Inoculation effect of Azospirillum brasilense on basil grown under aquaponics production system

Abstract

The potential of Azospirillum brasilense to enhance basil growth under aquaponics system was evaluated using the three strains, i.e., Sp7, Sp7-S, and Sp245. Basil seedlings were inoculated with strains of A. brasilense a week after sowing and before transplanting. Impacts of inoculation on some parameters associated with plant growth, and physiological and metabolic activities were evaluated at seedling stage and at harvest of marketable plant size from aquaponics system. Likewise, impacts of inoculation on the existing bacterial communities were assessed at the end of each stage. At seedling stage, inoculated seedlings produced longer (90 %) roots and taller (19 %) plants with more developed (25 %) and bigger (61 %) leaves. As a result, seedling fresh and dry biomasses were increased by 79 and 44 %, respectively, particularly for those seedlings inoculated with Sp7 and Sp245. Some of the plant metabolic activities were altered by inoculation such as elevated levels of enzyme peroxidase activity and total phosphorus content. In aquaponics, plants previously inoculated with the strains also showed superior growth performance. For instance, basil leaf area, fresh herbage yield, and root weight were increased by inoculation up to 27, 11 and 11 %, respectively. Inoculation also enhanced peroxidase activity (73 %), endogenous plant indole-3-acetic acid (IAA) (27 %) and protein contents (20 %) particularly for those plants inoculated with Sp7 and Sp7-S. Furthermore, Azospirillum inoculation brought no significant disturbance to the composition of indigenous bacterial communities present in the root rhizosphere of the seedlings and aquaponics-grown basil. Thus, this plant growth-promoting rhizobacteria (PGPR) could be an important resource in aquaponics farming to further enhance plant growth and more importantly to increase crop productivity.