Genome-informed multiplex conventional PCR for identification and differentiation of Xanthomonas citri pv. citri sub-pathotypes, the causal agents of Asiatic citrus canker

Abstract :

Asiatic citrus canker, one of the most important diseases of citrus, is caused by Xanthomonas citri pv. citri. It has high economic impact, can spread easily and disease is difficult to manage; it is a quarantine organism in many citrus-producing countries. X. citri pv. citri has been separated into three sub-pathotypes (A, A*, Aw) that differ in host range and geographical distribution, thus creating a need to differentiate sub-pathotypes for surveillance and disease management. Availability of useful diagnostic tools is the cornerstone of successful surveillance, quarantine, and eradication measures. In this study, a multiplex conventional PCR (cPCR) assay was developed for detection and sub-pathotype determination of X. citri pv. citri. Assay specificity was assessed by four different labs on a total of 146 X. citri pv. citri and 58 other Xanthomonas isolates. The assay demonstrated high analytical sensitivity, specificity and selectivity. False negatives were observed with A Lineage 2 strains and potential false positives were observed for X. citri pv. bilvae. Combined with a simple extraction protocol, the assay has been deployed successfully at the Plant Protection and Quarantine Plant Pathogen Confirmatory Diagnostics Laboratory. This assay has proven useful for differentiating Asiatic citrus canker sub-pathotypes from symptomatic citrus tissue.