Atividade da acetolactato sintase de plantas de milho e de amendoim-bravo (Euphorbia heterophylla) resistentes e suscetíveis ao imazaquin
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Data
2002-03-15
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Editor
Planta Daninha
Resumo
O amendoim-bravo, (Euphorbia heterophylla) é uma importante planta daninha em mais de 56 países, inclusive no Brasil, onde tem sido relatado o aparecimento de populações resistentes aos herbicidas inibidores da acetolactato sintase (ALS). O objetivo do trabalho foi avaliar o efeito do herbicida imazaquin na atividade da ALS extraída das plantas de milho e amendoim-bravo, resistentes e suscetíveis ao produto. Sementes de dois genótipos de milho e vários biótipos de amendoim-bravo provenientes de diferentes regiões agrícolas brasileiras foram cultivadas em casa de vegetação por 21 dias. A atividade da ALS extraída das folhas das plantas foi determinada na presença de doses de imazaquin. A etapa de purificação da enzima foi substituída por uma centrifugação de 2.800 rpm por dois minutos. Equações de regressão linear para absorbância em função do log da concentração de imazaquin foram ajustadas para cada população, visando obtenção do I50. A dose de imazaquin necessária para inibir 50% da atividade da ALS (I50) na variedade de milho Pioneer 3162 IR (I50 260 µM) foi 4.333 vezes maior que a dose requerida pela BRS 473 (0,06 µM), a qual é suscetível ao imazaquin. Os biótipos de amendoim-bravo provenientes do Rio Grande do Sul apresentaram valores de I50 de 1.961,3 e 13,8 mM para os biótipos resistentes e suscetíveis, respectivamente. Os biótipos provenientes de Cafelândia e Maringá (PR) e Viçosa (MG) apresentaram valores de I50 maiores que 5.000 mM para os biótipos resistentes e maiores que 1.000 mM para os suscetíveis. O amendoim-bravo coletado na Embrapa Milho e Sorgo, em área que nunca foi tratada com herbicidas inibidores da ALS, apresentou I50 de 12,2 mM. Conclui-se que a medida in vitro da atividade da ALS é um método sensível para determinação da presença de biótipos resistentes à ação do herbicida imazaquin. A etapa de purificação da ALS pode ser substituída por um método que envolve uma rápida centrifugação.
Wild poinsettia (Euphorbia heterophylla) is an important weed in more than 56 countries, including Brazil, where resistant biotypes to ALS inhibiting herbicides have been reported in soybean crops. The objectives of this research were to evaluate the effect of imazaquin on the activity of the acetolactate synthase (ALS), extracted from two corn varieties and several biotypes of E. heterophylla from Brazilian agricultural areas. Plants were grown under greenhouse conditions for 21 days. The ALS activity of wild poinsettia has shown resistance to imazaquin herbicide in soybean crops. In vitro acetolactate synthase (ALS) activity of imazaquin-resistant wild poinsettia collected in different soybean production areas from Brazil and the two corn populations was compared to that of imazaquin-sensitive populations. The activity of the ALS extracted from the leaves was measured with different imazaquin rates. The ALS purification process was substituted by centrifugation at 2800 rpm during two minutes. Linear regression equation for specific light length absorbance as a function of the log concentration of imazaquin was built to obtain I50 value (50% inhibition of the enzyme activity). The I50 values of Pioneer 3162 IR (I50 260 µM) corn genotype were 4,333 times higher than BRS 473-sensitive (0,06 µM). The wild poinsettia biotypes from the state of Rio Grande do Sul had I50 values of 1,961.3 µM and 13.8 µM for the resistant and sensitive biotypes, respectively. The resistant populations from Cafelândia, Maringá (PR) and Viçosa (MG) had I50 values higher than 5,000 µM, while the sensitive population had values higher than 1,000 µM. The I50 value for the wild poinsettia population collected from fields that had never been sprayed with imazaquin was of 12.2 µM. Therefore, the in vitro ALS activity was a sensitive method to detect wild poinsettia-resistant imazaquin and ALS purification can be substituted for a method involving a quick centrifugation process.
Wild poinsettia (Euphorbia heterophylla) is an important weed in more than 56 countries, including Brazil, where resistant biotypes to ALS inhibiting herbicides have been reported in soybean crops. The objectives of this research were to evaluate the effect of imazaquin on the activity of the acetolactate synthase (ALS), extracted from two corn varieties and several biotypes of E. heterophylla from Brazilian agricultural areas. Plants were grown under greenhouse conditions for 21 days. The ALS activity of wild poinsettia has shown resistance to imazaquin herbicide in soybean crops. In vitro acetolactate synthase (ALS) activity of imazaquin-resistant wild poinsettia collected in different soybean production areas from Brazil and the two corn populations was compared to that of imazaquin-sensitive populations. The activity of the ALS extracted from the leaves was measured with different imazaquin rates. The ALS purification process was substituted by centrifugation at 2800 rpm during two minutes. Linear regression equation for specific light length absorbance as a function of the log concentration of imazaquin was built to obtain I50 value (50% inhibition of the enzyme activity). The I50 values of Pioneer 3162 IR (I50 260 µM) corn genotype were 4,333 times higher than BRS 473-sensitive (0,06 µM). The wild poinsettia biotypes from the state of Rio Grande do Sul had I50 values of 1,961.3 µM and 13.8 µM for the resistant and sensitive biotypes, respectively. The resistant populations from Cafelândia, Maringá (PR) and Viçosa (MG) had I50 values higher than 5,000 µM, while the sensitive population had values higher than 1,000 µM. The I50 value for the wild poinsettia population collected from fields that had never been sprayed with imazaquin was of 12.2 µM. Therefore, the in vitro ALS activity was a sensitive method to detect wild poinsettia-resistant imazaquin and ALS purification can be substituted for a method involving a quick centrifugation process.
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Palavras-chave
Resistência a herbicida, ALS, Soja, Milho