|Almeida, S. d.|
Submitted to: Planta
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/2/2012
Publication Date: 8/27/2012
Citation: Franco, D.A., Almeida, S., Cerdeira, A.L., Duke, S.O., Moraes, R.M., Lacerda, A., Matallo, M.B. 2012. Evaluation of glyphosate application on transgenic soybean and its relationship with shikimic acid. Planta. 30(3):659-666. Interpretive Summary: The herbicide glyphosate is being used extensively with transgenic, glyphosate-resistant soybeans in Brazil. Glyphosate at rates used to kill weeds was found to have no effects on yield or seed quality of glyphosate-resistant soybeans under field conditions. In hydroponic culture, glyphosate-treated glyphosate-resistant soybean plants exuded glyphosate and one of its degradation products from roots. Non-transgenic glyphosate-susceptible soybeans grown in the same hydroponic containers were affected by root-exuded glyphosate from resistant plants. This study confirms that under Brazilian conditions, glyphosate doe not affect soybean yield or quality of seeds in glyphosate-resistant soybean. It also shows that resistant soybeans treated by spraying the leaves, exude glyphosate and a degradation product from its roots.
Technical Abstract: Glyphosate [N-(phosphonomethyl)glycine]-resistant crops (GRC) are the transgenic crops most extensively grown worldwide, with soybean being the major GRC. It is important to evaluate the impact of glyphosate on the shikimate pathway, growth and yield of GR soybean in the field. Furthermore, whether GR soybean exudes glyphosate and its metabolites from roots and, if so, whether these exudates can affect non GR plants is of interest. A field experiment was conducted at Engenheiro Coelho, SP, Brazil, during the agricultural year 2007/2008 to evaluate the growth, development and seed quality of GRC soybean variety BRS valiosa RR to glyphosate. A randomized block design was used with four replications. Glyphosate was applied at 720 and 960 g. a.e. (acid equivalent) ha-1and then in sequence at the following doses 720/720, 960/720, and 960/720/720 g a.e. (acid equivalent) ha-1. In order to evaluate the transfer from GRC soybean to non GRC soybean cultivated in nutrient solution, a pot experiment was conducted at Instituto Biológico, SP, Brazil. Glyphosate was applied on the GRC soybean (M8045RR) at 2400 g ha-1 a.e. Both GRC soybean and non GRC soybean were grown together in the same container with nutrient solution. At 0, 1, 3, 7 and 10 days after application shikimic acid was measured by HPLC and the levels of glyphosate and aminomethylphosphonic acid (AMPA) in nutrient solution was determined by GC-MS. The results showed that yield, plant height, and the content of seed oil and protein were not affected by glyphosate applications to GR soybean in the field. Shikimate levels were slightly elevated or slightly reduced in GRC soybean in the field, depending on the treatment. Glyphosate and AMPA were released through the roots of GRC soybean in nutrient solution, which were subsequently taken up by non-GRC soybean, exerting inhibitory effects on their shikimate pathway.