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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

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

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

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

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.

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 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.

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.

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.