Inoculation with Azospirillum lipoferum or Azotobacter chroococcum Reinforces Maize Growth by Improving Physiological Activities Under Saline Conditions

A pot study was performed to examine the effect of plant growth-promoting rhizobacteria (PGPR) including Azospirillum lipoferum or Azotobacter chroococcum on growth criteria (leaf area and seedlings fresh and dry weight), pigments [chlorophylls (Chl a and b) and carotenoids], osmolytes (soluble sugars, soluble proteins and proline), nutrient uptake, antioxidant enzyme activities, and oxidative stress in maize plants under normal and salt-affected soils. The results showed that salt stress induced a reduction in growth traits, pigments, soluble proteins, K+, and K+/Na+ ratio. On the other side, it increased soluble sugars, proline, Na+, malondialdehyde (MDA), and the activity of peroxidase (POD) and catalase (CAT). Meanwhile, salt stress did not significantly change the activity of ascorbate peroxidase (APX) in maize plants. The inoculation using Azospirillum lipoferum or Azotobacter chroococcum significantly enhanced growth parameters, pigments, K+, osmolytes, K+/Na+ ratio, and the activity of CAT, POD, and APX of the salt-affected maize plants as well as uninoculated control plants. In addition, the results showed that both types of bacteria have attributed to lower MDA and Na+ in maize plants. Interestingly, Azospirillum lipoferum has affected more compared to Azotobacter chroococcum in control and salt-stressed plants. We, therefore, have observed in this study that microbial inoculation significantly improved plant physiological activities and that adding bacteria such as Azospiroillum or Azotobacter to the soil could mitigate the negative effects of salt stress on maize plants.