Adaptive value of ryegrass biotypes with low-level resistance and susceptible to the herbicide fluazifop and competitive ability with the wheat culture

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 s