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Detection of Phytophthora cinnamomi in Azalea with Commercial Serological Assay Kits. D. M. Benson, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Plant Dis. 75:478-482. Accepted for publication 24 October 1990. Copyright 1991 The American Phytopathological Society. DOI: 10.1094/PD-75-0478.

Two commercial serological assay kits were compared to a culture plate method for detection of Phytophthora cinnamomi in root samples from inoculated azaleas. Both the multiwell E kit and the rapid assay F kit detected P. cinnamomi on azalea roots beginning 1 wk after inoculation. Agreement between immunoassay kits and culture plate results for detection of P. cinnamomi was most consistent beginning 35 wk after inoculation. Root symptoms, but not foliar symptoms, of Phytophthora root rot were evident during this period. There was a positive correlation between root rot severity in greenhouse trials and root sample absorbance (multiwell) or meter reading (rapid assay) but not between symptom severity and immunoassay results. Although color reactions in the rapid assay detectors became increasingly darker after completion of the test, results after 5 min were as reliable as those after 60 min, since readings for uninoculated controls used to determine test thresholds also increased with time. The multiwell kit detected P. cinnamomi in root samples containing as little as 1.0% infected root tissue. In a commercial nursery survey, 5 and 15% of the azalea root samples at two nurseries had positive ELISA values that were unconfirmed by culture plate. The rapid assay kit detected P. cinnamomi, was easy to use, and gave results in a short time.