Evolution of ACCase-inhibitor resistance in Chloris virgata is conferred by a Trp2027Cys mutation in the herbicide target site.

BACKGROUND: Chloris virgata is a troublesome weed in tropical regions. With the evolution of glyphosate resistance in key grass species, acetyl CoA carboxylase (ACCase) inhibitors have become a commonly used tool in soybean production areas in Brazil. We assessed if suspected resistant populations exhibited cross resistance to the different classes of ACCase inhibitors and investigated the resistance mechanisms in C. virgata. RESULTS: Dose-response experiments revealed resistance to haloxyfop-methyl and pinoxaden, with 432- and 3-fold resistance, respectively, compared to susceptible populations. Due to the lack of genetic resources for C. virgata, we sequenced, assembled, and annotated the genome using short-read Illumina technology. The k-mer analysis estimated a genome size of approximately 336 Mbp, with BUSCO completeness of 97%, and over 36 000 gene models were annotated. We examined if ACCase copy number variation and increased gene expression were involved in the resistance phenotype and found no difference when compared to a susceptible population. A mutation was detected in ACCase that encodes for amino acid position 2027, resulting in a tryptophan-to-cysteine (Trp2027Cys) substitution. We found the resistant population absorbed 11.4% less herbicide and retained 21% more herbicide on the treated leaf compared to the susceptible population. We developed a genotyping assay targeting the resistance-endowing Trp2027Cys substitution for quick resistance diagnosis. CONCLUSION: A Trp2027Cys amino acid substitution in ACCase confers resistance to haloxyfop and pinoxaden in C. virgata. We provide important insights into the evolutionary history of C. virgata and a draft genome as a useful resource to further our understanding of the biology in the genus Chloris. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

A Target-Site Mutation Confers Cross-Resistance to ALS-Inhibiting Herbicides in Erigeron sumatrensis from Brazil.

Cases of weed resistant to herbicides have changed the dynamics of agricultural areas in Brazil, and in recent years, Erigeron species have caused major problems to farmers in the country, mainly in relation to the ineffectiveness of herbicide treatments used. The objective of this study was to confirm the cross-resistance to ALS inhibitors in populations of Erigeron sumatrensis as well as to investigate the existence of mutations in the site of action of ALS-inhibiting herbicides. To do this, 30 populations collected in the 2016/2017 crop season were grown in a greenhouse. Dose-response (chlorimuron-ethyl and cloransulam-methyl), inhibition of cytochrome P-450 with malathion, and ALS gene sequencing experiments were carried out in the F1 generations of two fleabane populations. The results proved the cross-resistance to chlorimuron-ethyl and cloransulam-methyl herbicides applied in the post-emergence of the resistant population of E. sumatrensis. The higher activity of P450 enzymes is unlikely responsible for the resistance of the population studied. The resistance mechanism found in R was the target site mutation Pro197Ser at the ALS gene. This is the first study in Brazil to identify a target-site change as a survival mechanism in E. sumatrensis for the resistance to ALS-inhibiting herbicides.

Evolution of EPSPS double mutation imparting glyphosate resistance in wild poinsettia (Euphorbia heterophylla L.).

The evolution of glyphosate resistance (GR) in weeds is an increasing problem. Glyphosate has been used intensively on wild poinsettia (Euphorbia heterophylla L.) populations for at least 20 years in GR crops within South America. We investigated the GR mechanisms in a wild poinsettia population from a soybean field in southern Brazil. The GR population required higher glyphosate doses to achieve 50% control (LD50) and 50% dry mass reduction (MR50) compared to a glyphosate susceptible (GS) population. The ratio between the LD50 and MR50 of GR and GS resulted in resistance factors (RF) of 6.9-fold and 6.1-fold, respectively. Shikimate accumulated 6.7 times more in GS than in GR when leaf-discs were incubated with increasing glyphosate concentrations. No differences were found between GR and GS regarding non-target-site mechanisms. Neither population metabolized glyphosate to significant levels following treatment with 850 g ha-1 glyphosate. Similar levels of 14C-glyphosate uptake and translocation were observed between the two populations. No differences in EPSPS expression were found between GS and GR. Two target site mutations were found in all EPSPS alleles of homozygous resistant plants: Thr102Ile + Pro106Thr (TIPT-mutation). Heterozygous individuals harbored both alleles, wild-type and TIPT. Half of GR individuals were heterozygous, suggesting that resistance is still evolving in the population. A genotyping assay was developed based on the Pro106Thr mutation, demonstrating high efficiency to identify homozygous, heterozygous or wild-type EPSPS sequences across different plants. This is the first report of glyphosate-resistant wild-poinsettia harboring an EPSPS double mutation (TIPT) in the same plant.

