الفهرس 
Plant growth promoting rhizobacteriaOnly 14 pages are availabe for public view
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Abstract
5. In Egypt, increasing the demands of food due to increasing population, made the agricultural researchers pay much attention to increase the crop production and reduce the dependence of the plants on mineral fertilizers application using plant growth promoting rhizobacteria (PGPR). This objective could have both economic and environmental significance. Intensive application of chemical fertilizers imposes undesirable consequences of pollution besides to the increasing costs of such chemicals.
This study included isolation of endophytic bacteria from healthy roots of wheat and potato plants. These isolates were characterized and screened in vitro for their plant growth promoting traits like solubilization of inorganic phosphates, production of indole acetic acid (IAA), nitrogen fixation and siderophores production. Further studies were done in pot experiments to evaluate the effect of inoculation with most effective isolates on different growth parameters of wheat and potato plants.
Isolation and characterization of endophytic bacteria:
A number of 45 isolates were obtained from root of wheat and potato, 17 from wheat and 28 from potato plants. 20 were Gram positive and 25 were Gram negative bacteria. 40 isolates exhibited a positive reaction for Catalase test and 9 isolates were spore forming bacteria.
The results of screening the bacterial isolates in vitro for different functional properties could be summarized as follow:
1- Twenty six of tested bacteria exhibited a positive reaction for phosphate solubilization.
2 – Twenty eight of tested bacteria exhibited a positive reaction for IAA.
3- Eighteen of tested bacteria exhibited a positive reaction for siderophoes production.
Quantitative assessment of different beneficial activities by the most efficient eighteen bacterial isolates:
1- Fifteen bacterial isolates solubilized rock phosphate and seventeen isolate solubilized tri calcium phosphate using PVK agar medium, while all the isolates showed positive result by NBRIP broth medium.
2- Sixteen isolate produced IAA.
3-For nitrogen fixation only six isolates exhibited a positive reaction for acetylene reduction assay (ARA).
Factors affecting phosphate solubilization and IAA production:
1- Optimum pH and temperature for IAA production and phosphate solubilization by the tested bacterial isolates were 7 and 30ºC respectively.
2- The concentration of 0.1 mg/ml of L- tryptophan was the best for IAA production.
Putative endophytic features:
1-Root colonization assay was performed for the putative endophytic characteristics.
2- Fourteen and eleven isolates exhibited a positive reaction for cellulase and pectinase tests, respectively.
3- Twelve bacterial isolate were motile.
Pot experiment was conducted to evaluate the response of wheat and potato plants to inoculation with PGPR isolates
Table18 . Response of wheat plant to inoculation by the most efficient tested isolates.
Bacterial isolates Vegetative growth parameters Photosynthetic pigment production Nutrient uptake in shoots(%)
Root length Root dry weight Shoot length Shoot dry weight Chlorophyll a Chlorophyll b Carotenoids N P K
control 7.4i 0.0107k 31.6p 0.031n 0.87p 0.04o 0.47o 1.54k 0.16m 4.26n
W11 8.1bcd 0.033e 33.3g 0.087d 1.98g 0.28n 0.69l 2.81a o.22k 6.78e
W13 8.7a 0.041b 34.7c 0.088cd 2.96c 1.08h 1.36a 2.77a 0.43a 7.96b
P31 8.5a 0.039c 34.9b 0.09b 3.12b 1.2g 1.25c 2.24g 0.41b 4.58k
P35 8.6a 0.044a 35.1a 0.098a 3.16a 1.98b 0.88h 2.7b 0.39c 8.91a
Table 19. Response of potato plant to inoculation by the most efficient tested isolates.
Bacterial isolates Vegetative growth parameters Photosynthetic pigment production Nutrient uptake in shoots(%)
Root length Root dry weight Shoot length Shoot dry weight Chlorophyll a Chlorophyll b Carotenoids N P K
control 10.167m 0.019i 8.2n 0.041k 8.21n 5.35o 0.044p 2.22l 0.4h 6.82o
W11 13.7l 0.021i 14.6c 0.062c 10.19i 8.7e 0.21l 3.22d 0.55d 9.39e
W13 18.8a 0.033d 15.5ab 0.071b 11.56d 5.49n 0.09o 3.33c 0.756a 14.37a
P31 16.3f 0.041b 15.4b 0.057e 11.57d 5.59m 0.12n 3.51b 0.703b 8.51h
P35 18.3c 0.044a 15.6a 0.083a 12.23a 8.78d 2.22d 4.48a 0.58c 13.19b
The obtained results of wheat characteristics upon inoculation could be concluded as follow:
1- The isolates W13 and P35 showed the highest increase in root length and root dry weight respectively while, the isolate P35 had the highest shoot length and shoot dry weight.
2- The isolates P35 and W17 recorded the highest increase in chlorophyll a and chlorophyll b respectively whereas, the isolate W13 showed the maximum significant carotenoids content.
3- The isolate W11 showed the highest nitrogen uptake on the other hand, the maximum phosphorus and potassium uptake were recorded by the isolates W13 and P35.
The obtained results of potato characteristics upon inoculation could be concluded as follow:
1- The isolates W13 and P35 showed the highest increase in root length and root dry weight while, the isolates W13 and P35 showed the highest increasing in root length and root dry weight.
2- The isolates P35 and W2 recorded a significant increase in chlorophyll a and chlorophyll b on the other hand, the highest carotenoids content was recorded for the isolate W16.
3- The maximum nitrogen uptake was recorded for P35 isolate whereas, the isolate W13 showed the highest significant phosphorus and potassium content.
Identification of the most effective isolates:
Molecular analysis based on 16S rDNA sequencing identified the isolates W11, W13, P31 and P35 as Arthrobacter nicotianae FS1, Brevibacillus agri strain 2112, Bacillus cereus VCRCB 540 and Achromobacter xylosoxidans MN2 respec