Evaluation of a Rapid Diagnostic Field Test Kit for Identification of Phytophthora ramorum, P. kernoviae and Other Phytophthora Species at the Point of Inspection

Plant health regulations to prevent the introduction and spread of Phytophthora ramorum and P. kernoviae require rapid, cost effective diagnostic methods for screening large numbers of plant samples at the time of inspection. Current on-site techniques require expensive equipment, considerable expertise and are not suited for plant health inspectors. Therefore, an extensive evaluation of a commercially available lateral flow device (LFD) for Phytophthora species was performed involving four separate trials and 634 samples. The assay proved simple to use, provided results in a few minutes and on every occasion a control line reacted positively confirming the validity of the test. LFD results were compared to those from testing a parallel sample, using laboratory methods (isolation and real-time PCR). The diagnostic sensitivity of the LFD (87.6 percent) compared favourably to the standard laboratory methods although the diagnostic specificity was not as stringent (82.9 percent). There were a small number of false negatives, but for statutory purposes where all positive samples must be identified to species level by laboratory testing, overall efficiency was 95.6 percent as compared to visual assessment of symptoms of between 20-30 percent for P. ramorum and P. kernoviae. This work demonstrates the value of the lateral flow device for diagnosing Phytophthora species at the time of inspection and as a useful primary screen for selecting samples for laboratory testing to determine the species identification.