Silicon and Plant Growth-Promoting Rhizobacteria Pseudomonas psychrotolerans CS51 Mitigates Salt Stress in Zea mays L.

Salinity is a significant abiotic stress for crop plants and a threat to global food security. Optimizing yield without adversely affecting the ecosystem is necessary for a sustainable agriculture. Silicon and plant growth-promoting bacteria were reported for mitigating several abiotic and biotic stress in plants. In our study, we identified the salt-tolerant rhizobacterium Pseudomonas psychrotolerans CS51. This species produces several plant-growth-promoting biochemicals like indole-3-acetic acid (33 +/- 1.8 ng/mL) and gibberellic acid (GA3; 38 +/- 1.3 and GA4; 23 +/- 1.2 ng/mL) in Luria-Bertani(LB) media, and LB media spiked with 200 mM NaCl (indole-3-acetic acid(IAA); 17.6 +/- 0.4 ng/mL, GA3; 21 +/- 0.9 and GA4; 19 +/- 1.0 ng/mL). In the current study, we aimed to investigate the effect of isolate CS51 and exogenous silicon (3 mM) on maize under salinity stress (200 mM). Our results showed that the sole application of isolate CS51, Si, and combined CS51 + Si significantly enhanced maize biomass and chlorophyll content under normal and salinity stress. Phytohormonal results showed that salinity stress increased abscisic acid (ABA; three folds) and jasmonic acid (JA; 49.20%). However, the sole and combined isolate CS51 + Si application markedly reduced ABA (1.5 folds) and JA content (14.89%). Besides, the sole and isolate CS51 + Si co-application strengthened the antioxidant system, such as flavonoid (97%) and polyphenol (19.64%), and lowered the proline content (57.69%) under NaCl stress. Similarly, the CS51 and Si inoculation (solely or combined) significantly enhanced the Si uptake (4 folds) and reduced the Na+ uptake (42.30%) in maize plants under NaCl stress. In conclusion, the current finding suggests that combining CS51 with Si can be used against salinity stress in maize plants and may be commercialized as a biofertilizer.