Interaction of watermelon chlorotic stunt virus with satellites

Pumpkin (Cucurbita maxima) plants showing begomovirus-like yellowing, curling and stunting symptoms were observed in the Barka Governate, Oman in December 2016. Cloning and sequencing of rolling circle amplified circular DNA molecules showed the plants to be infected with watermelon chlorotic stunt virus (WmCSV); a bipartite Old World begomovirus that is a serious pathogen of cucurbit crops across the Middle East, Arabian Peninsula and North Africa. Although not known to interact with satellites, the risk of WmCSV possibly interacting with betasatellites and alphasatellites to agriculture in Oman, and beyond, was assessed. Tomato leaf curl betasatellite (ToLCB) and Ageratum enation alphasatellite (AEA) are commonly associated with other begomoviruses in Oman. A cognate pair of WmCSV DNA-A and DNA-B clones was highly infectious to Nicotiana benthamiana by Agrobacterium-mediated inoculation, inducing severe leaf curling and crumpling symptoms. Inoculation of only the DNA-A component with ToLCB or AEA did not result in symptoms or significant levels of the DNA-A or satellites in plants. Inoculation of both DNA-A and DNA-B with ToLCB or AEA resulted in a slight change in symptom phenotype and reduced DNA-A and DNA-B titers. Although ToLCB DNA levels in co-infected plants were low, the levels of AEA were high. This is the first identification of WmCSV infecting pumpkin in Oman and the isolates identified were typical of the virus previously identified in Oman, being distinct from the isolates occurring in the western Arabian Peninsula. Additionally the infectivity analyses suggest that WmCSV interaction with satellites, in contrast to some other bipartite begomoviruses, is unlikely to result in more serious disease in the field.