This work aimed to detect and determine the virulence in addition to the host range of Ralstonia solanacearum the causal of potato brown rot disease. Isolation from naturally infected potato tubers of three different cvs. (Spunta, Draga and Nicola) showing brown rot disease symptoms revealed that all isolated bacteria showed typical morphological growth of R. solanacearum on SMSA medium where; colonies were fluidal white with red center. Also, IFAS test (Immunoflurescence Microscope Antibody Staining) confirmed that these isolated bacteria are R. solanacearum. The traditional identification of the three tested pathogenic bacteria isolates exhibited similarity among them based on their cultural and morphological characteristics where, these isolates were non-sporulating short rods with weak Gram negative reaction. Also, their developed colonies on nutrient agar (NA) medium were irregularly/round, convex, smooth surface, entire margin, translucent and yellowish brown in colour. Meantime, these colonies were whitish-gray in colour on King’s B (KB) medium forming brown pigments in most cases. Also, the physiological and biochemical tests of the three bacterial isolates showed oxidative metabolism of glucose and positive results with oxidase reaction, catalase reduction, H2S production, nitrate reduction. However, the three isolates were negative to Indole production, gelatin liquefaction, Arginine dihydrolase, starch hydrolysis, Voges proskauer test and Levan formation. Also, the three tested isolates of R. solanacearum showed virulence against potato and tomato plants. While, these isolates were avirulent to eggplant, pepper, tobacco and banana plants under artificial inoculation conditions which reveal that theses isolates belong to race 3. Also, all three tested isolates utilized maltose, lactose, cellobiose and glucose but not oxidized mannitol, sorbitol and dulcitol. As for virulence of the three tested R. solanacearum isolates, results exhibited different percentages of disease severity on potato plants (cv.Nicola) at 15 days of incubation period. Also, Draga- isolate was the fastest one followed by Nicola -isolate. Draga-isolate of R. solanacearum infected many hosts with different degrees of wilt severity where it was virulent to tomato, mallow, datura and little hogweed. Also, positive results were obtained with SMSA, IF and PCR techniques to confirm the infection with Draga-isolate. |