Chemical Characterization and Phytotoxic Effects of the Aerial Parts of Ruzigrass (Urochloa ruziziensis).

Studies of the phytotoxic effects between plants can be a crucial tool in the discovery of innovative compounds with herbicide potential. In this sense, we can highlight ruzigrass (Urochloa ruziziensis), which is traditionally used in the crop rotation system in order to reduce weed emergence. The aim of this work was to characterize the secondary metabolites of ruzigrass and to evaluate its phytotoxic effects. In total, eight compounds were isolated: friedelin, oleanolic acid, α-amyrin, 1-dehydrodiosgenone, sitosterol and stigmasterol glycosides, tricin and p-coumaric acid. Phytotoxic effects of the crude methanolic extract and fractions of ruzigrass were assessed using germination rate, initial seedling growth, and biomass of Bidens pilosa, Euphorbia heterophylla and Ipomoea grandifolia. Chemometric analysis discriminated the weed species into three groups, and B. pilosa was the most affected by fractions of ruzigrass. The phytotoxic activities of 1-dehydrodiosgenone, tricin, and p-coumaric acid are also reported, and p-coumaric acid and 1-dehydrodiosgenone were active against B. pilosa.

A novel TIPT double mutation in EPSPS conferring glyphosate resistance in tetraploid Bidens subalternans.

BACKGROUND: Bidens subalternans (greater beggarticks) is a tetraploid and troublesome weed infesting annual crops in most tropical regions of the world. A glyphosate-resistant (GR) B. subalternans biotype was detected in a soybean field from Paraguay. A series of physiological and molecular analyses were conducted to elucidate its resistance mechanisms. RESULTS: The GR biotype had a high level of resistance (> 15-fold LD50 ), relative to a glyphosate-susceptible (GS) biotype. Shikimate accumulation was up to ten-fold greater for GS compared with GR. We found no differences in sensitivity when plants were treated and kept under lower (10/4 °C) or higher temperatures (25/20 °C). GS and GR had the same relative EPSPS gene copy number, and similar glyphosate absorption and translocation rates. Neither biotype metabolized glyphosate. A double amino acid substitution (TIPT - Thr102Ile and Pro106Thr) was found in only one EPSPS allele from one of the two EPSPS homoeologs present in tetraploid GR B. subalternans. CONCLUSION: This is the first report of a TIPT double mutation conferring high levels of glyphosate resistance in a weed species. The presence of both wild-type and TIPT mutant EPSPS on the polyploid genome of GR B. subalternans may offset a potential fitness cost, requiring additional research to confirm the absence of deleterious effects. © 2019 Society of Chemical Industry.

Effect of day time climatic conditions associated with different 2,4-D formulations on spray deposition and weed control.

The aim of this study was to evaluate the effect of time of the day and their associated climatic conditions on spray deposition of two 2,4-D formulations, as well as the influence on weed control. The experiment was installed in the field in complete randomized design. Treatments were arranged in factorial design 8 × 2, with 20 repetitions. First factor corresponded to different application time (1:00, 4:00, 7:00, 10:00, 13:00, 16:00, 19:00, and 22:00) with their respective climatic conditions. The second factor consisted of two formulations of 2,4-D applied at 776 g a.e. ha-1 (2,4-D amine and 2,4-D choline salt with Colex-D™ Technology) + glyphosate (816 g a.e. ha-1). There was more spray deposition when 2,4-D choline formulation was used, and such differences were more evident for applications performed under adverse climatic conditions. More spray deposition was found in applications performed at times of day with more favorable temperature and humidity of the air conditions. Only the initial control of the evaluated species was affected by the time of application.

The Activity of the Antioxidant Defense System of the Weed Species Senna obtusifolia L. and its Resistance to Allelochemical Stress.

Senna obtusifolia L., a common weed in the tropical and subtropical regions of the world, is able to germinate under adverse environmental conditions, suggesting that this species has efficient stress-adaptation strategies. The aims of the present work were to examine the energy metabolism and the antioxidant defense system of the Senna obtusifolia L. during seed germination and initial growth, and the responses to allelochemical-induced stress. Respiratory activity, the activities of alcohol dehydrogenase (ADH), superoxide dismutase (SOD), catalase (CAT),guaicol peroxidase (POD), ascorbate peroxidase (APX), glutathione reductase (GR), lipoxygenase (LOX) and the content of malondialdehyde (MDA) and glutathione (GSSG and GSH) were measured. Shortly after seed imbibition, mitochondrial respiratory activity was active and the presence of SOD, CAT, GR and LOX activity in embryos, along with significant KCN-insensitive respiration, indicated that the production of reactive oxygen species (ROS) is initiated as soon as mitochondrial respiration resumes. Among the fourteen allelochemicals assayed, only coumarin significantly supressed the growth of S. obtusifolia seedlings. Although coumarin reduced the activities of CAT, POD and APX, the GSH, GSSG and MDA levels were not altered. Alpha-pinene, quercetin and ferulic acid did not modify the activity of the antioxidant enzymes or the contents of GSH, GSSH and MDA. Thus the antioxidant defense system of S. obstusifolia may be effective in counteracting the harmful effects of ROS generated during seed germination and initial growth in the presence of toxic allelochemicals.

