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The incidence of volunteer EnlistTM soybean in the post-emergence of crops in succession, such as wheat, requires changes in chemical control. Thus, the objective of the work is to evaluate the efficiency of different post-emergence herbicides in the control of volunteer EnlistTM soybean and wild radish and their selectivity to wheat. For this, four experiments were conducted in 2017 and 2018 in field and greenhouse. The treatments tested were pyroxsulam, saflufenacil, pyroxsulam + saflufenacil, pyroxsulam + bentazon, pyroxsulam + metribuzin, saflufenacil + bentazon, and saflufenacil + metribuzin in 2017, and triclopyr, saflufenacil, MCPA, quinclorac, dicamba, pyroxsulam + metribuzin, metribuzin + metsulfuron, pyroxsulam + bentazon and bentazon + metsulfuron in 2018. The variables were the control of wild radish and volunteer EnlistTM soybean phytotoxicity to wheat crop, yield components, and yield total. The association of the herbicides pyroxsulam and saflufenacil is efficient in the management of volunteer soybean EnlistTM, showing selectivity to wheat. The isolated application of dicamba and the associations of pyroxsulam with metribuzin and metribuzin with metsulfuron represent alternatives for selective management of volunteer EnlistTM soybean in wheat, in addition to efficiently controlling wild radish in post-emergence.

Plants synthesize specialized metabolites to defend themselves against pathogens. These active compounds, when isolated and identified, can be used as template for fungicide development. Based on field observations, Heteranthera reniformis (kidney leaf mudplantain) could potentially synthesize compounds with antifungal activity. The goal of this study was to evaluate the fungicidal activity of H. reniformis leaf extracts on Bipolaris oryzae development. The activities of hexane, ethyl acetate, and methanol extracts of H. reniformis leaves were tested on mycelial growth, sporulation, and colony morphology. Due to the highest inhibition of B. oryzae sporulation, methanol extract was chosen for concentration tests. The effect of methanol extract on B. oryzae spore length and germination was also evaluated. Methanolic extract was the most active in inhibiting B. oryzae sporulation. The morphology of the colonies is altered when the fungus grows in medium containing H. reniformis leaf extracts. Higher concentration of methanol extract stimulates mycelial growth and suppresses B. oryzae sporulation. There are reductions in length and number of germinated B. oryzae spores caused by methanol extract of H. reniformis leaves. Methanolic extract has compounds with antifungal activity and should be subjected to bioassay-guided isolation for purification and identification of these active compounds.

The study of herbicide dynamics in the soil and their interaction with the components of the environment makes it possible to ensure the selectivity of crops and the agronomical efficiency. The aim of this research was to evaluate the influence of soil physicochemical properties on the emergence and growth of soybean, with pre-emergence application of various saflufenacil rates. An experiment was carried out in a greenhouse with a completely randomized design, testing different soil types containing “Erechim”, “Santa Maria” and “Eldorado do Sul”, at different saflufenacil rates: 0, 12.5, 25, 50, 100, 200, 400 g a.i. · ha–1. The application was performed 1 day after soybean sowing, and analyzed variables were: the phytotoxicity emergence of seedlings, dry mass and height of the soybean. The saflufenacil effective dose of 50% response in soybean (ED50) and the characteristics of the soils showed that the soil contained clay and sand which were the components most related to the saflufenacil availability to the plants. A lower ED50 by phytotoxicity to the soybean was found in soil with lower and greater content of clay and sand, respectively. The physicochemical properties of soil influenced the saflufenacil activity, having greater potential of injury to soybean in the soil from Eldorado do Sul, due to its clay and sand content.

Competition with weeds and lack of selective herbicides registered for bird’s-foot trefoil crops affect their development and limit productivity. Therefore, this study aimed at evaluating selectivity of pre-emergent herbicides in bird’s-foot trefoil crops. Experiments were carried out in a greenhouse and on a field where the following herbicides were evaluated and compared with the control: imazethapyr, diclosulam, flumetsulam, metribuzin, s-metolachlor, sulfentrazone, clomazone and isoxaflutole. Regarding variables under evaluation, phytotoxicity (PHYTO), plant stature, dry mass of the aerial part (DMAP) and dry mass of roots (DMR) were evaluated in the greenhouse, while plant population, PHYTO and DMAP were assessed on the field. The criterion to determine selectivity were: PHYTO below 15% and not reducing the plant population nor morphological variables, by comparison with the control. The variables were negatively affected by the herbicides clomazone, metribuzin, isoxaflutole, diclosulam, s-metolachlor, in which the crop population was reduced in 98, 92, 83, 63, 48 and 22%, respectively. Following the criteria, only the herbicide sulfentrazone as a pre-emergente is selective to bird’s-foot trefoil crop (cultivar ‘Sao Gabriel’).

Synergic effects of glyphosate and saflufenacil have been reported to control Conyza spp. However, the mechanism of this synergic combination is unknown. The objectives of this study were to investigate the effects of the combination of glyphosate and saflufenacil on the control and resistance status of glyphosate-resistant (GR) C. bonariensis, as well as on oxidative stress and lipidic peroxidation. Glyphosate-resistant and glyphosate-sensitive (GS) biotypes were treated with different rates of saflufenacil, glyphosate, and glyphosate combined with saflufenacil. The combination of glyphosate (1480 g ae ha-1) and saflufenacil (&ge, 15 g ha&minus, 1) presented the best control of GR plants compared with their individual effects. It also reduced the resistance factor from 19.6 to 4.6 (4.3-fold) and represents a good alternative for resistance management. The combination of glyphosate and saflufenacil resulted in higher oxidative stress and lipidic peroxidation compared with the effects of either herbicide alone. The oxidative stress and lipid peroxidation promoted by the combination of the herbicides occurred earlier after treatment and remained at higher levels over a longer period (12&ndash, 192 h) compared with their individual results. The combined oxidative stress and lipid peroxidation at high levels over a long time is likely to be one reason that the combination of glyphosate and saflufenacil effectively controls GR C. bonariensis.

Italian ryegrass (Lolium multiflorum, LOLMU) is one of the most troublesome weeds in temperate regions in the world. This weed species interfere with wheat, corn, rye, and oat, causing significant crop yield losses. This species has evolved glyphosate resistance, making it difficult to control. The mechanisms of glyphosate resistance are still unknown, and an understanding thereof will favor the development of new strategies of management. The present study is the first transcriptome study in LOLMU using glyphosate-resistant and -sensitive biotypes, aiming to identify and to provide a list of the candidate target genes related to glyphosate resistance mechanism. The transcriptome was assembled de novo, producing 87,433 contigs with an N50 of 740 bp and an average length of 575 bp. There were 92 and 54 up- and down-regulated genes, respectively, in the resistant biotype, while a total of 1683 were differentially expressed in the sensitive biotype in response to glyphosate treatment. We selected 14 highly induced genes and seven with repressed expression in the resistant biotype in response to glyphosate. Of these genes, a significant proportion were related to the plasma membrane, indicating that there is a barrier making it difficult for glyphosate to enter the cell.

Biochemical assays in a time-course were employed to evaluate stresses induced by glyphosate treatment in resistant and sensitive biotypes of Conyza bonariensis. Two experiments were conducted assessing glyphosate doses and time-course after treatment. The doses of glyphosate ranged from 0 to 11840 g ae·ha–1 and assessments performed until 552 h after glyphosate treatment (HAT). The objectives of this study were to evaluate the oxidative stress and differential antioxidant enzyme activity in glyphosate-resistant and -sensitive biotypes of hairy fleabane after glyphosate treatment. After treatment, both studied biotypes accumulated similar levels of shikimic-acid until 96 h. The sensitive biotype died at192 HAT. Shikimic-acid and hydrogen peroxide (H2O2) accumulation in glyphosate-resistant biotype were transient and did not differ from untreated plants at 288 and 500 HAT, respectively. In both glyphosate-resistant and -sensitive biotypes, a correlation analysis established a cause-and-effect relationship after glyphosate treatment, which leads to shikimic-acid and hydrogen peroxide accumulation, lipid peroxidation (indicates tissue damage) and an enhancement in the activity of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) enzyme. However, in the glyphosate-resistant biotype, the oxidative stress and tissue damage were lower, and antioxidant enzyme activities SOD, CAT, and APX were higher than in the -sensitive biotype. It indicates that antioxidant enzyme in glyphosate-resistant biotype might be related to the glyphosate-resistance process in Conyza bonariensis. This study is the first report of differential antioxidant enzyme activity in hairy fleabane.

Ryegrass management has been difficult by the occurrence of resistant biotypes to several herbicides with different action mechanisms. Since herbicides mixes and rotations are an important alternative for resistant weed management, the objective of this work was to evaluate the interaction of the dose of the herbicides glufosinate and atrazine on ryegrass control and its seeds’ quality exposed to their association. For this study, three experiments were carried out using factorial design in field, laboratory, and greenhouse conditions. Two factors (A and B) were evaluated in each experiment, where factor A and B represented the doses of glufosinate and atrazine, respectively. Ryegrass control was evaluated in field experiment, while germination percentage and Emergence Speed Index (ESI), were obtained in laboratory and greenhouse analyses, respectively. The data were submitted to variance analysis (P≤0.05) and the significant results were analyzed through response surface graphs. For ryegrass control data, the effect of the interaction was analyzed by the Colby method; glufosinate provides efficient ryegrass control, but its association with atrazine reduces the efficiency, being characterized as an antagonism between molecules. Glufosinate herbicide application, independent of atrazine presence, reduced the ryegrass seeds quality at the post-flowering stage. RESUMEN El manejo de raigrás es difícil debido a la ocurrencia de biotipos resistentes a diversos herbicidas con diferentes mecanismos de acción. Dado que la mezcla de herbicidas y sus rotaciones son una alternativa importante para el manejo de malezas resistentes, el objetivo de este trabajo fue evaluar la interacción de las dosis de los herbicidas glufosinato y atrazina para el control de raigrás y la calidad de sus semillas expuestas a su asociación. Se realizaron tres experimentos usando diseño factorial en condiciones de campo, laboratorio e invernadero. Dos factores (A y B) fueron evaluados en cada experimento, donde el factor A y B representaron las dosis de glufosinato y de atrazina, respectivamente. El control de raigrás fue evaluado en el experimento de campo, mientas que el porcentaje de germinación y el Índice de Velocidad de Emergencia (IVE) se determinaron en laboratorio e invernadero, respectivamente. Los datos fueron sometidos a análisis de la varianza (P≤0,05) y los resultados significativos fueron analizados a través de gráficos de superficie de respuesta. Para los datos de control, el efecto de las interacciones fue analizado por medio del método Colby; el glufosinato proporcionó un eficiente control de raigrás, pero su asociación con atrazina reduce su eficacia, siendo caracterizando como antagonismo entre moléculas. La aplicación del herbicida glufosinato, independiente de la presencia de atrazina, redujo la calidad de las semillas de raigrás en la fase de post-floración.

Background: Plants synthesize compounds of specialized metabolism to defend themselves against biotic and abiotic stresses. These compounds could be used as models for pesticide development. Among the species that have not yet been studied for the potential to produce active compounds is the kidney leaf mud plantain (Heteranthera reniformis). Objective: The goal was to evaluate the effect of hexanic, ethyl acetate and methanolic extracts of H. reniformis leaves on cress (Lepidium sativum) seed germination to determine which one have the highest biological activity; and to evaluate different concentrations of extract with the highest biological activity on lettuce (Lactuca sativa), barnyard grass (Echinochloasp.) and giant arrowhead (Sagittaria montevidensis) germination. Methods: The seeds were placed on petri dishes containing two sheets of germitest paper, and after the application of the extract, they were sealed and placed in growth chambers with controlled temperature and photoperiod. The variables analyzed were 1st and 2nd germination count, germination speed index and length of the aerial part and roots. Results: The ethyl acetate extract provided greater phytotoxicity on cress than the other extracts. In general, the highest concentration of ethyl acetate extract was the most efficient in reducing variables for all species. Conclusions: The ethyl acetate extract of H. reniformis presents inhibitory activity on the seeds of cress, lettuce, giant arrowhead and barnyard grass, but this activity was dependent on the concentration of the extract and the species studied. H. reniformis synthesizes compounds with phytotoxic activity and purification of extracts is required to isolate, identify and characterize the action mechanism of the compounds with herbicide activity, so that in the future these can be used as models for the development of herbicides.

