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Sensitivity and Clinical Use of Phytophthora-Specific Immunoassay Kits. J. W. Pscheidt, Assistant Professor, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2903. J. Z. Burket, S. L. Fischer, and P. B. Hamm. Research Assistant, Diagnostician, Department of Botany and Plant Pathology, Oregon State University, Corvallis 97331-2903; and Associate Professor, Hermiston Agricultural Research and Extension Center, P.O. Box 105, Hermiston, OR 97838. Plant Dis. 76:928-932. Accepted for publication 13 April 1992. Copyright 1992 The American Phytopathological Society. DOI: 10.1094/PD-76-0928.

The sensitivity of a Phytophthora-specific immunoassay kit was tested on 17 species of Phytophthora collected throughout the world, including 18 isolates each of P. cinnamomi and P. cactorum. Kits were also used in the diagnosis of plant specimens with symptoms characteristic of Phytophthora infection, which were sent to Oregon State University’s Plant Disease Clinic. All Phytophthora isolates tested produced a positive reaction with the immunoassay kit. The lowest absorbencies relative to other species were obtained from P. cinnamomi and P. megasperma (originally isolated from cherry). Variation in absorbance was high among isolates of P. cinnamomi but low among P. cactorum. Clinic samples with typical symptoms of Phytophthora infection produced a positive reaction with the immunoassay, as did pure cultures of Phytophthora sp. isolated from these samples. Cross-reactions occurred with several Pythium spp. isolated from clinic samples and with several specimens infected with Peronospora spp. Other samples without typical Phytophthora symptoms but associated with other pathogens did not produce a positive reaction with the immunoassay. Cross-reactivity with some Pythium spp. made interpretation difficult, but when kit results were combined with field histories and symptomology, the immunoassays proved to be a useful tool in clinical diagnosis.

Keyword(s): blackberry downy mildew.