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.

Comparative sorption, desorption and leaching potential of aminocyclopyrachlor and picloram.

Sorption and desorption of aminocyclopyrachlor (6-amino-5-chloro-2-cyclopropylpyrimidine-4-carboxylic acid) were compared to that of the structurally similar herbicide picloram (4-amino-3,5,6-trichloro-2-pyridinecarboxylic acid) in three soils of differing origin and composition to determine if picloram data is representative of aminocyclopyrachlor behavior in soil. Aminocyclopyrachlor and picloram batch sorption data fit the Freundlich equation and was independent of concentration for aminocyclopyrachlor (1/n = 1), but not for picloram (1/n = 0.80-0.90). Freundlich sorption coefficients (K f) for aminocyclopyrachlor were lowest in the eroded and depositional Minnesota soils (0.04 and 0.12 µmol ((1-1/n)) L(1/n) kg(-1)) and the highest in Molokai soil (0.31 µmol ((1-1/n)) L(1/n) kg(-1)). For picloram, K f was lower in the eroded (0.28 µmol ((1-1/n)) L(1/n) kg(-1)) as compared to the depositional Minnesota soil (0.75 µmol ((1-1/n)) L(1/n) kg(-1)). Comparing soil to soil, K f for picloram was consistently higher than those found for aminocyclopyrachlor. Desorption of aminocyclopyrachlor and picloram was hysteretic on all three soils. With regard to the theoretical leaching potential based on groundwater ubiquity score (GUS), leaching potential of both herbicides was considered to be similar. Aminocyclopyrachlor would be ranked as leacher in all three soils if t1/2 was > 12.7 days. To be ranked as non-leacher in all three soils, aminocyclopyrachlor t1/2 would have to be <3.3 days. Calculated half-life that would rank picloram as leacher was calculated to be ∼15.6 d. Using the current information for aminocycloprachlor, or using picloram data as representative of aminocycloprachlor behavior, scientists can now more accurately predict the potential for offsite transport of aminocycloprachlor.

Sorption-desorption of indaziflam in selected agricultural soils.

Indaziflam, a new alkylazine herbicide that inhibits cellulose biosynthesis, is under current development for soil applications in perennial crops and nonagricultural areas. Sorption and desorption of indaziflam in six soils from Brazil and three soils from the United States, with different physical chemical properties, were investigated using the batch equilibration method. Sorption kinetics demonstrated that soil-solution equilibrium was attained in <24 h. The Freundlich equation described the sorption behavior of the herbicide for all soils (R(2) > 0.99). K(f) values of the Brazilian oxisols ranged from 4.66 to 29.3, and 1/n values were ≥ 0.95. Sorption was positively correlated to %OC and clay contents. U.S. mollisol K(f) values ranged from 6.62 to 14.3; 1/n values for sorption were ≥ 0.92. K(f) values from mollisols were also positively correlated with %OC. These results suggest that indaziflam potential mobility, based solely on its sorption coefficients, would range from moderate to low in soil. Desorption was hysteretic on all soils, further decreasing its potential mobility for offsite transport.

Sorption-desorption of aminocyclopyrachlor in selected Brazilian soils.

Aminocyclopyrachlor sorption/desorption was investigated in 14 soils from Brazil, representing a range of pH, and organic carbon (OC) and clay contents. The Freundlich equation adequately described behavior of aminocyclopyrachlor in soil. Freundlich sorption coefficient (K(f)) values ranged from 0.06 to 1.64 and 1/n values for ranged from 0.9 to 1.0. Sorption was correlated to OC (K(f,oc) ranged from 11 to 64) and clay contents. The lowest sorption was found for soils with very low OC contents (0.50-0.65%) and loamy-sand to sand textures. The 1/n values for desorption were lower than those observed for sorption, suggesting that aminocyclopyrachlor sorption by soil was not reversible; hysteresis coefficients ranged from 0.13 to 0.74. The results suggest that although aminocyclopyrachlor would be very mobile based on its sorption coefficients, its potential depth of leaching may be overestimated due to the hysteretic desorption.

