Ferrous iron-induced increases in capitate glandular trichome density and upregulation of CbHO-1 contributes to increases in blinin content in Conyza blinii.

MAIN CONCLUSION: Ferrous iron can promote the development of glandular trichomes and increase the content of blinin, which depends on CbHO-1 expression. Conyza blinii (C. blinii) is a unique Chinese herbal medicine that grows in Sichuan Province, China. Because the habitat of C. blinii is an iron ore mining area with abundant iron content, this species can be used as one of the best materials to study the mechanism of plant tolerance to iron. In this study, C. blinii was treated with ferrous-EDTA solutions at different concentrations, and it was found that the tolerance value of C. blinii to iron was 200 µM. Under this concentration, the plant height, root length, biomass, and iron content of C. blinii increased to the maximum values, and the effect was dependent on the upregulated expression of CbHO-1. At the same time, under ferrous iron, the photosynthetic capacity and capitate glandular trichome density of C. blinii also significantly increased, providing precursors and sites for the synthesis of blinin, thus significantly increasing the content of blinin. These processes were also dependent on the high expression of CbHO-1. Correlation analysis showed that there were strong positive correlations between iron content, capitate glandular trichome density, CbHO-1 gene expression, and blinin content. This study explored the effects of ferrous iron on the physiology and biochemistry of C. blinii, greatly improving our understanding of the mechanism of iron tolerance in C. blinii.

Investigation of glyphosate resistance levels and target-site based resistance (TSR) mechanisms in Conyza canadensis (L.) from apple orchards around areas of Bohai seas and Loess Plateau in China.

The resistance levels to glyphosate and target-site based resistance mechanisms in susceptible (S) and resistant (R) Conyza canadensis (L.) populations, which were collected from apple orchards around areas of Bohai seas and Loess Plateau in China, were investigated. Among forty C. canadensis populations, eighteen populations (45%) were still susceptible; fourteen populations (35%) evolved low resistance levels resistance to glyphosate with resistance index (RI) of 2.02 to 3.90. In contrast, eight populations (20%) evolved medium resistance levels with RI of 4.35 to 8.38. The shikimic acid concentrations in R populations were highly negative relative with the glyphosate resistance levels in C. canadensis, the Pearson correlation coefficient was -0.82 treated by glyphosate at 1.8mg/L. Three 5-enoylpyruvylshikimate 3'-phosphate synthase genes (EPSPS1, EPSPS2 and EPSPS3) were cloned in all S and glyphosate-resistant C. canadensis populations. No amino acid substitution was identified at site of 102 and 106 in three EPSPS genes, which were reported to confer glyphosate resistance in other weed species. The relative expression level of EPSPS mRNA in R populations (SD07, LN05, SHX06 and SD09) was 4.5 to 13.2 times higher than in S biotype. The Pearson correlation coefficient between EPSPS expression levels and RI was 0.79, which indicated the over expression of EPSPS mRNA may cause these R populations evolve higher resistance level to glyphosate.

Lead tolerance mechanism in Conyza canadensis: subcellular distribution, ultrastructure, antioxidative defense system, and phytochelatins.

We used hydroponic experiments to examine the effects of different concentrations of lead (Pb) on the performance of the Pb-tolerable plant Conyza canadensis. In these experiments, most of the Pb was accumulated in the roots; there was very little Pb accumulated in stems and leaves. C. canadensis is able to take up significant amounts of Pb whilst greatly restricting its transportation to specific parts of the aboveground biomass. High Pb concentrations inhibited plant growth, increased membrane permeability, elevated antioxidant enzyme activity in roots, and caused a significant increase in root H2O2 and malondialdehyde content. Analysis of Pb content at the subcellular level showed that most Pb was associated with the cell wall fraction, followed by the nucleus-rich fraction, and with a minority present in the mitochondrial and soluble fractions. Furthermore, transmission electron microscopy and energy dispersive X-ray analysis of root cells revealed that the cell wall and intercellular space in C. canadensis roots are the main locations of Pb accumulation. Additionally, high Pb concentrations adversely affected the cellular structure of C. canadensis roots. The increased enzyme activity suggests that the antioxidant system may play an important role in eliminating or alleviating Pb toxicity in C. canadensis roots. However, the levels of non-protein sulfhydryl compounds, glutathione, and phytochelatin did not significantly change in either the roots or leaves under Pb-contaminated treatments. Our results provide strong evidence that cell walls restrict Pb uptake into the root and act as an important barrier protecting root cells, while demonstrating that antioxidant enzyme levels are correlated with Pb exposure. These findings demonstrate the roles played by these detoxification mechanisms in supporting Pb tolerance in C. canadensis.

