Transmission biology of two tomato begomoviruses by Bemisia tabaci

Tomato yellow leaf curl disease (TYLCD) can cause yield losses as high as 100% in tomato and is emerging as a serious threat to global tomato production. TYLCD is associated with a group of phylogenetically related viruses referred to as tomato yellow leaf curl viruses. These viruses belong to the genus Begomovirus of the family Geminiviridae and are transmitted by whiteflies. Studies have shown that the invasion of begomoviruses into a region is correlated with expansion of Bemisia tabaci population. A survey revealed the progressive displacement of Tomato leaf curl Taiwan virus (ToLCTWV) by Tomato yellow leaf curl Thailand virus (TYLCTHV) from 2007 to 2009 in tomato fields in Taiwan. To determine the cause of the displacement, we compared how efficiently B. tabaci transmitted TYLCTHV and ToLCTWV and investigated whether these viruses were transovarially transmitted to offspring of whiteflies. The minimum AAP and IAP for TYLCTHV and ToLCTWV were similar transmitted by B. tabaci. The transmission rate peaked with a 12-hour IAP for ToLCTWV, but the highest transmission rate for ToLCTWV was around 50%. The results suggested that B. tabaci transmitted TYLCTHV more efficiently than ToLCTWV. The study also demonstrated that B. tabaci transmitted TYLCTHV transovarially and the progeny of whiteflies remained infective. In contrast, there was no evidence that transovarial transmission of ToLCTWV by B. tabaci occurred. This virus-vector interaction may contribute to the replacement of ToLCTWV by TYLCTHV in the tomato field in Taiwan within few years.