Molecular detection of olive-infecting viruses

Olive (Olea europaea L.) hosts 13 viruses belonging in seven different genera. However the large occurrence of double stranded RNAs (dsRNAs) in trees from which no viruses can be recovered by mechanical inoculation, suggested that a number of non-mechanically transmissible viruses infect olive in nature. Since sanitary selection seems to be the only measure to control virus dissemination through propagating material, it can be successfully carried out only if detection methods more sensitive and reliable than those currently available (biological and serological) are developed. DsRNA analysis, dot-blot hybridisation with digoxigenin-labelled riboprobes in separate reactions or in mixture and RT-PCR assays were optimised and their efficiency in olive virus detection compared. We detected dsRNAs in 210 of 286 olive accessions (73.4 %) coming from six different Italian regions. RT-PCR yielded much better results using TNA extracts than crude sap. Dot blot hybridisation of denatured dsRNAs with digoxigenin-labelled virus-specific riboprobes proved to be the most reliable detection method currently available.