Amélioration de la croissance du blé dur en milieu salin par inoculation avec Bacillus sp. et Pantoea agglomerans isolées de sols arides

Abstract

The study on the inoculation of wheat durum seeds by Bacillus sp and Pantoea agglomerans in the presence of salt is carried out in order to assess the positive impact of plant growth promoting rhizobacteria (PGPR , Plant Growth Promoting Rhizobacteria ) on vigor and crop productivity especially when subjected to salt stress. The effectiveness of the bacterial inoculum is related to the characterization of multiple PGP activities such as the production indole acetic acid (IAA ) , hydrogen cyanide ( HCN ) , siderophores , ammonia (NH3 ) , of phosphate solubilization , the antifungal activity as well as the capacity to synthesize an ACC deaminase. A total of 62 bacterial strains (BG- and BG+ sporulated ) were isolated and selected from three rhizosphere of arid and semi -arid soils. The majority (> 80 %) strains produce NH3. 75% of Bacillus inhibit three fungal strains and more. 77% of BG- synthesize AIA at rate ≥ 10μg/ml. Only six strains possess ACC deaminase. The ability of phosphate solubilization by Bacillus strains ( n = 10 ) tested on NBRIP medium decrease in the presence of NaCl. This activity remains low in salt stress and even in presence of osmoprotecteurs : glycine betaine and proline (1 mM). The two most powerful strains selected and identified by sequencing the 16S rRNA gene are Bacillus sp. SCH1 and Pantoea agglomerans lma2 . The latter has an halophilic character and expresses PGP activities (production of siderophores AIA and phosphate solubilization ) high at salinities between 100 and 400 mM NaCl. The seeds inoculation of durum wheat variety Waha by Bacillus sp and/or P. agglomerans under salt stress (0, 100 and 200 mM /NaCl ) improves significantly ( P ≤ 0.01 ) morphological parameters of the plant (fresh and dry weight of roots and leaves, root elongation and the plant elongation). Leaf dry weight increase after inoculation with Bacillus sp. To 38% at 100 mM and to 158 % at 200 mM /NaCl . The leaves are growing from 27.31 % with Bacillus sp., 15.90 % with P. agglomerans and only 8.62 % for the co-inoculation. The chlorophyll synthesis is induced after inoculation regardless of the salt content. The accumulation of proline increases to 200 mM / NaCl. It falls in the presence of P. agglomerans. Rates of intracellular Na + are important at 100 and 200 mM / NaCl . The inhibitor effect of salt on the K + absorption is reduced in presence of bacterial inoculum . The interaction between salinity and bacterial inoculation is significant. However the co inoculation is not synergistic . Ultimately, Bacillus sp and P. agglomerans bioinoculants are effective in restoring growth of durum wheat in arid and saline areas.