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.

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Resumo -As principais plantas daninhas encontradas na cultura do trigo são o nabo e o azevém, e seu controle em pós-emergência é baseado em herbicidas inibidores da enzima acetolactato sintase (ALS) e acetil coenzima A carboxilase (ACCase) que, em função da resistência, limita as opções de controle. Associações de herbicidas têm sido utilizadas em pós-emergência do trigo, porém, seus efeitos na cultura são pouco conhecidos. O objetivo deste trabalho foi avaliar a seletividade de associações de herbicidas e doses aplicados em pós-emergência do trigo. Foram realizados três experimentos a campo em sistema de semeadura direta, no delineamento de blocos ao acaso com três repetições. Os experimentos foram conduzidos nos municípios de Santa Bárbara do Sul-RS, Cruz Alta-RS e Tupanciretã-RS. Foram estudadas doses e associações entre os herbicidas 2,4-D, metsulfuron-methyl, iodosulfuron, piroxsulam e saflufenacil aplicados no perfilhamento do trigo. As variáveis avaliadas foram fitotoxicidade aos sete, 14, 21 e 35 dias após a aplicação (DAA), rendimento de grãos (kg ha -1 ) e peso hectolitro dos grãos de trigo (PH), sendo os dados dos três experimentos analisados de forma conjunta. Aos 35 DAA as maiores fitotoxicidades foram observadas para metsulfuron-methyl na dose de 9 g i.a. ha -1 e para saflufenacil associado ao metsulfuron-methyl. Os resultados de rendimento de grãos demonstraram que a associação entre 2,4-D e metsulfuron-methyl, saflufenacil isolado ou associado à metsulfuron-methyl e o iodosulfuron-methyl foram seletivos para o trigo. O aumento da dose de metsulfuron-methyl (6 e 9 g i.a. ha -1 ) e a dose de registro de piroxsulam causaram redução significativa na rendimento de grãos de grãos de trigo na média dos três experimentos. O PH dos grãos de trigo não foi influenciado pelos herbicidas estudados. Palavras-chave: Triticum aestivum, mistura de herbicidas, mistura em tanque, resistência Abstract -The main weeds in wheat are wild radish and ryegrass, and its post-emergence control is based on herbicides inhibiting the enzyme acetolactate synthase (ALS) and acetyl coenzyme A carboxase (ACCase), which as a function of resistance limits the control options. Herbicide combinations have been used for post-emergence of wheat; however, the effects of herbicidal combinations are poorly understood. The objective of this work was to evaluate the selectivity of Piasecki et al. Rev. Bras. Herb., v.16, n.4, p.286-295, out./dez. 2017 287

Planta Daninha 2018; v36:e018161420 PIASECKI, C. et al. Interference of GR ® volunteer corn population and origin on soybean grain yield losses 2 de grãos da soja reduziu de forma expressiva quando em competição com populações inferiores a uma planta ou touceira m -2 , sendo de 16% e 46% na população de 0,5 planta individual e touceira m -2 , respectivamente.Palavras-chave: Glycine max, Zea mays, competição, plantas individuais, touceiras, perdas na colheita.

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 ‘rescue’ 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.

Unmanned aerial vehicle (UAV) technology is an emerging powerful approach for high-throughput plant phenotyping field-grown crops. Switchgrass (Panicum virgatum L.) is a lignocellulosic bioenergy crop for which studies on yield, sustainability, and biofuel traits are performed. In this study, we exploited UAV-based imagery (LiDAR and multispectral approaches) to measure plant height, perimeter, and biomass yield in field-grown switchgrass in order to make predictions on bioenergy traits. Manual ground truth measurements validated the automated UAV results. We found UAV-based plant height and perimeter measurements were highly correlated and consistent with the manual measurements (r = 0.93, p < 0.001). Furthermore, we found that phenotyping parameters can significantly improve the natural saturation of the spectral index of the optical image for detecting high-density plantings. Combining plant canopy height (CH) and canopy perimeter (CP) parameters with spectral index (SI), we developed a robust and standardized biomass yield model [biomass = (m × SI) × CP × CH] where the m is an SI-sensitive coefficient linearly varying with the plant phenological changing stage. The biomass yield estimates obtained from this model were strongly correlated with manual measurements (r = 0.90, p < 0.001). Taking together, our results provide insights into the capacity of UAV-based remote sensing for switchgrass high-throughput phenotyping in the field, which will be useful for breeding and cultivar development.

The cultivation of GR® corn prior to soybean favors the occurrence of GR® volunteer corn plants interfering in soybean crops. The interference of volunteer corn causes the soybean yield losses, and the magnitude of losses varies with the corn density. The soybean yield losses can be partially explained by the occurrence of oxidative stress, which occurs by the higher content of reactive oxygen species (ROS), such as hydrogen peroxide (H2O2). The objective of this study was to quantify H2O2 content and the activity of superoxide dismutase (SOD), catalase (CAT) and ascorbate peroxidase (APX) on soybean as a function of interference of populations of GR® volunteer corn originated from individual plants and clumps (clumps are seven corn plants emerged at the same point) in different times, as well as to determine wheter this interference alters stress metabolism on soybean. Quantification was performed at 20, 35 and 46 days after emergence (DAE) of soybean. The mean volunteer corn populations were 0, 0.5, 1, 2, 4, 8, 10 and 12 plants or clumps m-2. The results show changes in H2O2 content and SOD, CAT and APX activity as a response to interference with volunteer corn populations and origins. The higher activity was observated for SOD. Soybean yield reduce with the increase of populations of volunteer corn originated from individual plants and clumps.

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.