الفهرس 
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Abstract
The aim of this work was to isolate nitrogen-fixing bacteria (Symbiotic and non-symbiotic), from different economic plants at Beni-Suef Governorate, and to determine some phenotypic characters (e.g., tolerance to salt, heat, pH, heavy metals, utilization of carbon and nitrogen sources, and antibiotic resistant). Effect of salinity on growth and nitrogen fixation of Vicia faba plants was investigated. Effects of PGPR and nitrogen fertilizer on growth of V. faba and Triticum vulgare were determined under greenhouse conditions.
The results obtained in this study are summarized as the following:
A. Symbiotic nitrogen-fixing bacteria
* Rhizobia (50 isolates, 32 from V. faba and 18 from G. max) were isolated from different areas (Alalma, Beni-Suef, Fashin, Beba and Somosta) at Beni-Suef Governorate.
* The bacterial isolates were confirmed as rhizobia by re-inoculating each respective legume. About 13 isolates from V. faba succeeded to renodulate V. faba and only 3 isolates succeeded to renodulate G. max.
*Rhizobial isolates displayed various colony characteristics, some colonies were circular and milky or opaque when grown on YMA medium.
* Most of isolates from various areas showed growth at high concentration of NaCl up to 8 % , 2 isolates of V. faba from Alalma grew at 9 % NaCl, and also 2 isolates of G. max from Fashin area grew at 10 % NaCl concentration
* All isolates from V. faba and G. max were able to utilize glucose and mannitol as carbon source. .
* The majority of isolates utilize B-alanine and D-tyrosine as nitrogen source, while vanilline was the lowest nitrogen source to be utilized by V. faba and G. max isolates.
* The optimum temperature for growth of all isolates was in the range 20-40 °C, most of the isolates survived at 50 °C
* All isolates succeeded to grow at 6-9 pH values, but the majority of isolates grew at pH 11.
* Isolates of V. faba and G. max were resistant to cefotaxim (30 µg) and cephradine (30 µg), while most of isolates showed sensitivity to genatamicine (10 µg).
* The majority of isolates resisted at different concentration (0.01%, 0.1%) of Zn, Pb, Cu and Fe.
* All isolates showed positive catalase enzyme test, the majority of isolates showed positive amylase test.
* Numerical analysis showed that isolates of V. faba and G. max were not diverse as they were each divided into 2 clusters and some isolates were not included at any of the two clusters.
* Effects of salinity on the growth, nodulation and nitrogen fixation of V. faba plants were determined. .
* Salinity reduced the dry weight of both shoots and roots, shoots were more sensitive to salinity than roots. Dry matter yield of both shoots and roots were decreased when salt added after nodules had formed, nitrogenase activity was reduced at both levels of NaCl (50 and 100 mM).
* Effects of PGPR and nitrogen fertilizer on growth and nitrogen fixation of V. Faba plants were determined.
* In case of (R. leguminosarum RVA1) addition of nitrogen fertilizer inhibited nodule formation and reduced of dry weight of shoots and roots. Inoculation of V. faba by (RVA1) isolate, together with the non-symbiotic bacterial strains, did not improve growth and nitrogenase activity.
* In case of (RVB2), addition of nitrogen fertilizer increased dry weight of shoots and roots, and did not inhibit nitrogenase activity or nodule formation.
* Inoculation of V. faba by rhizobium strains (RVB2) and non-symbiotic bacterial strain led to an increase in dry weight of roots and shoots and stimulation of nitrogenase activity.
B. Non-symbiotic nitrogen-fixing bacteria.
* In the present investigation, 100 bacterial isolates were obtained from the rhizosphere of Triticum vulagre and Zea mays from different sites of Beni-Suef Governorate.
* 19 isolates were found to fix nitrogen. Identification of the isolates were carried out according to Bergy’s Manual.
* Effects of PGPR and nitrogen fertilizer on yield and dehydrogenase enzyme of Triticum vulgare plants were determined. * from 100, 19 isolates (12 isolates from T. vulgare and 7 isolates from Z. mays) selected to complete this study.
* The isolates were classified into three groups according to some phenotypic characters, cell shape and Gram stain.
* The first group includes 5 isolates, related to Bacillus species, the bacterial isolates are Gram positive, rod-shaped, spore-forming, motile, have nitrogenase enzyme, catalase and amylase activity positive, utilized mannitol, glucose, fructose as a carbon sources, and grow at high pH (10).
* The second group includes 6 isolates related to Azospirillum species, these isolates are Gram negative, rod shaped, motile, have nitrogenase, catalase and amylase activity, positive nitrate reduction test, utilized mannitol, glucose and fructose as a carbon sources, grew at pH (10), most of the isolates grew at 50 °C and have ability to grow at 5 % NaCl.
* The third group includes 8 isolates related to Azotobacter species, the isolates are Gram negative, coccoids or oval shaped, motile, have nitrogenase enzyme, grew at 5 % NaCl, and 50 °C, all isolates have catalase enzyme, nitrate reduction positive, utilized mannitol, glucose and sucrose as a carbon sources and grew at high pH value.
* Inoculation of wheat with nitrogen-fixing bacteria increased yield of wheat and increased dehydrogenase enzyme activity, also addition of nitrogen fertilizer together with bacteria increased yield and activity of dehydrogenase enzyme.