الفهرس 
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Abstract
Enhanced efficiency of the bio-control agent of rifampicin/ chloramphenicol Stenotrophomonas maltophilia mutant strain (PD 4560), isolated from eggplant rhizosphere was evaluated for control of potato bacterial wilt caused by the pathogenic Ralstonia solanacearum race 3 biovar 2 Phylotype II, sequevar 1 in an in vitro culture plate bioassay and in an in vivo planta under greenhouse conditions. These evaluations were carried out using the latest advances in molecular biology techniques. Functional genomics and metabolimics approaches were utilized. These advanced approaches led to detection of biomarkers which can be developed to be applied in molecular breeding strategy. The most effective use of the bio-control agent used for the control of wilt disease was accomplished through an integrated coordinated friendly environmental based approaches. Effective means of culturing and utilization of this bio-control agent were developed. Peatmoss as organic carrier , cowpea soil, and maize soil were used. Beside these means, ammonium sulfate (A. sulfate) and salicylic acid (SA) that known previously as signalling inducers of defense responses, were also applied. Another bio-control agent Pseudomonas putida (potato rhizospheric isolate) was also used in combination with S. maltophilia (PD 4560). S. maltophilia (PD 4560), is evident to be an effective bio-control agent in an in vitro and in an in vivo against potato wilt pathogenic bacteria R. solanacearum Phylotype II, sequevar 1. It was able to dramatically suppress the Ralstonia pathogen in vitro plate bioassay due to its ability to produce alkaline serine protease enzyme with molecular weight 40 KDa by SDS-PAGE analyses. Serine protease has shown to account in the antibacterial activity of S. maltophilia. Cowpea and maize crops are the suitable crops that promote the highest survival of the bio-control agent S. maltophilia in clay and sandy soil under greenhouse conditions. Presence of S. maltophilia in soil has a negative correlation with Ralstonia wilt disease incidence in potato plants. The root exudates of cowpea and maize contained methionine sulfur amino acid as revealed by amino acid analyses. Methionine is considered a growth promoting factor for S. maltophilia. Therefore, these crops would be highly recommended in crop rotation with potato plants. The best two methods for applying S. maltophilia in soil for controlling potato Ralstonia wilt were by the adhesion on potato tubers, by using-carboxy methyl cellulose (CMC), or by using black peat-moss as an organic carrier for the bio-control agent in soil. In addition, spraying SA on potato leaves at both vegetative and the tuber initiation growth stages led to an increase in the efficacy of S. maltophilia to control the Ralstonia potato wilt. However, spraying of A. sulfate did not affect the bio-control efficacy when it was applied at similar growth stages described in SA treatment. It affected only on the count of the Ralstonia pathogen in clay soil. The bio-control activity of S. maltophilia was attributed to the involvement of direct and indirect mechanisms. The direct one, being the alkaline serine proteolytic enzyme which was determined in an in vitro plate bioassay and in an in vivo planta through expression of PrtP gene encoded for serine protease. This PrtP gene was highly expressed at either tuber initiation or maturation growth stage. The indirect bio-control mechanisms are through the induction of the host induced resistance and enhancement of systemic acquired resistance (SAR). Expression of pathogenesis related proteins (PR1 and PRQ), using RT- PCT with bio-control agent treatment alone or in combination with SA was evident. Tuber bulking is proved to be the most suitable physiological stage to apply either SA or the bio-control agent. Furthermore,SA induces the expression pathogenesis related protein genes (PR) in potato leaves tested through various growth stages. Among these expressed genes, is the PRQ gene encoding for acidic chitinase and extracellular β-l, 3-glucanase. It was the most abundant and highly expressed gene at the tuber bulking stage among other different potato growth stages studied based on RT- PCR analyses. Other mechanisms employed by the bio-control agent to affect Ralstonia potato wilt were clarified. Multiple and different mechanisms were involved in the bio-protection. This bio-protection was achieved by S. maltophilia as an efficient bio-control agent with SA, as an effective defense signal. They were proved to be active in triggering and enhancing the induction of induced resistance and the systemic acquired resistance, in association with either identified defense responses. Other mechanism for S. maltophilia and SA are induction and enhancing production of different terpenoid phytoalexins precursors as revealed by GC-MS analyses, in potato leaves at tuber bulking stage that matching the high expression level in particular of PRQ gene. Other metabolites including phenolics, carotenoids, protein related compounds were detected and identified by GC-MS analyses. The potato leaves ethyl acetate extract of phytoalexin possessed inhibitory activity in vitro culture plate bioassay against theRalstonia pathogen but, they did not exhibited activity against bio-control bacteria.Overall, the findings of this study in respect to SA, addresses the contribution of multiple defense mechanisms, functioning in an integrated, coordinated fashion (as a networking biosynthetic system) operated, through various metabolic pathways. These involve biosynthesis of terpenoid phytoalexins and their precursors pathways, phenolics, carotenoids, and protein pathways. In addition, the association between the operation of these various defense mechanisms and certain functional selected genes related to defense are clarified and discussed. Combination between P. putida and S. maltophilia as a mixed bio-control inoculants agents do not increase the efficiency for controlling Ralstonia potato wilt disease otherwise, they are effective individually in an in vitro culture platebioassays and the experimental conditions used in this study in the greenhouse.