A Distinct Strain of Tomato leaf curl Sudan virus Causes Tomato Leaf Curl Disease in Oman

Tomato leaf curl disease (ToLCD) is a significant constraint for tomato production in the Sultanate of Oman. The disease in the north of the country has previously been shown to be caused by the monopartite begomoviruses (family Geminiviridae) Tomato yellow leaf curl virus and Tomato leaf curl Oman virus. Many tomato plants infected with these two viruses were also found to harbor a symptom enhancing betasatellite. Here an analysis of a virus isolated from tomato exhibiting ToLCD symptoms originating from south and central Oman is reported. Three clones of a monopartite begomovirus were obtained. One of the clones was shown to be infectious to tomato and Nicotiana benthamiana and to induce symptoms typical of ToLCD. Analysis of the cloned sequences show them to correspond to isolates of Tomato leaf curl Sudan virus (ToLCSDV), a virus that occurs in Sudan and Yemen. However, the sequences showed less than 93% nucleotide sequence identity to previously characterized ToLCSDV isolates, indicating that the viruses represent a distinct strain of the species, for which we propose the name "Oman" strain (ToLCSDV-OM). Closer analysis of the sequences showed them to differ from their closest relative, the "Tobacco" strain of ToLCSDV originating from Yemen, in three regions of the genome. This suggests that the divergence of the "Oman" and "Tobacco" strains has occurred due to recombination. Surprisingly, ToLCSDV-OM was not found to be associated with a betasatellite, even though the isolates of the other ToLCSDV strains have been shown to be. The significance of these findings and the possible reasons for the distinct geographic distributions of the tomato-infecting begomoviruses within Oman are discussed.