A comparative study of plant growth promoting rhizobacteria (PGPR) and sowing methods on nutrient availability in wheat and rhizosphere soil under salinity stress

Abstract

An experiment was conducted to evaluate the role of plant growth promoting rhizobacteria and sowing methods on physicochemical properties, nutrients and heavy metals content of rhizosphere soil and their translocation to plant. Wheat cv. Inqlab-91 seeds were inoculated with cultures of Pseudomonas mendocina Khsr2, Pseudomonas putida Khsr4, Pseudomonas stutzeri Khsr3 and Azotobacter vinelandii Khsr1 3 h prior to sowing. Broadcast, drill and ridge methods of sowing were applied. The PGPR inoculations significantly decreased the pH, electrical conductivity and sodium adsorption ratio of rhizosphere soil of inoculated plants over that of uninoculated soil. The applied bacterial strains significantly improved the transfer of K,Ca, Mg and Zn from soil to plant shoots and reduced the transfer of Cr .In contrast K and Ca transfer factor was much lower but Cr transfer factor was higher for plants experiencing differing sowing methods. The ridge sowing enabled the plant to have better transfer factor for K and Ca, Mg and Zn as compared to other sowing methods. Pseudomonas putida Khsr4 inoculated plant leaves also exhibited significantly higher Zn and Fe content. The maximum K+/Na + ratio of rhizosphere soil and wheat leaves were recorded in Pseudomonas putida Khsr4 inoculation. The effect of Pseudomonas putida Khsr4 was more pronounced on yield and size of grain as measured by 1000 grain weight of plant. The applied PGPR helped in selective uptake of K over Na and enhanced transfer of nutrients resulting in higher yield. Yield of ridge sown plot was 3.59% higher than drill sown plot, and 10.87% higher than broadcast sown plot respectively. The Ridge method of sowing was better than drill and broadcast to combat salt stress and also influenced the nutrient uptake by plants and reduced heavy metal uptake. It is inferred that growing PGPR inoculated plants using ridge sowing can better induce salt tolerance to plant through selective uptake of K, Ca, Mg and Zn and suppressing heavy metal uptake resulting in higher yield and large sized grains.