The intensive use of acetolactate synthase (ALS) inhibitor herbicides in soybean production areas at São Gabriel d'Oeste, State of Mato Grosso do Sul (Brazil), selected a resistant biotype of Bidens pilosa to this type of herbicide. However, field biochemical characterization of this resistance is difficult. Therefore, it was developed a bioassay to test the lack of sensitivity of the ALS enzyme of this biotype to the inhibitor herbicides. The bioassay consisted of simultaneous application of herbicides inhibitors of ALS and KARI (ketoacidreductoisomerase). CPCA (1,1-ciclopropanodi-carboxilic acid) was used for the inhibition of the KARI enzyme. This bioassay confirmed that the resistance of the R biotype of Bidens pilosa is due to a lack of sensitivity of the ALS enzyme to these herbicides: the higher acetoin contents produced, the higher enzyme activity and more intense the color developed.
herbicide resistance; biotypes; Bidens pilosa
