The objective of this research was to characterize foliar absorption, translocation and metabolism of 14C-glyphosate by the weeds Commelina benghalensis, Ipomoea grandifolia, and Amaranthus hybridus. Glyphosate was applied through four drops of 0.5 µL of a solution containing the commercial product, at the recommended dose of 720 g a.e.ha-1 mixed with 14Cglyphosate, on the adaxial surface of the second true leaf of the studied plants. The evaluations were conducted at 2, 4, 8, 12, 24, 48 and 72 hours after herbicide treatment (HAT) for the absorption and translocation experiments and 72 HAT for the metabolism experiment. The absorption and translocation results showed that A. hybridus absorbed more than 90% of the glyphosate applied after 72 HAT. The major part of the herbicide remained in the treated leaf, with a glyphosate translocation rate of 25%. In I. grandifolia, 80% of the herbicide was absorbed after 72 HAT; however, there was a lower translocation, and only 2.2; 3.5 and 4.6% of the 14C-glyphosate were present in the shoot, branch and root, respectively. C. benghalensis presented an absorption rate of 66% after 72 HAT, thus differential glyphosate penetration was the mechanism responsible for tolerance of this weed. In this evaluation, 39% of the glyphosate was present in the treated leaf and 15.2 and 11.6% in the shoot and root, respectively. In the metabolism studies, the metabolite aminomethylphosphonic acid (AMPA) was detected only in C. benghalensis, with differential metabolism being the mechanism of tolerance of this weed. The overall conclusion of this research is that glyphosate tolerance of C. benghalensis is due to the differential absorption and translocation of the herbicide by the weed. In I. grandifolia, the tolerance is due to the lower translocation of the herbicide, with no data evidence that differential metabolism of the herbicide occurs in this weed.
tolerance; Commelina benghalensis; Ipomoea grandifolia; Amaranthus hybridus; AMPA
