A DIPSTICK IMMUNOASSAY FOR THE SPECIFIC DETECTION OF PHYTOPHTHORA-CINNAMOMI IN SOILS

A dipstick immunoassay that is specific for Phytophrhora 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 w ith soil or other organic matter that adhered to the membrane. The ass ay was as sensitive as a Eucalyptus sieberi baiting assay and, when ru n together with the baiting assay, was quantitative for an infested so il-water suspension from 2.5 X 10(2) to 5 X 10(3) zoospores per millil iter. 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 comp ared with traditional procedures: familiarity with Phytophthora taxono my is not required; the assay can be performed by unskilled personnel; and soil rather than infected plant tissues can be assayed. Field tes ting of the assay showed that in kit form, it could be used as a relia ble diagnostic tool to replace or augment current isolation and detect ion methods. The dipstick assay should find broad use for the detectio n of P. cinnamomi in soil from forests and plant communities and in th e horticultural and ornamental crops affected by this pathogen.