Pseudomonas in Hippophae rhamnoides Rhizosphere Affecting Growth of Ipomoea aquatica

  Objective  Pseudomonas sp. in the rhizosphere of Hippophae rhamnoides were isolated and studied for potential application as a biofertilizer.

  Method  Microorganisms in the rhizosphere soil of Hippophae rhamnoides sinensis subsp. in the wild in Qinghai Province were isolated by using selected media and purified by plate streaking. Candidate Pseudomonas strains were morphologically, physiologically, and biochemically identified as well as 16S rDNA sequenced. Abilities of the isolates to degrade organic and inorganic phosphorus, potassium, cellulose and/or to fix nitrogen were examined. Effects of spraying the bacterial culture broth of the individual isolates on the seed germination and seedling growth of Ipomoea aquatica Forssk were observed.

  Result   On different media of specific formulations, the diameters of the turbid circles born by the 7 isolated Pseudomonas strains cultured for 3d ranged 4.28-13.71mm with 5.15-25.41 μg·mL^-1 of dissolved organic phosphorus, those of clear circles 3.51-7.62mm with 2.15-22.26 μg·mL⁻¹ of dissolved inorganic phosphorus, those of halos 11.12-21.85mm with 5.07-14.33 μg·mL^-1 of dissolved potassium, those of transparent circles 4.61-10.22 mm of cellulose-degradation, and the ratios of the nitrogen-fixing clear circle diameter (D) to the colony growth circle diameter (d) 1.33-1.86. The isolated Pseudomonas strains significantly improved the I. aquatica seed germination rate and seedling growth. Among them, ZGSJ-3 showed the largest increases of 35.2% on the 3.69 mm leaf width and of 41.2% on the 50.25 mm stem length over control.

  Conclusion  Presence of the Pseudomonas sp., especially ZGSJ-3 and ZGSJ-7, isolated in this study significantly improved the seed germination and seedling growth of I. aquatica.