Effects of nozzle types and 2,4-D formulations on spray deposition.

The objective of this study was to evaluate the effects of nozzle types and 2,4-D formulations on spray deposition on different targets. Two field experiments were carried out in a completely randomized design, and treatments were arranged in a factorial scheme. Species in experiment 1 were Sumatran fleabane (Conyza sumatrensis) and Brazil pusley (Richardia brasiliensis) and in experiment 2 were soybeans (Glycine max) and Benghal dayflower (Commelina benghalensis). For both experiments, the first factor corresponded to spray nozzles with different settings (AD 110.015 - 61 and 105 L ha-1; AD 015-D - 75 and 146 L ha-1; XR 110.0202 - 200 L ha-1; and ADIA-D 110.02 - 208 L ha-1) and the second factor consisted of two formulations of 2,4-D (amine and choline). The formulation of 2,4-D choline has contained Colex-D™ Technology. Similar or higher spray deposition was observed on the leaves and artificial targets when using 2,4-D choline as compared to the 2,4-D amine formulation, and these differences in deposition were more evident for nozzles applying lower spray volumes. Deposition was more affected by nozzle type when amine formulation was used, compared to choline formulation.

Conyza species: distribution and evolution of multiple target-site herbicide resistances.

MAIN CONCLUSION: Distribution of Conyza species is well correlated with human interference. Multiple herbicide resistance is caused by the attempt to overcome resistance to one mode of action by overuse of another. Conyza canadensis (CC) and Conyza bonariensis (CB) are troublesome weeds around the world. Extensive use of herbicides has led to the evolution of numerous Conyza spp. herbicide-resistant populations. Seeds of 91 CC and CB populations were collected across Israel. They were mostly found (86 %) in roadsides and urban habitats, two disturbed habitats that had been dramatically impacted by human activities, thus we classify these species as anthropogenic. Although pyrithiobac-sodium was only used in cotton fields, 90 % of Conyza spp. populations were identified as pyrithiobac-sodium resistant, suggesting possible natural resistance to pyrithiobac-sodium. CC21 and CC17 C. canadensis populations were highly resistant to all tested ALS inhibitors due to a substitution in the ALS gene from Trp574 to Leu. They were also atrazine resistant due to a substitution in the psbA gene from Ser264 to Gly. The high level of imazapyr and pyrithiobac-sodium resistance observed in the CC10 population was due to an Ala205 to Val substitution. However, high resistance to sulfometuron methyl and pyrithiobac-sodium in population CC6 was due to a point mutation at Pro197 to Ser. All resistant plants of CC21 population showed both psbA (Ser264 to Gly) and ALS (Trp574 to Leu) substitutions, leading us to the conclusion that the attempt to overcome resistance to one mode of action by overuse of another will most likely lead to multiple herbicide resistance. Furthermore, we concluded that only individuals that carry both mutations could survive the shift between the two modes of action and overcome the fitness cost associated with the PSII resistance.

De novo genome assembly of the economically important weed horseweed using integrated data from multiple sequencing platforms.

