Encapsulation of Pseudomonas libanensis in alginate beads to sustain bacterial viability and inoculation of Vigna unguiculata under drought stress.

Conventional agricultural practices based on the application of synthetic fertilizers are increasingly considered as unsustainable. Under a forecasted scenario of drought for the next decades, there is a global demand for innovative and sustainable approaches to ameliorate plant performance. Here, encapsulating beneficial microbes (BMs) to promote plant growth is gaining attention. This study evaluates bacterial encapsulation using polymeric beads of alginate, testing the survival of Pseudomonas libanensis TR1 stored up to 90 days. Produced beads were subjected to different treatments (fresh, air-dried and pulverized), which resulted in a variable size range (1200-860 µm). After storage, bacterial viability was maintained, and air-dried beads displayed a higher number of colony-forming units (2 × 107). Then, a glasshouse experiment investigated the drought resistance (plant growth, biomass, and photosynthetic responses) of Vigna unguiculata plants inoculated with these alginate beads. After 10 days of complete water restriction, turgidity and relative water content of V. unguiculata were still high under drought stress (> 80%). Leaf and root growth and biomass did not evidence significant changes after water restriction even after P. libanensis inoculation. Plant photosynthetic parameters (stomatal conductance, net photosynthetic rate, leaf CO2 concentration, or F v'/F m') were slightly affected due to inoculation but the level of stress-induced minimal plant responses. In our experiment, water restriction might have been insufficient to downregulate photosynthetic efficiency and reduce plant growth, limiting our understanding of the role of P. libanensis inoculation in alleviating drought stress in V. unguiculata, but highlighting the important relationship between the stress level and agricultural benefits of using encapsulated BMs. © King Abdulaziz City for Science and Technology 2021.