Identification and molecular analysis of watermelon chlorotic stunt virus infecting snake gourd in Saudi Arabia

Snake gourd (Trichosanthes cucumerina) plants exhibiting typical begomovirus-like symptoms of stunted growth, leaf yellowing and mottling were observed at an open field in the Eastern region of Saudi Arabia. Sequencing analysis of the amplified complete DNA molecules revealed that the plants were infected with watermelon chlorotic stunt virus (WmCSV), which is a bipartite begomovirus prevalent mostly in the Old World and a serious threat to cucurbit production in the Arabian Peninsula, Middle East and Africa. The two WmCSV DNA-A isolates (SG31A and SG52A) were 98.9% identical and showed their highest nucleotide (nt) sequence identities (98.7%) with the isolates from Iran and Saudi Arabia. The DNA-B isolates (SG31B and SG52B), on the other hand, were 97.4% identical and exhibited their highest nt sequence identities (99.5 and 97%) with isolates reported from Iran and Oman. In the phylogenetic dendrograms the identified isolates clustered closely with previously reported WmCSV isolates from Iran and Saudi Arabia. Infectivity assays revealed that the DNA-A components alone could not induce infection in Nicotiana benthamiana plants however, together with DNA-B these isolates successfully caused typical begomovirus symptoms and both components were detected successfully using Southern blot hybridization. This study highlights the importance of conducting extensive future begomovirus surveillance to detect spillover events that could threaten native vegetable production in Saudi Arabia. This is crucial as begomoviruses pose a serious threat to vegetable cultivation throughout the Middle East.