FIRST IDENTIFICATION OF CITRUS EXOCORTIS VIROID CEVd AND CITRUS DWARF VIROID CVdIII IN CITRUS ORCHARDS IN SYRIA
R. Abou Kubaa, M. Saponari, A. El-Khateeb, K. Djelouah
Following the first finding of Hop stunt viroid (HSVd) in Syria (Abou Kubaa et al., 2011), a
survey of citrus was conducted during the summer 2013 to investigate the presence of other
viroids in the country. Leaf samples were collected from 65 stunted trees from four commercial
orchards located in Lattakia and Tartous, the most important citrus-producing areas in Syria.
Each sample consisted of young leaves taken from four sides of each tree. The samples were
tested for the presence of Citrus exocortis viroid (CEVd) and Citrus dwarf viroid (CVd-III).
Total plant RNAs were extracted from leaves according to Foissac et al. (2001), and used as
templates for reverse transcription (RT)-PCR using specific primers for both viroids. PCR
products of the expected size (297 bp and 370 bp) for CVd-III and CEVd, respectively, were
cloned and sequenced. Furthermore, previously infected budwood from five infected citrus
trees were graft inoculated onto an Etrog citron (Citrus medica) indicator plants and maintained
in a temperature controlled greenhouse. Biological indexing evidenced mild epinasty, leaf
curling and typical stunting symptoms, confirming the presence of viroids. Results of RT-PCR
showed that 24 out of 65 samples were infected by citrus viroids, including ten and eight that
reacted positively to CEVd and CVd-III, respectively, and six that showed mixed infection by
both viroids. The retrieved sequences were deposited in GenBank under accession numbers
LN681197 and LN681196 for CVd-III and CEVd, respectively. To our knowledge, this is the
first molecular identification of CEVd and CVd-III in citrus trees in Syria.