الفهرس 
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Abstract
Soybean (Glycine max L.) is among the most important legume crops feeding a large number of people throughout the world. It is a suitable source of protein and oil, and develops a symbiotic association with the N-fixing bacterium Bradyrhizobium japonicum, so a significant amount of research work has been done to increase the growth and production of soybean, worldwide. Salinity is among the most important stresses adversely affecting plant growth and crop production. The unfavorable effects of salinity on the growth of plants occur by decreasing water potential and by the toxic effects of ions such as sodium (Na+) and chloride (Cl−). In this study, an interesting technique was used to counteract the stress of salinity on the growth and yield of soybean under greenhouse conditions by soaked soybean seeds in specific bacterium Bradyrhizobium japonicum with plant growth promoting bacteria (PGPB). This study has been design in order to alleviate effect of salt stress on growth and yield of soybean. In order to achieve this aim, it was very important to find promising bacterial strains that can tolerate salt stress and considered as (PGPB) that have plant growth promoting criteria as ammonia, siderophores, IAA and GA3. The first step was done by selecting eight bacterial strains (B. japonicum, MAP3, MAP4, MAP7, MAP8, ASA235, DeltaPSK and delta YSK) and tests the growth of them under different concentrations of NaCl ranged from 0 to 2000 mM NaCl, then test the ability of these bacterial strains to produce ammonia, siderophores, IAA and GA3 under normal and the selected stressed conditions (0 and 150mM NaCl). from these experiments four promising bacterial strains; B. japonicum, MAP3, MAP8 and DeltaPSK were selected. Then these bacteria were tested by made combinations between them as follow: control, B. japonicum, B. japonicum+ MAP3, B. japonicum+MAP8, B. japonicum +DeltaPSK. Soybean germination experiment was carried out under normal and salt conditions by soaking soybean seeds in the bacterial combinations and irrigated by NaCl solution (zero, 75 and 150mM) for ten days. In this experiment, growth and germination parameters, membrane features and antioxidant enzymes activity were determined. It can be concluded from this experiment that, the presoaking of soybean seeds in plant growth promoting bacteria enhance growth and germination of soybean seeds in absence and presence of salt. In addition, B. japonicum +DeltaPSK treatment show the best effeciency while B. japonicum+MAP8 treatment can’t enhance soybean growth significantly more than control especially in presence of salt. In addition 150 mM of NaCl had negative effect on growth and germination of soybean seeds either in absence or presence of plant growth promoting bacteria. from afro-mentioned results, the suitable bacterial strains (B. japonicum, B. japonicum + MAP3 and B. japonicum + DeltaPSK) and salt stress range (zero, 75 and 100 mM NaCl) according to the obtained data of the preliminary experiments were selected. Bacterial combinations were applied as follow: control, B. japonicum, B. japonicum+ MAP3 and B. japonicum +DeltaPSK moreover use Al-Aqdin compound (bacterial inoculum for legume crops from Agriculture Research Center that used as a biofertilizer) to compare its effect with the used bacteria combinations. A semifield experiment was carried out to alleviate the harmful effect of salinity on growth, metabolism and productivity of soybean plant by PGPB application. In this experiment the most effective bacterial combination during four stages; seedling, vegetative, flowering and yield could recommended. At seedling stage (21-days old), soybean plant was treated with bacterial combination without salinity application. B. japonicum + DeltaPSK and Al-Aqdin compound treatments were the most effective on growth parameters, photosynthetic pigment, carbohydrates content and other determined parameters. While at vegetative stage (40-days old), soybean plants were exposed to salt stress (0, 75 and 100 mM NaCl) and the following parameters; growth parameters, membrane features, carbohydrates contents, antioxidant activity compounds and antioxidant activity enzymes were determined. It was found from the results that treatments with B. japonicum + DeltaPSK, B. japonicum + MAP3 and Al-Aqdin compound were the most effective without salt stress, but in case of salt application; either 75 or 100 mM NaCl, the B. japonicum + DeltaPSK treatment was the most hopeful treatment not only in alleviating the harmful salt effect on soybean growth but also in recording the highest amount in the determined parameters followed by B. japonicum + MAP3 treatment. At flowering stage (60-days old), the samples of soybean plant were used to determine legheamglobin, Glycine betain, IAA, GA3, ABA), percentage of some elements (N, P, K, Na & Cl) in shoot and root and rhizospheric soil mineral contents (N, P, K, Na & Cl), EC and pH value of the soil were also determined in addition to that determined in vegetative stage. The results at this stage were more or less comparable to that of vegetative stage, i.e without effect of salt stress B. japonicum + DeltaPSK, B. japonicum + MAP3 and Al-Aqdin compound treatments were the most effective treatments while at salinity stress 75 and 100 mM NaCl, the most promising treatments was B. japonicum + DeltaPSK that can keep soybean healthy by increasing antioxidant activity either compounds or enzymes, phytohormones and beneficial elements N, P, K and retard the harmful elements as Na, Cl. At yield stage (95- days old), the yield attributes were determined; shoot length, shoot fresh wt., shoot dry wt., relative grain yield, harvest index and pods characteristics; length of pods, number of pods/ plants, pods fresh wt., pods dry wt., wt. of 100 grains, furthermore two biochemical aspects of the yielded seeds; protein, total soluble sugar were also determined. But ethically, the soybean plants that exposed to 100 mM NaCl cannot reach to this stage, so the yield attributes and biochemical aspects were only determined in case of 0 and 75 mM NaCl treatments. The results in this stage show that, B. japonicum + DeltaPSK treatment record the highest yield quality and quantity of soybean plant, in absence or presence of salt. In conclusion: The present work demonstrates that, the presoaking treatment of Glycine max L. seeds in PGPB before sowing, more or less alleviated the harmful effect of salt stress on growth criteria, some metabolites, certain enzymes and mineral contents. The obtained results also declared that, B. japonicum + DeltaPSK has more stimulatory influence on the growth and metabolic activities than other treatments.