Horseweed (Conyza canadensis), a member of the Compositae (Asteraceae) family, was the first broadleaf weed to evolve resistance to glyphosate. Horseweed, one of the most problematic weeds in the world, is a true diploid (2n = 2x = 18), with the smallest genome of any known agricultural weed (335 Mb). Thus, it is an appropriate candidate to help us understand the genetic and genomic bases of weediness. We undertook a draft de novo genome assembly of horseweed by combining data from multiple sequencing platforms (454 GS-FLX, Illumina HiSeq 2000, and PacBio RS) using various libraries with different insertion sizes (approximately 350 bp, 600 bp, 3 kb, and 10 kb) of a Tennessee-accessed, glyphosate-resistant horseweed biotype. From 116.3 Gb (approximately 350× coverage) of data, the genome was assembled into 13,966 scaffolds with 50% of the assembly = 33,561 bp. The assembly covered 92.3% of the genome, including the complete chloroplast genome (approximately 153 kb) and a nearly complete mitochondrial genome (approximately 450 kb in 120 scaffolds). The nuclear genome is composed of 44,592 protein-coding genes. Genome resequencing of seven additional horseweed biotypes was performed. These sequence data were assembled and used to analyze genome variation. Simple sequence repeat and single-nucleotide polymorphisms were surveyed. Genomic patterns were detected that associated with glyphosate-resistant or -susceptible biotypes. The draft genome will be useful to better understand weediness and the evolution of herbicide resistance and to devise new management strategies. The genome will also be useful as another reference genome in the Compositae. To our knowledge, this article represents the first published draft genome of an agricultural weed.

In vivo ³¹P-nuclear magnetic resonance studies of glyphosate uptake, vacuolar sequestration, and tonoplast pump activity in glyphosate-resistant horseweed.

Horseweed (Conyza canadensis) is considered a significant glyphosate-resistant (GR) weed in agriculture, spreading to 21 states in the United States and now found globally on five continents. This laboratory previously reported rapid vacuolar sequestration of glyphosate as the mechanism of resistance in GR horseweed. The observation of vacuole sequestration is consistent with the existence of a tonoplast-bound transporter. (31)P-Nuclear magnetic resonance experiments performed in vivo with GR horseweed leaf tissue show that glyphosate entry into the plant cell (cytosolic compartment) is (1) first order in extracellular glyphosate concentration, independent of pH and dependent upon ATP; (2) competitively inhibited by alternative substrates (aminomethyl phosphonate [AMPA] and N-methyl glyphosate [NMG]), which themselves enter the plant cell; and (3) blocked by vanadate, a known inhibitor/blocker of ATP-dependent transporters. Vacuole sequestration of glyphosate is (1) first order in cytosolic glyphosate concentration and dependent upon ATP; (2) competitively inhibited by alternative substrates (AMPA and NMG), which themselves enter the plant vacuole; and (3) saturable. (31)P-Nuclear magnetic resonance findings with GR horseweed are consistent with the active transport of glyphosate and alternative substrates (AMPA and NMG) across the plasma membrane and tonoplast in a manner characteristic of ATP-binding cassette transporters, similar to those that have been identified in mammalian cells.

Hemin-induced increase in saponin content contributes to the alleviation of osmotic and cold stress damage to Conyza blinii in a heme oxygenase 1-dependent manner.

Hemin can improve the stress resistance of plants through the heme oxygenase system. Additionally, substances contained in plants, such as secondary metabolites, can improve stress resistance. However, few studies have explored the effects of hemin on secondary metabolite content. Therefore, the effects of hemin on saponin synthesis and the mechanism of plant injury relief by hemin in Conyza blinii were investigated in this study. Hemin treatment promoted plant growth and increased the antioxidant enzyme activity and saponin content of C. blinii under osmotic stress and cold stress. Further study showed that hemin could provide sufficient precursors for saponin synthesis by improving the photosynthetic capacity of C. blinii and increasing the gene expression of key enzymes in the saponin synthesis pathway, thus increasing the saponin content. Moreover, the promotion effect of hemin on saponin synthesis is dependent on heme oxygenase-1 and can be reversed by the inhibitor Zn-protoporphyrin-IX (ZnPPIX). This study revealed that hemin can increase the saponin content of C. blinii and alleviate the damage caused by abiotic stress, and it also broadened the understanding of the relationship between hemin and secondary metabolites in plant abiotic stress relief.

Novel Candidate Genes Differentially Expressed in Glyphosate-Treated Horseweed (Conyza canadensis).

