IDENTIFICATION AND CHARACTERIZATION OF SALT-TOLERANT AND THERMO-TOLERANT LEUCAENA-NODULATING RHIZOBIUM STRAINS

Rhizobium-legume symbioses are important for their nitrogen input, but salinity and elevated temperature in arid and semi-arid areas limit t heir effectiveness, and therefore plant growth and productivity. Sixte en Rhizobium strains isolated from root nodules of Leucaena trees grow n in different geographical areas of Egypt varied in their degree of t olerance to salinity and in their symbiotic effectiveness with Leucaen a leucocephala under saline conditions. Three strains were tolerant to >3% NaCl. L. leucocephala grown in the greenhouse at concentrations o f NaCl up to 1.0% and inoculated either with strain DS 78 or strain DS 158 displayed significantly better growth than those plants grown at the same levels of salinity and inoculated with reference strain TAL 5 83. Although nine of the Rhizobium strains grew at 42 degrees C, their mean generation times were lengthened two- to fourfold. When daylight growth temperatures were elevated from 30 degrees C to 42 degrees C, nodule number and mass, nitrogenase activities and shoot top dry weigh t of plants inoculated with strains DS 78, DS 157 and DS 158 significa ntly increased, whereas these parameters decreased in plants inoculate d with strain TAL 583. Rhizobium strains that effectively nodulate Leu caena under adverse saline conditions and at high temperatures were th us isolated, identified and characterized.