Absorption and translocation of 14C-glyphosate was studied in greenhouse-grown Erythroxylum coca and E. novogranatense. Autoradiography indicated that translocation patterns were similar for both species and that E. novogranatense absorbed and translocated more glyphosate than E. coca. In both young and mature plants, absorption of leaf-applied 14C-glyphosate increased with increased exposure time, and 288 h after application, absorption was higher in E. novogranatense (79 and 52% of applied, respectively) compared with E. coca (60 and 14% of applied, respectively). Similarly, translocation of 14C-glyphosate increased with time in both species. In mature plants, after 288 h more 14C-glyphosate translocated in E. novogranatense (6.9% of applied) than E. coca (2.5%), but the opposite occurred in young plants. Most of the radioactivity translocated from the treated leaf accumulated in the main stems and roots of both species with little accumulation in tissues above the treated leaf. However, most of the applied radioactivity remained in the treated leaf regardless of growth stage and species. The absorption of 14C-glyphosate in young and mature plants of E. coca was 1.3 and 3.6 times lower, respectively, than in E. novogranatense 288 h after treatment. Differences in absorption and translocation of glyphosate in E. coca and E. novogranatense may partially explain the reported differential response to glyphosate.
Nomenclature: Glyphosate; Erythroxylum coca var. coca Lam.; E. novogranatense var. novogranatense (Morris) Hieron.