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 legumes inhabiting diverse ecological regimes, revealed a broad genetic base in their salt tolerance. Some strains tolerated extremely high, hitherto unreported, levels of salt (up to 1.88 M NaCl). Strains from very similar ecological conditions showed similarity in NaCl tolerance suggesting the ecological basis for salt tolerance. The tolerance was broadly strain-specific and may, therefore, be used as a taxonomic character for identifying rhizobial strains in association with other parameters. Four out of five strains of induced salt-tolerant rhizobia showed significantly decreased symbiotic efficiency, indicating that they were less efficient in symbiotic nitrogen fixation possibly due to depression in their nitrogenase activity during salt stress. Nodule growth was significantly reduced in treatments involving salt-acclimated rhizobia.