الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Plant growth promoting rhizobacteria (PGPR) are the rhizosphere bacteria that
can be used to perform important functions such as increase plant growth and protection
from several diseases caused by different plant pathogens. The objectives of this study
were to identify and characterize the native PGPR bacteria strains isolated from sugar
beet (Beta vulgaris L. ssp. vulgaris) rhizosphere and to evaluate their in vitro antagonistic
activity against three of the most common phytopathogen. Therefore, thirty bacterial
strains, differentiating in color, texture, morphology, were successfully isolated from
sugar beet rhizosphere and characterized at different levels. The data of the conducted
experiments could be summarized as follow:
1- Most of the isolates produced fast-growing colonies with smooth surfaces and
were aerobic, rod shaped, Gram positive.
2- About 50% of the isolates were motile conferring their ability to move and
colonize roots.
3- Only five isolates shown clear phosphate solubility by formation sharp halo
zones of P solubilization on solid Pikovskaya medium.
4- About two-third of the tested isolates showed positive results for catalase
production suggesting their ability to neutralize the toxic effects of H2O2.
5- Twenty-three isolates were able to produce gelatinase into nutrient gelatin deep
tubes while, 17 isolates have the ability to produce amylase enzyme into starch
agar medium.
6- The antibiotic sensitivity/resistance assay of the thirty isolates to seven different
antibiotics (Nitrofurantion, Tetracycline, Amoxycillin, Streptomycin, Fusidin
acid, Ceftriaxone, Chloramphenicol) revealed a greater diversity to antibiotics
resistance amongst rhizobacterial isolates.
7- In vitro antagonistic activity of rhizobacterial isolates against three of the major
phytopathogenic fungi (Fusarium solani, Fusarium oxysporium and Rhizoctonia
solani), examined by dual culture test, revealed a considerable diversity ofantagonism. Many isolates were significantly reduced mycelial growth of F.
solani which reached 57% for some isolates (AM-3). Some isolates showed a
good degree of antagonistic activity against F. oxysporium (60%) while the
antagonistic activity against R. solani was varied from 0.0 to 56.5%. Out of the 30
isolates, four isolates (AM-7, AM-12, AM-26, and AM-27) showed high
antagonistic activity against mycelium growth of all phytopathogens without
exception.
8- Concerning to the potential role of eight selected rhizobacterial isolates in growth
promotion of sugar beet plants, in the presence or absence of the studied
phytopathogenic fungi, different growth parameters (i.e., shoot and root length;
fresh and dry weight for shoot and root) were measured after 30 days of sowing.
The results revealed the positive effect of inoculation with most of the
rhizospheric bacterial isolates in addition to their in vivo anti-phytopathogenic
effectiveness against phytopathogenic fungi (F. solani, F. oxysporium and R.
solani).
9- With respect to seedling’s growth factors, such as germination percentage,
seedling length and vigor index, most of the treatments with bacterial showed a
significant increase of seed germination, seedling length as well as vigor index of
sugar beet compared to control treatment as well as fungal treatments in the
absence of bacterial islets.
10- Effect of PGPR on sugar beet growth in field trials were recorded, as measured by
the fresh and dry weight of seedling shoots and roots after being treated with
bacterial isolates in the presence or absence of the studied phytopathogenic fungi.
Many treatments exhibited a significant promotion in root fresh weight (125 g
compared to 36.67g of the control) while almost all treatments showed a slight
increase at shoot fresh weight specially those treated with fungi only. Regarding
to root dry weight, many treatments showed a significant increase at root dry
weight as compared to the control and fungal treatments in the absence of
bacterial islets as well.