The effect of salts commonly found in irrigation water on survival and growth of Rhizobium meliloti were determined. Sodium chloride at concentrations up to 250 mM did not influence viability of the bacterium suspended in water or in soil. A completely defined growth medium of low osmolarity was developed and the effects of added Na⁺, K⁺, Ca⁺², Mg⁺², PO₄^-3, HCO₃^-1, SO₄^-2, Cl^–, and CH₃COO^– (acetate) on the growth rate of various strains of R. meliloti was determined. Of these ions, only Mg⁺², PO₄^-3, and CH₃COO^– inhibited growth of concentrations of 200 mM or less. Sensitivity to some of the salts was affected by molybdate ion and by the presence of proline or glutamate. Strains of R. meliloti isolated from alfalfa fields in various parts of New Mexico were found to be comparable to laboratory strains with respect to salt tolerance.

These experiments suggest that salinity in concentrations normally encountered in irrigation water in arid regions does not influence survival or growth of R. meliloti growing independent of the host plant alfalfa. This work has been expanded to determine the effects of salinity on establishment of the symbiotic relationship between R. meliloti and alfalfa that results in biological nitrogen fixation.

Project Numbers: A-062-NMEX, 1423622, 1423618