Balancing water deficit stress with plant growth-promoting rhizobacteria: A case study in maize

Plant growth promoting rhizobacteria are proposed as a beneficial economic strategy, where crops are cultivated with water deficit constraints, with the aim of maximizing the plant production potential. A collection of studies reviewed in this article demonstrate the positive effect of PGPR for improving water deficit stress tolerance during drought conditions. These studies showed that strains of PGPR maintain the plant's water status and improve water shortage endurance by causing physiological and morphological adaptations in the plant. These changes include altering root growth characteristics and increasing water and nutrient uptake, increasing rela-tive water content, increasing the activity of enzymatic antioxidants to reduce oxidative damage to cell mem-branes and reducing MDA content and electrolyte leakage, increasing osmolytes accumulation and improving the activity of photosynthetic pigments. It is evident that PGPR have a prominent role in plant water deficit toler-ance. However, the stability of PGPR activity in the field environments is still unconvincing. The cause of this issue is low inoculum quality and the competitivity of the inoculum bacteria with the established indigenous populations under unfavorable conditions. The strains that are inoculated must have rhizosphere traits necessary to compete for resources, survive, and colonize root surfaces. Therefore, it is recommended to apply a high concentration of beneficial bacteria to avoid rare rhizosphere bacteria because they are uncompetitive in agri-cultural soils. If a single strain of bacteria is not capable of providing sufficient water deficit tolerance, a com-bination of strains in mixed inocula with complementary strains can be effective. Additionally, the method of inoculation is equally important, and incorrect use can produce inaccurate results. These methods include seed, seedling and leaf treatment or adding to the soil.