الفهرس 
Introduction and aim of the workOnly 14 pages are availabe for public view
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Abstract
Brown rot disease of potato is a worldwide problem that damage potato plantation all over the world. The causal agent of this disease is a gramnegative bacterium called Ralstonia solanacearum that had wide host range and can persist latent in soil for many years and also detected in water ways. Therefore, this work aimed to find out biological tools to control the causal agent of this disease (R. solanacearum). R. solanacearum was isolated from infected tubers collected from different locations at Dakahlia and Dameietta Governorates. The biovar of theses isolates of R. solanacearum is biovar 2 (race 3) and the pathogenicity test was done. Four lytic phages (RSP4, RSP5, RSP6 and RSP7) were isolated from soil samples from the root zone of healthy potato plants cultivated in different locations at Dakahlia and Dameietta Governorates. All of the four isolated phages belong to Caudovirales order. The phage RSP4 has short tail, so, it belong to Podoviridae family, while the other three phages have long tails and belong to Siphoviridae family. All of the four isolated phages are polyvalent; they infect virulent strain of R. solanacearum (biovar 2), Psedomonas flueresence and Erwinia amylovora. No lysogenic bacteria were isolated for the four isolated phage. Forty isolates of actinomycetes were isolated from the same soil samples used for isolation of phages. Four isolates of actinomycetes (A11, A36, A39 and A84) were active against R. solanacearum. These four isolated were characterized morphologically and physiologically and also the antimicrobial activities of them were studied. The four selected actinomycetes strains were identified as the following; A11: Streptomyces mutabilis, A36: S. sparogenes, A39: S. luridus and A84: S. pyridomyceticus. The antimicrobial effects of 16 commercial essential oils against R. solanacearum were tested. Anise oil recorded the best results. Anise oil has a wide antimicrobial spectrum; it inhibited different species of bacteria, fungi and yeasts. Filtrate of water extract of Pleurotus spp. spent wheat straw and filtrate of water extract of wheat straw inhibited growth of R. solanacearum. Furthermore, nine tested basidiomycetes inhibited the growth of R. solancearum. Greenhouse experiment was conducted to reveal the effectiveness of the most active biocontrol agents against R. solanacearum phage cocktail of the four isolated phages recorded the best results. Also, in field experiment phage cocktail and S. mutabilis recorded good results in increasing the productivities of potato plant and decreasing the percentage of infected tubers.