Isolation of plant growth promoting rhizobacteria from wheat rhizosphere and their effect on improving growth, yield and nutrient uptake of plants

This study was conducted to isolate plant growth promoting rhizobacteria (PGPR) from wheat rhizosphere and to evaluate their potential use for improving growth, yield and nutrient uptake of wheat. Eight PGPR strains were isolated and studied for their morphological and cultural characteristics, phosphate solubilization and indole acetic acid (IAA) production. All isolates produced IAA ranging from 5.5–31.0 μg/ml, while four isolates were P-solubilizers. On the basis of morphological characteristics, IAA production and P solubilization, strains WPR-32, WPR-42, and WPR-51 were identified as PGPR and selected for further study. Efficiency of these three PGPR isolates and their mixtures (combinations) at two N levels (N at the rate of 50 and 100 kg ha⁻¹) was evaluated in wheat under greenhouse conditions. Application of PGPR significantly increased plant height, shoot fresh weight and shoot dry weight by 25, 45, and 86%, respectively, while increase in root length, root fresh and dry weight was 27, 102, and 76%, respectively, over the un-inoculated control. PGPR also increased number of tillers per plant, 1000-grain weight and grain yield by 23, 48 and 59% over the control. Uptake of N and P by plant shoot was increased by three-fold, while K uptake was increased by 58% with PGPR application. The rate of increase in growth, yield and nutrient accumulation was even higher in treatments receiving combined application of PGPR and N-fertilizer. The concentration of [sbnd]N and available P in soil also increased with PGPR treatments. Results indicated that among the PGPR isolates, efficiency of mixture of isolates was higher than the individual isolates and isolate S₇ was relatively more consistent than the remaining strains. This study demonstrated that application of PGPR with N fertilizer increased the fertilizer N efficiency by increasing N content and N uptake in plants. This study also indicated that use of PGPR had similar effects on growth, yield and nutrient uptake of wheat when compared with the low N level, i.e. N₅₀. Therefore, application of PGPR with low fertilizer rates could be a viable supplementary strategy for maximum benefits in terms of cost of production and sustaining productivity. However, the applicability of this approach has to be tested in further field studies.