RESUMO
AIMS: To determine the reliable combination of protocols for specific detection and identification of R. solanacearum race 3 biovar 2 (R3bv2) through a comprehensive comparison among currently available techniques. METHODS AND RESULTS: Sensitivity and specificity of the conventional isolation, bioassay, serological assays, conventional and real-time PCR and multiplex PCR were assessed for the detection of 25 strains of R. solanacearum biovars 1, 2 and 3 (Phylotypes I, II, III and IV) in spiked potato saps. Results indicated that all assays evaluated varied in complexity and sensitivity and should be applied strategically in indexing schemes to maximize efficiency of testing without compromising accuracy of the results. CONCLUSIONS: The TaqMan PCR assay, with an internal reaction control and confirmation by melting curve and electrophoretic analysis, achieved best sensitivity at 10(2) -10(3 ) CFU ml(-1) for all eighteen strains of R. solanacearum R3bv2. Selective enrichment on mSMSA medium plates enhanced the detection sensitivity up to 10-100 CFU ml(-1) for the conventional PCR-based assays. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first time nine different assays were compared side by side for their sensitivity and specificity in detection and identification of R. solanacearum R3bv2. The data accumulated here will provide basis for regulatory applications for low level detection and rapid identification of latently infections caused by R. solanacearum R3bv2.
