الفهرس 
AcknowledgmentOnly 14 pages are availabe for public view
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Abstract
The present investigation was undertaken during the period from 2009-12 at the Department of Plant Pathology, Faculty of Agriculture Farm, greenhouse and laboratories, University of Assiut, Assiut, Egypt. The specific objectives were to isolate and identify of native plant growth promoting rhizobacteria (PGPR) isolates from tomato and potato rhizosphere, screen them against Ralstonia solanacearum causing bacterial wilt of tomato and to elucidate their mechanisms of biocontrol. The ability of the isolates to promote plant growth and to reduce disease incidence has also assessed in greenhouse and field conditions. In vitro screening of certain plant essential oils against R. solanacearum and selected PGPR isolates. Evaluation the effect of PGPR isolates, plant essential oils, and the Arbuscular Mycorrhiza (AM) individually or in combinations against the pathogen under greenhouse and field conditions. The salient features of the findings have summarized below.
1. Out thirty-three of tomato tissue, water and soil samples collected from different location, shown tomato bacterial wilt symptoms or taken from location hit by the disease, only fifteen isolates have typical morphological and cultural characteristics resembling to R. solanacearum . The highly number of isolates was obtained from Minia governorate (7 isolates) followed by Assiut governorate (6 isolates) while the lowest number was obtained from Sohag governorate (2 isolates).
2. Fifteen isolates of pathogen have tested for their pathogenicity under greenhouse conditions. All isolates of pathogen were pathogenic on tomato plants and produced typical symptoms of wilt. Isolates No. 2 and No. 1 exhibited the highest disease index percentage with 97 and 81% wilting, followed by isolates No. (3, 7, 8 and 12) which caused 74-70% wilting, while the rest isolates caused the moderate percentage (less than 60% wilting) after four weeks from inoculation .
3. Fifteen pure cultures of pathogen isolates have typical cultural characteristics and have proving to be pathogenic to tomato plants have identified, and all isolates identified as Ralstonia solanacearum.
4. Twelve isolates of non-pathogenic bacteria isolated from tomato and potato rhizosphere samples. Five isolates were identified as Pseudomonas fluorescens. Two isolates were identified as Pseudomonas putida and three isolates were identified as Bacillus subtilis, while the rest of isolates were identified as Enterobacter aerogenes.
5. In vitro, among twelve isolates evaluated against R. solanacearum. Pseudomonas fluorescens (RB1), P. putida (RB7), Bacillus subtilis and Enterobacter aerogenes (RB10) showed inhibitory activity against R. solanacearum.
6. In vitro, the seed inoculation with four rhizobacteria significantly enhanced seed germination. However, the highly rate of germination noted by Pseudomonas fluorescens (84.38%), Pseudomonas putida and Bacillus subtilis (80%), while Enterobacter aerogenes record the least rate of germination (71.88%). All PGPR isolates except Enterobacter aerogenes, increased seed germination up to 14.29% over nontreated control.
7. Under greenhouse conditions, the PGPR isolates populations has evaluated on roots of tomato plants grown. Populations observed for the four PGPR isolates have found to progressively converge and decrease, stabilizing around 1.37 x 107 cfu/g. Pseudomonas fluorescens show the highest root-colonization ability of tomato plants (2.32 × 107 cfu/g) followed by P. putida (2 × 107 cfu/g), while E. aerogenes gave the lowest ability of root-colonization (1.09 × 105 cfu/g).
8. Under greenhouse conditions, results of PGPR isolates evaluation experiment revealed that P. fluorescens exhibited the highest disease reduction percentage of disease (55.27%) followed by P. putida (46.05%) and then B. subtilis (38.16%), E. aerogenes showed lowest percentage (25.01%). In addition, all PGPR isolates caused significantly increasing in the growth of treated plants compared to infected control.
9. Under field conditions, results illustrated that P. fluorescens exhibited the highest disease reduction percentage of tomato bacterial wilt disease (57.9%) followed by P. putida and B. subtilis (43.3 and 36%, respectively). PGPR isolates have found to be effective in increasing yield per plant. P. fluorescens recorded the highest increase percentage (348%) while B. subtilis achieved the lowest increase percentage (90.76%).
10. All isolates of PGPR produced siderphore and HCN except Bacillus subtilis.
11. In vitro, nine plant essential oils (Caraway, Thyme, Peppermint, Marjoram, Sage, Jojopa, Camomile, Basil and Black cumin) were tested against Rolstonia solanacearum and selected PGPR strains (Pseudomonas fluorescens and P. putida). Thyme and peppermint oils exhibited inhibitory activity against R. solanacearum and no inhibitory activity against PGPR isolates.
12. Under greenhouse conditions, thyme oil, peppermint oil and Glomus mosseae and six combinations of PGPR isolates and previous treatments have evaluated for their control efficacy against tomato bacterial wilt. In general, thyme showed maximum disease reduction (83.33%), followed by thyme+peppermint treatment (72.22%) while G. mosseae showed minimum disease reduction (22.22%). The shoot length, root length and dry weight of shoot and root as well as total biomass of tomato plants as influenced by treatments has recorded. PGPR isolates significantly enhanced the plant growth parameters while the least recoded by thyme oil.
13. Under field conditions, the perusal of data indicated that the highest control efficacy caused by thyme was 95.92%, in both trials followed by thyme+peppermint that achieved 85.91%. Lowest control efficacy was detected in the case of G. mosseae (28.17 %). In addition, P. fluorescens achieved the highest yield increasing percentage in both trials about 233.52%, followed P. putida by 213.13%, while thyme recorded the lowest yield increase percentage about 38.54%.