Glyphosate tolerance by Clitoria ternatea and Neonotonia wightii plants involves differential absorption and translocation of the herbicide

Glyphosate tolerance by Clitoria ternatea, Neonotonia wightii and Amaranthus hybridus was studied in whole plants from Mexico. Experiments in a controlled growth chamber showed both legumes to be highly tolerant of glyphosate, with and ED50 values of 600.18 g ae ha(-1) for C. ternatea and 362.94 g ae ha(-1) for N. wightii. On the other hand, A. hybridus was highly susceptible to the herbicide (ED50 = 42.22 g ae ha(-1)). Shikimate accumulation peaked 96 h after treatment in the tolerant plants and the susceptible weed under 500 g ae ha(-1) glyphosate. The shikimic acid content of whole leaves was 4.0 and 5.0 times higher in the susceptible weed than in N. wightii and C. ternatea, respectively. C-14-glyphosate absorption and translocation tests showed A. hybridus to absorb 30% more herbicide than the legumes 24 h after glyphosate foliar application. C-14-glyphosate translocation as measured by quantified autoradiography revealed increased translocation of the herbicide to untreated leaves and roots in A. hybridus relative to the two legumes. The cuticular surface of A. hybridus exhibited very low wax coverage relative to the epicuticular surface of N. wightii and, especially, C. ternatea. No significant degradation of glyphosate to aminomethylphosphonic acid and glyoxylate metabolites was detected among the tolerant leguminous plants or the susceptible weed population. These results indicate that the high glyphosate tolerance of Clitoria ternatea and Neonotonia wightii is mainly a result of poor penetration and translocation of the herbicide to apical growing points in their plants.