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Abstract
The efficiency of culturing Ralstonia solanacearum on Semi selective Modified South Africa medium (SMSA), inoculation in SMSA broth (SMSB) enrichment, immunofluorescent antibody staining (IFAS) using polyclonal antibodies, tomato bioassay and conventional polymerase chain reaction (PCR) methods were evaluated for their sensitivity in routine detection of the brown rot bacterium, Ralstonia solanacearum, in potato piece. The experiments were performed using potato extracts of two cultivars; Spunta and Cara, also using two types of soil; sandy and clay. Potato extracts were prepared from 200 tubers according to the EPPO procedure. The sensitivity of the different detection methods was compared by adding bacterial suspensions ranging from 10⁸ to 10² CFU per ml to potato extracts prepared from two cultivars. Also, inoculated two types of soil with bacterial suspensions ranging from 10⁸ to 10² CFU per ml were used. The results showed that 3.6{u00D7}10² and 3.6{u00D7}10³ CFU per ml were the lowest bacterial number detected by isolation on SMSA medium using artificially inoculated potato extracts of cv. Cara and Spunta, respectively. In soil the limit of the detection was 3.5{u00D7}10² CFU per g soil in both types of the soil. In comparison, a tomato bioassay has shown to detect bacterial populations number between 3.6{u00D7}104 and 3.6{u00D7}105 CFU per ml in potato extracts of cv. Cara and Spunta respectively, and the same limit of bacterial detection 3.5{u00D7}10⁴ and 3.5{u00D7}10⁵CFU per g soil was observed in sandy and clay soil samples, respectively