This work aimed to evaluate the effects of glyphosate commercial formulations on Bradyrhizobium strains under laboratory conditions. The formulations were applied in the concentration of 43.2 µg L-1 of the a.e. and the strains were inoculated in yeast extract manitol (YM). Herbicide effect on the growth of the Bradyrhizobium strains was assessed by optic density reading in a spectrophotometer. Twenty seven treatments arranged in a factorial design were evaluated and consisted of one strain of B. japonicum: SEMIA 5079; and two strains of B. elkanii: SEMIA 5019 and SEMIA 587, under the effect of nine glyphosate formulations: Zapp QI®, Roundup®, Roundup Multiação®, Roundup Transorb®, Roundup WG®, Trop®, Agrisato®, technical glyphosate [N-(phosphonomethyl) glycine] and control without herbicide addition (as the strain control treatment), with six replications. A growth curve was established for each strain. It could be observed that the different glyphosate formulations Zapp Qi, Roundup, Roundup Multiação, Roundup transorb, Roundup WG, Trop and Agrisato caused differentiated effects on the strains of Bradyrhizobium SEMIA 5019, SEMIA 5079 and SEMIA 587. It was verified that the Zapp Qi formulation was the least toxic to the strains. The highest toxicity was observed for Roundup Transorb, which reduced growth over 94% for all the strains assessed. Correlation was not observed among the type of salt, isopropylamine, ammonium or potassic, present in the formulation herbicides, and the toxicity degree to the strains. The strain SEMIA 587 was the least tolerant to most formulations while SEMIA 5019 was the most sensitive to the control treatment N- (phosphonomethyl) glycine, without salts or other additives.
biological fixation of N2; herbicide; rhizobium; transgenic soybean
