Nile tilapia (Oreochromis niloticus), liver morphology,CYP1A activity and thyroid hormones after Endosulfan dietary exposure

Endosulfan is a worldwide used insecticide suspected to be highly toxic to aquatic organisms, including fish. Most of the available studies have focused in water exposures, although this pollutant can be transferred through food chain. Therefore, in the present study, the effects of Endosulfan on tilapia (Oreochromis niloticus), when administered through the diet. Fish were fed 21 days with diets containing 1 and 0.5 μg g⁻¹ of Endosulfan, after which qualitative histological liver analysis showed that Endosulfan induced hepatocyte destruction, vessel endothelium rupture and increased melanomacrophages aggregates. To test lower environmentally relevant doses of Endosulfan could induce hepatic damage, as well as other negative effects, such as altered phase I metabolism and plasma thyroid hormone levels. Hence, tilapia were orally exposed to 0.1 and 0.001 μg g⁻¹ for 35 days. Low environmentally realistic doses of Endosulfan were still able to induce liver histopathological damage such as increased hepatocyte vacuolization and increased eosinophil granular cell aggregates. Liver cytochrome P450 1A activity, evaluated through ethoxyresorufin-o-deethylase (EROD), was enhanced in tilapia exposed to 0.001 μg g⁻¹, whereas the highest dose had no measurable effects in this enzyme activity. Fish exposed to 0.1 μg g⁻¹ of Endosulfan had depressed T4 plasma levels. Overall, the results of the present study further demonstrate the toxic effects of Endosulfan in tilapia when administered in the diet at environmentally relevant concentrations, which indicates that in the field food chain transfer may also be an importance source of this pollutant.     

Oxygen consumption and ammonia excretion of the freshwater crab Trichodactylus borellianus exposed to chlorpyrifos and endosulfan insecticides

The effects of lethal and sublethal concentrations of chlorpyrifos and endosulfan on oxygen consumption and ammonia excretion rate of the crab Trichodactylus borellianus were evaluated. Oxygen consumption and energy expenditure had significant effect in relation to exposure times. Regarding endosulfan, a significant difference in consumption among times of exposure was registered in 625 μg L⁻¹. Moreover, at the highest concentration, energy expenditure rate was observed stabilized during 1–3 h. A significant increase in ammonia excretion was evidenced in 150 and 300 μg L⁻¹ of chlorpyrifos. The O:N ratio showed a decrease in chlorpyrifos and in 2500 μg L⁻¹ of endosulfan. This indicated a shift towards protein primary metabolism. An increment in the O:N ratio was observed in the lower endosulfan solutions. The relation oxygen:nitrogen showed a shift towards lipid and carbohydrate primary metabolism. This work indicated the complexity of the metabolism in the freshwater crab affected by xenobiotic elements.     

Agrobacterium induces plant cell death in wheat (Triticum aestivum L.)

The symptoms of gall or hairy root do not occur in the interactions between wheat (Triticum aestivum L.) and other monocotyledonous plants, with Agrobacterium tumefaciens or Agrobacterium rhizogenes. However, both bacteria colonized wheat root surfaces at similar levels (2.0 × 10⁷ colony forming U g⁻¹ root) and grew without inhibition in suspension with intact or wounded wheat embryos or root segments present. Suspension-cultured wheat embryo cells grown in 7.4 m M O₂ displayed 23% cell death after 1 h exposure to Agrobacterium cells, while the extent of cell death with 2.1 m M O₂ averaged 8%. Cultured wheat embryo and root cells rapidly produced hydrogen peroxide (H₂O₂) when contacted with A. tumefaciens or A. rhizogenes. Production of H₂O₂ was lower at 2.1 m M O₂ than 7.4 mM O₂. Browning and autofluorescence of epidermal cells of callus derived from wheat embryos and wheat roots was observed after inoculation with Agrobacterium. An increase in ferulic acid was detected in the walls of roots exposed to Agrobacterium. However, neither lignin nor callose was detected by diagnostic staining methods. These findings suggest that Agrobacterium induced a resistance-like response in wheat that may reduce the efficacy of transformation and limit the normal symptom formation.     

