The interaction of two tomato-infecting begomoviruses in Bemisia tabaci and its effect on vector transmission

According to a field survey, tomato yellow leaf curl Thailand virus (TYLCTHV) quickly replaced tomato leaf curl Taiwan virus (ToLCTV) after the former invaded Taiwan. These two viruses are exclusively transmitted by Bemisia tabaci, so the virus replacement in tomato fields is possibly related to the virus-vector interaction. In this study, B. tabaci was given two virus acquisition periods fed on single infected or co-infected plants, and the amount of virus in the tissues of B. tabaci were determined by quantitative PCR to study the interaction of these two viruses in whitefly. Further, transmission assays were performed to examine the effect of virus-virus interaction on vector transmission. The results showed that whether TYLCTHV was acquired first or later, the titer of TYLCTHV in the tissues of B. tabaci significantly decreased when co-ingested with ToLCTV. In contrast, the titer of ToLCTV in the tissues of B. tabaci that co-ingested ToLCTV and TYLCTHV was not significantly different from those only acquired ToLCTV. Transmission assays showed that the transmission rate of either virus decreased when co-ingested with the other whether these two viruses were acquired first or later. Taken together, ToLCTV had a negative effect on the infection of TYLCTHV in B. tabaci, and these two viruses were antagonistic in host plant.