Inoculation with Azospirillum brasilense and/or Pseudomonas geniculata reinforces flax (Linum usitatissimum) growth by improving physiological activities under saline soil conditions

Abstract

Abstract Background Salinized soils negatively affect plant growth, so it has become necessary to use safe and eco-friendly methods to mitigate this stress. In a completely randomized design, a pot experiment was carried out to estimate the influence of the inoculation with endophytic bacterial isolates Azospirillum brasilense, Pseudomonas geniculata and their co-inoculation on growth and metabolic aspects of flax (Linum usitatissimum) plants that already grown in salinized soil. Results The results observed that inoculation of salinity-stressed flax plants with the endophytes A. brasilense and P. geniculata (individually or in co-inoculation) increases almost growth characteristics (shoot and root lengths, fresh and dry weights as well as number of leaves). Moreover, contents of chlorophylls and carotenoids pigments, soluble sugars, proteins, free proline, total phenols, ascorbic acid, and potassium (K+) in flax plants grown in salinized soil were augmented because of the inoculation with A. brasilense and P. geniculata. Oppositely, there are significant decreases in free proline, malondialdehyde (MDA), hydrogen peroxide (H2O2), and sodium (Na+) contents. Regarding antioxidant enzymes, including superoxide dismutase (SOD), peroxidase (POD), and ascorbate peroxidase (APX), the inoculation with the tested endophytes led to significant enhancements in the activities of antioxidant enzymes in stressed flax plants. Conclusions The results of this work showed that the use of the endophytic bacterial isolates Azospirillum brasilense, Pseudomonas geniculata (individually or in co-inoculation) could be regarded as an uncommon new model to alleviate salinity stress, especially in salinized soils.