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Biotic and abiotic factors such as competition with weeds and water deficit may cause significant losses to soybean productivity. This study aimed at evaluating the effect of water deficit and plant recovery in the interaction between soybean (Glycine max) and slender amaranth (Amaranthus viridis) by using growth variables. A replacement series experiment was performed and treatments were arranged in a factorial scheme; they were composed of two water regimes (field capacity and water deficit (50% of field capacity)) and different soybean and slender amaranth proportions (100:0, 50:50 and 0:100%). Water regimes were applied 20 days after plant transplant. Height, leaf area and shoot dry matter were evaluated in soybean and slender amaranth under field capacity and water deficit, returning to normal irrigation conditions to evaluate the water recovery. Soybean exhibited competitiveness which was equivalent to the slender amaranth, independent of the water regime. Water deficit negatively influenced height, leaf area and shoot dry matter of soybean and slender amaranth. There was a reduction in leaf area and shoot dry matter of soybean after plant recovery caused by the irrigation deficit period. Key words: Amaranthus viridis; competition; Glycine max; replacement series; water stress Made available in DSpace on 2021-02-09T14:18:34Z (GMT). No. of bitstreams: 1 Agostinetto-2020-e8132.pdf: 1623861 bytes, checksum: 5dff8a3232781154594795c15f572159 (MD5) Previous issue date: 2020

Herbicides are stressors that can have negative effects on plants. In Oryza sativa (L.), differential gene expression may be evalu-ated through real-time reverse transcription quantitative poly-merase chain reaction (RT-qPCR). The aim of this study was to evaluate the stability of candidate reference genes and to quan-tify the relative expression of oxidative stress genes at different times (12, 24, 48, and 96 hours after treatment [HAT]) with penoxsulam, cyhalofop-butyl, and bentazon herbicides. Norm-Finder, BestKeeper, and GeNorm software and the compara-tive ∆Ct method were used to assess expression stability and to determine the RT-qPCR threshold values of the candidate reference genes. The UBQ5 gene was the most stable among the reference genes analyzed. The gene expression results showed upregulation of OsCAT and OsMnSOD1 genes at all times after herbicide application. The OsA PX 2 and OsGST3 genes showed increased gene expression at 12 and 96 HAT for all herbicides. The OsHO -1 gene had the most significant expression changes, with maximum expression levels at 24 HAT with bentazon and at 96 HAT with penoxsulam and cyhalofop-butyl. Overall, antioxidant system gene expression increased after the applica-tion of bentazon, penoxsulam, and cyhalofop-butyl in rice Made available in DSpace on 2020-02-28T18:10:54Z (GMT). No. of bitstreams: 1 Agostinettoetal2019AgronomyJournal.pdf: 432880 bytes, checksum: d4170b7296de1f44a79e18b0760b6f3f (MD5) Previous issue date: 2019

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.

Wheat crop growth and development can be affected by weed infestation, especially ryegrass. Thus, the objective of this study was to evaluate the competitive ability of wheat cultivars wit h the diploid and tetraploid ryegrass biotypes. Greenhouse experiments were conducted in a completely randomized design with four replications. BRS Parrudo and TBIO Sinuelo wheat cultivars and the competitors ryegrass diploid and tetraploid were used. The population of each species was defined and then the replacement series experiments were carried out, containing the following proportions of wheat and ryegrass plants: 100:0, 75:25, 50:50, 25:75; and 0:100%, equivalent to 32:0; 24:8; 16:16; 8:24; and 0:32 plants per pot. Fifty days after species emergence, physiological traits, such as photosynthetic activity ( A ), stomatal conductance ( g S ), transpiration rate E ), internal concentration of mesophyll CO 2 (C i ), water use efficiency (WUE), and carboxylation ef ficiency (CE), were evaluated, along with the morphological traits of leaf area (LA), stem diameter (SD), number of tillers (NT), and shoot dry mass (DM). Competitiveness analysis was performed by means of diagrams applied to substitutive experiments using relative competitiveness indices. The ryegrass, both diploid and tetraploid, had a negative effect on the variables related to A , WUE and also those associated with plant growth. The ryegrass negatively changed the LA, DM, SD, and NT of the cultivars BRS Parrudo and TBIO Sinuelo, which demonstrates competition between the cultivars of wheat and the weed ryegrass with mutual damage to the species involved in th recommended for wheat cultivation. Made available in DSpace on 2021-02-08T14:19:07Z (GMT). No. of bitstreams: 1 vargas-2020-546.pdf: 947213 bytes, checksum: 349517576b3bb722144a0bd9f662d199 (MD5) Previous issue date: 2020

Italian ryegrass (Lolium multiflorum Lam.) is a troublesome weed found in temperate agricultural fields, wherein the future infestations depend on the soil seed bank. The aim of this research was to evaluate Italian ryegrass seed viability subjected to herbicide application in different phenological stages of development. Experiments were carried out in a completely randomized experimental design with four repetitions. Paraquat, ammonium-glufosinate, iodosulfuron-methyl and clethodim herbicides were applied in three development stages (pre-spike, anthesis, and grain filling) and compared to the control. The effects were evaluated by percentage of control at seven, 14, and 28 days after application (DAA), seeds per plant, 1000 seeds weight, and percentage of germination, abnormal seedlings, dead seeds, viable and non-viable dormant seeds. Control was greater than 97% at 28 DAA, with a decrease of more 90% for seed per plant, and strong reduction of 1000 seeds weight for the herbicides applied up to the anthesis stage. At the grain filling stage, clethodim reduced seed production by 18% and 1000-seeds weight by 36% compared to the control. Ammonium-glufosinate and paraquat herbicides applied up to the anthesis stage reduced seed viability by more than 98%. Overall, herbicide application reduces seed production, seed weight and viability, especially when applied before the grain filling stage. Highlighted Conclusions 1. Herbicide application up to the anthesis developmental stages reduces seed production, 1000 seeds weight, and seed viability. 2. Paraquat was the best herbicide to reduce seed production per plant, 1000-seeds weight and, viability of Italian ryegrass seeds, regardless of development stages. 3. Reducing future infestations of Italian ryegrass in cropping systems depends on herbicide application before the grain filling. Made available in DSpace on 2021-02-09T14:18:20Z (GMT). No. of bitstreams: 1 Cechin-2020-46.pdf: 293629 bytes, checksum: 5d7bbc4a0a08caff083d71af74c3b97b (MD5) Previous issue date: 2020

