INDUCED SALT-TOLERANT RHIZOBIA, FROM EXTREMELY SALT-TOLERANT RHIZOBIUM GENE POOLS, FORM REDUCED BUT EFFECTIVE SYMBIOSIS UNDER NONSALINE GROWTH-CONDITIONS OF LEGUME HOSTS

Screening of 45 strains of Rhizobium, isolated from 32 species of legu mes inhabiting diverse ecological regimes, revealed a broad genetic ba se in their salt tolerance. Some strains tolerated extremely high, hit herto unreported, levels of salt (up to 1.88 M NaCl). Strains from ver y similar ecological conditions showed similarity in NaCl tolerance su ggesting the ecological basis for salt tolerance. The tolerance was br oadly strain-specific and may, therefore, be used as a taxonomic chara cter for identifying rhizobial strains in association with other param eters. Four out of five strains of induced salt-tolerant rhizobia show ed significantly decreased symbiotic efficiency, indicating that they were less efficient in symbiotic nitrogen fixation possibly due to dep ression in their nitrogenase activity during salt stress. Nodule growt h was significantly reduced in treatments involving salt-acclimated rh izobia.