• Tasnime Maghraoui

• Noura Bechtaoui

• Antoine Galiana

• Sanaa Wahbi

• Robin Duponnois

• Mohamed Hafidi

• Khalid Daoui

• Zain El Abidine Fatemi

• Philippe de Lajudie

• Khalid Oufdou

تلخیص

Low Phosphorus availability in soil is worldwide a frequent major constraint for crops. Rhizobial strains, beneficial N2-fixing symbiotic partners of legumes, were reported to solubilize both organic and inorganic complex phosphates. Thus they may play a significant role as plant growth-promoting rhizobacteria (PGPR) in the biofertilization of crops. Natural rock phosphate may play a key role in sustainable agriculture, resulting in economic and environmental benefits. This work aims to evidence the capacity of rhizobial strains nodulating Vicia faba L. plants in Marrakech-Haouz region (Morocco) to solubilize Moroccan rock phosphate in vitro in either agar or liquid medium and to evaluate and compare the effect of these strains on growth and phosphorus uptake by V. faba plants of two Moroccan varieties (Defes and Aguadulce). Four rhizobial strains, contrasting for phosphate solubilization on agar medium, were further studied on liquid medium. RHOF147 and RHOF174 strains formed clear halos around colonies (1.37 cm and 1.2 respectively after 15 days); opposite RHOF170 and RHOF171 strains did not produce halo. The four strains were able to mobilize rock phosphate for growth in liquid medium (up to 0.59 mg/L of assimilated phosphorus). Lower pH values and most mobilized phosphorus production were registered for RHOF147 and RHOF174 strains. By screening the four rhizobial strains for growth on Chrome Azurol S (CAS) medium, only RHOF171 strain formed orange halo indicating its capacity to produce siderophores. Greenhouse experiments were undertaken including comparison of inoculated plants with these four rhizobial strains in the presence of rock phosphate as sole P source versus noninoculated plants growing on KH2PO4 as sole P source (P-fertilized plants). Results show that the root length, the root dry weight and the ratio root /shoot dry weights were generally higher in the inoculated plants than in the P-fertilized plants, indicating the adaptation of the inoculated plants to phosphorus deficiency conditions. The effect of rock phosphatesolubilizing bacteria on plant growth depends on the symbiotic combination of the inoculated strain and the plant genotype. As for phosphorus uptake, rhizobial strains made phosphorus available to the plant at significant increased concentrations in some symbiotic combinations (e.g. Aguadulce-RHOF147). The use of selected symbiotic combinations having the capacity to solubilize rock phosphate may improve soil fertility and phosphorus availability to plants.

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