الفهرس 
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Abstract
The present work was carried out for isolation, purification and selection of efficient bacterial isolates due to their PGP activities to verify their effects, as a biofertilizers on growth of Moringa oleifera Lam and a biocontrol agent against Rhizoctonia solani on Mentha spicata plant. The results could be summarized as follows:
1. Rhizospheric colonization
The rhizospheric samples of eleven medicinal plants (viz., Ocimum basilicum, Marrubium vulgare, Melissa officinals, Origanum syriacum, Quisqualis indica, Solidago virgaurea, Melilotus officinalis, Cymbopogon citratus, Matricaria chamomilla, Thymus vulgaris and Majorana hortensis), were collected to evaluate the counts of total microbial flora, actinomycetes, spore-forming bacteria, fungi, fluorescent pseudomonads and azotobacters.
The total microbial flora, spore- forming bacteria and fungi were found to be maximum (230×1010, 332×107 and 200×106 cfu/g) in rhizosphere of Ocimum basilicum and the minimum count of these microbial groups being 0.003×1010, 0.1×107 and 0.1×106 cfu/g was recorded in Matricaria chamomilla, respectively. The fluorescent pseudomonads were completely absent in the root samples of Majorana hortensis and Cymbopogon citratus. Higher load of actinomycetes and azotobacters were reported for Melilotus officinalis and Thymus vulgaris respectively, than other medicinal plants.
2. Isolation of root associated microorganisms
The rhizosphere samples supported a total of 112 bacterial isolates, with diversified characteristics. Isolation of different bacterial groups from the rhizosphere soil samples of eleven medicinal plants were made on specific media. The highest percentage of collected bacterial isolates being 34.82% followed by 18.8% and 10.71% were detected from Thymus vulgaris, Matricaria chamomilla and Melissa officinals rhizosphere samples, respectively. While the lowest percentage of collected isolates was 2.67% for Melilotus officinalis and origanum syriacum.
3. Evaluation of biological activities of collected isolates from medicinal plants
a. All 112 isolates were initially screened for their growth promoting activities (PGP) viz., indole acetic acid, and hydrogen cyanide production, and phosphate, potassium and chitin solubilization. The results indicated to :
Among the 112 bacterial isolates, 36 bacterial isolates (32.14%) showed indole acetic acid production, 39 (34.82%) phosphate solubilizing activity, 25 (22.32%) HCN production, 105 (93.75%) potassium solubilization and 57 (50.82%) chitin solubilization. None of the azotobacters and actinomycetes exhibited chitin solublization and hydrogen cyanide production, respectively.
b. Only eleven isolates were selected according to their metabolic activities namely, C110, Th99, Th92, Th71, Th100, C82, Th79, Th74, Th75, Th98 and Me11. These isolates were subjected to secondary screening by determine total phenols, IAA and siderophore production in liquid culture as well as assaying of antagonistic activity, all the selected isolates were positive for IAA production ranging from 0.1 to 17 μg/100 ml. Th75 isolate recorded the highest values of phenols (16.73 ppm) and siderophores (84 mMDFOM), followed by Th98 isolate being 12.97 ppm and 54.31 mMDFOM, in respective order. Antagonistic activity of the bacterial isolates was assessed in terms of inhibition zone diameter against the tested pathogenic fungi (Fusarium oxysporum 15E and Rhizoctonia solani 21E). The highest zone of inhibition (10 mm) was observed by isolate Th74 against F. oxysporum and isolate Th 98 against R. solani.