Glyphosate-resistant (GR) Italian ryegrass (LOLMU) and Alexandergrass (URPLA) are troublesome weeds in corn cropping systems in Southern Brazil. The emergence pattern of those weeds is not uniform and may change according to the season’s environmental characteristics. Also, herbicide resistance has been diminishing the success of the weed control programs. The objectives of this study were to evaluate the influence of corn-sowing date on LOLMU and URPLA densities and their control provided by pre- and post-emergent herbicides. Field trials were conducted in two crop seasons in Southern Brazil consisting of three corn sowing date (August, September, and October) and the application of atrazine + S-metolachlor (residual) in corn pre-emergence in different post-emergence weed control programs with glyphosate, ammonium-glufosinate, nicosulfuron, and atrazine. The results indicated that the sowing date had a significant influence on LOLMU and URPLA densities. Corn sown in the earliest period was exposed to a higher LOLMU density, whereas corn sown in the latest period had a higher density of URPLA. Also, the application of residual herbicide at corn pre-emergence reduced both weed species densities and decreased the pressure for the control of glyphosate-resistant LOLMU for the post-emergence herbicides. The use of residual herbicides in corn pre-emergence is an efficient strategy to be considered in the LOLMU and URPLA control programs, followed by post-emergence application of glyphosate, ammonium-glufosinate, atrazine, and nicosulfuron.

Italian ryegrass (Lolium multiflorum Lam.) is a grass weed found in winter cereals, with several glyphosate-resistant diploid populations. Furthermore, the use of Italian ryegrass tetraploid genotypes creates an opportunity to increase the forage demand in replacement of diploid populations. The aim of this research was to evaluate the crossing capacity between glyphosate-resistant diploid and tetraploid Italian ryegrass to transfer glyphosate resistance to the next generation. Reciprocal crosses were performed using the susceptible tetraploid cultivar INIA Titan and resistant diploid (SVA04 biotype) plants to obtain the F1 progeny. Germination testing, survival percentage, inheritance of glyphosate-resistance, and ploidy level were evaluated in F1 progeny. Crossing of susceptible tetraploid plants ♂ and glyphosate-resistant diploid ♀ affected the germination and exhibited 4.5% of triploid plants. F1 progeny from the glyphosate-resistant diploid ♂ and susceptible tetraploid ♀ did not show germination problems, but 46% of the plants died during the initial seedling stage. For this progeny, 10 and 25% of the seedlings were composed of triploid and pentaploid individuals, respectively. Crosses between susceptible tetraploid ♀ and resistant diploid ♂ did not transfer the glyphosate-resistant for the plants. Susceptible tetraploid ♂ crossing with diploid resistant ♀ had a reduction of 47% the glyphosate-resistant plants compared to the homozygous glyphosate-resistant progeny. Overall, tetraploid Italian ryegrass can be a safe tool to reduce and manage the increase of glyphosate-resistant diploid ryegrass in field conditions.

Technologies that advocate the use of herbicide-resistant crops are alternatives to weed control, but they may cause oxidative stress and change secondary metabolism of plants. Therefore, this study aimed to evaluate changes in the secondary metabolism of soybean plants which contained Cultivance® (CV), sulfonylurea-tolerant soybean (STS) and Roundup Ready® (RR) technologies submitted to the application of the mixture of herbicides imazapyr and imazapic in “plant-apply” and “apply-plant” management systems. Two field experiments, in which soybean cultivars were submitted to increasing doses of the mixture of herbicides imazapyr and imazapic, were performed. Aerial parts of plants were collected 10 days after crop emergence and stored at -83oC, until quantification of variables. In general, the soybean cultivar BRS382CV exhibited lower contents of chlorophyll than cultivars CD249STS and NA5909RR. Besides, increasing doses of the mixture of herbicides imazapyr and imazapic decreased contents of chlorophyll in the cultivars. Stress caused by herbicides induced more generation of ROS and effective response of the antioxidant system through enzymes SOD, CAT and APX. RESUMO: A adoção de tecnologias que preconizam a utilização de culturas resistentes a herbicidas é alternativa para controle de plantas daninhas, porém pode causar estresse oxidativo e alterar o metabolismo secundário da cultura. Dessa forma, o objetivo deste trabalho foi avaliar as alterações no metabolismo secundário de plantas de soja contendo as tecnologias Cultivance® (CV), tolerância às sulfonilureias (STS) e Roundup Ready® (RR), submetidas à aplicação da mistura dos herbicidas imazapyr e imazapic nos sistemas de manejo em “plante/aplique e “aplique/plante”. Foram realizados dois experimentos em campo, onde cultivares de soja foram submetidos a doses crescentes da mistura dos herbicidas imazapyr e imazapic. Aos dez dias após a emergência da cultura, foi realizada coleta da parte aérea e armazenada a -83 oC, até a quantificação das variáveis. O cultivar BRS382CV apresenta, em geral, menores teores de clorofila comparado aos cultivares CD249STS e NA5909RR, e o aumento da dose da mistura dos herbicidas imazapyr e imazapic diminui o teor de clorofila das cultivares. O estresse causado pelo herbicida induz maior formação de EROs, ocasionando elevada resposta do sistema antioxidante através das enzimas SOD, CAT e APX.

Background: Enlist E3™ soybean is tolerant to 2,4-D, glyphosate and ammonium-glufosinate and were developed for effective management of herbicide resistant weeds such as glyphosate Herbicides, even being selective, can cause damage to crop metabolism, affect growth and development and interfere with seed physiological quality. Objective: The aim of this research was to evaluate the physiological quality of Enlist E3™ soybean seeds submitted to herbicide application. Methods: The field trial was carried out in a randomized block design with four replications. The treatments tested were 2,4-D choline + glyphosate, 2,4-D choline, glyphosate + 2,4-D amine and ammonium-glufosinate; and control without application, sprayed at V6 soybean growth stage. After harvest, the seeds were submitted to first germination count, accelerated aging, germination speed index, shoot and root length, shoot and root dry mass and electrical conductivity tests. Results: The management of Enlist E3 soybeans with Enlist herbicides (2,4-D choline + glyphosate and 2,4-D choline) as well as glyphosate + 2,4-D amine and glufosinate did not negatively impact soybean parameters such as: vigor, germination count, accelerated aging, germination speed, aerial part and primary root length, aerial part and root dry mass and electrical conductivity. Conclusions: Those herbicides can be recommended to be used on post emergence (V6) of Enlist E3 soybean.

Background: Competition with weeds and the lack of selective herbicides registered for birdsfoot trefoil crops affect their development and limit their productivity. Objective: This study aimed to evaluate selectivity of post-emergent herbicides for weed control in birdsfoot trefoil crops. Methods: Experiments were carried out in a greenhouse and on a field, in both vegetative and reproductive development stages of birdsfoot trefoil crops. Treatments were composed of post-emergent herbicides recommended for soybean, corn and garlic cultivation. Phytotoxicity (PHYTO), plant height (HEI), shoot dry matter (SDM) and root dry matter (RDM) were evaluated. Data were submitted to the analysis of variance and when means were significant, they were compared by the Duncan’s Test (p≤0.05). In order to determine post-emergent herbicides which were selective to the crop, those that provided PHYTO below or equal to 15% were recommended, since they did not significantly interfere with morphological variables HEI, SDM and RDM, by comparison with the control. Results: Unlike results found in the vegetative stage, birdsfoot trefoil plants were more tolerant to phytotoxic effects of herbicides imazethapyr, chlorimuron-ethyl, cloransulam-methyl and fomesafen in the reproductive stage. The variables were negatively affected by the herbicides bentazon, glyphosate and carfentrazone-ethyl, with PHYTO higher than 40% at 20 days after treatment in the vegetative stage. Conclusions: Herbicides imazethapyr, chlorimuron-ethyl and flumetsulam, when applied as post-emergent ones, regardless of the development stage of the species, are selective to birdsfoot trefoil crops, without affecting crop development, whereas herbicides cloransulam-methyl and fomesafen are not selective to them.

The shifting of rice planting date to early spring improved weed control, which is important to achieve high yield. However, early planting date exposes rice seedlings to cold stress, slowing crop establishment and affecting herbicide selectivity. The objective of this study was determine the effects of cold stress and bispyribac-sodium application on rice seedlings’ gene expression and physiological patterns. The experiment was performed in greenhouse in a factorial arrangement, and treatments included: factor A – two planting dates: late September and early November; factor B consisted in bispyribac-sodium application at rate of 50 g ai ha−1 and untreated check. Bispiribac-sodium caused greatest injury to rice seedlings at the early planting date. Lipid peroxidation and total phenol accumulation was stimulated by low temperature but, was not affected by bispyribac-sodium application. Gene expression of OsSOD, OsCAT, OsAPX, OsDREB1A, OsCDPK13, OsCYP72A2, OsGSTL2 and OsGSTU10 were responsive to low temperature and presented upregulation when exposed to the herbicide, providing evidence of an interaction between temperature and herbicide applications. Cold stress likely affects herbicide metabolism and effect rice seedling e oxidation mechanism response to herbicide.

The goals of this study were to evaluate herbicide application rates at different timings for preharvest desiccation of wheat (Trial 1), as well as to evaluate the effect of the timing of herbicide desiccation at preharvest and harvest timing (Trial 2) on yield, germination, and herbicide residue in wheat seed. In Trial 1, treatments consisted of two application rates of glufosinate, glyphosate, paraquat, or paraquat+diuron and a control without application; application time periods were in the milk grain to early dough stage, soft dough to hard dough stage, and hard dough stage. In Trial 2, treatments consisted of different application time periods (milk grain to early dough stage, and soft dough to hard dough stage), different herbicides (glufosinate, 2,4-D+glyphosate, and untreated control), and different harvest times (5, 10 and 15 days after herbicide application). One thousand seeds weight, yield, first and final germination count, and herbicide residue on seeds were evaluated. Preharvest desiccation with paraquat, glufosinate, and 2,4-D+glyphosate at the milk grain to early dough stage reduces wheat yield. Regardless of the herbicide and application rate, application in the milk grain to early dough stage and soft dough to hard dough stage provides greater germination of wheat seeds, except at the lower dose of paraquat. Systemic herbicides accumulate more in wheat seeds. Resumo: Os objetivos foram avaliar doses de herbicidas em diferentes épocas de dessecação pré-colheita do trigo (Experimento 1); e, o efeito de herbicidas em diferentes épocas de dessecação pré-colheita e épocas de colheita (Experimento 2) sobre a produtividade, germinação e resíduos de herbicidas em sementes de trigo. No experimento 1, os tratamentos foram: duas doses e testemunha sem aplicação dos herbicidas glufosinate, glyphosate, paraquat, paraquat+diuron; e, as épocas de aplicação foram: grão leitoso a pastoso, grão pastoso a farináceo e grão farináceo duro. No experimento 2, os tratamentos foram as épocas de aplicação: grão leitoso a pastoso e grão pastoso a farináceo; os herbicidas: glufosinate, 2,4-D+glyphosate e testemunha sem aplicação; e, as épocas de colheitas: 5, 10 e 15 dias após aplicação. Avaliaram-se massa de mil sementes, produtividade, primeira e contagem final da germinação e resíduo dos herbicidas nas sementes. A dessecação pré-colheita com paraquat, glufosinate e 2,4-D+glyphosate em estádio de grão leitoso a pastoso reduz a produtividade do trigo. Independente do herbicida e dose, aplicação em estádio de grão leitoso a pastoso e grão pastoso a farináceo proporciona maior germinação de sementes de trigo, exceto a menor dose de paraquat. Herbicidas sistêmicos acumulam-se mais nas sementes de trigo.

