Does azospirillum brasilense promote salt stress tolerance during the germination of soybean seeds?

Soybean (Glycine max) requires favorable and adequate conditions to reach its maximum productive potential, as abiotic factors, particularly salinity, directly interfere with crop establishment and development. However, several resources are available on the market to protect plants during their initial development, notably the use of high-quality seeds and seed treatment with beneficial chemical or biological agents. This study aimed to evaluate the germination and initial development of soybean seeds, with and without inoculation of Azospirillum brasilense, under salt stress at different concentrations of sodium chloride (NaCl): 0.0, -0.3, -0.6, and -0.9 MPa. The variables analyzed were germination, germination speed index, seedling length, and seedling dry matter. The results were subjected to analysis of variance, and those showing significant differences at the 5% level were adjusted through regression analysis. Soybean seeds inoculated with Azospirillum brasilense showed better initial seedling development and tolerance to salt stress at the concentration of -0.3 MPa NaCl. However, at concentrations of -0.6 and -0.9 MPa NaCl, the seeds experienced severe osmotic and ionic stress, rendering them unable to germinate and develop in both treatments, with and without inoculation of Azospirillum brasilense.