Phaseolus vulgaris-rhizobia symbiosis increases the phosphorus uptake and symbiotic N2 fixation under insoluble phosphorus

Five north Tunisian native rhizobia were tested in symbiosis with ‘Coco-blanc’ variety under two phosphorus (P) supplies [P-sufficient and insoluble P (IP)] at 250 μmol P plant^?1. At flowering stage, responses against IP were assessed and indicated that inoculation with P.Ps.09 produced a high nodule biomass (0.12g). Similarly, P.Tb.09 produced 0.08 g nodule biomass under both P and P.Bj.09 that significantly increased nodule number under IP. Shoot biomass exhibited high dry weight with P.Tb.09 and CIAT899 (1.6 g plant^?1). Inoculation with CIAT899 produced a high root biomass under both P. Analysis of a halo diameter of clear zone rounding each colony under IP indicated that P.Tb.09 has developed high halo Ø (1.7cm). These variations were associated under IP with a decrease of pH by P.Ar.09 and with increase in shoot phosphatase activity by P.Ar.09, P.Bj.09, P.OM.09 and P.Ps.09. The use of P-efficient rhizobia may constitute an adaptive mechanism against P-deficiency tolerance.     

Rhizobial symbiosis efficiency increases in common bean under sparingly soluble calcium-phosphorus

The use of phosphate-solubilizing rhizobia as a rhizobial inoculant improves plant nutrient uptake (nitrogen (N) and phosphorus (P)) and subsequently crop yield stability. Three common bean varieties namely Coco blanc, Wafa, and Rebia were inoculated with the Rhizobium strain “Ar02” and grown under 250 μmol P as KH₂PO₄ Pi and 250 μmol P as Ca₃HPO₄ (Ca-P). Rebia showed the highest root biomass increase (35%) both under Pi and Ca-P supplies, while Wafa's root biomass significantly decreased under Ca-P condition. Application of Ca₃PO₄ stimulated acid phosphatase activities in shoots (50%), roots (45%) and nodules (49%) of Coco blanc variety as compared to Rebia and Wafa. Moreover, phenols content was enhanced in Wafa roots as compared to Coco blanc roots. N content increased in shoots (14% under Pi and Ca-P supplies) and nodules (6% under Ca-P supplies) of Coco blanc. P and K nutrition largely varied in response to P supplies through all plant parts.