Selection of osmotolerant and effective strains of Rhizobiaceae for inoculation of common bean (Phaseolus vulgaris) in Moroccan saline soils

The improvement of common bean production in the Mediterranean area require s first, the selection of effective Rhizobium strains and cultivars of Phas eolus vulgaris L., well adapted to the conditions of the semi-arid climate prevailing in this region. For this purpose, we have isolated 150 strains f rom 3 Moroccan soils and found that among them 30 were osmotolerant. When i noculated at NaCl concentrations equal to or higher than the minimal growth inhibitory concentration of each strain, differences of viability were fou nd between these strains. Therefore we suggest that viability under saline conditions should be taken into account when selecting osmotolerant strains for inoculation. These strains might use various solutes during the osmopr otection process, depending probably on their availability in the environme nt. Glutamate and aspartate, and less efficiently glycine betaine, relieved the growth inhibition of most of these strains under saline conditions. On the contrary, sucrose was used only by a limited number of strains. Among the 19 most osmotolerant strains, 10 showed an interesting potential of inf ectiveness and effectiveness. They should be tested in strain-cultivar inte raction experiments and in field inoculation trials using cultivars previou sly selected under typical Mediterranean conditions.