Resumo

GAMEZ, Arnaldo; ZAMBRANO, Castor  e  RAMIS, Catalina. Metabolic and enzymatic characterization of nicosulfuron resistance in biotypes of Rottboellia cochinchinensis (Lour.) WD Clayton. Bioagro [online]. 2013, vol.25, n.1, pp.3-10. ISSN 1316-3361.

Rottboellia cochinchinensis is a major weed and its chemical control is mainly based on the use of the herbicide nicosulfuron; however, there has been a decrease in the effect of the herbicide on the weed which has showed some levels of resistance. In order to perform a metabolic and enzymatic characterization of the resistance of R. cochinchinensis to nicosulfuron, some experiments were conducted to confirm the selected biotype resistance through an analysis of log-logistic regression and determine the resistance index (IR). The study of the resistance nature was done through inhibition tests of the P₄₅₀ monooxygenases complex by the use of malathion, and in vivo enzymatic assay where acetoin accumulation was measured by colorimetry as an indirect measure of the inhibition of ALS. The dose-response bioassay confirmed the resistance (IR = 3.87). There was no reduction in fresh biomass of resistant plants treated with malathion compared to the untreated ones, indicating that cytochrome P₄₅₀ monooxygenase isozymes that could be inhibited by malathion were not involved in the degradation of nicosulfuron in this bioassay. With the in vivo enzymatic assay, we demonstrated the insensitivity of the ALS enzyme of the resistant biotype to nicosulfuron, therefore it is concluded that the resistance mechanism of this biotype is in the action site of the herbicide.

Palavras-chave : Biotype; resistance mechanism; P₄₅₀ monooxigenase; acetolactate synthase.

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