The use of digoxigenin-labelled probes to detect DNA sequences specific for plant pathogenic bacteria.

Southern blot hybridization is a valuable method in the assessment of the pathogenicity of bacterial strains or isolates. It is also a powerful tool for the demonstration of the presence of foreign DNA sequences in the genome of genetically-engineered plant cells. In this respect, cold, digoxigenin-labelled DNA probes can be used in place of classical radioactive probes, whether hybridizations are performed on bacterial genomic or plasmidic DNA, or on plant genomic DNA. The versatility of this cold labelling makes it suitable for the detection of unique bacterial genomic or plasmid sequences, even though these are located on large plasmids. The sensitivity of this cold probe technique also permits the detection of subpicogram quantities of DNA in plant genomic preparations. Their long term storage stability allows them to be frequently re-used over long periods of time, making this technique quite cost efficient.