Phenotypic Characterization of Isolates of Ralstonia solanacearum and Evaluation of Some Tomato Varieties Against Bacterial Wilt

Abstract

Tomato is attacked by many bacterial diseases, among which bacterial wilt, caused by Ralstonia solanacearum Smith, is the most important in Ethiopia. The present study was made to characterize the pathogen phenotypically and to evaluate some tomato varieties against the disease. For phenotypic characterization, pathological, cultural, biochemical and physiological tests were done. For varietal evaluation, a greenhouse experiment was made using tomato.  varieties introduced from the Asian Vegetable Research and Development Center (AVRDC), Taiwan, and recently (2005) released varieties by Melkassa Agricultural Research Center
(MARC), Ethiopia, for resistance against the virulent strain R. solanacearum PPRC-Rs. According to the results of the study, strain PPRC-Rs of R. solanacearum caused necrosis of tobacco leaf but not wilting; whereas, the strain caused wilting of tomato and potato. The strains of R. solanacearum (PPRC-Rs and 262b) were catalase and oxidase positive. Both strains of the pathogen did not hydrolyse starch and gelatin. The strains utilized glucose, lactose and cellobiose, while neither utilized dulcitol. Based on the test results, the strains were designated as race 3, biovar II of R. solanacearum. In addition, two AVRDC tomato varieties, BL-1004 and BL-333, showed resistant reaction to the pathogen. Among the varieties released in Ethiopia, only Fetane (Picador) showed moderate resistance (50% survived) reaction; whereas the other varieties were susceptible. The susceptible reaction of the released varieties indicated the need to evaluate the varieties against the wilt pathogen before undertaking adaptation, agronomic or any other field trial.