Thesis (M.Sc.) - Cairo University - Faculty of Science - Department of Botany-Microbiology

Potato brown rot caused by ralstonia solanacearumrace 3 biovar 2 (phylovar II, sequevar 1) is one of the most devastating bacterial disease and have a negative impact in potato production and exportation. It is a quarantine disease with zero tolerance and exportation is restricted to pest free areas (PFAs) in the newly reclaimed areas. This thesis aimed to find new safe microorganism which can be used as potential biocontrol agent against potato brown rot. screening of antagonistic biocontrol agents was made from potato soil and rhizosphere following different fertilization regimes, five antagonistic bacterial isolates showed similarity with P. fluorescens, bacillus megaterium, azotobacter chroococcum and delftia sp. On the other hand, ten antagonistic actinomycetes strains were isolated mostly from sandy soils and showed antagonistic potential against R. solanacearum. Four Actinomycetes potential antagonists were identified using cultural characteristics, electron microscope scan and 16S rDNA. The four isolates showed similarity with S. griseoincarnatus, S. deserti, S. anulatus and S. thermocarboxydus. Some biochemical activity of these isolates were addressed in vitro. S. thermocarboxydus showed the highest proteolytic activity followed by S. anulatus and S. deserti showed minor activity. Also, streptomyces deserti gave the highest ammonia production followed by streptomyces thermocarboxydus and finally Streptomyces anulatus while S. griseoincarnatus showed no ammonia production. The same isolates showed similar phosphate solubilizing activity

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