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The causal agent of potato brown rot, Ralstonia (Pseudomonas) solanacearum was demonstrated for the first time to be present in surface (irrigation) water in Egypt. The bacterium was identified in both irrigation and drainage canals near to infected fields within three potato-growing areas in the delta that were already known to be infected. The bacterium was found in populations of up to 10(6) colony-forming units per litre. No weed hosts such as Solanum dulcamara were found along the canals. The bacterium was not detected anywhere in the desert area. These findings show that irrigation water can play a role in the epidemiology of the brown rot disease in Egypt and further studies are necessary to determine its exact role. The use of artesian water in the desert area and avoidance of re-use of irrigation water could be important factors in the avoidance of brown rot problems.