Inducing Drought Tolerance in Wheat through Exopolysaccharide-Producing Rhizobacteria

Wheat is the main staple food in the world, so it is the backbone of food security. Drought not only affects growth and development but also ultimately has a severe impact on the overall productivity of crop plants. Some bacteria are capable of producing exopolysaccharides (EPS) as a survival mechanism, along with other metabolites, which help them survive in stressful conditions. The present study was conducted with the aim of inducing drought stress tolerance in wheat through EPS-producing plant growth-promoting rhizobacteria (PGPR). In this regard, a series of laboratory bioassays were conducted with the aim to isolating, characterizing, and screening the EPS-producing PGPR capable of improving wheat growth under limited water conditions. Thirty rhizobacterial strains (LEW1-LEW30) were isolated from the rhizosphere of wheat. Ten isolates with EPS-producing ability were quantitatively tested for EPS production and IAA production ability. Four of the most efficient EPS-producing strains (LEW3, LEW9, LEW16, and LEW28) were evaluated for their drought tolerance ability along with quantitative production of EPS and IAA under polyethylene glycol (PEG-6000)-induced drought stress. The jar experiment was conducted under gnotobiotic conditions to examine the drought-tolerant wheat genotypes, and two wheat varieties (Johar-16, and Gold-16) were selected for further experiments. The selected varieties were inoculated with EPS-producing rhizobacterial strains and grown under control conditions at different stress levels (0, 2, 4, and 6% PEG-6000). The strain LEW16 showed better results for improving root morphology and seedling growth in both varieties. The maximum increase in germination, growth parameters, percentage, root diameter, root surface area, and root colonization was recorded in Johar-16 by inoculating LEW16 at 6% PEG-6000. Plant growth-promoting traits were tested on the top-performing strains (LEW3, LEW9, and LEW16). Through 16S rRNA sequencing, these strains were identified as Chryseobacterium sp. (LEW3), Acinetobacter sp. (LEW9), and Klebsiella sp. (LEW16), and they showed positive results for phosphorous and zinc solubilization as well as hydrogen cyanide (HCN) production. The partial sequencing results were submitted to the National Center for Biotechnology Information (NCBI) under the accession numbers MW829776, MW829777, and MW829778. These strains are recommended for their evaluation as potential bioinoculants for inducing drought stress tolerance in wheat.