Tolerance to Glyphosate in Broadleaf Buttonweed and White-Eye Biotypes

Infesting species of Rubiaceae family have great importance in soybean crops in Southwest of Paraná and North of Santa Catarina, especially due to the selection of tolerant populations caused by the pressure of selection exerted by intensive use of glyphosate. The study aimed to evaluate the levels of tolerance to glyphosate in biotypes of broadleaf buttonweed (Borreria latifolia) (BL) and white-eye (Richardia brasiliensis) (RB) by means of dose-response curves. Two experiments were conducted in a greenhouse, in completely randomized design (CRD), with four replications. Fourteen BL biotypes and eleven RB biotypes were evaluated, collected in soybean fields of Paraná and Santa Catarina. The doses of glyphosate were 0, 74, 163, 360, 792 and 1,742 g ha-1, applied when the plants had 6 to 8 leaves. Visual control was evaluated at 14 and 28 days after application (DAA), as well as mass of green shoots and mass of dry shoots at 28 DAA. It was verified that there is response variability among the biotypes studied. BL biotypes 277, 283 and 300, and RB biotypes 283, 285 and Papanduva were not controlled with glyphosate at doses superior to those normally used in crops (720 g ha-1), indicating selection by the recurrent use of glyphosate. The tolerance factors ranged from 1.1 to 4.1 and 2.8 to 8.1 for RB and BL, respectively. The greatest difficulties of control were reported in areas where RR technology had been adopted for more than six years.