Risk Analysis of Brown Rot Disease in Potato Seeds Caused by Ralstonia solanacerum Race 3 in Sudan

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Sunhori,Salwa Balla Mohamed Ahmed
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University of Khartoum
This work aimed to study the possible pest risk posed by the introduction of the brown rot disease in potato crop, caused by the bacteria Ralstonia solanacearum (Smith) Yabuuchi et al. ( Pseudomonas solanacearum) Race 3 and to decide if it is quarantine pest or not. The bacterium was intercepted in a potato seed variety Pelleini consignment imported from France in 2006. Zalinge local potato variety previously collected from the local market reported to be infected by the bacterium. A brownish discoloration of the vascular ring was detected in 80% of Pelleini tubers, when the tuber was cut into two halves across the stem end. When the tubers were slightly squeezed creamy fluid exudates was observed oozing from the vascular ring. The same symptoms were observed on infected Zalinge potato tubers. Growth of the bacterium for 24 hours on nutrient agar resulted in small, irregular, smooth cream coloured and translucent colonies. The bacteria were short rods, motile and negative to gram reaction. When the bacteria were isolated and injected in potato plants, typical symptoms of brown rot appeared in the inoculated plants, the plants ultimately wilted and died. The soil and plant debris mixed with the inoculums of R. solanacearum Race 3 were left under the sun during the summer months (May-November). Certified potato seeds were then planted in this soil. Neither the potato plants grown on neither infested soil nor those grown on non infested soil showed disease symptoms. The average plant height was 12.62 and 11.66 cm in infested soil and non infested soil, respectively. No bacterium was re-isolated from the plants. This study revealed that the disease can not over summer in central Sudan environmental conditions where the average maximum temperature reached during that season was 46 0C. A through pest risk analysis was conducted, the probability of introduction was high as the pest can be introduced with plant material intended for planting (seed potato) from Europe or with private individuals carrying infected material from neighboring countries i.e. Egypt, Saudi Arabia, Eritrea and Ethiopia. From this study survival in the soil is rated low risk. Survival of the bacterium in irrigation water is rated high. The study concludes that R. solanacearum Race 3 should be classified as a quarantine pest in Sudan. Seed potato has to be imported from pest free areas only and the ban of ware potato from neighboring countries has to continue
75 Pages
Sudan;Potato;Tomato;soil;economic;season;Egypt;Saudi Arabia;bacterium ,