Sensibilidade de estirpes de Bradyrhizobium ao glyphosate

Abstract

Sensitivity of Bradyrhizobium strains to glyphosateGlyphosate applications to glyphosate-resistant soybean may impair symbiosis with Bradyrhizobium, a symbiotic bacterium. This study evaluated the sensitivity to glyphosate of three Bradyrhizobium strains used commercially in soybean crop in Brazil. The concentrations (0.0; 5.4; 10.8; 21.6 e 43.2 μg L -1 ) of the active ingredient glyphosate [N-(phosphonomethyl)glycine] were added to YM liquid medium for the growth of one strain of B. japonicum (SEMIA 5079) and two strains of B. elkanni (SEMIA 5019 and SEMIA 587) inoculated as pure culture. The herbicide effect on the growth of the tested strains was assessed by optical density and growth curves were established for each strain. Reduction in growth of strains in the lowest glyphosate concentration were 18% for SEMIA 5079, 29% for SEMIA 5019 and 35% for SEMIA 587. In general, the higher the concentration of the herbicide in the culture medium, the greater the growth inhibition. The strains showed differential sensitivity only at the lowest concentrations of glyphosate, allowing the determination of the following order of sensitivity: SEMIA 587>SEMIA 5019>SEMIA 5079. This differential sensitivity is dependent on the herbicide concentration, since in the presence of 43.2 μg L -1 all strains severely reduced growth, not showing difference among them.

Associação de Rhizobium sp. a duas leguminosas na tolerância à atrazina

“…Segundo Santos et al (2006), a aplicação de herbicidas sobre culturas que realizam simbiose com bactérias fixadoras de nitrogênio pode prejudicar a eficiência na assimilação deste nutriente, sendo que a maior interferência desses compostos ocorre quando eles agem sobre a biossíntese de aminoácidos, ou sobre as rotas metabó-licas comuns entre micro-organismos e plantas. Jacques et al (2010) ao realizarem experimento para avaliar a sensibilidade de três estirpes de Bradyrhizobium à aplicação do glifosato sobre a soja resistente a este herbicida, verificaram que as estirpes apresentaram sensibilidade diferenciada somente nas concentrações mais baixas do glifosato, com prejuízo à simbiose. Além disso, consideraram que essa sensibilidade foi dependente da concentração do herbicida, pois nas doses mais elevadas todas as estirpes tiveram o crescimento severamente reduzido.…”

Nodulation and agronomic performance of soybean grown in different seeding periods and glyphosate formulations

“…Certain glyphosate formulations may damage the symbiotic activity of nodules, depending of the bacteria strain present in the soil, some may present larger susceptibility to determined glyphosate salt, harming the performance of normal nodules (Jacques et al, 2010). A higher soybean nodulation in roots have a larger advantage to recover from determined stresses and present a higher yield, due to its larger nitrogen assimilation (Zilli et al, 2008).…”

Glyphosate Effect on Nitrogen Fixation and Metabolization in RR Soybean

“…These herbicides and their derivatives metabolites can interact with root symbionts. Jacques et al (2010) reported that glyphosate lead to growth inhibition of Bradyrhizobium elkanni. Santos et al (2007), in an experiment whose treatments were composed by the application of three different formulations of glyphosate (Roundup Ready ® and R.Transorb ® , both containing the isopropylamine salt, and Zapp Qi ® , formulated with potassium salt), were applied at the dose of 2000 g ha -1 (commercial recommended dose) of the acid equivalent.…”