Determination of Races and Biovars of Ralstonia solanacearum Causing Bacterial Wilt Disease of Potato

A survey was carried out in some selected potato growing districts of Bangladesh during December to February 2011 to know the status of bacterial wilt of potato caused by Ralstonia solanacearum in terms of its incidence and severity. The results showed that the highest wilt incidence was recorded in Munshigonj (22.65%), followed by Nilphamari (19.98%) and the lowest incidence was recorded in Jamalpur (9.07%). The highest bacterial wilt severity was recorded in Munshigonj (3.80), while the lowest wilt severity was recorded in Jamalpur (2.90). A total of 44 isolates (R. solanacearum) were obtained from the wilted potato plant samples i.e. 20 from Munshigonj, 17 from Nilphamari and 7 from Jamalpur and the isolates were divided into three groups. The production of pink or light red colour with whitish margin on TZC medium by the bacterial isolates indicated all groups of R. solanacearum isolates were virulent. The results of pathogenicity test revealed that all groups of R. solanacearum isolates were able to cause wilt symptoms in potato plants and brown rot symptoms in potato tuber. On the other hand, all biochemical tests were used for the identification of R. solanacearum isolates. The biovar test using the oxidization of disaccharides (sucrose, lactose, maltose) and sugar alcohols (manitol, sorbitol and dulcitol) by R. solanacearum isolates confirmed that all groups of R. solanacearum isolates belong to biovar III. The race identification of R. solanacearum isolates by pathogenicity test on brinjal, tomato, tobacco and chilli indicating a narrow host range (only in potato) and were categorized in race 3. Therefore, the R. solanacearum isolates causing bacterial wilt of potato in Bangladesh were belonging to Biovar III and Race 3.