Biochemical,physiological and morfological responses in common carp (Cyprinus carpio L.) after long-term exposure to terbutryn in real environmental concentration

The effects of terbutryn at concentrations of 0.02 (reported concentration in Czech rivers), 0.2, and 2.0 μg l^?1 were assessed in one-year-old common carp (Cyprinus carpio L.) exposed for 90 days. Influence on biometric parameters, hematology, biochemistry, histology, and oxidative stress was investigated. Exposure to 0.02, 0.2 and 2.0 μg l^?1 showed significant differences oxidative stress biomarkers compared to controls but exposure to 0.2 and 2.0 μg l^?1 significantly affected biochemical and hematological profiles. Long-term exposure of terbutryn in carp resulted in slight alterations in internal organs and increased reactive oxygen species formation, resulting in oxidative damage to lipids and proteins and inhibition of antioxidant capacities.     

Retraction notice to “Fluctuations of certain biochemical constituents and markers enzymes as a consequence of monocrotophos toxicity in the edible freshwater fish, Channa punctatus” [Pesticide Biochemistry and Physiology 94 (2009) 5-9]

A total of 185 hexanic, dichloromethanic, ethanolic and hydroethanolic extracts from 24 species of Cerrado plants, were tested against Zabrotes subfasciatus, Acanthoscelides obtectus, and human saliva α-amylases. Twelve crude extracts presented inhibition rates greater than 80% against digestive α-amylases of the insect pest Z. subfasciatus, at a concentration of 1 mg mL⁻¹. These extracts were also tested against A. obtectus and human saliva α-amylases to verify their affinity and specificity of action. The hydroethanolic Kielmeyera coriacea stem bark extract presented a strong inhibitory potential, with IC₅₀ values of 110 μg mL⁻¹ for Z. subfasciatus and 272.12 μg mL⁻¹ for A. obtectus, in addition to a 97.09% reduction in enzyme activity of human saliva α-amylases at 125 μg mL⁻¹. The hexanic Aspidosperma macrocarpon root wood extract totally inhibited the activity of Z. subfasciatus α-amylases, reduced the enzyme activity of A. obtectus by 14.69% at 1 mg mL⁻¹, but did not alter the activity of human saliva α-amylases, thus characterizing greater inhibition affinity and specificity. The results suggest that the application of plant extracts against insect α-amylases represent a promising biotechnological tool for development of new insect pest control strategies, with noticeable affinity and specificity of action against different target enzymes.     

Toxic effects of acephate on Paramecium caudatum with special emphasis on morphology,behaviour, and generation time

The continuous increase in the number of new chemicals as well as the discharges of solid and liquid wastes triggered the need for simple and inexpensive bioassays for routine testing. In recent years, there has been increasing development of methods (particularly rapid tests) for testing environmental samples. This paper describes the quick toxic evaluation of an organophosphorus insecticide, acephate (O,S-dimethyl acetylphosphoramidothioate) on Paramecium caudatum for acute and sub-acute toxicity studies with reference to morphology, behaviour, and its generation time. The lethal concentrations for 10 min and 2 h were determined by probit method, as 500 mg L⁻¹ and 300 mg L⁻¹, respectively. Higher concentrations of 10 min exposure caused cell lysis with disintegration of cell membrane and precipitation of protoplasm. Combination of conventional light microscopy and computerized video tracking systems were used to study the locomotor behaviour of paramecia. The test organism was under stress and exhibited an initial increase and subsequent decrease in the swimming speed when exposed to 1/4, 1/2, 3/4, and LC₅₀ concentrations for 10 min (125, 250, 375, and 500 mg L⁻¹, respectively). Similar changes were also noticed when paramecia were exposed to LC₅₀ for 2 h. In a separate set of experiments, the number of generations and generation time in 24 h was evaluated with respect to the different sub-lethal concentrations (30, 60, 120, and 240 mg L⁻¹). The number of generations decreased and generation time extended significantly in a concentration dependent manner. The results indicate that the Paramecium toxicity assay could be used as a complimentary system to rapidly elucidate the cytotoxic potential of insecticides. The major advantages associated with these tests are: they are inexpensive, simple, user-friendly, space saving, and seem to be attractive alternatives to conventional bioassays.     