Herbicide resistance can confer lower competitive abilities; however scarse information is available about the photosynthetic performance between glyphosate-resistant and -susceptible hairy fleabane biotypes coming from areas with similar weed management history. Thus, the goal was to evaluate the photosynthetic performance under different light intensities between glyphosate-resistant and -susceptible hairy fleabane biotypes, from RR soybean fields with a similar weed management history. The tested factors were glyphosate resistant and susceptible biotypes and 12 levels of photosynthetic photon flux density. Plants were cultivated in plastic cups, and at the stage of 10-12 leaves they were subjected to treatments with artificial lighting systems. The net photosynthetic rate, stomatal conductance, substomatal CO2 concentration, transpiration rate, instantaneous water use efficiency, light compensation point and quantum yield were evaluated. In all the evaluated photosynthetic parameters, biotype R showed superior characteristics compared to susceptible biotypes, with the exception of the transpiration rate, where there were no differences. The differences between biotypes may not be associated to glyphosate resistance or susceptibility, but to the evolutionary characteristics of the biotypes. RESUMO: A resistência a herbicidas pode conferir menor capacidade competitiva, porém limitadas informações estão disponíveis sobre o desempenho fotossintético entre biótipos resistentes e suscetíveis ao glyphosate provenientes de área com similar histórico no manejo de plantas daninhas. Assim, o objetivo deste trabalho foi avaliar o desempenho fotossintético sob diferentes intensidades luminosas entre biótipos de buva resistente e suscetível ao glyphosate, oriundos de área de lavoura de soja Roundup Ready® com histórico similar de manejo de plantas daninhas. Os fatores testados foram biótipos resistentes e suscetíveis ao glyphosate e 12 níveis de densidade de fluxo de fótons fotossintéticos. As plantas foram cultivadas em copos plásticos e, no estádio de 10-12 folhas submetidas ao tratamento com sistema de luz artificial. Foram avaliados taxa fotossintética líquida, condutância estomática, concentração de CO2 subestomática, taxa transpiratória, eficiência instantânea do uso da água, ponto de compensação de luz e rendimento quântico. Em todos os parâmetros fotossintéticos avaliados, o biótipo R apresentou características superiores comparado ao biótipo suscetível, com exceção da taxa transpiratória, em que não houve diferenças. As diferenças entre biótipos podem não estar associadas à resistência ou suscetibilidade ao glyphosate, e sim às características evolutivas dos biótipos.

The goosegrass (Eleusine indica (L.) Gaertn) is an annual plant that has a low-level resistance to glyphosate (LLRG), resulting in control failure in genetically modified soybean crops for resistance to this herbicide. Alleles related to resistance may cause changes in the plant biotype, such as inferior competitive ability. Thus, the objective of this work was to evaluated the competitive ability of soybean crops and susceptible and resistant (LLRG) goosegrass biotypes. Replacement series experiments were conducted with soybean crops and goosegrass biotypes. The ratios of soybean to susceptible or resistant (LLRG) goosegrass plants were 100:0, 75:25, 50:50, 25:75 and 0:100, with a total population of 481 plants m-2. The leaf area, plant height and shoot dry weight were evaluated at 40 days after emergence of the soybean crops and weeds. The soybean crop had superior competitive ability to the susceptible and resistant (LLRG) goosegrass biotypes. The soybean crop showed similar competitive ability in both competitions, either with the susceptible or resistant (LLRG) goosegrass biotypes. The intraspecific competition was more harmful to the soybean crop, while the interspecific competition caused greater damage to the goosegrass biotypes competing with the soybean crop. RESUMO O capim pé-de-galinha (Eleusine indica (L.) Gaertn) é uma planta anual, que apresenta resistência de nível baixo (RNB) ao herbicida glifosato o que acarreta em falhas de controle em lavouras de soja geneticamente modificadas para resistência ao herbicida. Os alelos relacionados com a resistência podem acarretar em custos de adaptação ao biótipo, conferindo menor habilidade competitiva. Diante disso, o objetivo da pesquisa foi comparar a habilidade competitiva da cultura da soja com os biótipos de capim pé -de-galinha suscetível ou com RNB. Para isso, foram conduzidos experimentos em série de substituição entre a cultura da soja e os biótipos de capim pé-de-galinha. As proporções entre plantas de soja e capim pé-de-galinha suscetível ou com RNB foram de 100:0, 75:25, 50:50, 25:75 e 0:100, com população total de 481 plantas m -2. Avaliaram-se a área foliar (AF), estatura de planta (EST) e a massa da matéria seca da parte aérea (MMSPA), aos 40 DAE da cultura da soja e da planta daninha. A cultura da soja tem habilidade competitiva superior aos biótipos de capim pé-de-galinha suscetível ou com RNB. A habilidade competitiva da soja não foi diferencial frente à competição com os biótipos de capim pé-de-galinha suscetível ou com RNB. A competição intraespecífica para a cultura da soja e a competição interespecífica para os biótipos de capim pé-de-galinha, causam maiores danos aos competidores.

High seed production and dispersal capacity and glyphosate resistance are among the main factors that have made hairy fleabane (Conyza bonariensis) one of the most important and dispersed weeds in the world. Herbicide-resistant weeds populations may have fitness cost due to molecular, physiological, and biochemical changes. This study aimed to evaluate the physiological quality of seeds of Conyza spp. and determine whether glyphosate resistance causes fitness costs for resistant biotypes. Seeds from six hairy fleabane biotypes, three glyphosate-resistant and three -sensitive, with a resistance factor average of 11.7 were studied. Among the studied biotypes, five were identified as C. bonariensis and one as C. blakei. Seed analyses were performed in a completely randomized design with ten replications of 100 seeds each (1,000 seeds per biotype). The analyzed seeds were originated from second-generation self-pollinating plants with known segregation rate. The mean results indicate that, in relation to sglyphosate-sensitive biotypes of C. bonariensis, seeds from -resistant biotypes showed a 16% reduction in vigor and 13% in germination, a 44% increase in the number of empty seeds and approximately five times more viable dormant seeds. The lower physiological quality of glyphosateresistant hairy fleabane seeds regarding to -sensitive indicates that resistance affect the seed’s physiology and causes a fitness costs. It implies a reduction of invasive potential and persistence in the environment of resistant biotypes. Therefore, in the absence of glyphosate as a selective factor, the frequency of resistant biotypes tends to decrease and increase the predominancy of glyphosate-sensitivre biotypes. However, the highest number of viable dormant seeds of resistant biotypes supplies the soil seed bank. All biotypes of C. bonariensis showed higher physiological quality of seeds when compared to C. blakei, indicating that the first species is more adaptably evolved for survival in agricultural and disturbed areas. Keywords: herbicide resistance, integrated weed management, weed biology, soil seed bank, Conyza blakei. RESUMO - A alta capacidade de produção e dispersão de sementes e a resistência ao glyphosate estão entre os principais fatores que tornaram a buva (Conyza bonariensis) uma das mais importantes e dispersas plantas daninhas no mundo. Populações de plantas resistentes a herbicidas podem apresentar penalidades em função das alterações moleculares, fisiológicas e bioquímicas. O objetivo deste trabalho foi avaliar a qualidade fisiológica das sementes de biótipos de Conyza spp. e determinar se a resistência ao glyphosate causa penalidades aos biótipos resistentes. Foram avaliadas sementes de seis biótipos de buva, sendo três resistentes e três sensíveis ao glyphosate, com fator de resistência de 11,7. Entre os biótipos estudados, cinco foram identificados como C. bonariensis e um como C. blakei. As análises das sementes foram realizadas no delineamento completamente casualizado com dez repetições de 100 sementes cada (1.000 sementes por biótipo). As sementes utilizadas nas análises foram originadas de plantas de segunda geração de autopolinização com taxa de segregação conhecida. Os resultados médios indicam que, em relação aos biótipos sensíveis de C. bonariensis, as sementes dos biótipos resistentes apresentaram redução de 16% no vigor e 13% na germinação, aumento de 44% no número de sementes vazias e em torno de cinco vezes mais sementes dormentes viáveis. A menor qualidade fisiológica de sementes da buva resistente ao glyphosate indica que a resistência causa penalidade. Essa penalidade implica redução do potencial invasivo e persistência no ambiente dos biótipos resistentes. Assim, na ausência do fator seletivo glyphosate, a frequência de biótipos resistentes tende a diminuir e retornar a suscetibilidade. Entretanto, o maior número de sementes dormentes viáveis dos biótipos resistentes abastece o banco de sementes do solo. Todos os biótipos de C. bonariensis apresentaram maior qualidade fisiológica das sementes em comparação ao biótipo de C. blakei, indicando que a primeira espécie é mais evoluída do ponto de vista adaptativo para sobrevivência em áreas agrícolas. Palavras-chave: resistência a herbicidas, manejo integrado de plantas daninhas, biologia de plantas daninhas, banco de sementes do solo, Conyza blakei. Made available in DSpace on 2019-12-03T18:11:06Z (GMT). No. of bitstreams: 1 ID447962019v37e019213902PlantaDaninha.pdf: 1041990 bytes, checksum: 4269f611fd5639090a217be0ff586616 (MD5) Previous issue date: 2019

The commercialization of ryegrass seeds with the presence of resistant biotypes is a serious issue that increses the dispersion of resistance to new areas without this problem. Therefore, this study aimed to develop a quick test to detect susceptible and resistant seeds to the glyphosate herbicide in order to identify contaminated seed lots with glyphosate resistance. Three experiments were carried out, one in greenhouse and the other two in the seed laboratory. First, the resistance factor (RF) was determined by a dose-response curve experiment in biotypes suspected to be resistant and susceptible to glyphosate. Then, the germination test was conducted with the selected biotypes under increasing glyphosate rates (0, 3.5, 6.9, 13.9, 27.8, 55.5, 111, 222, 445, 890, and 1,780 mg a.e. L-1), as the second experiment. The third experiment was made to verify the methodological efficiency of the germination test with glyphosate to identify different contamination ratios (0, 4, 12, 36, and 100%) of the resistant biotype in the seed lot. The different levels of susceptibility of the biotypes to glyphosate were confirmed by the RF of 154.7 based on C50. Germination of the susceptible biotype was inhibited more than 99% by the rate of 127 mg a.e. L-1, while the resistant biotype was a little affected. The germination test with 127 mg a.e. L-1 of glyphosate showed contaminations of 2, 5, 19, 39, and 86% in lots with 0, 4, 12, 36, and 100% of contaminated seeds, respectively. This methodology can detect glyphosate susceptible and resistant seeds and identify contaminated seed lots with resistant glyphosate biotypes. RESUMO: A comercialização de sementes de azevém com a presença de biótipos resistentes promove a dispersão da resistência para áreas isentas do problema. Diante disso, o objetivo deste trabalho foi desenvolver teste rápido para diferenciação de sementes suscetíveis e resistentes ao herbicida glifosato, visando identificar lotes contaminados com sementes de biótipos resistentes. Foram realizados três experimentos, sendo um em casa de vegetação e dois em laboratório. No primeiro, determinou-se o fator de resistência (FR) em experimento de curva dose-resposta em biótipos com suspeita de serem resistente e suscetível. No segundo, realizou-se teste de germinação dos biótipos, sob doses crescentes de glifosato (0; 3,5; 6,9; 13,9; 27,8; 55,5; 111; 222; 445; 890; e 1.780 mg e.a. L-1. No terceiro, avaliou-se a eficiência da metodologia do teste de germinação com glifosato para identificação de diferentes proporções de contaminação (0, 4, 12, 36 e 100%) do biótipo resistente no lote de sementes. A suspeita dos biótipos foi comprovada em razão dos diferentes níveis de suscetibilidade ao herbicida glifosato, sendo o FR de 154,7 com base na C50. A dose de 127 mg e.a. L-1 inibiu em mais de 99% a germinação do biótipo suscetível, enquanto o biótipo resistente foi pouco afetado. A partir do teste de germinação, identificou-se contaminação de 2, 5, 19, 39 e 86% em lotes com a presença de 0, 4, 12, 36 e 100% de sementes contaminadas, respectivamente, quando expostas à dose de 127 mg e.a. L-1. A metodologia testada possibilitou diferenciar sementes suscetíveis e resistentes ao herbicida glifosato e identificar lotes de sementes contaminadas com biótipos resistentes.

