaFil: Vigna, Mario Raúl. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Bordenave; ArgentinaFil: Torra, Joel. Universidad de Lleida. Departamento de Horticultura y Fruticultura. Agrotecnio; EspañaFil: de Prado, Rafael. Universidad de Córdoba. Departamento de Química Agrícola y Edafología; Españ

Low temperatures enhance the absorption and translocation of 14C-glyphosate in glyphosate-resistant Conyza sumatrensis

Influence of low temperatures on the glyphosate efficacy was studied in glyphosate-resistant (R) and -susceptible (S) Conyza sumatrensis biotypes.For this purpose, the physiological and enzymatic aspects involved werecharacterized under two growing temperature regimes [high (30/20 oC) andlow 15/5oC temperatures day/night]. The R biotype was 5.5 times moreresistant than the S biotype at high temperatures; however, this R-to-S ratio decreased to 1.6 at low temperatures. At 96 h after treatment (HAT), theshikimic acid accumulation was higher in the S biotype in both temperatureregimes (4.6 and 1.9 more shikimic acid at high and low temperatures,respectively), but the accumulation of the R biotype increased 2.6 times at lowtemperatures compared to high ones. From 24 to 96 HAT, the 14C-glyphosateabsorption ranged from 28 to 65% (percentage reached from 48 HAT) at lowtemperatures and from 20 to 50% at high temperatures (gradual increase), butthere were no differences between C. sumatrensis biotypes within eachtemperature regime. At high temperatures, the 14C-glyphosate translocationwas different between biotypes, where the R one retained at least 10% moreherbicide in the treated leaves than the S biotype at 96 HAT. So, the S biotypetranslocated 40% of 14C-glyphosate absorbed to roots, and the R biotypetranslocated only 28% of herbicide at the same period. At low temperatures,there were no differences between biotypes, and at 96 HAT, the 14C-glyphosate found in treated leaves was ~47% and up to ~42% reached the roots, i.e., the resistance mechanism was suppressed. The basal and enzymaticactivities of the 5-enolpyruvyishikimate 3-phosphate synthase were differentbetween temperature regimes, but there was no differences between biotypeswithin each temperature regime, showing that target-site resistancemechanisms did not contribute in the glyphosate resistance of the R biotype.Low temperatures enhanced the absorption and translocation of glyphosate bysuppressing the resistance mechanisms improving its efficacy on resistantplants. This is the first characterization about the role of temperatures in theglyphosate efficacy on C. sumatrensis.Fil: Palma Bautista, Candelario. Universidad de Córdoba; EspañaFil: Alcántara de la Cruz, Ricardo. Universidade Federal do São Carlos; BrasilFil: Rojano Delgado, Antonia María. Universidad de Córdoba; EspañaFil: Dellaferrera, Ignacio Miguel. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Instituto de Ciencias Agropecuarias del Litoral. - Universidad Nacional del Litoral. Instituto de Ciencias Agropecuarias del Litoral.; Argentina. Universidad Nacional del Litoral; ArgentinaFil: Domínguez Martínez, Pablo Alfredo. National Institute of Forestry, Agriculture and Livestock Research; MéxicoFil: De Prado, Rafael. Universidad de Córdoba; Españ

Liquid chromatography-diode array detection to study the metabolism of glufosinate in Triticum aestivum T-590 and influence of the genetic modification on its resistance

The resistance to glufosinate of two lines - genetically modified (GM) and unmodified (T-590 and T-549, respectively) - of Triticum aestivum has been studied. In the GM line, the bar gene was introduced to increase the resistance to glufosinate. Experiments in a controlled growth chamber showed that line T-590 presented a high resistance to glufosinate with an ED50 value of 478.59 g active ingredient per hectare (g ai ha-1) versus 32.65 g ai ha-1 for line T-549. The activity of glutamine synthetase (GS) in leaf extracts from both lines was investigated. The I50 for line T-590 was 694.10 μM glufosinate versus 55.46 μM for line T-549, with a resistance factor of 12.51. Metabolism studies showed a higher and faster penetration of glufosinate in line T-549 than in line T-590. LC-TOF/MS analysis of glufosinate metabolism at 48 h after herbicide treatment (300 g ai ha -1) revealed an 83.4% conversion of the herbicide (66.5% in N-acetyl-glufosinate metabolite), while in line T-549 conversion of the herbicide was about 40% (0% to N-acetyl-glufosinate). These results suggest that metabolism of glufosinate by the bar gene is a key mechanism of resistance in line T-590 that explains such high levels of herbicide tolerated by the plant, together with other mechanisms due to unmodified pathway, absorption and loss of glufosinate affinity for its target site.© 2013 Elsevier Ltd. All rights reserved.The authors thank to the Spanish Ministerio de Ciencia e Innovación (MICINN) and FEDER program for financial support through Projects No. AGL-2010 16774, CTM2009-07430 and CTQ2012-37428. F.P.C. is also grateful to the MICINN for a Ramón y Cajal contract (RYC-2009-03921).Peer Reviewe

First Resistance Mechanisms Characterization in Glyphosate-Resistant Leptochloa virgata

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.This work was funded by AGL2013-48946-C3-1-R and CONACYT-231972 projects.Peer reviewedPeer Reviewe

Differential content of glyphosate and its metabolites in Digitaria insularis biotypes

Experiments were carried out in controlled conditions to analyze the role of metabolism of glyphosate in Digitaria insularis (sourgrass) biotypes with differential response to the herbicide. Contents of glyphosate, aminomethylphosphonic acid (AMPA), glyoxylate, and sarcosine was detected in leaf tissues by using reversed-polarity capillarity electrophoresis. Glyphosate content in the A biotype increased from 19.7 up to 65.5 µg g fresh weight-1, whereas decreasing from 19.9 down to 5.0 µg g fresh weight-1 in the B biotype, from 48 up to 168 hours after treatment. At 168 hours after treatment, percentage of the sum of AMPA, glyoxylate, and sarcosine was > 56% in the B biotype, whereas a small percentage of metabolites (< 10%) was found in the A biotype. Thus, the faster herbicide degradation in the B biotype is evidence that a differential metabolism of glyphosate can be conferring its lesser susceptibility to the herbicide

The First Case of Glyphosate Resistance in Johnsongrass (Sorghum halepense (L.) Pers.) in Europe

Six Johnsongrass populations suspected of being glyphosate resistant were collected from railways and freeways near Cordoba (SW Spain), where glyphosate is the main weed control tool. The 50% reduction in shoot fresh weight (GR50) values obtained for these six populations ranged from 550.4 to 1169 g ae ha-1, which were 4.2 to 9 times greater than the value obtained for the susceptible population. Glyphosate was equally metabolized to the same extent in both resistant and susceptible populations, with no significant di erences in either 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibition or basal activity. No amino acid substitutions were observed in any of the resistant populations. Slight but significant differences in glyphosate penetration were observed among some but not all of the resistant populations and for the times of incubation assayed, although these differences were not considered further. The proposed primary mechanism of resistance in these six glyphosate-resistant Johnsongrass populations is reduced herbicide translocation, because the amount of glyphosate that translocated from treated leaves to shoots and roots in the susceptible population was double that observed in the resistant populations. As glyphosate multiple resistance due to more than one mechanism is not uncommon, this is the first time that glyphosate-resistant Johnsongrass populations have been fully described for all known mechanisms.This research was funded by the Spanish Ministry of Economy and Competitiveness (AGL2016-78944-R) and the Asociación de Agroquímicos y Medioambiente