Specific Detection of Xanthomonas axonopodis pv. manihotis with a DNA Hybridization Probe

A dot-blot assay was developed for the detection of Xanthomonas axonopodis pv. manihotis (Xam), the causal agent of cassava bacterial blight. A 898 bp DNA fragment unique to Xam strains was cloned and evaluated as a diagnostic DNA probe. The DNA probe (p898) hybridized with the total DNA of 362 Xam strains tested but not with any of the 40 other Xanthomonas strains tested or with saprophytes associated with the cassava plant. A quick colony hybridization procedure was developed to identify Xam strains. The probe also detected Xam strains in crude extracts of leaf and stem lesions, and in cassava fruits and sexual seeds that were naturally infected. The overall sensitivity of the dot blot method for detecting Xam in stem and leaf samples was about 103 colony-forming units per reaction. Because the dot-blot hybridization technique is sensitive and rapid, it can be easily used for culture indexing.