The use of herbicides to anticipate harvesting in species with easy seed dehiscence may be an alternative to avoid maturation losses. However, the appropriate time for herbicide application is extremely important as it prevents the seeds from remaining in the field for long periods. The objective of this study was to evalu ate the efficiency of the application of maturing herbicides in two distinct seasons, and their effects on the physical, physiological, and sanitary quality of canola seeds. A randomized block experimental design arranged in a factorial scheme (herbicide x season + control) with four replications was used. Hybrid 50 canola plants were matured with the herbicides: glufosinate, paraquat, glyphosate, diquat, saflufenacil, 2,4 D, and paraquat + diuron twice during the crop cycle, G3 and G4, and two controls wit hout applicati on for each epoch, with the first being harvested the day of product application, and the second kept in the field until the final crop cycle. Analyses of one thousand seed weight, electrical conductivity, emergence speed index, and a sanity test were performed. The application of maturing herbicides to canola increases the one thousand seed weight and rate of emergence speed. At the same time, it increases electrical conductivity and the incidence of ungi. Plants that remained in the field u ntil the end of the crop cycle and did not receive herbicide application resulted in higher quality seeds. The most appropriate moment to apply maturation herbicides to canola is in the G4 season.herbicides to canola is in the G4 season. Made available in DSpace on 2021-02-08T14:19:21Z (GMT). No. of bitstreams: 1 Pilla-2020-721.pdf: 300263 bytes, checksum: 19fe9a0306f1f7aa68a21b45e38b9f1f (MD5) Previous issue date: 2020

Crop-weed competition induces stress in plants causing physiological changes which can be evaluated using the RT-qPCR technique. The aim of this study was to evaluate the stability of candidate reference genes and measure the relative gene expression of antioxidant enzymes and components of the photosynthetic apparatus in soybean in competition with glyphosate-susceptible and resistant Italian ryegrass (Lolium multiflorum Lam.). The experiment was carried out in a greenhouse using replacement series between soybean and Italian ryegrass biotypes. In this study, candidate reference genes were evaluated for use as controls in RT-qPCR to quantify gene expression. An evaluation was made of genes that encode catalase, ascorbate peroxidase, superoxide dismutase, chlorophyll a/b, phytochrome A and cytochrome P450 at 50 days after emergence of the soybean. The SKIP and GAPDH genes were the most stable for soybean and Italian ryegrass, respectively. The soybean subjected to the interspecific competition with the glyphosate-resistant Italian ryegrass biotype showed an increase in superoxide dismutase gene expression. The catalase and cytochrome P450 genes were up-regulated in the susceptible biotype while the other genes were down-regulated. However, the soybean crop under interspecific competition with glyphosate-resistant biotye showed as up-regulated for all the genes evaluated. For the photosynthetic apparatus, cytochrome P450 gene was up-regulated under intraspecific competition on both Italian ryegrass biotypes, while the phytochrome A was up-regulated only in the resistant biotype. Thus, the increase in genes investigated represents a potential tool for the genetic improvement of plants to enhance their competitive capacity. Made available in DSpace on 2021-02-09T14:17:51Z (GMT). No. of bitstreams: 1 Beneman-2020-718.pdf: 1099168 bytes, checksum: 76076bf3375a498fc75e649233a30229 (MD5) Previous issue date: 2020

Italian ryegrass (Lolium multiflorum Lam.) is a weed broadly found in fields cultivated with wheat and barley crops. Seed inputs into the soil before harvesting winter crops increase seed bank, ensuring survival. This study evaluated the persistence of Italian ryegrass seeds subjected to burial depths over time. Experiments were carried out in the field for two years in randomized block experimental design with four repetitions. Dormant seeds harvested from mother-plants were put in nylon bags containing soil. Previously, seed viability was evaluated in a 1 % tetrazolium solution, and 50 viable seeds by repetition were buried at 0.5, 5.0, 10, and 20 cm depths. Seed persistence was evaluated by the percentage of deteriorated and remaining seeds, non-dormant seeds, abnormal seedlings, and viable and non-viable dormant seeds at 0, 30, 60, 90, 180, 360, 540, and 720 days after burial (DAB). Seed persistence increased at 10 and 20 cm of burial depth compared to seeds in the soil layers up to 5 cm. Moreover, burial depth at 10 and 20 cm showed lower percentage of deteriorated seeds (10 % lower) compared to 0.5 cm at 360 DAB. For non-dormant seeds, a higher percentage was found at 90 DAB, regardless of seed burial depth. Dormancy breakage occurred until 180 DAB, and more rapidly at 10 and 20 cm depths. At 540 DAB, more than 95 % of seeds were unviable, demonstrating short persistence of Italian ryegrass in the soil seed bank. Made available in DSpace on 2021-02-08T14:18:53Z (GMT). No. of bitstreams: 1 Vargas-2020-e20190078.pdf: 838643 bytes, checksum: 445228980f554b0d5829aba6bd5ed0ec (MD5) Previous issue date: 2020

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. Made available in DSpace on 2021-02-09T13:18:35Z (GMT). No. of bitstreams: 1 Piasecki-2020-285.pdf: 264629 bytes, checksum: 9eae754ec72262cd23e97e0716fd8e5f (MD5) Previous issue date: 2020

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. Key words: Lolium multiflorum Lam., ploidy level, chromosome counting, resistance. Made available in DSpace on 2021-02-09T14:18:05Z (GMT). No. of bitstreams: 1 Schmitz-2020-335.pdf: 5447691 bytes, checksum: 19af3b8a42788b77cac91f1b24053a73 (MD5) Previous issue date: 2020

Plant growth analysis is useful for determining adequate management practices and exploring the maximum yield potential of cultivars or hybrids. Canola hybrids with resistance to herbicides have been studied and registered for Brazilian conditions, as they improve weed management in canola crops. This study evaluated the growth of canola hybrids resistant to triazine or imidazolinone herbicides compared to a sensitive hybrid. The experiment was conducted using a completely randomized design, with four replications, in a bifactorial scheme using three hybrids and six sampling times. The canola hybrids used were Hyola 571CL (resistant to imidazolinones), Hyola 555TT (resistant to triazines), and Hyola 61 (sensitive to both herbicides). Height, leaf area, and dry matter of roots, leaves, stems, and shoots of the plants were evaluated at 14, 28, 42, 56, 70, and 119 days after emergence (DAE). The physiological indices absolute growth rate, leaf area ratio, specific leaf area, and net assimilation rate were calculated, and yield indices evaluated. Compared to Hyola 61, the Hyola 555TT hybrid showed lower values of leaf dry matter at 70 DAE, absolute growth rate up to 56 DAE, and net assimilation rate at 14 and 28 DAE, and a higher leaf area ratio at 56 DAE, whereas the hybrid Hyola 571CL presented lower leaf area and lower leaf dry matter at 70 DAE. At flowering, compared to Hyola 61, the hybrid Hyola 571CL presents lower leaf area, and the hybrids Hyola 555TT and Hyola 571CL have lower leaf dry matter accumulation. Differences in the growth of canola hybrids Hyola 555TT, Hyola 571CL and Hyola 61 do not cause differences in their grain yield. Key words: Brassica napus L. Dry matter. Growth rate. Leaf area. Yield indic Made available in DSpace on 2021-02-09T13:18:21Z (GMT). No. of bitstreams: 1 Durigon-2020-2911.pdf: 393500 bytes, checksum: cfb7e5894220a5627cf6c819515cf8d7 (MD5) Previous issue date: 2020

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

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.