Ethylene production by Colletotrichum musae in vitro

Seven isolates of the pathogen Colletotrichum musae (Berk & Curt.) v. arx. were isolated from banana fruit. These isolates produced ethylene to varying degrees in methionine-amended Czapek Dox liquid medium as both shake and static cultures. Rates of ethylene production by C. musae were positively associated with the concentration of methionine in the growth medium. C. musae did not produce ethylene on basal medium containing l-glutamate, α -ketoglutarate or l-cysteine. Isolate CM 100 produced the highest cumulative amount of ethylene (2·27 μm g⁻¹ dry wt) over 12 days on 35 mm methionine-amended shake cultures of basal medium. In the presence of methionine, ethylene biosynthesis by C. musae occurred via 2-keto-4-methylthiobutyric acid (KMBA). The capacity of C. musae to produce ethylene may have a role in its pathogenicity on climacteric banana fruit.     

Metabolic effects in rapeseed (Brassica napus L.) seedlings after root exposure to glyphosate

Metabolic effects in rapeseed (Brassica napus L.) seedlings after root exposure to sublethal concentrations of glyphosate were examined in order to evaluate the possibilities of using a response pattern in plants as a measure of exposure to glyphosate through the growth media, more sensitive than the well-known biomarker shikimate. Rapeseed seedlings were grown in hydroponic nutrient solutions containing varying sublethal concentrations of glyphosate (1–50 μM). After 9 days of glyphosate exposure, the shoots of the seedlings were analysed with respect to the effects on selected metabolites downstream from the primary affected metabolite shikimate, which accumulated linearly in response to glyphosate exposure (from 0 to ∼126 μmol/g DW). The selected metabolites analysed, comprising the free amino acids, and the glucosinolates derived therefrom, showed complex patterns in response to glyphosate exposure. Most noteworthy was though that they responded at the lowest concentrations of exposure to glyphosate (1 μM), where no visual effects, decrease in shoot DW or shikimate could be detected, indicating that a biomarker response more sensitive than that of shikimate can be established for plants exposed to glyphosate.     

A soluble carbohydrate elicitor from Blumeria graminis f. sp. tritici is recognized by a broad range of cereals

Wheat plants rapidly recognize pathogenic and non-pathogenic conidia of the powdery mildew fungusBlumeria (syn. Erysiphe)graminis on their leaf surfaces. This suggests that a chemical signal emanates from conidia at the pre-penetration stage of infection. Conidia of B. graminis f. sp. tritici were found to contain an elicitor that was easily washed off their surface. The elicitor activity is heat stable and could not be removed by phenol extraction. By contrast, elicitor activity is sensitive to periodate oxidation and partial acid hydrolysis suggesting that the elicitor activity resides in a carbohydrate moiety. Analysis of carbohydrates revealed mostly glucose, with smaller amounts of xylose and mannose. The glucosyl residues of the B. graminis elicitor were found to be linked (1 → 2)-, (1 → 4), and (1 → 6)-, with (1 → 4, 1 → 6)- branch point residues, and no 3-linked glucose residues were detected. As treatment with β -mannanase significantly reduced elicitor activity, mixed-linkage (1 → 4), (1 → 6)-mannosyl residues appeared to be important for elicitor activity. The B. graminis elicitor induced the expression of all defence-related genes tested in wheat and also induced resistance to subsequent attack by B. graminis f. sp. tritici. In contrast, a hypersensitive response was not induced by the elicitor in the absence or the presence of a challenging inoculum of B. graminis f. sp. tritici. The elicitor also induced the accumulation of thaumatin-like proteins in barley, oat, rye, rice and maize, but did not induce necrosis in any of these species. This suggests that the B. graminis elicitor represents a host non-specific determinant of non-self recognition in cereals activating general defence responses other than the hypersensitive reaction.     

