Submitted to: Phytopathology
Publication Type: Abstract Only
Publication Acceptance Date: May 13, 2013
Publication Date: June 1, 2013
Citation: Bock, C.H., Gottwald, T.R., Graham, J.H. 2013. A comparison of culture and bioassay for detecting citrus canker. Phytopathology. 103:S2.16 http:11apsjournals.apsnet.org/loi/phyto. Technical Abstract: Citrus canker (Xanthomonas citri subsp. citri, Xcc) causes serious crop losses in tropical and subtropical citrus production regions. Detecting Xcc is important for quarantine purposes, research and disease management. Although PCR methods are available for detecting and quantifying viable bacteria, in many circumstances alternative methods are required. We compared washes of lesions from fruit, leaves and shoots using a culture-based method for detection compared to a “gold-standard” bioassay of injection-infiltrated leaves of susceptible ‘Duncan’ grapefruit. There was good agreement in detection of active lesions identified by culture and bioassay (26.9-87.8% active by culture compared to 16.3-88.9% by bioassay). False negatives were low (0.9% to 6.5% of lesions). False positives ranged from 4.3 to 21.4%. Accuracy of culture ranged from 0.73 to 0.90%. Comparing culture positives in relation to bioassay negatives showed that the greatest proportion was obtained when lesion bacteria flux density (BFD) of Xcc was =102 bacteria/mm2/min. A Receiver Operator Characteristic analysis of these data demonstrated good to excellent accuracy of culture in detecting Xcc (Area Under the Curve = 0.79-0.98). Both empirical and binormal curve fits showed in most cases sensitivity was greater using culture (i.e. at low concentrations of Xcc, culture tended to detect Xcc when the bioassay did not). Compared to bioassay, culture can be a reliable way to detect Xcc in lesion samples.