Canola is an important rotation crop for the winter season and the use of atrazine-resistant hybrids can lead to an increase in yield. This work was aimed at evaluating the effect of atrazine on photochemical and biochemical processes of photosynthesis in triazine-resistant canola. The experiment was conducted in a greenhouse, with triazine-resistant hybrid Hyola® 555TT, in a randomized block design with three replications. The treatments consisted of application or no application of atrazine on canola plants. The plants were assessed at one, three, five, and eight days after application (DAA) for chlorophyll indexes, modulated chlorophyll a fluorescence and gas exchange. Chlorophyll indexes were higher in canola plants treated with atrazine. Application of atrazine caused an increase in fluorescence at steady state and a reduction in quantum efficiency of photosystem II and electron transport rate, at 1 DAA, and a reduction in photochemical quenching, at 1 and 3 DAA. Lower stomatal conductance, at 1 DAA, and higher net carbon assimilation rate, at 8 DAA, were found in plants treated with atrazine. The application of atrazine temporarily reduces electron transport between photosystems and increases chlorophyll indexes in resistant canola plants, raising the net carbon assimilation rate at eight days after application. Keywords: Brassica napus, chlorophyll indexes, gas exchange, modulated fluorescence. RESUMO - A canola é uma importante cultura para rotação na estação fria, e o uso de híbridos com resistência à atrazina pode contribuir para o aumento da produtividade. Este trabalho objetivou avaliar o efeito da atrazina nos processos fotoquímicos e bioquímicos da fotossíntese em canola resistente a triazinas. O experimento foi conduzido em casa de vegetação, com o híbrido resistente à triazina Hyola® 555TT, no delineamento em blocos casualizados com três repetições. Os tratamentos consistiram da aplicação ou não de atrazina nas plantas de canola. As plantas foram avaliadas em um, três, cinco e oito dias após a aplicação (DAA) quanto aos índices de clorofila, fluorescência modulada da clorofila a e troca de gases. Os índices de clorofila foram maiores nas plantas de canola tratadas com atrazina. A aplicação deste herbicida ocasionou aumento na fluorescência em estado estável e redução na eficiência quântica do fotossistema II e na taxa de transporte de elétrons, em 1 DAA, bem como redução na dissipação fotoquímica, em 1 e 3 DAA. Menor condutância estomática, em 1 DAA, e maior taxa de assimilação líquida de carbono, em 8 DAA, foram observados em plantas tratadas com atrazina. A aplicação de atrazina temporariamente o transporte de elétrons entre os fotossistemas e aumenta os índices de clorofila em plantas de canola resistentes, aumentando a taxa de assimilação líquida de carbono aos oito dias após a aplicação. Palavras-chave: Brassica napus, índices de clorofila, troca de gases, fluorescência modulada. Made available in DSpace on 2019-10-23T00:39:48Z (GMT). No. of bitstreams: 1 ID447062019v37e019190367PlantaDaninha.pdf: 429239 bytes, checksum: 4defe2ddff023b057310709907333d32 (MD5) Previous issue date: 2019

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.

The antioxidant defense system acts to maintain the equilibrium between the production of reactive oxygen species (ROS) and the elimination of toxic levels of ROS in plants. Overproduction and accumulation of ROS results in metabolic disorders and can lead to the oxidative destruction of the cell. Several stress factors cause ROS overproduction and trigger oxidative stress in crops and weeds. Recently, the involvement of the antioxidant system in weed interference and herbicide treatment in crops and weeds has been the subject of investigation. In this review, we address ROS production and plant mechanisms of defense, alterations in the antioxidant system at transcriptional and enzymatic levels in crops induced by weed interference, and herbicide exposure in crops and weeds. We also describe the mechanisms of action in herbicides that lead to ROS generation in target plants. Lastly, we discuss the relations between antioxidant systems and weed biology and evolution, as well as the interactive effects of herbicide treatment on these factors.

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.

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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.

Ryegrass(Lolium multiflorum)is one of the most worrisome species with regard to herbicide resistance. This study aimed at characterizing the acetolactate synthase (ALS) enzyme activity of resistant biotypes (NC and AR) and susceptible biotypes to iodosulfuron-methyl-sodium (iodosulfuron). Different concentrations of pyruvate (1, 10, 20, 40, 60, 80 and 100 mM), of iodosulfuron (0 to 100 µM for the resistant biotypes and 0 to 0.5 µM for the susceptible biotype) and concentrations of valine, leucine and isoleucine (0, 0.001, 0.01, 0.1, 1, 10 and 100 mM) were used for the in vitro characterization. According to the results, the Michaelis constant (Km) values (pyruvate) for the assessed biotypes were similar. With iodosulfuron, resistant biotypes needed 395 to 779 times more herbicide in order to inhibit 50% of the enzyme activity, compared to the susceptible biotype. This confirmed a sensitivity modification of the ALS enzyme in the resistant biotypes. The resistant biotypes were less sensitive to the inhibition of the enzyme activity in the presence of the three amino acids. It was possible to conclude that biotype resistance was due to the enzyme insensitivity to iodosulfuron.

