Lazarovits, G., Agricultural Canada, Research Centre, University Sub Post Office, London, Ont., Canada.
Zutra, D., Agricultural Canada, Research Centre, University Sub Post Office, London, Ont., Canada.
Bar-Joseph, M., Agricultural Canada, Research Centre, University Sub Post Office, London, Ont., Canada.

The usefulness of enzyme-linked immunosorbent assay on nitrocellulose membranes (dot-ELISA) for diagnosis and identification of plant pathogenic bacteria was tested. Five pathovars of Xanthomonas campestris and two antisera, one produced against pv. vesicatoria and the other against pv. translucens, were used in a model system. A 10-min incubation of the bacterial cells, dot blotted on membranes, in diluted sera, followed by either alkaline phosphatase conjugated protein A or goat antirabbit globulin, resulted in a specific reaction between the homologous serum and bacteria. Populations of 1000-2000 cfu per spot (ca. 0.3 cm2) could be detected with these reagents. The streptavidin-biotinylated peroxidase complex produced a definitive reaction with as few as 800 cfu, but cross-reactions became evident at the higher cell concentrations among all five pathovars in tests with both antisera. Cell-free extracts, obtained by centrifugation of boiled bacteria, reacted similarly to live cells. Unrelated bacteria did not react with either antiserum. Extracts of lesions from tomato and pepper leaves infected with X. campestris pv. vesicatoria reacted positively with the antiserum produced against this pathovar but not that produced with pv. translucens. Samples of supernatants from boiled lesions reacted with similar intensity as those from homogenized tissues.