Chlorpyrifos induced alterations in the levels of hydrogen peroxide,nitrate and nitrite in rat brain and liver

Organophosphate pesticides are among the most widely used synthetic chemicals for controlling a wide variety of pests. Chlorpyrifos (CPF) is among the leading organophosphate (OP) pesticides used extensively throughout the world including India. Besides being potent anticholinesterase compounds, these OP pesticides are known to generate oxidative stress. Present study was carried out to see the level of reactive oxygen species (ROS), hydrogen peroxide (H₂O₂), nitrate (NO₃⁻) and nitrite (NO₂⁻) in different parts of rat brain and liver after giving different doses of CPF intramuscularly for 3 days or for 1 month. Results of the present study clearly revealed that levels of H₂O₂, NO₃⁻ and NO₂⁻ were increased significantly in all the three parts of rat brain i.e., fore-, mid- and hind-brain as well as in liver of rats given for 3 days or 1 month due to exposure of different doses of CPF. The study clearly demonstrated that CPF generated oxidative stress in all the three brain regions as well as liver of rats and the ROS were accumulated. Accumulation of ROS in all the regions of brain and other tissues may disturb the normal physiological functions aggravating the toxicity symptoms of CPF.     

Histochemical studies on the accumulation of reactive oxygen species (O2− and H2O2) in the incompatible and compatible interaction of wheat—Puccinia striiformis f. sp. tritici

The generation and accumulation of reactive oxygen species (ROS), superoxide anion (O₂⁻) and hydrogen peroxide (H₂O₂), were studied in the interaction between wheat cv. ‘Suwon 11’ and two races of Puccinia striiformis f. sp. tritici (avirulent and virulent). Generation of O₂⁻ and H₂O₂ was analyzed histochemically using nitroblue tetrazolium (NBT) and 3,3-diamino-benzidine (DAB), respectively. At the pre-penetration stage during appressorium formation both stripe rust races induced H₂O₂ accumulation in guard cells. In the incompatible interaction, a rapid increase of O₂⁻ and H₂O₂ generation at infection sites was detected. The percentage of infection sites showing NBT and DAB staining was 36.1% and 40.0%, respectively, 12 h after inoculation (hai). At extended incubation time until 24 hai, percentage of infection sites showing H₂O₂ accumulation further increased, whereas those exhibiting O₂⁻ accumulation declined. The early infection stage from 12 to 24 hai coincided with primary haustoria formation in mesophyll cells. In contrast, in the compatible interaction, O₂⁻ and H₂O₂ generation could not be detected in most of the infection sites. In the incompatible interaction, intensive DAB staining was also determined in mesophyll cells, especially in cell walls, surrounding the infected cells 16–24 hai; thereafter, these cells contained fluorescing compounds and underwent hypersensitive response (HR). The number of necrotic host cells surrounding the infection sites increased continuously from 20 to 96 hai. It might be concluded that H₂O₂ accumulation during the early infection stage is associated with the occurrence of hypersensitive cell death and that resistance response is leading to arrest the avirulent race of the obligate stripe rust pathogen. In the compatible interaction at 96 hai, H₂O₂ accumulation was observed in mesophyll cells surrounding the rust lesion.     

Induction of disease resistance against Botrytis cinerea by heat shock treatment in melon (Cucumis melo L.)

