Unraveling the Plant Growth-Promoting Mechanisms of Stenotrophomonas sp. CV83 for Drought Stress Tolerance and Growth Enhancement in Chickpea

Drought stress is a key risk factor for chickpea production globally, becoming more prevalent due to climate change activities. To attenuate the adverse effects of drought stress and plant growth promotion, application of plant growth-promoting rhizobacteria (PGPR) is a promising approach. With this aim, in the present study, a drought-tolerant rhizobacteria CV83 that tolerates polyethylene glycol up to 30% concentration was isolated from chickpea rhizosphere, grown in Varanasi district of eastern Uttar Pradesh, India. The polyphasic identification methods confirm the identity of the rhizobacteria CV83 as Stenotrophomonas sp. Strain CV83 retains multiple PGP activities such as production of indole acetic acid (96.52 µg/ml), ACC deaminase (38.35 α-ketobutyrate/mg protein), siderophore (1.22 SPI), and ammonia production, solubilizes phosphate (1.74 PSI) and zinc (2.84 ZSI), as well as produces exopolysaccharide (2.18 g/100 ml) under higher drought stress conditions. Results of plant growth experiments showed that drought stress negatively affects vegetative growth and biochemical parameters. However, rhizobacteria CV83-inoculated plants had superior drought tolerance, as revealed in enhanced vegetative growth parameters and water content. In addition, rhizobacteria inoculation progressively increased proline content in T-4 (28.9%) (Moderate drought stress) and T-6 (22.4%) (Severe drought stress) treatments, respectively, as compared to their respective un-inoculated control plants. Similarly, photosynthetic pigment, sugar, and protein content also increased in the presence of rhizobacterial inoculation. Furthermore, CV83-inoculated chickpea seedlings displayed significantly lower MDA content by 32.3 (T-4) and 54.7% (T-6) in comparison to the un-inoculated (T-3 and T-5) control seedlings. Further, upon exposure to drought stress condition, the activities of defense-related antioxidant enzymes such as superoxide dismutase, catalase, ascorbate peroxidase, peroxidase, and lipoxygenase enzymes were also up-regulated in PGPR-inoculated plants. Overall, our results suggested that Stenotrophomonas sp. CV83 alleviates adverse impact of drought on chickpea plants. Thus, this rhizobacterium may be used as a biostimulant for drought tolerance and growth promotion of chickpea plants under water stress condition. However, further, a detailed field-level study with chickpea and other crop plants under extreme environmental conditions need to be explored.