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This work aimed to compare the competitive ability of canola hybrids susceptible (conventional) or resistant to triazine or imidazolinone group herbicides, with turnip. The experiments were conducted in greenhouse, in a completely randomized design, with four replicates. The hybrids Hyola 571CL (resistant to imidazolinone), Hyola 555TT (resistant to triazine), and Hyola 61 (conventional) were used. The treatments consisted of ratios (100:0; 75:25; 50:50; 25:75; 0:100%) of canola and turnip plants. The evaluation was performed 44 days after emergence, determining the leaf área (AF), dry matter of aerial part (MSPA), and stature (EST) of the plants. The competitiveness analysis was performed through diagrams and interpretation of the competitiveness indexes. For the canola hybrids, the competition occurred by the same mean resources. There was damage to the crop growth in competition with the turnip. The turnip was not benefited only when in competition with Hyola 571CL hybrid, for the EST variable, and with the conventional canola, for the variable AF. There was significance for the competitiveness indexes, demonstrating that turnip is more competitive then the crop. Greater AF, MSPA, and EST occurred for canola plants in the smallest proportions of turnip and, for turnip plants, in the largest proportions of canola. The ability to compete with turnip is similar among hybrids, with injury to the crop and benefit to the weed, when competing. Interspecific competition is more damaging to canola hybrids; and intraspecific competition is more damaging to turnip. Keywords: Brassica napus L., Raphanus sativus L., interference, competitiveness. RESUMO - Este trabalho objetivou comparar a habilidade competitiva de híbridos de canola, suscetível (convencional) ou com resistência aos herbicidas do grupo das triazinas ou das imidazolinonas, com o nabo. Os experimentos foram conduzidos em casa de vegetação, no delineamento inteiramente casualizado com quatro repetições. Foram utilizados os híbridos Hyola 571CL (resistente a imidazolinonas), Hyola 555TT (resistente a triazinas) e Hyola 61 (convencional). Os tratamentos consistiram de proporções (100:0; 75:25; 50:50; 25:75; 0:100%) de plantas de canola e do nabo. A avaliação foi realizada aos 44 dias após a emergência, determinando-se a área foliar (AF), matéria seca de parte aérea (MSPA) e estatura (EST) de plantas. A análise da competitividade foi feita por meio de diagramas e interpretação dos índices de competitividade. Para os híbridos de canola, a competição ocorreu pelos mesmos recursos do meio. Houve prejuízo ao crescimento da cultura em competição com o nabo. O nabo somente não foi beneficiado quando em competição com o híbrido Hyola 571CL, para a variável EST, e com a canola convencional, para a variável AF. Houve significância para os índices de competitividade, demonstrando que o nabo é mais competitivo que a cultura. Maior AF, MSPA e EST ocorreu para plantas de canola nas menores proporções de nabo e, para plantas de nabo, nas maiores proporções de canola. A habilidade em competir com o nabo é semelhante entre os híbridos, havendo prejuízo à cultura e benefício à planta daninha, quando em competição. A competição interespecífica é mais prejudicial para os híbridos de canola, e a competição intraespecífica, para o nabo. Palavras-chave: Brassica napus L., Raphanus sativus L., interferência, competitividade. Made available in DSpace on 2020-02-28T18:11:19Z (GMT). No. of bitstreams: 1 DurigonM.R.MarianiFetall.pdf: 343476 bytes, checksum: eef70cdc03cc03c7e81f1916d8388134 (MD5) Previous issue date: 2019

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.

Horseweed control through application of 2.4-D in the winter season is an alternative to manage biotypes resistant to herbicides that belong to other mechanisms of action. The objectives of this study were to assess the physiological quality of wheat seeds and determine the rate of 2.4-D residue, as function of application stages and herbicide rates. The treatments were arranged in factorial scheme, with three application stages (flowering, soft dough and hard dough), and four 2.4-D rates (0; 504; 1,008 and 2,015 g a.i. ha-1). The application of 2.4-D in the wheat crop changed physiological seed quality by increased the rate and total percentage of germination. The application of 2.4-D resulted in herbicide accumulation in seeds, especially when application was carried out at the soft dough stage. Also, the increase in herbicide rate increased the level of residue in the seeds. However, regardless of stage of application for 2.4-D and herbicide rate in use, the values of residue found in the seeds were below the allowed maximum limit. RESUMO: O controle de buva através da aplicação de 2,4-D na estação hibernal de cultivo é alternativa para o manejo de biótipos com resistência a herbicidas pertencentes a outros mecanismos de ação. Os objetivos do estudo foram avaliar a qualidade fisiológica das sementes de trigo e determinar o resíduo de 2,4-D, em função do estádio de aplicação e de doses do herbicida. Os tratamentos foram arranjados em esquema fatorial, sendo três estádios de aplicação (florescimento, grão pastoso e massa firme) e quatro doses do herbicida 2,4-D (0, 504, 1.008 e 2.015 g i.a. ha-1). A aplicação de 2,4-D na cultura do trigo alterou a qualidade fisiológica das sementes, resultando em aumento da velocidade e da porcentagem total de germinação. A aplicação do 2,4-D resultou em acúmulo de resíduo do herbicida nas sementes, principalmente quando a aplicação foi feita no estádio de grão pastoso, e o aumento da dose herbicida elevou a concentração de resíduo. Contudo, independentemente da época em que o 2,4-D foi aplicado, assim como da dose utilizada, os valores de resíduo observados nas sementes encontraram-se abaixo do limite máximo permitido.

The objective of this study was to evaluate the relative competitive ability of soybean with different development stages of hairy fleabane. Two experiments were conducted in greenhouse, in a completely randomized design. In the experiment it was tested soybean and hairy fleabane competition at different stage of development (rosette and 15 cm height) at the proportions 100:0, 75:25, 50:50, 25:75 and 0:100, and total plant population was 315 plant m-2. The variables evaluated were plant height, leaf area, and shoot dry matter (leaves and stems). Competitive analysis was performed by diagrams and interpreting the competitiveness index. The soybean has greater competitive ability that horseweed for both development stages. The intraspecific competition is more intense for soybean when in hairy fleabane rosette stage, and the competitive relations are equivalent between soybean and hairy fleabane of 15 cm tall. The both hairy fleabane stages were injured in the soybeans competition.

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.

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.

Mutations in the gene that encodes the enzyme acetolactate synthase (ALS), conferring plant resistance to ALS inhibitor herbicides, can reduce or inhibit enzymatic function. The objective of this work was to determine the functionality and kinetic characteristics of the enzyme ALS and evaluate the action of the herbicides imazapic (imidazolinone) and metsulfuron-methyl (sulfonylurea) on the activity of the enzyme ALS in canola hybrid Hyola 571CL (imidazolinone resistant), compared to hybrids Hyola 555TT (triazine resistant) and Hyola 61 (conventional). The plants were grown in a greenhouse, and leaves were collected to perform ALS activity analysis. The concentration of pyruvate to provide initial velocity equal to half the maximum reaction rate (Km) and the maximum reaction rate (Vmax) was determined, as well as the enzyme’s activity in the presence of imazapic and metsulfuron-methyl inhibitors. There was no change in the Km and Vmax in the hybrid Hyola 571CL in relation to Hyola 61. The hybrid Hyola 555TT presented Vmax higher than the other hybrids. In the hybrid Hyola 571CL, the activity of ALS was reduced only by the application of metsulfuron-methyl, and the functionality of the enzyme did not change in relation to the other hybrids. The hybrid Hyola 571CL is resistant only to the imidazolinone group herbicide and this resistance does not cause adaptive cost in relation to the other hybrids.

