Spiroplasma citri detection by enzyme-linked immunosorbent assay (ELISA), culture and dot hybridization.

We have used ELISA and culture of spiroplasmas in SP4 or M1A medium to detect Spiroplasma citri in citrus trees, periwinkles (Catharantus roseus) and leafhoppers in Iraq and Syria. On the basis of hundreds of analyses, we have found that the sensitivity of ELISA and culture are of the same order of magnitude. With citrus, both tests are able to detect S. citri in 95% of symptomatic nursery or field trees. The tests are not sensitive enough to reliably detect S. citri in symptomless trees. Therefore, a DNA hybridization technique was developed. The radioactive DNA probe was prepared either with total S. citri DNA or with the cloned DNA fragment carrying the spiralin gene of S. citri. Used in dot hybridization, the probe was able to detect concentrations of S. citri one 100th the size of those revealed by ELISA.