Effects of Bacillus sp. MR-1/2 and magnetite nanoparticles on yield improvement of rice by urea fertilizer under different watering regimes.

AIMS: The present research aimed to examine the use of magnetite nanoparticles (MNPs) in combination with phyto-beneficial rhizobacterium (PhBR) for improvement of applied N recovery (ANR) from urea fertilizer in rice grown under deficient and optimum watering conditions. METHODS AND RESULTS: The Bacillus sp. MR-1/2 was positive for acetylene reduction, phosphate solubilization and ACC deaminase activity at temperature ranges 35-45°C. In a pot experiment, urea, MNPs and Bacillus sp. MR-1/2 were applied either alone or in combination to rice plants grown in pots under water deficit and optimal watering conditions. Combined application of urea, MNPs and Bacillus sp. MR-1/2 increased the plant N content and ANR by 27 and 65%, respectively, over their respective control values in rice grown under optimum watering conditions, whereas these increases were 27 and 41%, respectively, in rice grown under water deficit conditions. This treatment also increased the kernel weight and plant dry matter by 36 and 60%, respectively, over control (urea alone) values in rice grown under water deficit conditions, whereas these increases were 31 and 21·8%, respectively, in rice grown under optimum watering conditions. Values of malondialdehyde (MDA) contents, ascorbate peroxidase (APX), catalase and ethylene concentration were higher in control treatment under both the watering regimes. The application of Bacillus sp. MR-1/2 either alone or in combination with MNPs and urea reduced MDA contents, APX, catalase and ethylene production in the rice plants. CONCLUSION: The combined application of MNPs+Bacillus sp. MR-1/2 reduced the N losses from applied urea, increased N uptake and ANR in rice, decreased MDA contents, APX and catalase activity and ethylene level in rice grown under deficit and optimum water conditions. SIGNIFICANCE AND IMPACT OF THE STUDY: The application of MNPs together with Bacillus sp. MR-1/2 may help to increase ANR and rice productivity under water deficit conditions with low cost of production.

Inoculation of pqqE gene inhabiting Pantoea and Pseudomonas strains improves the growth and grain yield of wheat with a reduced amount of chemical fertilizer.

OBJECTIVE: The present study was performed to examine the role of pqqE inhabiting rhizobacteria in organic acid production and relationship of the organic acids with phosphate solubilization by the bacteria in vitro as well as in vivo. METHODS AND RESULTS: The pqqE gene was PCR amplified and sequenced in genomic DNA of Pantoea sp. WP-5 and Pseudomonas sp. NN-4. Nucleotide sequence obtained from WP-5 and NN-4 showed maximum sequence similarity (88 and 89%, respectively) with the pqqE gene of Pseudomonas fluorescens strain CMR12a (KM251420). Deduced amino acid sequence from pqqE gene of Pseudomonas sp. NN-4 and Pantoea sp. WP-5 showed 75 and 93% similarity, respectively, with protein pyrroloquinoline quinone. Phosphate solubilization and acid production assay were quantified on spectrophotometer and high-profile liquid chromatograph, respectively, by each bacterial strain. Both strains produced organic acids such as acetic, citric, gluconic, succinic and malic acid and lowered the pH of Pikovskaya broth medium under laboratory conditions. Phosphate solubilization by Pantoea sp. WP-5 was 311 ± 4 and 204 ± 3 µg ml-1 in the culture medium supplemented with glucose and sucrose as carbon source, respectively. Pseudomonas sp. NN-4 solubilized 176 ± 3 and 298 ± 5 µg ml-1 phosphate in Pikovskaya broth medium under similar conditions. In field experiments conducted during two consecutive years, the concentration of acetic acid and gluconic acid was higher in root exudates of plants treated with Pantoea sp. WP-5 at 30% reduced doses of nitrogen (N)- and phosphorus (P)-based chemical fertilizers as compared to non-inoculated plants. Values of chlorophyll contents, crop growth rate, leaf area index, straw yield and P contents were recorded higher in plants inoculated with Pantoea sp. WP-5 and Pseudomonas sp. NN-4 as compared to non-inoculated control. Grain yield was increased by 10-12% due to inoculation with Pantoea sp. WP-5 and Pseudomonas sp. NN-4 over non-inoculated control in the field experiments. CONCLUSIONS: These results lead to the conclusions that the rhizobacteria inhabiting pqqE gene produced organic acids and solubilized the phosphate in vitro. On inoculation to wheat plants in field experiments, these strains produced the organic acids, solubilized the phosphate, and improved the P uptake and productivity of wheat. SIGNIFICANCE AND IMPACT OF THE STUDY: The Pantoea sp. WP-5 and Pseudomonas sp. NN-4 are the potential candidates for inoculation to wheat as phosphate solubilizer even with reduced chemical fertilizer dose. The inoculation of the strains may enhance grain yield and net income of the farmer even with less chemical fertilizer application. This practice will be helpfull inminimizing environmental pollution.