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portuguesNo Brasil, a buva (Conyza spp.) e uma das principais plantas daninhas devido a resistencia a herbicidas e alta competividade com as culturas. Esta e responsavel por perdas de produtividade em culturas como soja, milho, algodao e trigo cuja implementacao da semeadura direta e a resistencia aos herbicidas favorecem seu estabelecimento. O conhecimento do efeito da temperatura na germinacao permite prever as regioes com maior potencial de colonizacao e auxiliar no manejo. Assim, objetivou-se com este trabalho determinar o efeito da temperatura na germinacao, viabilidade e longevidade de sementes de buva em solo de terras altas. As temperaturas testadas foram 10, 20 e 30oC e os periodos de avaliacao 0, 15, 30, 45 e 60 dias. As sementes foram acondicionadas em saco de malha de nylon (5 x 5cm), distribuidas em 10g de solo de terras altas (Argissolo Vermelho Amarelo, de textura franco-arenosa), e, alocadas em caixas gerbox com solo a profundidade de 0 a 0,5 cm, nas temperaturas descritas. Avaliou-se em percentagem de sementes remanescentes, primeira e segunda contagem de germinacao, plântulas anormais, sementes mortas, dormentes, viaveis e nao viaveis. A semente de buva atinge dormencia secundaria, nas temperaturas de 10, 20 e 30oC e sua qualidade e longevidade sao prejudicadas nas temperaturas de 20 e 30oC. Palavras-chave: dormencia secundaria; profundidade; manejo; qualidade de sementes EnglishIn Brazil, horseweed is one of the most important weeds because of the resistance to herbicides and high competitive for the crops. A large of losses were reported in major crops such as soybeans, wheat and corn, where the use a no-tillage system and the herbicide resistance promote better establishment. A correct understanding of the way temperature influences germination enables the prediction of the regions with the highest potential for colonization by this weed and thus facilitates its control. The objective of this study; therefore, was to discern the ways temperature affected the germination, viability and longevity of horseweed seeds. Testing was done at 10, 20 and 30°C, while evaluation occurred on days 0, 15, 30, 45 and 60. Seeds were packed in a nylon mesh bag (5x5cm), with 10g of upland soil (Yellow Red Argissolo, sandy loam texture), placed in transparent plastic boxes at 0 to 0.5cm soil depth, at the temperatures specified. Percentage of remaining seeds, first and second germination counts, abnormal seedlings, and dead, dormant, viable and non-viable seeds, were assessed. Horseweed seeds achieve secondary dormancy at 10, 20 and 30°C, while their quality and the longevity showed damage at 20 and 30°C temperatures. Key words: secondary dormancy; depth; management; seed quality

RESUMO - Populacoes de azevem resistente aos inibidores da enzima ALS tem aumentado rapidamente nos campos cultivados. Para o manejo da resistencia, sao necessarios estudos de heranca da resistencia, os quais permitem entender a evolucao da resistencia, a estrutura genetica da populacao e a dinâmica de adaptacao dos biotipos resistentes. Este trabalho teve como objetivo identificar o tipo de heranca, o numero de genes envolvidos e o grau de resistencia dos biotipos de azevem, homozigotos e heterozigotos, resistentes ao iodosulfuron. A partir da selecao dos biotipos homozigoto resistente (R) e homozigoto suscetivel (S), foram realizados cruzamentos (R x S) para obtencao de plantas F1, e estas, cruzadas para obtencao da F2, e realizaram-se retrocruzamentos entre plantas F1 e os respectivos genitores masculinos e femininos resistentes (RCr) e sensiveis (RCs). As sementes F1, F2, RCr, RCs e dos genitores foram semeadas em bandejas e avaliadas, com aplicacao do iodosulfuron, quanto a sua suscetibilidade ou resistencia. Plantas F1 e dos genitores foram tratadas com doses crescentes do herbicida. A avaliacao de controle dessas plantas pelo iodosulfuron foi feito por meio de notas (0 a 100), referentes aos sintomas de intoxicacao e pela massa da materia seca da parte aerea acumulada. Os genitores masculino ou feminino transmitiram a caracteristica para a prole, sendo esta 100% resistente, indicando gene de resistencia dominante. A geracao F2 apresentou segregacao 3:1 resistente/suscetivel, confirmando a caracteristica de dominância. O teste de dominância das plantas F1 evidenciou que as plantas homozigotas resistentes e as heterozigotas apresentam grau de resistencia semelhante. Conclui-se que a resistencia do azevem ao iodosulfuron e codificada por gene dominante nuclear com dominância completa. Palavras-chave: Lolium spp., genetica, herbicida.

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 main limiting factors for the productive potential of wheat crops are related to the competition with weeds for resources such as water, light and nutrients. Nitrogen (N) is an important nutrient used to maintain crop productivity, as well as promoting the competitive ability of crops and therefore suppress the weed growth. In this context, the goal of this study was to evaluate the effects of wheat plants in competition with ryegrass under different levels of nitrogen fertilization. Treatments were arranged in a factorial design, where factor A consisted in nitrogen rates (0, 60, 120, 180 and 240 kg ha-1) and factor B consisted in ryegrass and wheat plants ratios, which were: 100/0 (pure stand of 64 wheat plants), 50/50 (32 wheat plants and 32 ryegrass plants) and 0/100 (pure stand of 64 ryegrass plants). Competition between the culture and ryegrass by N resulted in mutual damages, but the culture was more competitive than weeds, regardless of the N dose. The use of doses up to 120 kg N ha-1 increased the evaluated variables for wheat and ryegrass. Interspecific competition and nitrogen in higher than 120 kg N ha-1 doses reduced the morphological variables mass of the aerial part dry matter and leaf area of wheat and ryegrass. RESUMO Os principais fatores limitantes do potencial produtivo da cultura do trigo estão relacionados à competição das plantas daninhas por recursos como água, luz e nutrientes. O nitrogênio (N) é importante nutriente utilizado para manter a produtividade das culturas, além de favorecer a habilidade competitiva da cultura e, com isso, suprimir o crescimento das plantas daninhas. Nesse contexto, o objetivo deste trabalho foi avaliar os efeitos da competição de plantas de trigo e azevém sob diferentes níveis de adubação nitrogenada. Os tratamentos foram arranjados em esquema fatorial, em que o fator A constituiu-se de doses de nitrogênio (0, 60, 120, 180 e 240 kg ha-1) e o fator B, de proporções de plantas de azevém e trigo, as quais foram: 100/0 (estande puro de 64 plantas de trigo), 50/50 (32 plantas de trigo e 32 plantas de azevém) e 0/100 (estande puro de 64 plantas de azevém). A competição entre a cultura e o azevém pelo N acarretou prejuízo mútuo, porém a cultura mostrou maior competitividade do que a planta daninha, independentemente da dose de N. A utilização de doses até 120 kg N ha-1 aumentaram as variáveis avaliadas para o trigo e para o azevém. A competição interespecífica e o nitrogênio nas doses superiores a 120 kg N ha-1 reduziram as variáveis morfológicas massa da matéria seca da parte aérea e área foliar do trigo e do azevém.

