Detection and identification of the two Candidatus Liberobacter species associated with citrus huanglongbing by PCR amplification of ribosomal protein genes of the beta operon.

Huanglongbing, previously called greening, is a destructive disease of citrus in Asia and Africa. It is caused by an uncultured, phloem-restricted bacterium for which two species Candidatus Liberobacter asiaticum and Candidatus Liberobacter africanum have been characterized. In 1996, a polymerase chain reaction (PCR) detection method based on the amplification of the 16S ribosomal operon was developed and proved to be efficient for the detection of both liberobacter species. However, in order to distinguish between Candidatus Liberobacter asiaticum and Candidatus Liberobacter africanum, digestion of the amplified DNA with XbaI was required. We have now developed a new PCR detection method based on the amplification of ribosomal protein genes which allows direct identification of the liberobacter species by the size of the amplified DNA. This PCR method is as specific, and at least as sensitive as the previously described one for detection of the two liberobacter species