Identification of watermelon chlorotic stunt virus from watermelon and zucchini in Saudi Arabia

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Symptomatic and non-symptomatic leaf samples of cucumber, zucchini, melon and watermelon plants were collected from three locations (Al-Ahsa in the East, Jizan in the South and Tabuk in the North) in the Kingdom of Saudi Arabia during 2013–2014. The detection of begomovirus infection was commenced with serological assay, rolling circle amplification and PCR amplification with universal begomovirus primers. The zucchini and watermelon samples tested positive for the presence of begomovirus infection in 53 and 39.6%, and 54.5 and 41.5% samples using serological and PCR-based detection, respectively. Based upon the core coat protein sequence, the full-length genomes of DNA-A and DNA-B were amplified and subsequently sequenced. The sequence analysis revealed that the two clones of DNA-A shared 96.9% nucleotide (nt) sequence identity with each other while they shared 95.9–98.4% nt sequence identity with watermelon chlorotic stunt virus (WmCSV) isolates reported so far. Similarly, the two DNA-B clones showed 91.8% mutual nt sequence identity, while sharing 95.2–95.5% nt sequence identity with all other reported DNA-B sequences. The phylogenetic dendrogram grouped both DNA-A clones into separate sub-groups, suggesting that both isolates were introduced separately into Saudi Arabia. The identification of WmCSV from zucchini in Saudi Arabia and other hosts in the neighbouring countries suggests that this virus is becoming an emerging threat to cucurbits in this region.