This study compared growth, nodulation, nitrogen fixation, and nodular enzyme activities in response to salinity in some common bean-rhizobia symbiotic combinations. Seeds of Paulista and Efequince, two varieties of the common bean (Phaseolus vulgaris) were germinated and seedlings were transferred to pots containing vermiculite inoculated with the reference Rhizobium strain CIAT899 or with RhM11 or RhM14, two local strains. Plants were grown in a temperature-controlled glasshouse at 28°C and irrigated with a nutrient solution without NaCl (control) or supplemented with 25 mM NaCl (stressed). Plants were harvested at the flowering stage. The results showed that in controls, inoculation with RhM11 improved plant and nodule growth compared with those inoculated with RhM14 and CIAT 899. NaCl treatment generally had a negative affect on plant and nodule growth. Under the saline treatment, symbiotic nitrogen fixation was not significantly affected in the CIAT899-Paulista, CIAT899-Efequince and RhM11-Paulista combinations. Plant mineral nutrition was negatively affected under salt treatment for all of the tested symbiotic combinations. Inoculation with CIAT899 and RhM11 conferred more plant tolerance to salinity than inoculation with RhM14. The nodular phosphoenolpyruvate carboxylase (PEPC) and malate dehydrogenase (MDH) exhibited higher activities and were less affected by salinity in plants inoculated with the reference strain CIAT899 than those inoculated with local strains. We conclude that plants inoculated with CIAT899 and RhM11 showed more salinity stress tolerance than those inoculated with RhM14.

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