First report of Tomato yellow leaf curl Thailand virus in Taiwan.
During the 2006 winter and 2007 spring seasons, tomato lines carrying the Ty2 gene, which confers resistance to Tomato leaf curl virus-Taiwan (ToLCV-Taiwan), showed severe yellowing, leaf curl, and stunting symptoms in several locations in Tainan County, Taiwan. Whiteflies were found to be associated with symptomatic plants, and disease incidences of almost 100% were observed. The presence of a new resistance breaking begomovirus was suspected. Six symptomatic leaf samples of 3 different tomato plants from each infected field were collected in Liouying (LY3, 7 and 8) and Sigang (SG9, 13 and 18) townships in Tainan County. On the basis of their 95% nucleotide identity, they are considered isolates of the same species. BLASTn analysis and sequence comparison with those available in the GenBank database indicated that the 2 isolates had the highest nucleotide identity (more than 98.4%) with the DNA-A of the Tomato yellow leaf curl virus-Thailand (TYLCV-Th). However, DNA-B was detected in all 6 samples, providing further evidence that the 2 isolates were the same as the bipartite TYLCV-Th. All samples, except for LY3, were also found to be infected with ToLCV-Taiwan. A pure TYLCV-Th isolate of LY3 was obtained in Lycopersicon esculentum TK70 by transmission with Bemisia tabaci biotype B. The isolated TYLCV-Th was found to infect L. esculentum H24 (resistant to ToLCV-Taiwan) and induce typical yellow leaf curl symptoms. This is thought to be the first report of the presence of TYLCV-Th in Taiwan.