The evolution of herbicide-resistant weed species is a serious threat for weed control. Therefore, we need an improved understanding of how gene regulation confers herbicide resistance in order to slow the evolution of resistance. The present study analyzed differentially expressed genes after glyphosate treatment on a glyphosate-resistant Tennessee ecotype (TNR) of horseweed (Conyza canadensis), compared to a susceptible biotype (TNS). A read size of 100.2 M was sequenced on the Illumina platform and subjected to de novo assembly, resulting in 77,072 gene-level contigs, of which 32,493 were uniquely annotated by a BlastX alignment of protein sequence similarity. The most differentially expressed genes were enriched in the gene ontology (GO) term of the transmembrane transport protein. In addition, fifteen upregulated genes were identified in TNR after glyphosate treatment but were not detected in TNS. Ten of these upregulated genes were transmembrane transporter or kinase receptor proteins. Therefore, a combination of changes in gene expression among transmembrane receptor and kinase receptor proteins may be important for endowing non-target-site glyphosate-resistant C. canadensis.

Target-site EPSPS Pro-106-Ser mutation in Conyza canadensis biotypes with extreme resistance to glyphosate in Ohio and Iowa, USA.

Documenting the diversity of mechanisms for herbicide resistance in agricultural weeds is helpful for understanding evolutionary processes that contribute to weed management problems. More than 40 species have evolved resistance to glyphosate, and at least 13 species have a target-site mutation at position 106 of EPSPS. In horseweed (Conyza canadensis), this p106 mutation has only been reported in Canada. Here, we sampled seeds from one plant (= biotype) at 24 sites in Ohio and 20 in Iowa, screened these biotypes for levels of resistance, and sequenced their DNA to detect the p106 mutation. Resistance categories were based on 80% survival at five glyphosate doses: S (0×), R1 (1×), R2 (8×), R3 (20×), or R4 (40×). The p106 mutation was not found in the19 biotypes scored as S, R1, or R2, while all 25 biotypes scored as R3 or R4 had the same proline-to-serine substitution at p106. These findings represent the first documented case of target-site mediated glyphosate resistance in horseweed in the United States, and the first to show that this mutation was associated with very strong resistance. We hypothesize that the p106 mutation has occurred multiple times in horseweed and may be spreading rapidly, further complicating weed management efforts.

Physiological response of Conyza Canadensis to cadmium stress monitored by Fourier transform infrared spectroscopy and cadmium accumulation.

The cadmium(Cd) pollution of soil causes serious environmental problems. Cd is a high toxic and high water soluble element without biological function, and it is easily taken in by plants owing to its high bioavailability. Thus it easily entered the food chain and threaten people's health. Here，different concentrations of Cd solutions were used to study the physiological response and Cd accumulation characteristics of Conyza Canadensis (L.) Cronq. The physiological response was characterized by Fourier Transform Infrared (FTIR) spectroscopy, and Cd accumulation in plant and distribution were tested by Atomic absorption spectroscopy (AAS) under different concentrations Cd stress. When Cd concentrations toxicity <3 mg·L-1, the C. Canadensis (L.) Cronq. could grow normally without any symptoms, and the Cd concentrations increased to 7 mg·L-1, the C. Canadensis (L.) Cronq. had a little lower biomass, but there was no significant difference in the biomass among treatment concentrations. The peak shape of each component remained unchanged before and after Cd treatment. Only the absorption peak of some functional groups involved in Cd adsorption shifted with different degrees, such as hydroxy groups (3417-3429 cm-1), carboxyl groups (1380-1386 cm-1), and acid amide groups (1631-1637 cm -1). The characteristic peak absorption intensity of root, stem and leaf was different with the increase of heavy metal concentration. The absorbance of the roots with high Cd concentration was higher than that with medium-low Cd concentration. This shows that high concentration of Cd could induce C. Canadensis (L.) Cronq. seedlings to produce a large number of protein, amino acid and other substances, and through osmotic regulation to enhance stress resistance, provide nitrogen source, reduce heavy metal toxicity, and stabilize the internal environment. After Cd treatment, the characteristic peaks of stem and leaf were higher than or close to the control. This is due to the high tolerance of C. Canadensis (L.) Cronq. seedlings to heavy metals. The Cd accumulation in the shoots (stems and leaves) of C. Canadensis (L.) Cronq. was obviously lower than that in roots and the Cd content in the shoots usually increased with increasing Cd concentration. The maximum accumulation of Cd in shoots was 1898.07 mg·kg-1 after 11 days grown in the water spiked with 7 mg·L-1 Cd concentration. The study suggests that C. Canadensis (L.) Cronq. has some remediation effect and endurance ability against heavy metal polluted contaminated soil and has potential utilization value in the technical field of phytoremediation of Cd polluted soil.

