الفهرس 
IntrductionOnly 14 pages are availabe for public view
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Abstract
Potato is one of the most important vegetable crops in Egypt, both for local consumption and for export. Therefore, The Central Administration for Plant Quarantine (CAPQ), Ministry of Agriculture in Egypt, has recently set up a Directorate for imported Potato seeds Quarantine in order to protect local yield against diseases especially the critical bacterial diseases such as ring rot and brown rot.
Brown rot or bacterial wilt of potato caused by Ralstonia solanacearum (Smith, 1896, and Yabuuchi et al. 1995) is one of the most important quarantine disease world wide as well as in Egypt. For that, isolation, purification and identification of the causal organism from two governorates; (El-behera and El-Gharbia), using rapid and accurate methods were carried out. from several collected samples, 12 pathogenic isolates were detected from potato tubers and soil. Pathogenic capability of these isolates was confirmed on tomato seedlings. The aforementioned twenty two pathogenic isolates were identified as Ralstonia solanacearum according to their biochemical and physiological properties, plating on King’s B and SMSA media, immunofluorescence antibody assay (IFAs) and DNA assay using PCR, Box-PCR and Real time PCR techniques.
Disease developmental in different parts of potato plants after inoculation at different periods were studied, With different degrees of colonization but the main observations was all bacterial cell appearing as very short rod nearest the spherical shape without flagella under scanning electronic microscope, the Cells of Ralstonia solanacearum which was inoculated in potato plants soil was examined with a transmission electron microscope at different times during 80 days of cultivation. The binary fission was observed in R. solanacearum, indicating its reproduction. Cells appeared singly as short rods, during the lag phase of its growth curve, mostly with size (0.9–2.0) μm × (0.5–0.8) μm. During the logarithmic phase, each circular DNA strand then attached to the cell membrane after the entire prokaryotic DNA was duplicated. The cell wall and cell membrane started growing transversely from near the middle of the dividing cell; this separated the parent cell into two nearly equal daughter cells, each having a nucleous. The cell membrane then invigorated (grown inwards) and split the cell into two daughter cells
Biological control of plant pathogens has become a very powerful tool in order to decrease damage and losses caused by important diseases. In this research work, rhizosphere samples were collected from healthy potato plants grown in infected potato fields to isolate associated bioagents and to examine their inhibitory effects against Ralstonia solanacearum, in vitro and in vivo. Among the isolated bacteria and actinomycetes, obtained from rhizosphere experiment, only six bacterial isolates and four actinomycetes isolates showed antagonistic effect against Ralstonia solanacearum. These isolates were roughly identified and tested under greenhouse conditions. Bacterial isolates especially Pseudomonas sp., Bacillus sp. and Streptomyces sp. are powerful antagonistic of plant pathogenic and has been found to be very potential biocontrol agent against Ralstonia solanacearum under greenhouse conditions. The potential antagonistic effect of some plant extracts against the growth of Ralstonia solanacearum, the causal agent of bacterial wilt of potato, was studied. The efficacy test was conducted by paper disc diffusion method on double layer nutrient agar. Four plant extracts (chamomile, calendula, lemongrass, thyme) obtained by using water, methyl alcohol, and acetone, were tested. The four plant extracts could inhibit the growth of R. solanacearum and showed visible inhibition zones. The lemongrass extracted by methanol was varying effectively against potato bacterial wilt disease caused by R. solanacearum than that extracted by water and acetone; chamomile and calendula extracted by acetone were also varying effectively against potato bacterial wilt disease caused by R. solanacearum than that extracted by water and methanol. Thyme extracted by methanol was varying effectively than that extracted by water and acetone.