First report of Apple dimple fruit viroid in Lebanon.

In the Bekaa valley of Lebanon in 2005, apple fruits of cv Starking Delicious were observed that had depressed green spots 3-4 mm in diameter scattered on the whole fruit surface and around the calyx, where they sometimes merged to give large discoloured areas. These symptoms closely resembled those of apple dimple fruit and dapple apple diseases that are induced by Apple dimple fruit viroid (ADFVd) (Di Serio et al., 1996) and Apple scar skin viroid (ASSVd) (Hashimoto and Koganezawa, 1987), respectively. Total nucleic acids (TNA) were extracted from symptomatic fruits and from symptomless fruits of apparently healthy plants of the same variety and tested by dotblot hybridization using digoxigenin-labelled riboprobes of cRNA to ADFVd or ASSVd. Hybridization signals were obtained only with TNA from symptomatic fruits exposed to the ADFVd-specific probe. Further evidence that ADFVd was associated with the observed symptoms was obtained by using a multiplex RT-PCR amplification assay specific for detecting this viroid in both single and mixed infections with ASSVd (Di Serio et al., 2002). An amplification product of 250 nt, the size expected for ADFVd, was obtained only when testing TNA preparations that had tested positive for ADFVd by dot-blot hybridization. Conclusive evidence that only ADFVd was present in diseased Lebanese apple trees was that the sequence of the 250 nt amplicon was that expected for part of ADFVd cDNA. To our knowledge, this is the first report of ADFVd in Lebanon and the first report of this viroid in a country other than Italy.