الفهرس 
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Abstract
This study was conducted on maize and onion plant to investigate the effect of some phosphate fertilizer source. (rock phosphate and super phosphate phosphate- solubilizing microorganisms (Vesicular- arabuscular mycorrhiza VAM and PDB) either single and /or in combination growth of maize and onion plants.
Forty colonies which showed positive reaction on the plates prepared for PDB which had a well-defined clear zone were isolated at random to study their efficiency.
All isolates had an ability to solubilize inorganic phosphate .During the incubation period of the selected isolates. The pH values showed an inverse correlation with the quantity of soluble phosphorus .As the pH of the medium decrease the quantity of soluble phosphorus increase, that amounts of phosphorus solubilized ranged from 143.22 to 552 ppm. On the other hand ,pH value in medium of isolates ranged from 3.90 to 7.20.
Solubilization index for the tested isolated are compatible with the acidity (pH values) produced in their cultures, The highest phosphate solubilizing index was recorded by the isolates No 35 and the lowest by isolates No 13.
Morphological of most efficient PDB isolates showed that aerobic spore-formers exceeds other groups out of the 10 isolates 6 were aerobic sporoforming ( 60%). All isolates showed positive reaction with Gram staining .
Greenhouse experiments were carried out pot during 2018/2019and 2019/2020 growing seasons at the Microbiological Dept. Fac of Agric Minia Univ.Egypt to study the effect of maize and onion inoculation with phosphate solubilizing microorganisms using different sources of phosphate fertilizer on growth of maize and onion, as well as counts of some microorganisms in rhizosphere of maize and onion plants.
Inoculation of maize plants with mixture of PDB and VAM gave higher counts of total bacteria as compared with other treatments Highest counts were recorded at 60 days, the obtained figure with treatments amended with rock phosphate. The combined treatments inoculation of PDB and VAM seemed to more effective than the single ones. The best results were obtained by using rock phosphate and inoculum mixture of PDB and VAM. In both soil amended with rock phosphate or superphosphate in treatments inoculated with mixture of VAM and PDB gave higher counts of total bacteria followed by treatments inoculated with VAM only then treatment inoculated with PDB.
The combined treatments are much superior effect compared to single ones .The highest counts of PDB were observed in case of treatment of rock phosphate with inoculum mixture of both VAM and PDB ,followed by inoculated with PDB then treatments inoculated with VAM. The obtained results clearly showed that in treatment inoculated with either VAM or Mixture and amended with superphosphate in general gave higher counts of spore formers than treatment amended with rock phosphate .
High counts of actinomycetes were recorded in treatments amended with rock phosphate and inoculated with mixture of PDB and VAM , higher counts were recorded in treatments inoculated with inoculum mixture followed by PDB then VAM.
In onion plant total counts of bacteria, sporeformers , actinomysetes and PDB were affected with either inoculation with PDB bacteria and \or vesicular arabuscular mycorrhiza either inoculation with single and or in combination, as well as phosphate fertilizer source.
Counts of phosphate dissolving bacteria higher counts were recorded in treatment amended with super phosphate as compared to amended with rock phosphate. Generally, in treatments inoculated with the tested microorganisms (VAM and or PDB single or incombiened) higher counts were observed in treatments inoculated with mixed inoculates followed by PDB treatments then VAM treatments.
Inoculated of onion plant with inoculum mixture (VAM+PDB) gave higher counts of spore formers followed by treatments inoculated with VAM then inoculated with PDB. Higher counts were recorded in treatments amended with super phosphate. Higher counts of actinomycetes were recorded in treatments amended with super phosphate compared to amended with rock phosphate on the other hand , higher counts were found in treatments inoculated with mixture followed by PDB then VAM .
Vegetative growth of maize received chemical P-fertilizer sources were generaly better than plants of the control treatments. The highest values of vegetative growth parameters were obtained in plants fertilized with rock phosphate compared with those fertilized with super phosphate. Inoculation with inoculum mixture ( BDP + VAM ) and amended with rock phosphate was more effective on plant height.
The highest values of growth parameters recorded in soil amended with rock phosphate and inoculated with inoculum mixture followed by VAM treatment then PDB ,
The vegetative growth of maize and onion plants received chemical P-fertilizer sources were generally better than plants of the control treatments. The highest values of vegetative growth parameters were obtained in plants fertilized with rock phosphate compared with those fertilized with super phosphate. Increases in plant height, number of leaf, as well as fresh and dry weight/plant were observed. It is notable, that there were no significant effects between super phosphate or rock phosphate fertilizer. Inoculation with inoculum mixture ( BDP + VAM ) and amended with rock phosphate was more effective on plant height.
The highest values of fresh and dry weight of maize plants recorded in soil amended with rock phosphate and inoculated with inoculum mixture followed by VAM treatment then PDB. But in onion plants the highest values were observed when plants inoculated with inoculum mixture followed by BDP then VAM.
Nitrogen and phosphorus percentages in maize and onion plants were affected by inoculation with VAM and phosphate dissolving bacteria single or/ and mixture .However, the higher presents of nitrogen in onion plants were recorded in treatments amended with rock phosphate. On the other hand, higher percentage were recorded in treatments inoculated with inoculum mixture followed by VAM then PDB.
The obtained results indicated that mycorrhizal root infection percentage in maize plants was significantly affected by inoculation with endomycorrhizal fungi.
The best results were obtained when application mixture of bioagents: (phosphate dissolving bacteria PDB – and vesicular arbuscular mycorrhiza VAM) in combination with rock phosphate fertilizer as it showed an increasing vegetative growth characteristics of maize and onion (plant height, fresh weight, dry weight, number of laves, nitrogen % and phosphorus % ).