Symbiotic responses to insoluble phosphorus supply in common bean (Phaseolus vulgaris L.): Rhizobia symbiosis
The common bean (Phaseolus vulgaris L.) is often grown under various environmental constraints in soil as well as phosphorus (P) deficiency. In worldwide soils, P massively exists in insoluble forms especially in acidic and basic soils, where it is greatly combined with Al, Fe and Ca ions hydroxide. In order to study the effect of insoluble phosphorus (IP) in hydroponic culture, two common bean varieties, that is, WAFA and REBIA were inoculated separately with three rhizobia strains (P.Tb.09, CIAT899 and P.OM.09) and were grown under mineral P (250 ìmol P (KH2PO4)) versus IP (250 ìmol P (Ca2HPO4)). Results show that inoculation of both varieties under 250 ìmol P with P.Tb.09 and CIAT899 had produced a high nodule biomass of about 0.11 g plant-1. However, inoculation of WAFA with P.Tb.09 and P.OM.09 yielded in a low nodule biomass (0.06 g plant-1) in comparison with REBIA variety showing no variation of the strains used. The last variety in symbiosis with all the three strains, exhibited a high shoot biomass that was not significantly different with plants supplied with 250 ìmol P. By contrast, a high acid phosphatase activity was more stimulated under IP conditions in leaves of WAFA inoculated with CIAT899 and P.Tb.09. Likewise, root acid phosphatase (APase) activity has increased in REBIA inoculated with P.Tb.09 for both P forms; meanwhile, inoculation with CIAT899 under IP has significantly increased roots acid phosphate (AP) activity. However, this stimulation was not associated with high plant N accumulation that was highly accumulated by both varieties inoculated with P.Tb.09 but grown under 250 ìmol P. In addition, analysis of phenols content in roots showed a high stimulation when plants had received IP than those under 250 ìmol P, but to the high extent in roots of REBIA inoculated with P.Tb.09 under IP conditions. We concluded that the use of P-efficient symbiotic combinations against P deficiency seems to be an interesting biological approach to increase legumes P assimilation for N2 fixation and thus for agricultural sustainability.
Key words: Symbiosis, Phaseolus vulgaris, rhizobia, insoluble phosphorus, phosphatase, phenolics content.