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RESUMO – O presente estudo teve por objetivo avaliar a eficacia de herbicidas pos-emergentes registrados para a cultura do milho, assim como futuras alternativas de controle quimico, no manejo de biotipos de capim-amargoso resistente ao glyphosate. Tres experimentos, em condicao de casa de vegetacao, foram realizados no delineamento de blocos ao caso, com tres repeticoes. Herbicidas de reconhecida eficiencia agronomica no controle de gramineas na cultura do milho (tembotrione, mesotrione e nicosulfuron) e futura alternativas de controle quimico (haloxyfop-p-methyl e ammonium-glufosinate) foram aplicados em diferentes periodos de desenvolvimento sobre o capim-amargoso. Foram avaliados os sintomas de intoxicacao e a porcentagem de reducao do acumulo da massa de materia seca (MMS) da infestante apos a ultima avaliacao de controle. Os herbicidas nicosulfuron, haloxyfop-p-methyl e ammonium-glufosinate ocasionaram a morte da planta independentemente do momento de aplicacao. Tembotrione e mesotrione, apesar de reduzirem a porcentagem de acumulo da MMS, nao ocasionaram morte das plantas. Conclui-se que o nicosulfuron se caracteriza como importante ferramenta no controle de capim-amargoso. As moleculas haloxyfop-p-methyl e ammonium-glufosinate apresentam potencial para serem utilizadas como alternativas de controle quimico da infestante. Os herbicidas tembotrione e mesotrione, apesar de reconhecida acao graminicida, nao sao indicados para o controle do capim-amargoso. Palavras-chave: Zea mays , herbicidas, resistencia, planta daninha. ALTERNATIVES OF CHEMICAL CONTROL FOR SOURGRASS ( Digitaria insularis ) ON MAIZE CROP ABSTRACT – This study aimed to evaluate the efficacy of registered herbicides for weed control in maize crop and to test future alternatives of chemical control for management of sourgrass biotypes resistant to glyphosate. Three experiments, in the greenhouse, were carried out in a randomized block design with three replicates. Herbicides of recognized agronomic efficiency in grass control on maize (tembotrione, mesotrione and nicossulfuron) and future alternatives of chemical control (haloxyfop-p-methyl e ammonium-glufosinate), as well as, standard herbicide treatment used on maize off-season glyphosate resistant (glyphosate + atrazine), were sprayed on sourgrass plants at different growth periods. The parameters evaluated were intoxication symptoms and the decrease in dry mass accumulation. The herbicides nicossulfuron, haloxyfop-p-methyl and ammonium-glufosinate caused the death of plants, regardless of their developmental stage. In spite of causing a decrease in weed dry mass accumulation, tembotrione and mesotrione did not cause plant death. It is concluded that nicossulfuron is characterized as an important tool in control of sourgrass. The molecules haloxyfop-p-methyl and ammonium-glufosinate have potential to be used as alternatives to control this infestant. The herbicides tembotrione and mesotrione despite recognized grass control were notindicated to control of sourgrass. Keywords: Zea mays , herbicide, resistance, weed.

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.

Horseweed (Conyza spp.) is an annual weed, infesting soybean crops in southern Brazil, with chlorimuron-ethyl being one of the most commonly used herbicides for its control. However, in recent soybean harvests, an unsatisfactory control of this weed using this herbicide was observed, generating suspicion regarding the selection of resistant biotypes. The objective of this study was to evaluate the susceptibility of horseweed biotypes to the herbicide chlorimuron-ethyl. Two experiments were conducted in a greenhouse; in the first one, the biotypes were selected selected, and the second experiment was arranged in a 5 x 5 factorial in a completely randomized design with four replications. The treatments used in the preparation of the dose response curves were doses of the herbicide chlorimuron-ethyl (0.0, 1.56, 3.13, 6.25, 12.5, and 25 g ha-1), applied on the five horseweed biotypes at the 3-4 leaf growth stage. The variables evaluated were visual control percentage and shoot dry weight, compared to the control without herbicide application, and plant acetolactate accumulation. It was concluded that there is a differential susceptibility among the biotypes at doses of less than 20 g ha-1 (dose response curves), which indicates low-level resistance. The practical consequences are the indications of chlorimuron-ethyl application at the maximum doses recomended and that the practice of rotating mechanisms of action must be used in the chemical weed management of these areas.

Conyza bonariensis (hairy fleabane) is one of the most problematic and widespread glyphosate-resistant weeds in the world. This highly competitive weed species significantly interferes with crop growth and substantially decreases crop yield. Despite its agricultural importance, the molecular mechanisms of glyphosate resistance are still unknown. The present RNA-Seq study was performed with the goal of identifying differentially expressed candidate transcripts (genes) related to metabolism-based non-target site glyphosate resistance in C. bonariensis. The whole-transcriptome was de novo assembled from glyphosate-resistant and -sensitive biotypes of C. bonariensis from Southern Brazil. The RNA was extracted from untreated and glyphosate-treated plants at several timepoints up to 288 h after treatment in both biotypes. The transcriptome assembly produced 90,124 contigs with an average length of 777 bp and N50 of 1118 bp. In response to glyphosate treatment, differential gene expression analysis was performed on glyphosate-resistant and -sensitive biotypes. A total of 9622 genes were differentially expressed as a response to glyphosate treatment in both biotypes, 4297 (44.6%) being up- and 5325 (55.4%) down-regulated. The resistant biotype presented 1770 up- and 2333 down-regulated genes while the sensitive biotype had 2335 and 2800 up- and down-regulated genes, respectively. Among them, 974 up- and 1290 down-regulated genes were co-expressed in both biotypes. In the present work, we identified 41 new candidate target genes from five families related to herbicide transport and metabolism: 19 ABC transporters, 10 CYP450s, one glutathione S-transferase (GST), five glycosyltransferases (GT), and six genes related to antioxidant enzyme catalase (CAT), peroxidase (POD), and superoxide dismutase (SOD). The candidate genes may participate in metabolic-based glyphosate resistance via oxidation, conjugation, transport, and degradation, plus antioxidation. One or more of these genes might &lsquo, rescue&rsquo, resistant plants from irreversible damage after glyphosate treatment. The 41 target genes we report in the present study may inform further functional genomics studies, including gene editing approaches to elucidate glyphosate-resistance mechanisms in C. bonariensis.

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.

