Development of Primers for Improved PCR Detection of the Potato Zebra Chip Pathogen, 'Candidatus Liberibacter solanacearum'.

Zebra chip disease poses a major economic threat to potato production. The causative agent is a phloem-limited bacterium identified as 'Candidatus Liberibacter solanacearum' that is transmitted by the potato/ tomato psyllid. Currently, there are no effective controls and existing control strategies depend largely on the early detection of the pathogen via polymerase chain reaction (PCR) assays. Most primer sets used for PCR detection target a region of the bacterial 16S rDNA gene, and detection of the pathogen in symptomatic potato tissue with existing primers has been variable depending on the specific primer sets used. This study describes the development of two new primer sets that target a conserved intergenic region between the 16S and 23S rDNA genes and a conserved bacterial housekeeping gene, adenylate kinase (adk). Results demonstrate that the new primer sets are more reliable in detecting 'Ca. L. solanacearum' in field and glasshouse samples than the currently used LsoF/OI2 primers. The newly developed primers differentiated between 'Ca. L. solanacearum' and a closely related 'Ca. Liberibacter' spp. and were more sensitive than the LsoF/OI2 primers. The low detection limit for the new primers was four times lower (0.65 ng) than the limit (2.5 ng) for the LsoF/OI2 primers.