Search

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. [ABSTRACT FROM AUTHOR]

Methane utilizing bacteria (MUB) are known to inhabit the flooded paddy ecosystem where they play an important role in regulating net methane (CH4) emission. We hypothesize that efficient MUB having plant growth-promoting (PGP) attributes can be used for developing novel bio-inoculant for flooded paddy ecosystem which might not only reduce methane emission but also assist in improving the plant growth parameters. Hence, soil and plant samples were collected from the phyllosphere, rhizosphere, and non-rhizosphere of five rice-growing regions of India at the tillering stage and investigated for efficient methane-oxidizing and PGP bacteria. Based on the monooxygenase activity and percent methane utilization on NMS medium with methane as the sole C source, 123 isolates were identified and grouped phylogenetically into 13 bacteria and 2 yeast genera. Among different regions, a significantly higher number of isolates were obtained from lowland flooded paddy ecosystems of Aduthurai (33.33%) followed by Ernakulum (20.33%) and Brahmaputra valley (19.51%) as compared to upland irrigated regions of Gaya (17.07%) and Varanasi (8.94%). Among sub-samples, a significantly higher number of isolates were found inhabiting the phyllosphere (58.54%) followed by non-rhizosphere (25.20%) and rhizosphere (15.45%). Significantly higher utilization of methane and PGP attributes were observed in 30 isolates belonging to genera Hyphomicrobium, Burkholderia, Methylobacterium, Paenibacillus, Pseudomonas, Rahnella, and Meyerozyma. M. oryzae MNL7 showed significantly better growth with 74.33% of CH4 utilization at the rate of 302.9 ± 5.58 and exhibited half-maximal growth rate, Ks of 1.92 ± 0.092 mg CH4 L−1. Besides the ability to utilize CH4, P. polymyxa MaAL70 possessed PGP attributes such as solubilization of P, K, and Zn, fixation of atmospheric N and production of indole acetic acid (IAA). Both these promising isolates can be explored in the future for developing novel biofertilizers for flooded paddies. [ABSTRACT FROM AUTHOR]