Identification of a Cd accumulator Conyza canadensis.

One of key steps of phytoremediating heavy metal contaminated soils is still the identification of hyperaccumulator and accumulator. In a former published article, Conyza canadensis L. Cronq. expressed some basic properties of Cd-hyperaccumulators. In this study, concentration gradient experiment and two sample-analyzing experiments were used to identify whether this plant is a Cd-hyperaccumulator. When grown on soil spiked with Cd at the rate of 10 and 25 mg kg(-1) in concentration gradient experiment, C. canadensis had both Cd enrichment factor (EF) and Cd translocation factor (TF) greater than 1, while the shoot biomass did not differ significantly as compared to the control. On the other hand, with Cd-spiking rates of 10 and 25 mg kg(-1), the Cd concentration in the shoot did not exceed 100 mg kg(-1), which is considered as the minimum shoot Cd concentration to qualify as a hyperaccumulator. In the sample-analysis experiments from a Pb-Zn mine area and wastewater irrigation region, C. canadensis also showed Cd-accumulator characteristics. Based on the results accomplished, we propose C. canadensis as a Cd-accumulator.

The effect of several adjuvants on glufosinate effectiveness in Conyza species.

The effect of several adjuvants on the effectiveness of glufosinate and the role of adherence and contact angle modifications due to the presence of these adjuvants in the spraying solution on the increase in efficacy observed on the broadleaved weeds Conyza albida and Conyza bonariensis has been determined under laboratory controlled conditions. The adjuvants used on the experiment were a mixture of methyl oleate and palmitate (MO/MP), a dodecylbenzene ammonium sulphonate (DBAS), a paraffinic oil (PO), an alkylglycol ester (AGE), and a lecithin + propionic acid + non ionic surfactant based product (LI-700). Dose-response experiments showed that C. albida displayed higher susceptibility to glufosinate than C. bonariensis, no matter the adjuvant tested. However, none of the mixtures increased the herbicide effectiveness on C. atlbida, with LI 700 and PO showing an antagonistic effect on the herbicide efficacy. On C. bonariensis, MO/MP and DBAS showed significant better results than non-amended glufosinate controls, with LI 700 showing again an antagonistic effect. Both adherence and contact angle studies were inconclusive, since adjuvants with best adherence and contact angle values were not the most effective ones. Therefore, other unknown parameters putatively modified by adjuvants such as herbicide penetration should be questioned.

Increased temperatures and elevated CO2 levels reduce the sensitivity of Conyza canadensis and Chenopodium album to glyphosate.

Herbicides are the most commonly used means of controlling weeds. Recently, there has been growing concern over the potential impacts of global climate change, specifically, increasing temperatures and elevated carbon dioxide (CO2) concentrations, on the sensitivity of weeds to herbicides. Here, glyphosate response of both Conyza canadensis and Chenopodium album was evaluated under different environmental conditions. Reduced glyphosate sensitivity was observed in both species in response to increased temperature, elevated CO2 level, and the combination of both factors. Increased temperature had greater effect on plant survival than elevated CO2 level. In combination, high temperature and elevated CO2 level resulted in loss of apical dominance and rapid necrosis in glyphosate-treated plants. To investigate the mechanistic basis of reduced glyphosate sensitivity, translocation was examined using 14C-glyphosate. In plants that were subjected to high temperatures and elevated CO2 level, glyphosate was more rapidly translocated out of the treated leaf to shoot meristems and roots than in plants grown under control conditions. These results suggest that altered glyphosate translocation and tissue-specific sequestration may be the basis of reduced plant sensitivity. Therefore, overreliance on glyphosate for weed control under changing climatic conditions may result in more weed control failures.

