Growth, morphological, metabolic and photosynthetic responses of clones of eucalyptus to glyphosate

We hypothesized that eucalyptus has clone-dependent responses to glyphosate, and such differential responses might be associated with morphological, metabolic and/or photosynthetic changes. Experiments were carried out under controlled conditions of temperature, photoperiod and nutrition, focusing on evaluating the response of Eucalyptus x urograndis clones (GG100 and 1144) to increasing doses of glyphosate (0-1440 g ha(-1) acid equivalent - AE) and to WA whether a differential plant response would be associated to alterations in leaf morphology, plant and herbicide metabolism and photosynthesis. There was a significant reduction of plant height, stem diameter, number of leaves, leaf area and shoot dry mass caused by low doses of glyphosate (<= 180 g AE ha(-1), while a strong plant growth reduction (similar to 60%) was caused by glyphosate field doses (>= 720 g AE ha(-1)), in both clones. The GG100 clone was more susceptible to glyphosate field doses, while the 1144 clone was more susceptible to glyphosate low doses. The stomatal index increased by 31% and the nervure thickness was reduced by 17% at 30 days after application of glyphosate at 180 g AE ha(-1) (DAA) in the GG100 clone. Traces of glyphosate (< 28 g mg(-1 )of dry mass) were found in leaf tissues of both clones at 1 DAA. Shikimic acid accumulated earlier (after 1 DAA) and in greater amounts (90%) in the 1144 clone. Aminomethylphosphonic acid (AMPA) was not detected in either treated clone. The CO2 assimilation rate, transpiration rate and stomatal conductance were reduced earlier (after 1 DAA) and more intensely (65%) in the 1144 clone. The clone-dependent response is apparently associated with changes in plant metabolism related to glyphosate mode of action and gas exchange response differences between the clones.