Inoculation of pqqE gene inhabiting Pantoea and Pseudomonas strains improve 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 HPLC, respectively by each bacterial strain. Both strains produced organic acids like 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 µg mL-1 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 µg mL-1 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 (CGR), leaf area index (LAI), straw yield and phosphorous 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, improved the P uptake and productivity of wheat. This article is protected by copyright. All rights reserved.