NODULATION AND NITROGEN-FIXATION IN FABA BEAN (VICIA-FABA L) PLANTS UNDER SALT STRESS

Faba bean cultivar Giza 3 inoculated with Rhizobium leguminosarum RCR 1001 was grown in a pot experiment and irrigated with saline water (mixture of NaCl and CaCl2 0.25 Ca:Na on molar basis). Salinity levels of 5.8, 8.8, 11.6 and 14.6 dSm-1 (equivalent to 50, 75, 100 and 125 mM NaCl) significantly decreased nodule number, nodule fresh weight and total nitrogenase activity. Salinity inhibited specific nitrogenase activity, protein, leghaemoglobin and carbohydrate content of the nodules at 11.6 and 14.6 dSm-1 (100 and 125 mM NaCl). Salinity levels of 8.8, 11.6 and 14.6 dSm-1 (75, 100 and 125 mM NaCl) caused a significant reduction in dry weights of roots, stems, leaves and total plant nitrogen. The results indicated that Rhizobium leguminosarum RCR 1001 formed an infective and effective symbiosis with faba bean under saline conditions. A noticeable decline in nitrogenase activity and total nitrogen concentration in the plant under saline conditions could be attributed to nodule senescence, as shown by the lowering trend of leghaemoglobin, soluble protein and carbohydrate contents of cytosol and bacteroids.