In the State of Rio Grande do Sul (RS), Southern Brazil, glyphosate has not been capable of controlling wild poinsettia (Euphorbia heterophylla L.) in soybean fields, thus, suggesting resistance to this herbicide. Therefore, this study aimed at evaluating sensitivity of wild poinsettia biotypes to glyphosate, identifying the occurrence of resistance of wild poinsettia to the herbicide in RS state and determining the resistance factor of wild poinsettia biotypes under suspicion, besides assessing other herbicides as alternative controls. Two greenhouse experiments, which lasted two years, were conducted by a completely randomized design with four replications. Six biotypes (Factor A) and eight doses of glyphosate (Factor B) were used for getting the dose-response curve. Regarding the alternative control, post-emergence herbicides for soybean and corn crops were tested. Control and dry mass of the shoot were analyzed as variables. Resistance factors of resistant biotypes 20.2 and 21.1 were 4.83 and 5.29, respectively, by comparison with the susceptible biotype (11.4). In RS state, there has currently been high selection pressure due to the intensive use of glyphosate against wild poinsettia plants, as the result of the occurrence of biotypes 20.2 and 21.1 which have low levels of resistance to glyphosate and very little control by ALS-inhibiting herbicides. Therefore, an alternative to mitigate the problem is the use of herbicides with different mechanisms of action. As falhas de controle de leiteira (Euphorbia heterophylla L.) após aplicação de glyphosate em lavouras de soja do Rio Grande do Sul (RS) são frequentes, sugerindo a resistência ao herbicida. Diante disso, os objetivos foram avaliar a sensibilidade de biótipos de leiteira ao herbicida glyphosate, identificar a ocorrência da resistência, determinar o fator de resistência de biótipos de leiteira com suspeita de resistência e avaliar herbicidas alternativos para o seu controle. Foram conduzidos dois experimentos em casa de vegetação, em delineamento inteiramente casualizado com quatro repetições ambos realizados em dois anos. No experimento de curva dose-resposta foram utilizados cinco biótipos (fator A) e oito doses do herbicida glyphosate (fator B). Para o controle alternativo, foram testados herbicidas em pós emergência das culturas de soja e milho. As variáveis analisadas foram controle e massa seca da parte aérea. O fator de resistência dos biótipos resistentes (20.2 e 21.1) foram 4,83 e 5,29 comparativamente ao biótipo suscetível (11.4) respectivamente. Existe elevada pressão de seleção pelo glyphosate em plantas de leiteira no RS, observando-se a ocorrência de biótipos 20.2 e 21.1 com resistência de nível baixo ao herbicida e com controle reduzido pelos herbicidas inibidores de ALS. Portanto, uma alternativa para atenuar o problema é o uso de herbicidas com diferentes mecanismos de ação.

Resistance to herbicides is one of the main factors responsible for weed control failures. Once uncontrolled and stressed, resistant weeds demand a new application of herbicides from different modes of action, which results in higher monetary costs and environmental impact. Knowledge of weed sensitivity levels to herbicides before making decisions for their management in the field is paramount to increasing the efficiency of integrated weed management. Thus, methods that allow the rapid determination of sensitivity levels can help to the correct recommendation before the application, and thus, favor the greater technical, economic and environmental efficiency of weed management. The objective of this work was to validate a rapid method to detect the levels of sensitivity of black picker (Bidens pilosa) and horseweed (Conyza sumatrensis) to saflufenacil. Dose-response experiments were performed in growth chamber, greenhouse and field. The control provided by different doses of the saflufenacil herbicide was evaluated in each environment, and the results correlated within each species. The results showed a significant positive correlation for the results obtained in growth chamber and greenhouse for black picker and horseweed. These results indicate that the method developed in the growth chamber can replace greenhouse tests for determination of the sensitivity of black picker and horseweed to saflufenacil.

Ryegrass is an important weed in wheat cultivations due to the evolution of resistance to different mechanisms of action. This study aimed to compare the phenological development, fitness cost, and competitive ability between ryegrass biotypes susceptible and with multiple resistance to 5-enolpyruvylshikimate3-phosphate synthase (EPSPs) and acetolactate synthase (ALS) inhibiting herbicides. Fitness cost and phenological development were evaluated from biotypes grown in pots, and morphological growth variables were determined up to 140 days after emergence. Phenological development was evaluated with a fitness cost. Competitive ability was determined in a replacement-series experiment with proportions of resistant and susceptible ryegrass. The tested proportions were 100:0 (pure resistant ryegrass stand), 75:25, 50:50, 25:75, and 0:100% (pure susceptible ryegrass stand), where the number of tillers, height, leaf area, and shoot dry matter were evaluated at 50 days after emergence. The longer tillering period of resistant ryegrass was the main factor involved in the difference in phenological development between biotypes. The resistant biotype was superior to the susceptible regarding height, shoot dry matter, and absolute growth rate, while the susceptible biotype had a higher number of tillers and leaf area ratio. Thus, the resistant biotype had no fitness cost. For competitive ability, no difference was observed between biotypes in the different tested proportions when they occupied the same ecological niche. Keywords: Lolium multiflorum, EPSPs, ALS, competition. RESUMO - O azevém é planta daninha importante nos cultivos de trigo devido à evolução da resistência a diferentes mecanismos de ação. O objetivo deste estudo foi comparar o desenvolvimento fenológico, custo adaptativo e habilidade competitiva entre biótipos de azevém suscetível e com resistência múltipla aos herbicidas inibidores da 5-enolpiruvilchiquimato-3-fosfato sintase (EPSPs) e acetolactato sintase (ALS). Para avaliar o custo adaptativo e o desenvolvimento fenológico, os biótipos foram cultivados em vasos, e as variáveis morfológicas de crescimento foram avaliadas até os 140 dias após a emergência. O desenvolvimento fenológico foi avaliado juntamente com o custo adaptativo. A habilidade competitiva foi determinada em experimento de série de substituição com proporções de azevém resistente e suscetível. As proporções testadas foram: 100:0 (estande puro de azevém resistente), 75:25, 50:50, 25:75 e 0:100% (estande puro de suscetível), onde o número de afilhos, a estatura, área foliar e massa seca da parte aérea foram avaliados aos 50 dias após a emergência. O maior período de afilhamento do azevém resistente é o principal fator envolvido na diferença do desenvolvimento fenológico entre os biótipos. O biótipo resistente é superior ao suscetível quanto a estatura (EP), massa seca da parte aérea (MSPA) e taxa de crescimento absoluto (TCA), enquanto o suscetível possui maior número de afilhos (NA) e razão de área foliar (RAF). Assim, o biótipo resistente não apresenta custo adaptativo. Para a habilidade competitiva, verificou-se que não há diferença entre os biótipos nas diferentes proporções testadas quando ocupam o mesmo nicho ecológico. Palavras-chave: Lolium multiflorum, EPSPs, ALS, competição Made available in DSpace on 2019-10-23T00:39:15Z (GMT). No. of bitstreams: 1 ID447052019v37e019197532PlantaDaninha.pdf: 5383418 bytes, checksum: 1cd23988c21aaaf119344389707802ef (MD5) Previous issue date: 2019

Glyphosate-resistant hairy fleabane [Conyza bonariensis (L.) Cronq.] is one of the most important weeds in the world. Among the factors that make this weed species widely distributed in the most diverse environments is the high seed production capacity and dispersal. Hairy fleabane plants not controlled by herbicide application regrowth and overcome crop canopy, use environmental resources, interfere with crops, and complete their life cycle by producing thousands of seeds and replenishing the seed bank. Management strategies that reduce production and viability of hairy fleabane seeds can be adopted within the integrated management to reduce the seed bank and prevent further infestations. In this way, experiments were carried out in a greenhouse and laboratory of seed analysis to evaluate the effect of glyphosate (1,480 g a.e. ha-1) on the production and viability of glyphosate-resistant hairy fleabane seeds when applied at the vegetative and reproductive stages. Seed production was reduced by 68.4 and 100% when glyphosate was applied on hairy fleabane plants at the vegetative and early reproductive stages, respectively, regarding to the control. The viability of hairy fleabane seeds was not influenced by treatments at the evaluated stages. However, glyphosate treatment reduced the hairy fleabane seed production when applied at the vegetative stage . Hairy fleabane seed production is not feasible when glyphosate is applied at the early reproductive stage. RESUMO: A buva [Conyza bonariensis (L.) Cronq.] resistente ao glyphosate é uma das principais plantas daninhas do mundo. Um dos fatores que fazem com que esta planta esteja amplamente distribuída nos mais diversos ambientes é sua alta capacidade de produção e dispersão de sementes. Plantas de buva não controladas pela aplicação de herbicidas rebrotam e sobressaem-se ao dossel da cultura, se beneficiam dos recursos do ambiente, interferem com as culturas, completam seu ciclo produzindo milhares de sementes e realimentando o banco de sementes. Estratégias de manejo que reduzam a produção e viabilidade de sementes de buva podem ser adotadas dentro do manejo integrado, a fim de o banco de sementes e prevenir futuras infestações. Foram realizados experimentos em casa de vegetação e em laboratório de análise de sementes com o objetivo de avaliar o efeito da aplicação de glyphosate nos estádios vegetativo e reprodutivo na produção e viabilidade de sementes de buva resistente ao glyphosate (1.480 g e.a. ha-1). Os resultados demonstram que a produção de sementes reduziu em 68,4% e 100% quando o glyphosate foi aplicado em plantas de buva nos estádios vegetativo e início do reprodutivo, respectivamente, em relação a plantas não tratadas. A viabilidade das sementes de buva não foi influenciada pelos tratamentos nos estádios avaliados. Entretanto, a aplicação do glyphosate no estádio vegetativo da buva reduz a produção de sementes. A produção de sementes de buva é inviabilizada quando o glyphosate é aplicado no início do estádio reprodutivo.

Among the species of the genus Cyperus occurring in paddy rice, C. esculentus, C. difformis and C. iria are the most important, and the latter two are reported as resistant to herbicides in Rio Grande do Sul (RS). The aim of this work was to characterize and mapping the occurrence of resistant plants of the genus Cyperus in areas of paddy rice in RS State, and to analyze the agronomic factors that interfere in the resistance selection. Seeds from individual plants were harvested in the 2014/15 crop, characterized as control failures by the application of acetolactate synthase inhibitors (ALS), totaling 43 samples. At the time of collection, the grower was inquired on aspects related to the management of weeds in the crop. Seeds were germinated in BOD and when seedlings were in two leaves stage they were transplanted into 0.3 L pots containing substrate. When the plants had 4-6 leaves, imazapyr + imazapic was spray at the registration rate. Thirty days after application, control of the tested biotypes was evaluated, converting the data to binary scale, where zero (0) and one (1) correspond to susceptibility and resistance, respectively. The agronomic factors that denote the high selection pressure of resistant biotypes are the consecutive use of Clearfield® technology, the use of higher doses than the registration and the low crop rotation adoption. Although not mentioned as one of the main weeds, it is observed that almost half of the samples collected from plants of the genus Cyperus are resistant to the ALS inhibitors, distributed in almost all the growing regions. RESUMO: Entre as espécies do gênero Cyperus ocorrentes na lavoura de arroz, destacam-se C. esculentus, C. difformis e C. iria, sendo as duas últimas relatadas como resistentes a herbicidas no Rio Grande do Sul (RS). Os objetivos deste trabalho foram caracterizar e mapear a ocorrência de plantas resistentes do gênero Cyperus em áreas de arroz irrigado no RS e analisar os fatores agronômicos que interferem na seleção da resistência. Foram realizadas coletas de sementes de plantas individuais na safra de 2014/15, caracterizadas como falhas de controle pela aplicação de inibidores da acetolactato sintase (ALS), totalizando 43 amostras. Por ocasião da coleta, o produtor foi arguido sobre aspectos relacionados ao manejo de plantas daninhas na lavoura. Na sequência, as sementes foram germinadas em BOD e, quando as plântulas estavam em estádio de até duas folhas, transplantadas para vasos com capacidade para 0.3 L contendo substrato. Quando as plantas apresentavam entre 4 e 6 folhas, foi aplicado imazapyr+imazapic na dose de registro. Aos 30 dias após a aplicação, foi avaliado controle dos biótipos testados, convertendo-se os dados em escala binária, em que zero (0) e um (1) correspondem a suscetibilidade e resistência, respectivamente. Os fatores agronômicos que denotam a alta pressão de seleção de biótipos resistentes são o uso consecutivo da tecnologia Clearfield®, o uso de doses superiores à de registro e a baixa adoção de rotação de culturas. Mesmo não sendo citada como uma das principais plantas daninhas, observa-se que quase a metade das amostras coletadas de plantas do gênero Cyperus são resistentes aos inibidores da ALS, distribuídas na quase totalidade das regiões de cultivo.

