Abstract
This study looked at the synergistic effect of Pseudomonas alkylphenolica PF9 and Sinorhizobium meliloti Rm41 on the Moroccan alfalfa population (Oued Lmaleh) grown under symbiotic nitrogen fixation and limited phosphorus (P) availability. The experiment was conducted in a growth chamber and after two weeks of sowing, the young seedlings were inoculated with Sinorhizobium meliloti Rm41 alone or combined with a suspension of Pseudomonas alkylphenolica PF9. Then, the seedlings were submitted to limited available P (insoluble P using Ca(3)HPO(4)) versus a soluble P form (KH(2)PO(4)) at a final concentration of 250 μmol P·plant(-1)·week(-1). After two months of P stress, the experiment was evaluated through some agro-physiological and biochemical parameters. The results indicated that the inoculation of alfalfa plants with Sinorhizobium strain alone or combined with Pseudomonas strain significantly (p < 0.001) improved the plant growth, the physiological and the biochemical traits focused in comparison to the uninoculated and P-stressed plants. For most sets of parameters, the improvement was more obvious in plants co-inoculated with both strains than in those inoculated with Sinorhizobium meliloti Rm41 alone. In fact, under limited P-availability, the co-inoculation with two strains significantly (p < 0.01) enhanced the growth of alfalfa plants evaluated by fresh and dry biomasses, plant height and leaf area. The results indicated also that the enhancement noted in plant growth was positively correlated with the shoot and root P contents. Furthermore, the incensement in plant P contents in response to bacterial inoculation improved cell membrane stability, reflected by low malonyldialdehyde (MDA) and electrolyte leakage (EL) contents, and photosynthetic-related parameters such as chlorophyll contents, the maximum quantum yield of PS II (Fv/Fm) and stomatal conductance (g(s)). Our findings suggest that Pseudomonas alkylphenolica PF9 can act synergistically with Sinorhizobium meliloti Rm41 in promoting alfalfa growth under low-P availability.