Glyphosate affects seed composition in glyphosate-resistant soybean.

The cultivation of glyphosate-resistant (GR) soybeans has continuously increased worldwide in recent years mainly due to the importance of glyphosate in current weed management systems. However, not much has been done to understand eventual effects of glyphosate application on GR soybean physiology, especially those related to seed composition with potential effects on human health. Two experiments were conducted to evaluate the effects of glyphosate application on GR soybeans compared with its near-isogenic non-GR parental lines. Results of the first experiment showed that glyphosate application resulted in significant decreases in shoot nutrient concentrations, photosynthetic parameters, and biomass production. Similar trends were observed for the second experiment, although glyphosate application significantly altered seed nutrient concentrations and polyunsaturated fatty acid percentages. Glyphosate resulted in significant decreases in polyunsaturated linoleic acid (18:2n-6) (2.3% decrease) and linolenic acid (18:3n-3) (9.6% decrease) and a significant increase in monounsaturated fatty acids 17:1n-7 (30.3% increase) and 18:1n-7 (25% increase). The combined observations of decreased photosynthetic parameters and low nutrient availability in glyphosate-treated plants may explain potential adverse effects of glyphosate in GR soybeans.

Bioavailability of diuron, imazapic and isoxaflutole in soils of contrasting textures.

This research was aimed at understanding the dynamics of the herbicides diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea], imazapic [2-(4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl)-5-methylnicotinic acid] and isoxaflutole [5-cyclopropyl-4-(2-methanesulfonyl-4-trifluoromethyl benzoyl)isoxazole] in two soils of different physico-chemical properties. To accomplish such intent, several greenhouse experiments were run. The bioavailability of diuron (0; 1.6 and 3.2 kg ha(-1)), imazapic (0; 98 and 122.5 g ha(-1)) and isoxaflutole (0; 35 and 70 g ha(-1)) was measured in samples from a sandy loam soil and a clay soil, by sowing a bioindicator (Brachiaria decumbens), at 0, 25, 50, 75 and 100 days after herbicides application (DAA). Diuron was very stable in clay soil, providing control equal to or higher than 92% of bioindicator, up to 100 DAA, as assumed by biomass accumulation. No differential effect was observed in sandy loam soil, even when 2x labeled rate were applied. Imazapic provided a short bioavailability in relation to B. decumbens, independent of rates applied. The persistence of isoxaflutole was longer in clay soil (28 to 30 days).

Sorption-desorption of atrazine and diuron in soils from southern Brazil.

The objective of this study was to investigate the behavior of sorption and desorption of the herbicides atrazine (6-chloro-N2-ethyl-N4-isopropyl-1,3,5-triazine-2,4-diamine) and diuron [3-(3,4-dichlorophenyl)-1,1-dimethyleurea] in soil samples from a typical lithosequence located in the municipality of Mamborê (PR), southern Brazil. Five concentrations of 14C-atrazine and 14C-diuron were used for both herbicides (0.48, 0.96, 1.92, 3.84, and 7.69 mg L(-1)). Sorption of both herbicides correlated positively with the organic carbon and clay content of the soil samples. Sorption isotherms were well described by the Freundlich model. The slope values of the isotherm (N) ranged from 0.84 to 0.90 (atrazine) and from 0.75 to 0.79 (diuron) for the lithosequence samples. Sorption of diuron was high regardless of the soil texture or the concentration added. The desorption isotherms for atrazine and diuron showed good fit to the Freundlich equation (R2 >or= 0,87). Atrazine slope values for the desorption isotherms were similar for the different concentrations and were much lower than those observed for the sorption isotherms. Significant hysteresis was observed in the herbicide desorption. When the two herbicides were compared, it was found that diuron (N = 0.06-0.22) presented more pronounced hysteresis than atrazine. The results showed that, quantitatively, a greater atrazine fraction applied to these soils remains available to be leached in the soil profile, as compared to diuron.

Impact of sublethal doses of 2,4-D, simulating drift, on tomato yield.

Tomato is considered one of the most sensitive crops regarding 2,4-D drift. In many cases, such susceptibility has led to important restrictions in the use of 2,4-D based products. Field experiments were carried out for two consecutive years in tomato, by applying sublethal doses of 2,4-D (ranging from 0.42 to 13.44 g a.i. ha(-1)) directly to plants, at different stages of growth, as a simulation of eventual drifts to the crop. The range of rates was based on the assumption of a 0.0625-2.0% drift level of a 1 L ha(-1) of the most common formulated herbicides. For this crop, the range of rates between 0.42 and 13.44 g a.i ha(-1) applied at the beginning of flowering caused a linear crop reduction. On the other hand, rates < or = 13.44 g a.i. ha(-1) applied after full development of fourth truss stage or latter had no effect on crop yield or development. For tomato, tolerance to 2,4-D strongly increases with plant age.

