Encapsulation in alginate enhanced the plant growth promoting activities of two phosphate solubilizing bacteria isolated from the phosphate mine of Gafsa

Mounira Ben Farhat, Salma Taktek and Hichem Chouayekh

Net Journal of Agricultural Science
Published: December 15 2014
Volume 2, Issue 4
Pages 131-139

Abstract

To develop a maize inoculant allowing the use of sparingly soluble inorganic phosphates, the potential of two phosphate solubilizing bacteria isolated from the Gafsa rock phosphate mine, namely Serratia marcescens CTM 50650 and Enterobacter sp. US468 was assessed. At first, these phosphate solubilizing bacteria were analyzed for plant growth promoting activities like acid and alkaline phosphatase, and indole acetic acid production. Both isolates produced alkaline and acid phosphatase at 35.73 and 86.86 mU mg^-1 of proteins for CTM 50650 and at 44.95 and 81.24 mU mg^-1 for US468, respectively; while indole acetic acid was significantly released only by CTM 50650 at 134.7 µg ml^-1. Investigation of the effect of humic acids, showed that their addition to the growth medium at 0.2%, stimulated growth and ability of free and encapsulated CTM 50650 and US468 cells to solubilize Gafsa rock phosphate. Subsequently, the potential of application of these phosphate solubilizing bacteria (free or encapsulated in alginate enriched or not with humic acids), as bioinoculants for maize plants, was evaluated in growth chamber. Accordingly, compared to control, we observed that bacterial inoculation increased significantly (P ≤ 0.05), the mycorrhizal percent (Myc%) from 22.69 to 29.06 and 27.36% for free cells of CTM 50650 and US468, and from 25.26 to 31.8 and 28.3% for encapsulated ones, respectively. The addition of humic acids, particularly in immobilized system, has improved significantly (P ≤ 0.05) root colonization by arbuscular mycorrhizal fungi compared to control, as well as Myc% since it increased to 33.17 and 31.15% for alginate encapsulated CTM 50650 and US468 cells.

Keywords: Maize inoculant, growth medium, alkaline phosphatase, Gafsa rock phosphate, alginate encapsulated.

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