EFFECT OF SALINITY ON SURVIVAL AND SYMBIOTIC PERFORMANCE BETWEEN RHIZOBIUM-MELILOTI AND MEDICAGO-SALIVA L. IN SAUDI-ARABIAN SOILS

The effect of salinity an the growth and survival of different local a nd imported strains of Rhizobium meliloti in liquid media for 72 h was studied in the laboratory. The rhizobial strains were tested for thei r symbiotic efficiencies with lucerne grown in salinized sand culture and in natural Saudi Arabian soils of different salinities in the gree nhouse. Results have shown that growth of all rhizobial strains invest igated in liquid media was adversely affected by high salinity with re latively slight salt tolerance in the local rhizobial strains. Saliniz ation of sand culture to high concentration (100-250 mM NaCl) greatly affected nodulation and symbiotic N-2-fixation of lucerne plants grown in it. Growing lucerne in sand of high salt concentration (250 mM NaC l) completely prevented the formation of nodules. Inoculation of lucer ne plants grown in sand culture with local isolates of R. meliloti has shown slight salt tolerance up to 100 mM NaCl. These local isolates g ave relatively higher symbiotic N-2-fixation than the rest of the inoc ulated rhizobial strains. High salinity of natural sells (9.1 and 14.1 dS m(-1)) deleteriously affected the nodule formation and the symbiot ic N-2 fixation ill lucerne plants inoculated with all rhizobial strai ns. Inoculation of lucerne plants with rhizobial strains showing toler ance to salinity in sand culture did not show the same tolerance in na tural saline soils, and this could be attributed to the competitive po tentiality of the strain used in the soil.