Abstract Background Eragrostis plana is the main invasive plant in the Pampa Biome of southern Brazil. This plant is highly competitive, tolerant to abiotic stresses, and very difficult to manage. Plants exposed to abiotic stresses and herbicides develop mechanisms that help alleviate or reduce damage caused by stressors and transmit this ability to the progenies. Objective The study’s objectives were to ascertain whether acclimatization to stress due to drought and sub-lethal doses of glyphosate may decrease plant sensitivity to glyphosate and investigate the possible memory mechanisms involved in this process. Methods A population of E. plana was submitted to drought, glyphosate, or a combination of drought plus glyphosate for two generations. The progenies were analyzed for sensitivity to the herbicide glyphosate and for biochemical, metabolites, and molecular responses. Results When testing sensitivity to glyphosate in the G 2 generations, the DRYxGLY (plants stressed with drought plus glyphosate) was the least sensitive (ED50 443.0 g a.e. ha-1), while CHK (without stresses) was the most sensitive (ED50 278.0 g a.e. ha-1). Evaluating the effects of glyphosate, the CHK population showed a greater accumulation of oxidative damage and shikimic acid. While DRYxGLY had greater antioxidant activity and higher expressions of the EPSPS and ABC-carrier MRP10 genes. Conclusions Recurrent selection with drought stress and sub-lethal rate of glyphosate (DRYxGLY) showed reduced sensitivity to glyphosate in the second generation ( G 2 ). The conjunction of factors, including the upregulation of EPSPS and the ABC MRP10 transporter, antioxidant enzymes seem to decrease the sensitivity of the DRYxGLY population to glyphosate.

ABSTRACT The aim of the present study was to assess the relative competition between white clover (cv. BRS URS Entrevero) and weed species Silene gallica L. through replacement series. The experiments followed a completely randomized design with four replications. The first study showed that the shoot dry mass of both species (white clover and S. gallica) became constant with 16 plants.pot-1 or 400 plants.m-2. In 2017, a study was conducted and it was repeated in 2018 in order to assess white clover competition with S. gallica under different crop: weed proportions pot-1 (100:00; 75:25; 50:50; 25:75 and 00:100). Competitiveness analysis was carried out through diagrams applied to replace experiments and through the relative competition indices. Morphological parameters such as plant height, leaf area and shoot dry mass of the crop and the weed were measured when S. gallica plants bloomed (105 days after species emergence). Results have proven the phenotypic plasticity of temperate-climate foragers such as white clover. This outcome shows that the competitive relationship with Silene gallica changes due to plant proportions composing the association. Therefore, it was possible to conclude that the species show similar competitive ability.

RESUMO No Brasil, a buva destaca-se entre as principais plantas daninhas da cultura da soja, devido à sua agressividade e resistência ao glifosato. Dessa forma, para evitar a seleção de populações resistentes ao herbicida glifosato, o uso de outros herbicidas tornou-se fundamental para o manejo dessa planta daninha. Este estudo objetivou avaliar a eficiência de controle dos herbicidas glifosato e saflufenacil em plantas de buva (Conyza bonariensis), bem como o tipo de interação da combinação desses herbicidas no controle de buva resistente a glifosato. O delineamento utilizado foi o de blocos ao acaso, com quatro repetições. Os tratamentos foram compostos por combinações de doses de glifosato (0 g ha-1; 270 g ha-1; 540 g ha-1; 1.080 g ha-1; 2.160 g ha-1; 4.320 g ha-1; 8.640 g ha-1; 17.280 g ha-1) e saflufenacil (0 g ha-1; 0,55 g ha-1; 1,09 g ha-1; 2,18 g ha-1; 4,37 g ha-1; 8,75 g ha-1; 17,5 g ha-1; 35 g ha-1), formando seis curvas de dose-resposta. Houve efeito sinérgico entre os herbicidas glifosato e saflufenacil para o controle de buva resistente ao glifosato, sendo a mistura considerada eficiente para o biótipo estudado. Além disso, a adição de glifosato (540 g ha-1) ao herbicida saflufenacil (35 g ha-1) preveniu a ocorrência de rebrote e a dispersão de novas sementes de buva, o que não ocorre em plantas tratadas apenas com saflufenacil.

ABSTRACT In Brazil, hairy fleabane stands out among the main weeds of soybean crops, due to its aggressiveness and resistance to glyphosate. Thus, to avoid the selection of resistant populations to the glyphosate herbicide, the use of other herbicides has become critical to the management of this weed. This study aimed to evaluate the control efficiency of glyphosate and saflufenacil herbicides in hairy fleabane plants (Conyza bonariensis), as well as the type of interaction of the combination of those herbicides for controlling glyphosate-resistant hairy fleabane. A randomized blocks design, with four replications, was used. Treatments consisted of glyphosate doses (0 g ha-1; 270 g ha-1; 540 g ha-1; 1,080 g ha-1; 2,160 g ha-1; 4,320 g ha-1; 8,640 g ha-1; 17,280 g ha-1) combined with saflufenacil (0 g ha-1; 0.55 g ha-1; 1.09 g ha-1; 2.18 g ha-1; 4.37 g ha-1; 8.75 g ha-1; 17.5 g ha-1; 35 g ha-1), making six dose-response curves. A synergistic effect was observed between the glyphosate and saflufenacil herbicides for controlling the glyphosate-resistant hairy fleabane, being the mixture considered efficient for the biotype studied. Furthermore, the addition of glyphosate (540 g ha-1) to the saflufenacil herbicide (35 g ha-1) prevented the occurrence of regrowth and the dispersion of new hairy fleabane seeds, what does not occur in plants treated exclusively with saflufenacil.