RAPID DETECTION OF XANTHOMONAS-CAMPESTRIS PV DIEFFENBACHIAE IN ANTHURIUM PLANTS WITH A MINIPLATE ENRICHMENT ELISA SYSTEM

A miniplate enrichment/ELISA system was developed for rapid detection and identification of Xanthomonas campestris pv. dieffenbachiae, causal agent of anthurium blight. Tissue exudates were applied to individual wells of 96-well tissue-culture plates filled with 150 mul of esculin trehalose medium, which promotes growth of X. c. dieffenbachiae and turns brown, indicating esculin hydrolysis. Cells were transferred to a 96-well microtiter plate, and identity of X. c. dieffenbachiae was confirmed by ELISA using an X. c. dieffenbachiae-specific monoclonal antibody (Xcd 108). Sensitivity and specificity of the miniplate enrichment/ELISA were determined using 10-mul subsamples containing end-point dilutions of X. c. dieffenbachiae or mixed suspensions containing various ratios of competitive bacteria to X. c. dieffenbachiae. The miniplate enrichment/ELISA system is sufficiently sensitive to detect one or more colony-forming unit per well. Monoclonal antibody Xcd 108 reacted with all strains of X. c. dieffenbachiae pathogenic to anthurium but not with most nonpathogenic strains isolated from anthurium. When 142 leaf samples with and without symptoms were assayed, the miniplate enrichment/ELISA system gave positive results for every sample from which X. c. dieffenbachiae was isolated by standard procedures, but 3.3% of the samples that gave a positive reaction in the miniplate enrichment/ELISA system were negative using standard procedures. When compared with standard isolation procedures, the predictive value of test results for the miniplate enrichment/ELISA system was 97.9%. The miniplate enrichment/ ELISA system also was useful for detection of epiphytic populations of X. c. dieffenbachiae on leaf surfaces.