First report of ‘ Candidatus Liberibacter europaeus’ associated with psyllid infested Scotch broom

In the Canterbury region (mid-South Island), New Zealand, in November 2011, disease symptoms resembling those associated with 'Candidatus Liberibacter' species were observed in common or Scotch broom (Cytisus scoparius), an invasive leguminous exotic shrub. Symptoms included stunted growth of shoots, shortened internodes, and leaf dwarfing and leaf tip chlorosis (Fig. 1). A large population of broom psyllid, Arytainilla spartiophila, was noted on the plants. Total DNA was extracted from the stems of 19 Scotch broom plants as well as seven broom psyllid samples collected from infested plants using CTAB. Each DNA sample was tested for the presence of 'Ca. Liberibacter' by amplification of a partial 16S rDNA sequence using a liberibacter-specific semi-nested PCR based on primers Lib16s01F, Lib16s01R and OA2 (Beard et al., 2012). A 578 bp partial 16S rDNA fragment indicative of the presence of a 'Ca. Liberibacter' was amplified from 15 out of 19 plant samples and from five out of seven broom psyllid samples. Amplicons from seven of these samples were directly sequenced, trimmed to 510 bp and subsequently used in a phylogenetic comparison with partial 16S rDNA sequences of 'Ca. Liberibacter' from other hosts using Mr. Bayes v. 3.0b4. The resulting majority rule consensus tree clustered the partial 16S rDNA sequences from Scotch broom and broom psyllid with that of 'Ca. Liberibacter europaeus' (Fig. 2). 'Ca. L. europaeus' has been previously associated with the pear psyllid, Cacopsylla pyri, and shown to be transmitted to pear plants where it apparently behaves as an endophyte (Raddadi et al., 2011).