PROBLEMS WITH INTERPRETATION OF SEROLOGICAL ASSAYS IN A VIRUS SURVEY OF ORCHID SPECIES FROM PUERTO-RICO, ECUADOR, AND FLORIDA

Leaf samples collected in May 1990 from wild and cultivated orchids in Puerto Rico were tested for odontoglossum ringspot virus (ORBV), cymb idium mosaic virus (CymMV), tobacco mosaic virus common strain, tobacc o mild green mosaic virus. two strains of cucumber mosaic virus, and c ymbidium ringspot virus (CymRSV) with sodium dodecyl sulfate immunodif fusion, enzyme-linked immunosorbent assay (ELISA), and/or Western blot (immunoblot) procedures. Leaf tissue from orchids cultivated in Gaine sville, FL, and from the wild in Ecuador were similarly tested. No vir us was detected in the 277 wild orchids, and only ORSV, CymMV, or both ORSV and CymMV were detected in 20, 73, and 22 cultivated orchids, re spectively, from Puerto Rico and Florida. Several orchid plants gave E LISA reactions greater than three times the negative control with all the virus antisera tested. Other methods did not confirm the presence of virus in these plants, however. Indeed, several preimmune sera also reacted with some of these plants. Caution must be used in interpreta tion of low ELISA values even when these reactions are clearly greater than those of uninfected controls. These results illustrate the need to utilize more than one diagnostic technique before discarding a valu able orchid plant.