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A Dipstick Immunoassay for the Specific Detection of Phytophthora cinnamomi in Soils. D. M. Cahill, Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, G.P.O. Box 475, Canberra, Australian Capital Territory 2601; A. R. Hardham, Plant Cell Biology Group, Research School of Biological Sciences, Australian National University, G.P.O. Box 475, Canberra, Australian Capital Territory 2601. Phytopathology 84:1284-1292. Accepted for publication 9 August 1994. Copyright 1994 The American Phytopathological Society. DOI: 10.1094/Phyto-84-1284.

A dipstick immunoassay that is specific for Phytophthora cinnamomi was developed for use in soils. Azo dye detection of monoclonal antibody-labeled cysts attached to a nylon membrane provided a rapid, sensitive assay suitable for field use. There was no cross-reaction with other Phytophthora and Pythium species in controlled environment assays or with soil or other organic matter that adhered to the membrane. The assay was as sensitive as a Eucalyptus sieberi baiting assay and, when run together with the baiting assay, was quantitative for an infested soil-water suspension from 2.5 102 to 5 103 zoospores per milliliter. The assay was used successfully to detect P. cinnamomi in a wide range of soil samples collected from beneath a diverse range of host species. There are several advantages to using the dipstick assay compared with traditional procedures: familiarity with Phytophthora taxonomy is not required; the assay can be performed by unskilled personnel; and soil rather than infected plant tissues can be assayed. Field testing of the assay showed that in kit form, it could be used as a reliable diagnostic tool to replace or augment current isolation and detection methods. The dipstick assay should find broad use for the detection of P. cinnamomi in soil from forests and plant communities and in the horticultural and ornamental crops affected by this pathogen.

Additional keywords: disease diagnosis, Oomycetes, soilborne pathogens.