A comparison between serological and biological assays in detecting grapevine leafroll associated viruses

The efficacy of the serological procedure enzyme-linked immunosorbent assay (ELISA) for detecting grapevine leafroll associated viruses (GLRaV types -1, -2, -3, and -4) was compared with indexing on Vitis vinifera L. cv. Cabernet Franc. Results of the biological assays confirmed the infectious nature of all grapevine sources testing positive by ELISA for GLRaV-1 (9 sources), GLRaV-2 (14 sources), and GLRaV-4 (14 sources), and the noninfectious nature of ELISA-negative grapevines (75 sources). However, among 57 sources testing positive by ELISA for GLRaV-3, or 24 sources with multiple infections, 8 and 1 sources, respectively, were negative by Cabernet Franc assays. Serological assays were repeated on all graft-inoculated indicators and only symptomatic ones reacted positively. Also, the 8 original GLRaV-3 sources that had tested positive by ELISA and negative by bioassay were found positive using immunocapture/reverse transcription-polymerase chain reaction (IC/RT-PCR). The single multiple-infected source was not available for retesting. The distribution of GLRaV in infected grapevines was tested by assaying 20 to 40 samples per source of 36 plants infected with GLRaV-1, -2, -3, or -4. The incidence of GLRaV-positive canes as determined by ELISA ranged from 0 to 100%, suggesting that GLRaV can be unevenly distributed in chronically infected grapevines.