الفهرس 
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Abstract
The present study aimed to isolate, screen and identify plant growth promoting rhizobacteria (PGPR) obtained from the rhizosphere soil of three field crops cultivated at different sites in Ismailia. Of 15 bacterial cultures, 4 isolates were selected and identified by phenotypic properties and genotypic characterization (16S rRNA gene sequencing). The ability of the selected PGPR for solubilization of inorganic phosphates and production of indole acetic acid (IAA) and siderophores was studied. Arbuscular mycorrhizal (AM) fungal inoculums ( a mixture of G.intraradices ,G.monosporum and G.eutnicatum ) was obtained from the Microbiological Resource Center (MIRCN), Cairo. Pot and field trials were carried out to evaluate AM fungi, PGPR and their interactions as biofertilizers for wheat and corn at different levels (50, 75, 100%) of the recommended levels of mineral N and P fertilizers.
The obtained results can be summarized as follows:
The 4 isolates were identified as Pseudomonas fluorescns KW1 , Serratia liquefaciens EW1 , Bacillus subtilis EF1 and B. megaterium TF2. All identified isolates solubilized insoluble inorganic phosphate and produced IAA and siderophores. All the tested microbial inoculants significantly increased shoot dry weight of wheat as compared to the uninoculated control. Yield components of wheat and corn plants were significantly improved by microbial inoculants compared to the uninoculated control. S. liquefaciens EW1 and B. megaterium TF2 proved to be the most efficient strains on wheat and corn yields. Seed inoculation with all microbial inoculants increased the uptake of N, P and K by plants. The soil pH values were not significantly affected by AM fungi or NP levels while all PGPR strains significantly reduced them compared to the uninoculated control. Levels of available P were significantly increased by inoculation with AM fungi relative to the control. PGPR strains significantly increased levels of available N and P in the soil as compared to the uninoculated control. A highly significant negative correlation was observed between soil pH values and levels of soil available P. The activity of urease was not significantly affected by inoculation with AM fungi as compared to the uninoculated control. However, the activities of both acid and alkaline phosphatases were significantly enhanced due to inoculation with AM fungi relative to the uninoculated control. Furthermore, PGPR strains significantly improved the activities of the three enzymes in all soil samples as compared to the uninoculated control.
Based on the foregoing results, the Egyptian farmers could be recommended to use one of these promising inoculants as a suitable biofertilizer for corn grown in sandy soil to reduce the current application rate of NP fertilizers by ca 25% without any reduction in crop production. The usefulness of inoculants is not only in saving agricultural costs, but also to rescue the environment. However, this study needs to be evaluated in the field under different soils and environmental conditions before using these microbes as biofertilizers.
Keywords: AM fungi, rhizobacteria, 16S rRNA, IAA, siderophores, P solubilization, Soil enzymes, wheat, corn, nutrient uptake