The present study investigated resistance against Botrytis cinerea after heat shock treatment in melon plants. Heat shock at 50 °C for 20 s 0–24 h before inoculation resulted in maximal B. cinerea symptom reduction and peroxidase gene expression, which peaked 12 and 72 h post-treatment and decreased 24–48 h post-treatment, suggesting pathogenesis-related protein expression priming. Hot water dipping did not directly inhibit mycelia growth. Plants treated with 2-benzisothiazol-3(2H)-one 1,1-dioxide, which induces systemic acquired resistance, demonstrated higher peroxidase gene expression but no B. cinerea resistance, indicating possible involvement of additional novel mechanisms in heat shock-activated resistance of melon against B. cinerea.     

Characterization of glyphosate resistance in cloned Amaranthus palmeri plants

Glyphosate‐resistant Palmer amaranth from Georgia (GA), USA, possesses multiple copies of the gene that encodes 5‐enolpyruvylshikimate‐3‐phosphate synthase (EPSPS), the enzyme target site of this herbicide. The cloned plants of glyphosate‐resistant and glyphosate‐susceptible Palmer amaranth biotypes from Mississippi (MS), USA, and GA were evaluated for glyphosate injury (digital imaging) in leaf disc bioassays. Four groups (three resistant groups: two from MS [G and R] and one from GA [C7]; one susceptible group from GA [C3]) were chosen for cloning to facilitate long‐term studies. After exposure to glyphosate (1.0 mmol L^–1, 144 h), the level of injury (mean value) was low in the resistant groups, while a higher level of injury was found in the susceptible group. However, the individual injury values within all groups varied widely. The mean EPSPS gene copy number of these groups was G ≥ R > C7 >>> C3. However, a higher copy number did not always convey increased resistance in these bioassays. When the copy number was high (>20), 81.5% of the bioassayed plants exhibited little or no injury and only ～20% were significantly injured, while 50% of the plants with a low copy number (<20) remained healthy. Overall, no strong statistical correlation of the copy number versus injury occurred in these cloned plants and no statistical relationship of resistance and copy number with the sex of the MS plants was observed. The results suggest that although an elevated copy number of the EPSPS gene can instill resistance, other mechanisms might contribute to the overall glyphosate resistance of Palmer amaranth in these plants.     

In vivo growth and pathotoxin production by the maize pathogen Cochliobolus carbonum

Conidia of Cochliobolus carbonum secrete a toxin (HC-toxin) during appressorium formation on maize leaves. Plasma desorption mass spectrometry revealed that approximately 70 ng of toxin per 10⁶ conidia were secreted during the first 16 h of morphogenesis. Growth of the fungus was monitored microscopically. Extensive fungal growth occurred in the susceptible interaction by 24 h. In spite of a substantial amount of HC-toxin, the fungus failed to become established in the resistant host even after 36 h. Results suggest that the resistance conditioned by Hm1, which encodes a toxin reductase, causes inactivation of the toxin early in the interaction.     

Effects of Low Doses of Glyphosate on Agronomic Traits of Upland Rice

Research has shown the occurrence of the hormesis effect in some upland rice cultures resulting from low-dose application of glyphosate. Glyphosate herbicide is widely used in Brazilian agriculture for controlling the large quantity of weeds. The aim of this work was to verify the effects of low-dose application of glyphosate herbicide on agronomic characteristics in upland rice. The experimental design used was randomized blocks comprising five low-dose applications of glyphosate herbicide (10, 20, 40, 70, and 100?g acid equivalent [a.e.] ha^?1) and the control, in two stages of development of the rice culture (tillering [V4] and floral differentiation [R1]) with four repetitions. The agronomic traits of upland rice were evaluated. Data were subjected to variance analysis, polynomial regression analysis for the quantitative factor, and Tukey’s test for the qualitative factor at p?<?0.05. The grain yield and the number of spikelets per panicle increased with the application of 10?g a.e. ha^?1 of glyphosate at the floral differentiation stage. Until the low dose of 75?g a.e. ha^?1, there was an increase in the number of panicles. Low doses between 70 and 100?g a.e. ha^?1 applied in R1 provided less spikelets per panicle, lower 100-grain weight, and lower grain yield. The leaf flavonoid content increased due to the increase in the low doses of glyphosate herbicide.

