Résumé
Low soil phosphorus availability is among the major constraints for crops especially when they are depending on symbiotic nitrogen fixation. Rhizobial strains, beneficial N2-fixing symbiotic partners of legumes, were reported to solubilize both organic and inorganic complex phosphates. The current study is carried out to select rhizobial strains isolated from nodules of faba bean cultures in Marrakech-Haouz region in Morocco and to investigate their ability to solubilize the complex mineral P. Our results revealed that among 80 isolates of rhizobia strains, 20 are able to solubilize the mineral P forming halo around their colonies on TCP agar. We evaluated and compared the effect of 8 strains on growth and phosphorus uptake by two Moroccan varieties of faba bean (Vicia faba L.) plants (Aguadulce and Defes). The Greenhouse experiments showed contrasting effect of strains on nodulation rate and plant growth depending on the inoculated strain and the symbiotic combination. The molecular characterization of rhizobial strains was performed by PCR amplification and sequencing of 16s rRNA coding gene, rec A and nod D genes and also the pqq C gene encoding the pyrroloquinoline quinone synthase C applied in the phosphate-solubilization by bacteria. The majority of the rhizobial strains belonged to Rhizobium leguminosarum. Some strains were identified as Ensifer meliloti (formely Sinorhizobium meliloti). The gene pqq C was detected in 9 rhizobia strains. (Texte intégral)