Glyphosate effects on carbon exchange rate of two Lolium perenne L. populations with differential herbicide-sensitivity.

YANNICCARI, MARCOS EZEQUIEL; TAMBUSSI, EDUARDO; ISTILART, MARÍA CAROLINA; GIMÉNEZ, DANIEL OSCAR; CASTRO, ANA MARÍA

Congreso; 2012 Weed Science Society of America Annual Meeting; 2012

WSSA

Ryegrass (Lolium sp.) is a common weed problem in wheat and barley crops in the South region of Buenos Aires province (Argentina). Glyphosate is frequently used to control weeds on field prior to crop sowing or emergence. The herbicide triggers the inhibition of the target enzyme pone el nombre completo (EPSP sinthetase). Also, The initial effect in photosynthesis is an immediate decline of ribulose-1,5-biphosohate levels (the primary acceptor of CO2 in the Calvin cycle), followed by decreased levels of other intermediates in carbon fixation. In the last years, several Lolium spp. populations were characterized as glyphosate-resistant weeds. The aim of this work was to assess the glyphosate effects on the net photosynthetic rate (An) of two Lolium perenne L. populations with differential herbicide-sensitivity. Plants of resistant and susceptible populations were grown in a greenhouse and treated with 1,020 g ae.ha-1 of glyphosate. The last fully expanded leaf was used to determine the An with a portable infrared gas analyzer with a photon flux density 1,000 µmol photons.m-2.s-1, 360ppm CO2 at 25°C. The recordings were repeated periodically until 10 days post-application (DPA). At 2 DPA, the An decreased 23% in the susceptible population sprayed with glyphosate. From that moment, the glyphosate promoted a gradually inhibition in the An that reached 80% of inhibition at 10 DPA. In contrast, An in the resistant population did not decrease significantly until 5 DPA when the reduction was 22%. This difference remained stable up to 10 DPA. The current results contribute to the physiological characterization of glyphosate-resistant perennial ryegrass population.