The appearance of soybean cultivars that are tolerant to herbicides from the imidazolinone group enables irrigated rice rotation conducted on Clearfield® system. The objective of this work was to evaluate the morphological and metabolic changes of soybean cultivars containing Cultivance® (CV), which is tolerant to imidazolinone, sulphonylurea toletant (STS) and Roundup Ready® (RR), which is tolerant to glyphosate as affected by carryover of increasing doses of imazapyr and imazapic herbicides mixture, applied in the management of irrigated rice crop. Thus, experiments were conducted on the field and in greenhouse, evaluating phytotoxicity, height, leaf area, shoot dry matter, as well as variables related to the secondary metabolism of plants like chlorophyll, carotenoids, hydrogen peroxide, lipid peroxidation and electrolytes leakage. Soybean cultivars RR and STS are susceptibles to the carryover of imazapyr and imazapic mixture applied in the management of irrigated rice crop, whereas the CV cultivar is resistant. The rise in the herbicide carryover dose increases the reactive oxygen species (ROS) production in soybean plants. The RR cultivar, in general, shows higher ROS production compared to the other soybean cultivars. RESUMO: O surgimento de cultivares de soja tolerante a herbicidas do grupo das imidazolinonas possibilita a rotação de culturas com arroz irrigado, cultivado em sistema Clearfield®. O objetivo deste trabalho foi avaliar as alterações morfológicas e metabólicas de cultivares de soja contendo as tecnologias Cultivance® (CV), que é tolerante às imidazolinonas, tolerância às sulfonilureias (STS), e Roundup Ready® (RR), que é tolerante ao glyphosate, frente ao resíduo de doses crescentes da mistura dos herbicidas imazapyr e imazapic, aplicados no manejo da cultura do arroz irrigado. Para isso, foram realizados experimentos em campo e em casa de vegetação, onde foram avaliadas a fitotoxicidade, estatura, área foliar, massa da matéria seca da parte aérea, além de variáveis relacionadas ao metabolismo secundário das plantas, como teor de clorofilas e carotenoides, teor de peróxido de hidrogênio, peroxidação lipídica e extravasamento de eletrólitos. Os cultivares de soja RR e STS são suscetíveis ao resíduo da mistura dos herbicidas imazapyr e imazapic aplicado no manejo da cultura do arroz irrigado, enquanto o cultivar CV é resistente. A elevação da dose do resíduo do herbicida aumenta a produção de espécies reativas de oxigênio (EROs) em plantas de soja. O cultivar RR, em geral, apresenta maior produção de EROs, comparado aos demais.

The hairy fleabane ( Conyza bonariensis (L.) Cronq.) is among the most problematic glyphosate-resistant weeds to manage around the world. In weed science, molecular approaches such as RNA sequencing (RNA-Seq) and quantitative reverse-transcription polymerase chain reaction (RT-qPCR) have been employed to study molecular responses to glyphosate treatment in Conyza species. Glyphosate treatment leads to reactive oxygen species (ROS) production in plants which could damage the RNA. Degraded RNA is an issue and can compromise further molecular analysis. Thus, the objective of this study was to evaluate whether glyphosate treatment interferes negatively on RNA integrity of glyphosate-resistant and -sensitive hairy fleabane biotypes. Two experiments were performed using glyphosate doses from 0 to 11,840 g a.e. ha-1 and evaluated in a time-course until 288 hours after treatment. The total of 86 RNA samples were evaluated. The RNA integrity was evaluated in a Bioanalyzer 2100 equipment according to RNA integrity number (RIN) scores and electrophoresis gel. The RIN scores ranged from 5.1 to 9.0. Glyphosate doses do not reduce the RIN scores in both glyphosate-resistant and -sensitive biotypes of hairy fleabane. Visual and automatic analysis of electrophoresis gel show suitable results for all RNA samples, with well-defined bands at 28S and 18S positions and no degradation. The results of the analysis indicate that glyphosate treatment does not affect the RNA integrity of glyphosate-resistant and -sensitive biotypes of hairy fleabane until 288 and 192 hours after glyphosate treatment, respectively. The RNA integrity analysis provides useful results to evaluate the RNA condition for further analysis. However, the costs were around US$ 14.25 per sample, considering only reagents. These results are useful for planning future time-course experiments in Conyza spp. after glyphosate treatment. RESUMO: A buva (Conyza bonariensis (L.) Cronq.) está entre as plantas daninhas resistentes ao glifosato mais difíceis de serem manejadas em todo o mundo. Na ciência das plantas daninhas, abordagens moleculares, como o sequenciamento de RNA (RNA-Seq) e a reação da transcriptase reversa da polimerase em tempo real (RT-qPCR), têm sido empregadas para estudar as respostas moleculares ao tratamento com glifosato em espécies de Conyza. No entanto, o tratamento com glifosato leva à produção de espécies reativas de oxigênio (ROS) em plantas, que podem danificar o RNA. A degradação do RNA é um problema e pode comprometer futuras análises moleculares. Assim, o objetivo deste estudo foi avaliar se o tratamento com glifosato interfere negativamente na integridade do RNA de biótipos de buva resistente e sensível ao glifosato. Dois experimentos foram realizados utilizando doses de glifosato de 0 a 11.840 g e.a. ha-1 e avaliados em um tempo de até 288 horas após o tratamento. O total de 86 amostras de RNA foram avaliadas. A integridade do RNA foi avaliada em um equipamento Bioanalyzer 2100 de acordo com escores de número de integridade de RNA (RIN) e em gel de eletroforese. Os escores do RIN variaram de 5,1 a 9,0. Doses de glifosato não reduziram os escores do RIN em biótipos de buva resistentes e sensíveis ao glifosato. A análise visual e automática do gel de eletroforese mostrou resultados adequados para todas as amostras de RNA, com bandas bem definidas nas posições 28S e 18S e sem degradação. Os resultados da análise indicam que o tratamento com glifosato não afeta negativamente a integridade do RNA dos biótipos resistentes e sensíveis ao glifosato da buva até 288 e 192 horas após o tratamento com glifosato, respectivamente. A análise da integridade do RNA fornece resultados úteis. Entretanto, os custos são altos e ficaram em torno de US $ 14,25 por amostra, considerando apenas os reagentes. Esses resultados são úteis para o planejamento de experimentos futuros em Conyza spp. após o tratamento com glifosato.

The objective of this work was to compare wild poinsettia (Euphorbia heterophylla) biotypes as to their morphological characteristics, as well as to determine their genetic similarity in the state of Rio Grande do Sul, Brazil, and to confront the light compensation point of susceptible biotypes and of biotypes with low-resistance level to glyphosate. Besides the morphology analysis, the study included the genetic characterization, by AFLP, of susceptible (GR50= 58.65 g ha-1 a.e.) biotypes and of biotypes with low resistance (GR50= 310.36 g ha-1 a.e.) to glyphosate. The competitive ability of the biotypes was inferred according to their light compensation point. The observed morphological characteristics do not allow to differentiate biotypes as to their geographical location, or their resistance level to glyphosate. The genetic analysis identified low genetic diversity among the 15 tested biotypes, with a large amount of subgroups. The biotypes with low resistance formed an isolated group. The susceptible biotypes showed the lowest values of light compensation point and, possibly, they have a greater competitive ability under low-luminosity conditions. The evaluated characteristics do not enable to differentiate genotypes with different levels of glyphosate resistance. Resumo: O objetivo deste trabalho foi comparar biótipos de leiteira (Euphorbia heterophylla) quanto a suas características morfológicas, assim como determinar sua similaridade genética no Rio Grande do Sul e confrontar o ponto de compensação de luz de biótipos suscetíveis e com baixa resistência ao glifosato. Além da análise morfológica, o estudo incluiu a caracterização genética, por meio de AFLP, dos biótipos suscetíveis (GR50= 58,65 g ha-1 e.a.) e dos biótipos com baixa resistência (GR50= 310,36 g ha-1 e.a.) ao glifosato. A habilidade competitiva dos biótipos foi inferida por meio de seus pontos de compensação de luz. As características morfológicas observadas não permitem diferenciar os biótipos quanto à localização geográfica ou ao grau de resistência ao glifosato. A análise genética identificou baixa diversidade genética entre os 15 biótipos de leiteira testados, com formação de elevado número de subgrupos. Os biótipos com baixa resistência formaram um grupo isolado. Os biótipos suscetíveis apresentaram os menores valores de ponto de compensação de luz e, possivelmente, têm maior habilidade competitiva em condições de baixa luminosidade. As características avaliadas não permitem diferenciar os genótipos com diferentes níveis de resistência ao glifosato.

The interference of glyphosate resistant hairy fleabane (Conyza bonariensis) has caused yield losses in soybean crop. Knowledge of the economic threshold is an important aspect for the economic management of resistant weeds. Because of it, the interference of the glyphosate resistant hairy fleabane density on the soybean yield loss was evaluated, as well as to estimate the economic threshold. Two experiments were conducted to verify the effect of different weed densities on the yield of two soybean cultivars (BRS Estância and BMX Turbo). Weed density ranged from 0 to 124 plants m-2. The yield of the BRS Estância decreased by 1.4% to the increase of one single plant, while for the BMX Turbo the loss was 25.9%. Soybean yield and economic threshold were lower for the BMX Turbo cultivar compared to the cultivar BRS Estância, which can be attributed to the genotype, competitive ability, weed development stage and/or environment. Increases in crop yield expectation, soybean price and herbicide efficiency reduce the economic threshold, indicating that the adoption of control measures should be taken when the weed density is low. Due to the high cost of hairy fleabane control, it is only feasible at high densities. RESUMO: A interferência de plantas de buva (Conyza bonariensis) resistente ao herbicida glyphosate tem causado perdas de produtividade na cultura da soja. O conhecimento do nível de dano econômico é um importante fator para o manejo econômico de plantas daninhas resistentes na cultura da soja. Para isso, foi avaliada a interferência da densidade de buva resistente ao glyphosate sobre a perda de rendimento da soja, bem como estimado o nível de dano econômico. Dois experimentos foram conduzidos para verificar o efeito de diferentes densidades da planta daninha sobre a produtividade de dois cultivares de soja (BRS Estância e BMX Turbo). As densidades de buva variaram de 0 a 124 plantas m-2. A produtividade do cultivar BRS Estância reduziu 1,4% ao aumento de uma planta, enquanto para o cultivar BMX Turbo a perda foi de 25,9%. A produtividade da soja e o nível de dano econômico foram menores para o cultivar BMX Turbo, em comparação com o cultivar BRS Estância, o que pode ser atribuído ao genótipo, à habilidade competitiva, ao estádio de desenvolvimento da buva e/ou a ambiente. Aumentos na expectativa de produtividade da cultura, no preço da soja e na eficiência dos herbicidas reduzem o nível de dano econômico, indicando que a adoção de medidas de controle deve ser tomada quando a população de buva é baixa. Em função do elevado custo de controle da buva, este somente é viável em altas densidades.

