Problems with Interpretation of Serological Assays in a Virus Survey of Orchid Species from Puerto Rico, Ecuador, and Florida

Abstract

Leaf samples collected in May 1990 from wild and cultivated orchids in Puerto Rico were tested for odontoglossum ringspot virus (ORSV), cymbidium mosaic virus (CymMV), tobacco mosaic virus common strain, tobacco mild green mosaic virus, two strains of cucumber mosaic virus, and cymbidium ringspot virus (CymRSV) with sodium dodecyl sulfate immunodiffusion, enzyme-linked immunosorbent assay (ELISA), and/or Western blot (immunoblot) procedures. Leaf tissue from orchids cultivated in Gainesville, FL, and from the wild in Ecuador were similarly tested. No virus 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, respectively, from Puerto Rico and Florida. Several orchid plants gave ELISA 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 interpretation 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 valuable orchid plant.