Physiological, biochemical and molecular bases of resistance to tribenuron-methyl and glyphosate in Conyza canadensis from olive groves in southern Spain.

Multiple resistance to acetolactate synthase (ALS, EC 2.2.1.6) and 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS, EC 2.5.1.19) inhibitor herbicides was studied in two populations of Conyza canadensis (RTG and STG) harvested in southern Spain. Dose-response and enzymatic activity studies for the ALS-inhibiting herbicides showed only cross-resistance to sulfonylureas group but not to the other ALS chemical groups in the RTG population. Regarding glyphosate, the dose-response studies showed that the RTG population was 11.8 times more resistant than the STG population, while the inhibition of EPSPS enzyme (I50) was similar for both populations. Altered/reduced absorption and translocation were the main resistance mechanisms for glyphosate but not for tribenuron-methyl. The metabolic studies to find differences in the amounts of metabolites between the two populations were carried out using thin layer chromatography (for tribenuron-methyl) and capillary electrophoresis (for glyphosate). Metabolites were significantly differed among the two populations for tribenuron-methyl but not for glyphosate. The sequencing of the target-site ALS gene from RTG plants revealed a single point mutation, Pro-197-Ala, that causes resistance to sulfonylurea herbicide in C. canadensis.

High Levels of Glyphosate Resistance in Conyza canadensis from Agricultural and Non-Agricultural Sites in Ohio and Iowa.

Glyphosate is an important herbicide worldwide, but its efficacy has been compromised where weed species have evolved glyphosate resistance. To better understand evolutionary outcomes of continued and strong selection from glyphosate exposure, we characterized variation in resistance in self-pollinating Conyza canadensis (horseweed) in Ohio and Iowa, where glyphosate resistance was first reported in 2002 and 2011, respectively. In 2015, we collected seeds from a total of 74 maternal plants (biotypes) from no-till soybean fields vs. non-agricultural sites in each state, using one representative plant per site. Young plants from each biotype were sprayed with glyphosate rates of 0x, 1x (840 g ae ha-1), 8x, 20x, or 40x. Resistant biotypes with at least 80% survival at each dosage were designated as R1 (1x), R2 (8x), R3 (20x), or R4 (40x). Nearly all Ohio agricultural biotypes were R4, as were 62% of biotypes from the non-agricultural sites. In Iowa, R4 biotypes were clustered in the southeastern soybean fields, where no-till agriculture is more common, and 45% of non-agricultural biotypes were R1-R4. Our results show that resistance levels to glyphosate can be very high (at least 40x) in both states, and that non-agricultural sites likely serve as a refuge for glyphosate-resistant biotypes.

Gene expression in response to glyphosate treatment in fleabane (Conyza bonariensis) - glyphosate death response and candidate resistance genes.

BACKGROUND: This study takes a whole-transcriptome approach to assess gene expression changes in response to glyphosate treatment in glyphosate-resistant fleabane. We assessed gene expression changes in both susceptible and resistant lines so that the glyphosate death response could be quantified, and constitutively expressed candidate resistance genes identified. There are three copies of the glyphosate target site (5-enolpyruvylshikimate-3-phosphate; EPSPS) gene in Conyza and because Conyza bonariensis is allohexaploid, there is a baseline nine copies of the gene in any individual. RESULTS: Many genes were differentially expressed in response to glyphosate treatment. Known resistance mutations are present in EPSPS2 but they are present in a glyphosate-susceptible line as well as resistant lines and therefore not sufficient to confer resistance. EPSPS1 is expressed four times more than EPSPS2, further reducing the overall contribution of these mutations. CONCLUSION: We demonstrate that glyphosate resistance in C. bonariensis is not the result of EPSPS mutations or overexpression, but due to a non-target-site mechanism. A large number of genes are affected by glyphosate treatment. We present a list of candidate non-target-site-resistance (NTSR) genes in fleabane for future studies into these mechanisms. © 2017 Society of Chemical Industry.

