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Detection of the zebra chip pathogen Candidatus Liberibacter solanacearum in Canadian psyllids

Lawrence Kawchuk: Agriculture & Agri-food Canada

<div>Zebra chip (ZC) is a relatively new and economically important disease of potato (<em>Solanum tuberosum</em> L.). It has been documented in commercial potato fields in the United States, Mexico, Central America, and New Zealand. ZC is caused by the unculturable phloem-restricted α2-proteobacterium, <em>Candidatus</em> Liberibacter solanacearum (Lso). Disease symptoms include stunting, wilting, leaf rolling, chlorosis and/or purpling, and sometimes plant death. The most striking symptom of this disease is the appearance of dark stripes in infected tubers that alters flavor and makes the products unmarketable. Five Lso strains (hap A to E) have been described in different crops, with only hap A and B being associated with ZC in potato. Both pathogen strains are vectored and transmitted to solanaceaeous plants by the tomato/potato psyllid, <em>Bactericera cockerelli</em> (Šulc), (Hemiptera: Trizoidae). Over 1,000 plant samples and 7,000 yellow sticky cards were collected across Canada between 2013 and 2017. Low but increasing potato psyllid numbers were observed from AB, SK, and MB (between 2 and over 200 potato psyllids per annum). Sequence analysis of the cytochrome oxidase from individual potato psyllids confirmed the presence of Central and Western haplotypes on the Canadian prairies. A late season Lso positive potato psyllid was detected from four locations in southeastern AB in 2017. Sequence of the Lso 16S rDNA indicates the Canadian pathogen closely resembles hap A from WA, ID, and OR. Best management practices are being developed to prevent the occurrence of ZC in Canada.</div>