The resistance of weeds to herbicides is a consequence of one or more mechanisms in the plant, responsible for not allowing the herbicide to act properly at the active site. The objective of this study was to investigate the mechanism(s) of resistance to glyphosate in Conyza bonariensis. An experiment was conducted in November and December, 2012 and repeated in February and March, 2013 using a factorial arrangement of the treatments, where the factor A corresponded to biotypes of hairy fleabane, susceptible (S) and resistant (R); the factor B to seven rates of glyphosate from 0 to 11,520 g e.a. ha-1, and factor C were simulated environmental conditions of winter (12/8 oC day/night of temperature and 10/14 h of photoperiod) and summer (28/20 oC day/night of temperature and 14/10 h of photoperiod). An assay evaluating the shikimic acid was performed twice in the month of July 2013, with treatments arranged in a factorial arrangement, being factor A biotypes of hairy fleabane, S and R and the factor B seven glyphosate rates (0 to 28,8 mg a.e. L-1). The R biotype of C. bonariensis does not appear to present the sequestration of herbicide in the vacuole as the mechanism of resistance. However, the low accumulation of shikimate by the R biotype characterizes lower sensitivity of EPSPs enzyme to glyphosate, inferring that this is the present mechanism of resistance in plants of C. bonariensis. However, the resistance cannot be associated to a unique mechanism of resistance, requiring further studies to its understanding. RESUMO A resistência de plantas daninhas aos herbicidas é consequência da ocorrência de um ou mais mecanismos na planta, responsáveis por não deixarem o herbicida atuar de forma eficiente sobre o local de ação. O objetivo deste estudo foi investigar o(s) mecanismo(s) de resistência em Conyza bonariensis ao herbicida glyphosate. Um experimento foi conduzido de novembro a dezembro de 2012 e repetido em fevereiro e março de 2013, com arranjo fatorial, em que o fator A correspondeu aos biótipos de buva suscetível (S) e resistente (R); o fator B, a sete doses de glyphosate, que variaram de 0 a 11.520 g e.a. ha-1; e o fator C às condições que simularam o inverno (temperatura de 12/8 oC dia/noite e fotoperíodo de 10/14 horas) e verão (temperatura de 28/20 oC dia/noite e fotoperíodo de 14/10 horas). Um ensaio que avaliou o acúmulo de shiquimato foi realizado duas vezes no mês de julho de 2013, com tratamentos dispostos em esquema fatorial, sendo o fator A os biótipos de buva, S e R, e o fator B, sete doses de glyphosate (0 a 28,8 mg e.a. L-1). O biótipo R de C. bonariensis aparenta não apresentar o mecanismo de sequestro do herbicida no vacúolo como mecanismo de resistência. Entretanto, o menor acúmulo de shiquimato pelas plantas do biótipo R caracteriza a menor sensibilidade da enzima EPSPS ao glyphosate, inferindo que esse seja o mecanismo de resistência presente em plantas de C. bonariensis. Contudo, a resistência pode não estar atrelada a apenas um mecanismo de resistência, exigindo, para seu inteiro entendimento, estudos complementares.

Herbicide resistance can cause biochemical, physiological, morphological and phenological changes in weeds, altering their competitive ability against crops. The aim of the study was to assess physiological changes and cellular damage in susceptible and resistant biotypes of ryegrass and soybeans under competition. Three experiments were conducted in a greenhouse using a completely randomized design with four replications performed in a replacement series. The ratios of soybean and to susceptible (experiment 1) and resistant ryegrass (experiment 2) and of susceptible to resistant (experiment 3) ryegrass were 100:0, 75:25, 50:50, 25:75 and 0:100. Forty days after the emergence of the soybean crop and 60 days after the emergence of the ryegrass plants, the leaves of the competing plants were collected. The following variables were assessed: the levels of carotenoids, chlorophylls and total phenolic compounds; amount of hydrogen peroxide; degrees of lipid peroxidation and electrolyte leakage; and activity of enzymes catalase, superoxide dismutase and ascorbate peroxidase. The production of phenols and increased oxidative damage due to interspecies competition with ryegrass was, in general, observed in the soybeans; the ryegrass biotypes, susceptible and resistant to glyphosate, coexisting with soybean have generally higher oxidative damage due to intraspecific competition; since when these biotypes coexist not present modifications of these parameters.

The application of herbicides, even if selective, can cause biochemical and physiological changes, resulting in oxidative stress. This stress comes from the accumulation of reactive oxygen species produced due to exposure to the herbicide. However, plants have developed defense strategies, which can be enzymatic or non-enzymatic. The objective of this study was to evaluate the morphological and metabolic changes such as photosynthetic parameters, oxidative damage and antioxidant enzyme activity of rice plants after applying herbicides. For this, a study was conducted in a greenhouse and laboratory and the treatments consisted of application of imazapic + imazapyr, quinclorac, bentazon, cyhalofop-butyl, penoxsulan, bispyribac-sodium and carfentrazone-ethyl, in addition to control without herbicide. The phytotoxicity in plants was strong and there was a reduction in photosynthesis, stomatal conductance and efficiency of water use in plants treated with carfentrazone-ethyl. Furthermore, the application of carfentrazone-ethyl resulted in lower chlorophylls and carotenoids and increased lipid peroxidation and proline accumulation. Changes in the activity of enzymes belonging to the antioxidant system were inspected by applying herbicides. The application of herbicide alters the physiology of rice plants, triggering responses to oxidative stress, which are more pronounced when used carfentrazone-ethyl. RESUMO A aplicação de herbicidas, mesmo seletivos às culturas, podem causar alterações bioquímicas e fisiológicas, acarretando estresse oxidativo. Esse estresse é proveniente do acúmulo de espécies reativas de oxigênio produzidas em função da exposição ao herbicida. No entanto, as plantas evoluíram com estratégias de defesa, sendo estas enzimáticas ou não enzimáticas. O objetivo deste estudo foi avaliar as alterações morfológicas e metabólicas, como os parâmetros fotossintéticos, danos oxidativos e atividade das enzimas antioxidantes, de plantas de arroz após a aplicação de herbicidas. Para isso, foi realizado um estudo em casa de vegetação e laboratório, e os tratamentos foram compostos pela aplicação de imazapic + imazapyr, quinclorac, bentazon, cyhalofop-butyl, penoxsulan, bispyribac-sodium e carfentrazone-ethyl, além da testemunha sem herbicida. A fitotoxicidade nas plantas foi acentuada, bem como ocorreu redução na fotossíntese, condutância estomática e eficiência do uso da água nas plantas tratadas com carfentrazone-ethyl. Além disso, a aplicação deste herbicida resultou em menor teor de clorofilas e carotenoides, maior peroxidação lipídica e acúmulo de prolina. Alterações na atividade das enzimas pertencentes ao sistema antioxidante também foram verificadas em função da aplicação dos herbicidas. A aplicação de herbicidas altera a fisiologia das plantas de arroz, desencadeando respostas como estresse oxidativo, sendo estas mais acentuadas quando utilizado carfentrazone-ethyl.

Ryegrass is a weed of annual cycle that is present in winter crops, in orchards and vineyards of the South region of Brazil. The species is normally controlled by the glyphosate herbicide, but the continuous use of this product caused the selection of resistant biotypes. The use of ACCase inhibitor herbicides is the main alternative for the control of this species, but it has not been satisfactory in some places, thus causing suspicion of resistance to this action mechanism. Thus, the objective of this paper was to evaluate the occurrence and geographic distribution of ryegrass biotypes that are resistant to the clethodim herbicide in the state of Rio Grande do Sul. For that, seeds of ryegrass plants that survived the application of clethodim were collected in crops from the north region of RS, summing up to a total of 152 samples from 72 cities. The biotypes were submitted to the application of 120 g i.a. ha-1 (maximum registered dose) and 60 g i.a. ha-1 de clethodim (half the maximum registered dose). According to the results, among the samples of ryegrass seeds collected, there were no biotypes resistant to the clethodim herbicide when the maximum registered dose was applied and in the stage of three to four leaves. However, there were biotypes with lower susceptibility that survived half the maximum registered dose. RESUMO O azevém é uma planta daninha de ciclo anual presente em lavouras de inverno, em pomares e vinhedos da região Sul do Brasil. A espécie normalmente é controlada pelo herbicida glyphosate, porém o uso continuado desse produto selecionou biótipos resistentes. O uso de herbicidas inibidores da ACCase é a principal alternativa para o controle dessa espécie, o qual não tem sido satisfatório em alguns locais, provocando a suspeita da ocorrência de resistência a esse mecanismo de ação. Assim, o objetivo deste trabalho foi avaliar a ocorrência e distribuição geográfica de biótipos de azevém resistente ao herbicida clethodim no Estado do Rio Grande do Sul. Para isso, sementes de plantas de azevém que sobreviveram a aplicações de clethodim foram coletadas em lavouras da região norte do RS, totalizando 152 amostras de 72 municípios. Os biótipos foram submetidos à aplicação de 120 g i.a. ha-1 (dose máxima de registro) e 60 g i.a. ha-1 de clethodim (metade da máxima dose de registro). De acordo com os resultados, entre a amostras de sementes de azevém coletadas não foram encontrados biótipos resistentes ao herbicida clethodim quando aplicada a máxima dose de registro e no estádio de três a quatro folhas. No entanto, observaram-se biótipos com menor suscetibilidade, que sobreviveram à metade da máxima dose de registro.

The objective of this study is to determine the dose required to control 50% population (C50) and to reduce 50% dry matter production (GR50) of resistant biotypes of ryegrass in comparison to that of a susceptible biotype as well as to evaluate the mechanism of resistance by cyt-P450 inhibitor application. The study was conducted in a greenhouse in Rio Grande do Sul, Brazil on plants that survived clethodim herbicide application, which were suspected of possessing resistance. For plants surviving field application, the biotypes were 50% controlled with herbicide dose of 28.4- and 29.5-times greater compared to that of susceptible biotypes; 50% of dry matter reduction occurred with doses of 540- and 574-times greater than the susceptibility dose of a biotype, since the dose required to reduce 50% of susceptible biotype was 0.2 g a.i. ha-1. The biotypes showed metabolism of clethodim herbicide as regards the inhibition by piperonyl butoxide, indicating that metabolism is the probable cause of control failures in the field. Key words: Lolium multiflorum, acetyl coenzyme A carboxilase, weed, mechanism of resistance; metabolization.

Understanding the physiological defense behavior of plants subjected to herbicide application may help to identify products with higher or lower capacity to cause oxidative stress in crops. This study aimed at evaluating the effect of herbicides in the antioxidant activity of rice plants. The experimental design was completely randomized, with six replications. Treatments consisted of the herbicides bentazon (photosystem II inhibitor; 960 g ha-1), penoxsulam (acetolactate synthase inhibitor; 60 g ha-1), cyhalofop-butyl (acetyl coenzyme-A carboxylase inhibitor; 315 g ha-1) and a control. After the herbicides application, samples of rice shoots were collected at 12, 24, 48 and 96 hours after application (HAA). The components evaluated were hydrogen peroxide (H2O2), lipid peroxidation and activity of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT). Bentazon (up to 24 HAA) and penoxsulam (48 and 96 HAA) reduced the CAT activity. Moreover, these herbicides increased the levels of H2O2, lipid peroxidation and SOD activity, indicating a condition of oxidative stress in rice plants. The cyhalofop-butyl herbicide did not alter the antioxidant activity, showing that it causes less stress to the crop. RESUMO O entendimento do comportamento fisiológico de defesa de plantas submetidas à aplicação de herbicidas auxilia na identificação de produtos com maior ou menor capacidade de causar estresse oxidativo na cultura. Objetivou-se avaliar o efeito de herbicidas na atividade antioxidante de plantas de arroz. O delineamento experimental utilizado foi o completamente casualizado, com seis repetições. Os tratamentos constituíram-se dos herbicidas bentazona (inibidor de fotossistema II; 960 g ha-1), penoxsulam (inibidor de acetolactato sintase; 60 g ha-1), cialofope-butílico (inibidor de acetilcoenzima A carboxilase; 315 g ha-1) e testemunha sem aplicação. Após aplicação dos herbicidas, foram realizadas coletas da parte aérea do arroz às 12, 24, 48 e 96 horas após a aplicação (HAA). As variáveis avaliadas foram peróxido de hidrogênio (H2O2), peroxidação lipídica e atividade das enzimas antioxidantes superóxido dismutase (SOD) e catalase (CAT). Bentazona (até 24 HAA) e penoxsulam (48 e 96 HAA) reduziram a atividade da CAT. Além disso, esses herbicidas aumentaram o nível de H2O2, peroxidação lipídica e atividade da SOD, indicando condição de estresse oxidativo nas plantas de arroz. O herbicida cialofope-butílico não alterou a atividade antioxidante, sinalizando menor capacidade de causar estresse à cultura.

