IMPACT OF SALINITY STRESS ON RHIZOBIUM SURVIVAL, FABA BEAN YIELD AND THEIR SYMBIOTIC PERFORMANCE

Experiments were executed to investigate the survival of Rhizobium leguminosarum under salinity stress and their symbiotic performance with faba bean plants as well as its nodulation capacity and plant growth and productivity as affected by varying salinity conditions. Preliminary trial was conducted to examine the symbiotic effectiveness of Rhizobium leguminosarum as affected by different antibiotics. Results exhibited that streptomycin resistant strains were superior in increasing root nodulation and plant growth and shoot-N content of faba bean plants as compared with other tested antibiotics. Survival of the different strains of rhizobia cultured onto two different media supplemented with various extracts of saline soils, having EC ranging from 1.80 to 12.10 dS/m was investigated. Obtained data revealed that increasing the salinity level resulted in a gradual depression of the log numbers of viable colonies of all tested strains, particularly those cultured on BAM media after 72 hr. of their age. Also, streptomycin resistant strains were more withstanding against the graded salinity levels rather than their parent ones. Results of greenhouse experiment exerted that increasing of salinity stress in soil resulted in severe a depression in nodulation status, overall plant growth, nutrient uptake and productivity of faba beans. Additionally, inoculation of faba bean seeds with different rhizobial strains had led to improve root nodulation, plant dry mass, nutrients uptake and protein content, whereas, it showed no effect on ion concentrations of the plant tissues. Results of field experiment conducted on moderate saline soil (EC= 6.64 dS/m) showed that inoculation of faba bean seeds with the different strains of Rhizobium leguminosarum resulted in a significantly enhanced nodulation status, plant dry matter and its contents of N and P, as compared with absolute control. Moreover, the inoculated plants with such strains attained higher values of faba bean yield and its attributes than the absolute control (uninoculated plants), and they achieved almost the same yield resulted from N-fertilized plants.