Salinity tolerance of Rhizobium mutants: Growth and relative efficiency of symbiotic nitrogen fixation

A salinity-tolerant strains of Rhizohium able to grow and fix nitrogen in symbiosis with lentil (Lens esculenta) in saline soil was derived frorn effective Rhizobium strain RL 5. A forced mutation with the mutagen nitrosoguanidine resulted in the isolation of five different mutant strains. The salinity tolerance, streptomycin resistance, growth, nodulation behaviour and relative efficiency of symbiotic N₂-fixation of these strains were studied. Among the five mutants and parent, LM 4 and LM 1 successfully tolerated 200 μ g ml^-1 streptomycin and 1.5%NaCl. These two mutants also significantly increased number and dry weight of nodules per plant, dry matter yield of the crop and N₂-fixation. Between the two, LM 4 seemed generally the better.