Plant growth promoting bacteria mitigates salt stress during Handroanthus impetiginosus in vitro rooting

Key messageBacillus sp. L15 or Sphingobacterium sp. L22 inoculation promotes H. impetiginosus in vitro rooting under NaCl stress conditions by improving rooting percentages, modifying biochemical parameters and mitigating anatomical alterations produced by sal stress. Salinity is one of main abiotic stresses that causes adverse effects on plant growth and affects millions of hectares around the world. Variability of physical and chemical properties of soils has made field experiments notoriously difficult to evaluate. Plant tissue culture has been used as a model system to study physiological responses induced by salinity. The aim of this work was to evaluate the tolerance to salinity of Handroanthus impetiginosus 'pink lapacho' and the effect of inoculation with plant growth-promoting bacteria previously isolated from adult plants. Shoots induced for 3 days in half-strength Murashige and Skoog medium with 30 mu M of indole butyric acid were used and then transferred to auxin-free medium, supplemented with 0, 40, 80 or 160 mM NaCl and inoculated or not with 10(8) cfu of Bacillus sp. L15 or Sphingobacterium sp. L22. At the end of experiments (40 days), 50% Inhibitory Concentration 50 (IC50) was determined from regression curves constructed with rooting percentages. Bacterization with L15 and L22 strains displaced IC50 to higher NaCl concentrations (147 and 160 mM, respectively) relative to controls (109 mM). Furthermore, inoculation with L22 improved biometric parameters index (BPI) at 40 mM NaCl. Finally, bacterization and NaCl concentration modified proline, phenolics and chlorophylls contents during the first 15 days of culture. Bacteria inoculation also mitigated anatomical alterations produced by salt stress. In conclusion, bacteria tested in this work promoted in vitro rooting and alleviated negative effects from salt stress in H. impetiginosus.