Specificities of Monoclonal Antibodies to Phytophthora cinnamomi in Two Rapid Diagnostic Assays. B. K. Gabor, Plant Cell Biology Group, Research School of Biological Sciences, The Australian National University, G.P.O. Box 475, Canberra, ACT 2601, Australia. E. T. O’Gara, B. A. Philip, D. P. Horan, and A. R. Hardham. Plant Cell Biology Group, Research School of Biological Sciences, The Australian National University, G.P.O. Box 475, Canberra, ACT 2601, Australia. Plant Dis. 77:1189-1197. Accepted for publication 18 August 1993. Copyright 1993 The American Phytopathological Society. DOI: 10.1094/PD-77-1189.

Twenty-four monoclonal antibodies (MAbs) previously raised against aldehyde-fixed zoospores and cysts of the fungus Phytophthora cinnamomi were screened for their diagnostic specificities. Forty-five isolates of P. cinnamomi, 96 isolates encompassing 20 Phytophthora species, 17 Pythium species, three Saprolegnia species, and one isolate each of Fusarium, Verticillium, Rhizoctonia, and Schizophyllum were tested using an immunofluorescence assay (IFA) and an enzyme-linked immunosorbent assay (ELISA). In the IFA, 11 MAbs reacted with zoospores and cysts of all isolates of P. cinnamomi and no other species. These MAbs were thus species-specific in the IFA. One MAb reacted with zoospores and cysts of all the isolates of Phytophthora and was thus genus-specific in this assay. Preliminary screening of the 24 MAbs with the ELISA indicated that only 10 MAbs could detect their antigens in mycelial extracts of P. cinnamomi. When the 10 MAbs were tested on all fungal isolates, two detected all isolates of P. cinnamomi and no other species. These results indicated that these two MAbs were species-specific in the ELISA. No MAbs were found to be genus-specific in the ELISA. Only one MAb, Lpv-2, was species-specific in both assays. No MAbs were genus-specific in both assays.