Hormesis effect of 2, 4- dichlorophenoxiacetic acid in soy seeds

Herbicides of the auxin mimic group, such as 2,4-dichlorophenoxyacetic (2,4-D), at low dosages may show a direct relation to the growth and development of the plant, in order to evaluate the influence of the different dosages of this plant herbicide in soybean (Glycine max) crop. The seeds were treated with fungicides and insecticides and then with 2,4-dichlorophenoxyacetic dimethylamine salt and inoculated. The experimental design was completely randomized (DIC), composed of five treatments with eight replicates, using seeds without inoculant and with inoculant of Bradyrhizobium sp. Plant length evaluations were performed at 7, 14, 21 and 28 days after emergence and at 30 days after emergence for the other variables analyzed (chlorophyll content, root length, green shoot mass). In the experiments with inoculated seeds, the dose of 0.5 mL ha-1 of 2,4-dichlorophenoxyacetic acid showed inhibition of plant development. In the seeds without inoculant, the results showed that in doses from 5.0 mL ha-1 2,4-D caused damages in the development of the plants, however in lower dosages the herbicide presented hormonal action allowing the development of soybean plants.