CONICET | Buscador de Institutos y Recursos Humanos

Glyphosate is a systemic herbicide that is translocated to shoot and root apexes and underground organs of reserve. However, there are studies that characterize its movement with a "self-limitation" because this herbicide reduces net assimilation of CO2 in source leaves. The objective of the current research was to evaluate the effect of glyphosate on the transport of assimilates, during 6 days post-application of herbicide (DPA), comparing a susceptible and a glyphosate-resistant populations of Lolium perenne. Plants growing in hydroponics were sprayed with glyphosate (1,080 g ae.ha-1) at tillering. Another set of plants remained as controls without herbicide. At 1, 3, and 6 DPA, the latest expanded leaves on the main tiller were labeled at the down side with glucose (14C (U)). Plants were dissected 24h after labeling and the samples were digested with NaOH (9 N). Finally, the percentage of labeled glucose in each organ was quantified in dpm, using a liquid scintillation counter. Glucose uptake did not differ significantly between treatments over time in both populations. At 1 DPA, susceptible plants treated with glyphosate retained 53.2% more glucose in the labeled area than their controls reflecting a reduction on the transport. This retention was increased at 3 and 6 DPA. The reduction of assimilates transport did not affect differentially the different sources of the labeled leaf. By comparing the control plants of both populations, the resistant ones holded more glucose in the labeled area. Otherwise, this biotype did not show differences in the assimilate transference under herbicide treatment compared to their controls, during 6 days DPA. Consequently, glyphosate significantly affected the phloem loading of assimilates in the susceptible population without damage in the resistant one.