Response of Lolium multiflorum Lam to ACCase enzyme inhibitors herbicides

O azev??m ?? uma planta daninha de ciclo anual, encontrada em praticamente todas as lavouras de inverno, em pomares e vinhedos da regi??o Sul do Brasil. A esp??cie ?? normalmente controlada pelo herbicida glyphosate, no entanto, o uso continuado desse produto selecionou bi??tipos resistentes. O manejo com herbicidas inibidores da enzima acetil Coenzima A carboxilase (ACCase) ?? a principal alternativa para o controle dessas esp??cies, o qual n??o tem sido satisfat??rio em alguns locais, provocando a suspeita de que estejam sendo selecionados bi??tipos resistentes a este grupo de herbicidas. Assim, o objetivo da pesquisa foi avaliar a distribui????o dos bi??tipos de azev??m resistentes aos herbicidas inibidores da enzima ACCase no Rio Grande do Sul (RS); avaliar, por meio de curvas de dose-resposta, bi??tipos de azev??m resistente e suscet??vel ao herbicida fluazifop; estimar o valor adaptativo de bi??tipo suscet??vel e resistente ao fluazifop; e, investigar a habilidade competitiva desses bi??tipos entre si e com a cultura do trigo. Para isso, sementes de plantas de azev??m que sobreviveram a aplica????es de inibidores da enzima ACCase foram coletadas em lavouras na regi??o norte do RS, totalizando 80 munic??pios. Os resultados demonstraram que existem bi??tipos de azev??m resistentes ao herbicida fluazifop quando aplicado na dose m??xima de 125g i.a.ha-1 e est??dio indicado pelo fabricante. Os bi??tipos de azev??m apresentam diferentes n??veis de resist??ncia ao herbicida, sendo que o bi??tipo de azev??m TUC 11 apresenta resist??ncia de n??vel baixo ao herbicida fluazifop. Na avalia????o de habilidade competitiva e valor adaptativo verificou-se que os bi??tipos de azev??m suscet??vel e com resist??ncia de n??vel baixo, em geral, apresentam valores similares para estas vari??veis. A cultura do trigo, cultivar FUNDACEP Horizonte, em geral, apresentou maior habilidade competitiva que o bi??tipo com n??vel baixo de resist??ncia e equivalente ao suscet??vel.Ryegrass is an annual cycle weed, found in virtually all winter crops, orchards and vineyards of Southern Brazil. The species is usually controlled by glyphosate, however, continued use of the product selected resistant biotypes. The managing with acetyl Coenzime A carboxylase (ACCase) enzyme inhibiting herbicides is the main alternative to control these species, which has not been satisfactory in some places, causing suspicion of being selected biotypes that are resistant to this herbicide group. The objective of this research was to evaluate the distribution of ryegrass biotypes resistant to ACCase enzyme inhibitors herbicides in Rio Grande do Sul (RS); assess by means of dose-response curves ryegrass biotypes resistant and susceptible to the herbicide fluazifop; estimate the fitness cost of susceptible and resistant biotype to fluazifop, and to investigate the competitive ability of these biotypes among themselves and with the wheat crop. Thus, seeds of ryegrass plants that survived applications of ACCase enzyme inhibitors were collected from farms in Northern RS, comprising 80 towns. The results showed that there were ryegrass resistant biotypes to the herbicide fluazifop when applied at the maximum dose of 125g a.i.ha-1 and stage specified by the manufacturer. Ryegrass biotypes have different levels of herbicide resistance, and the biotype of ryegrass TUC 11 has low-level resistance to the herbicide fluazifop. In the assessment of competitive ability and fitness cost it was found that the susceptible ryegrass and low level resistance, in general, have similar values for these variables. Wheat cultivar FUNDACEP Horizonte, in general, showed greater competitive ability than the low level resistance biotype and equivalent to the susceptible