Survey of viruses infecting tomato in Taiwan

In a field survey in 2016 and 2017, leaf samples were collected from 880 tomato plants with virus-like symptoms in order to identify the predominant and emerging virus diseases in Taiwan. More than 700 (80%) of the samples tested positive for the presence of Begomovirus DNA by PCR with universal Begomovirus primers. While almost 90% of samples from southern Taiwan tested positive, only about 61% of samples from eastern Taiwan tested positive. Testing with specific primers for the two begomoviruses previously identified as important in tomato in Taiwan, Tomato yellow leaf curl Thailand virus (TYLCTHV) and Tomato leaf curl Taiwan virus (ToLCTV), revealed that TYLCTHV was present in 80% of the samples from southern Taiwan, but only in 28% of samples from eastern counties, while no samples tested positive for ToLCTV. This confirmed that TYLCTHV remains the most common virus affecting tomato production. However, the absence of ToLCTV and the discrepancy between the results using universal Begomovirus and specific Begomovirus primers suggested the presence of distinct begomoviruses in all areas of the country, but at greater incidence in the eastern counties. The samples also were tested by RT-PCR with primers for the whitefly-transmitted Tomato chlorosis virus (ToCV; Crinivirus) and 361 (41%) samples tested positive. Of these, 331 were also positive for Begomovirus (242 positive for TYLCTHV), while only 30 were positive for ToCV alone. Aphid-, thrips- and mechanically-transmitted viruses, evaluated using ELISA, were detected in a relatively small proportion of the samples. This indicates that that ToCV is now well established and whitefly-transmitted viruses remain the most common constraint to tomato production in Taiwan.