O capim-rabo-de-burro é uma Poaceae, considerada planta daninha recente nas lavouras desoja por seus crescentes níveis de infestação e dificuldades de controle. Diante disso,objetivou-se com este trabalho avaliar a eficiência de diferentes doses de herbicidasaplicados isolados ou em associação, no controle de capim-rabo-de-burro em diferentesestádios de aplicação. Foram realizados três experimentos, um em casa de vegetação complantas em estádio inicial de desenvolvimento e dois a campo com touceiras. Os herbicidastestados foram glyphosate; fluazifop; sethoxydim; fenoxaprop; clethodim; quizalofop;haloxyfop; pinoxaden, nicosulfuron; glufosinate e as misturas de glyphosate com clethodim,quizalofop, haloxyfop ou sethoxydim. Os tratamentos com glyphosate, isolado ou emmistura, apresentaram maiores níveis de controle em todos experimentos. Além deglyphosate, glufosinate, clethodim, haloxyfop e sethoxydim foram eficientes no controle decapim-rabo-de-burro nos estádios iniciais de desenvolvimento. Para manejo de touceiras, osherbicidas glyphosate e haloxyfop isolados demonstraram eficiência superior a 90%independente da dose e clethodim e sethoxydim na dose mais alta. Os herbicidas pinoxadene nicosulfuron não são alternativas para controle de capim-rabo-de-burro.

The successive use of Roundup Ready crops may difficult the management of volunteer plants originated from seed losses during harvest. In soybean, volunteer corn plants can exhibit higher interference and cause reduce yield depending on their density. The aim of this study was to quantify the economic threshold level (ETL) in soybean as a function of the competition of volunteer corn and to evaluate the chemical control in different phenological stages of development. The ETL and chemical control experiments were conducted in the field, under completely randomized and randomized block designs with one and three replicates, respectively. The variables analyzed were yield and ETL as functions of the competition of different volunteer corn populations (control, 1, 2, 4, 6, 8, 10, 12, 16, 20, 24 and 32 plants m-2) and the chemical control with acetyl coenzyme-A carboxylase (ACCase) inhibitor herbicides alone or mixed with glyphosate in different phenological stages of development (V2-V3, V4-V5 and V6-V8) that were evaluated at seven, 14 and 21 days after application (DAA). The results showed higher competitive potential of volunteer corn in which the presence of one plant m-2 reduces the soybean yield in 17%. The ETL ranged from 0.14 to 0.78 plants m-2 and the control of volunteer corn must be carried out in low populations. The use of ACCase inhibitors herbicides alone or mixed with glyphosate demonstrated greater than 85% control in the V2-V3 phenological stage independent of the period evaluated. The effectiveness of all herbicides decreased with application delay with a control level above 87%, in the V6-V8 phenological stage, obtained only for fluazifop and haloxyfop herbicides alone or in mixed with glyphosate at 14 and 21 days after application. O uso sucessivo de culturas “Roundup Ready” pode dificultar o manejo de plantas voluntárias originadas de sementes perdidas durante a colheita. Na soja, plantas de milho voluntário podem apresentar elevadainterferência e causar redução da produtividade dependendo da sua densidade. O objetivo do estudo foi quantificar o nível de dano econômico (NDE) na soja em função da competição de milho voluntário e avaliar o controle químico em diferentes estádios fenológicos de desenvolvimento. Os experimentos de NDE e controle químico foram conduzidos a campo, em delineamento inteiramente e blocos casualizados com uma e três repetições, respectivamente. As variáveis analisadas foram a produtividade e o NDE em função da competição das diferentes populações de milho voluntário (zero; um; dois; quatro; seis; oito; 10; 12; 16; 20; 24 e 32 plantas m-²) e o controle químico com herbicidas inibidores da enzima acetil CoA carboxilase (ACCase) isolados ou misturados com o glifosato em diferentes estádios fenológicos de desenvolvimento (V2-V3; V4-V5 e V6-V8) que foram avaliados aos sete, 14 e 21 dias após a aplicação (DAA). Os resultados demonstraram maior potencial competitivo do milho voluntário onde a presença de uma planta m-2 reduziu a produtividade da soja em 17%. O NDE variou de 0,14 a 0,78 plantas m-2 e o controle do milho voluntário deve ser realizado em populações baixas. O uso de herbicidas inibidores da ACCase isolados ou misturados com o glifosato proporcionaram controle superior 85% no estádio fenológico V2-V3 independente do período avaliado. A eficácia de todos os herbicidas decresceu com o atraso da aplicação com um nível de controle acima de 87%, no estádio fenológico V6-V8, obtido apenas para os herbicidas fluazifope e haloxifope isolado ou em mistura com o glifosato aos 14 e 21 dias após aplicação.

Soybean crop rotation with irrigated rice is an alternative for the management of weedy rice (Oryza sativa) resistant to herbicides from the imidazolinone chemical group. This work had the purpose to evaluate the phytotoxicity of soybean crops containing the technologies Cultivance® (CV) and tolerance to sulphonylurea and Roundup Ready® (RR), deriving from increasing doses of the imazapyr and imazapic herbicide mixture, applied in the irrigated rice crop management. Thus, the experiment was performed on field, where treatments consisted in three soybean cultivars (BRS382CV, CD249STS and NA5909RR) and five doses of the imazapyr and imazapic herbicides mixture (0, 49, 98, 196 and 392 g a.i. ha-1). The evaluated variables were phytotoxicity, yield components and physiological quality of the seeds. Soybean cultivar BRS382CV is tolerant to herbicide carryover, applied in the management of weedy rice in irrigated rice crops, but the other cultivars are susceptible to it. Cultivar productivity, yield components and physiological quality of the seeds are affected by the carryover increase of the imazapyr and imazapic herbicide mixture. RESUMO: A rotação da cultura da soja ao arroz irrigado é alternativa para manejo de arroz-vermelho (Oryza sativa) resistente aos herbicidas do grupo químico das imidazolinonas. Objetivou-se avaliar a fitotoxicidade cultivares de soja contendo as tecnologias Cultivance® (CV) e tolerância às sulfonilureias (STS) e Roundup Ready® (RR), em decorrência do resíduo no solo de doses crescentes da mistura dos herbicidas imazapyr e imazapic, aplicados no manejo de plantas daninhas na cultura do arroz irrigado. O experimento foi realizado em campo, e os tratamentos consistiram de três cultivares de soja (BRS382CV, CD249STS e NA5909RR) e de cinco doses da mistura dos herbicidas imazapyr e imazapic (0, 49, 98, 196 e 392 g i.a. ha-1). As variáveis avaliadas foram fitotoxicidade, componentes da produtividade e qualidade fisiológica das sementes. O cultivar de soja BRS382CV é tolerante ao resíduo da mistura desses herbicidas, aplicado no manejo de arroz-vermelho na cultura do arroz irrigado, sendo os demais cultivares suscetíveis. A produtividade dos cultivares, os componentes de produtividade e a qualidade fisiológica das sementes de soja são afetados pelo aumento do resíduo da mistura dos herbicidas imazapyr e imazapic.

Herbicides used in Clearfield(r) rice system may persist in the environment, damaging non-tolerant crops sown in succession and/or rotation. These damages vary according to soil characteristics, climate and soil management. The thickness of the soil profile may affect carryover effect; deeper soils may allow these molecules to leach, reaching areas below the roots absorption zone. The aim of this study was to evaluate the effect of the thickness of soil profile in the carryover of imazethapyr + imazapic on ryegrass and non-tolerant rice, sown in succession and rotation to rice, respectively. Lysimeters of different thicknesses (15, 20, 30, 40, 50 and 65 cm) were constructed, where 1 L ha-1 of the imazethapyr + imazapic formulated mixture was applied in tolerant rice. Firstly, imidazolinone-tolerant rice was planted, followed by ryegrass and non-tolerant rice in succession and rotation, respectively. Herbicide injury, height reduction and dry weight of non-tolerant species were assessed. There was no visual symptoms of herbicide injury on ryegrass sown 128 days after the herbicide application; however it causes dry weight mass reduction of plants. The herbicides persist in the soil and cause injury in non-tolerant rice, sown 280 days after application, and the deeper the soil profile, the lower the herbicides injury on irrigated rice.

Accelerated herbicide degradation consists in its faster degradation in areas where it has been previously applied, due to the adaptation of microbial population to that particular compound. Accelerated degradation can reduce herbicide persistence and reduce its efficacy in soil. The objective of this study was to investigate if imidazolinone herbicides have enhanced microbial degradation in rice paddy soils. A laboratory experiment was conducted, evaluating the CO2 evolution rate from soils with and without history of herbicide application (imazapyr + imazapic and imazethapyr + imazapic), incubated with imidazolinone herbicides: imazethapyr, imazapyr, imazapic, imazamethabenz, imazamox and an untreated check. The amount of CO2 released from the soil was measured. As a result, the prior application of imidazolinones does not stimulate microbial degradation of herbicides from the same chemical group.

Acetolactate synthase inhibitors are the main group of herbicides used in winter crops in Southern Brazil where their intensive use has selected for herbicide-resistant biotypes of radish. The resistance affects the efficacy of herbicides, and identifying the resistance mechanism involved is important for defining management strategies. The aim of this study was to elucidate the resistance mechanism of radish biotypes by quantifying the enzyme activity, ALS gene sequencing and evaluating the response of biotypes to iodosulfuron and imazethapyr herbicide application after treatment with a cytochrome P450 monooxygenase inhibitor. The susceptible (B1) and resistant (B4 and B13) biotypes were from wheat fields in the Northwest of Rio Grande do Sul State. The results demonstrated that the enzyme affinity for the substrate (KM) was not affected in biotypes B4 and B13 but that the Vmax of the resistant biotypes was higher than that of biotype B1. The resistant biotypes showed no differential metabolic response to iodosulfuron and imazethapyr herbicides when inhibited by malathion and piperonyl butoxide. However, gene sequencing of ALS showed a mutation at position 574, with an amino acid substitution of tryptophan for leucine (Trp-574-Leu) in resistant biotypes. RESUMO. Os inibidores da acetolactato sintase são o principal grupo de herbicidas usados em culturas de inverno do Sul do Brasil onde seu uso intenso selecionou biótipos resistentes de nabo. A resistência afeta a eficácia dos herbicidas, e a identificação do mecanismo de resistência envolvido é importante na definição de estratégias de manejo. O objetivo deste estudo foi elucidar o mecanismo de resistência em biótipos de nabo através da quantificação da atividade da enzima, sequenciamento do gene ALS e avaliar a resposta dos biótipos à aplicação do herbicida iodosulfurom e imazetapir após tratamento com inibidores do metabolismo da citocromo P450 monooxigenase. Os biótipos suscetível (B1) e resistentes (B4 e B13) eram de lavouras de trigo da região Noroeste do Estado do Rio Grande do Sul. Os resultados demonstraram que a afinidade da enzima pelo substrato (KM) não foi afetada nos biótipos B4 e B13, porém o Vmax dos biótipos resistentes foi superior quando comparado ao biótipo B1. Os biótipos resistentes não apresentaram resposta metabólica diferencial ao herbicida iodosulfurom e imazetapir quando inibidos pelo malathion e butóxido de piperolina. Entranto, o sequenciamento do gene ALS evidenciou mutação na posição 574 com uma substituição do aminoácido triptofano por leucina (Trp-574-Leu) nos biótipos resistentes.

