This study examined the effects of inoculation with 2 rhizobacteria strains, Pseudomonas putida (PP) and Pseudomonas fluorescens (PF), on growth parameters, chlorophyll, proline, leaf relative water content (RWC), antioxidant enzyme activities (including superoxide dismutase (SOD), peroxidase (POX), and catalase (CAT)), tropane alkaloids (such as hyoscyamine (HYO) and scopolamine (SCO)), and production of Hyoscyamus niger under 3 water deficit stress (WDS) levels, i.e. 30% (W1), 60% (W2), and 90% (W3) water depletion of field capacity. The results showed that inoculation with PP and PF strains minimized the deleterious effects of WDS on growth parameters. The activities of SOD and POX in root and leaf were increased to a significant extent with inoculation of PP and PF, and also with WDS treatment, whereas CAT activity decreased with increasing WDS, except for in plants treated with the PF strain. The maximum proline, HYO, and SCO content were recorded in PF-treated plants under W3 conditions. In contrast, the highest root and shoot alkaloids yield were obtained in plants bacterized with PP against W1 conditions. PP was the most effective strain under low WDS, PF had the highest efficiency in improving the growth and alkaloid production in the presence of severe (W3) WDS. Integrative use of effective plant growth promoting rhizobacteria (PGPR) and WDS could be an encouraging and eco-friendly strategy for increasing alkaloid yield and content in Hyoscyamus niger organs.
