Molecular detection of olive viruses*

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Abstract
Olive hosts 13 viruses belonging in seven different genera. Additional non‐mechanically transmissible viruses probably infect olive in nature, as suggested by the widespread occurrence of double‐stranded RNAs (dsRNAs) in trees from which no viruses can be recovered by manual inoculation. Because sanitary selection appears to be the only measure for restraining virus dissemination through propagating material, detection methods are needed which are more sensitive and reliable than those currently available (biological and serological). The following molecular techniques have therefore been used and their efficiency compared: (1) dsRNA analysis; (2) dot‐blot hybridization with digoxigenin‐labelled riboprobes in separate reactions or in mixture; and (3) reverse transcription‐polymerase chain reaction (RT‐PCR). It was found that: (1) dsRNAs were detected in 210 out of 286 olive accessions (73.4%) coming from six different Italian regions; (2) one‐step RT‐PCR yielded much better results using TNA extracts than crude sap; and (3) dot‐blot hybridization of denatured dsRNAs with digoxigenin‐labelled virus‐specific riboprobes was the most reliable detection method available.