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.