Synergistic effect of plant growth promoting rhizobacteria (PGPR) and kinetin on growth of maize (Zea mays L.)

Plant growth-promoting rhizobacteria (PGPR) are soil bacteria that colonize the plant roots and promote plant growth. PGPR improve growth and yield by different mechanisms. Production of plant growth regulators is one of them. Exogenously applied growth regulator can improve the efficiency of PGPR and synergistic effect of this interaction might be multiplied. To evaluate this, an initial laboratory trial was carried out to study the effect of PGPR and cytokinin on growth of maize under controlled conditions. Results regarding laboratory trial indicated that the most efficient strain of bacteria was bacterial isolate S1 which showed positive interaction with the kinetin and significantly increased the plant height (98.235%), root length (four folds), fresh biomass of plant ( two and half fold) and shoot dry matter content (nine folds) as that of un-inoculated control. While root fresh and dry weight was expressed significantly by isolate-4 with combination of kinetin. Following the laboratory trial, a pot trial was conducted in the wire house under natural conditions. For pot trial, maize seeds were inoculated with selective isolates and sown in pots containing 12 kg soil. The effect of these isolates was tested in the presence and absence of cytokinin. Nitrogen, potassium and phosphatic fertilizers were applied @ 175-160-100 kg/h as urea, diammonium phosphate (DAP) and sulphate of potash (SOP). Experiment was laid out according to Completely Randomized Design (CRD). Data regarding, plant height, no. of leaves, root length, fresh weight of root and shoot, oven dry weight of shoot and root was recorded. Plant was analyzed for N, P and K contents. Experimental data was analyzed by following standard statistical procedure. Data regarding physical parameter demonstrated that combine use of bacterial strains with the kinetin has increased plant height (78.55%), shoot fresh weight (47%), root length (49.93%), shoot dry weight (1.32 fold) and number of leaves (50%) as compare to the sole application of kinetin. Root fresh weight (20.68%) and root dry weight (16.04%) was significantly enhanced by synergistic effect of bacterial strain S3 and kinetin. Results of chemical analysis revealed that interaction of bacterial isolate S1 and kinetin was responsible for improvement in shoot phosphorus (55.55%), root phosphorus (100%), shoot potassium (29.83%), root potassium (30%), shoot nitrogen (96.46%) and root nitrogen (52.66%) as compared to the single application of kinetin.