Goosegrass (Eleusine indica) infests various crops, being reported as low-level resistant (LLR) to glyphosate. The objectives of this study were to evaluate the mechanisms of resistance to glyphosate in goosegrass by the cyt-P450 complex to identify changes in leaf anatomy of these plants and quantify the accumulation of shikimate in biotypes susceptible and with LLR. The metabolic rate was assessed by applying the cyt-P450 malathion inhibitor 30 minutes before the herbicide application. The analysis of the leaf anatomy consisted of a characterization of anatomic cross-sections and evaluation of the effect of glyphosate on the leaf epidermis and the conducting vessels. Plant tissue was collected 24 hours after treatment (HAT) of the dose-response curve to evaluate the accumulation of shikimate. The LLR biotype has not shown glyphosate metabolism by the early application of malathion due to the control of about 65% with or without applying the inhibitor. There is no anatomical evidence to determine the differential absorption of glyphosate by LLR biotypes. However, there is evidence of lower absorption and translocation of glyphosate in this biotype by lower stomatal density and a smaller diameter of the phloem. However, the LLR biotype presents diameter of phloem of 0.027 mm and stomatal density of 91.23 mm-2, values which are below the observed ones on the susceptible biotype. The susceptible biotype presents shikimate accumulation 17% higher compared to the biotype with LLR at a dose of 1,080 g e.a. ha-1, allowing to infer that the resistance mechanism is related to the enzyme insensitivity to the herbicide, which enables the use of appropriate management practices to control this weed. RESUMO O capim-pé-de-galinha (Eleusine indica) é infestante de diversos cultivos, sendo relatado como resistente de nível baixo (RNB) ao herbicida glyphosate. Os objetivos deste trabalho foram avaliar mecanismos de resistência de capim-pé-de-galinha ao glyphosate, por meio de metabolização do herbicida pelo complexo cyt-P450, alterações na anatomia foliar e acúmulo de chiquimato nos biótipos suscetível e com RNB. A metabolização foi avaliada mediante a aplicação do inibidor de cyt-P450 malathion 30 min antes do herbicida. A análise da anatomia foliar constou da caracterização de cortes anatômicos e avaliação do efeito do glyphosate na epiderme foliar e nos vasos condutores. Para avaliar o acúmulo de chiquimato, foi coletado tecido vegetal 24 horas após tratamento (HAT) da curva de dose-resposta. O biótipo RNB não evidenciou metabolismo do glyphosate pela aplicação prévia de malathion, não diferindo do tratamento somente com o herbicida. Não existem evidências anatômicas que determinem a absorção diferencial do herbicida glyphosate pelo biótipo RNB. Entretanto, o biótipo RNB apresentou diâmetro do floema de 0,027 mm e densidade de estômatos de 91,23 mm-2, valores inferiores aos observados no biótipo suscetível, levando a indícios de menor absorção e translocação de glyphosate nesse biótipo. O biótipo suscetível apresentou acúmulo de chiquimato 17% superior, comparado ao biótipo RNB, na dose de 1.080 g a.e. ha-1, permitindo inferir que o mecanismo de resistência seja relacionado à insensibilidade da enzima-alvo ao herbicida, o que possibilita o uso de práticas de manejo adequadas para o controle dessa planta daninha.

Among the methods of weed control, stands out chemical control. However, even selective, herbicides can trigger the production of reactive species of oxygen and cause oxidative stress. The aim of the study was to evaluate changes in photosynthetic parameters, oxidative damage, antioxidant enzyme activity and altered metabolism of rice plants after applying pre-emergent herbicides. The experiment was conducted in a greenhouse and herbicides used were oxadiazon, pendimethalin and oxyfluorfen, beyond the control without herbicide. There was a reduction of photosynthetic rate and efficiency of carboxylation, compared to the control, when applied herbicides oxyfluorfen and pendimethalin. The major lipid peroxidation and proline accumulation was observed for the herbicide oxyfluorfen. The oxyfluorfen and oxadiazon herbicides also resulted in increased activity of superoxide dismutase, compared to control. When evaluated ascorbate peroxidase activity, there was a higher enzyme activity in plants treated with oxadiazon and pendimethalin. Even selective herbicides registered for weed control in rice crops cause phytotoxicity, reduce height and alter the metabolism of plants, generating reactive oxygen species, which activate enzymatic and non-enzymatic defense systems and result in the degradation of photosynthetic pigments and in reduced protein content. RESUMO Dentre os métodos de controle de plantas daninhas, destaca-se o controle químico. No entanto, mesmo seletivos a cultura, os herbicidas podem desencadear a produção de espécies reativas de oxigênio e causar estresse oxidativo. O objetivo do estudo foi avaliar alterações nos parâmetros fotossintéticos, danos oxidativos, atividade das enzimas antioxidantes e alterações do metabolismo de plantas de arroz após a aplicação de herbicidas pré-emergentes. O experimento foi conduzido em casa de vegetação e os herbicidas utilizados foram: oxadiazon, oxyfluorfen e pendimethalin, além do controle sem herbicida. Observou-se redução da taxa fotossintética e na eficiência da carboxilação, em relação à testemunha, quando aplicado os herbicidas oxyfluorfen e pendimethalin. A maior peroxidação lipídica e acúmulo de prolina foi observado para o herbicida oxyfluorfen. Os herbicidas oxyfluorfen e oxadiazon também resultaram em maior atividade da superóxido dismutase, comparado à testemunha. Quando avaliada a atividade da ascobato peroxidase, verificou-se maior atividade da enzima em plantas tratadas com oxadiazon e pendimethalin. Mesmo seletivos e registrados para controle de plantas daninhas na cultura do arroz, os herbicidas causam fitotoxicidade, reduzem a estatura e alteram o metabolismo das plantas, gerando espécies reativas de oxigênio, as quais ativam o sistema de defesa enzimático e não enzimático e resultam em degradação dos pigmentos fotossintéticos e redução no teor de proteínas.

Resumen en: The aim of this study was to determine changes in the photosynthetic process and the inhibition of 5-enolpyruvylshikimate-3- phosphate synthase (EPSPs) b...

Os herbicidas utilizados no Sistema Clearfield(r) de produção de arroz irrigado caracterizam-se por serem móveis no solo. Tal mobilidade contribui para a contaminação ambiental e intensificação do residual no solo. A irrigação por inundação utilizada na lavoura arrozeira é uma das principais causas de livixiação de imidazolinonas, contudo, manejos alternativos de irrigação podem contribuir para sua diminuição. Assim, o objetivo do trabalho foi estimar, através de bioensaio, a lixiviação de imidazolinonas frente a diferentes manejos de irrigação. Para isso, foram conduzidos dois experimentos em casa de vegetação e em colunas de solo. Em ambos, foram testados três manejos de irrigação, sendo eles: contínuo, intermitente e capacidade de campo. Os herbicidas foram aplicados na superfície do solo e, após 48 horas, iniciou-se a irrigação. Aos 45 e 90 dias de irrigação, para o primeiro e segundo experimentos, respectivamente, as colunas de solo foram cortadas longitudinalmente e realizou-se bioensaio utilizando solo das diferentes profundidades. Os resultados permitem concluir que a mistura formulada imazapic + imazapyr apresenta maior lixiviação. Para os herbicidas testados isoladamente, o imazapic lixivia mais, seguido do imazethapyr e imazapyr. Os manejos de irrigação contínuo e intermitente não diferem entre si e promovem maior lixiviação dos herbicidas, quando comparado ao solo na capacidade de campo

O uso intenso de herbicidas com o mesmo mecanismo de ação tem selecionado espécies de plantas daninhas resistentes como, por exemplo, o arroz-vermelho (Oryza sativa L.) com resistência à mistura formulada dos herbicidas imazapyr + imazapic. A competição de plantas daninhas ocasiona perda de produtividade das culturas, geralmente crescente, quanto mais semelhantes forem suas características morfofisiológicas. Ainda, a capacidade competitiva do biótipo geralmente é alterada pela característica de resistência, e seu conhecimento é fundamental para a compreensão da dinâmica da população resistente. Diante disso, o objetivo da pesquisa foi estudar a habilidade competitiva entre biótipos de arroz-vermelho resistente e suscetível ao herbicida imazapyr + imazapic com arroz irrigado, utilizando o método de série de substituição. Para isso, foram conduzidos experimentos com a cultivar Puitá INTA CL, competindo com o biótipo de arroz-vermelho suscetível ou resistente. As populações de plantas por vaso totalizaram 24, o equivalente a 942 plantas m-2. Para o arroz-vermelho suscetível ou resistente ao herbicida, a competição interespecífica é favorável em relação à competição intraespecífica, enquanto para a cultura do arroz irrigado o competidor independe. A cultivar Puitá INTA CL, em geral, apresenta habilidade competitiva equivalente aos biótipos de arroz-vermelho suscetível ou resistente ao herbicida imazapyr + imazapic, competindo pelos mesmos recursos do ambiente. The intensive use of herbicides with the same mechanism of action has selected resistant weeds, among which is the red rice (Oryza sativa L.) after the use of the formulated herbicide mixture of imazapyr and imazapic. The competition of weeds leads to usually increasing yield losses of crops, the more similar the morphological and physiological characteristics between weed and crop. Moreover, the competitive ability of the biotype is generally modified by the resistance characteristic; besides, the knowledge of competitive ability is fundamental to understand the dynamics of the resistant population. Therefore, the aim of this research was to study the competitive ability of red rice biotypes that are resistant and susceptible to imazapyr and imazapic herbicide with rice, using the series substitution method. Experiments were conducted with Puitá INTA CL cultivar competing with susceptible or resistant biotypes of red rice. The total plant populations per pot were of 24, similar to 942 plants m-2. For red rice that is resistant or susceptible to herbicide, the interspecific competition is favorable with regard to intraspecific competition, while for the irrigated rice the competitor is independent. Generally, the Puitá INTA CL cultivar presents competitive ability equivalent to red rice biotypes that are susceptible or resistant to imazapyr and imazapic herbicide, competing for the same resources from the environment.

Red rice is one of the major troublesome and difficult weeds to control in rice production regions. The introduction of the Clearfield&#174 technology allowed producers to control red rice using rice genotypes tolerant to the imidazolinone herbicides. However, because the consecutive use of this technology red rice biotypes have evolved resistance to imidazolinone herbicides, the rice-soybean rotation has been an alternative used by producers to control this weed. This system allows the use of herbicides with different modes of action to control red rice, such as S-metolachlor. Thus, greenhouse and field experiments were carried out during the 2011 to 2012 and 2012 to 2013 growing seasons to evaluate: 1) sensitivity of imidazolinone-resistant red rice to S-metolachlor; 2) red rice control and soybean tolerance in response to associations of S-metolachlor and glyphosate. In greenhouse, S-metolachlor effectively controlled both susceptible and imidazolinone-resistant red rice in preemergence. In field, preemergence applications of S-metolachlor provided greater red rice control in comparison to S-metolachlor alone in early postemergence. The association of S-metolachlor with glyphosate did not improve red rice control in preemergence application. However, association of S-metolachlor with glyphosate significantly improved red rice control in early postemergence applications. S-metolachlor injury to soybean increased with early postemergence applications. These results indicate that S-metolachlor effectively control imidazolinone-resistant red rice in rice-soybean rotation.

Chemical control with herbicides, especially glyphosate, is the main method used to control ryegrass. However, the repeated use of glyphosate has selected resistant ryegrass biotypes. Thus, the ACCase inhibitor herbicides have become the main alternative to control glyphosate-resistant biotypes, being widely used by farmers in Rio Grande do Sul. Repeated use of ACCase inhibitors, in turn, have selected ryegrass biotypes resistant to this herbicide mechanism. Thus, the objective of this study was to evaluate the response of ryegrass biotypes to different clethodim rates by dose-response curves. Increasing doses (0, 12, 24, 48, 72, 96, 144 and 192 g a.i. ha-1) of the herbicide clethodim were applied at the 3-4 ryegrass leaf stage. The variables control at 14 and 28 days after treatment (DAT) and shoot dry weight were evaluated. The data were fitted by nonlinear regression log-logistic and C50 and GR50 were calculated based on the equation. The resistance factor was obtained by the ratio of C50 or GR50 of the resistant biotype by matching the susceptible biotype. Based on the equation parameters, the doses of GR50 64.7 and 234.5 g a.i. ha-1 clethodim and C50 11.2 and 172.1 g a.i. ha-1 clethodim were obtained, at 28 DAT for the susceptible and resistant biotypes, respectively. The ryegrass biotype denominated Cotril is resistant to clethodim, being controlled with a dose 15.3 times greater than that of the susceptible biotype, and a 50% reduction of this biotype occurs with a dose 3.62 times higher than that of the susceptible one.