Mechanisms of glyphosate resistance and response to alternative herbicide-based management in populations of the three Conyza species introduced in southern Spain.

BACKGROUND: In perennial crops, the most common method of weed control is to spray herbicides, and glyphosate has long been the first choice of farmers. Three species of the genus Conyza are among the most problematic weeds for farmers, exhibiting resistance to glyphosate. The objectives of this study were to evaluate resistance levels and mechanisms, and to test chemical control alternatives in putative resistant (R) populations of Conyza bonariensis, Conyza canadensis and Conyza sumatrensis. RESULTS: Plants from the three R populations of Conyza spp. survived high doses of glyphosate compared with plants from susceptible (S) populations. The rate of movement of 14 C glyphosate out of treated leaves in plants from S populations was higher than in plants from R populations. Only plants from the R population of C. sumatrensis contained the known target site 5-enolpyruvylshikimate-3-phosphate synthase mutation Pro106-Thr. Field responses to the different alternative herbicide treatments tested indicated injury and high effectiveness in most cases. CONCLUSIONS: The results indicate that non-target site resistant (NTSR) mechanisms explain resistance in C. bonariensis and C. canadensis, whereas both NTSR and target site resistant (TSR) mechanisms contribute to resistance in C. sumatrensis. The results obtained in the field trials suggest that the resistance problem can be solved through integrated weed management. © 2018 Society of Chemical Industry.

Sumatran fleabane (Conyza sumatrensis [Retz.] E. Walker) control in soybean with combinations of burndown and preemergence herbicides applied in the off-season

Sumatran fleabane (Conyza sumatrensis [Retz.] E. Walker) can be found in many different agricultural environments and impact different crops, such as soybeans and corn. It is believed that the application of burndown and preemergence herbicides in the off-season are effective in controlling Sumatran fleabane in soybean crops. The objective was to evaluate the effectiveness of burndown and preemergence herbicides in the off-season, with one or two applications, in the control of Sumatran fleabane in soybean cultivation. Five field experiments were conducted in Maripá, state of Paraná (PR), Brazil. The treatments consisted of the application of burndown herbicides in combinations with preemergence ones, with one or two applications. Control of Sumatran fleabane and soybean yield were evaluated. With the set of experiments, it is highlighted that the strategy combining more applications, with different herbicides, burndown and preemergence, is more promising in the control of Sumatran fleabane. When comparing synthetic auxins, dicamba and triclopyr stand out. For sequential application, worse performance was observed for diquat. Combinations between burndown and preemergence herbicides were effective in controlling Sumatran fleabane, for pre sowing application in soybean. With emphasis on managements with sequential applications of saflufenacil with glufosinate or glyphosate. The strategy combining more applications, with different herbicides, burndown and preemergence herbicides, is more promising in the control of Sumatran fleabane.

Non-target-site glyphosate resistance in Conyza bonariensis is based on modified subcellular distribution of the herbicide.

BACKGROUND: Conyza spp. were the first broadleaf weeds reported to have evolved glyphosate resistance. Several mechanisms have been proposed for glyphosate resistance. In an effort to elucidate the mechanism of this resistance in Conyza bonariensis, possible target-site and non-target-site mechanisms were investigated in glyphosate-resistant (GR) C. bonariensis biotypes. RESULTS: Using differential glyphosate applications and analyses of shikimate accumulation, we followed the herbicide effect in different plant organs and monitored the herbicide's apparent mobility. We found high shikimate levels in the roots and young leaves of glyphosate-sensitive (GS) plants, regardless of the site of application, whereas in GR plants, shikimate accumulated mainly in treated young leaves. 14 C-glyphosate studies, however, revealed the expected source-to-sink translocation pattern in both GS and GR plants. Sequencing of the appropriate EPSPS DNA fragments of GR and GS plants revealed no alteration at the Pro106 position. CONCLUSION: These data support the hypothesis that the glyphosate resistance of our C. bonariensis GR biotypes is associated with altered subcellular distribution of glyphosate, which keeps the herbicide sequestered away from the EPSPS target site in the chloroplast. © 2016 Society of Chemical Industry.