PCR detection of the two 'Candidatus' Liberobacter species associated with greening disease of citrus.

Greening is a severe and widespread disease of citrus in two main citrus growing areas of the world, Asia and Africa. It is caused by an uncultured phloem restricted bacterium that we have recently characterized from the sequence of its 16S ribosomal DNA. The bacterium is a new "Candidatus' genus, Liberobacter, in the alpha subdivision of the proteobacteria, and two 'Candidatus species' have been recognized: Liberobacter asiaticum and Liberobacter africanum. In this paper we describe a PCR method to detect the two liberobacter species in citrus trees by amplification of a 1160 bp fragment of their 16S rDNA. Distinction between the two species has also been achieved by Xbal digestion of the amplicons.