     

Effects of trichlorfon and sodium dodecyl sulphate on antioxidant defense system and acetylcholinesterase of Tilapia nilotica in vitro

The effects of organophosphorus insecticide trichlorfon, surfactant sodium dodecyl sulphate (SDS), and the mixture of trichlorfon and SDS on the antioxidant defense system and acetylcholinesterase (AChE) in Tilapia nilotica were assessed in vitro. Various concentrations of trichlorfon (0, 0.0001, 0.001, 0.01, 0.1 and 1 g/L) and SDS (0, 0.0625, 0.125, 0.25, 0.5, 1 g/L) were incubated with homogenate of liver and muscle, respectively, at 25 °C for 0, 30, 60 and 90 min. Two concentrations of mixture of trichlorfon and SDS (0.0001 g/L trichlorfon + 0.5 g/L SDS, 0.1 g/L trichlorfon + 0.5 g/L SDS) and 0.0001 g/L trichlorfon, 0.1 g/L trichlorfon, 0.5 g/L SDS and control, were incubated simultaneously with homogenate of liver and muscle, respectively, at 25 °C for 60 min. After incubation, the content of reduced-glutathione (GSH) and the activity of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) in homogenate of liver were determined, and the activities of AChE in homogenate of muscle were also measured.Treatment with trichlorfon caused a significant concentration-dependent and time-related inhibition of AChE activity at all treatment concentrations and times since trichlorfon is a cholinesterase inhibitor. For the same trichlorfon treatment, an apparent decrease in GSH content was found in concentration of 0.01, 0.1, 1 g/L, whereas no significant alteration in antioxidant enzyme activity were found at all experiment concentrations and times, which might indicate that antioxidant enzymes have not involved in the metabolism of trichlorfon. The depletion of GSH might indicate that ROS could be involved in the toxic effects of trichlorfon. Exposure of SDS can inhibit activities of AChE, GST and CAT at concentrations of 0.5 and/or 1 g/L, which could be due to the denaturing process of SDS to the enzymes. For the mixture exposure of trichlorfon and SDS, the effect of the mixture of 0.0001 g/L trichlorfon and 0.5 g/L SDS on inhibition of AChE shows synergistic other than simple additive of trichlorfon and SDS. The combined effects of chemicals and detergents deserve to be particularly noted. It should be noted that the toxicity experiments were made in tissue homogenates instead of whole organisms. The responses against the toxic compounds will not be the same in both systems.     

Effect of miconazole,an antifungal agent,on allene oxide synthase: Inhibition,kinetics, and binding

We investigated the inhibition of allene oxide synthase (AOS), a key enzyme in jasmonic acid biosynthesis, by miconazole. Kinetic analysis indicated that miconazole was a mixed-type inhibitor of AOS with a K_i value of approximately 8.4 ± 0.2 μM. Analysis of the interactions between miconazole and AOS by optical difference spectroscopy revealed that miconazole binding induces type II binding spectra with a K_d value of approximately 6.0 ± 0.2 μM.     

