Phosphate-Solubilizing and Auxin-Producing Rhizobacteria Promote Plant Growth Under Saline Conditions

Abstract

The world loses 3 ha of arable lands every minute due to salinization. To counteract adverse effects of salinity on plants, the use of PGPR is an efficient/cheaper method that induces salt stress tolerance in plants. The aim of the present work was to study auxin production and inorganic phosphate solubilization capacities of Pseudomonas fluorescens Ms-01 (A newly isolated strain from grapevine rhizosphere) and Azosprillum brasilense DSM1690 (DSMZ strain isolated from Digitaria decumbens roots) under hypersaline conditions. The objective was to assess their synergetic action in the promotion of wheat plant growth in saline conditions. The results showed a prominent ability of the studied strains to grow in high NaCl concentrations of about 600 mM. In addition, both auxin production and phosphate solubilization activities were maintained in hypersaline conditions. In fact, with an initial IAA production of 32 \(\upmu \hbox {g}\,\hbox {ml}^{-1}\), A. brasilense DSM 1690 maintained a good production in hypersaline conditions (\(22.5\pm 4.1\,\upmu \hbox {g}\,\hbox {ml}^{-1}\) in 400 mM NaCl). Phosphate solubilization activity of P. fluorescens Ms-01 was also significantly improved with increase in salinity, reaching \(22.6\pm 1.7\, \upmu \hbox {g}\,\hbox {ml}^{-1}\,\hbox {P}_{2}\hbox {O}_{5}\) in 600 mM NaCl. The inoculation of wheat plants with the studied bacteria increased the plant height and weight under normal and saline conditions. Results showed significant increase in proline accumulation and in the activity of POD and APX antioxidant enzymes in wheat plants inoculated with P. fluorescens Ms-01 in saline soil conditions. The correlation between proline accumulation and antioxidant enzymes activities indicated that the inoculation improved the defense pathway of plants against salt stress.