Screening of diverse Psylloidea species in Taiwan reveals the presence of both known and potentially novel “ <i>Candidatus</i> Liberibacter” species in multiple psyllid lineages

Psyllids (Psylloidea) are host-specific, phloem-feeding insects that are associated with the transmission of destructive plant diseases caused by the bacterial genus "<i>Candidatus</i> Liberibacter". While psyllid-liberibacter interactions have been studied in great detail, most research mainly focused on species associated with important crop diseases. Therefore, a more general understanding of the associations between these two groups of organisms remains limited. The present study investigated the occurrence of infection by "<i>Ca</i>. Liberibacter" across undercharacterized psyllid lineages in Taiwan. Samples of 46 psyllid species, representing six of the seven known Psylloidea families from host plants spanning 22 families, were obtained. The presence of "<i>Ca</i>. Liberibacter" in adult psyllid DNA samples was determined by PCRs targeting 16S rDNA of "<i>Ca</i>. Liberibacter". PCR tests amplifying mitochondrial 16S DNA of the psyllids were also carried out for quality confirmation. The assays detected "<i>Ca</i>. Liberibacter" in five of the psyllid species tested, namely <i>Calophya nigridorsalis</i>, <i>Homotoma radiata</i>, <i>Cacopsylla tobirae</i>, <i>Epipsylla albolineata</i>, and <i>Trioza quadrimaculata</i>. BLASTn searches and phylogenetic analysis on near-full-length 16S rDNA sequences identified the strain detected in <i>C. tobirae</i> as "<i>Ca</i>. Liberibacter europaeus" and showed that <i>E. albolineata</i> carried a strain closely related to a "<i>Ca</i>. Liberibacter" strain found in Bhutan, while the remaining detected strains could potentially be novel "<i>Ca</i>. Liberibacter" species. The findings from this study showed that a large diversity of "<i>Ca</i>. Liberibacter" could exist among underexplored psyllid and plant species, opening new avenues for investigating the ecology of "<i>Ca</i>. Liberibacter".IMPORTANCEBacteria of the genus "<i>Candidatus</i> Liberibacter" can cause some of the most devastating plant diseases. Gaining a broader perspective on the diversity of associations between these bacteria and their psyllid vectors is crucial for both fundamental and applicative purposes. By taking advantage of the biological diversity in Taiwan, the present study conducted one of the broadest surveys on the presence of "<i>Ca</i>. Liberibacter" in psyllids, in terms of the diversities of the psyllids examined. The data from this work indicated that previously unknown "<i>Ca</i>. Liberibacter" genotypes and perhaps even novel species may be more prevalent among psyllid species than previously known. These findings highlight the potential importance of exploring psyllid-liberibacter associations from a broader ecological perspective.