Comparison of diagnostic approaches for Phytophthora ramorum from California forests.

Vettraino, A.M., Sukno, S., Vannini, A., and Garbelotto, M. 2008.  9Th Internacional Congress of Plant Pathology (ICCP). Turin, Italy. July 2008.



The sensitivity, specificity, and robustness of five methods for detection of Phytophthora ramorum including culturing the pathogen on two selective media, an ELISA-based polyclonal assay, a nested PCR-based assay, and a Taqman Real Time PCR assay, were compared on symptomatic plant material sampled in fields at different times and from different host species, and processed in two different laboratories in the USA.  With all methods P. ramorum could be detected in all sites, sampling periods and laboratory. About 80% of collected samples resulted positive to P. ramorum Over 41 species were analyzed, and 3 species M. fabaceous, R. ursinus and Symphoricarpos sp. were recorded as new hosts of P. ramorum. All diagnostic assays were highly correlated with one another, and with disease symptoms, but only the  ELISA-based assay was not affected by sampling period, laboratory processing, hosts and substrates.  Assays involving pathogen culturing were strongly affected by time of sampling, host species, and processing laboratory.  The two PCR-based assays were more robust than culturing, but differed from one another. While the nested PCR assay was more sensitive and least affected by time of sampling, host species, provenance of samples, and testing laboratory, it was also prone to higher rate of false positive diagnoses. Conversely, the Taqman assay was more specific to its target, but it proved to be less sensitive and more significantly affected by time of sampling, provenance of samples and testing laboratory.

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