Association of tomato leaf curl betasatellite (Betasatellite solani) with the turncurtovirus sesame curly top virus (Turncurtovirus sesami) increases the severity of symptoms in watermelon plants

The damage caused by majority of monopartite- and several bipartite begomoviruses as well as by two mastreviruses is intensified in the presence of betasatellites in many economically important crops. Previously, we reported infection of watermelon plants with sesame curly top virus (SeCTV, Turncurtovirus sesami ) in Jiroft, southeastern Iran showing severe symptoms including severe upward leaf curling and brittle leaves. Due to the detection of tomato leaf curl betasatellite (ToLCB, Betasatellite solani ) in original SeCTV infected watermelon samples, the potential role of ToLCB in inducing severe symptoms in watermelon plants was investigated. Watermelon seedlings were agroinoculated either with previously constructed infectious clone of SeCTV or with a combination of SeCTV and a newly constructed infectious clone of ToLCB. Results showed that the combination of SeCTV + ToLCB induced more severe symptoms, such as yellowing, leaf curling and brittle leaves, compared to plants agroinoculated with SeCTV alone. Based on the results from this research, in addition to begomoviruses and mastreviruses, the association of a betasatellite molecule with a turncurtovirus can increase disease severity caused by the helper virus.