LAUSR

'Candidatus Liberibacter' species are associated with severe, economically important diseases. Nearly all known species are putatively insect-transmitted, specifically by psyllids. Detection of 'Ca. Liberibacter' in plants is complicated by their uneven distribution in host plants and largely fastidius nature. The death of black (Fraxinus nigra) and mancana (Fraxinus mandshurica) ash trees in Saskatchewan, Canada has been associated with infestation by the cottony ash psyllid (Psyllopsis discrepans). A combination of conventional polymerase chain reaction (PCR) amplification and Sanger sequencing of the 16S rDNA was used to detect and identify 'Ca. Liberibacter' in psyllids collected from ash trees in Saskatchewan. BLAST analysis of two 16S sequences that were 1058 and 1085 bp long (NTHA 5: GenBank accession number MK942379 and NTHA 6: GenBank accession number MK937570, respectively) revealed they were 99-100% similar to a 'Ca. Liberibacter solanacearum' sequence (GenBank accession number: KX197200) isolated from the Nearctic psyllid (Bactericera maculipennis) of United States (US) provenance. Sequencing the psyllid genes CO1 and Cyt-b confirmed that the psyllids from which the bacterial DNA was isolated were P. discrepans based on comparisons with sequences in GenBank and BOLD and a reference sample from the United Kingdom. These results provide the first evidence that 'Ca. Liberibacter solanacerum' species are associated with psyllids collected from ash trees and specifically P. discrepans. The recent episodes of dieback of ash in Saskatchewan associated with psyllid feeding are consistent with disease symptoms caused by 'Ca. Liberibacter' pathogens and this possibility warrants further study.