Correlation between sensitivity of barley to Pyrenophora teres toxins and susceptibility to the fungus

Detached leaves of 25 barleys, ranging from highly susceptible to highly resistant to Pyrenophora teres f. teres and Pyrenophora teres f. maculata, were tested for their reaction to three phytotoxins isolated from cultures of the fungus: toxin A [ L, L - N -(2-amino-2-carboxyethyl)aspartic acid], toxin C (aspergillomarasmine A) and toxin B (anhydroaspergillomarasmine A). 0.75 m M toxin A caused mainly dark yellow chlorotic symptoms but little necrosis, whereas leaves treated with 0.25 m M toxin C developed distinct necrotic symptoms and zones of light yellow chlorosis. Toxin B is only weakly toxic, and toxin B and control solutions containing aspartic acid in the concentration of 0.75 m M did not cause any symptoms. The best differentiation between the barleys was obtained by scoring chlorosis after 120 h, and the optimal toxin concentrations for this differentiation were 0.75 m M toxin A and 0.25 m M toxin C, respectively. Results with different toxin concentrations inducing distinct variation in symptom expression indicate that the two toxins have different potencies as phytotoxins. The reaction of the barleys to toxins A and C correlated well with their reaction to infection by P. teres f. teres and P. teres f. maculata, suggesting that toxins A and C may be used to select resistant barley lines in the early stages of a breeding programme.     

Low doses of glyphosate change the responses of soyabean to subsequent glyphosate treatments

Many herbicides promote plant growth at doses well below the recommended application rate (hormesis). The objectives of this study were to evaluate glyphosate‐induced hormesis in soyabean (Glycine max) and determine whether pre‐treating soyabean seedlings with low doses of glyphosate would affect their response to subsequent glyphosate treatments. Seven doses (1.8–720 g a.e. ha^?1) of glyphosate were applied to 3‐week‐old seedlings, and the effects on the electron transport rate (ETR), metabolite (shikimate, benzoate, salicylate, AMPA, phenylalanine, tyrosine and tryptophan) levels and dry weight were determined. The lowest dose stimulated ETR and increased biomass the most. Benzoate levels increased 203% with 3.6 g a.e. ha^?1 glyphosate. Salicylate content and tyrosine content were unaffected, whereas phenylalanine and tryptophan levels were increased by 60 and 80%, respectively, at 7.2 g a.e. ha^?1. Dose–response curves for these three amino acids were typical for hormesis. In another experiment that was replicated twice, soyabean plants were pre‐treated with low doses of glyphosate (1.8, 3.6 or 7.2 g a.e. ha^?1) and treated with a second application of glyphosate (1.8, 3.6, 7.2, 36, 180 or 720 g a.e. ha^?1) 14 days later. For total seedling dry weight, a 3.6 and 7.2 g a.e. ha^?1 glyphosate dose preconditioned the soyabean seedlings to have greater growth stimulation by a later glyphosate treatment than plants with no preconditioning glyphosate exposure. Optimal hormetic doses were generally higher with pre‐treated plants than plants that had not been exposed to glyphosate. Thus, pre‐exposure to low doses of glyphosate can change the hormetic response to later low‐dose exposures.     

Effect of target spot on soybean yield and factors affecting this relationship

The lack of robust estimates of soybean yield losses due to target spot led to this study. The objective was to determine whether soybean yield at stage R8 (W, expressed as kg ha⁻¹) was related to target spot severity at soybean stage R5–R6 (S, expressed as %) and to identify variables that could affect this relationship. Plot-level estimates of mean disease severity and yield from 41 selected Uniform Fungicide Trials carried out in Brazil during 2012–2016 growing seasons were used to estimate linear regression coefficients for the relationship between yield and target spot severity through random-coefficient mixed effects model analysis. The overall estimated mean regression intercept and slope were  = 3564 kg ha⁻¹ (disease-free yield) and  = −17.1 kg ha⁻¹ %⁻¹ (W decrease per percent increase in S), respectively. The model was then refitted with different covariates to determine their effects on model parameters. β₀ was influenced by baseline yield (less than or greater than 3300 kg ha⁻¹) and β₁ was affected by yield response to fungicide treatments. Estimated yield loss at 50% target spot severity ranged from 8% to 42%. Cultivar also had a significant effect on the magnitude of yield reduction due to target spot, which ranged from 11% to 42%, depending on the cultivar.