Milho resistente ao glifosato inoculado com Azospirillum sp.

Abstract

Maize is one of the world's major cereals, but presents challenges for the correct management of herbicides and fertilization. The intensity of weed competition and the use of nitrogen fertilizers have been one of the main factors responsible for the excessive rates of herbicides and nitrogen fertilizers applied in the crop. Diazotrophic bacteria can fix atmospheric, produce growth promoting substances, and may reduce the use of nitrogen fertilizers in corn. To test this hypothesis, this first work had the objective of evaluating the effect of glyphosate application on glyphosate resistant maize cultivars inoculated with Azospirillum sp. and in the second experiment to evaluate the effect of doses of glyphosate under inoculation. The work was carried out under greenhouse conditions. The treatments were arranged in 6 x 2 factorial scheme for the six glyphosate resistant maize hybrids (Nidera 90, Nidera 92, Dekalb 330, Dekalb 340, Impact and Status) with and without the use of Azospirillum sp. bacteria, with five replicates. In the second experiment, the experimental design was also completely randomized, and the treatments were arranged in 5 x 2 factorial scheme for five doses of glyphosate (0, 0,96, 1,92, 2,88 and 3,84 Kg a.i. ha-1), with and without inoculation with bacteria Azospirillum sp., five replicates. The cultivar used in the experiment was the simple hybrid Status. In the full flowering stage 45 days after emergence (DAE), phenological stage R2, chlorophyll index and photosynthesis were evaluated, after the evaluation the plants were cut close to the soil, separating aerial part and roots. Root length and volume were measured. It was quantified the leaf nutrient concentration N, P, K, Ca, Mg, S, Cu, Fe, Mn and Zn. The visible symptoms of phytotoxicity were observed in the plants, the day after the application, with yellowing of the new leaves, in both experiments. The application of glyphosate in the studied hybrids increased root volume, root dry mass, photosynthetic rate of Status hybrid and N, P, Fe uptake when inoculated. In the second experiment the gas exchange and photosynthetic efficiency were not significant, however, what promoted increasing in root length, root volume, root dry mass and leaf Mn concentration when the plants were inoculated, there was a reduction of the mass dry matter, leaf content of Fe and Mn, when glyphosate doses were high. The inoculation of the Azospirillum bacterium promoted increase of the root components did not have effect in the fixation of the N and the glyphosate induced the immobilization of Fe and Mn in the plants, besides reducing the dry mass of the aerial part.