Ryegrass is the main weed in wheat crop, causing yield loss due to competition by environmental resources. The objectives of this study were to estimate the fitness cost of ryegrass biotypes with low-level resistance and susceptible to fluazifop and to investigate the relative competitive ability of these biotypes between themselves and against the crop. Thus, fitness cost and competitive ability experiments were conducted under greenhouse conditions. For the fitness cost experiments, the low-level resistant ryegrass biotypes and those susceptible to fluazifop were used. For competitive ability, the treatments were arranged in a replacement series, with five proportions of the wheat cultivar FUNDACEP Horizonte and the low-level resistant and susceptible ryegrass biotypes 100:0, 75:25, 50:50, 25:75 and 0:100. Competitive analysis was carried out through diagrams applied to the replacement experiments and use of relative competitiveness indices. Variables evaluated were plant height, in the fitness cost experiment, and leaf area and shoot dry biomass in both experiments. The ryegrass biotypes show overall similar fitness cost and competitive ability. The wheat cultivar FUNDACEP Horizonte is superior in competitive ability to the ryegrass biotype with low-level resistance and equivalent to the susceptible biotype. O azevém é a principal planta daninha da cultura do trigo, a qual contribui para a perda de produtividade devido à competição exercida por recursos do ambiente. Os objetivos deste trabalho foram estimar o valor adaptativo de biótipos de azevém com resistência de nível baixo e suscetível ao herbicida fluazifop e investigar a habilidade competitiva relativa desses biótipos entre si e com a cultura do trigo. Para isso, foram realizados experimentos de valor adaptativo e habilidade competitiva em casa de vegetação. Para valor adaptativo, utilizaram-se biótipos de azevém com resistência de nível baixo e suscetível ao herbicida fluazifop. Quanto à habilidade competitiva, os tratamentos foram arranjados em série de substituição, constituindo-se de cinco proporções de plantas de trigo cultivar FUNDACEP Horizonte e biótipos de azevém com resistência de nível baixo e suscetível: 100:0, 75:25, 50:50, 25:75 e 0:100. A análise da competitividade foi efetuada por meio de diagramas aplicados a experimentos substitutivos e uso de índices de competitividade relativa. As variáveis avaliadas foram estatura, no experimento de valor adaptativo, e área foliar e matéria seca da parte aérea, em ambos. Os biótipos de azevém apresentam, em geral, valor adaptativo e habilidade competitiva similares. O trigo cultivar FUNDACEP Horizonte apresenta habilidade competitiva superior à do biótipo de azevém com resistência de nível baixo e equivalente à do suscetível.

A determinação da habilidade competitiva de cultivares de cevada com plantas daninhas torna-se relevante para a adoção do método de manejo cultural; desse modo, podemse diminuir os custos de produção, bem como os impactos ambientais causados por outros métodos de manejo, como o químico. Este trabalho comparou as habilidades competitivas relativas de três cultivares de cevada e um biótipo de azevém. Foram realizados experimentos em casa de vegetação na estação de crescimento 2008/09, utilizando-se delineamento experimental de blocos casualizados, com quatro repetições. Os tratamentos foram arranjados em série de substituição e constituíram-se de cinco proporções de plantas de cevada e do azevém competidor com a cultura: 100:0, 75:25, 50:50, 25:75 e 0:100. A cevada foi representada pelos cultivares BRS Greta, BRS Elis e BRS 225, e o competidor, pelo azevém. A análise da competitividade foi efetuada por meio de diagramas aplicados a experimentos substitutivos, mais uso de índices de competitividade relativa. As variáveis estudadas foram: afilhamento, estatura, área foliar e massa da matéria seca da parte aérea das plantas. O azevém afetou o afilhamento, a área foliar e a massa da matéria seca da parte aérea de plantas dos cultivares de cevada BRS Greta, BRS Elis e BRS 225, demonstrando grande habilidade competitiva com a cultura pelos recursos disponíveis no meio. Entre os cultivares de cevada avaliados, BRS Elis foi o mais competitivo na presença do azevém, que é uma das espécies daninhas que necessitam de controle mesmo quando presente em baixas proporções na cultura da cevada. Characterization of the competitive ability of barley varieties against weed species is relevant for the adoption of the cultural method of weed control; thus, it is possible to reduce both the production costs and environmental impacts caused by other management methods, including the use of chemicals. This work assessed the competitive ability of barley varieties against ryegrass. Trials were installed under greenhouse conditions at the 2008/2009 cropping season, in a completely randomized block design, with four replications. Treatments were arranged in a substitution series design constituted by five proportions of plants of both species: 100:0; 75:25; 50:50; 25:75; and 0:100. Barley varieties BRS Greta, BRS Elis and BRS 225 were tested against ryegrass as the competitor. The competitive analysis was carried out through diagrams applied to the substitutive design, plus determination of relative competitiveness indexes. Plant height, tillering, leaf area and shoot dry mass were evaluated. The presence of ryegrass reduced tillering, leaf area and dry mass accumulation for all varieties of barley tested, showing to be an aggressive competitor. Among the barley varieties tested, BRS Elis showed the highest competitive ability against ryegrass. Ryegrass requires the adoption of control techniques even when present at low proportions in the field.

O potencial de produtividade da cultura do trigo é limitado pela competição exercida pelas plantas daninhas, especialmente pelos recursos luz, água e nutrientes. Em sistemas de produção, a disponibilidade de nitrogênio (N) quase sempre é limitante, influenciando o crescimento da planta mais do que qualquer outro nutriente. O objetivo deste trabalho foi avaliar variáveis morfológicas e componentes da produtividade da cultura do trigo em competição com azevém, em função de épocas de aplicação e doses de N. Os tratamentos foram dispostos em esquema fatorial (2 x 3 x 5), em que o primeiro fator constou de condição de competição (ausência e presença de azevém), o segundo testou épocas de aplicação de N (100% aplicado no início do afilhamento; 50% no início do afilhamento e 50% no início da diferenciação da espiga (IDE); e 100% no IDE) e o terceiro avaliou doses de N (0, 40, 80, 120 e 160 kg ha-1), na forma de ureia aplicada a lanço. As variáveis analisadas foram: área foliar (AF), massa seca da parte aérea (MSPA), número de afilhos (NA), número de colmos (NC), teor de N da cultura (TN), número de grãos por espigueta (NGES), número de grãos por espiga (NGE), número de espiguetas por espiga (NESE), produtividade biológica (PB), massa média de mil grãos (MMG) e produtividade de grãos (P). O azevém compete com o trigo pelo recurso N, reduzindo a AF, MSPA, NA, NC, TN, NGES, NGE, NESE, PB, MMG e P da cultura. A aplicação do N no início do afilhamento ou fracionada, nas duas doses mais elevadas, aumenta a AF e MSPA. O aumento da dose de N incrementa o TN na cultura do trigo, independentemente da presença ou ausência do competidor. A aplicação de N no IDE ou o incremento da dose de N aumenta o NGES e NGE.

