Caracterização de biótipos de capim-arroz (Echinochloa crusgalli) resistentes e suscetíveis ao quinclorac e desenvolvimento de método para detecção rápida da resistência

• Ano de defesa: 2008
• Autor(a) principal: Concenço, Germani
• Orientador(a): Ferreira, Francisco Affonso
• Banca de defesa: Soares, Plínio Cesar , Karam, Décio , Souza, Moacil Alves de
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Viçosa
• Programa de Pós-Graduação: Doutorado em Fitotecnia
• Departamento: Plantas daninhas, Alelopatia, Herbicidas e Resíduos; Fisiologia de culturas; Manejo pós-colheita de
• País: BR
• Palavras-chave em Português: Arroz irrigado; Planta daninha; Resistência; Herbicidas
• Palavras-chave em Inglês: Irrigated rice; Weeds; Resistance; Herbicides
• Área do conhecimento CNPq: CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA
• Link de acesso: http://locus.ufv.br/handle/123456789/1101

The Echinochloa genus is the most important in the Poaceae family associated to the irrigated rice, due to its adaptability for the rice crop environment. The herbicide quinclorac is an auxin-mimic herbicide used in the rice culture, whose characteristics are the flexibility in relation to the mode of application (pre- and post- emergence), high efficiency in the Echinochloa spp. and Aeschynomene spp. control, low toxicity to humans and animals, and selectivity to the rice crop. The barnyardgrass (Echinochloa crusgalli) biotypes resistant to quinclorac are vastly distributed in all the rice production areas of Rio Grande do Sul and Santa Catarina states, where the management practices include intensive systems based in the chemical control of weeds and absence of crop rotation. The objectives of these works were to characterize Echinochloa biotypes resistant and susceptible to quinclorac and to develop a method for quick identification of resistance in unknown biotypes. All the trials were installed under controlled environments. In the first trial, the treatments consisted of densities of both barnyardgrass biotypes, resistant (ECH-13) or susceptible (ECH-17) to quinclorac, collected in the rice region of Itajaí/SC. At the center of the plot one plant of the biotype considered as the treatment was maintained, under competition with 0, 1, 2, 3, 4 or 5 plants of the opposite biotype at the periphery of the plot. Forty days after the emergence (DAE) the plant height, tillers and leaves number, leaf area and the fresh and dry matter of shoots were evaluated. In the second trial, the treatments consisted of one rice plant at the center of the plot surrounded by 0, 1, 2, 3, 4 or 5 barnyardgrass plants of the resistant or susceptible biotype, according to the treatment. The stomatal conductance of water vapor, substomatal water pressure, leaf temperature and transpiration rate were evaluated, being obtained yet the water use efficiency by the relation between the photosynthesis and the transpiration rates 50 DAE. In the third trial, the treatments consisted of quinclorac rates (0, 0.5, 1, 2, 4, 16 and 64 mg L-1), applied to the shoot or roots of barnyardgrass seedlings 10 DAE. Forty DAE the length, fresh and dry mass were obtained independently for the shoot and the roots of the evaluated plants. The fourth trial consisted of two phases, being the first one conducted under laboratory (quick test) and the second one under greenhouse (standard test). In the trial conducted at germination chamber, seeds of four Echinochloa biotypes, characterized as resistant or susceptible to quinclorac, were sowed under concentrations of 0, 3.75, 18.75, 37.5, 187.5, 375 and 1875 mg L-1 of quinclorac for 14 days at 25ºC. Under greenhouse conditions, the same biotypes were sowed in vases containing 10 liters of soil and treated with rates of 0, 5.5, 187.5, 375, 750, 1500 and 3000 g ha-1 of quinclorac. In this trial the dry mass and plant height were evaluated 25 DAE, and at germination chamber, the dry mass and plant height were evaluated 14 days after sowing (DAS), and the survival was evaluated 7 DAS. The barnyardgrass biotypes studied, resistant or susceptible to quinclorac, are similar in relation to the competitive ability when under high competition levels, with some advantages for the susceptible one under low or moderate competition levels. The rice plants are affected in a similar way by both biotypes. When the dry mass of the plant sections of the susceptible biotype were compared as a function of mode of quinclorac application, it was observed that the quinclorac is more effective when applied to the roots. However, for the resistant biotype, due to the high resistance level (above 128 times the recommended dose) it was not possible to determine the quinclorac dose that caused 50% of reduction in the dry mass accumulation (GR50), nor the resistance index (RI) between biotypes. According to these data, it is possible to speculate that the resistance of barnyardgrass to quinclorac may be due to an alteration at the quinclorac target site in the plant. The quick test, conducted in laboratory for resistance identification, demanded less time, human and material resources than the standard test, with the same precision. In addiction, it was possible to differ resistant biotypes in relation to their resistance level.