Azospirillum brasilense increased salt tolerance of jojoba during in vitro rooting

•Azospirillum brasilense reduced the undesirable effects of NaCl on jojoba rooting.•A. brasilense Cd and Az39 promoted jojoba growth even at 160 mM NaCl.•A method for evaluating plant-bacteria interactions under salt stress was established.•This method allows selection of beneficial bacterial strains tolerant to salinity.•A standardized parameter (IC50) for quantifying NaCl plant-tolerances was established.

Jojoba and Azospirillum brasilense can survive at high NaCl concentrations but with some undesirable effects. The aim of this work was to evaluate whether A. brasilense inoculation reduced the negative effects of salinity on several clonal lines of the jojoba plant. Shoots were induced in half-strength Murashige-Skoog medium with 24.6 μM or 49.2 μM indole-3-butyric acid for 6 days and grown in an auxin-free medium with 0, 40, 80, 120 or 160 mM NaCl and inoculated or not with 107 cfu of A. brasilense Cd or Az39 for 45 days. Rooting percentage, shoot and root biometric parameters, and root index were determined. Regressions of rooting percentage and root index with respect to NaCl concentration were performed for each combination of bacterization and indole-3-butyric acid induction, and the 50% inhibitory concentration (IC50) was determined. A. brasilense Cd and Az39 promoted rhizogenesis and increased root index and IC50, reducing the undesirable effects of NaCl on jojoba rooting. Both strains were successfully reisolated at the end of the experiment. Here, we establish a useful model for evaluating plant-bacteria interactions and selecting strains that promote plant growth under saline conditions.

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