Incomplete septal cirrhosis: an enigmatic disease.

UNLABELLED: Incomplete septal cirrhosis is a form of macronodular cirrhosis characterized by fine and incomplete septa, which delimit rudimentary regeneration nodules. Its etiopathogeny is uncertain and is associated with various diseases such as regenerative nodular hyperplasia, idiopathic portal hypertension, and partial non-cirrhotic nodular transformation, as well as with progression and regression of cirrhosis of any etiology. Few studies are available in the literature describing the clinical and biological characteristics of incomplete septal cirrhosis. GOAL: The objective of the present descriptive study was to study this entity in the city of Salvador, Bahia, Brazil, and to compare the histopathological, biological and clinical data obtained with those reported in the specialized literature. MATERIALS AND METHODS: We reviewed eight cases of incomplete septal cirrhois of varieties etiologies. Hepatitis C, autoimmune hepatitis, alcoholic liver disease and criptogenic liver disease were present in our cases. Fibrosis progression as well as cirrhosis regression could be identified in these patients. CONCLUSIONS: We concluded that Incomplete septal cirrhosis is not a disease itself but it could be considered as a stage of progression and regression of liver fibrosis.

Sorption kinetics of atrazine and diuron in soils from southern Brazil.

Sorption kinetics of atrazine and diuron was evaluated in soil samples from a typical landscape in Paraná. Samples were collected (0-20 cm) in a no-tillage area from Mamborê, PR, which has been cultivated under a crop rotation for the last six years. Six sampling points of the slope were selected to represent a wide range of soil chemical and physical properties found in this area. Radiolabeled tracers (14C-atrazine and 14C-diuron) were used and the radioactivity was detected by liquid scintillation counting (LSC). Sorption was accomplished for increasing equilibration periods (0.5, 1.5, 3, 6, 12, 24, and 48 h). Kinetics data fitted adequately well to Elovich equation, providing evidences that soil reaction occurs in two distinct stages: a fast, initial one followed by a slower one. During the fast phase, 34-42 and 71-79% of total atrazine and diuron applied were sorbed to soil samples. No important differences were found among combinations of soil and herbicide sorption during the slow phase. The unrealistic conditions under batch experiments should be overestimating sorption in the fast phase and underestimating diffusion in the slow phase. Sorption of both herbicides was positively correlated to organic carbon and clay contents of soils, but atrazine was much less sorbed than diuron, showing its higher potential to contaminate groundwater, specially in sandy, low organic carbon soils.

Glycoinositolphospholipids from Trypanosoma cruzi interfere with macrophages and dendritic cell responses.

To investigate the possible effects of glycoinositolphospholipid (GIPL) from Trypanosoma cruzi on human antigen presenting cells, we tested their effects on lipopolysaccharide (LPS)-stimulated human macrophages and dendritic cells (DC). Human macrophages or DC were incubated with GIPL (50 microg/ml) and LPS (500 pg/ml) and tumor necrosis factor alpha (TNF-alpha), interleukin 8 (IL-8), IL-10, and IL-12p40 levels in supernatants were analyzed by enzyme-linked immunosorbent assay. TNF-alpha, IL-10, and IL-12 secretion were significantly decreased by GIPL both in macrophages and DC. In contrast, GIPL did not alter IL-8 production. We also analyzed the expression of CD80, CD86, HLA-DR, CD40, and CD57 on the macrophage surface after stimulation with LPS in the presence or absence of T. cruzi GIPL. GIPL led to a down-regulation in the expression of all tested molecules. We additionally examined the influence of T. cruzi GIPL on the response of human DC to LPS. LPS-induced HLA-DR, CD83, and CD86 up-regulation was significantly inhibited by GIPL. A slight down-regulation in CD80 and CD40 expression on DC surfaces in the presence of GIPL was also noticed. Similarly, GIPL led to down-modulation of CD83, CD80, CD86, and HLA-DR surface expression and TNF-alpha and IL-10 production when DC were stimulated by CD40L. The ceramide portion of GIPL was responsible for most of the activity exhibited by the whole molecule. Considering the important role of the immune response in determining the fate of the host-parasite relationship, the immunoregulatory activities of T. cruzi GIPL are potentially important for parasite evasion and then pathogenesis of infection with protozoan parasites.