Em biótipos de plantas daninhas resistentes a herbicidas pode haver menor habilidade competitiva, comparativamente aos biótipos suscetíveis. O objetivo da pesquisa foi investigar a habilidade competitiva entre biótipos de Cyperus difformis L. resistente ou suscetível a herbicidas e destes com arroz irrigado. Foram realizados quatro experimentos em casa de vegetação, em 2007 e 2008, em delineamento inteiramente casualizado, com quatro repetições, sendo os tratamentos do primeiro arranjado em série aditiva e dos demais arranjados em série de substituição. Em cada experimento, as proporções entre biótipos de C. difformis resistente e suscetível e destes com arroz foram de 100:0, 75:25, 50:50, 25:75 e 100:0%, com população total de 1060 plantas m-2. As variáveis avaliadas foram área foliar, estatura e matéria seca da parte aérea. A análise da competitividade foi realizada por aplicação de diagramas e interpretações dos índices de competitividade. Biótipos de C. difformis resistente e suscetível a herbicidas inibidores de ALS, em geral, possuem habilidade competitiva equivalente; a cultura do arroz, com a cultivar BRS Querência, tem habilidade competitiva superior a C. difformis resistente ou suscetível a herbicidas inibidores de ALS; para a cultura do arroz, a competição intraespecífica é mais importante, enquanto para C. difformis resistente ou suscetível a herbicidas inibidores de ALS, a mais importante é a competição interespecífica. Biotypes of weeds resistant to herbicides may have lower competitive ability compared to susceptible biotypes. The objective of the study was to investigate the relative competitive ability between biotypes of Cyperus difformis L. resistant or susceptible to ALS-inhibitor herbicides and with rice. Four experiments were carried out under greenhouse, in a completely randomized design with four replications, in 2007 and 2008. Treatments were arranged in additive series and replacement series assay. In each series, the proportion among C. difformis resistant and susceptible plants related to rice were: 100:0, 75:25, 50:50, 25:75 and 100:0%, always with a total population of 1060 plants m-2. Leaf area, plant height and shoot dry mass were evaluated. Competitiveness statistical analysis consisted in applying diagrams to the replacement series and alternative interpretations of the competitiveness indexes. In general, biotypes C. difformis resistant and susceptible to ALS-inhibitors herbicides have equivalent competitive ability; the rice cultivar BRS Querência has superior competitive ability in relation to C. difformis resistant or susceptible to ALS-inhibitors herbicides; and for rice, the intraspecific competition is more important, while for C. difformis resistant or susceptible to ALS-inhibitors herbicides, the most important is the interspecific competition.

The Wild Poinsettia (Euphorbia heterophylla L.) has elevated potential to reduce the soybean yield and is a difficult to control plant due to herbicide resistance. The objectives of this study were to determine the changes in the photosynthetic physiological parameters, secondary metabolite levels, cellular damage, and antioxidant system activity in soybean plants and Wild Poinsettia biotypes with a low level of resistance or susceptibility to glyphosate in competition with soybeans. Two replacement series experiments were conducted in a greenhouse under competition between soybeans and the low-level resistant biotype (experiment I) or susceptible biotype (experiment II). The treatments consisted of different proportions of soybean plants and Wild Poinsettia [100:0 (pure stand of soybean), 50:50, and 0:100 (pure stand of Wild Poinsettia)] and different evaluation periods (the 2013/14 and 2014/15 growing seasons). The following parameters were analyzed: the chlorophyll, carotenoid (CRT), total phenol, hydrogen peroxide (H2O2), and lipid peroxidation levels and the catalase (CAT), ascorbate peroxidase (APX), and superoxide dismutase (SOD) enzyme activity. Generally, competition between the soybeans and the Wild Poinsettia biotypes did not alter the photosynthetic parameters or the photosynthetic pigment levels of the crop. For the weed biotypes, competition with the soybeans negatively affected photosynthesis. Greater losses of chlorophylls and CRTs were observed for the susceptible biotype when in competition with soybeans, whereas the opposite trend was observed for the biotype with a low level of resistance. No cellular damage or alterations in antioxidant system enzyme activity was observed, which indicated a lack of oxidative stress.

Nos Estados do Rio Grande do Sul e do Paraná, há frequentes relatos de falhas de controle de Conyza sumatrensis com chlorimuron-ethyl em lavouras de soja. Assim, os objetivos deste trabalho foram caracterizar morfologicamente as folhas de Conyza sumatrensis e avaliar o controle com herbicidas aplicados em biótipos dessa planta daninha em três estádios de desenvolvimento. Foram realizados dois estudos, com experimentos em casa de vegetação, em delineamento inteiramente casualizado com quatro repetições. No primeiro estudo, os biótipos de buva foram coletados e identificados; já no segundo estudo avaliou-se a resposta de biótipos aos herbicidas, doses e estádios de desenvolvimento. As doses de herbicidas foram: 0,0; 6,25; 12,5; 25; 50; 100; 200; e 400, representadas em porcentagem da dose de registro dos herbicidas chlorimuron-ethyl (20 g ha-1) e glyphosate (720 g e.a. ha-1), aplicadas de modo isolado ou associadas em três estádios de desenvolvimento dos quatro biótipos (2, 5, 17 e 20) de Conyza sumatrensis (altura de 0,5-1 cm e 3-4 folhas; altura 1-2 cm e 6-7 folhas; e altura de 10-12 cm e 12-14 folhas). As variáveis analisadas foram controle, fitomassa seca da parte aérea e as densidades tricomática e estomática da superfície foliar dos biótipos em diferentes estádios de desenvolvimento. Os resultados demonstram que os estádios de desenvolvimento alteram a eficácia dos herbicidas, e aplicações em estádios avançados de desenvolvimento diminuem a eficácia de controle. A exceção foi o biótipo 5 de Conyza sumatrensis, que demonstrou resistência ao glyphosate, independentemente do estádio de desenvolvimento no momento da aplicação do herbicida. Houve variação no número de tricomas entre os biótipos em todos os estádios de desenvolvimento, e o número de estômatos diminuiu com o desenvolvimento dos biótipos. In the states of Rio Grande do Sul and Paraná, there are frequent reports of failure to control Conyza sumatrensis with chlorimuron-ethyl in soybean crops. Thus, the objectives of this study were to characterize Conyza sumatrensis leaves morphologically and evaluate herbicide control in biotypes of this weed at three stages. Two studies were conducted, with experiments in a greenhouse in a completely randomized design with four replications. In the first study, horseweed biotypes were collected and identified, and the second study evaluated the responses of herbicide rates and development stages. The herbicide rates were: 0.0, 6.25, 12.5, 25, 50, 100, 200 and 400, represented as a percentage of the dose registry of herbicides chlorimuronethyl (20 g ha-1) and glyphosate (720 g e.a. ha-1) applied in isolation or associated at three developmental stages of four Conyza sumatrensis (2, 5, 17 and 20) biotypes (height = 0.5-1 cm and 3-4 leaves, height = 1-2 cm and 6-7 leaves, height = 10-12 cm, 12-14 leaves). The variables analyzed were control, shoot dry weight and trichome and stomatal densities biotypes of the leaf surface at different stages of development. The results obtained demonstrate that the developmental stages affect the effectiveness of the herbicides, and applications at advanced stages of development decrease the effectiveness of control. The exception was biotype 5 of Conyza sumatrensis, which shows resistance to glyphosate, regardless of stage of development at the time of herbicide application. There was variation in the number of trichomes among biotypes at all stages of development, and the number of stomata decreased with the development of biotypes.