Plant Growth Promoting Rhizobacteria (PGPR) Induced Improvements in the Growth, Photosynthesis, Antioxidants, and Nutrient Uptake of Rapeseed (Brassica napus L.)

The use of microbial inoculants (biofertilizers) is a propitious technology for more sustainable farming systems in view of quickly declining macro and micronutrient reserves in the rhizosphere. To carry out an examination of the role of microbial inoculants, canola seeds were pre-treated with plant growth-promoting rhizobacteria (PGPR). Different bacterial species (Rhizobium species, Bacillus subtilis, Pseudomonas aeruginosa) were cultured in Luria Bertani (LB) medium and cells were picked after fractionation at 5000 rpm for 10 min and inoculum was prepared in sterilized distilled water at the concentration level of 10⁸ cells per milliliter (10⁸ CFU/mL). Healthy seeds of canola were dipped in PGPR suspensions of each treatment for about 30 min with continuous stirring at 100 rpm. Three bacterial species and their consortium were used for priming canola seeds prior to sowing in plastic pots. The growth, physiological and biochemical data of canola seedlings were recorded at the vegetative and maturity stage, while yield was recorded only at maturity stage after ^~ 90 days. In a greenhouse experiment, inoculation (either with Rhizobium sp., Pseudomonas sp., Bacillus sp. or consortium) resulted in significantly higher shoot/root length (SL, RL), shoot fresh/dry weight (SFW, SDW), root fresh/dry weight (RFW, RDW) at both growth stages of canola. Particularly, at maturity stage the consortium treatment increased SL, RL, RFW, SDW, and RDW up to 23%, 109%, > 100%, 117%, and > 100%, respectively. Seed priming with consortium treatment significantly increased (> 100%) the efficiency of oxidant quenching enzymes (catalase; ascorbate peroxidase: superoxide dismutase; and peroxidase). The consortium treatment resulted in increase in number of siliqua/plant, the number of seeds per siliqua, 100 seed weight, and seed yield per plant upto 38%, 52%, 24%, and 38% respectively, compared to non-treated plants. This provides insights into the essential requirement of these PGPR on morphological, physiological, yield, and antioxidant potential of canola plants.